阅读说明：本技术 一种聚乙烯醇缩醛树脂的制备方法及其应用 (Preparation method and application of polyvinyl acetal resin ) 是由 李良彬 严琦 王道亮 于 2020-12-31 设计创作，主要内容包括：本发明公开一种聚乙烯醇缩醛树脂的制备方法及其应用,聚乙烯醇缩醛的制备方法包括以下步骤：S10、将聚乙烯醇、酸性催化剂溶解于纯水中,充分搅拌形成混合溶液,将混合溶液冷却至20℃以下；S20、向冷却后的混合溶液加入聚乙烯醇缩醛原料、乳化剂和醛,并在30～70℃下搅拌1.5～5h,得到混合液A；S30、向混合溶液A加入氢氧化钠溶液,以终止反应,得到含有固体物的悬浮液；S40、去除悬浮液中的杂质,再将悬浮液固液分离,并将得到的固体物洗涤、干燥,即可得到聚乙烯醇缩醛树脂；其中,聚乙烯醇缩醛原料中的内消旋与外消旋缩醛异构体之比为3.5～15。通过向低温阶段的反应中加入高m/r的聚乙烯醇缩醛原料,制得了缩醛度为78％以上、m/r为3.5以上的聚乙烯醇缩醛树脂。(The invention discloses a preparation method and application of polyvinyl acetal resin, wherein the preparation method of the polyvinyl acetal resin comprises the following steps: s10, dissolving polyvinyl alcohol and an acid catalyst in pure water, fully stirring to form a mixed solution, and cooling the mixed solution to below 20 ℃; s20, adding a polyvinyl acetal raw material, an emulsifier and aldehyde into the cooled mixed solution, and stirring for 1.5-5 h at the temperature of 30-70 ℃ to obtain a mixed solution A; s30, adding a sodium hydroxide solution into the mixed solution A to terminate the reaction, so as to obtain a suspension containing solids; s40, removing impurities in the suspension, then carrying out solid-liquid separation on the suspension, and washing and drying the obtained solid to obtain polyvinyl acetal resin; wherein the ratio of meso to racemic acetal isomers in the polyvinyl acetal raw material is 3.5 to 15. A polyvinyl acetal resin having an acetalization degree of 78% or more and an m/r of 3.5 or more is obtained by adding a polyvinyl acetal raw material having a high m/r to a reaction in a low-temperature stage.)

1. A method for producing a polyvinyl acetal resin, characterized by comprising the steps of:

s10, dissolving polyvinyl alcohol and an acid catalyst in pure water, fully stirring to form a mixed solution, and cooling the mixed solution to below 20 ℃;

s20, adding a polyvinyl acetal raw material, an emulsifier and aldehyde into the cooled mixed solution, and stirring for 1.5-5 h at the temperature of 30-70 ℃ to obtain a mixed solution A;

s30, adding a sodium hydroxide solution into the mixed solution A to terminate the reaction, so as to obtain a suspension containing solids;

s40, removing impurities in the suspension, carrying out solid-liquid separation on the suspension, washing and drying the obtained solid to obtain polyvinyl acetal resin;

wherein the ratio of meso to racemic acetal isomer in the polyvinyl acetal raw material is 3.5 to 15.

2. The method for producing a polyvinyl acetal resin according to claim 1, wherein in step S10: the mass ratio of the polyvinyl alcohol to the acidic catalyst to the pure water is 100: (10-40): (600-1500); and/or the presence of a gas in the gas,

in step S20: the mass ratio of the polyvinyl acetal raw material to the emulsifier to the aldehyde is (5-30): (0.1-1): (50-90).

3. The method for producing a polyvinyl acetal resin according to claim 1, wherein in step S20:

the aldehyde comprises at least one of formaldehyde, acetaldehyde, butyraldehyde, valeraldehyde, isovaleraldehyde, caproaldehyde, heptaldehyde, caprylic aldehyde, nonanal, decanal, benzaldehyde and phenylacetaldehyde; and/or the presence of a gas in the gas,

the emulsifier comprises at least one of sodium dodecyl benzene sulfonate, sodium lauryl sulfate, sodium dioctyl sulfosuccinate, sodium dihexyl sulfosuccinate, sodium dinonyl sulfosuccinate, sodium didecyl sulfosuccinate, sodium di-decyl sulfosuccinate, sodium docosyl sulfosuccinate and sodium tridecyl sulfosuccinate.

4. The method for producing a polyvinyl acetal resin according to claim 1, wherein in step S20:

the ratio of meso to racemic acetal isomers in the polyvinyl acetal raw material is 4 to 12.

5. The method for producing a polyvinyl acetal resin according to claim 1, wherein in step S20:

the degree of acetalization of the polyvinyl acetal raw material is 50 to 75%.

6. The method for producing a polyvinyl acetal resin according to claim 1, wherein in step S20, the step of adding a polyvinyl acetal raw material, an emulsifier, and an aldehyde to the cooled mixed solution includes:

and adding a polyvinyl acetal raw material and an emulsifier into the cooled mixed solution, and then adding aldehyde into the mixed solution for 0-1.5 h.

7. The method for producing a polyvinyl acetal resin according to claim 1, wherein in step S20, the step of stirring at 30 to 70 ℃ for 1.5 to 5 hours to obtain a mixed solution a includes:

and (3) heating the temperature to 30-50 ℃, stirring for 0.5-2 h, heating the temperature to 50-70 ℃, and stirring for 1-3 h to obtain a mixed solution A.

8. The method for producing a polyvinyl acetal resin according to claim 1, wherein step S40 includes:

and repeatedly washing the suspension with pure water, adjusting the pH value of the suspension to be more than 10 to remove impurities in the suspension, carrying out solid-liquid separation on the suspension, washing the obtained solid, and drying to obtain the polyvinyl acetal resin.

9. A polyvinyl acetal intermediate film characterized in that the components of the polyvinyl acetal intermediate film include a polyvinyl acetal resin, wherein the polyvinyl acetal resin is obtained by the method for producing a polyvinyl acetal resin according to any one of claims 1 to 8.

10. A laminated glass comprising a first glass layer, a second glass layer, and a polyvinyl acetal intermediate film between the first glass layer and the second glass layer, wherein the polyvinyl acetal intermediate film is the polyvinyl acetal intermediate film according to claim 9.

Technical Field

The invention relates to the technical field of high polymer materials, and particularly relates to a preparation method and application of polyvinyl acetal resin.

