JP7240119B2 - Method for producing polyvinyl acetal resin - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polyvinyl acetal resin by combining a small-sized mixer and a large-sized reactor, and a high-quality resin with high bulk density and excellent transportability.

Polyvinyl acetal resin is excellent in adhesiveness and compatibility with various organic and inorganic substrates, and solubility in organic solvents. It is used as a sealing material for batteries. Conventionally, a polyvinyl acetal resin is produced by adding an acid catalyst and an aldehyde to an aqueous solution of polyvinyl alcohol in a reactor to allow the acetalization reaction to proceed, followed by neutralization, washing with water, and drying. method is common.

As a method for producing a polyvinyl acetal resin, a batch system has conventionally been adopted in which an acetalization reaction is performed by adding aldehydes to a mixed solution of a polyvinyl alcohol solution and a catalyst charged in advance in a reactor. However, in this batch method, when the reactor becomes large, the aldehydes and catalyst may not be uniformly dispersed in the polyvinyl alcohol solution at the start of the reaction, causing local differences in the concentrations of the aldehydes and catalyst. However, the quality of the resulting polyvinyl acetal resin may be deteriorated, such as generation of coarse particles.
In addition, in the batch method, in order to avoid problems caused by local differences in concentration, the concentration of the polyvinyl alcohol solution supplied to the reactor is lowered to lower the viscosity of the solution and achieve uniformity in a shorter time. Aldehydes and catalysts are dispersed in the As a result, the concentration of the polyvinyl acetal resin in the slurry containing the polyvinyl acetal resin obtained after completion of the acetalization reaction may also become low.
Furthermore, in the batch mode, to avoid problems caused by local concentration differences, the raw materials are fed to the reactor such that precipitation of the polyvinyl acetal does not occur until the aldehydes and catalyst are uniformly dispersed. The temperature was lowered during the process.

In order to solve these quality and productivity problems, various proposals have been made regarding reaction methods and production methods. For example, a method of performing a reaction at a high temperature by a continuous process using a high shear force mixer (Patent Document 1), a method of continuously supplying raw materials to a closed reactor, and continuously A method in which water or an aqueous solution in which an acid catalyst is dissolved is charged in advance in a reactor (Patent Document 3), a micro-disperser, a tubular reactor and an aging reactor are used. method (Patent Document 4).

Japanese Patent Publication No. 2012-524152 JP 2003-226714 A JP-A-2004-217763 Chinese Patent Application Publication No. 105399877

However, conventionally known methods and the above methods have high productivity, but the washing and removal of the catalyst is not sufficient, and there is a problem in the quality of the resulting polyvinyl acetal resin, or the polyvinyl acetal resin having high quality Acetal resin can be obtained, but productivity may not be sufficient. Moreover, when considering production on a commercial scale, it is also desired to reduce transportation costs by taking measures against clogging of pipes with resin and by producing polyvinyl acetal resins with higher bulk density.

The present inventors have made intensive studies to solve the above problems, and as a result, have found a stable production method that greatly improves productivity compared to conventional production methods, and polyvinyl acetal obtained by this production method. The inventors have found that the resin has excellent catalyst removability and high bulk density, and completed the present invention.

According to the present invention, the above problems are
[1] In a method for producing a polyvinyl acetal resin by reacting polyvinyl alcohol with an aldehyde,
In the presence of a catalyst, a mixed solution of a polyvinyl alcohol solution and an aldehyde is stirred in a mixer at a temperature of 20 to 35° C., and the average degree of acetalization of the polyvinyl acetal produced in the mixed solution is less than 10 mol %. , step (I) of continuously supplying the mixed solution to a reactor; and
Step (II) of performing an acetalization reaction of the supplied mixed solution in the reactor;
A method for producing a polyvinyl acetal resin comprising;
[2] The method for producing a polyvinyl acetal resin according to [1] above, wherein the mixed solution of the polyvinyl alcohol solution and the aldehydes is obtained by mixing a solution obtained by mixing the polyvinyl alcohol solution and the catalyst in advance with the aldehydes;
[3] The method for producing a polyvinyl acetal resin according to [1] or [2], wherein the concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 10 to 20% by mass;
[4] The method for producing a polyvinyl acetal resin according to any one of [1] to [3], wherein the mixed solution is stirred in a mixer at a shear rate of 600 to 2000 [1/s];
[5] The method for producing a polyvinyl acetal resin according to any one of [1] to [4] above, wherein the mixed solution has a linear velocity of 0.5 to 3.0 [m/s] from the mixer to the reactor;
[6] The method for producing a polyvinyl acetal resin according to any one of [1] to [5] above, wherein the average residence time of the mixed solution from the mixer to the reactor is 5 seconds or less;
[7] The method for producing a polyvinyl acetal resin according to any one of [1] to [6] above, including step (III) of stopping supply of the mixed solution from the mixer to the reactor after step (I);
[8] In step (II), the temperature in the reactor is raised at a temperature elevation rate of 0.50 to 1.0°C/min, and the mixed solution is subjected to an acetalization reaction at 50°C to 80°C. 1] The method for producing a polyvinyl acetal resin according to any one of [7];
[9] Any of the above [1] to [8], wherein in step (II), the temperature in the reactor is raised, and the reaction time of the acetalization reaction of the mixed solution after the temperature rise is 1 to 3 hours. A method for producing a polyvinyl acetal resin;
[10] The method for producing a polyvinyl acetal resin according to any one of the above [1] to [9], wherein the polyvinyl acetal resin produced in step (II) has an average degree of acetalization of 65 mol% or more;
[11] The method for producing a polyvinyl acetal resin according to any one of [1] to [10] above, wherein the resulting polyvinyl acetal resin has a bulk density of 200 kg/m ³ or more and a sodium ion content of 40 ppm or less;
[12] A polyvinyl acetal resin obtained by the production method according to any one of [1] to [11];
[13] A polyvinyl acetal resin having a bulk density of 200 kg/m ³ or more and a specific surface area of 1.5 to 1.65 m ² /g;
is resolved by providing

