Preparation method of polyvinyl butyral resin for photovoltaic module

Abstract

The invention discloses a preparation method of polyvinyl butyral resin for a photovoltaic module, and relates to the technical field of high polymer materials. The preparation method comprises the following steps: dissolving polyvinyl alcohol and an emulsifier into water to form a first mixed solution; uniformly mixing n-butyraldehyde and ethylene glycol dimethyl ether, and dropwise adding the mixture into the first mixed solution to obtain a second mixed solution; reducing the temperature of the second mixed solution to 20 DEG C or below, dropwise adding a catalyst, and reacting for 0.5-1 hour after dropwise adding; gradually raising the temperature to be not lower than 45 DEG C, continuously keeping the temperature and reacting for more than 2 hours, and then filtering, washing with water and drying to obtain the polyvinyl butyral resin. The preparation method of the polyvinyl butyral resin for the photovoltaic module is simple in process, and the obtained resin particles are uniform, small in particle size and high in acetalization degree; a resin adhesive film prepared from the resin particles is high in light transmittance, low in haze, high in peel strength and excellent in aging resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to a method for preparing polyvinyl butyral resin for photovoltaic modules. Background Art

[0002] Polyvinyl acetal resin is prepared by condensing polyvinyl alcohol (PVA) and aldehyde. During the condensation process, the ring structure and branched structure formed can simultaneously improve the flexibility and mechanical properties (such as adhesion) of the resin. Among them, polyvinyl butyral (PVB) is the most important polyvinyl acetal resin. PVB has excellent transparency, good solubility, and good light resistance, water resistance, heat resistance, cold resistance, and film-forming properties. The functional groups it contains can undergo various reactions such as saponification of acetyl groups, esterification and sulfonation of hydroxyl groups, and have high adhesion to materials such as glass and metal (especially aluminum). Therefore, PVB has been widely used in many fields, such as the manufacture of laminated safety glass, inks, adhesives, ceramic decals, aluminum foil, electrical materials, fiberglass products, and fabric treatment agents.

[0003] In the field of photovoltaic cell encapsulation, PVB is superior to the commonly used EVA material due to its higher thermal stability and aging resistance. In addition, as a thermoplastic material, PVB can be recycled into battery components in photovoltaic modules through melting, thereby reducing production costs and meeting environmental protection requirements. In China, in order to address environmental issues, the preparation process of PVB mostly adopts the aqueous precipitation method. However, in the actual preparation process, as the acetalization rate increases, unreacted hydroxyl groups or catalysts are likely to remain inside the PVB precipitated particles, which not only limits the further increase of the acetalization rate, but may also lead to cross-linking or uneven acetal distribution, thereby affecting key properties such as light transmittance during encapsulation. Therefore, although PVB has many advantages as a high-performance resin material, it still faces some technical challenges in the preparation process, and the preparation process needs to be further optimized to improve product quality and application performance. Summary of the Invention

[0004] The present invention aims to provide a method for preparing a polyvinyl butyral resin for photovoltaic modules to address the aforementioned problems of the prior art. The present method for preparing a polyvinyl butyral resin for photovoltaic modules is simple, produces uniform, small-sized resin particles, and has a high degree of acetalization. The resin film prepared from these resin particles exhibits high light transmittance, low haze, high peel strength, and excellent aging resistance.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The present invention provides a method for preparing polyvinyl butyral resin for photovoltaic modules, comprising the following steps:

[0007] dissolving polyvinyl alcohol and an emulsifier in water to form a first mixed solution;

[0008] uniformly mixing n-butyraldehyde and ethylene glycol dimethyl ether and then dropwise adding the mixture into the first mixed solution to obtain a second mixed solution;

[0009] The temperature of the second mixed solution is lowered to below 20° C., a catalyst is added dropwise, and the mixture is reacted for 0.5-1 hour after the addition is completed; the temperature is gradually raised to a temperature not lower than 45° C. and the mixture is kept warm for more than 2 hours, and then filtered, washed with water, and dried to obtain the polyvinyl butyral resin.

[0010] Furthermore, the catalyst is an acidic catalyst.

