JP6565274B2 - Method for producing polyvinyl acetal resin - Google Patents

Description

The present invention relates to the manufacture how the port polyvinyl acetal resin.

  A lithium ion secondary battery electrode is usually formed by applying a slurry obtained by mixing a binder, an active material, a solvent, and optionally other components onto a current collector and drying it. As the binder used for forming the lithium ion secondary battery electrode, polyvinylidene fluoride, styrene butadiene rubber or the like is generally used. Since the binder to be used is desired to have as low a swellability as possible with respect to the carbonate-based electrolyte, when using a polyvinyl acetal resin as a binder, the degree of acetalization is low with respect to the electrolyte, And in order to improve the durability of an electrode, 11-40 mol% is preferable.

Examples of a method for producing a polyvinyl acetal resin include a method in which polyvinyl alcohol is dissolved in water and reacted with an aldehyde compound.
However, if an attempt is made to produce a polyvinyl acetal resin having an acetalization degree of 11 to 40 mol%, the solubility of the polyvinyl acetal resin in the reaction solution is reduced, and the polyvinyl acetal resin is not completely insolubilized. A large amount of scale is generated in the manufacturing apparatus. When the scale is generated, the recovery rate is lowered, the cleaning time of the reaction can and the like is increased, and contamination is generated, so that the production efficiency is lowered.

Therefore, in order to improve the solubility of the polyvinyl acetal resin, a method of adding alcohol to suppress the generation of scale can be considered. For example, Patent Document 1 describes a method for producing a polyvinyl acetal resin using a mixed solvent of water and alcohol as a reaction solvent.
However, when polyvinyl alcohol having a high degree of saponification is used as a raw material, polyvinyl alcohol is not completely dissolved in a mixed solvent of water and alcohol, and a part of the polyvinyl alcohol is insoluble and production efficiency is lowered.

Patent Document 2 discloses a method for producing a polyvinyl acetal resin in which water is initially used as a reaction solvent and an acetalization reaction between polyvinyl alcohol and an aromatic aldehyde is performed. Is described as a mixed solvent.
Furthermore, Patent Document 3 discloses a method for producing a polyvinyl acetal resin in which water is initially used as a reaction solvent and an acetalization reaction between polyvinyl alcohol and an aromatic aldehyde is performed. A method of using a solvent is described.
However, although the generation of scale can be suppressed by these methods, when the degree of acetalization exceeds 10 mol%, the acetalization reaction becomes a heterogeneous reaction, so that the acetal distribution in the polyvinyl acetal resin becomes nonuniform. Accordingly, since the resulting polyvinyl acetal is slowly dissolved in a solvent (NMP: N-methylpyrrolidone, DMF: dimethylformamide, etc.) when used as a binder for a lithium ion secondary battery electrode, production efficiency is reduced. There is a possibility that the battery becomes defective when undissolved.

JP-A-62-96506 Japanese Patent Laid-Open No. 9-255721 JP-A-11-116619

Then, this invention aims at provision of the method which can produce a polyvinyl acetal resin with which an acetal distribution is hard to generate | occur | produce and which has a uniform acetal distribution, when manufacturing the polyvinyl acetal type resin whose acetalization degree is 11-40 mol%. .

  As a result of intensive investigations in view of the above circumstances, the inventors of the present invention made the initial reaction solvent aqueous, and added alcohol when the viscosity of the reaction liquid started to increase, so that all steps of the acetalization reaction were uniformly reacted. It was confirmed that the generation of scale was suppressed and the dissolution in the solvent was accelerated.

  That is, the present invention is a method for producing a polyvinyl acetal resin having an acetalization degree of 11 to 40 mol%, wherein a polyvinyl alcohol resin having a saponification degree of 97 mol% or more and an aldehyde compound are reacted in water. The present invention provides a method for producing a polyacetal resin, wherein an alcohol having 1 to 4 carbon atoms is added to the reaction solution when the viscosity of the reaction solution starts to increase.