The method for producing a polyvinyl acetal resin of the present invention has higher productivity than conventional production methods, is excellent in catalyst removability, and can obtain a polyvinyl acetal resin having a high bulk density.

The present invention relates to a method for producing polyvinyl acetal resin by reacting polyvinyl alcohol and aldehydes, wherein a mixed solution of polyvinyl alcohol solution and aldehydes is stirred in a mixer at a temperature of 20 to 35° C. in the presence of a catalyst. a step (I) of continuously supplying the mixed solution to a reactor in a state where the average degree of acetalization of the polyvinyl acetal produced in the mixed solution is less than 10 mol%; It relates to a method for producing a polyvinyl acetal resin, comprising the step (II) of performing an acetalization reaction of the solution.

In the production method of the present invention, the polyvinyl alcohol solution, catalyst and aldehydes are continuously supplied to a small mixer and mixed, and then this mixed solution is continuously supplied to a reactor larger than the mixer. A high-quality polyvinyl acetal resin can be obtained without causing local differences in the concentrations of aldehydes and catalysts.

In the production method of the present invention, the problem of local differences in concentration of aldehydes and catalyst does not occur, so the concentration of the polyvinyl alcohol solution supplied to the reactor can be increased. Therefore, compared with the batch method, it is possible to increase the amount of polyvinyl alcohol that can be supplied to a reactor of the same size. As a result, according to the production method of the present invention, even if the reactor of the same size is used, the production amount of polyvinyl acetal resin can be increased as compared with the batch method.

In the production method of the present invention, the problem of local differences in concentration of aldehydes and catalyst does not occur, so raw materials can be supplied to the reactor at a higher temperature than in the batch method. According to the production method of the present invention, since the acetalization reaction proceeds at a higher temperature, the rate of progress of the acetalization reaction is increased, and the heating time for carrying out the acetalization reaction at a high temperature can be shortened. can. As a result, it is possible to produce a polyvinyl acetal resin in a shorter time than the conventional batch method.

(Step (I))
In step (I), a mixed solution of a polyvinyl alcohol solution and an aldehyde is stirred in a mixer at a temperature of 20 to 35°C in the presence of a catalyst, and the polyvinyl acetal produced in the mixed solution has an average degree of acetalization of 10. It is a step of continuously supplying the mixed solution to the reactor in a state of less than mol %.

The polyvinyl alcohol solution can be obtained, for example, by charging water and polyvinyl alcohol in a stirring tank or the like, heating the mixture to 90° C. or higher with stirring, and dissolving the mixture. The resulting polyvinyl alcohol solution is cooled to 20-35° C. and then supplied to a mixer.

The polyvinyl alcohol concentration in the polyvinyl alcohol solution is preferably 10% by mass or more, more preferably 11% by mass or more, and even more preferably 13% by mass or more. The polyvinyl alcohol concentration is preferably 20% by mass or less, more preferably 16% by mass or less, and even more preferably 14% by mass or less. When the polyvinyl alcohol concentration is less than 10% by mass, the production efficiency of the polyvinyl acetal resin tends to be low. If the concentration of polyvinyl alcohol is higher than 20% by mass, the viscosity of the mixed solution increases, which may reduce the mixing ability in the mixer. In addition, if the linear velocity of the mixed solution supplied to the reactor is reduced in order to suppress an increase in pressure loss, the average residence time of the mixed solution tends to increase.

The viscosity average polymerization degree of polyvinyl alcohol is preferably 100 or more, more preferably 300 or more, more preferably 400 or more, still more preferably 600 or more, particularly preferably 700 or more, and most preferably 750 or more. When the viscosity-average degree of polymerization of polyvinyl alcohol is less than 300, the melt viscosity of the resulting polyvinyl acetal resin tends to decrease. The viscosity average degree of polymerization of polyvinyl alcohol is preferably 5000 or less, more preferably 3000 or less, still more preferably 2500 or less, particularly preferably 2300 or less, and most preferably 2000 or less. If the viscosity-average degree of polymerization of polyvinyl alcohol exceeds 5000, it may become difficult to mold the resulting polyvinyl acetal resin.

The viscosity-average degree of polymerization of the polyvinyl acetal resin of the present invention coincides with the viscosity-average degree of polymerization of the raw polyvinyl alcohol. The viscosity average degree of polymerization of polyvinyl alcohol is measured according to JIS K 6726, and the preferable viscosity average degree of polymerization of polyvinyl alcohol matches the preferable viscosity average degree of polymerization of polyvinyl acetal resin.

