Preparation method of polyvinyl butyral-ethanol-toluene mixed solution

Abstract

The invention relates to a preparation method of a polyvinyl butyral-ethanol-toluene mixed solution, and belongs to the technical field of multilayer ceramic capacitors. The preparation method of the polyvinyl butyral-ethanol-toluene mixed solution comprises the following steps: reacting polyvinyl alcohol and n-butyl alcohol in a solvent, then adding a toluene and ethanol mixed solution, continuously reacting, and separating out an organic phase, thereby obtaining the polyvinyl butyral-ethanol-toluene mixed solution, the solvent comprises a deep eutectic solvent and water. The mixed solution obtained by the invention can be directly used in the tape casting production process of the chip multilayer ceramic capacitor. According to the method, agglomeration of PVB products in an existing production process and difficulty in separation of the PVB products from unreacted PVA raw materials are reduced, and meanwhile, the defects that solid PVB is slow in dissolution, time-consuming and labor-consuming, and bubbles, cracks and the like are caused by residual PVB micelles which are not completely dissolved in a multi-layer ceramic capacitor tape casting production process are overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of multilayer ceramic capacitors, and in particular relates to a method for preparing a polyvinyl butyral-ethanol-toluene mixed solution. Background Art

[0002] Tape casting is the key to multilayer ceramic technology, the pillar technology of chip-type multilayer ceramic devices, and also a necessary technology for the production of electronic components. The tape casting process mainly includes the preparation of slurry, tape casting, drying, degreasing and sintering, and the preparation of slurry and the control of tape casting process play a key role. In the tape casting process, the raw materials such as powder, solvent, dispersant, binder and plasticizer must first be ball-milled to obtain an electronic slurry with suitable viscosity and stable dispersion performance. The reagent that plays the role of dispersing, bonding and inhibiting the sedimentation of inorganic particles is mainly polyvinyl butyral (PVB). The solubility, bonding, dispersion and sedimentation inhibition of inorganic particles of PVB are the key to forming a uniform, stable and well-dispersed electronic slurry.

[0003] However, in the actual production process, due to the inherent property limitations of high molecular polymers, the swelling and dissolution process of PVB powder in solvents is relatively slow, which seriously restricts the improvement of production efficiency. At the same time, since it is often difficult to intuitively judge whether PVB has been completely dissolved during the operation, partially swollen but not completely dissolved PVB remains in the system, which causes cracks in the ceramic substrate during the subsequent sintering process and scraps. In addition, in the traditional process of synthesizing PVB with water and ethanol as solvents, whether it is a two-step method or a one-step method, since the acetalization reaction is a dehydration process, the presence of a large amount of water is not conducive to the reaction; and, since the product PVB is insoluble in water, as the degree of acetalization increases, the solubility of PVA in water gradually decreases, and PVB precipitates from the system to form agglomerated block materials, and is mixed with some unacetalized or low-acetalized PVA, and the product purity is not high; in addition, the catalysts used in the water system are inorganic acids such as sulfuric acid and hydrochloric acid, which will be wrapped in the precipitated PVB particles, resulting in a relatively complicated post-processing process.

[0004] Therefore, it is urgent to explore a simpler method for preparing PVB and overcome the problem of incomplete dissolution of PVB causing the ceramic substrate to be scrapped. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a method for preparing a polyvinyl butyral-ethanol-toluene mixed solution.

[0006] The present invention is achieved through the following technical solutions:

[0007] The object of the present invention is to provide a method for preparing a polyvinyl butyral-ethanol-toluene mixed solution, comprising the following steps: reacting polyvinyl alcohol (PVA) and n-butanol in a solvent, adding a mixed solution of toluene and ethanol, continuing the reaction, and separating an organic phase to obtain the polyvinyl butyral-ethanol-toluene mixed solution; the solvent comprises a deep eutectic solvent (DES) and water.