According to the method for producing a polyvinyl acetal resin of the present invention, it is possible to produce a polyvinyl acetal resin that is difficult to generate scale and has a uniform acetal distribution.
Moreover, since this polyvinyl acetal resin has a uniform acetal distribution, the dissolution in a solvent such as NMP is accelerated, and an effect that a uniform solution can be obtained is obtained.
Furthermore, since the binder for lithium ion secondary battery electrodes containing this polyvinyl acetal resin can be uniformly dissolved in a solvent, the effect that it is hard to produce the defective product of a lithium ion secondary battery electrode is acquired.

  The reason why the acetalization reaction becomes uniform according to the present invention is presumed to be because a solvent showing solubility is added at a stage before aggregation of the polymer or the like occurs.

Hereinafter, although it demonstrates in detail about the structure of this invention, these show an example of a desirable embodiment, and this invention is not specified by these content.
The polyvinyl acetal resin of the present invention is obtained by acetalizing a polyvinyl alcohol resin and an aldehyde compound. Hereinafter, the polyvinyl alcohol resin (hereinafter referred to as PVOH) and the aldehyde compound will be described.

<PVOH>
The PVOH used in the present invention can be usually obtained by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester monomer.
Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, and benzoic acid. Examples thereof include vinyl acid vinyl and vinyl versatate. Of these, vinyl acetate is preferred from the viewpoint of economy.
These monomers may be used alone or in combination of two or more.

The PVOH used in the present invention has a structure derived from other ethylenically unsaturated monomers other than the above vinyl ester monomers within a range that does not impair the effects of the present invention (for example, less than 10 mol%). You may have a unit.
The ethylenically unsaturated monomer is not particularly limited, and examples thereof include α-olefins such as propylene, isopropylene, butylene, isobutylene, pentylene, hexylene, cyclohexylene, cyclohexylethylene, and cyclohexylpropylene; 3-butene-1 Hydroxy group-containing α-olefins such as -ol, 4-penten-1-ol, 3-butene1,2 diol; vinylene carbonates, acrylic acid, methacrylic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid Unsaturated acids such as itaconic acid or its salts or mono- or dialkyl esters; Nitriles such as acrylonitrile; Amides such as acrylamide and methacrylamide; Olefin such as ethylene sulfonic acid, allyl sulfonic acid and methallyl sulfonic acid Sulfonic acid Or a salt thereof; 3,4-diasiloxy-1-butene such as 3,4-dihydroxy-1-butene and 3,4-diacetoxy-1-butene; 3-acyloxy-4-hydroxy-1-butene and 4-acyloxy -3-hydroxy-1-butene, 3,4-diasiloxy-2-methyl-1-butene, 4,5-dihydroxy-1-pentene, 4,5-diasiloxy-1-pentene, 4,5-dihydroxy-3 Glycerol monoallyl ethers such as methyl-1-pentene, 4,5-diacyloxy-3-methyl-1-pentene, 5,6-dihydroxy-1-hexene, 5,6-diacyloxy-1-hexene; -Diacetoxy-1-allyloxypropane; 2-acetoxy-1-allyloxy-3-hydroxypropane; 3-acetoxy-1-allyloxy- - hydroxypropane; glycerin monovinyl ether; and glycerol mono isopropenyl ether and the like.
In addition, vinyl ethylene carbonate, vinyl trimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, allyltrimethoxysilane, allylmethyldimethoxysilane, allyldimethylmethoxy Silane, allyltriethoxysilane, allylmethyldiethoxysilane, allyldimethylethoxysilane, vinyltris (β-methoxyethoxy) silane, vinylisobutyldimethoxysilane, vinylethyldimethoxysilane, vinylmethoxydibutoxysilane, vinyldimethoxybutoxysilane, vinyltri Butoxysilane, vinylmethoxydihexyloxysilane, vinyldimethoxyhexyloxysilane, vinyltrihexylo Sisilane, vinyl methoxydioctyloxy silane, vinyl dimethoxy octyloxy silane, vinyl trioctyloxy silane, vinyl methoxy dilauryl silane, vinyl dimethoxy lauryloxy silane, vinyl methoxy dioleoxy silane, vinyl dimethoxy oleyloxy silane etc. . Hydroxymethyl vinylidene diacetate is also mentioned, and specifically, 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, 1,3-dibutyronyloxy-2 -Methylenepropane and the like. Among these, 1,3-diacetoxy-2-methylenepropane is preferably used in terms of ease of production.
Also use terminal-modified polyvinyl alcohol obtained by copolymerizing vinyl ester monomer such as vinyl acetate with ethylene in the presence of thiol compounds such as thiol acetic acid and mercaptopropionic acid, and saponifying it. Can do.
These monomers may be used alone or in combination of two or more.