As will be described later, the vinyl acetate unit content of the resulting polyvinyl acetal resin is preferably set to 30 mol% or less, so the degree of saponification of the polyvinyl alcohol is preferably 70 mol% or more, more preferably 95 mol% or more. .

As polyvinyl alcohol, a polyvinyl alcohol-based polymer obtained by saponifying a copolymer of vinyl ester and other monomers can also be used. Here, the other monomers include α-olefins such as ethylene, propylene, n-butene and isobutylene; acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, acrylic acid; Acrylic acid esters such as i-propyl, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and its salts; methacrylic acid methyl, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc. methacrylic acid esters of; acrylamide; N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts thereof, acrylamide derivatives such as N-methylolacrylamide and derivatives thereof; salts thereof or quaternary salts thereof, methacrylamide derivatives such as N-methylol methacrylamide and derivatives thereof; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t- Vinyl ethers such as butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; Nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl chloride and vinyl fluoride; Vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid and fumaric acid, salts thereof, esters thereof or anhydrides thereof; vinylsilyl compounds such as vinyltrimethoxysilane; .

The catalyst used for the acetalization reaction is preferably an acid catalyst. Both organic acids and inorganic acids can be used as the acid catalyst, and examples thereof include acetic acid, p-toluenesulfonic acid, hydrochloric acid, sulfuric acid, and nitric acid. Among them, hydrochloric acid, sulfuric acid and nitric acid are preferably used. For example, when hydrochloric acid is used as an aqueous solution as a catalyst, the concentration of the aqueous hydrochloric acid solution is preferably 10% by mass or more, more preferably 15% by mass or more. Moreover, the concentration of hydrochloric acid is preferably 25% by mass or less, more preferably 20% by mass or less.

As aldehydes used in the acetalization reaction of polyvinyl alcohol, aldehydes having 1 or more carbon atoms and 12 or less carbon atoms are preferable. When the number of carbon atoms in the aldehyde exceeds 12, the reactivity of the acetalization reaction is lowered, the resin tends to block during the reaction, and the synthesis of the polyvinyl acetal resin tends to be difficult.

Examples of aldehydes include formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, valeraldehyde, isovaleraldehyde, n-hexylaldehyde, 2-ethylbutyraldehyde, n-heptylaldehyde, n-octylaldehyde, 2 -ethylhexylaldehyde, n-nonylaldehyde, n-decylaldehyde, benzaldehyde, cinnamaldehyde and other aliphatic, aromatic and alicyclic aldehydes. Among them, aliphatic aldehydes having 2 or more carbon atoms and 6 or less carbon atoms are preferred, and butyraldehyde is particularly preferred. Moreover, an aldehyde may be used independently and may use 2 or more types together. Furthermore, polyfunctional aldehydes and aldehydes having other functional groups may be used in combination.

In step (I), the polyvinyl alcohol solution, the catalyst, and the aldehydes are each continuously supplied to the mixer at a constant supply rate and stirred in the mixer to obtain a mixed solution. Before supplying the mixer to the mixer, the reaction progresses unevenly in the pipes, and there is a risk of adhesion and clogging of the pipes. are preferably mixed to form a mixed solution. For example, a solution obtained by mixing a polyvinyl alcohol solution and a catalyst with an in-line mixer is supplied to a mixer, and aldehydes can be separately supplied to the mixer. Thus, by preparing a solution in which a polyvinyl alcohol solution and a catalyst are mixed in advance and mixing the solution and aldehydes to form a mixed solution, when the catalyst is an aqueous solution such as hydrochloric acid, the polyvinyl alcohol solution and the catalyst The viscosity of the mixed solution tends to be low, and it becomes easy to mix uniformly.

In addition, the polyvinyl alcohol solution and the aldehydes may be mixed in advance, for example, a method of directly adding the catalyst or the aldehydes to the preparation tank of the polyvinyl alcohol solution, or installing an in-line mixer such as a static mixer in front of the mixer. , a method of continuously adding at a constant rate, and the like.

The flow rates of the polyvinyl alcohol solution, the catalyst and the aldehydes can be appropriately changed according to the volume of the mixer and the diameter and length of the connecting pipe connecting the mixer and the reactor. The ratio of the flow rate of the catalyst solution to the mixer to the flow rate of the polyvinyl alcohol solution to the mixer (flow rate of the catalyst solution to the mixer)/(flow rate of the polyvinyl alcohol solution to the mixer) is 0.05 or more. Preferably, 0.09 or more is more preferable. Moreover, the ratio of the flow rates is preferably 0.2 or less, more preferably 0.17 or less. If the flow rate ratio exceeds 0.2, the amount of catalyst remaining in the resulting polyvinyl acetal resin tends to increase, and if the flow rate ratio is less than 0.05, the progress of the acetalization reaction slows down. There is a tendency.

The ratio of the flow rate of the aldehydes to the mixer to the flow rate of the polyvinyl alcohol solution to the mixer (flow rate of the aldehydes to the mixer)/(flow rate of the polyvinyl alcohol solution to the mixer) is 0.08 or more. Preferably, 0.09 or more is more preferable. Moreover, the ratio of the flow rates is preferably 0.12 or less, more preferably 0.11 or less. If the flow rate ratio exceeds 0.12, or if the flow rate ratio is less than 0.08, it may not be possible to obtain a polyvinyl acetal resin having desired physical properties.

