阅读说明：本技术 一种超亲水防雾涂层及其制备方法 (Super-hydrophilic anti-fog coating and preparation method thereof ) 是由 蒋永东 柯冲 张陈华 于 2021-11-29 设计创作，主要内容包括：本发明公开一种超亲水防雾涂层的制备方法,其包括以下步骤：将硅烷前驱体进行水解,得到溶液a；于溶剂中加入纳米二氧化硅粉末,超声分散得到悬浮液b；取所述溶液a加入至所述悬浮液b中,超声分散得到混合液c；将所述混合液c涂覆于基材上,烘烤制得超亲水防雾涂层；还公开一种超亲水防雾涂层。本发明开创性地改良硅烷前驱体、催化剂的选用组分,并严格控制各组分的摩尔比、质量比或体积比,以使涂层具有极佳的表面亲水性、防雾性能和力学性能；所选的硅烷前驱体组合含有氨基,反应形成具有三维网状结构以及具有亲水基团的溶胶,该溶胶与纳米二氧化硅粒子混合后可于纳米二氧化硅表面嫁接亲水基团,进而提升超亲水防雾涂层的超亲水性能。(The invention discloses a preparation method of a super-hydrophilic anti-fog coating, which comprises the following steps: hydrolyzing a silane precursor to obtain a solution a; adding nano silicon dioxide powder into a solvent, and performing ultrasonic dispersion to obtain a suspension b; adding the solution a into the suspension b, and performing ultrasonic dispersion to obtain a mixed solution c; coating the mixed solution c on a substrate, and baking to obtain a super-hydrophilic anti-fog coating; also discloses a super-hydrophilic antifogging coating. The invention creatively improves the selected components of the silane precursor and the catalyst, and strictly controls the molar ratio, the mass ratio or the volume ratio of each component, so that the coating has excellent surface hydrophilicity, antifogging property and mechanical property; the selected silane precursor combination contains amino, the sol with a three-dimensional network structure and hydrophilic groups is formed by reaction, and the sol and nano-silica particles are mixed and then can be grafted with hydrophilic groups on the surface of the nano-silica, so that the super-hydrophilic performance of the super-hydrophilic antifogging coating is improved.)

1. The preparation method of the super-hydrophilic antifogging coating is characterized by comprising the following steps of:

step 1, hydrolyzing a silane precursor to obtain a solution a;

step 2, adding nano silicon dioxide powder into a solvent, and performing ultrasonic dispersion to obtain a suspension b;

step 3, adding the solution a into the suspension b, and performing ultrasonic dispersion to obtain a mixed solution c;

and 4, coating the mixed solution c on a base material, and baking to obtain the super-hydrophilic antifogging coating.

2. The method for preparing the super-hydrophilic antifogging coating according to claim 1, wherein the solution a obtained by hydrolysis in the step 1 is obtained by adding deionized water and a catalyst into the silane precursor and then performing magnetic stirring reaction at a certain temperature;

optionally, the molar ratio of the silane precursor to the deionized water to the catalyst is 1: 2-6: 0.02-0.06.

3. The method for preparing the super-hydrophilic anti-fog coating according to claim 2, wherein the silane precursor comprises one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane;

optionally, the silane precursor comprises 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane in a molar ratio of 0.1-1: 0-1.

4. The method for preparing the superhydrophilic anti-fog coating of claim 2, wherein the catalyst is an acidic catalyst;

optionally, the acidic catalyst is one or a combination of two of acetic acid and citric acid;

optionally, the molar ratio of acetic acid to citric acid in the catalyst is 0.5-1: 0-1.

5. The method for preparing the superhydrophilic anti-fog coating of claim 1, wherein the hydrolysis conditions of the step 1 are as follows: the hydrolysis temperature is between room temperature and 50 ℃, the hydrolysis time is 2-24 hours, and the magnetic stirring time is 10-30 minutes.

6. The preparation method of the super-hydrophilic antifogging coating according to claim 1, characterized in that, in the step 2, the mass fraction of the nano silica powder in the suspension b is 0-3%;

optionally, the particle size range of the silicon dioxide powder is 7-12 nanometers.

