Binder-free molecular sieve particle material, preparation method and micro speaker

Abstract

The present invention provides a method for preparing a binder-free molecular sieve particulate material, comprising the following steps: step S1, adding chitosan to an acidic aqueous solution, stirring and dissolving, and then ultrasonicating to prepare a chitosan solution; step S2, adding molecular sieves to the chitosan solution, stirring evenly, and obtaining a suspension; step S3, pouring the suspension into an oil phase dispersed with an emulsifier under magnetic stirring to obtain an oil-in-water emulsion; step S4, adding a crosslinking agent to the oil-in-water emulsion, stirring and then standing to obtain a mixed solution of oil and water layers; step S5, recovering the upper oil phase of the mixed solution, and washing and drying the solid particles precipitated in the lower layer of the mixed solution to obtain a crude product; step S6, high-temperature roasting of the crude product to obtain a binder-free molecular sieve particulate material. The above-mentioned preparation method is simple to operate, and can prepare molecular sieve particles with good dispersion, uniform size, and high sphericity. The particles can be directly filled into the back cavity of the speaker, which can significantly improve the low-frequency acoustic performance of the speaker.

Description

Technical Field

[0001] The invention relates to a method for preparing molecular sieve particles, and in particular to a binder-free molecular sieve particle material, a preparation method and a micro loudspeaker. Background Art

[0002] With the rapid development of multimedia devices, speakers are widely used in ultra-thin mobile phones, laptops, headphones, smart watches and other electronic devices. At the same time, the development trend of miniaturization, lightweight and integration of speakers has put forward higher requirements on the size and sound quality of speakers. However, the pursuit of small-sized speakers will lead to limited back cavity volume, which is theoretically contrary to high-quality low-frequency sound output performance. In order to make small-sized speakers have the same low-frequency response as large-sized speakers, acoustic filling materials have been gradually developed.

[0003] In recent years, porous materials such as activated carbon, silica, molecular sieves, and mesoporous materials have been used as acoustic filling materials to expand the acoustic virtual volume of the speaker's back cavity, improve the acoustic compliance of the back cavity, and thus expand the low-frequency output range. Among them, microporous molecular sieves (~0.5nm) with a pore size slightly larger than that of air gas molecules have shown a more obvious effect. However, molecular sieves are generally 10nm-10μm powders, which are difficult to be directly used in the back cavity of a micro-speaker with air pressure disturbances. They usually need to be prepared into particles of hundreds of microns to fill the back cavity of the speaker.

[0004] The existing methods for preparing molecular sieve particles of 100 micrometers are mainly adhesive bonding method, "in-situ" synthesis, and alginate gel method. The main problems are: the adhesive blocks the micropores of the molecular sieve during the molding process, reducing its gas adsorption performance, and in subsequent work, the volatilized organic matter will occupy the molecular sieve adsorption site, weakening its acoustic performance; the "in-situ" synthesis method limits the distribution of the molecular sieve, and the product morphology is poorly uniform, and the crystal distribution is uneven, which limits its acoustic performance to a certain extent; in addition, the scope of use of the alginate gel method is very limited, and it is only suitable for hydrogen-type, sodium, potassium and other monovalent metal cation molecular sieves, and divalent magnesium ion-loaded molecular sieves. Summary of the invention

[0005] The present invention is made to solve the above-mentioned problems, and aims to provide a binder-free molecular sieve particle material, a preparation method and a micro speaker.

[0006] The present invention provides a method for preparing a binder-free molecular sieve particulate material, which has the following characteristics and comprises the following steps:

[0007] Step S1, adding chitosan into an acidic aqueous solution, stirring and dissolving, and then performing ultrasound to prepare a chitosan solution;

[0008] Step S2, adding molecular sieves to the chitosan solution and stirring evenly to obtain a suspension;

[0009] Step S3, pouring the suspension into the oil phase dispersed with an emulsifier under magnetic stirring to obtain a water-in-oil emulsion;

[0010] Step S4, adding a crosslinking agent to the water-in-oil emulsion, stirring and then standing to obtain a mixed solution of oil-water layers;

[0011] Step S5, recovering the upper oil phase of the mixed solution, and washing and drying the solid particles precipitated in the lower layer of the mixed solution to obtain a crude product;

[0012] Step S6, calcining the crude product at high temperature to obtain a binder-free molecular sieve particle material.

[0013] The method for preparing the binder-free molecular sieve particulate material provided by the present invention may also have the following characteristics: wherein the acidic aqueous solution is a mixed solution of glacial acetic acid and deionized water, the volume of the acidic aqueous solution is 50 mL-100 mL, preferably 50 mL, the mass fraction of glacial acetic acid is 0.5 wt%-5.0 wt%, preferably 1.5 wt%, and in step S1, chitosan is added to the acidic aqueous solution, stirred to dissolve and then ultrasonicated for 1 hour to prepare a chitosan solution.