  In addition, the PVOH used in the present invention may contain PVOH modified within a range not inhibiting the effects of the present invention (usually 15 mol% or less, preferably less than 10 mol%). Examples of PVOH include PVOH formalized product, acetalized product, acetoacetylated product, butyralized product, urethanized product, esterified product with sulfonic acid, carboxylic acid, and the like.

  Polymerization of vinyl ester monomers, or in some cases, polymerization of vinyl ester monomers and ethylenically unsaturated monomers may be any known polymerization method such as solution polymerization, suspension polymerization, emulsion polymerization, etc. Can be performed. Especially, it is preferable to perform the solution polymerization which can remove reaction heat efficiently under recirculation | reflux. As the solvent for the solution polymerization, alcohol is usually used, and preferably a lower alcohol having 1 to 3 carbon atoms is used.

  The viscosity average polymerization degree (measured according to JIS K 6726) of the polyvinyl ester is preferably 500 or more, particularly preferably 1000 to 3000, and further preferably 2500 to 3000. When the average degree of polymerization is too high, the viscosity of the binder prepared using the obtained polyvinyl acetal resin tends to be too high and the electrode manufacturing workability tends to be reduced. When the average degree of polymerization is too low The effect of the present invention tends to be difficult to obtain efficiently.

For the saponification of the polyvinyl ester, a known saponification method that has been used can be employed. That is, it can be carried out using an alkali catalyst or an acid catalyst in a state where the polyvinyl ester is dissolved in an alcohol or a water / alcohol mixed solvent.
Examples of the alkali catalyst include alkali metal hydroxides and alcoholates such as potassium hydroxide, sodium hydroxide, sodium methylate, sodium ethylate, potassium methylate, and lithium methylate.
Usually, an ester exchange reaction using an alkali catalyst in an anhydrous alcohol solvent is suitably used in terms of reaction rate and reduction of impurities such as fatty acid salts.

  The reaction temperature of the saponification reaction is usually 20 ° C to 60 ° C. If the reaction temperature is too low, the reaction rate tends to decrease and the reaction efficiency tends to decrease. If it is too high, the reaction solvent may have a boiling point or higher, and the safety in production tends to decrease. In addition, when saponifying under high pressure using a tower type continuous saponification tower having high pressure resistance, it is possible to saponify at a higher temperature, for example, 80 to 150 ° C., and a small amount of saponification catalyst. It is also possible to obtain a high saponification degree for a short time.

  The saponification degree of PVOH (measured according to JIS K 6726) is usually 97 mol% or more, preferably 98 to 100 mol%, particularly preferably 98 to 99.9 mol%. When the saponification degree is too low, the swelling property of the obtained polyvinyl butyral with respect to the electrolytic solution tends to be high. On the other hand, PVA with a high saponification degree, especially complete saponification, tends to be industrially difficult to produce, and it is difficult to completely dissolve in water. This is not preferable because the acetalization reaction becomes non-uniform or a site that does not undergo the acetalization reaction occurs.

In the production method of the present invention, the PVOH aqueous solution is prepared by dissolving PVOH in water prior to the reaction with the aldehyde compound. Such water may contain an organic solvent miscible with water in a range not inhibiting the dissolution of PVOH (for example, less than 20% by weight, preferably less than 10% by weight of the solvent).
Examples of the organic solvent include amide solvents such as N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, and methylformamide, sulfoxides such as dimethyl sulfoxide, lower C1-C4 such as methanol and ethanol. Examples thereof include alcohols and alcohol solvents such as 1,1,1,3,3,3-hexafluoro-2-propanol.