7. The method for preparing the super-hydrophilic antifogging coating according to claim 1, wherein in the step 2, the solvent is selected from one or more of butanone, toluene, ethanol and isopropanol;

optionally, the volume ratio of butanone, toluene, ethanol and isopropanol in the solvent is 0-0.5: 0.5-1: 0-0.3.

8. The preparation method of the super-hydrophilic antifogging coating according to claim 1, characterized in that, in the step 3, the mass ratio of the solution a to the suspension b is 1: 50-200.

9. The method for preparing the superhydrophilic anti-fog coating of claim 1, wherein the dispersion conditions of step 2 and step 3 are as follows: the magnetic stirring time is 10-30 minutes, and the ultrasonic dispersion time is 10-30 minutes;

optionally, the baking conditions in step 4 are: the baking temperature is 80-160 ℃, and the baking time is 1-24 hours.

10. A super-hydrophilic anti-fog coating, characterized in that, it is made by the preparation method of the super-hydrophilic anti-fog coating of any claim 1 to 9.

Technical Field

The invention relates to the technical field of surface modification of transparent substrates, in particular to a super-hydrophilic anti-fog coating and a preparation method thereof.

Background

Fogging refers to a phenomenon in which water vapor condenses on the surface of an object when the surface temperature of the object is lower than the dew point. At this temperature, when the contact angle of the condensed water drops on the surface of the substrate is large (>40 °), light transmitted through the substrate is greatly scattered, and a phenomenon of visual blurring occurs in the transparent object. The fogging phenomenon can cause serious influence on the application of automobile glass, medical instruments, optical components and the like, so that the preparation and the research and development of the antifogging coating have important significance and practical value for the application in the fields.

The main current anti-fogging methods include: coating a surface active agent on the surface of a matrix; coating a water-absorbing organic coating on the surface of the substrate; thirdly, the evaporation of the water drops on the surface of the matrix is accelerated by heating, ultrasonic and other modes. The water-absorbing coating of the method II has low water resistance and wear resistance, and the method III needs additional heating and ultrasonic element devices, so that the structure is complex and the cost is high.

In addition to the above methods, it is now intended to achieve an antifogging effect by preparing a superhydrophilic surface to change the wettability of the substrate surface, keeping the contact angle of a water droplet upon condensation below 10 ° to form a water film that does not affect the optical properties of the substrate. At present, the research on the antifogging effect achieved by preparing a super-hydrophilic coating has made great progress. For example, chinese patent application No. 202110616163.2 discloses a method for preparing a lens with anti-fog and anti-bacterial functions by using titanium dioxide (TiO)₂) The photocatalytic property of the particles gives good hydrophilicity and antifogging properties to the lens, however the hydrophilicity of this technique relies on the TiO₂The photocatalytic property of the particles requires high hydrophilicity in an environment where ultraviolet rays are irradiated, and thus the practicability of the technology is lowered. For another example, chinese patent application No. 201010533381.1 discloses a hydrophilic Silica (SiO)₂) The preparation method of the antifogging coating is realized by preparing mesoporous SiO₂The particles and the electrostatic self-assembly process prepare a transparent antifogging coating on a glass substrate, but the coating needs to be calcined at high temperature for a long time, and the preparation cost of the coating is high. As another example, the Chinese patent with application number 202010872334.3 preceded various silanesAnd the driver adopts a plasma chemical vapor deposition process to prepare the antifogging coating, the coating has good antifogging performance, however, the plasma chemical vapor deposition process needs expensive equipment, and thus, the preparation cost of the coating is improved.

Also disclosed in chinese patent application No. 201910449053.4 is a method for improving the hydrophilicity of a coating layer, which comprises pretreating a nano-silica particle with a coupling agent having a carbon-carbon double bond to graft the carbon-carbon double bond onto the nano-silica particle, thereby improving the surface activity, and finally grafting a hydrophilic group onto the nano-silica particle to provide a hydrophilic group on the surface, thereby providing the coating layer with an anti-fogging property. Therefore, the development of the preparation method of the antifogging coating with simple preparation process and low cost has wide application prospect.