[0014] The method for preparing the binder-free molecular sieve particulate material provided by the present invention may also have the following characteristics: in the suspension, the mass fraction of chitosan is 1.49wt% to 6.38wt%, preferably 1.49wt%, and the mass fraction of the molecular sieve is 13.56wt% to 40wt%, preferably 23.88wt%.

[0015] The method for preparing the binder-free molecular sieve particulate material provided by the present invention may also have the following characteristics: wherein the molecular sieve comprises a framework and extra-framework cations,

[0016] The skeleton includes SiO2, non-metal or metal oxide M x O y , metal oxide M x O y In the above formula, M is any one or more of aluminum, titanium, boron, magnesium or iron, preferably aluminum.

[0017] The extra-framework cation is at least one of a hydrogen ion, an alkali metal ion or an alkaline earth metal ion, including Ca 2+ , Ba 2+ , K + 、Na + 、Ti 2+ wait.

[0018] The topological structure of the molecular sieve is any one or more of MFI, FAU, MWW, MOR, BEA, FER, CHA, MTN, MEL, AEL, ATO, NON, and RUT, preferably LTA, MWW, and MOR.

[0019] The method for preparing the binder-free molecular sieve particulate material provided by the present invention may also have the following characteristics: wherein, in the water-in-oil emulsion, the volume ratio of the oil phase to the water phase is 1:(2-7), preferably 1:6,

[0020] The oil phase is any one or more of liquid paraffin, glycerol, and ethylene glycol, preferably liquid paraffin.

[0021] The emulsifier dispersed in the oil phase is any one or more of polyoxyethylene, polyoxypropylene copolymer, sorbitan fatty acid ester, sucrose fatty acid, polyoxyethylene fatty alcohol ether, polyoxyethylene polyfatty alcohol ether, sorbitan oleate, polyoxyethylene oleyl alcohol ether, polyoxyethylene beeswax, and sorbitan trioleate, preferably sorbitan oleate.

[0022] The method for preparing the binder-free molecular sieve particulate material provided by the present invention may also have the following characteristics: wherein the cross-linking agent is formaldehyde, glutaraldehyde or epichlorohydrin, preferably glutaraldehyde (25wt% aqueous solution), and the amount of the cross-linking agent added is 0.4mL-4.0mL,

[0023] In step S4, after adding the crosslinking agent to the water-in-oil emulsion, the mixture is stirred for 10 min to 60 min, preferably 30 min, and allowed to stand for 12 h to 48 h, preferably 24 h.

[0024] The method for preparing the binder-free molecular sieve particulate material provided by the present invention may also have the following characteristics: wherein, in step S5, during washing and drying, the solid particles settled in the lower layer are washed with deionized water and then placed in an oven at 80° C. for drying for 24 hours.

[0025] The method for preparing the binder-free molecular sieve particulate material provided by the present invention may also have the following characteristics: wherein, in step S6, during high-temperature calcination, the crude product is placed in a muffle furnace and heated to 500°C-600°C, preferably 550°C, and calcined for 6 hours.

[0026] The present invention also provides a binderless molecular sieve particulate material having the following characteristics: it is prepared by any of the above-mentioned methods for preparing a binderless molecular sieve particulate material, wherein the interior of the binderless molecular sieve particulate material is a multi-level pore structure, including nanoscale micropores and mesopores, and the particle size of the binderless molecular sieve particulate material is 100μm-1000μm, preferably 300μm-400μm.

[0027] The present invention also provides a micro speaker having the following characteristics: the back cavity filling material of the micro speaker adopts the above-mentioned binder-free molecular sieve particle material.

[0028] Functions and Effects of the Invention

[0029] According to the binder-free molecular sieve particulate material and preparation method thereof involved in the present invention, firstly, a chitosan aqueous solution is prepared as an aqueous phase, mixed with a molecular sieve powder to obtain a uniform emulsion, and then an oil phase dispersed with an emulsifier is added, and under the action of shear force, chitosan and zeolite mixed droplets of 100 microns are generated to obtain an oil-in-water emulsion, and a cross-linking agent is added to rapidly solidify the droplets, and after washing and drying, high-temperature roasting is performed to remove organic matter to obtain binder-free molecular sieve particles with uniform morphology, high sphericity, and good dispersion. The present invention adopts a chitosan cross-linking method to shape the molecular sieve, realizes the preparation of binder-free molecular sieve microspheres of 100 microns, good sphericity, and uniform size, and solves the problem that alginate reacts quickly with divalent cation molecular sieves and cannot be formed.

[0030] Furthermore, the present invention adds an emulsifier to the oil-in-water system to stabilize the surface of the spherical droplets, so that the droplets are fully cross-linked to obtain spherical particles, thereby avoiding the problems of particle agglomeration and non-spherical particles obtained by screening of debris during the molding process. At the same time, after the cross-linking reaction is completed, during the oil-water separation process, the chitosan microspheres settle due to gravity, and the solid phase is collected and washed with water and then dried to obtain chitosan molecular sieve composite microspheres, thereby avoiding the problem of the existing method requiring sufficient washing of the organic phase.