[0011] The acidic catalyst of the present invention can be any catalytically effective acid. Taking into account factors such as raw material availability, catalytic effectiveness, and post-processing, hydrochloric acid is preferred. The mass concentration of the hydrochloric acid can range from 5% to 36.5%. To avoid excessive dilution of the polyvinyl alcohol solution, higher concentrations, such as 15% to 36.5%, are more preferred. This invention is described in detail using only 20% hydrochloric acid as an example, and this should not be construed as limiting the invention. When 20% hydrochloric acid is used, its amount is preferably 8% to 50% of the mass of the polyvinyl alcohol.

[0012] The present invention discloses a method for preparing a polyvinyl butyral resin for photovoltaic modules using a mixed solvent system of water and ethylene glycol dimethyl ether. This enhances the solubility of the polyvinyl acetal and slows down the precipitation of the polyvinyl acetal through the solubilizing effect of the ethylene glycol dimethyl ether, thereby further increasing the degree of acetalization and making the resulting resin particles more uniform and having a smaller particle size. However, the amount of ethylene glycol dimethyl ether should not be too high, as this may affect the stability of the resin particles and cause adhesion, resulting in reduced particle uniformity. The amount of ethylene glycol dimethyl ether used is preferably no more than 15% of the mass of the water, and more preferably 3.5% to 14.5% of the mass of the water.

[0013] The mass concentration of the polyvinyl alcohol aqueous solution in the acetalization reaction is generally not recommended to exceed 25%. Otherwise, the excessive viscosity of the system may affect mass transfer and thus the uniformity of the acetal distribution in the product. Therefore, it is preferably not more than 20%. Considering production capacity, it is not recommended to be too low, so 4.5% to 20% is more preferred.

[0014] The preparation method of the polyvinyl butyral resin for photovoltaic modules of the present invention requires the addition of an appropriate amount of an emulsifier, preferably a polyoxyethylene ether. Generally, the amount should not exceed 1% by weight of the polyvinyl alcohol, otherwise it will affect the mechanical properties of the resin. However, since the polyoxyethylene ether has a stabilizing effect in the system, its dosage should not be too low, otherwise the resin's particle uniformity will be reduced and the resin's haze will also be affected. Therefore, the amount used is more preferably 0.2% to 1% by weight of the polyvinyl alcohol.

[0015] In order to obtain a higher degree of acetalization, the amount of n-butyraldehyde used should be no less than 60% of the mass of the polyvinyl alcohol used. However, the amount of n-butyraldehyde used is not necessarily the better. When the amount of n-butyraldehyde increases to a certain level, it has no effect on increasing the degree of acetalization. Therefore, the amount of n-butyraldehyde used is preferably 61% to 78% of the mass of the polyvinyl alcohol, and more preferably 61% to 76%.

[0016] When dissolving polyvinyl alcohol in water, it is preferably dissolved under heating to accelerate the dissolution rate, and the heating temperature is preferably between 90°C and 100°C. To ensure sufficient dissolution, it is preferably kept at 90°C to 100°C for a period of time, usually for more than 1 hour, more preferably for 1.5 to 2 hours.

[0017] When adding n-butyraldehyde and ethylene glycol dimethyl ether dropwise, it is preferred to first cool the polyvinyl alcohol aqueous solution to a suitable temperature, such as below 60°C, more preferably below 45°C. However, it is not recommended to cool the polyvinyl alcohol aqueous solution too low, as this will hinder the thorough mixing of n-butyraldehyde and polyvinyl alcohol. To ensure thorough mixing, the stirring time after the dropwise addition can be appropriately increased depending on the specific situation.

[0018] When adding the acidic catalyst, it is recommended to keep the material temperature low, such as below 20°C, preferably below 15°C. Excessively high material temperatures at this point are detrimental to the formation of small and uniformly sized resin particles. After the acidic catalyst is added and the material is kept at low temperature for an appropriate period of time, it is preferred to raise the material temperature to no less than 45°C and continue the reaction at this temperature for a period of time to improve the reaction conversion rate and the degree of acetalization. To ensure reaction uniformity, it is recommended to use programmed temperature ramping during the heating process to avoid large temperature differences within the material, which could affect the uniformity of acetalization distribution.

[0019] The present invention also provides a polyvinyl butyral resin for photovoltaic modules prepared by the above preparation method.