The temperature of the mixed solution in the mixer is 20° C. or higher, preferably 25° C. or higher, more preferably 27° C. or higher. The temperature of the mixed solution in the mixer is 35° C. or lower, preferably 34° C. or lower, more preferably 33° C. or lower. If the temperature of the mixed solution is lower than 20° C., the viscosity of the raw material is high and the pressure loss in the raw material supply pipe increases, so there is a possibility that the supply time will be prolonged due to the decrease in the flow rate. In addition, since the reaction rate is lowered, there is a possibility that the subsequent batch reaction will take a long time. If the temperature of the mixed solution is higher than 35° C., the polyvinyl acetal particles precipitated during the reaction agglomerate to form hard coarse particles, making it impossible to obtain a polyvinyl acetal resin of high quality. In addition, aggregation of the polyvinyl acetal particles prevents the obtained polyvinyl acetal resin from becoming porous, making it difficult to remove the catalyst by washing after the acetal reaction. As the acetalization reaction progresses in the mixed solution in the mixer, reaction heat is generated, but the temperature can be maintained at 20 to 35° C. by means of a heat exchanger.

The mixed solution is preferably stirred in a mixer at a shear rate of 600 [1/s] or higher, more preferably 800 [1/s] or higher, and 900 [1/s] or higher. is more preferred. Further, the mixed solution is preferably stirred in a mixer at a shear rate of 2000 [1/s] or less, more preferably 1600 [1/s] or less, and stirred at 1100 [1/s] or less. more preferably. When the shear rate of stirring is less than 600 [1/s], the catalyst and aldehydes are not uniformly dispersed in the polyvinyl alcohol solution, and coarse particles tend to be generated. When the shear rate of stirring is higher than 2000 [1/s], it tends to be difficult to control the primary particle size, or it becomes difficult to control the reaction due to the progress of local reactions due to shear heat generation. Examples of the method of setting the shear rate for stirring to 1000 to 2000 [1/s] include a method of stirring using an in-line mixer such as a dynamic mixer or static mixer.

The volume of the mixer is preferably 0.01 A [L] or more, more preferably 0.05 A [L] or more, relative to the reactor volume A [L]. The volume of the mixer is preferably 1 A [L] or less, more preferably 0.5 A [L] or less. If the volume of the mixer is less than 0.01 A [L], the retention time of the mixed solution in the mixer tends to be short, making it difficult to uniformly disperse the raw materials. If the volume of the mixer is larger than 1A [L], the average residence time of the mixed solution from the supply of the raw materials to the mixer to the supply to the reactor becomes long, and clogging of the mixer and connecting pipes occurs. It may cause

By the time the mixed solution is supplied to the reactor, the average degree of acetalization of the polyvinyl acetal produced in the mixed solution is less than 10 mol%, preferably less than 8 mol%, more preferably less than 6 mol%. When the average degree of acetalization of the polyvinyl acetal produced in the mixed solution is 10 mol % or more, it becomes impossible to obtain a polyvinyl acetal resin with a high bulk density, and it becomes difficult to remove the catalyst by washing. Means for reducing the degree of acetalization of the polyvinyl acetal before being supplied to the reactor to less than 10 mol% include, for example, the volume of the mixer, and the diameter and length of the connecting pipe from the mixer to the reactor. There is a method of adjusting appropriately.

The linear velocity (flow velocity) of the mixed solution from the mixer to the reactor is preferably 0.5 [m/s] or more. The linear velocity of the mixed solution from the mixer to the reactor is preferably 3.0 [m/s] or less, more preferably 2.7 [m/s] or less, and even more preferably 2.5 [m/s] or less. . When the linear velocity of the mixed solution from the mixer to the reactor is less than 0.5 [m/s], the acetalization reaction progresses considerably before the mixed solution is supplied from the mixer to the reactor, It may cause clogging of connecting pipes. When the linear velocity of the mixed solution from the mixer to the reactor exceeds 3.0 [m/s], the pressure loss in the connecting pipe increases, and the load on the liquid feed pump that feeds the mixed solution increases. This tends to increase the burden on equipment. As means for adjusting the linear velocity (flow velocity) of the mixed solution from the mixer to the reactor to 0.5 to 3.0 [m/s], for example, a method of appropriately adjusting the pipe diameter and pipe length of the connecting pipe. are mentioned. By narrowing and shortening the connecting pipe, the linear velocity of the mixed solution increases.

The average residence time of the mixed solution from the mixer to the reactor includes, if there is a pipe connecting the mixer and the reactor, the time for the mixed solution to pass through the pipe. The average residence time from the mixer to the reactor is preferably within 5 seconds, more preferably within 3 seconds, from the viewpoint of suppressing clogging and adhesion of polyvinyl acetal resin precipitated in the mixed solution. Means for making the average residence time of the mixed solution within 5 seconds from the raw materials supplied to the mixer to the reactor are, for example, the volume of the mixer, and the connecting pipe from the mixer to the reactor and a method of appropriately adjusting the pipe diameter and pipe length.