[0008] The method of the present invention uses DES as a solvent and a catalyst, and a small amount of water as a co-solvent. PVA and n-butyraldehyde are reacted under the catalytic action of DES to obtain polyvinyl butyral (PVB). A toluene-ethanol mixed solution is added during the reaction. Since the polarity of the product PVB is much lower than that of the raw material PVA, it can be well dissolved in the toluene-ethanol mixed solvent. Therefore, when the PVA acetalization reaction reaches a certain degree, the PVB will be transferred from the low-polarity eutectic solvent to the organic extraction phase, so that the product and the raw material are separated, and a PVB-ethanol-toluene mixed solution with a certain mass concentration is directly obtained. After the viscosity is appropriately adjusted, it can be directly applied to a chip multilayer ceramic capacitor (MLCC) tape casting molding process, and the separated DES can also be reused.

[0009] The invention uses the strong solubility and catalytic performance of DES to dissolve PVA in DES under the action of a small amount of water, and can quickly perform acetalization after adding n-butyraldehyde; the water content in the DES system is low, which is conducive to the acetalization reaction. After the acetalization reaction is carried out to a certain extent, a good solvent for PVB, that is, a mixed solution of toluene and ethanol, is added, and the polarity of the highly acetalized PVB is greatly reduced, and it is transferred from the highly polar DES to the toluene-ethanol mixed solution. Since this process is a precipitation and dissolution transfer process, and PVA is insoluble in toluene-ethanol, unreacted PVA and acid impurities will not be wrapped in the product, the product purity is high, and the agglomeration of PVB is avoided at the same time, and the acetalization degree is controllable.

[0010] As a preferred embodiment of the method for preparing the polyvinyl butyral-ethanol-toluene mixed solution of the present invention, the weight average molecular weight of the polyvinyl alcohol is 10,000-50,000.

[0011] Preferably, the alcoholysis degree of the polyvinyl alcohol is not less than 98%; more preferably, the alcoholysis degree of the polyvinyl alcohol is not less than 99%.

[0012] As a preferred embodiment of the method for preparing the polyvinyl butyral-ethanol-toluene mixed solution of the present invention, the mass ratio of the polyvinyl alcohol to the solvent is 1:(5-20).

[0013] Preferably, the mass ratio of the polyvinyl alcohol to the solvent is 1:(5-15), and further, the mass ratio of the polyvinyl alcohol to the solvent is 1:(10-15).

[0014] As a preferred embodiment of the method for preparing the polyvinyl butyral-ethanol-toluene mixed solution of the present invention, the molar ratio of the n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is (1-2):1.

[0015] As a preferred embodiment of the method for preparing the polyvinyl butyral-ethanol-toluene mixed solution of the present invention, the low eutectic solvent includes choline chloride and p-toluenesulfonic acid, and the mass ratio of choline chloride to p-toluenesulfonic acid is 1:(1-3); more preferably, the mass ratio of choline chloride to p-toluenesulfonic acid is 1:(1-1.5).

[0016] The present invention uses a low eutectic solvent as a solvent and a catalyst. Preferably, choline chloride is used as a hydrogen bond acceptor of the low eutectic solvent, and p-toluenesulfonic acid is used as a hydrogen bond donor. The low eutectic solvent composed of the two can swell and dissolve PVA. Adding a small amount of water helps the p-toluenesulfonic acid in the system to play a better catalytic role. Under heating conditions, the hydroxyl group in the PVA and the aldehyde group of n-butyraldehyde undergo an acetalization reaction to form PVB.

[0017] Specifically, the preparation method of the low eutectic solvent comprises the following steps: heating and mixing choline chloride and p-hydroxybenzoic acid to obtain a low eutectic solvent. Preferably, the heating temperature is 100°C-120°C; the mixing method is preferably stirring and mixing; and the mixing time is preferably 1h-2h.

[0018] As a preferred embodiment of the method for preparing the polyvinyl butyral-ethanol-toluene mixed solution of the present invention, in the solvent, the mass ratio of the water to the low eutectic solvent is 1:(5-15); more preferably, the mass ratio of the water to the low eutectic solvent is 1:(5-10).

[0019] As a preferred embodiment of the method for preparing the polyvinyl butyral-ethanol-toluene mixed solution of the present invention, the temperature of the reaction and the continued reaction is 50°C-75°C.