[0031] Therefore, the preparation method of the binder-free molecular sieve particulate material of the present invention is simple to operate, has mild conditions, and has high repeatability. It can be used to form various commonly used types of molecular sieves, and the preparation raw materials are green and economical. At the same time, the product can be optimized by changing the preparation conditions such as the amount of molecular sieve added, the oil phase volume, the amount of chitosan added, and the amount of cross-linking agent added.

[0032] In addition, the preparation method of the present invention avoids adding a binder during the molding process, and can maintain the original pore structure of the molecular sieve after calcining to remove organic matter in chitosan, greatly retaining the effective adsorption specific surface area, avoiding the problem of volatile organic matter occupying adsorption sites during use, and further optimizing the low-frequency acoustic performance. Therefore, the binder-free molecular sieve particulate material prepared by the present invention can be used as an acoustic filling material and directly filled in the back cavity of a micro-speaker, which can significantly improve the low-frequency acoustic performance of the micro-speaker, expand the low-frequency acoustic output range, solve the problem of impaired sound quality caused by the miniaturization and lightweight development of speakers, and provide a new idea for the further development of micro-speakers. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1is a schematic flow chart of a method for preparing a binder-free molecular sieve particulate material in Example 1 of the present invention;

[0034] Figure 2 is the XRD spectrum of 5A powder versus 5A molecular sieve particles in Example 1 of the present invention;

[0035] Figure 3 is a comparison diagram of nitrogen adsorption-desorption isotherms of molecular sieve particles prepared in Example 1 of the present invention;

[0036] Figure 4 is a pore size distribution curve of the molecular sieve particles prepared in Example 1 of the present invention;

[0037] Figure 5 This is a comparison of optical microscope photos of 5A molecular sieve particles obtained by adding different masses of chitosan in Example 1 of the present invention;

[0038] Figure 6 This is a comparison of optical microscope photographs of 5A molecular sieve particles obtained by adding different volumes of cross-linking agent in Example 1 of the present invention;

[0039] Figure 7 is a comparison of optical microscope photographs of 5A molecular sieve particles obtained by using different volumes of oil phase in Example 1 of the present invention;

[0040] Figure 8 This is a comparison of optical microscope photographs of 5A molecular sieve particles obtained by adding different masses of 5A zeolite in Example 1 of the present invention;

[0041] Fig. 9 is the XRD spectrum of the MWW powder and the MWW molecular sieve particles in Example 2 of the present invention;

[0042] Fig.10 is the XRD spectrum of the MOR powder compared with the MOR molecular sieve particles in Example 3 of the present invention;

[0043] Fig.11 It is a comparison diagram of optical microscope photographs of molecular sieve particles prepared in Example 1, Example 2, and Example 3 of the present invention.

[0044] Fig.12 is an impedance curve diagram of the molecular sieve particles prepared in Example 1 of the present invention before and after being filled in a micro speaker;

[0045] Fig.13 is an impedance curve diagram of the molecular sieve particles prepared in Example 2 of the present invention before and after being filled in a micro speaker;

[0046] Fig.14is an impedance curve diagram of the molecular sieve particles prepared in Example 3 of the present invention before and after being filled in a micro speaker; DETAILED DESCRIPTION

[0047] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the following embodiments and drawings specifically describe a binder-free molecular sieve particle material, preparation method and micro speaker of the present invention.

[0048] <Example 1>

[0049] Figure 1 It is a schematic flow chart of the method for preparing the binder-free molecular sieve particulate material in Example 1 of the present invention.

[0050] like Figure 1 As shown, a method for preparing a binder-free molecular sieve particle material in this embodiment comprises the following steps:

[0051] Step S1, adding chitosan to an acidic aqueous solution, stirring and dissolving, and then performing ultrasound to prepare a chitosan solution. The specific process is as follows:

[0052] Weigh 1.0 g of chitosan (200 mPa·s~400 mPa·s) and add it to 50 mL of acidic aqueous solution (5.0 wt% glacial acetic acid). Stir at room temperature until the chitosan is completely dissolved to obtain a transparent gel solution. Continue ultrasonication for 60 min to remove bubbles in the gel solution to obtain a chitosan solution with good fluidity.

[0053] Step S2, adding molecular sieves to the chitosan solution, stirring evenly, to obtain a suspension, the specific process is as follows:

[0054] Under stirring conditions, 16 g of 5A molecular sieve (purchased from Dalian Zhuoran Environmental Protection Technology Co., Ltd., cage-structured calcium aluminosilicate, particle size 3 μm to 6 μm, silicon-aluminum ratio of about 2.2) was slowly added to the chitosan solution, and stirred at room temperature until homogeneous to obtain a white suspension.

[0055] Step S3, pouring the suspension into the oil phase dispersed with the emulsifier under magnetic stirring to obtain a water-in-oil emulsion, the specific process is as follows:

[0056] The suspension was poured into 300 mL of liquid paraffin under magnetic stirring, in which 1 g of sorbitan oleate (Span80) was dispersed. The magnetic stirring speed was adjusted to 850 rpm. Under shearing action, the suspension formed droplets of about 350 μm with good dispersion to obtain a water-in-oil emulsion.