The concentration of PVOH in the PVOH aqueous solution is preferably 1 to 20% by weight, particularly preferably 1 to 10% by weight.
As a method of dissolving PVOH in a solvent, for example, a method of dissolving at a high temperature of about 120 ° C. in a state of being pressurized in an autoclave can be mentioned.

<Aldehyde compound>
Examples of the aldehyde compound used in the present invention include alkyl aldehydes and aromatic aldehydes, and specific examples include butyraldehyde, propyl aldehyde, acetaldehyde, formaldehyde, and benzaldehyde.

Moreover, the aldehyde compound which has a functional group containing an ethylenically unsaturated bond can also be used as an aldehyde compound. When such a functional group contains an ethylenically unsaturated bond, it is crosslinked by carrying out a crosslinking reaction with heat or light, and becomes a resin having a network structure. Such an ethylenically unsaturated bond is at least one selected from a terminal vinyl structure and an internal alkene structure.
The number of ethylenically unsaturated bonds in the functional group containing an ethylenically unsaturated bond is usually 1 to 5, preferably 1 to 3. At this time, since the ethylenically unsaturated bond constituting the aromaticity of the aromatic compound does not have a crosslinking ability, it is not included in the “ethylenically unsaturated bond” in the present invention.
Note that the functional group containing an ethylenically unsaturated bond may have an unsaturated bond other than the ethylenically unsaturated bond, such as a carbonyl group or an amide bond.

Examples of the aldehyde compound having a functional group containing an ethylenically unsaturated bond include acrolein, crotonaldehyde, methacrolein, trans-2-pentenal, trans-2,4-hexadienal, citronellal, cinnamic aldehyde, acrylamide acetaldehyde, Examples include methacrylamide acetaldehyde and all-trans retinal.
These aldehyde compounds may be used alone or in combination of two or more.

<Acetalization reaction>
The acetalization reaction can be carried out under known general conditions. Usually, an aldehyde compound is added to an aqueous PVOH solution in the presence of an acid catalyst to cause an acetalization reaction. With the progress of the acetalization reaction, polyvinyl acetal resin particles are precipitated, and thereafter, a method of advancing the reaction in a heterogeneous system is generally performed. In the present invention, the acetalization reaction is performed in a homogeneous system.

Such acetalization reaction is preferably initiated at a low temperature. For example, I) A method in which an aqueous PVOH solution is cooled and an acid and a predetermined amount of an aldehyde compound are added to start the reaction. II) An aldehyde compound is added to the PVOH aqueous solution, and the reaction is started by adding an acid after cooling. III) A method in which an acid is added to a PVOH aqueous solution, and after cooling, an aldehyde compound is added to start the reaction.
In general, in preparing an aqueous solution containing PVOH, it is preferable to dissolve the solution by heating. In the above I) to III), unless otherwise specified, it means an aqueous solution that is cooled to room temperature after being heated and dissolved.

The aldehyde compound may be added all at once or may be added separately. For example, a part may be added before cooling, and the rest may be added after cooling. Preferably, an aqueous solution in which PVOH is dissolved in water is prepared, cooled to 5 to 50 ° C., an aldehyde compound is added thereto, and then the reaction is started by blending an acid.
In the present invention, a part of an aldehyde compound necessary for acetalizing PVOH is added, and an alcohol having 1 to 4 carbon atoms described later is added to water, and then the remaining aldehyde compound is added to acetal. May be completed.

  Examples of the acid used for the acetalization reaction include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic acids such as p-toluenesulfonic acid. These acids may be used alone or in combination. More than one species may be used in combination.

  The acetalization reaction is preferably performed with stirring. Moreover, in order to perform acetalization reaction completely, it is preferable to continue reaction normally at 50-80 degreeC. The acetalization reaction is usually performed for 1 to 10 hours.

In the method for producing the polyvinyl acetal resin of the present invention, when the viscosity of the reaction solution starts to increase, an alcohol having 1 to 4 carbon atoms is added to the reaction solution.
Here, when the viscosity of the reaction liquid starts to increase, it can be detected that the stirring torque starts to increase or the contact between the can wall and the liquid surface of the reaction liquid starts to decrease.