[0020] The present invention also provides application of the polyvinyl butyral resin in photovoltaic cell packaging.

[0021] The present invention discloses the following technical effects:

[0022] The present invention develops a method for preparing polyvinyl butyral resin for photovoltaic modules. The method utilizes a mixed solvent system of water and ethylene glycol dimethyl ether to enhance the solubility of the polyvinyl acetal. The solubilizing effect of the ethylene glycol dimethyl ether slows the precipitation of the polyvinyl acetal, thereby further increasing the degree of acetalization. The method for preparing the polyvinyl butyral resin for photovoltaic modules is simple, resulting in uniform, small-sized resin particles with a high degree of acetalization. The resin film prepared from the resin particles exhibits high light transmittance, low haze, high peel strength, and excellent aging resistance. DETAILED DESCRIPTION

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0025] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0026] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0027] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0028] The degree of acetalization refers to the degree to which polyvinyl alcohol (PVA) reacts with aldehyde compounds to form an acetal structure. This parameter directly affects the performance of the resin. A high acetalization degree improves the heat resistance and chemical stability of polyvinyl butyral resin, while also enhancing its adhesion to materials such as glass. The degree of acetalization is typically determined by chemical analysis, calculating the number of acetal groups.

[0029] Resin screening involves sifting resin particles through a screen of a specific mesh size to achieve the desired particle size distribution. A 40-mesh screen, with a pore size of approximately 0.42 mm, is commonly used for this process. Different resin types have different physical properties, including particle size and density, which affect screening performance.

[0030] Light transmittance refers to the ability of a material to allow light to penetrate. For polyvinyl butyral (PVB) resin, high light transmittance is one of its important characteristics as a component in the photovoltaic cell encapsulation field.

[0031] Haze is a measure of the degree to which a transparent material scatters light. Low haze means higher transparency and less light scattering, which is crucial for maintaining the optical quality of PVB film. To achieve lower haze values, researchers have developed a variety of technologies, such as the use of new high-efficiency mixed shear reaction technology and emulsion-free acetalization reaction technology. These technologies help improve the PVB molecular chain structure, thereby reducing light scattering.

[0032] The 180° peel strength test measures the strength of a standard specimen composed of a flexible material bonded to another rigid or flexible material when peeled at a 180° peel angle. Commonly used rigid materials include metal, plastic, and wood, while flexible materials include metal, rubber, fabric, and plastic. The test principle is to apply pressure through the 180° peel method to produce a specific fracture rate at the metal-to-metal bonded joint.

[0033] Polyvinyl butyral film will be affected by aging to a certain extent during processing, storage, transportation and use, so it is very important to study its aging resistance. The key characteristics of aging resistance include anti-yellowing performance and tensile strength change rate. Anti-yellowing performance refers to its ability to maintain color stability under conditions such as light and high temperature. This is especially important for applications that require long-term exposure to the natural environment. Anti-yellowing performance is related to the molecular structure and functional groups of polyvinyl butyral. Its good light resistance and heat resistance help to improve anti-yellowing ability. The tensile strength change rate refers to the degree to which the tensile strength of the material changes with external conditions (such as temperature, strain rate, etc.) during the stress process.

[0034] The present invention develops a method for preparing polyvinyl butyral resin for photovoltaic modules. The method utilizes a mixed solvent system of water and ethylene glycol dimethyl ether, which enhances the solubility of the polyvinyl acetal. The solubilizing effect of the ethylene glycol dimethyl ether slows the precipitation process of the polyvinyl acetal, further improving the degree of acetalization and making the resulting resin particles more uniform and smaller in size. The amount of ethylene glycol dimethyl ether should not be too high, as this may affect the stability of the resin particles and cause adhesion, resulting in reduced particle uniformity. The amount of ethylene glycol dimethyl ether used is preferably no more than 15% by weight of the water used, and more preferably 3.5% to 14.5% by weight of the water used.

[0035] Polyvinyl alcohol 2488 and polyvinyl alcohol 1788 used in the following examples were purchased from Chengdu Blue Whale Technology Co., Ltd.; polyoxyethylene ether was purchased from Hubei Xinghengye Technology Co., Ltd.