Disclosure of Invention

In order to overcome the technical problems, the invention discloses a super-hydrophilic anti-fog coating and a preparation method thereof.

The technical scheme adopted by the invention for realizing the purpose is as follows:

the preparation method of the super-hydrophilic antifogging coating is characterized by comprising the following steps of:

step 1, hydrolyzing a silane precursor to obtain a solution a;

step 2, adding nano silicon dioxide powder into a solvent, and performing ultrasonic dispersion to obtain a suspension b;

step 3, adding the solution a into the suspension b, and performing ultrasonic dispersion to obtain a mixed solution c;

and 4, coating the mixed solution c on a base material, and baking to obtain the super-hydrophilic antifogging coating.

In the preparation method of the super-hydrophilic antifogging coating, the solution a obtained by hydrolysis in the step 1 is obtained by adding deionized water and a catalyst into the silane precursor and then performing magnetic stirring reaction at a certain temperature;

optionally, the molar ratio of the silane precursor to the deionized water to the catalyst is 1: 2-6: 0.02-0.06; preferably, the molar ratio of the silane precursor to the deionized water to the catalyst is 1: 3-4: 0.03-0.04.

The preparation method of the super-hydrophilic antifogging coating comprises the following steps of preparing a silane precursor, wherein the silane precursor comprises one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane;

optionally, the silane precursor comprises 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane in a molar ratio of 0.1-1: 0-1;

optionally, the silane precursor comprises 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane in a molar ratio of 0.5-1: 0-0.5.

The preparation method of the super-hydrophilic antifogging coating is characterized in that the catalyst is an acidic catalyst;

optionally, the acidic catalyst is one or a combination of two of acetic acid and citric acid;

optionally, the molar ratio of acetic acid to citric acid in the catalyst is 0.5-1: 0-1.

The preparation method of the super-hydrophilic antifogging coating comprises the following steps of (1): the hydrolysis temperature is between room temperature and 50 ℃, the hydrolysis time is 2-24 hours, and the magnetic stirring time is 10-30 minutes; preferably, the hydrolysis time is 4 to 8 hours.

In the step 2, the mass fraction of the nano silicon dioxide powder in the suspension b is 0-3%; preferably, the mass fraction of the nano silicon dioxide powder in the suspension b is 0.5-2%.

Optionally, the particle size range of the silicon dioxide powder is 7-12 nanometers.

The preparation method of the super-hydrophilic antifogging coating is that in the step 2, the solvent is selected from one or more of butanone, toluene, ethanol and isopropanol;

optionally, the volume ratio of butanone, toluene, ethanol and isopropanol in the solvent is 0-0.5: 0.5-1: 0-0.3.

In the step 3, the mass ratio of the solution a to the suspension b is 1: 50-200; preferably, the mass ratio of the solution a to the suspension b is 1: 50-100.

The preparation method of the super-hydrophilic antifogging coating comprises the following steps of: the magnetic stirring time is 10-30 minutes, and the ultrasonic dispersion time is 10-30 minutes;

optionally, the baking conditions in step 4 are: the baking temperature is 80-160 ℃, and the baking time is 1-24 hours.

The super-hydrophilic anti-fog coating is prepared by the preparation method of the super-hydrophilic anti-fog coating.

The beneficial effects of the invention include the following:

(1) the invention creatively improves the selected components of the silane precursor and the catalyst, and strictly controls the molar ratio, the mass ratio or the volume ratio of each component, so that the prepared antifogging coating has excellent surface hydrophilicity, surface strength, friction resistance, water resistance, antifogging performance and the like;

