阅读说明：本技术 一种超薄木质振膜的制备方法 (Preparation method of ultrathin wood vibrating diaphragm ) 是由 杨蕊 詹先旭 梅长彤 董安然 孟祥真 董先银 于 2021-07-01 设计创作，主要内容包括：一种超薄木质振膜的制备方法,一定温度下通过以氯化胆碱、乙酸酐、乙酸等混合形成的均匀透明液体在微波中处理木材试件,再用溶剂洗涤,最后经过热压,得到超薄木质振膜；经过上述处理得到的振膜可以减少振膜表面的亲水基团,使得振膜不易吸潮,更加稳定,品质更好。(A preparation method of an ultrathin wood diaphragm comprises the steps of treating a wood test piece in microwave by using uniform transparent liquid formed by mixing choline chloride, acetic anhydride, acetic acid and the like at a certain temperature, washing the wood test piece by using a solvent, and finally carrying out hot pressing to obtain the ultrathin wood diaphragm; the vibrating diaphragm obtained through the processing can reduce hydrophilic groups on the surface of the vibrating diaphragm, so that the vibrating diaphragm is not easy to absorb moisture, and is more stable and better in quality.)

1. A preparation method of an ultrathin wood diaphragm comprises the following operation steps:

s1: mixing choline chloride, acetic anhydride and acetic acid to form uniform transparent liquid, wherein the weight ratio of choline chloride: acetic anhydride: the molar ratio of acetic acid is 1: (1-3): (1-3) obtaining a DES system mixed solution;

s2: soaking the wood test piece into the DES system mixed solution in the step S1, and performing microwave treatment to obtain a modified wood test piece; the mass ratio of the wood test piece to the DES system mixed liquid is 1: (10-30);

s3: taking out the modified wood test piece in the step S2, cooling to room temperature, and soaking in a first solvent to remove residual reaction liquid to obtain a pretreated wood test piece; in the step, the soaking time is 2-6 h;

s4: taking out the pretreated wood test piece in the step S3, and soaking the pretreated wood test piece in a second solvent formed by absolute ethyl alcohol or acetone to obtain a fine-treated wood test piece;

s5: and (4) carrying out hot pressing on the fine-processed wood test piece in the step S4 to obtain the ultrathin wood diaphragm.

2. The method for preparing an ultrathin wood diaphragm according to claim 1, wherein in step S2, the temperature of the microwave treatment is 50 to 90 ℃ and the power is 500 to 1000W.

3. The method for preparing an ultrathin wood diaphragm according to claim 2, wherein in step S2, the processing time of the microwave treatment is 5-15 min.

4. The method of claim 1, wherein in step S2, the wood test piece is made of one selected from balsa wood, fir wood and paulownia wood.

5. The method for preparing the ultrathin wood diaphragm according to claim 1, wherein the wood test piece has the specification: the longitudinal direction is (0.1 to 0.5) mx (0.1 to 0.5) mm.

6. The method of claim 1, wherein in step S3, the first solvent is one selected from ether, petroleum ether, benzene, and carbon disulfide.

7. The method for preparing an ultrathin wood diaphragm according to claim 1, wherein in step S4, the mass ratio of the pretreated wood specimen to the second solvent is 1: (3-8).

8. The method for preparing the ultrathin wood diaphragm according to claim 1, wherein in step S5, the hot pressing temperature in the hot pressing process is controlled to be 100 to 120 ℃, and the hot pressing pressure is controlled to be 10 to 20 MPa.

9. The method for preparing an ultrathin wood diaphragm according to claim 8, wherein in step S5, the hot pressing time of the hot pressing process is 12-24 hours.

10. The method for preparing an ultrathin wood diaphragm according to claim 1, wherein in step S1, the temperature of the choline chloride, acetic anhydride and acetic acid is controlled to 80-100 ℃.

Technical Field

The invention relates to the technical field of earphone accessory manufacturing, in particular to a preparation method of an ultrathin wood diaphragm.

Background

The global headset market has continued to rise in recent years, benefiting from the development of the global smart terminal market and the consumer fashion of ear wear. The element in the earphone that generates the vibrations is a diaphragm. When an electric signal passes through the coil, the magnetic field changes to cause the diaphragm to deform under stress, and the diaphragm vibrates at a high speed along with the rapid change of the electric signal to enable surrounding air to fluctuate, so that sound waves are generated. The diaphragms of different materials, sizes and shapes can be distinguished in sound performance, so that the diaphragms play a decisive role in the sound performance of the earphone unit.