[0057] Step S4, adding a crosslinking agent to the water-in-oil emulsion, stirring and then standing to obtain a mixed solution of oil and water layers, the specific process is as follows:

[0058] Add 0.8 mL of crosslinking agent glutaraldehyde (25 wt % aqueous solution) to the oil-in-water system and continue stirring for 30 min. The droplets are crosslinked and solidified, and the color of the mixed liquid changes from white to light brown. Stop stirring, the solid particles begin to settle, and let it stand for 24 h to obtain an oil-water layered mixed liquid.

[0059] Step S5, recovering the upper oil phase of the mixed solution, and washing and drying the solid particles precipitated in the lower layer of the mixed solution to obtain a crude product, the specific process is as follows:

[0060] The upper organic phase of the mixed solution was recovered, and the solid particles settled in the lower layer were washed with deionized water for several times, and then placed in an oven at 80° C. and dried for 24 hours to obtain chitosan and 5A molecular sieve composite particles, which were the crude product.

[0061] Step S6, calcining the crude product at high temperature to obtain a binder-free molecular sieve particle material, the specific process is as follows:

[0062] The crude product was placed in a muffle furnace and programmed to heat up to 550°C, and calcined for 6 hours to remove the organic components in the chitosan, thereby obtaining a pure white binder-free 5A molecular sieve particulate material.

[0063] Figure 2 It is the XRD spectrum of 5A powder and 5A molecular sieve particles in Example 1 of the present invention.

[0064] like Figure 2 As shown, the XRD of the binder-free 5A molecular sieve particulate material prepared in Example 1 matches the characteristic peaks of the 5A molecular sieve powder before molding, indicating that the crystal structure of the 5A molecular sieve is not destroyed during the molding process, and confirming that the molding process is relatively mild.

[0065] Figure 3 It is a comparison diagram of nitrogen adsorption-desorption isotherms of the molecular sieve particles prepared in Example 1 of the present invention.

[0066] like Figure 3 As shown in the figure, it can be seen from the nitrogen adsorption-desorption isotherm curve that the total pore volume of the binder-free 5A molecular sieve microsphere material prepared in this embodiment is 0.33 cc / g, which is slightly larger than 0.31 cc / g of the original zeolite powder; the total specific surface area is 574.15 m 2 / g, slightly less than zeolite powder 635.26m 2 / g. This indicates that the molecular sieve microsphere material retains the characteristics of the original zeolite to a large extent after molding, has a rich pore structure and a large specific surface area, can adsorb a large number of gas molecules on its surface, and utilize the adsorption-desorption effect of gas molecules to increase the volume of the virtual back cavity.

[0067] Figure 4It is a pore size distribution curve diagram of the molecular sieve particles prepared in Example 1 of the present invention.

[0068] like Figure 4 As shown in the figure, the DFT model was used to calculate and analyze the pore size distribution of the 5A molecular sieve powder before molding and the microspheres after molding. Before molding, the pore size distribution of the 5A molecular sieve was around 0.59nm, 1.40nm, 1.76nm and 4nm; after molding, the pore size distribution of the molecular sieve particles was around 0.59nm, 1.11nm, 1.77nm and 3.47nm. The results show that during the entire molding process, mild conditions did not change the pore size of the original 5A molecular sieve powder, ensuring its pore size and porosity distribution for effective adsorption of air gas molecules.

[0069] In this embodiment, different masses of chitosan (0.6 g-1.1 g) were added under the condition of adding sufficient glacial acetic acid and cross-linking agent to prepare binder-free 5A molecular sieve particulate materials. The preparation material ratio is as follows: chitosan: water (5wt% acetic acid): 5A molecular sieve: glutaraldehyde: paraffin oil: Span80 = 0.6g-1.1g: 50mL: 16g: 0.8mL: 300mL: 1g.

[0070] Figure 5 This is a comparison of optical microscope photographs of 5A molecular sieve particles obtained by adding different masses of chitosan in Example 1 of the present invention.

[0071] like Figure 5 As shown, the morphology of the binder-free 5A zeolite molecular sieve particles prepared in this embodiment 1 is related to the amount of chitosan added. When the amount of chitosan added is 0.6g, a dispersed irregular block material is obtained; when the amount added is 0.7g, spherical particles with uniform morphology are formed, but there is mutual adhesion of particles, resulting in poor dispersibility, which is due to the fact that the trace amount of cross-linking of chitosan is not enough to wrap the added zeolite; when the amount added is increased to 0.8g~1.0g, zeolite particles with uniform scale, uniform morphology and good dispersibility are obtained; when it continues to increase to 1.1g, due to the increase in viscosity, shearing leads to the formation of ellipsoidal monodisperse particles. In addition, as the chitosan content increases, the color of the obtained product changes from light brown to dark brown, which is caused by the increase in the degree of cross-linking in a single particle.