[0020] As a preferred embodiment of the method for preparing the polyvinyl butyral-ethanol-toluene mixed solution of the present invention, the reaction time is 0.1h-0.5h, and the continued reaction time is 0.5h-4h.

[0021] As a preferred embodiment of the method for preparing the polyvinyl butyral-ethanol-toluene mixed solution of the present invention, the mass ratio of the mixed solution of toluene and ethanol to the polyvinyl alcohol is 200:(10-25), and more preferably, the mass ratio of the mixed solution of toluene and ethanol to the polyvinyl alcohol is 200:(12-20).

[0022] As a preferred embodiment of the method for preparing the polyvinyl butyral-ethanol-toluene mixed solution of the present invention, in the mixed solution of toluene and ethanol, the volume ratio of ethanol to toluene is (3:7)-(7:3); more preferably, the volume ratio of ethanol to toluene is (4:6)-(6:4).

[0023] Preferably, the organic phase is separated and dried to obtain the polyvinyl butyral-ethanol-toluene mixed solution; more preferably, anhydrous sodium sulfate is used for drying.

[0024] Specifically, in the preparation method of the present invention, PVB is first heated in a solvent to fully dissolve, and then n-butyraldehyde is added and stirred for reaction. Preferably, the heating temperature is 50° C.-75° C., and the heating time is 0.5 h-5 h.

[0025] The present invention has the following beneficial effects:

[0026] The method for preparing PVB of the present invention is simple to operate, and the concentration and quality are controllable. It can be directly used for the preparation of MLCC electronic paste, avoiding the time-consuming and inefficient dissolution process of PVB during on-site use and the difficulty in monitoring the complete dissolution process of PVB, effectively improving production efficiency, and avoiding the phenomenon that partially swollen but not completely dissolved PVB remains in the system to cause cracks in the ceramic substrate, thereby improving the product yield. At the same time, the DES after separating the organic phase can be used continuously, which can reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The molecular weight distribution diagram of PVB obtained in Examples 1, 2, 4, 5, and 6;

[0028] Figure 2 This is the thermal decomposition curve of PVB obtained in Example 3;

[0029] Figure 3 This is a photograph of the effect of the PVB-toluene-ethanol mixed solution obtained in Example 3 on the sedimentation inhibition of ceramic powder inorganic particles for MLCC. DETAILED DESCRIPTION

[0030] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] Unless otherwise specified, the experimental methods used in the examples are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0032] Example 1

[0033] A method for preparing a polyvinyl butyral-ethanol-toluene mixed solution comprises the following steps:

[0034] Choline chloride and p-toluenesulfonic acid were mixed in a mass ratio of 1:1.6, and stirred at 110°C for 1 hour to obtain a low eutectic solvent. PVA was evenly mixed with a solvent (the solvent was obtained by mixing the low eutectic solvent and water in a mass ratio of 10:1) in a mass ratio of 1:20, and stirred and dissolved at 70°C for 1 hour. Then, n-butyraldehyde was added, and the reaction was carried out at 70°C for 0.3 hour. Then, a mixed solution of toluene and ethanol was added, and the reaction was continued with stirring for 0.5 hour. The organic phase was separated, and anhydrous sodium sulfate was added and dried to obtain a PVB-ethanol-toluene mixed solution.

[0035] The PVA used in this embodiment has a weight average molecular weight of 31,000 and a degree of alcoholysis of 99%. It is purchased from McLean. The molar ratio of n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is 2:1. The mass ratio of the mixed solution of toluene and ethanol to PVA is 10. In the mixed solution of toluene and ethanol, the volume ratio of ethanol to toluene is 3:7.

[0036] The acetal degree of PVB was determined by alcoholysis and sodium hydroxide back titration (the same below). After testing, the acetal degree of the obtained PVB was 52% and the polydispersity index was 1.12.