(2) compared with the traditional method of taking tetraethoxysilane as a silane precursor, the silane precursor selected by the application contains amino functional groups, the sol with a three-dimensional network structure and hydrophilic groups is formed by reaction, and the hydrophilic groups can be grafted on the surface of the nano silicon dioxide after the sol is mixed with nano silicon dioxide particles, so that the super-hydrophilic performance of the super-hydrophilic antifogging coating is improved; the amino in the silane precursor has stronger hydrophilicity, so that the hydrophilicity and the antifogging property of the surface of the coating are greatly improved, the adhesion of the coating on different matrixes is optimized and enhanced, and the super-hydrophilic antifogging coating is suitable for different matrixes;

(3) based on the silane precursor with specific composition and proportion, the silicon dioxide particles increase the roughness of the surface of the coating, further improve the hydrophilicity of the coating, and can promote the coating to achieve super-hydrophilic and anti-fog performance without multiple coating and drying steps;

(4) compared with the traditional method of using strong acid such as hydrochloric acid and the like as catalysts, the catalyst selected by the method, such as acetic acid and citric acid, is weak acid, can effectively control the hydrolysis reaction rate of the silane precursor, and the silica sol generated by hydrolysis has smaller and more uniform size and is more suitable for constructing a rough surface structure, so that the hydrophilic property of the coating is improved;

(5) the method has the advantages of easily obtained and low-priced raw materials, shorter reaction time, simple preparation process, simple and convenient operation, high safety of the preparation process, low pollution, no need of expensive production equipment, low production cost, high practical value and easy large-scale production, and can effectively reduce energy consumption.

Detailed Description

The present invention is further illustrated by the following specific examples, which are intended to facilitate the understanding and appreciation of the technical solutions of the present invention, rather than to limit the invention thereto.

The invention provides a preparation method of a super-hydrophilic anti-fog coating, which is characterized by comprising the following steps:

step 1, hydrolyzing a silane precursor to obtain a solution a;

step 2, adding nano silicon dioxide powder into a solvent, and performing ultrasonic dispersion to obtain a suspension b;

step 3, adding the solution a into the suspension b, and performing ultrasonic dispersion to obtain a mixed solution c;

and 4, coating the mixed solution c on a base material, and baking to obtain the super-hydrophilic antifogging coating.

In the preparation method of the super-hydrophilic antifogging coating, the solution a obtained by hydrolysis in the step 1 is obtained by adding deionized water and a catalyst into the silane precursor and then performing magnetic stirring reaction at a certain temperature;

optionally, the molar ratio of the silane precursor to the deionized water to the catalyst is 1: 2-6: 0.02-0.06; preferably, the molar ratio of the silane precursor to the deionized water to the catalyst is 1: 3-4: 0.03-0.04.

The preparation method of the super-hydrophilic antifogging coating comprises the following steps of preparing a silane precursor, wherein the silane precursor comprises one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane;

optionally, the silane precursor comprises 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane in a molar ratio of 0.1-1: 0-1;

optionally, the silane precursor comprises 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane in a molar ratio of 0.5-1: 0-0.5.

The preparation method of the super-hydrophilic antifogging coating is characterized in that the catalyst is an acidic catalyst;

optionally, the acidic catalyst is one or a combination of two of acetic acid and citric acid;

optionally, the molar ratio of acetic acid to citric acid in the catalyst is 0.5-1: 0-1.

The preparation method of the super-hydrophilic antifogging coating comprises the following steps of (1): the hydrolysis temperature is between room temperature and 50 ℃, the hydrolysis time is 2-24 hours, and the magnetic stirring time is 10-30 minutes; preferably, the hydrolysis time is 4 to 8 hours.

In the step 2, the mass fraction of the nano silicon dioxide powder in the suspension b is 0-3%; preferably, the mass fraction of the nano silicon dioxide powder in the suspension b is 0.5-2%.

Optionally, the particle size range of the silicon dioxide powder is 7-12 nanometers.

The preparation method of the super-hydrophilic antifogging coating is that in the step 2, the solvent is selected from one or more of butanone, toluene, ethanol and isopropanol;

optionally, the volume ratio of butanone, toluene, ethanol and isopropanol in the solvent is 0-0.5: 0.5-1: 0-0.3.

In the step 3, the mass ratio of the solution a to the suspension b is 1: 50-200; preferably, the mass ratio of the solution a to the suspension b is 1: 50-100.