  Examples of the alcohol having 1 to 4 carbon atoms include methyl alcohol, ethyl alcohol, 1-propanol, 2-propanol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, and preferably methyl alcohol. These alcohols may be used alone or in combination of two or more.

  The addition amount of the alcohol having 1 to 4 carbon atoms is preferably 50 to 150 parts by weight, particularly preferably 75 to 125 parts by weight with respect to 100 parts by weight of water in the reaction solution. If the amount of alcohol added is too small, the polyvinyl acetal resin tends to precipitate, and if the amount of alcohol added is too large, the acetalization reaction tends to hardly proceed.

When the degree of acetalization falls within the range of 11 to 40 mol%, a neutralizing agent is added to neutralize the acetalization reaction catalyst (acid) to complete the reaction.
As such a neutralizing agent, an alkali compound is used, for example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal carbonates such as sodium carbonate and calcium carbonate, ammonia, triethylamine, Examples include amine compounds such as pyridine.
By adding a non-aqueous solvent such as acetone after completion of the reaction, a powdery reaction product is obtained. The polyvinyl acetal resin of the present invention can be obtained by drying after washing as necessary.

The degree of acetalization in a polyvinyl acetal resin refers to the ratio of the number of hydroxyl groups acetalized with an aldehyde compound, based on the number of hydroxyl groups in the vinyl alcohol resin that is a precursor of the polyvinyl acetal resin. That is, the degree of acetalization can be calculated by adopting a method for calculating the number of hydroxyl groups of the vinyl alcohol resin subjected to acetalization, and calculating the mol% of the degree of acetalization. Specifically, it can be calculated by a known method by ¹ H-NMR measurement.

According to the manufacturing method of the present invention, since the scale hardly occurs, an effect that the manufacturing efficiency is good is obtained. In addition, the polyvinyl acetal resin obtained by the production method of the present invention (hereinafter also referred to as the polyvinyl acetal resin of the present invention) has an acetalization degree of 11 to 40 mol% and a uniform acetal distribution. The effect that it can be dissolved in a solvent such as a fast and uniform solution can be obtained. Therefore, by using the polyvinyl acetal resin of the present invention as a binder for lithium ion secondary battery electrodes, it can be uniformly dissolved in a solvent such as NMP, so that it is difficult for defective lithium ion secondary battery electrodes to occur. An effect is obtained. Hereinafter, the binder for lithium ion secondary battery electrodes using the polyvinyl acetal resin of the present invention is also referred to as the binder for lithium ion secondary battery electrodes of the present invention.

<Binder for lithium ion secondary battery electrode>
The binder for lithium ion secondary battery electrodes of the present invention (hereinafter also referred to as electrode binder) includes the polyvinyl acetal resin of the present invention.
In the binder for electrodes of the present invention, other polyvinyl acetal resins may be blended together with the polyvinyl acetal resin of the present invention.
In addition, other compounding agents may be blended, such as light stabilizers, ultraviolet absorbers, thickeners, leveling agents, thixotropic agents, antifoaming agents, freezing stabilizers, matting agents, cross-linking reaction catalysts, Pigment, curing catalyst, cross-linking agent {boric acid, methylolated melamine, zirconium carbonate, diisopropoxytitanium bis (triethanolaminate), etc.}, anti-skinning agent, dispersant, wetting agent, antioxidant, UV absorber, Rheology control agents, film forming aids, rust inhibitors, dyes, plasticizers, lubricants, reducing agents, antiseptics, antifungal agents, deodorants, anti-yellowing agents, antistatic agents or charge control agents, etc. It may be blended. They can be selected or combined according to their purpose.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to a following example, unless the summary is exceeded. In the examples, “%” and “parts” mean weight basis.