[0037] Example 2

[0038] A method for preparing a polyvinyl butyral-ethanol-toluene mixed solution comprises the following steps:

[0039] Choline chloride and p-toluenesulfonic acid were mixed in a mass ratio of 1:1.4, and stirred at 110°C for 0.2h to obtain a low eutectic solvent. PVA was evenly mixed with a solvent (the solvent was obtained by mixing the low eutectic solvent and water in a mass ratio of 10:1) in a mass ratio of 1:20, and stirred and dissolved at 70°C for 1h. Then, n-butyraldehyde was added, and the reaction was carried out at 70°C for 0.3h. Then, a mixed solution of toluene and ethanol was added, and the reaction was continued with stirring for 0.5h. The organic phase was separated, and anhydrous sodium sulfate was added and dried to obtain a PVB-ethanol-toluene mixed solution.

[0040] The PVA used in this embodiment has a weight average molecular weight of 27,000 and a degree of alcoholysis of 99%. It is purchased from McLean. The molar ratio of n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is 2:1. The mass ratio of the mixed solution of toluene and ethanol to PVA is 10. In the mixed solution of toluene and ethanol, the volume ratio of ethanol to toluene is 4:6.

[0041] After testing, the acetal degree of the obtained PVB was 62% and the polydispersity index was 1.09.

[0042] Example 3

[0043] A method for preparing a polyvinyl butyral-ethanol-toluene mixed solution comprises the following steps:

[0044] Choline chloride and p-toluenesulfonic acid were mixed in a mass ratio of 1:1.2, and stirred at 110°C for 0.3h to obtain a low eutectic solvent. PVA was evenly mixed with a solvent (the solvent was obtained by mixing the low eutectic solvent and water in a mass ratio of 10:1) in a mass ratio of 1:20, and stirred and dissolved at 70°C for 1h. Then, n-butyraldehyde was added, and the reaction was carried out at 70°C for 0.3h. Then, a mixed solution of toluene and ethanol was added, and the reaction was continued with stirring for 0.5h. The organic phase was separated, and anhydrous sodium sulfate was added and dried to obtain a PVB-ethanol-toluene mixed solution.

[0045] The PVA used in this embodiment has a weight average molecular weight of 27,000 and a degree of alcoholysis of 99%. It is purchased from McLean. The molar ratio of n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is 2:1. The mass ratio of the mixed solution of toluene and ethanol to PVA is 15. In the mixed solution of toluene and ethanol, the volume ratio of ethanol to toluene is 4:6.

[0046] After testing, the acetal degree of the obtained PVB was 68% and the polydispersity index was 1.02.

[0047] Example 4

[0048] A method for preparing a polyvinyl butyral-ethanol-toluene mixed solution comprises the following steps:

[0049] Choline chloride and p-toluenesulfonic acid were mixed in a mass ratio of 1:1.2, and stirred at 110°C for 0.2h to obtain a low eutectic solvent. PVA was evenly mixed with a solvent (the solvent was obtained by mixing the low eutectic solvent and water in a mass ratio of 12:1) in a mass ratio of 1:15, and stirred and dissolved at 70°C for 1h. Then, n-butyraldehyde was added, and the reaction was carried out at 70°C for 0.3h. Then, a mixed solution of toluene and ethanol was added, and the reaction was continued with stirring for 0.5h. The organic phase was separated, and anhydrous sodium sulfate was added and dried to obtain a PVB-ethanol-toluene mixed solution.

[0050] The number average molecular weight of PVA used in this embodiment is 47000, the alcoholysis degree is 99%, and it is purchased from McLean. The molar ratio of n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is 2:1, the mass ratio of the mixed solution of toluene and ethanol to PVA is 20, and the volume ratio of ethanol to toluene in the mixed solution of toluene and ethanol is 4:6.

[0051] After testing, the acetal degree of the obtained PVB was 54% and the polydispersity index was 1.12.

[0052] Example 5

[0053] A method for preparing a polyvinyl butyral-ethanol-toluene mixed solution comprises the following steps:

[0054] Choline chloride and p-toluenesulfonic acid were mixed in a mass ratio of 1:1.2, and stirred at 110°C for 0.3h to obtain a low eutectic solvent. PVA was evenly mixed with a solvent (the solvent was obtained by mixing the low eutectic solvent and water in a mass ratio of 8:1) in a mass ratio of 1:10, and stirred and dissolved at 70°C for 1h. Then, n-butyraldehyde was added, and the reaction was carried out at 70°C for 0.3h. Then, a mixed solution of toluene and ethanol was added, and the reaction was continued with stirring for 0.5h. The organic phase was separated, and anhydrous sodium sulfate was added and dried to obtain a PVB-ethanol-toluene mixed solution.