[0072] In this embodiment, different volumes of cross-linking agent (0.5 mL-1.0 mL) were added under the condition of adding sufficient amount of chitosan and glacial acetic acid to prepare binder-free 5A molecular sieve particulate materials. The preparation material ratio is as follows: chitosan: water (5wt% acetic acid): 5A molecular sieve: glutaraldehyde: paraffin oil: Span80 = 1.0 g: 50 mL: 16 g: 0.5 mL-1.0 mL: 300 mL: 1 g.

[0073] Figure 6 This is a comparison of optical microscope photographs of 5A molecular sieve particles obtained by adding different volumes of cross-linking agent in Example 1 of the present invention.

[0074] like Figure 6 As shown, the morphology of the binder-free 5A zeolite molecular sieve particles prepared in this embodiment 1 is closely related to the amount of cross-linking agent added. When the amount of cross-linking agent added is 0.5mL-0.7mL, only trace particles with uneven size distribution can be obtained, and multi-particle bonding phenomenon occurs; when the amount added is 0.8mL, spherical particles with good dispersibility and uniform size are obtained; continuing to increase the amount of cross-linking agent will not affect the morphology of 5A zeolite molecular sieve particles. Therefore, 0.8mL is the minimum value of the cross-linking agent when the binder-free 5A zeolite molecular sieve particles are formed in this embodiment.

[0075] In this embodiment, different volumes of liquid paraffin (220 mL-320 mL) were added under the conditions of adding sufficient amounts of chitosan, cross-linking agent and glacial acetic acid to prepare binder-free 5A molecular sieve particulate materials. The preparation material ratios were as follows: chitosan: water (5 wt% acetic acid): 5A molecular sieve: glutaraldehyde: paraffin oil: Span80 = 1.0 g: 50 mL: 16 g: 0.8 mL: 220 mL-320 mL: 1 g.

[0076] Figure 7 This is a comparison of optical microscope photographs of 5A molecular sieve particles obtained by using different volumes of oil phase in Example 1 of the present invention.

[0077] like Figure 7 As shown, the morphology of the binderless 5A zeolite molecular sieve particles prepared in the present embodiment 1 is related to the amount of paraffin oil used. When the oil phase addition amount is 220mL-280mL, particles with uneven scale distribution are obtained, and multi-particle bonding phenomenon occurs. This is due to insufficient oil phase volume, which leads to emulsion instability during cross-linking, resulting in collision bonding; when the addition amount is 300mL, spherical particles with good dispersion and uniform scale are obtained; continue to increase the amount of oil phase, and 5A zeolite molecular sieve particles with good morphology and uniform scale can be obtained. Therefore, 300mL is the minimum value of the amount of oil phase added when the binderless 5A zeolite molecular sieve particles are formed in the present embodiment.

[0078] In this embodiment, different masses of molecular sieves (8g-22g) were added under the conditions of adding sufficient amounts of chitosan, cross-linking agent, glacial acetic acid and oil phase to prepare binder-free 5A molecular sieve particulate materials. The preparation material ratio is as follows: chitosan: water (5wt% acetic acid): 5A molecular sieve: glutaraldehyde: paraffin oil: Span80=1.0g:50mL:8g-22g:0.8mL:300mL:1g.

[0079] Figure 8 This is a comparison of optical microscope photographs of 5A molecular sieve particles obtained by adding different masses of 5A zeolite in Example 1 of the present invention.

[0080] like Figure 8 As shown, the binder-free 5A zeolite molecular sieve particle load prepared in the present embodiment 1 has an optimal value. Based on the above-mentioned preparation material ratio, only the zeolite addition amount is changed. When the 5A zeolite addition amount is 8g, uneven morphology and mutually bonded particles are obtained, which is due to the high concentration of chitosan in a single microsphere, resulting in collision bonding during the cross-linking process; when the addition amount is 10g, spherical particles with better morphology are obtained; when 5A is added and increased to 12g-18g, microspheres with uniform scale and high sphericity are obtained; when the addition amount of 5A is continued to be increased to 20-22g, de-powdering occurs on the surface of the particles, and as the addition amount gradually increases, because the residual carbon calcined after chitosan cross-linking in the particles, the upper limit of the zeolite, i.e., the zeolite loading amount is too high. In addition, as the addition amount of 5A zeolite increases, the microspheres gradually change from brown to white, because the relative content of chitosan in a single microsphere decreases, and the relative content of 5A zeolite increases.

[0081] <Example 2>

[0082] A method for preparing a binder-free molecular sieve particle material in this embodiment comprises the following steps:

[0083] Step S1, adding chitosan to an acidic aqueous solution, stirring and dissolving, and then performing ultrasound to prepare a chitosan solution. The specific process is as follows:

[0084] Weigh 1.0 g of chitosan (200 mPa·s~400 mPa·s) and add it to 50 mL of acidic aqueous solution (5.0 wt% glacial acetic acid). Stir at room temperature until the chitosan is completely dissolved to obtain a transparent gel solution. Continue ultrasonication for 60 min to remove bubbles in the gel solution to obtain a chitosan solution with good fluidity.