The preparation method of the super-hydrophilic antifogging coating comprises the following steps of: the magnetic stirring time is 10-30 minutes, and the ultrasonic dispersion time is 10-30 minutes;

optionally, the baking conditions in step 4 are: the baking temperature is 80-160 ℃, and the baking time is 1-24 hours.

The invention also discloses a super-hydrophilic anti-fog coating which is prepared by the preparation method of the super-hydrophilic anti-fog coating.

The preparation process according to the invention is now described in detail in the following examples:

example 1:

the invention provides a preparation method of a super-hydrophilic anti-fog coating, which is characterized by comprising the following steps:

step 1, taking 2.21g of 3-aminopropyltriethoxysilane (0.01mol), adding deionized water and 1.65g of 0.2M acetic acid, and magnetically stirring for 2 hours at 50 ℃ to obtain a solution a, wherein the molar ratio of a silane precursor to the deionized water to an acetic acid catalyst is 1:3.33: 0.033;

step 2, adding 0.85g of hydrophilic silicon dioxide powder with the particle size of 7 nanometers into 63.12g of ethanol, magnetically stirring for 30 minutes, uniformly mixing, and ultrasonically dispersing for 20 minutes to obtain a suspension b, wherein the mass fraction of the silicon dioxide powder in the suspension b is 1.3%;

step 3, adding 0.66g of the solution a into the suspension b, magnetically stirring for 30 minutes, uniformly mixing, and ultrasonically dispersing for 20 minutes to obtain a mixed solution c, wherein the mass ratio of the solution a to the suspension b is 1: 96.92;

and 4, coating the sol mixture c on a substrate in a dip coating mode, and baking for 6 hours at 120 ℃ to obtain the super-hydrophilic antifogging coating.

The performance of the prepared super-hydrophilic antifogging coating is measured, and the result is as follows: the surface hardness of the coating is H (GB/T6739-2006), the light transmittance of the coating is 91.2%, and the haze is 0.78%; the water contact angle of the coating is 7 degrees, the coating is placed on hot water at the temperature of 80 ℃ for 10cm, and the fogging phenomenon does not occur within 10 minutes; the coating is dried after being soaked in deionized water for 30 minutes, and the antifogging property is not reduced.

Example 2:

the preparation method of the super-hydrophilic anti-fog coating provided by the embodiment comprises the following steps:

step 1, taking 1.11g (0.005mol) of 3-aminopropyltriethoxysilane and 0.90g (0.005mol) of 3-aminopropyltrimethoxysilane, adding deionized water and 2.0g of 0.2M acetic acid, and magnetically stirring for 6 hours at room temperature to obtain a solution a, wherein the molar ratio of a silane precursor to the deionized water to a catalyst is 1:3.33: 0.04;

step 2, adding 1.0g of hydrophilic silicon dioxide powder with the particle size of 7 nanometers into 63.12g of ethanol, magnetically stirring for 30 minutes, uniformly mixing, and ultrasonically dispersing for 20 minutes to obtain a suspension b, wherein the mass fraction of the silicon dioxide powder in the suspension b is 1.6%;

step 3, adding 0.88g of the solution a into the suspension b, magnetically stirring for 30 minutes, uniformly mixing, and ultrasonically dispersing for 20 minutes to obtain a mixed solution c, wherein the mass ratio of the solution a to the suspension b is 1: 72.86;

and 4, coating the mixed solution c on a base material in a dip-coating mode, and baking for 2 hours at 120 ℃ to obtain the super-hydrophilic antifogging coating.

The performance of the prepared super-hydrophilic antifogging coating is measured, and the result is as follows: the surface hardness of the coating is 2H, the light transmittance of the coating is 91.8%, the haze is 0.59%, and the water contact angle of the coating is 6 degrees; the coating is placed on hot water at 80 ℃ for 10cm, and the fogging phenomenon does not occur within 10 minutes; the coating is dried after being soaked in deionized water for 30 minutes, and the antifogging property is not reduced.