The types of the vibrating diaphragms include paper vibrating diaphragms, plastic vibrating diaphragms, metal vibrating diaphragms, ceramic vibrating diaphragms, carbon-based material vibrating diaphragms and the like. The pure paper diaphragm has poor moisture resistance, and a coating needs to be sprayed on the paper base or modified, so that the paper diaphragm has a complex process and is not environment-friendly. Most plastic diaphragms are difficult to degrade and are not environment-friendly. Metal, ceramic and carbon-based material diaphragms are generally more costly than plastic diaphragms and are complicated to manufacture, limiting their widespread use. In comparison, the diaphragm is more competitive with the wooden diaphragm. From the aspect of steady-state vibration, the main requirement of the diaphragm is to be as large as possible than the dynamic elastic modulus (E/rho); the wood has the characteristic requirements of low density and high elastic modulus required by the vibrating diaphragm material, the theoretical tensile strength of the wood fiber can reach 7.5 GPa at most, and the elastic modulus can reach 120 GPa, which is higher than the mechanical properties of common metal, ceramic and other composite materials. Therefore, the natural degradable wood is used for preparing the acoustic diaphragm, so that the excellent acoustic characteristics of the wood can be exerted, and the wood has the mechanical property matched with the requirement of the diaphragm, so that the wood diaphragm has the advantages of high conduction rate, good natural attenuation, contribution to high-frequency analysis and extension, reduction of segmentation vibration and the like. However, the current research on the wood diaphragm still has some problems to be further solved.

For example, chinese patent application with a patent application number of CN201610391578.3 discloses a method for preparing a novel wooden earphone diaphragm, which comprises the following steps: (1) cutting high-quality wood into veneer with the length of 2 cm, the width of 2 cm and the thickness of 0.3-0.5 mm, and then placing the veneer into hot air drying equipment to be dried for 2-3 hours, wherein the drying temperature is set to be 60-80 ℃; (2) preparing 65% ethanol solution, adding titanium dioxide powder with the mass of 3-5% of the solution into the ethanol solution, fully stirring for 15-20 minutes, putting the veneer dried in the step (1) into the solution, soaking for 10-12 hours, taking out and naturally drying; (3) soaking the veneer dried in the step (2) in glycerol for 5-7 hours, taking out, draining, and drying in hot air drying equipment for 3-4 hours at the drying temperature of 60-80 ℃; (4) and (4) vertically cutting a gap from the center point to one side of the dried veneer in the step (3), then putting the veneer into a die for 10-15 minutes, taking out, and then shearing and bonding the veneer according to the shape of the die to form a vibrating diaphragm. However, the diaphragm prepared by the method has the defects of easy moisture absorption and easy deformation.

Disclosure of Invention

In order to solve the technical problem, the invention provides a preparation method of an ultrathin wood diaphragm.

The technical scheme of the invention is as follows: a preparation method of an ultrathin wood diaphragm comprises the following operation steps:

s1: mixing choline chloride, acetic anhydride and acetic acid to form uniform transparent liquid, wherein the weight ratio of choline chloride: acetic anhydride: the molar ratio of acetic acid is 1: (1-3): (1-3) obtaining a DES system mixed solution;

s2: soaking the wood test piece into the DES system mixed solution in the step S1, and performing microwave treatment to obtain a modified wood test piece; the mass ratio of the wood test piece to the DES system mixed liquid is 1: (10-30);

s3: taking out the modified wood test piece in the step S2, cooling to room temperature, and soaking in a first solvent to remove residual reaction liquid to obtain a pretreated wood test piece; in the step, the soaking time is 2-6 h;

s4: taking out the pretreated wood test piece in the step S3, and soaking the pretreated wood test piece in a second solvent formed by absolute ethyl alcohol or acetone to obtain a fine-treated wood test piece;

s5: and (4) carrying out hot pressing on the fine-processed wood test piece in the step S4 to obtain the ultrathin wood diaphragm.