[0036] Example 1

[0037] 1) Add 100 g of polyvinyl alcohol 2488 and 0.5 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0038] 2) mixing 70 g of n-butyraldehyde and 80 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0039] 3) The temperature of the second mixed solution was lowered to 10°C, and 10 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 10°C for 45 minutes;

[0040] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0041] Example 2

[0042] 1) Add 100 g of polyvinyl alcohol 2488 and 0.5 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0043] 2) mixing 61 g of n-butyraldehyde and 80 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0044] 3) The temperature of the second mixed solution was lowered to 10°C, and 10 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 10°C for 45 minutes;

[0045] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0046] Example 3

[0047] 1) Add 100 g of polyvinyl alcohol 2488 and 0.5 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0048] 2) mixing 65 g of n-butyraldehyde and 80 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0049] 3) The temperature of the second mixed solution was lowered to 10°C, and 10 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 10°C for 45 minutes;

[0050] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0051] Example 4

[0052] 1) Add 100 g of polyvinyl alcohol 2488 and 0.5 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0053] 2) mixing 74 g of n-butyraldehyde and 80 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0054] 3) The temperature of the second mixed solution was lowered to 10°C, and 10 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 10°C for 45 minutes;

[0055] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0056] Example 5

[0057] 1) Add 100 g of polyvinyl alcohol 2488 and 0.5 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0058] 2) mixing 76 g of n-butyraldehyde and 80 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0059] 3) The temperature of the second mixed solution was lowered to 10°C, and 10 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 10°C for 45 minutes;

[0060] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0061] Example 6

[0062] 1) Add 100 g of polyvinyl alcohol 2488 and 0.5 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0063] 2) mixing 78 g of n-butyraldehyde and 80 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0064] 3) The temperature of the second mixed solution was lowered to 10°C, and 10 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 10°C for 45 minutes;

[0065] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0066] Example 7

[0067] 1) Add 100 g of polyvinyl alcohol 2488 and 0.2 g of polyoxyethylene ether to 400 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0068] 2) mixing 70 g of n-butyraldehyde and 57 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0069] 3) The temperature of the second mixed solution was lowered to 10°C, and 10 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 5°C for 30 minutes.

[0070] 4) gradually raising the temperature to 45° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0071] Example 8

[0072] 1) Add 100 g of polyvinyl alcohol 2488 and 1 g of polyoxyethylene ether to 2000 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0073] 2) mixing 70 g of n-butyraldehyde and 80 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0074] 3) The temperature of the second mixed solution was lowered to 14°C, and 50 g of a 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 14°C for 1 hour.

[0075] 4) gradually raising the temperature to 65° C. and continuing the reaction at this temperature for 4 hours, followed by filtering, washing with water, and drying to obtain polyvinyl butyral resin.

[0076] Example 9

[0077] 1) Add 100 g of polyvinyl alcohol 2488 and 0.7 g of polyoxyethylene ether to 700 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0078] 2) mixing 70 g of n-butyraldehyde and 80 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0079] 3) The temperature of the second mixed solution was lowered to 8°C, and 20 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 8°C for 50 minutes.

[0080] 4) gradually raising the temperature to 55° C. and continuing the reaction at this temperature for 2 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0081] Example 10

[0082] 1) Add 100 g of polyvinyl alcohol 1788 and 0.35 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0083] 2) mixing 72 g of n-butyraldehyde and 115 g of ethylene glycol dimethyl ether uniformly and then adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0084] 3) The temperature of the second mixed solution was lowered to 12°C, and 25 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 12°C for 45 minutes.

[0085] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0086] Example 11

[0087] 1) Add 100 g of polyvinyl alcohol 1788 and 0.6 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0088] 2) mixing 70 g of n-butyraldehyde and 60 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0089] 3) The temperature of the second mixed solution was lowered to 11°C, and 30 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 11°C for 45 minutes;

[0090] 4) gradually raising the temperature to 55° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0091] Example 12

[0092] 1) Add 100 g of polyvinyl alcohol 2488 and 0.5 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0093] 2) mixing 70 g of n-butyraldehyde and 130 g of ethylene glycol dimethyl ether uniformly and then adding dropwise to the first mixed solution to obtain a second mixed solution;

[0094] 3) The temperature of the second mixed solution was lowered to 10°C, and 8 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 10°C for 45 minutes.