Example 3:

the preparation method of the super-hydrophilic anti-fog coating provided by the embodiment comprises the following steps:

step 1, uniformly mixing 1.48g (0.0067mol) of 3-aminopropyltriethoxysilane and 0.73g (0.0033mol) of N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, adding deionized water, 0.83g of 0.2M acetic acid and 0.83g of 0.2M citric acid, and magnetically stirring for 3 hours at 40 ℃ to obtain a solution a, wherein the molar ratio of a silane precursor to the deionized water to a catalyst is 1:3.33: 0.033;

step 2, adding 1.0g of hydrophilic silicon dioxide powder with the particle size of 7 nanometers into 63.12g of ethanol, magnetically stirring for 30 minutes, uniformly mixing, and ultrasonically dispersing for 20 minutes to obtain a suspension b, wherein the mass fraction of the silicon dioxide powder in the suspension b is 1.6%;

step 3, adding 0.66g of the solution a into the suspension b, magnetically stirring for 30 minutes, uniformly mixing, and ultrasonically dispersing for 20 minutes to obtain a mixed solution c, wherein the mass ratio of the solution a to the suspension b is 1: 96.92;

and 4, coating the mixed solution c on a base material in a dip-coating mode, and baking for 4 hours at 90 ℃ to obtain the super-hydrophilic antifogging coating.

The performance of the prepared super-hydrophilic antifogging coating is measured, and the result is as follows: the surface hardness of the coating is 2H, the light transmittance of the coating is 92.0%, the haze is 0.49%, and the water contact angle of the coating is 4 degrees; the coating is placed on hot water at 80 ℃ for 10cm, and the fogging phenomenon does not occur within 10 minutes; the coating is dried after being soaked in deionized water for 30 minutes, and the antifogging property is not reduced.

Example 4:

the preparation method of the super-hydrophilic anti-fog coating provided by the embodiment comprises the following steps:

step 1, uniformly mixing 0.89g (0.005mol) of 3-aminopropyltriethoxysilane, 0.45g (0.0025mol) of N- (2-aminoethyl) -3-aminopropyltrimethoxysilane and 0.66g (0.0025mol) of N- (2-aminoethyl) -3-aminopropyltriethoxysilane, adding deionized water and 2.0g of 0.2M acetic acid, and magnetically stirring for 3 hours at 50 ℃ to obtain a solution a, wherein the molar ratio of a silane precursor to the deionized water to a catalyst is 1:3.33: 0.04;

step 2, adding 1.2g of hydrophilic silicon dioxide powder with the particle size of 7 nanometers into 63.12g of ethanol, magnetically stirring for 30 minutes, uniformly mixing, and ultrasonically dispersing for 20 minutes to obtain a suspension b, wherein the mass fraction of the silicon dioxide powder in the suspension b is 1.9%;

step 3, adding 0.88g of the solution a into the suspension b, magnetically stirring for 30 minutes, uniformly mixing, and ultrasonically dispersing for 20 minutes to obtain a mixed solution c, wherein the mass ratio of the solution a to the suspension b is 1: 73.09;

and 4, coating the sol mixture c on a base material in a dip coating mode, and baking for 2 hours at 100 ℃ to obtain the super-hydrophilic antifogging coating.

The performance of the prepared super-hydrophilic antifogging coating is measured, and the result is as follows: the surface hardness of the coating is 3H, the light transmittance of the coating is 91.5%, the haze is 0.61%, and the water contact angle of the coating is 3 degrees; the coating is placed on hot water at 80 ℃ for 10cm, and the fogging phenomenon does not occur within 10 minutes; the coating is dried after being soaked in deionized water for 30 minutes, and the antifogging property is not reduced.

The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Those skilled in the art can make many possible variations and modifications to the invention using the above disclosed technical means and teachings, or can modify equivalent embodiments with equivalent variations, without departing from the scope of the invention. Therefore, all equivalent changes made according to the shape, structure and principle of the present invention should be covered by the protection scope of the present invention without departing from the contents of the technical scheme of the present invention.