[0055] The weight average molecular weight of PVA used in this embodiment is 27000, purchased from McLean, the molar ratio of n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is 1:1, the mass ratio of the mixed solution of toluene and ethanol to PVA is 20, and the volume ratio of ethanol to toluene in the mixed solution of toluene and ethanol is 4:6.

[0056] After testing, the acetal degree of the obtained PVB was 53% and the polydispersity index was 1.09.

[0057] Example 6

[0058] A method for preparing a polyvinyl butyral-ethanol-toluene mixed solution comprises the following steps:

[0059] Choline chloride and p-toluenesulfonic acid were mixed in a mass ratio of 1:1.2, and stirred at 110°C for 0.3h to obtain a low eutectic solvent. PVA was evenly mixed with a solvent (the solvent was obtained by mixing the low eutectic solvent and water in a mass ratio of 8:1) in a mass ratio of 1:10, and stirred and dissolved at 60°C for 1h. Then, n-butyraldehyde was added, and the reaction was carried out at 60°C for 0.3h. Then, a mixed solution of toluene and ethanol was added, and the reaction was continued with stirring for 0.5h. The organic phase was separated, and anhydrous sodium sulfate was added and dried to obtain a PVB-ethanol-toluene mixed solution.

[0060] The PVA used in this embodiment has a weight average molecular weight of 27,000 and a degree of alcoholysis of 99%. It is purchased from McLean. The molar ratio of n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is 2:1. The mass ratio of the mixed solution of toluene and ethanol to PVA is 13. In the mixed solution of toluene and ethanol, the volume ratio of ethanol to toluene is 5:5.

[0061] The test showed that the acetal degree of the obtained PVB was 74% and the polydispersity index was 1.12.

[0062] Example 7

[0063] A method for preparing a polyvinyl butyral-ethanol-toluene mixed solution comprises the following steps:

[0064] Choline chloride and p-toluenesulfonic acid were mixed in a mass ratio of 1:1.2, and stirred at 110°C for 0.3h to obtain a low eutectic solvent. PVA was evenly mixed with a solvent (the solvent was obtained by mixing the low eutectic solvent and water in a mass ratio of 8:1) in a mass ratio of 1:10, and stirred and dissolved at 75°C for 1h. Then, n-butyraldehyde was added, and the reaction was carried out at 75°C for 0.3h. Then, a mixed solution of toluene and ethanol was added, and the reaction was continued with stirring for 0.5h. The organic phase was separated, and anhydrous sodium sulfate was added and dried to obtain a PVB-ethanol-toluene mixed solution.

[0065] The PVA used in this embodiment has a weight average molecular weight of 27,000 and a degree of alcoholysis of 99%. It is purchased from McLean. The molar ratio of n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is 2:1. The mass ratio of the mixed solution of toluene and ethanol to PVA is 15. In the mixed solution of toluene and ethanol, the volume ratio of ethanol to toluene is 6:4.

[0066] After testing, the acetal degree of the obtained PVB was 68% and the polydispersity index was 1.05.

[0067] Example 8

[0068] A method for preparing a polyvinyl butyral-ethanol-toluene mixed solution comprises the following steps:

[0069] Choline chloride and p-toluenesulfonic acid were mixed in a mass ratio of 1:1.2, and stirred at 110°C for 0.3h to obtain a low eutectic solvent. PVA was evenly mixed with a solvent (the solvent was obtained by mixing the low eutectic solvent and water in a mass ratio of 10:1) in a mass ratio of 1:20, and stirred and dissolved at 70°C for 1h. Then, n-butyraldehyde was added, and the reaction was carried out at 70°C for 0.2h. Then, a mixed solution of toluene and ethanol was added, and the reaction was continued with stirring for 1h. The organic phase was separated, and anhydrous sodium sulfate was added and dried to obtain a PVB-ethanol-toluene mixed solution.