[0095] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0096] Comparative Example 1

[0097] The same as Example 1, except that the amount of ethylene glycol dimethyl ether was adjusted to 145 g.

[0098] Comparative Example 2

[0099] 1) Add 100 g of polyvinyl alcohol 2488 and 0.5 g of polyoxyethylene ether to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0100] 2) adding 70 g of n-butyraldehyde dropwise to the first mixed solution to obtain a second mixed solution;

[0101] 3) The temperature of the second mixed solution was lowered to 10°C, and 10 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 10°C for 45 minutes;

[0102] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0103] Comparative Example 3

[0104] 1) Add 100 g of polyvinyl alcohol 2488 to 900 g of water, stir, heat to 90° C., and fully dissolve until uniform and transparent to form a first mixed solution;

[0105] 2) mixing 70 g of n-butyraldehyde and 80 g of ethylene glycol dimethyl ether uniformly and adding the mixture dropwise to the first mixed solution to obtain a second mixed solution;

[0106] 3) The temperature of the second mixed solution was lowered to 10°C, and 10 g of 20% hydrochloric acid solution was added dropwise. After the addition was complete, the mixture was kept at 10°C for 45 minutes;

[0107] 4) gradually raising the temperature to 50° C. and continuing the reaction at this temperature for 3 h. The mixture was then filtered, washed with water, and dried to obtain a polyvinyl butyral resin.

[0108] Comparative Example 4

[0109] The same as Example 1, except that the amount of polyoxyethylene ether was adjusted to 1.2 g.

[0110] Comparative Example 5

[0111] Same as Example 1, except that ethylene glycol dimethyl ether is replaced by methanol.

[0112] Effect Test Example 1

[0113] The polyvinyl butyral resins prepared in Examples 1-12 and Comparative Examples 1-5 were subjected to performance tests, including acetalization degree, yield after passing through a 40-mesh sieve, light transmittance, haze, 180° peel strength, and aging resistance. The test methods are as follows:

[0114] 1. Acetal degree

[0115] (1) Accurately weigh 0.4 g of sample into a 250 mL conical flask, add 20 mL of anhydrous ethanol to dissolve the sample. After complete dissolution, add 10 mL of 1 mol / L hydroxylamine hydrochloride solution;

[0116] (2) After the sample is evenly mixed, a spherical condenser is installed on the conical flask, and the mixture is heated in a 95°C water bath and refluxed for 2.5 h.

[0117] (3) After sufficient cooling (usually about 1 hour), add 50 mL of distilled water to rinse the condenser, and then add the washing liquid into the conical flask. Take out the conical flask and cool it to room temperature.

[0118] (4) Add 5 drops of bromophenol blue indicator and titrate with 0.1 mol / L sodium hydroxide solution until the color of the solution changes from yellow to yellow-green-green-green and then disappears and turns blue. This is the endpoint of the titration and the titration volume is V.

[0119] (5) Perform a blank test and the titration amount is V0.

[0120] The degree of acetalization was calculated according to the following formula: B = 14.2 × (V-V0) × N / (m × P);

[0121] Wherein: B is the percentage of butyraldehyde, %; m is the mass of the sample, g; P is the purity of the sample, %; V is the amount of sodium hydroxide solution used in the sample test, mL; V0 is the amount of sodium hydroxide solution used in the blank test, mL; N is the molar concentration of the sodium hydroxide solution, mol / L. Two parallel tests are performed and the arithmetic mean is taken as the test result. The difference between the two values of the parallel test results shall not exceed 0.3%.

[0122] 2. Yield after passing through 40 mesh sieve

[0123] Weigh 100g of resin powder, calculate the ratio of the weight after passing through a 40-mesh sieve to the total weight, and calculate the yield of PVB resin after passing through a 40-mesh sieve.

[0124] 3. Light transmittance and haze

[0125] According to the relevant standards specified in JG / T 449-2014 Polyvinyl butyral (PVB) films for building photovoltaic modules, the polyvinyl butyral resins prepared in Examples 1-12 and Comparative Examples 1-5 were respectively prepared into qualified test samples, and the transmittance and haze were tested using a haze meter.