In the prior art, the vibrating diaphragm for the earphone is prepared by drying the veneer, soaking the veneer in an ethanol solution of titanium dioxide, air-drying, soaking in glycerol, drying and pressing, but the structure shown by wood is not changed by the treatment, and hydrophilic groups on the surface still exist, so that the property of the vibrating diaphragm is slightly changed due to the fact that moisture is easily absorbed in the use process in the future, and the sounding function of the earphone is damaged; simultaneously because many times of stoving can make the too much structure water of vibrating diaphragm loss, inner structure is destroyed, compresses tightly afterwards, can produce the internal stress in vibrating diaphragm inside, and the warpage can be changeed to the wooden vibrating diaphragm of preparation, is difficult to guarantee the good dimensional stability of wooden vibrating diaphragm.

In the technical scheme, the thin wood chips are subjected to partial delignification and hemicellulose treatment through a ternary DES system consisting of choline chloride, acetic anhydride and acetic acid, lignin and hemicellulose combined with saccharides are dissolved, wood densification treatment is carried out after the lignin and the hemicellulose are removed, the thickness of the wood chips can be reduced by 97% (reduced from 300 mu m to 8 mu m), the vibration membrane is made thinner, the sound transmission speed can be improved, simultaneously, the attenuation caused by vibration is reduced, the sound energy efficiency is improved, the precise amplitude of the vibrating diaphragm is ensured, and the diaphragm also has excellent tensile strength (342 MPa) and elastic modulus (43.65 GPa) compared with the original wood, the tensile strength of the vibrating diaphragm is improved by nearly 20 times, the elastic modulus of the vibrating diaphragm is improved by 35 times, the rigidity of the vibrating diaphragm is very strong, the vibrating diaphragm is difficult to deform, and the good dimensional stability of the wooden vibrating diaphragm is ensured; the ternary DES system which is composed of choline chloride, acetic anhydride and acetic acid and used for removing lignin and hemicellulose can modify the surface of the veneer, the number of surface hydrophilic groups is reduced, an ester group is formed by replacing hydrogen on hydroxyl with an acetyl ketone group of the acid anhydride, the hydrophobic treatment of the surface of the veneer is completed through the formation of the ester group, the diaphragm prepared after the treatment is not easy to absorb moisture, the service life of the earphone is prolonged, and the quality of the earphone is ensured.

Preferably, in step S2, the microwave treatment temperature is 50-90 ℃ and the power is 500-1000W.

Preferably, in step S2, the processing time of the microwave treatment is 5-15 min.

Preferably, in step S2, the material of the wood specimen is selected from one of basha, fir and paulownia.

Preferably, the wood test piece has the following specifications: the longitudinal direction is (0.1 to 0.5) mx (0.1 to 0.5) mm.

Preferably, in step S3, the first solvent is selected from one of ethyl ether, petroleum ether, benzene and carbon disulfide.

Preferably, in step S4, the mass ratio of the pretreated wood specimen to the second solvent is 1: (3-8).

Preferably, in step S5, the hot pressing temperature in the hot pressing process is controlled to be 100 to 120 ℃, and the hot pressing pressure is controlled to be 10 to 20 MPa.

Preferably, in step S5, the hot pressing time of the hot pressing process is 12-24 h.

Preferably, in step S1, the temperature of the choline chloride, acetic anhydride and acetic acid is controlled to be 80-100 ℃.

In conclusion, the beneficial effects of the invention are as follows:

(1) according to the invention, after the wood test piece is treated by the ternary DES system consisting of choline chloride, acetic anhydride and acetic acid, hydrogen of hydroxyl on the surface of the prepared diaphragm is replaced by hydrophobic groups, so that the diaphragm has good moisture-proof and deformation-resistant capabilities; but the wood is easy to deform, and the vibrating diaphragm is very thin and has high elastic modulus through hot pressing after lignin and hemicellulose are removed, so that the prepared wood vibrating diaphragm has higher rigidity and is less prone to warping deformation, and the good dimensional stability of the wood vibrating diaphragm is further ensured;

(2) according to the invention, the ternary DES system consisting of choline chloride, acetic anhydride and acetic acid is adopted to delignify and hemicellulose from the wood chips, so that the problems that waste such as sulfite is difficult to treat, the energy consumption of the treatment process is high, the environment is polluted and the like in the traditional sodium hydroxide/sodium sulfite method for preparing the wood diaphragm by using the delignification and hemicellulose in the past are avoided;

(3) the preparation method of the invention can not dissolve cellulose, can not destroy the crystal form of the cellulose, can not reduce the crystallinity of the cellulose, can not cause the reduction of the specific dynamic elastic modulus and the increase of the logarithmic decrement coefficient, and can not influence the acoustic property;

(4) the invention only partially removes lignin and hemicellulose, and compared with completely removing lignin and hemicellulose, the mechanical property, especially the compression property, of the wood chip is better.