Background

Due to its excellent physical and chemical properties, polyvinyl acetal resin is widely used in various fields of human production and life, such as automobile safety glass, building safety glass, solar photovoltaic modules, coatings, printing ink, priming paint and the like. The most typical polyvinyl acetals include polyvinyl formal (PVF) and polyvinyl butyral (PVB). Taking PVB as an example, the PVB has high light transmittance, excellent cold resistance and impact resistance, and excellent adhesion to glass, ceramics, fibers, wood and other materials, and a polyvinyl acetal interlayer film prepared from PVB is a key material for manufacturing laminated safety glass. Since the birth of the 20 th century and the 30 s, PVB has gradually become the best adhesive material for laminated safety glass. With the increasing attention on safety problems and the rapid development of new industries such as new energy automobiles, solar photovoltaics and the like, the development of PVB resin and intermediate films, particularly high-performance PVB resin and intermediate films, has a wider market demand.

The excellent and stable impact resistance and adhesion performance are key performance indexes for determining the quality of the laminated safety glass. By its very nature, these key macroscopic performance indicators are directly influenced by the intrinsic molecular structure parameters of the interlayer film prepared from PVB. From the viewpoint of the stereochemistry of the PVB molecule, the acetal ring formed by PVA and butyraldehyde comprises both meso (m) and racemic (r) acetal isomers. The relative proportions (m/r) of these two isomers in PVB is critical to the final macroscopic properties of PVB. In general, the higher the proportion of meso acetal isomer, the more rigid and more excellent impact resistance can be obtained in an interlayer film produced from a PVB resin. Meanwhile, the higher the degree of acetalization of PVB, the better the impact resistance.

At present, polyvinyl acetal resins are generally produced industrially by a precipitation method, in which the reaction process includes two-part reactions of a homogeneous reaction in a liquid phase in a low-temperature stage and a heterogeneous reaction in a subsequent temperature-raising stage. In the homogeneous reaction at the low temperature stage, the concentration of reactants is high and the distribution is uniform, the meso acetal isomer is firstly produced, and the acetalization degree is greatly increased until a large amount of granular polyvinyl acetal resin is gradually precipitated. However, in order to further increase the acetalization degree, a heterogeneous reaction is generally carried out after the homogeneous reaction, and the process is generally carried out under high temperature conditions. At this time, the degree of acetalization is further increased, and the agglomeration and crosslinking of the polyvinyl acetal resin are also increased, which causes the particle diameter and the distribution of the degree of acetalization of the final resin to be uneven. From a more microscopic point of view, the proportion of the racemic acetal isomer will increase greatly in the process, i.e., the proportion of the meso isomer decreases, resulting in a decrease in the macroscopic impact resistance in back-end applications of polyvinyl acetal resins.

As can be seen from the above, in the process of producing PVB, the ratio of racemic to racemic acetal isomers gradually decreases as the degree of acetalization increases, and therefore, PVB that can be produced at present generally has a high degree of aldolization, a low degree of meso to racemic acetal isomers, or a high degree of meso to racemic acetal isomers, and a low degree of aldolization cannot satisfy the requirement of high-performance PVB having both a high degree of acetalization and a high degree of meso to racemic acetal isomers, and when PVB is used for an interlayer film of laminated glass, impact resistance is poor.

Disclosure of Invention

The invention mainly aims to provide a preparation method and application of polyvinyl acetal resin, and aims to provide a preparation method of polyvinyl acetal resin with high degree of aldehyde condensation and high proportion of meso-acetal isomer and racemic acetal isomer.

In order to achieve the above object, the present invention provides a method for preparing a polyvinyl acetal resin, comprising the steps of:

s10, dissolving polyvinyl alcohol and an acid catalyst in pure water, fully stirring to form a mixed solution, and cooling the mixed solution to below 20 ℃;

s20, adding a polyvinyl acetal raw material, an emulsifier and aldehyde into the cooled mixed solution, and stirring for 1.5-5 h at the temperature of 30-70 ℃ to obtain a mixed solution A;

s30, adding a sodium hydroxide solution into the mixed solution A to terminate the reaction, so as to obtain a suspension containing solids;

s40, removing impurities in the suspension, carrying out solid-liquid separation on the suspension, washing and drying the obtained solid to obtain polyvinyl acetal resin;

wherein the ratio of meso to racemic acetal isomer in the polyvinyl acetal raw material is 3.5 to 15.

Alternatively, in step S10: the mass ratio of the polyvinyl alcohol to the acidic catalyst to the pure water is 100: (10-40): (600-1500); and/or the presence of a gas in the gas,

in step S20: the mass ratio of the polyvinyl acetal raw material to the emulsifier to the aldehyde is (5-30): (0.1-1): (50-90).

Alternatively, in step S20:

the aldehyde comprises at least one of formaldehyde, acetaldehyde, butyraldehyde, valeraldehyde, isovaleraldehyde, caproaldehyde, heptaldehyde, caprylic aldehyde, nonanal, decanal, benzaldehyde and phenylacetaldehyde; and/or the presence of a gas in the gas,

the emulsifier comprises at least one of sodium dodecyl benzene sulfonate, sodium lauryl sulfate, sodium dioctyl sulfosuccinate, sodium dihexyl sulfosuccinate, sodium dinonyl sulfosuccinate, sodium didecyl sulfosuccinate, sodium di-decyl sulfosuccinate, sodium docosyl sulfosuccinate and sodium tridecyl sulfosuccinate.

Alternatively, in step S20:

the ratio of meso to racemic acetal isomers in the polyvinyl acetal raw material is 4 to 12.

Alternatively, in step S20:

the degree of acetalization of the polyvinyl acetal raw material is 50 to 75%.

Optionally, in step S20, the step of adding a polyvinyl acetal raw material, an emulsifier and an aldehyde to the cooled mixed solution includes:

and adding a polyvinyl acetal raw material and an emulsifier into the cooled mixed solution, and then adding aldehyde into the mixed solution for 0-1.5 h.

Optionally, in step S20, the step of stirring at 30-70 ℃ for 1.5-5 h to obtain a mixed solution a includes:

and (3) heating the temperature to 30-50 ℃, stirring for 0.5-2 h, heating the temperature to 50-70 ℃, and stirring for 1-3 h to obtain a mixed solution A.

Optionally, step S40 includes:

and repeatedly washing the suspension with pure water, adjusting the pH value of the suspension to be more than 10 to remove impurities in the suspension, carrying out solid-liquid separation on the suspension, washing the obtained solid, and drying to obtain the polyvinyl acetal resin.