After step (I), it is preferable to include step (III) of stopping supply of the mixed solution from the mixer to the reactor. After supplying an appropriate amount of the mixed solution according to the volume of the reactor, the continuous supply of the mixed solution is stopped.

(Step (II))
Step (II) is a step of acetalizing the mixed solution in a reactor.

From the viewpoint of efficiently performing the acetalization reaction of the mixed solution, the formula (a):
0.01≤V/(V+V')≤0.1 (a)
(Wherein, V [L] represents the volume of water or an aqueous solution in which the catalyst is dissolved in the reactor in advance, and V' [L] represents the total volume of the mixed solution supplied to the reactor in step (I). ), it is preferable to charge the reactor with water or an aqueous solution in which the catalyst is dissolved in advance.

The lower limit of V/(V+V') is preferably 0.01, more preferably 0.05. The upper limit of V/(V+V') is preferably 0.1, more preferably 0.08. When V/(V+V') is within the above range, the mixed state in the reactor and the concentration of the mixed solution are within appropriate ranges, resulting in excellent reaction efficiency.

From the viewpoint of efficiently performing the acetalization reaction of the mixed solution, formula (b):
0.03 ≤ V/v ≤ 0.3 (b)
(In the formula, V [L] represents the volume of water or an aqueous solution in which the catalyst is dissolved, which is previously charged to the reactor, and v [L/hr] represents the volume per unit time of the mixed solution supplied to the reactor. ), it is preferable to charge water or an aqueous solution in which the catalyst is dissolved in advance into the reactor.

The lower limit of V/v is preferably 0.03, more preferably 0.05. If the value of V/v is less than the lower limit, the quality of the polyvinyl acetal resin to be obtained may be deteriorated, or the process load may increase due to increased pressure loss. More specifically, if the amount of water charged in advance to the reactor is small, the mixed solution may solidify due to insufficient stirring by the stirring blades. In addition, the supply speed of the mixed solution to the reactor is high, pressure loss increases, and the process load may increase.

The upper limit of V/v is preferably 0.3, more preferably 0.1. If the value of V/v exceeds the upper limit, productivity may decrease. More specifically, the amount of water charged into the reactor is large, and the concentration of polyvinyl alcohol in the mixed solution may decrease, resulting in a decrease in productivity. In addition, there is a possibility that production will decrease due to the slow supply speed of the mixed solution.

Also in step (II), the temperature of the mixed solution in the reactor is preferably maintained at 20°C or higher, more preferably at 25°C or higher, and even more preferably at 27°C or higher. Also, the temperature of the mixed solution in the reactor is preferably maintained at 35° C. or lower, more preferably 34° C. or lower, and even more preferably 33° C. or lower. When the temperature of the mixed solution is lower than 20°C, the acetalization reaction tends to be difficult to proceed sufficiently. On the other hand, when the temperature of the mixed solution is higher than 35° C., the polyvinyl acetal particles precipitated during the reaction are aggregated to form hard coarse particles, which may make it impossible to obtain a high-quality polyvinyl acetal resin. In addition, aggregation of the polyvinyl acetal particles does not make the resulting polyvinyl acetal resin porous and tends to make it difficult to remove the catalyst by washing after the acetal reaction.

The time for the acetalization reaction while maintaining the temperature of the mixed solution in the reactor at 20 to 35° C. is preferably 0.1 hour or longer, more preferably 0.3 hour or longer. The time for the acetalization reaction while maintaining the temperature of the mixed solution in the reactor at 20 to 35° C. is preferably 1.0 hours or less, more preferably 0.7 hours or less.

After maintaining the temperature of the mixed solution in the reactor at 20 to 35° C. for 0.1 to 1.0 hours, the temperature in the reactor and the mixed solution is lowered to a predetermined temperature in order to proceed with the acetalization reaction. It is preferable to raise the temperature to The temperature in the reactor is preferably raised at a rate of 0.5°C/min or higher, more preferably 0.6°C/min or higher, and 0.7°C/min or higher. more preferably. In step (II), the temperature in the reactor is preferably raised at a temperature elevation rate of 1.0°C/min or less, more preferably 0.9°C/min or less, and 0.8°C. /min or less is more preferable. If the rate of temperature rise in the reactor is slower than 0.5° C./min, the time required for the temperature in the reactor to reach a predetermined temperature tends to increase, resulting in a decrease in production efficiency. If the rate of temperature rise in the reactor is faster than 1.0 ° C./min, the particles tend to coalesce and the resulting resin tends to coarsen.

In step (II), after raising the temperature in the reactor, the mixed solution is preferably acetalized at 50°C or higher, more preferably 58°C or higher, and 65°C or higher. It is more preferable to carry out the acetalization reaction at . After raising the temperature in the reactor, the mixed solution is preferably acetalized at 80°C or lower, more preferably at 77°C or lower, and acetalized at 75°C or lower. is more preferable. If the temperature in the reactor after the temperature rise during the acetalization reaction is less than 50°C, the rate of the acetalization reaction is insufficient, and the production efficiency tends to be low. If the temperature in the reactor after the temperature rise becomes higher than 80° C., the particles tend to coalesce and the resulting resin tends to coarsen.