Drawings

Fig. 1 is an analysis graph of resonance frequency dependence of acoustic performance characterization of the diaphragm in example 1.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the following detailed description will be made with reference to the embodiments of the present invention, which are only for explanation and not for limitation of the present invention.

Example 1

A preparation method of an ultrathin wood diaphragm comprises the following operation steps:

s1: mixing choline chloride, acetic anhydride and acetic acid at 80 ℃ to form a uniform transparent liquid, wherein the weight ratio of choline chloride: acetic anhydride: the molar ratio of acetic acid is 1: 1: 1, obtaining DES system mixed liquor;

s2: soaking the wood test piece into the DES system mixed solution in the step S1, and performing microwave treatment to obtain a modified wood test piece; the mass ratio of the wood test piece to the DES system mixed liquid is 1: 20;

s3: taking out the modified wood test piece in the step S2, cooling to room temperature, and soaking in a first solvent to remove residual reaction liquid to obtain a pretreated wood test piece; in the step, the soaking time is 6 hours;

s4: taking out the pretreated wood test piece in the step S3, and soaking the pretreated wood test piece in a second solvent formed by absolute ethyl alcohol to obtain a fine-treated wood test piece;

s5: and (4) carrying out hot pressing on the fine-processed wood test piece in the step S4 to obtain the ultrathin wood diaphragm.

In step S2, the temperature of the microwave treatment is 90 ℃ and the power is 1000W.

In step S2, the processing time of the microwave processing is 15 min.

In step S2, the material of the wood specimen is balsa wood.

The specification of the wood test piece is as follows: the longitudinal direction x the chord direction x the radial direction is 0.1m x 0.3 mm.

In step S3, the first solvent is diethyl ether.

In step S4, the mass ratio of the pretreated wood specimen to the second solvent is 1: 5.

in step S5, the hot pressing temperature of the hot pressing process is controlled to 100 ℃, and the hot pressing pressure is controlled to 10 MPa.

In step S5, the hot pressing time of the hot pressing process is 12 h.

Example 2

A preparation method of an ultrathin wood diaphragm comprises the following operation steps:

s1: mixing choline chloride, acetic anhydride and acetic acid at 80 ℃ to form a uniform transparent liquid, wherein the weight ratio of choline chloride: acetic anhydride: the molar ratio of acetic acid is 1: 3: 3, obtaining DES system mixed liquid;

s2: soaking the wood test piece into the DES system mixed solution in the step S1, and performing microwave treatment to obtain a modified wood test piece; the mass ratio of the wood test piece to the DES system mixed liquid is 1: 20;

s3: taking out the modified wood test piece in the step S2, cooling to room temperature, and soaking in a first solvent to remove residual reaction liquid to obtain a pretreated wood test piece; in the step, the soaking time is 6 hours;

s4: taking out the pretreated wood test piece in the step S3, and soaking the pretreated wood test piece in a second solvent formed by absolute ethyl alcohol to obtain a fine-treated wood test piece;

s5: and (4) carrying out hot pressing on the fine-processed wood test piece in the step S4 to obtain the ultrathin wood diaphragm.

In step S2, the temperature of the microwave treatment is 90 ℃ and the power is 1000W.

In step S2, the processing time of the microwave processing is 15 min.

In step S2, the material of the wood test piece is balsa wood

The specification of the wood test piece is as follows: the longitudinal direction x the chord direction x the radial direction is 0.1m x 0.3 mm.

In step S3, the first solvent is selected from one of ethyl ether, petroleum ether, benzene and carbon disulfide.

In step S4, the mass ratio of the pretreated wood specimen to the second solvent is 1: 5.

in step S5, the hot-pressing temperature in the hot-pressing process is controlled to be 100 to 120 ℃, and the hot-pressing pressure is controlled to be 10 MPa.

In step S5, the hot pressing time of the hot pressing process is 12 h.