The invention also provides a polyvinyl acetal intermediate film, which comprises the polyvinyl acetal resin, wherein the polyvinyl acetal resin is prepared by the preparation method of the polyvinyl acetal resin.

Further, the present invention also provides a laminated glass, including a first glass layer, a second glass layer, and a polyvinyl acetal intermediate film located between the first glass layer and the second glass layer, wherein the polyvinyl acetal intermediate film is the polyvinyl acetal intermediate film described above.

In the technical scheme provided by the invention, a polyvinyl acetal raw material with high meso-acetal isomer ratio and racemic acetal isomer ratio is added into the reaction at a low temperature stage, so that in the reaction process, the acetalization degree is further improved, and simultaneously, more meso-acetal isomers are generated, and finally, a polyvinyl acetal resin with the acetalization degree of more than 78% and the ratio of meso-acetal isomer to racemic acetal isomer of more than 3.5 is obtained, namely, the polyvinyl acetal resin with high aldolization degree and high meso-acetal isomer ratio is obtained, so that when the prepared polyvinyl acetal resin is used for preparing an intermediate film of laminated glass, the prepared polyvinyl acetal resin has high impact resistance and sound insulation performance; in addition, the preparation method is simple to operate, saves cost and has good market competitiveness.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other related drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic flow chart showing one example of a process for producing a polyvinyl acetal resin according to the present invention;

FIG. 2 is the molecular structure of the meso acetal isomer and the racemic acetal isomer proposed by the present invention;

FIG. 3 is a hydrogen nuclear magnetic resonance spectrum of the meso-to racemic acetal isomer ratio (m/r) of a polyvinyl acetal resin prepared by an example provided in the present invention;

FIG. 4 is a cross-sectional view of an embodiment of a polyvinyl acetal intermediate film provided by the present invention;

FIG. 5 is a cross-sectional view of another embodiment of a polyvinyl acetal intermediate film provided by the present invention;

fig. 6 is a schematic structural view of the laminated glass according to the present invention.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In addition, the meaning of "and/or" appearing throughout includes three juxtapositions, exemplified by "A and/or B" including either A or B or both A and B. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Polyvinyl acetal resins are widely used in various fields of human production and life such as automobile safety glass, architectural safety glass, solar photovoltaic modules, paints, inks, primers and the like because of their excellent physicochemical properties, and most typical polyvinyl acetals include polyvinyl formal (PVF) and polyvinyl butyral (PVB). Taking PVB as an example, the PVB that can be prepared at present is generally PVB with high degree of acetal, low ratio of meso to racemic acetal isomer, or high ratio of meso to racemic acetal isomer, and low degree of acetal, and cannot meet the requirement of high-performance PVB with high degree of acetal, high ratio of meso to racemic acetal isomer, so that when PVB is used in an interlayer film of laminated glass, the impact resistance is poor.

In view of this, the present invention provides a method for producing a polyvinyl acetal resin, which can produce a polyvinyl acetal resin having a high acetalization degree and a high meso-acetal isomer ratio. Referring to fig. 1, the preparation method of the polyvinyl acetal resin includes the following steps:

and step S10, dissolving polyvinyl alcohol and an acid catalyst in pure water, fully stirring to form a mixed solution, and cooling the mixed solution to below 20 ℃.

The invention is not limited to the specific addition amounts of the polyvinyl alcohol, the acid catalyst and the pure water, and in the embodiment, the mass ratio of the polyvinyl alcohol to the acid catalyst to the pure water is 100: (10-40): (600-1500), namely the mass ratio of the three can be 100: 10: 600. or 100: 20: 800. or 100: 20: 1000. or 100: 40: 1500, etc., preferably the mass ratio of the polyvinyl alcohol to the acidic catalyst to the pure water is 100: 20: 1000.

the invention does not limit the specific kind of the acidic catalyst, and in the embodiment, the acidic catalyst is hydrochloric acid with a mass concentration of 36-38% in consideration of catalytic efficiency, corrosiveness of a reaction vessel, and performances such as particle size and acetalization degree of a finally prepared polyvinyl acetal product.

Since the acetalization reaction is very vigorous at high temperature, in order to avoid the premature agglomeration and crosslinking behavior of the polyvinylacetal resin particles, in this example, the temperature of the mixed solution is first cooled to below 20 ℃ before adding other reaction components such as aldehyde, so as to reduce the rate of the subsequent acetalization reaction. Thus, by controlling the aggregation and crosslinking phenomena of the polyvinyl acetal resin in the heterogeneous reaction stage, the acetalization degree is improved while more meso isomer is generated instead of racemic isomer, thereby increasing the proportion of meso acetal isomer.

The invention is not limited to the specific structure of the polyvinyl alcohol, and in one embodiment, the polyvinyl alcohol has an average polymerization degree of 1700. Preferably, the polyvinyl alcohol is dissolved in pure water at 80-100 ℃.

In an embodiment, step S10 specifically includes: dissolving polyvinyl alcohol in pure water, stirring at 80-100 ℃ until the polyvinyl alcohol is fully dissolved, cooling to 40 ℃, then adding an acid catalyst, stirring uniformly to obtain a mixed solution, and cooling the mixed solution to below 20 ℃.

Step S20, adding a polyvinyl acetal raw material, an emulsifier and aldehyde into the cooled mixed solution, and stirring for 1.5-5 h at the temperature of 30-70 ℃ to obtain a mixed solution A; wherein the ratio of meso to racemic acetal isomer in the polyvinyl acetal raw material is 3.5 to 15.

At present, increasing the proportion of meso to racemic acetal isomers in polyvinyl acetals is generally continued by increasing the emulsifier content and controlling the temperature during the reaction. The method increases the difficulty of removing the emulsifier, and consumes a large amount of water and cost in the washing process; in addition, the residual emulsifier can reduce the light transmittance and the adhesive property of the PVB intermediate film, and the final product performance is influenced. Therefore, in this example, by adding a starting polyvinyl acetal material having a high meso/racemic acetal isomer ratio, the reaction process in which the degree of partial acetalization is further improved can be advanced to the initial low-temperature reaction stage in which the concentration of aldehyde and catalyst is high, and the average meso isomer ratio of the finally obtained polyvinyl acetal resin can be increased.