[0070] The PVA used in this embodiment has a molecular weight of 27,000 and a degree of alcoholysis of 99%. It is purchased from McLean. The molar ratio of n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is 2:1. The mass ratio of the mixed solution of toluene and ethanol to PVA is 13. In the mixed solution of toluene and ethanol, the volume ratio of ethanol to toluene is 5:5.

[0071] After testing, the acetal degree of the obtained PVB was 65% and the polydispersity index was 1.08.

[0072] The molecular weight of PVB obtained in Examples 1, 2, 4, 5, and 6 was tested, and the test results showed that Figure 1 In. From Figure 1It can be seen that by regulating the molecular weight of PVA and the synthesis process, PVB with a specific molecular weight and acetalization degree can be obtained. The molecular weight distribution index of the synthesized PVB is narrow, ranging from 1.02 to 1.12, and the acetalization degree is controllable. For PVB used in MLCC, a specific acetalization degree, molecular weight and its molecular weight distribution are the key to its good solubility, dispersibility and thermal decomposition performance.

[0073] Figure 2 The thermal decomposition curve of PVB prepared in Example 3 is as follows: Figure 2 It can be seen that the thermal decomposition residue of the synthesized PVB is low, and the thermal decomposition residue at 600 degrees Celsius is less than 3%.

[0074] Figure 3 This is a photo of the effect of the PVB-toluene-ethanol mixed solution obtained in Example 3 on the sedimentation inhibition of MLCC ceramic powder inorganic particles. The ratio of MLCC ceramic powder inorganic particles to PVB-toluene-ethanol mixed solution is 30% (g / mL). 1# and 2# are parallel samples synthesized twice by the same process. Figure 3 It can be seen that after 7 days of placement, it still has a good effect of inhibiting the sedimentation of ceramic powder.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a polyvinyl butyral-ethanol-toluene mixed solution, characterized in that: The following steps are involved: Polyvinyl alcohol and n-butanol are reacted in a solvent, and then a mixed solution of toluene and ethanol is added, and the reaction is continued, and the organic phase is separated to obtain the polyvinyl butyral-ethanol-toluene mixed solution; the solvent includes a low eutectic solvent and water.

2. The method for preparing a polyvinyl butyral-ethanol-toluene mixed solution according to claim 1, characterized in that: The weight average molecular weight of the polyvinyl alcohol is 10,000-50,000.

3. The method for preparing a polyvinyl butyral-ethanol-toluene mixed solution according to claim 1, characterized in that: The mass ratio of the polyvinyl alcohol to the solvent is 1:(5-20).

4. The method for preparing a polyvinyl butyral-ethanol-toluene mixed solution according to claim 1, characterized in that: The molar ratio of the n-butyraldehyde to the hydroxyl group in the polyvinyl alcohol is (1-2):

1.

5. The method for preparing a polyvinyl butyral-ethanol-toluene mixed solution according to claim 1, characterized in that: The low eutectic solvent comprises choline chloride and p-toluenesulfonic acid, and the mass ratio of choline chloride to p-toluenesulfonic acid is 1:(1-3).

6. The method for preparing the polyvinyl butyral-ethanol-toluene mixed solution according to claim 5, characterized in that: In the solvent, the mass ratio of the water to the low eutectic solvent is 1:(5-15).

7. The method for preparing a polyvinyl butyral-ethanol-toluene mixed solution according to claim 1, characterized in that: The temperature of the reaction and the continued reaction is 50°C-75°C.

8. The method for preparing a polyvinyl butyral-ethanol-toluene mixed solution according to claim 1, characterized in that: The reaction time is 0.1h-0.5h, and the continued reaction time is 0.5h-4h.

9. The method for preparing a polyvinyl butyral-ethanol-toluene mixed solution according to claim 1, characterized in that: The mass ratio of the mixed solution of toluene and ethanol to the polyvinyl alcohol is 200:(10-25).

10. The method for preparing a polyvinyl butyral-ethanol-toluene mixed solution according to claim 1, characterized in that: In the mixed solution of toluene and ethanol, the volume ratio of ethanol to toluene is (3:7)-(7:3).

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