[0085] Step S2, adding molecular sieves to the chitosan solution, stirring evenly, to obtain a suspension, the specific process is as follows:

[0086] Under stirring conditions, 10 g of MWW molecular sieve (purchased from Aos Catalytic Materials (Dalian) Co., Ltd., sheet-like aluminosilicate zeolite, silicon-aluminum ratio of about 50, diameter of 0.5 micron to 2 microns) was slowly added to the chitosan solution, and stirred at room temperature until homogeneous to obtain a white suspension.

[0087] Step S3, pouring the suspension into the oil phase dispersed with the emulsifier under magnetic stirring to obtain a water-in-oil emulsion, the specific process is as follows:

[0088] The suspension was poured into 300 mL of liquid paraffin under magnetic stirring, in which 1 g of sorbitan oleate (Span80) was dispersed. The magnetic stirring speed was adjusted to 850 rpm. Under the action of shear, the suspension formed droplets of about 300 to 400 μm with good dispersion, thereby obtaining an oil-in-water emulsion.

[0089] Step S4, adding a crosslinking agent to the water-in-oil emulsion, stirring and then standing to obtain a mixed solution of oil and water layers, the specific process is as follows:

[0090] Add 2.5 mL of crosslinking agent glutaraldehyde (25 wt % aqueous solution) to the oil-in-water system and continue stirring for 30 min. The droplets are crosslinked and solidified, and the color of the mixed liquid changes from white to light brown. Stop stirring, the solid particles begin to settle, and let it stand for 24 h to obtain an oil-water layered mixed liquid.

[0091] Step S5, recovering the upper oil phase of the mixed solution, and washing and drying the solid particles precipitated in the lower layer of the mixed solution to obtain a crude product, the specific process is as follows:

[0092] The upper organic phase of the mixed solution was recovered, and the solid particles settled in the lower layer were washed with deionized water for multiple times, and then placed in an oven at 80° C. to dry for 24 hours to obtain chitosan and MWW molecular sieve composite particles, which were the crude product.

[0093] Step S6, calcining the crude product at high temperature to obtain a binder-free molecular sieve particle material, the specific process is as follows:

[0094] The crude product was placed in a muffle furnace and heated to 550°C, and calcined for 6 hours to remove the organic components in the chitosan and obtain a pure white binder-free MWW molecular sieve particulate material.

[0095] Fig. 9 The XRD pattern of the MWW powder in Example 2 of the present invention is compared with the MWW molecular sieve particles.

[0096] like Fig. 9 As shown, the XRD of the binder-free MWW molecular sieve particulate material prepared in Example 2 matches the characteristic peaks of the MWW molecular sieve powder before molding, indicating that the crystal structure of the MWW molecular sieve is not destroyed during the molding process, and confirming that the molding process is relatively mild.

[0097] <Example 3>

[0098] A method for preparing a binder-free molecular sieve particle material in this embodiment comprises the following steps:

[0099] Step S1, adding chitosan to an acidic aqueous solution, stirring and dissolving, and then performing ultrasound to prepare a chitosan solution. The specific process is as follows:

[0100] Weigh 1.0 g of chitosan (200 mPa·s~400 mPa·s) and add it to 50 mL of acidic aqueous solution (5.0 wt% glacial acetic acid). Stir at room temperature until the chitosan is completely dissolved to obtain a transparent gel solution. Continue ultrasonication for 60 min to remove bubbles in the gel solution to obtain a chitosan solution with good fluidity.

[0101] Step S2, adding molecular sieves to the chitosan solution, stirring evenly, to obtain a suspension, the specific process is as follows:

[0102] Under stirring conditions, 16 g of MOR molecular sieve (purchased from Zhuoran Environmental Protection Technology Co., Ltd., caged aluminosilicate zeolite, silicon-aluminum ratio of about 40, diameter of 2.0 microns to 6.0 microns) was slowly added to the chitosan solution, and stirred at room temperature until homogeneous to obtain a white suspension.

[0103] Step S3, pouring the suspension into the oil phase dispersed with the emulsifier under magnetic stirring to obtain a water-in-oil emulsion, the specific process is as follows:

[0104] The suspension was poured into 300 mL of liquid paraffin under magnetic stirring, in which 1 g of sorbitan oleate (Span80) was dispersed. The magnetic stirring speed was adjusted to 850 rpm. Under shearing action, the suspension formed droplets of about 350 μm with good dispersion to obtain a water-in-oil emulsion.

[0105] Step S4, adding a crosslinking agent to the water-in-oil emulsion, stirring and then standing to obtain a mixed solution of oil and water layers, the specific process is as follows:

[0106] Add 2.5 mL of crosslinking agent glutaraldehyde (25 wt % aqueous solution) to the oil-in-water system and continue stirring for 30 min. The droplets are crosslinked and solidified, and the color of the mixed liquid changes from white to light brown. Stop stirring, the solid particles begin to settle, and let it stand for 24 h to obtain an oil-water layered mixed liquid.