Wherein, the meso and racemic isomers represent different stereochemical structures of acetal ring, and the meso structure is defined by an acetal ring structure formed by polyvinyl alcohol and aldehyde with two hydroxyl groups at the same side of the molecular chain, which is arranged in an isotactic manner; the acetal ring structure formed by the syndiotactic arrangement, i.e. polyvinyl alcohol with two hydroxyl groups on different sides of the molecular chain, and an aldehyde is defined as a racemic structure. The specific molecular structure of polyvinyl butyral (PVB) is shown in fig. 2. When the content of polyvinyl acetal resin particles as a raw material is too high, poor dispersion in a liquid phase can be caused, and agglomeration can occur too early, so that the quality of a finally prepared polyvinyl acetal resin product is influenced; however, the polyvinyl acetal resin with high degree of aldehyde condensation, high meso-and racemic isomers cannot be obtained from the polyvinyl acetal raw material with too low content.

Since the polyvinyl alcohol, the aldehyde and the acidic catalyst are all present in a uniform liquid phase, and the polyvinyl acetal particles as the raw material are distributed in a solid phase in the reaction system, in order to improve the dispersion of the polyvinyl acetal raw material in the liquid phase and avoid the premature agglomeration and crosslinking reaction, in this embodiment, an emulsifier is added to the reaction system.

Further, in this embodiment, the mass ratio of the polyvinyl acetal raw material, the emulsifier, and the aldehyde is (5-30): (0.1-1): (50-90). At this addition, the polyvinyl acetal raw material particles are well dispersed in the liquid phase, the emulsifier is easily removed, and the final polyvinyl acetal resin with high degree of aldehyde condensation and high meso isomer ratio can be prepared.

In this embodiment, the aldehyde includes at least one of formaldehyde, acetaldehyde, butyraldehyde, valeraldehyde, isovaleraldehyde, caproaldehyde, heptaldehyde, caprylic aldehyde, nonanal, decanal, benzaldehyde, and phenylacetaldehyde. Further, the emulsifier includes at least one of sodium dodecylbenzene sulfonate, sodium lauryl sulfate, sodium dioctyl sulfosuccinate, sodium dihexyl sulfosuccinate, sodium dinonyl sulfosuccinate, sodium didecyl sulfosuccinate, sodium di-decyl sulfosuccinate, sodium docosyl sulfosuccinate, and sodium tridecyl sulfosuccinate

The aldehyde is preferably added in a stepwise manner, preferably for 0.5 to 1.5 hours, that is, the aldehyde may be added to the reaction system at one time or may be added stepwise, but too fast addition of the aldehyde causes a violent initial acetalization reaction, too fast agglomeration of the produced polyvinyl acetal resin, and further reaction of the added polyvinyl acetal raw material to produce meso-acetal isomers, and thus the aldehyde is preferably added in a stepwise manner, preferably for 0.5 to 1.5 hours.

In addition, the step of stirring for 0.5-5 hours at 30-70 ℃ to obtain the mixed solution A comprises the following steps: and (3) heating the temperature to 30-50 ℃, stirring for 0.5-2 h, heating the temperature to 50-70 ℃, and stirring for 1-3 h to obtain a mixed solution A. Therefore, through temperature regulation and control, agglomeration and crosslinking phenomena generated in a heterogeneous reaction stage are further reduced, so that the generation of a meso isomer is promoted, and the proportion of meso and racemic acetal isomers is further improved.

In one embodiment, the ratio of meso to racemic acetal isomers in the polyvinyl acetal starting material added is 3.5 to 15. Preferably, the ratio of meso to racemic acetal isomer in the polyvinyl acetal raw material is 4 to 12.

The present invention is not limited to the acetalization degree of the polyvinyl acetal raw material, and in the present example, the acetalization degree of the polyvinyl acetal raw material is 50 to 75%. In the production of polyvinyl acetal, in a homogeneous reaction at a low temperature stage, a reaction product has a high concentration and is uniformly distributed, a meso acetal isomer is first formed, the acetalization degree is also greatly increased until a large amount of a granular polyvinyl acetal resin is gradually precipitated, and a heterogeneous reaction is required to further increase the acetalization degree, and at this time, the meso acetal isomer ratio is decreased, and particularly, when the acetalization degree is 75 to 80%, the meso acetal isomer ratio is drastically decreased. Therefore, when the meso acetal isomer ratio is high, polyvinyl acetal having an acetalization degree of 55 to 75% is easily obtained. More preferably, the degree of acetalization of the polyvinyl acetal raw material is 55 to 75%.

And step S30, adding a sodium hydroxide solution into the mixed solution A to terminate the reaction, so as to obtain a suspension containing solids.

When the acidity in the mixed solution a is reduced to a certain degree, the hydrogen ion concentration is reduced, and the reaction cannot be further effectively catalyzed, i.e., the reaction can be terminated. Therefore, in this example, a sodium hydroxide solution was added to the mixed solution a to a pH of the mixed solution of 4 or more to terminate the reaction, and a suspension containing a solid was obtained.

And step S40, removing impurities in the suspension, carrying out solid-liquid separation on the suspension, washing and drying the obtained solid to obtain the polyvinyl acetal resin.

It is noted that the impurities are typically an acidic catalyst and unreacted aldehyde. Thus, the removal of impurities in the suspension is the addition of sodium hydroxide solution to the suspension. Sodium hydroxide solution may be added directly to the suspension to a pH above 10 to neutralize the acidic catalyst in the suspension. However, this generates a large amount of sodium chloride, which affects the color of the finally obtained polyvinyl acetal resin. Therefore, in the present embodiment, step S40 includes: and repeatedly washing the suspension with pure water, adding a sodium hydroxide solution to a pH value of more than 10 to remove impurities in the suspension, filtering the suspension, washing and drying a solid obtained by filtering to obtain the polyvinyl acetal resin. Therefore, most of acid in the suspension is washed by pure water and neutralized by sodium hydroxide solution, so that residual sodium chloride is less, the finally obtained polyvinyl acetal resin has better color, and simultaneously, the alkali consumption can be reduced, and the cost is saved.

In the technical scheme provided by the invention, a polyvinyl acetal raw material with high meso-acetal isomer ratio and racemic acetal isomer ratio is added into the reaction at a low temperature stage, so that in the reaction process, the acetalization degree is further improved, and simultaneously, more meso-acetal isomers are generated, and finally, the polyvinyl acetal resin with high acetal degree and high meso-acetal isomer ratio is obtained, so that when the prepared polyvinyl acetal resin is used for preparing an intermediate film of laminated glass, the prepared polyvinyl acetal resin has high impact resistance and sound insulation performance; in addition, the preparation method is simple to operate, saves cost and has good market competitiveness.