In step (II), the reaction time for the acetalization reaction after heating the mixed solution is preferably 1 hour or longer, more preferably 2 hours or longer. The reaction time for the acetalization reaction of the mixed solution is preferably within 3 hours, more preferably within 2.5 hours. If the reaction time of the acetalization reaction of the mixed solution is less than 1 hour, the acetalization reaction may not proceed sufficiently and unreacted aldehydes may remain. If the reaction time for the acetalization reaction of the mixed solution exceeds 3 hours, the production efficiency tends to be low.

After the acetalization reaction is completed, the polyvinyl acetal resin can be obtained as a powder by performing neutralization, washing with water and drying. Methods for removing aldehydes and catalysts remaining in the polyvinyl acetal resin after the acetalization reaction include known methods. When an acid catalyst is used as the catalyst, the polyvinyl acetal resin is neutralized with an alkaline compound, but it is preferable to remove aldehydes remaining in the polyvinyl acetal resin as much as possible before neutralization. Methods for removing aldehydes prior to neutralization include a method of driving the reaction under conditions that increase the reaction rate of aldehydes, a method of thoroughly washing with water or a water/alcohol mixed solvent, etc., and a method of chemically treating aldehydes. It is useful to

When washing with water or a water/alcohol mixed solvent or the like in order to remove the aldehydes, it is preferable to repeat the washing of the aldehydes with water or a water/alcohol mixed solvent that is three times or more the resin amount of the polyvinyl acetal resin. It is more preferable to repeat washing with water or a water/alcohol mixed solvent that is at least 5 times the amount of the resin. Washing is preferably repeated three times or more.

Examples of the alkali compound used for neutralizing the polyvinyl acetal resin include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia; and amine compounds such as triethylamine and pyridine. Among them, alkali metal hydroxides are preferable from the viewpoint of being easily removable by washing with water.

An alkali neutralizing agent such as sodium hydroxide used for neutralization reacts with an acid catalyst to form a metal salt, which may impair the properties of the polyvinyl acetal resin such as transparency, moisture resistance and electrical insulation. As a method for removing metal salts generated by neutralization, it is preferable to repeat washing with water or a water/alcohol mixed solvent or the like, as in the case of removing aldehydes. In this case, the amount of water or water/alcohol mixed solvent used for washing is preferably 3 times or more, more preferably 4 times or more, and even more preferably 5 times or more that of the polyvinyl acetal resin. Washing is preferably repeated 4 times or more, more preferably 6 times or more.

(polyvinyl acetal resin)
Polyvinyl acetal resins are usually composed of vinyl acetal units, vinyl alcohol units and vinyl acetate units, and the content of each of these units in the polyvinyl acetal resin can be determined, for example, according to JIS K 6728 "Polyvinyl butyral test method" or nuclear It can be measured by magnetic resonance spectroscopy (NMR).

When the polyvinyl acetal resin contains units other than vinyl acetal units, the unit amount of vinyl alcohol and the unit amount of vinyl acetate are measured, and both of these unit amounts are compared to vinyl acetal when not containing units other than vinyl acetal units. By subtracting from the unit amount, the remaining vinyl acetal unit amount can be calculated.

The content of vinyl alcohol units in the polyvinyl acetal resin is preferably 15 mol % or more, more preferably 20 mol % or more, and even more preferably 25 mol % or more. Also, the content of vinyl alcohol units in the polyvinyl acetal resin is preferably 50 mol % or less, more preferably 40 mol % or less, and even more preferably 30 mol % or less.

The vinyl acetate unit content of the polyvinyl acetal resin is preferably 30 mol % or less. If the vinyl acetate unit content exceeds 30 mol %, coalescence between particles tends to occur during production of the polyvinyl acetal resin, making production difficult. The vinyl acetate unit content is preferably 20 mol % or less, more preferably 8 mol % or less, still more preferably 4 mol % or less, and particularly preferably 1 mol % or less.

The average degree of acetalization of the polyvinyl acetal resin is preferably 65 mol% or more, more preferably 70 mol% or more. The average degree of acetalization of the polyvinyl acetal resin is preferably 90 mol% or less, more preferably 85 mol% or less, even more preferably 80 mol% or less. If the average degree of acetalization of the polyvinyl acetal resin is less than 65 mol %, it may not be possible to obtain a film with sufficient strength when used as an interlayer film for safety glass, for example.

The particle size of the resulting polyvinyl acetal resin is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 100 μm or less. If the particle size of the polyvinyl acetal resin is less than 50 μm, the resulting resin may be included in the waste water during the washing process, or may be included in the exhaust gas during the drying process.

A polyvinyl acetal resin having a high bulk density can be obtained by the production method of the present invention. The bulk density of the resulting polyvinyl acetal resin is preferably 150 kg/m ³ or higher, more preferably 180 kg/m ³ or higher, still more preferably 200 kg/m ³ or higher, and particularly preferably 230 kg/m ³ or higher. When the bulk density is within the above range, the transportability of the obtained polyvinyl acetal resin is excellent.