Example 3

A preparation method of an ultrathin wood diaphragm comprises the following operation steps:

s1: mixing choline chloride, acetic anhydride and acetic acid at 80 ℃ to form a uniform transparent liquid, wherein the weight ratio of choline chloride: acetic anhydride: the molar ratio of acetic acid is 1: 1: 1, obtaining DES system mixed liquor;

s2: soaking the wood test piece into the DES system mixed solution in the step S1, and performing microwave treatment to obtain a modified wood test piece; the mass ratio of the wood test piece to the DES system mixed liquid is 1: 30, of a nitrogen-containing gas;

s3: taking out the modified wood test piece in the step S2, cooling to room temperature, and soaking in a first solvent to remove residual reaction liquid to obtain a pretreated wood test piece; in the step, the soaking time is 6 hours;

s4: taking out the pretreated wood test piece in the step S3, and soaking the pretreated wood test piece in a second solvent formed by absolute ethyl alcohol to obtain a fine-treated wood test piece;

s5: and (4) carrying out hot pressing on the fine-processed wood test piece in the step S4 to obtain the ultrathin wood diaphragm.

In step S2, the microwave treatment temperature is 50 ℃ and the power is 500W.

In step S2, the processing time of the microwave processing is 15 min.

In step S2, the material of the wood specimen is balsa wood.

The specification of the wood test piece is as follows: the longitudinal direction x the chord direction x the radial direction is 0.1m x 0.3 mm.

In step S3, the first solvent is diethyl ether.

In step S4, the mass ratio of the pretreated wood specimen to the second solvent is 1: 5.

in step S5, the hot pressing temperature of the hot pressing process is controlled to 100 ℃, and the hot pressing pressure is controlled to 10 MPa.

In step S5, the hot pressing time of the hot pressing process is 12 h.

Comparative example

A preparation method of a novel wooden earphone diaphragm comprises the following specific steps: (1) cutting high-quality wood into wood veneers with the length of 10 cm, the width of 10 cm and the thickness of 0.3mm, and then placing the wood veneers into hot air drying equipment to be dried for 2-3 hours, wherein the drying temperature is set to be 60-80 ℃; (2) preparing 65% ethanol solution, adding titanium dioxide powder with the mass of 3-5% of the solution into the ethanol solution, fully stirring for 15-20 minutes, putting the veneer dried in the step (1) into the solution, soaking for 10-12 hours, taking out and naturally drying; (3) soaking the veneer dried in the step (2) in glycerol for 5-7 hours, taking out, draining, and drying in hot air drying equipment for 3-4 hours at the drying temperature of 60-80 ℃; (4) and (4) vertically cutting a gap from the center point to one side of the dried veneer in the step (3), then putting the veneer into a die for 10-15 minutes, taking out, and then shearing and bonding the veneer according to the shape of the die to form a vibrating diaphragm.

With respect to the wood diaphragm obtained in the above embodiment, the inventors performed the following test experiments:

1. measurement of tensile Strength

Testing the tensile strength of the wood vibrating diaphragm by adopting a mechanical tensile testing machine, and firstly measuring the length, width and thickness of the wood vibrating diaphragm; respectively adjusting a force scale pointer and an extension scale pointer of the tester to respectively zero; the test speed is 100 mm/min, the test piece is parallelly arranged between the upper chuck and the lower chuck, the long axis direction of the test piece is consistent with the central line direction of the upper chuck and the lower chuck, and then the chucks are uniformly and firmly clamped to prevent the test piece from slipping but cannot be damaged; starting the motor, and testing one by one; when the sample is broken, the stretching is automatically stopped, and the reading is respectively carried out from the force disc; the test results are shown in table 1:

TABLE 1 tensile Strength test results

It can be seen from the above table that the diaphragm obtained by the method of the present invention is indeed superior in tensile strength to the diaphragms obtained by the prior art.

2. Measurement of modulus of elasticity

The elastic modulus is measured according to the detection method (three-point bending) provided in GB/T17657-2013, and the distance l between the two supports is respectively obtained₁Mm, specimen width b/mm, specimen thickness t/mm, increase F in linear section load on load-deflection curve₁-F₂N, increase of deformation in the middle of the specimen a₂-a₁In mm, the modulus of elasticity(ii) a The measurement results are shown in Table 2;

TABLE 2 measurement results of modulus of elasticity

The table shows that the vibrating diaphragm prepared by the method has larger elastic modulus, the rigidity of the vibrating diaphragm is larger, and the vibrating diaphragm is not easy to warp and deform, so that the wooden vibrating diaphragm has good dimensional stability;

3. the characterization of the acoustic properties of the diaphragm, i.e., the analysis of the resonance frequency dependence, is shown in fig. 1 for the test of example 1.

It can be seen that the sound production effect of the wood vibrating plate provided in example 1 is excellent.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.