Incidentally, the acetalization degree and the meso/racemic acetal isomer ratio (m/r) of the starting polyvinyl acetal and the finally obtained polyvinyl acetal resin were measured by a conventional method. Nuclear magnetic resonance hydrogen spectrum (¹H NMR or nuclear magnetic resonance carbon Spectroscopy (¹³C NMR) is determined by either or both techniques. For example, the nuclear magnetic resonance hydrogen spectrum characterization of polyvinyl butyral (PVB) can be performed by fully dissolving 5-10 mg of PVB in 0.6mL of DMSO-d₆The sample is scanned on a 400MHz nmr spectrometer at least 16 times more. The resulting nuclear magnetic spectrum was integrated using MestReNova software and the ratio of the mole fraction of H element at 4.5ppm (meso, m) and 4.75ppm (racemic, r) was calculated and referred to as the meso to racemic acetal isomer ratio (m/r). FIG. 3 is a hydrogen spectrum of a polyvinyl acetal resin obtained according to an example of the present invention for calculating m/r.

The acetalization degree is a mass percentage of the monomer having an acetal group in the entire polyvinyl acetal molecular chain. Similarly, the acetalization degree can also be calculated by nuclear magnetic resonance hydrogen spectroscopy by the following specific method:

degree of acetalization (mole fraction): VB_m＝2/((3*A_CH2/A_CH3)-6)。

Wherein A is_CH2And A_CH3Respectively at 1.0-1.9ppm of methylene-CH₂And 0.9ppm methyl-CH₃The integrated area of (a).

Wherein the degree of acetalization VB_mFor the relative mole fraction, it is also necessary to convert the relative mole fraction into a relative mass fraction VB for the description close to practical industrial processing_wThe specific method comprises the following steps:

degree of acetalization (mass fraction): VB_w＝142*VB_m/(142*VB_m+(1-VB_m)*44)。

The invention also provides a polyvinyl acetal intermediate film, which comprises the components of polyvinyl acetal resin, wherein the polyvinyl acetal resin is prepared by the preparation method of the polyvinyl acetal resin.

Further, in order to improve the flexibility and processability of the polyvinyl acetal intermediate film and lower the glass transition temperature thereof, the components of the polyvinyl acetal intermediate film may further include a plasticizer. The present invention is not limited to specific types of the plasticizer, and may include, but is not limited to, at least one of organic ester plasticizers such as monobasic organic acid esters and polybasic organic acid esters, and organic phosphoric acid plasticizers such as organic phosphoric acid plasticizers and organic phosphorous acid plasticizers, and preferably, organic ester plasticizers.

Still further, the organic ester plasticizers include, but are not limited to, triethylene glycol di-2-ethyl propionate, triethylene glycol di-2-ethylbutyrate, triethylene glycol di-2-ethylhexanoate, triethylene glycol dicaprylate, triethylene glycol di-n-caprylate, triethylene glycol di-n-heptanoate, dibutyl sebacate, dioctyl azelate, ethylene glycol di-2-ethylbutyrate, 1, 3-propylene glycol di-2-ethylbutyrate, 1, 4-butanediol di-2-ethylbutyrate, diethylene glycol di-2-ethylhexanoate, dipropylene glycol di-2-ethylbutyrate, triethylene glycol di-2-ethylvalerate, tetraethylene glycol di-2-ethylbutyrate, and mixtures thereof, At least one of diethylene glycol dicaprylate, dihexyl adipate, dioctyl adipate, and hexyl cyclohexyl adipate. Preferably triethylene glycol di-2-ethylhexanoate (3GO), triethylene glycol di-2-ethylbutyrate (3GH), and more preferably triethylene glycol di-2-ethylhexanoate (3 GO).

The present invention is not limited to the specific addition amount of the plasticizer, and in the present embodiment, the addition amount of the plasticizer is 10 to 50%, preferably 20 to 40%, of the total mass of the polyvinyl acetal intermediate film.

In one embodiment, the polyvinyl acetal intermediate film further comprises an antioxidant, and the antioxidant comprises at least one of a phenolic antioxidant and a phosphorous antioxidant. Wherein the phenolic antioxidant is an antioxidant with a phenolic skeleton, and the phosphorus antioxidant is an antioxidant containing phosphorus atoms. Further, the phenolic antioxidant includes, but is not limited to, at least one of 2, 6-di-t-butyl-p-cresol (BHT), Butyl Hydroxyanisole (BHA), 2, 6-di-t-butyl-4-ethylphenol, stearyl β - (3, 5-di-t-butyl-4-hydroxyphenyl) propionate, 2' -methylenebis- (4-methyl-6-butylphenol), 2' -methylenebis- (4-ethyl-6-t-butylphenol), 4' -butylidenebis- (3-methyl-6-t-butylphenol), 1, 3-tris- (2-methylhydroxy-5-t-butylphenyl) butane. Further, the phosphorus-based antioxidant includes, but is not limited to, at least one of tridecyl phosphite, triphenyl phosphite, tris (nonylphenyl) phosphite, bis (tridecyl) pentaerythritol diphosphite, bis (decyl) pentaerythritol diphosphite, tris (2, 4-di-t-butylphenyl) phosphite, bis (2, 4-di-t-butyl-6-methylphenyl) ethyl phosphite.

In order to balance the oxidation resistance of the prepared polyvinyl acetal intermediate film and the chromaticity of the finished product intermediate film, the addition amount of the antioxidant is 0.01-0.5%, preferably 0.05-0.2% of the total mass of the polyvinyl acetal intermediate film.

In one embodiment, the components of the polyvinyl acetal intermediate film may further include an ultraviolet absorber. The ultraviolet absorber includes, but is not limited to, at least one of an ultraviolet absorber having a benzotriazole structure (benzotriazole compound), an ultraviolet absorber having a benzophenone structure (benzophenone compound), an ultraviolet absorber having a triazine structure (triazine compound), and an ultraviolet absorber having a malonate structure (malonate compound), and is preferably an ultraviolet absorber having a benzotriazole structure. Further, the ultraviolet absorber having a benzotriazole structure includes at least one of 2- (2 '-hydroxy-3' -tert-butyl-5-methylphenyl) -5-chlorobenzotriazole (326), 2- (2 '-hydroxy-5' -tert-octylphenyl) benzotriazole (329), 2- (2 '-hydroxy-3', 5 '-dipentylphenyl) benzotriazole (328), and 2- (2' -hydroxy-3 ', 5' -di-tert-butylphenyl) benzotriazole (320). The ultraviolet absorber is preferably an ultraviolet absorber having a benzotriazole structure containing a halogen atom, and more preferably an ultraviolet absorber having a benzotriazole structure containing a chlorine atom.