[0107] Step S5, recovering the upper oil phase of the mixed solution, and washing and drying the solid particles precipitated in the lower layer of the mixed solution to obtain a crude product, the specific process is as follows:

[0108] The upper organic phase of the mixed solution was recovered, and the solid particles settled in the lower layer were washed with deionized water for multiple times, and then placed in an oven at 80° C. and dried for 24 hours to obtain chitosan and MOR molecular sieve composite particles, which were the crude product.

[0109] Step S6, calcining the crude product at high temperature to obtain a binder-free molecular sieve particle material, the specific process is as follows:

[0110] The crude product was placed in a muffle furnace and heated to 550°C, and calcined for 6 hours to remove the organic components in the chitosan and obtain a pure white binder-free MOR molecular sieve particulate material.

[0111] Fig.10 1 is the XRD spectrum of the MOR powder and the MOR molecular sieve particles in Example 3 of the present invention.

[0112] like Fig.10 As shown, the XRD of the binder-free MOR molecular sieve particulate material prepared in Example 3 matches the characteristic peaks of the MOR molecular sieve powder before molding, indicating that the crystal structure of the MOR molecular sieve is not destroyed during the molding process, and confirming that the molding process is relatively mild.

[0113] Fig.11 It is a comparison diagram of optical microscope photographs of molecular sieve particles prepared in Example 1, Example 2, and Example 3 of the present invention.

[0114] like Fig.11 As shown, the binderless molecular sieve particles prepared in Examples 1-3 have uniform morphology, high sphericity and good dispersion, indicating that the preparation method of the binderless molecular sieve particle material of the present invention can be used to shape a variety of molecular sieves and achieve the preparation of binderless molecular sieve microspheres with a size of hundreds of microns, good sphericity and uniform size.

[0115] <Test example>

[0116] In this test example, the binder-free molecular sieve microsphere material prepared in Examples 1-3 was tested for low-frequency acoustic performance, and the test method was as follows:

[0117] The 300μm to 400μm binder-free molecular sieve microsphere material obtained in Examples 1-3 was used as a low-frequency sound-absorbing material and filled in the rear cavity of a customized micro-speaker test unit. The rear cover was sealed with a transparent acrylic plate to ensure that there were no obstacles blocking the front and rear cavities of the speaker. The micro-speaker was connected to the multi-channel integrated system (KeyConnect Measurement System) of Ruisen Xinpu Technology using a signal sensor line. The parameters (rated input power, octave, output data Impedance, F0) were set using the Trust test system software. Click the test, the electrical signal is converted into an acoustic signal, and after the unit vibrates, it is transmitted to the integrated system through the electrical wire. The test results are shown in Table 1, and the data is collected to generate an impedance curve.

[0118] Table 1 Acoustic performance test results

[0119]

[0120] Fig.12 is an impedance curve diagram of the molecular sieve particles prepared in Example 1 of the present invention before and after being filled in a micro speaker, Fig.13is an impedance curve diagram of the molecular sieve particles prepared in Example 2 of the present invention before and after being filled in a micro speaker, Fig.14 It is an impedance curve diagram before and after the molecular sieve particles prepared in Example 3 of the present invention are filled in the micro speaker.

[0121] As shown in Table 1 and Figure 12-14 As shown, by comparing the impedance curve offset and the resonance frequency offset value, it is found that the resonance frequency of the rear cavity of the micro-speaker test unit is reduced after being filled with the binderless molecular sieve microsphere material of Examples 1-3, indicating that the binderless molecular sieve microsphere material prepared by the present invention can well change the low-frequency acoustic performance of the micro-speaker and expand the low-frequency sound output.

[0122] Functions and Effects of the Embodiments

[0123] According to the preparation method of the binder-free molecular sieve particle material involved in this embodiment, chitosan aqueous solution is used as the water phase and mixed with molecular sieve powder to obtain a uniform emulsion; liquid paraffin dispersed with emulsifier Span80 is used as the oil phase, and oil and water are mixed to obtain an oil-in-water emulsion. The emulsifier Span80 ensures the stability of the oil-in-water emulsion, so that the cross-linking reaction is completely carried out inside a single particle, and the particles do not stick together or agglomerate; after glutaraldehyde is added to the oil-in-water emulsion as a cross-linking agent, the droplets are rapidly solidified, and after washing and drying, high-temperature calcination is performed to remove organic matter to obtain binder-free molecular sieve particles with uniform morphology, high sphericity and good dispersion.

[0124] The preparation method of the binder-free molecular sieve particulate material of this embodiment removes organic matter in chitosan by calcination, avoids the addition of binders in the prior art, well retains the original specific surface area and pore size distribution of the molecular sieve, retains its adsorption and mass transfer performance, and eliminates the occurrence of organic matter volatilization occupying the micropores during the long-term use of the speaker, which can further optimize the low-frequency acoustic performance of the material. At the same time, after the organic matter is removed at high temperature, the particles still maintain the characteristics of high sphericity, good dispersion, and uniform morphology, and can be directly used as the acoustic filling material of the micro-speaker to fill it into the back cavity of the micro-speaker. It is tested through a low-frequency acoustic test platform, and the impedance curve offset and the resonance frequency offset values ​​are compared. It is found that the resonance frequency decreases, which effectively solves the problem of increased resonance frequency due to volume limitation, and can significantly expand the low-frequency acoustic performance of the micro-speaker.