[0126] 4. 180° peel strength

[0127] According to the relevant standards specified in JG / T 449-2014 Polyvinyl butyral (PVB) films for building photovoltaic modules, the polyvinyl butyral resins prepared in Examples 1-12 and Comparative Examples 1-5 were respectively prepared into qualified test specimens, and the 180° peel strength was tested using a tensile testing machine.

[0128] 5. Aging resistance

[0129] According to the relevant standards specified in JG / T 449-2014, Polyvinyl Butyral (PVB) Film for Architectural Photovoltaic Modules, qualified test specimens were prepared from the polyvinyl butyral resins prepared in Examples 1-12 and Comparative Examples 1-5. The aging resistance of the specimens was tested using a UV aging chamber. Specifically, the change in tensile strength and yellowness index after 2000 hours of spectral irradiation were used to characterize the specimens. Smaller changes in tensile strength and yellowness index indicate better aging resistance.

[0130] The test results of the acetalization degree, yield after passing through a 40-mesh sieve, light transmittance, haze, 180° peel strength, and aging resistance of the polyvinyl butyral resins prepared in Examples 1-12 and Comparative Examples 1-5 are shown in Table 1. The results show that the performance of the polyvinyl butyral resin prepared in the present invention is effectively improved, especially the acetalization degree reaches above 81%, the light transmittance reaches above 91%, and the haze is less than 0.5%.

[0131] The preparation method of polyvinyl butyral resin of the present invention adopts a solvent system mixed with water and ethylene glycol dimethyl ether to enhance the solubility of polyvinyl acetal. The solubility-promoting effect of ethylene glycol dimethyl ether slows down the precipitation process of polyvinyl acetal, which is beneficial to further improve the degree of acetalization and also makes the obtained resin particles more uniform and smaller in particle size. According to the performance test results of Example 1 and Comparative Example 2, it can be seen that the solvent system mixed with water and ethylene glycol dimethyl ether effectively improves the degree of acetalization. It is worth noting that the amount of ethylene glycol dimethyl ether should not be too high, otherwise it may affect the stability of the resin particles and cause adhesion, thereby reducing the uniformity of the particles. The amount of ethylene glycol dimethyl ether is preferably no more than 15% of the amount of water used, and more preferably 3.5% to 14.5% of the amount of water used.

[0132] Table 1 Performance test results of polyvinyl butyral resins prepared in Examples 1-12 and Comparative Examples 1-5

[0133]

[0134]

[0135] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing polyvinyl butyral resin for photovoltaic modules, characterized in that: The following steps are involved: dissolving polyvinyl alcohol and an emulsifier in water to form a first mixed solution; uniformly mixing n-butyraldehyde and ethylene glycol dimethyl ether and then dropwise adding the mixture into the first mixed solution to obtain a second mixed solution; The temperature of the second mixed solution is lowered to below 20° C., a catalyst is added dropwise, and the mixture is reacted for 0.5-1 hour after the addition is completed; the temperature is gradually raised to a temperature not lower than 45° C. and the mixture is kept warm for more than 2 hours, and then filtered, washed with water, and dried to obtain the polyvinyl butyral resin.

2. The preparation method according to claim 1, characterized in that The catalyst is an acidic catalyst.

3. The preparation method according to claim 1, characterized in that The acidic catalyst is hydrochloric acid.

4. The preparation method according to claim 1, characterized in that The amount of ethylene glycol dimethyl ether used is 3.5% to 14.5% of the mass of water in the first mixed solution.

5. The preparation method according to claim 1, characterized in that In the first mixed solution, the mass concentration of polyvinyl alcohol is 4.5% to 20%.

6. The preparation method according to claim 1, characterized in that The emulsifier is polyoxyethylene ether.

7. The preparation method according to claim 6, characterized in that The amount of the polyoxyethylene ether is 0.2% to 1% of the mass of the polyvinyl alcohol.

8. The preparation method according to claim 1, characterized in that The amount of n-butyraldehyde used is 61% to 78% of the mass of the polyvinyl alcohol.

9. A polyvinyl butyral resin for photovoltaic modules prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the polyvinyl butyral resin according to claim 9 in photovoltaic cell encapsulation.

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