In order to balance the ultraviolet resistance, transparency and chromaticity of the polyvinyl acetal intermediate film, the addition amount of the ultraviolet absorber is 0.01 to 1%, preferably 0.1 to 0.5% of the total mass of the polyvinyl acetal intermediate film.

In order to improve the adhesion of the polyvinyl acetal interlayer to other glass components of the laminated glass, in one embodiment, the composition of the polyvinyl acetal interlayer further comprises a metal salt. The metal salt includes at least one of magnesium salt, alkali metal salt and alkaline earth metal salt. Specifically, the metal salt comprises at least one of potassium formate, magnesium formate, potassium acetate, magnesium acetate, potassium propionate, magnesium 2-ethylbutyrate and potassium 2-ethylbutyrate.

The amount of the metal salt added is 10 to 200ppm, preferably 20 to 100ppm, based on the total mass of the polyvinyl acetal intermediate film, from the viewpoint of obtaining the best adhesion performance and maintaining the impact resistance of the polyvinyl acetal intermediate film.

The polyvinyl acetal intermediate film may further contain other functional additives such as heat insulating particles, surfactants, flame retardants, moisture resistance agents, and antistatic agents, as needed. The above additives may be used alone or in combination of two or more.

In this example, the thickness of the polyvinyl acetal interlayer is 0.2mm or more, preferably 0.25mm or more, from the viewpoint of both the practicability and the bending resistance and impact resistance of the laminated glass; further, it is preferably 2mm or less, more preferably 1.5mm or less. Thus, the polyvinyl acetal intermediate film can ensure excellent impact resistance while maintaining good transparency.

The present invention is not limited to the specific form of the polyvinyl acetal intermediate film, and may be a polyvinyl acetal intermediate film having a uniform thickness or a polyvinyl acetal intermediate film having a non-uniform thickness. For example, for Head-Up Display (Head-Up Display), the cross-sectional shape may be rectangular or wedge-shaped, as shown in fig. 4 and 5. In fig. 4, 1 indicates the rectangular polyvinyl acetal intermediate film, and in fig. 5, 1' indicates the wedge-shaped polyvinyl acetal intermediate film.

The present invention also provides a laminated glass, which is shown in fig. 6 and includes a first glass layer, a second glass layer, and a polyvinyl acetal interlayer located between the first glass layer and the second glass layer, wherein the polyvinyl acetal interlayer is the polyvinyl acetal interlayer as described above. In fig. 6, 1 is a polyvinyl acetal interlayer, and 2 and 3 are a first glass layer and a second glass layer, respectively.

Wherein, the first glass layer and the second glass layer can be inorganic glass or organic glass. Further, the inorganic glass includes, but is not limited to, a float glass plate, a heat ray absorbing glass plate, a heat ray reflecting glass plate, a polished glass plate, a pattern glass plate, a clip glass plate. The organic glass includes, but is not limited to, synthetic resin glass such as polycarbonate plate and poly (meth) acrylic plate, polycarbonate resin plate.

The thickness of the first glass layer and the second glass layer is not limited, and the thickness is preferably 1-5 mm. Since the polyvinyl acetal interlayer film provided by the present invention has excellent impact resistance, it can exhibit excellent impact resistance over a wide temperature range even when a glass layer slightly thinner than conventional laminated glass is used. This feature is very important for realizing the lightness and lightness of the laminated glass.

The invention is not limited to the specific manufacturing method of the laminated glass, and in one embodiment, the laminated glass is prepared by the following method: the interlayer film or the multilayer interlayer film is sandwiched between the first and second glass layers, and the air remaining between the first and second laminated glass components and the interlayer film or the multilayer interlayer film is degassed by sucking the interlayer film or the multilayer interlayer film under reduced pressure with a squeeze roll or a rubber bag. Then, the laminate is obtained by pre-bonding at about 70 to 110 ℃. Then, the laminated body is placed in an autoclave or extruded, and is pressed under the temperature of about 120-150 ℃ and the pressure of 1-1.5 MPa, so as to obtain the laminated glass.

The polyvinyl acetal intermediate film and the laminated glass can be used for automobiles, airplanes, trains, ships, buildings and the like. The polyvinyl acetal interlayer and the laminated glass are preferably used for an interlayer and a laminated glass for a vehicle or a building, and more preferably an interlayer and a laminated glass for a vehicle. The polyvinyl acetal interlayer and the laminated glass can be used for a front windshield, a side window glass, a rear window glass, a roof glass and the like of an automobile.

The technical solutions of the present invention are further described in detail below with reference to specific examples and drawings, it should be understood that the following examples are merely illustrative of the present invention and are not intended to limit the present invention.

Example A1

(1) Dissolving 100kg of polyvinyl alcohol with the average polymerization degree of 1700 in 1000kg of pure water, stirring for 1 hour at 85 ℃ to fully dissolve the polyvinyl alcohol, then cooling to 40 ℃, further adding 20kg of hydrochloric acid with the mass concentration of 36-38%, fully stirring to form a mixed solution, and cooling the mixed solution to 10 ℃.

(2) Adding 10kg of polyvinyl butyral raw material (the degree of acetalization is 65.4%, and the m/r ratio is 7.42) and 0.5kg of emulsifier (sodium dodecyl benzene sulfonate) into the cooled mixed solution, then gradually dripping 70kg of butyraldehyde under 0.5h, fully stirring, keeping at the temperature for 1h, then heating to 40 ℃, reacting at the temperature for 0.5h, heating to 60 ℃, and stirring and reacting at the temperature for 2.5h to obtain mixed solution A;

(3) adding a sodium hydroxide solution into the mixed solution A until the pH value is 4 to terminate the reaction, thereby obtaining a suspension containing solids;

(4) and repeatedly washing the suspension with pure water, adding a sodium hydroxide solution to adjust the pH value of the suspension to be more than 10, carrying out solid-liquid separation on the suspension, washing the obtained solid, and drying to obtain the white polyvinyl acetal resin particles.

Example A2

The procedure and conditions were the same as in example A1, except that the polyvinyl acetal starting material in step (2) was replaced with a polyvinyl acetal starting material having an acetalization degree of 53.8% and an m/r ratio of 11.31.

Example A3

The procedure and conditions were the same as in example A1, except that the polyvinyl acetal starting material in step (2) was replaced with a polyvinyl acetal starting material having an acetalization degree of 60.5% and an m/r ratio of 8.37.