[0125] Furthermore, the preparation method of the binderless molecular sieve particle material of the present embodiment is simple to operate, green, and economical, and can be extended to a variety of zeolite molecular sieves. At the same time, the product can be optimized by changing parameters such as the amount of chitosan added, the amount of cross-linking agent added, the amount of molecular sieve added, and the oil-water ratio to prepare binderless molecular sieve particles of the target size with uniform morphology, high sphericity, and good dispersion.

[0126] The above-mentioned embodiments are preferred examples of the present invention and are not intended to limit the protection scope of the present invention.

Claims

1. A method for preparing a binder-free molecular sieve particulate material, characterized in that: The following steps are involved: Step S1, adding chitosan into an acidic aqueous solution, stirring and dissolving, and then performing ultrasound to prepare a chitosan solution; Step S2, adding molecular sieves to the chitosan solution and stirring evenly to obtain a suspension; Step S3, pouring the suspension into the oil phase dispersed with an emulsifier under magnetic stirring to obtain a water-in-oil emulsion; Step S4, adding a crosslinking agent to the water-in-oil emulsion, stirring and then standing to obtain a mixed solution of oil and water layers; Step S5, recovering the upper oil phase of the mixed solution, and washing and drying the solid particles precipitated in the lower layer of the mixed solution to obtain a crude product; Step S6, calcining the crude product at high temperature to obtain a binder-free molecular sieve particle material. Wherein, in the suspension, the mass fraction of chitosan is 1.49wt% to 6.38wt%, the mass fraction of molecular sieve is 13.56wt% to 40wt%, The addition ratio of the chitosan to the molecular sieve is 0.8-1.0g:16g, The particle size of the binder-free molecular sieve particulate material is 300 μm to 400 μm.

2. The method for preparing the binder-free molecular sieve particulate material according to claim 1, characterized in that: in, The acidic aqueous solution is a mixed solution of glacial acetic acid and deionized water, the volume of the acidic aqueous solution is 50mL-100mL, the mass fraction of the glacial acetic acid is 0.5wt%-5.0wt%, In step S1, the chitosan is added into the acidic aqueous solution, stirred to dissolve, and then ultrasonicated for 1 hour to prepare the chitosan solution.

3. The method for preparing the binder-free molecular sieve particulate material according to claim 1, characterized in that: in, The molecular sieve comprises a framework and extra-framework cations, The skeleton includes SiO2, non-metal or metal oxide M x O y , the metal oxide M x O y In which, M is any one or more of aluminum, titanium, boron, magnesium or iron, The extra-framework cation is at least one of a hydrogen ion, an alkali metal ion or an alkaline earth metal ion, The topological structure of the molecular sieve is any one or more of MFI, FAU, MWW, MOR, BEA, FER, CHA, MTN, MEL, AEL, ATO, NON, and RUT.

4. The method for preparing the binder-free molecular sieve particulate material according to claim 1, characterized in that: in, In the water-in-oil emulsion, the volume ratio of the oil phase to the water phase is 1:(2-7), The oil phase is any one or more of liquid paraffin, glycerol, and ethylene glycol. The emulsifier dispersed in the oil phase is any one or more of polyoxyethylene, polyoxypropylene copolymer, sorbitan fatty acid ester, sucrose fatty acid, polyoxyethylene fatty alcohol ether, polyoxyethylene polyfatty alcohol ether, sorbitan oleate, polyoxyethylene oleyl alcohol ether, polyoxyethylene beeswax, and sorbitan trioleate.

5. The method for preparing the binder-free molecular sieve particulate material according to claim 1, characterized in that: in, The cross-linking agent is formaldehyde, glutaraldehyde or epichlorohydrin, and the amount of the cross-linking agent added is 0.4 mL to 4.0 mL. In step S4, after adding the crosslinking agent to the water-in-oil emulsion, the mixture is stirred for 10 min to 60 min and allowed to stand for 12 h to 48 h.

6. The method for preparing the binder-free molecular sieve particulate material according to claim 1, characterized in that: in, In step S5, during washing and drying, the solid particles settled in the lower layer are washed with deionized water and then placed in an oven at 80°C for drying for 24 hours.

7. The method for preparing the binder-free molecular sieve particulate material according to claim 1, characterized in that: in, In step S6, during high-temperature calcination, the crude product is placed in a muffle furnace and heated to 500° C.-600° C. for calcination for 6 hours.

8. A binder-free molecular sieve particulate material, characterized in that: The material is prepared by the method for preparing a binder-free molecular sieve particulate material according to any one of claims 1 to 7, wherein: The binder-free molecular sieve particle material has a multi-level pore structure inside, including nano-scale micropores and mesopores.

9. A micro speaker, characterized in that: The back cavity filling material of the micro speaker adopts the binder-free molecular sieve particulate material described in claim 8.

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