The specific surface area of the resulting polyvinyl acetal resin is preferably 1.5 m ² /g or more, more preferably 1.52 m ² /g or more, and even more preferably 1.6 m ² /g or more. Moreover, the specific surface area is preferably 1.65 m ² /g or less. The polyvinyl acetal resin obtained by the method for producing a polyvinyl acetal resin of the present invention is a porous powder, has a large specific surface area, and is excellent in catalyst removability.

The sodium ion content of the resulting polyvinyl acetal resin is preferably 40 ppm or less, more preferably 25 ppm or less, even more preferably 15 ppm or less. If the sodium ion content of the resulting polyvinyl acetal resin exceeds 40 ppm, the film or sheet may absorb moisture and whiten when the polyvinyl acetal resin is used as a film or sheet.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
13.84 kg of pure water and 2.16 kg of polyvinyl alcohol with a degree of saponification of 99 mol% (viscosity average degree of polymerization: 1700) are placed in a 20 kg stirring vessel, and heated to about 95°C under stirring conditions to complete dissolution. to prepare a 13.5% by mass polyvinyl alcohol aqueous solution.

Before starting the supply of raw materials, 0.4 L of pure water was charged into the reactor in advance, and stirring was started. Next, the obtained polyvinyl alcohol aqueous solution was cooled to 30° C. and in-line mixed with hydrochloric acid having a concentration of 16% by mass, and then continuously supplied to the mixer was started. At the same time, butyraldehyde (purity: >99.5%) also started to be continuously supplied to the mixer from another line, and stirring of the mixed solution of the three liquids was started in the mixer. The flow rates of the polyvinyl alcohol aqueous solution, hydrochloric acid and butyraldehyde were 3.9 L/h, 0.5 L/h and 0.4 L/h, respectively, and the shear rate of the mixer was 977 [1/s]. The mixed solution mixed in the mixer was continuously supplied to the reactor. The linear velocity of the mixed solution from the mixer to the reactor was 0.6 [m/s], and the average residence time of the mixed solution from the mixer to the reactor was 3 seconds. The time required to supply all mixed solutions to the reactor was 1.5 hours. The ratio of the volume of the mixer to the volume of the reactor was 0.13. When all of the polyvinyl alcohol solution had been fed to the mixer, the hydrochloric acid and butyraldehyde feeds to the mixer were stopped. When all of the mixed solution consisting of the raw materials supplied to the mixer was supplied to the reactor, the supply of the mixed solution to the reactor was stopped. The temperature of the mixer was maintained at 30° C. by means of a heat exchanger while these raw materials were supplied to the mixer and the mixed solution was supplied to the reactor. A portion of the mixed solution was sampled and measured just before it was supplied from the mixer to the reactor, and the average degree of acetalization of the mixed solution just before the reactor was 5 mol%.

After completing the supply of the mixed solution to the reactor, stirring was performed in the reactor while maintaining the temperature of the mixer at 30° C. for 30 minutes by jacket cooling. After 30 minutes had passed, the temperature of the mixed solution was started to rise (0.8°C/min), and the acetalization reaction was carried out at 71°C for 2 hours. In Example 1, V/v is 0.08 and V/(V+V') is 0.05. After that, the reaction solution was taken out and dehydrated to a concentration of 25% by mass, followed by dehydration and washing of hydrochloric acid with pure water five times the amount of the obtained resin, which was repeated three times. Then, an aqueous sodium hydroxide solution having a concentration of 10% by mass was added to adjust the pH to 10 to 10.5 for neutralization. Dehydration and washing of the salt were repeated three times with pure water five times the amount of the resin, and the resin was dried to obtain a polyvinyl butyral resin.

(evaluation)
[Degree of acetalization]
The degree of acetalization of the polyvinyl butyral resin in the mixed solution immediately before being supplied to the reactor and the polyvinyl butyral resin finally obtained was measured by IR elemental analysis. Table 1 shows the results.

[Particle size]
The particle size of the polyvinyl butyral resin was measured with a laser diffraction particle size distribution analyzer (Mastersizer 3000E, manufactured by Malvern). Table 1 shows the results.

[Specific surface area]
The BET specific surface area of the polyvinyl butyral resin was measured by a BET one-point specific surface area measuring device (MONOSORB, manufactured by Quantachrome). Table 1 shows the results.

[Residual sodium ion concentration]
The residual sodium ion content in the polyvinyl butyral resin was measured by ICP emission spectrometry. Table 1 shows the results.

[Evaluation of aggregated particles]
The ratio, shape and hardness of coarse particles of 1 mm or more obtained when measuring the particle size of the polyvinyl butyral resin were evaluated. The shape was evaluated as being spherical or irregular, and the hardness was evaluated as whether it could be easily pulverized with fingers.

(Example 2)
A polyvinyl butyral resin was obtained in the same manner as in Example 1, except that the shear rate of the mixer was 1222 [1/s]. Various evaluations of the obtained polyvinyl butyral resin were performed in the same manner as in Example 1. Table 1 shows the evaluation results.

(Example 3)
14.24 kg of pure water and 1.76 kg of polyvinyl alcohol with a degree of saponification of 99 mol% (viscosity average degree of polymerization: 1700) were charged in a 20 kg stirring vessel, and heated to about 95 ° C. under stirring conditions to dissolve 11 A polyvinyl alcohol aqueous solution of 0.0% by weight was prepared. A polyvinyl butyral resin was obtained in the same manner as in Example 2, except that the obtained polyvinyl alcohol aqueous solution was used. Various evaluations of the obtained polyvinyl butyral resin were performed in the same manner as in Example 1. Table 1 shows the evaluation results.