Example A4

The procedure and conditions were the same as in example A1, except that the polyvinyl acetal starting material in step (2) was replaced with a polyvinyl acetal starting material having an acetalization degree of 71.1% and an m/r ratio of 6.96.

Comparative example A1

The procedure and conditions were the same as in example A1, except that in step (2), no polyvinyl acetal starting material was added.

Comparative example A2

The procedure and conditions were the same as in example A1 except that the polyvinyl acetal raw material in step (2) was replaced with a polyvinyl acetal raw material having an acetalization degree of 78.2% and an m/r ratio of 3.32.

Comparative example A3

The procedure and conditions were the same as in example A1, except that in step (2), the polyvinyl acetal raw material was not added, and the amount of the emulsifier added in step (2) was changed to 2 kg.

Application example A1

(1) Weighing the additive and the polyvinyl acetal resin prepared in example A1, wherein the weight of the polyvinyl acetal resin is 300 kg; the additive comprises: 78kg of a plasticizer (triethylene glycol di-2-ethylhexanoate), 0.4kg of an ultraviolet absorber (2- (2 '-hydroxy-3' -tert-butyl-5-methylphenyl) -5-chlorobenzotriazole (326), 0.2kg of 2- (2 '-hydroxy-5' -tert-octylphenyl) benzotriazole (329), and 0.3kg of an antioxidant (2, 6-di-tert-butyl-p-cresol).

(2) And plasticizing and extruding the resin and the additive through an extruder to prepare the polyvinyl acetal intermediate film. Wherein, the technological parameters of the extruder are controlled as follows: the process parameters of the extruder are controlled as follows: the rotating speed of the extruder screw is 450 rmp; the temperature of the extruder body in each zone is 40 ℃, 80 ℃, 140 ℃, 130 ℃ and 125 ℃. The thickness of the polyvinyl acetal intermediate film obtained was 0.76 mm.

Application example A2

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in example A2, and the remaining steps and conditions were the same as those in application example A1.

Application example A3

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in example A3, and the remaining steps and conditions were the same as those in application example A1.

Application example A4

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in example A4, and the remaining steps and conditions were the same as those in application example A1.

Comparative application example A1

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in comparative example A1, and the remaining steps and conditions were the same as those of application example A1.

Comparative application example A2

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in comparative example A2, and the remaining steps and conditions were the same as those of application example A1.

Comparative application example A3

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in comparative example A3, and the remaining steps and conditions were the same as those of application example A1.

Example B1

(1) Dissolving 100kg of polyvinyl alcohol with the average polymerization degree of 1700 in 1000kg of pure water, stirring for 1 hour at 85 ℃ to fully dissolve the polyvinyl alcohol, then cooling to 40 ℃, further adding 20kg of hydrochloric acid with the mass concentration of 36-38%, fully stirring to form a mixed solution, and cooling the mixed solution to 10 ℃.

(2) Adding 5kg of polyvinyl butyral raw material (the degree of acetalization is 71.1%, and the m/r ratio is 6.96) and 0.2kg of emulsifier (sodium dodecyl benzene sulfonate) into the cooled mixed solution, then gradually dripping 65kg of butyraldehyde under 0.5h, fully stirring, keeping at the temperature for 1.5h, then heating to 40 ℃, reacting at the temperature for 0.5h, heating to 60 ℃, and stirring at the temperature for reacting for 2h to obtain mixed solution A;

(3) adding a sodium hydroxide solution into the mixed solution A until the pH value is 4 to terminate the reaction, thereby obtaining a suspension containing solids;

(4) and repeatedly washing the suspension with pure water, adding a sodium hydroxide solution to adjust the pH value of the suspension to be more than 10, carrying out solid-liquid separation on the suspension, washing the obtained solid, and drying to obtain the white polyvinyl acetal resin particles.

Example B2

The procedure and conditions were the same as in example B1 except that 15kg of the polyvinyl butyral raw material was used in the step (2) and that 75kg of butylaldehyde was used.

Example B3

The procedure and conditions were the same as in example B1 except that 20kg of the polyvinyl butyral raw material was used in the step (2) and that 80kg of butylaldehyde was used.

Example B4

The procedure and conditions were the same as in example B1, except that 30kg of the polyvinyl butyral raw material was used in the step (2) and that 90kg of butylaldehyde was used.

Comparative example B1

The procedure and conditions were the same as in example B1, except that 0kg of the polyvinyl butyral starting material was added in the step (2) and that 60kg of butylaldehyde was added.

Application example B1

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in example B1, and the remaining steps and conditions were the same as those of application example A1.

Application example B2

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in example B2, and the remaining steps and conditions were the same as those of application example A1.

Application example B3

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in example B3, and the remaining steps and conditions were the same as those of application example A1.

Application example B4

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in example B4, and the remaining steps and conditions were the same as those of application example A1.

Comparative application example B1

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in comparative example B1, and the remaining steps and conditions were the same as those of application example A1.

Example C1

(1) Dissolving 100kg of polyvinyl alcohol with the average polymerization degree of 1700 in 1500kg of pure water, stirring for 1h at 80 ℃ to fully dissolve the polyvinyl alcohol, then cooling to 40 ℃, further adding 10kg of hydrochloric acid with the mass concentration of 36-38%, fully stirring to form a mixed solution, and cooling the mixed solution to 10 ℃.

(2) Adding 10kg of polyvinyl formal raw material (with the acetalization degree of 50 percent and the m/r ratio of 15), 0.1kg of emulsifier (a mixture of dinonyl sodium sulfosuccinate, didecyl sodium sulfosuccinate, di-decyl sodium sulfosuccinate, docosyl sodium sulfosuccinate and tridecyl sodium sulfosuccinate) and 50kg of formaldehyde into the cooled mixed solution, fully stirring, keeping the temperature for 1h, then heating to 30 ℃, reacting for 2h at the temperature, heating to 50 ℃, and stirring at the temperature for 3h to obtain a mixed solution A;

(3) adding a sodium hydroxide solution into the mixed solution A until the pH value is 4 to terminate the reaction, thereby obtaining a suspension containing solids;

(4) and repeatedly washing the suspension with pure water, adding a sodium hydroxide solution to adjust the pH value of the suspension to be more than 10, carrying out solid-liquid separation on the suspension, washing the obtained solid, and drying to obtain the white polyvinyl acetal resin particles.