[Example 1]
PVOH (15 g) having a polymerization degree (P) of 2600 and a saponification degree (SV) of 99 mol% was put into a beaker containing 235 g of water, stirred and dispersed, heated to 90 ° C. and dissolved over 1.5 hours. I let you.
The obtained PVOH aqueous solution was adjusted to a concentration of 6%, 250 g of which was adjusted to 10 ° C., 1.6 g of hydrochloric acid having a concentration of 35% was added thereto, and 2.7 g of butyraldehyde was added dropwise over 10 minutes. When the reaction was carried out for 1 hour and the stirring torque started to increase, that is, when the viscosity of the reaction solution started to increase (the degree of acetalization was 7% at this time), 256 g of methanol was added and the concentration was 35%. 9.2 g of hydrochloric acid was added over 10 minutes. Thereafter, the solution was reacted at 25 ° C. for 30 minutes, further maintained at 60 ° C. for 5 hours, reacted, neutralized with an aqueous sodium carbonate solution to complete the reaction, and a polyvinyl butyral (PVB) resin solution was obtained.
After adding 256 g of methanol to the PVB solution, 2567 g of acetone was added to precipitate a PVB resin. The obtained PVB resin was filtered, washed with a mixed solvent of acetone / water (= 9/1), then washed with 500 mL of acetone three times, and dried at 80 ° C. to obtain a PVB resin. The degree of acetalization of the obtained PVB resin was 22%.
When the obtained PVB resin was dissolved in NMP at 80 ° C. so as to be 7%, it was completely dissolved in 20 minutes.

[Comparative Example 1]
15 g of PVOH having a polymerization degree (P) of 2600 and a saponification degree (SV) of 99 mol% was dissolved in 235 g of water at 90 ° C., the resin content was measured, and a 6% PVOH aqueous solution was adjusted to 250 g. An attempt was made to prepare a 50/50 methanol / water mixture by adding the same amount of methanol to the aqueous solution, but a polymer precipitated and a uniform solution could not be obtained.

[Comparative Example 2]
15 g of PVOH having a polymerization degree (P) of 2600 and a saponification degree (SV) of 99 mol% was dissolved in 235 g of water at 90 ° C., the resin content was measured, and a 6% PVOH aqueous solution was adjusted to 250 g.
The temperature was adjusted to 10 ° C. or lower, 1.6 g of 35% hydrochloric acid was added, and 7.9 g of butyraldehyde was added dropwise over 10 minutes, followed by aging at 10 ° C. for 1 hour. To this solution, 9.2 g of 35% strength hydrochloric acid was added over 10 minutes and aged for 30 minutes, and then the temperature was raised to 60 ° C. and aged for 5 hours. After the reaction, hydrochloric acid was neutralized with an aqueous sodium solution. After adding 256 g of methanol and dissolving the precipitated PVB resin, crystallization occurred by adding 256 g of methanol and adding 2567 g of acetone, and a PVB resin was obtained. The obtained PVB resin was filtered, washed with a mixed solvent of acetone / water (= 9/1), then washed with 500 mL of acetone three times and dried at 80 ° C. to obtain a PVB resin. The degree of acetalization of the obtained PVB resin was 22%.
When the obtained PVB resin was dissolved in NMP at 80 ° C. so as to be 7%, it took 40 minutes to complete dissolution.

The polyacetal-based resin obtained by the production method of the present invention has an acetalization degree of 11 to 40 mol% and a uniform acetal distribution, so that it can be quickly dissolved in a solvent such as DMF to form a uniform solution. Since the binder for lithium ion secondary battery electrodes is used after being dissolved in a solvent such as DMF, the polyacetal resin of the present invention can be suitably used as a binder for lithium ion secondary battery electrodes.

Claims (2)

A method for producing a polyvinyl acetal resin having an acetalization degree of 11 to 40 mol%,
When a polyvinyl alcohol resin having a saponification degree of 97 mol% or more and an aldehyde compound are reacted in water, and the viscosity of the reaction solution starts to increase, an alcohol having 1 to 4 carbon atoms is added to the reaction solution. A process for producing a polyacetal-based resin.   The method for producing a polyacetal resin according to claim 1, wherein the addition amount of the alcohol having 1 to 4 carbon atoms is 50 to 150 parts by weight with respect to 100 parts by weight of water in the reaction solution.