(Comparative example 1)
By changing the volume of the mixer, the diameter and length of the connecting pipe to the reactor, and setting the shear rate of the mixer to 2463 [1/s], the average residence time of the mixed solution was 11 seconds, and the reaction A polyvinyl butyral resin was obtained in the same manner as in Example 3, except that the average degree of acetalization of the mixed solution immediately before the vessel was 18 mol %. Various evaluations of the obtained polyvinyl butyral resin were performed in the same manner as in Example 1. Table 1 shows the evaluation results. In Comparative Example 1, the ratio of the volume of the mixer to the volume of the reactor was 0.8.

(Comparative example 2)
Polyvinyl butyral resin was produced in the same manner as in Example 2, except that the polyvinyl alcohol aqueous solution was cooled to 40°C, mixed in-line with hydrochloric acid having a concentration of 16% by mass, and the temperature of the mixer and reactor was maintained at 40°C. Obtained. Various evaluations of the obtained polyvinyl butyral resin were performed in the same manner as in Example 1. Table 1 shows the evaluation results.

(Comparative Example 3)
606 g of ion-exchanged water and 95 g of polyvinyl alcohol with a degree of saponification of 99 mol% (viscosity average degree of polymerization: 1700) were placed in a 1-liter glass vessel equipped with a reflux condenser, a thermometer, and an anchor-type stirring blade, and the temperature was raised to 95°C. to completely dissolve the polyvinyl alcohol. The resulting polyvinyl alcohol aqueous solution was cooled to 30° C., and while stirring at 700 rpm, 54 g of n-butyraldehyde and 71 mL of hydrochloric acid having a concentration of 16% by mass were added to carry out an acetalization reaction for 0.5 hours. After that, the temperature was started to rise (0.8°C/min), and the acetalization reaction was carried out at 71°C for 2 hours. After that, the reaction solution was taken out and dehydrated to a concentration of 25% by mass, followed by dehydration and washing of hydrochloric acid with pure water five times the amount of the obtained resin, which was repeated three times. Then, an aqueous sodium hydroxide solution having a concentration of 10% by mass was added to adjust the pH to 10 to 10.5 for neutralization. Dehydration and washing of the salt were repeated three times with pure water five times the amount of the resin, and the resin was dried to obtain a polyvinyl butyral resin. Various evaluations of the obtained polyvinyl butyral resin were performed in the same manner as in Example 1. Table 1 shows the evaluation results.

Claims (10)

In the method for producing polyvinyl acetal resin by reacting polyvinyl alcohol and aldehydes,
In the presence of a catalyst, a mixed solution of a polyvinyl alcohol solution and an aldehyde is stirred in a mixer at a temperature of 20 to 35° C., and the average degree of acetalization of the polyvinyl acetal produced in the mixed solution is less than 10 mol %. , step (I) of continuously supplying the mixed solution to a reactor; and in the reactor, maintaining the temperature of the supplied mixed solution at 20 to 35 ° C. for 0.1 to 1.0 hours, After performing the acetalization reaction, the step (II) of raising the temperature in the reactor and further performing the acetalization reaction;
including
The rate of temperature rise in the reactor in step (II) is 0.50 to 1.0°C/min, and the temperature of the mixed solution during the acetalization reaction after the temperature rise is 50°C to 80°C. , a method for producing a polyvinyl acetal resin. 2. The method for producing a polyvinyl acetal resin according to claim 1, wherein the mixed solution of the polyvinyl alcohol solution and the aldehydes is obtained by mixing a solution obtained by mixing the polyvinyl alcohol solution and the catalyst in advance with the aldehydes. 3. The method for producing a polyvinyl acetal resin according to claim 1, wherein the concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 10 to 20% by mass. The method for producing a polyvinyl acetal resin according to any one of claims 1 to 3, wherein the mixed solution is stirred in a mixer at a shear rate of 600 to 2000 [1/s]. The method for producing a polyvinyl acetal resin according to any one of claims 1 to 4, wherein the mixed solution has a linear velocity of 0.5 to 3.0 [m/s] from the mixer to the reactor. The method for producing a polyvinyl acetal resin according to any one of claims 1 to 5, wherein the average residence time of the mixed solution from the mixer to the reactor is 5 seconds or less. The method for producing a polyvinyl acetal resin according to any one of claims 1 to 6, comprising a step (III) of stopping supply of the mixed solution from the mixer to the reactor after step (I). The method for producing a polyvinyl acetal resin according to any one of claims 1 to 7 , wherein in step (II), the reaction time for the acetalization reaction of the mixed solution after raising the temperature is 1 to 3 hours. The method for producing a polyvinyl acetal resin according to any one of claims 1 to 8 , wherein the polyvinyl acetal resin produced in step (II) has an average degree of acetalization of 65 mol% or more. The method for producing a polyvinyl acetal resin according to any one of claims 1 to 9 , wherein the polyvinyl acetal resin to be obtained has a bulk density of 200 kg/m ³ or more and a sodium ion content of 40 ppm or less.