Example C2

(1) Dissolving 100kg of polyvinyl alcohol with the average polymerization degree of 1700 in 600kg of pure water, stirring for 1 hour at 100 ℃ to fully dissolve the polyvinyl alcohol, then cooling to 40 ℃, further adding 40kg of hydrochloric acid with the mass concentration of 36-38%, fully stirring to form a mixed solution, and cooling the mixed solution to 10 ℃.

(2) Adding 10kg of polyvinyl acetal raw material (the acetalization degree is 75%, and the m/r ratio is 3.5) and 1kg of emulsifier (a mixture of sodium lauryl sulfate, sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate) into the cooled mixed solution, then gradually dripping 90kg of a mixture of valeraldehyde and isovaleraldehyde under 1.5h, fully stirring, keeping the temperature for 1h, then heating to 50 ℃, reacting for 0.5h at the temperature, heating to 70 ℃, and stirring and reacting for 1h at the temperature to obtain a mixed solution A;

(3) adding a sodium hydroxide solution into the mixed solution A until the pH value is 4 to terminate the reaction, thereby obtaining a suspension containing solids;

(4) and repeatedly washing the suspension with pure water, adding a sodium hydroxide solution to adjust the pH value of the suspension to be more than 10, carrying out solid-liquid separation on the suspension, washing the obtained solid, and drying to obtain the white polyvinyl acetal resin particles.

Application example C1

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in example C1, and the remaining steps and conditions were the same as those in application example A1.

Application example C2

The polyvinyl acetal resin of step (1) was replaced with the polyvinyl acetal resin obtained in example C2, and the remaining steps and conditions were the same as those in application example A1.

(first) the polyvinyl acetal resins obtained in examples and comparative examples were examined for their acetalization degree and m/r ratio by the methods described above, and the results are shown in Table 1.

TABLE 1 measurement results of degree of acetalization and m/r of polyvinyl acetal resin

	Degree of acetalization (wt%)	m/r
			Example A1	79.3	4.07
Example A2	81.7	3.56
			Example A3	80.4	3.78
Example A4	79.6	4.15
			Comparative example A1	78.5	3.28
Comparative example A2	79.2	3.36
			Comparative example A3	79.6	3.58
Example B1	81.2	3.73
			Example B2	80.3	3.96
Example B3	78.8	4.02
			Example B4	78.7	3.66
Comparative example B1	78.2	3.30
			Example C1	78.7	3.51
Example C2	78.2	3.53

As can be seen from Table 1, the polyvinyl acetal resins obtained in the examples provided by the present invention all had an acetalization degree of 78% or more and an m/r of 3.5 or more, while the resin obtained in comparative example A1 in which no raw material of polyvinyl acetal resin was added had an acetalization degree of 78.5, an m/r of 3.36, a high aldol degree, a low m/r ratio; the acetal degree and m/r value of the resin obtained in comparative example A2, in which the polyvinyl acetal resin raw material added is not within the range of acetal degree and m/r provided by the present invention, are not much different from those of the raw material added, and the significance of the preparation is not great; the polyvinyl acetal resin with high degree of acetal and high proportion of meso isomer can be prepared by increasing the emulsifier. Therefore, the polyvinyl acetal resin provided by the invention has reasonable range of preparation method, can prepare the polyvinyl acetal resin with high acetalization degree and high meso-racemic acetal isomer ratio by adopting simple and easily available resin raw materials, and has obvious effect.

(II) the polyvinyl acetal intermediate films obtained in the application examples and comparative examples were cut into squares having a side of 5 mm. The cut film was immersed in liquid nitrogen for 10 minutes and then taken out. The impact resistance at low temperature was determined from the state after striking the impregnated resin film ten times with a hammer, based on the following criteria. Wherein, O: no obvious cracks appear; and (delta): a few cracks appear; x: the film broke up. The results are shown in Table 2.

TABLE 2 impact resistance of PVB intermediate films

	Impact resistance
		Application example A1	○
Application example A2	○
		Application example A3	○
Application example A4	○
		Comparative application example A1	×
Comparative application example A2	×
		Comparative application example A3	○
Application example B1	○
		Application example B2	○
Application example B3	○
		Application example B4	○
Comparative application example B1	×
		Application example C1	△
Application example C2	△

As can be seen from table 2, when the degree of acetalization of polyvinyl acetal is 78% or more and the meso isomer ratio is 3.5 or more, the impact resistance of the polyvinyl acetal intermediate film obtained is excellent, whereas when the degree of acetalization of polyvinyl acetal obtained by the conventional method is about 78% and the meso isomer ratio is about 3.3, the impact resistance of the polyvinyl acetal intermediate film obtained is poor.

And (III) cutting the polyvinyl acetal intermediate films obtained in the application examples and the application comparative examples into squares having a side length of 5 mm. The film is placed on a fluorescent lamp touch panel (Shenzhen Ciji kang electronics Limited, 12864-. And evaluated according to the following criteria:

o: the polyvinyl acetal intermediate film has uniform light transmission and no yellowing;

and (delta): the polyvinyl acetal intermediate film has uniform light transmission and slight yellow color;

x: the polyvinyl acetal intermediate film has uneven light transmission and yellow color;

TABLE 3 evaluation of the light transmittance and color appearance of PVB intermediate films

	Light transmission and color display effect
		Application example A1	○
Application example A2	○
		Application example A3	○
Application example A4	○
		Comparative application example A1	○
Comparative application example A2	○
		Comparative application example A3	×
Application example B1	○
		Application example B2	○
Application example B3	○
		Application example B4	○
Comparative application example B1	○
		Application example C1	○
Application example C2	○

As can be seen from Table 3, the polyvinyl acetal obtained by using comparative example A3 in which the emulsifier has a mass fraction of 1% or more has a poor color-developing effect and yellowing. The polyvinyl acetal intermediate film with the mass fraction of the emulsifier of 0.1-1% prepared by other application examples and application comparative examples has a good color display effect, so that the preparation method of the polyvinyl acetal resin provided by the invention can be used for preparing the polyvinyl acetal resin with high acetalization degree and high meso-isomer, so that the prepared polyvinyl acetal intermediate film has good impact resistance, and the polyvinyl acetal intermediate film has a good color display effect through the design of the method.

In conclusion, the preparation method of the polyvinyl acetal resin provided by the invention has the advantages that through the design of steps and experimental parameters, raw materials are easy to obtain, the cost is lower, and when the prepared polyvinyl acetal resin is applied to a polyvinyl acetal intermediate film, the impact resistance is excellent, the color display effect is good, and the market competitiveness is large.

The above is only a preferred embodiment of the present invention, and it is not intended to limit the scope of the invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall be included in the scope of the present invention.