JPH05140211A - Production of polyvinyl acetal resin - Google Patents

Abstract

PURPOSE:To obtain a polyvinyl acetal resin having a color improved to such an extent that any problem of quality does not arise by neutralizing a slurried reactional product with an alkali and adding a reducing agent to the neutralized slurry. CONSTITUTION:A process for producing a polyvinyl acetal resin comprising reacting PVA with an aldehyde (an aliphatic aldehyde such as formaldehyde or a mixture of at least two such aldehydes) in the presence of an acid catalyst (e.g. hydrochloric acid or p-toluenesulfonic acid), neutralizing the slurried reactional product with an alkali (e.g. NaOH) and washing the product with water and drying it, wherein a reducing agent (e.g. formic acid, oxalic acid or hydroquinone) is added after the neutralization with the alkali. According to the above process, a polyvinyl acetal resin of a color improved to such an extent that any problem of quality does not arise can be obtained because the water-insoluble compound (e.g. ferric chloride) formed by the use of the acidic catalyst is converted into a water-soluble compound (e.g. ferric formate) by the addition of the reducing agent and can be removed by washing with water.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyvinyl acetal resin whose color is improved to the extent that quality problems do not occur.

2. Description of the Related Art Polyvinyl acetal resins such as polyvinyl butyral are widely used in interlayer films for laminated glass, paints, adhesives, binders and the like. This kind of polyvinyl acetal resin is produced by reacting polyvinyl alcohol with an aldehyde in the presence of an acid catalyst, neutralizing the slurry of the reaction product with an alkali, washing with water and drying. A stainless steel reactor is generally used as the reactor. When a stainless steel reactor is used, there is a problem that mainly iron ions and chromium ions are eluted from the reactor into the reaction solution, and the obtained polyvinyl acetal resin is colored slightly yellow. In general, when the pH of the reaction solution is 5 or less, elution of iron ions and chromium ions from the reactor is a serious problem. The reason is considered as follows. That is, the eluted iron ions become water-soluble iron chloride or iron sulfate by an acid catalyst such as hydrochloric acid or sulfuric acid, and this becomes water-insoluble and yellow-brown iron hydroxide during the subsequent neutralization with alkali. It is considered that this iron hydroxide remains in the resin without being removed even by washing with water. The same applies to chromium ions. Although iron ions and chromium ions may remain in the raw material such as polyvinyl alcohol, the residual amount thereof is a trace amount and is not a problem. An intermediate film for laminated glass is produced using the resin obtained by such a method, and when it is used particularly in a thick film, it appears to be colored yellow, which is a defect in the appearance of the laminated glass. Further, even when the intermediate film is colored, the color tone changes, which causes inconvenience. Further, in the case of paints, adhesives, binders, etc., there are drawbacks similar to the above. In order to prevent such coloring of the polyvinyl acetal resin, Japanese Patent Publication No. 38-25040 discloses a reaction by adding a chelating agent which forms a complex compound with a metal ion, for example, tetrasodium salt of ethylenediaminetetraacetic acid. It is described to do.

However, the complex compound formed by the above chelating agent and a metal ion such as iron ion or chromium ion is generally colored yellow or the like, and The solubility in water is not sufficient, and even if it is washed with water, it is not completely removed and a part remains in the resin. Therefore, the obtained polyvinyl acetal resin is still colored, and a quality problem remains. The present invention is to provide a method for producing a polyvinyl acetal resin in which coloring is improved to the extent that quality problems do not occur.

In order to achieve the above object, the present invention comprises reacting polyvinyl alcohol with an aldehyde in the presence of an acid catalyst, neutralizing the slurry of the reaction product with an alkali, washing with water and drying. In the method for producing a polyvinyl acetal resin by performing the above, a reducing agent is added after neutralization with alkali. In this invention, polyvinyl alcohol generally has an average degree of polymerization of 200 to 2
600, polyvinyl alcohol having a saponification degree of 90% or more is used. Then, it is generally a solution of 5 to 12% by weight of water or alcohol. At this time, a conventional acid catalyst is added. As the acid catalyst, hydrochloric acid, phosphoric acid, sulfuric acid, paratoluenesulfonic acid, etc. may be used alone or in a mixture of two or more kinds. In general, an appropriate amount of these acid catalysts is added so that the pH of the reaction solution is 0.2 to 2. As the aldehyde, one or a mixture of two or more aliphatic aldehydes such as formaldehyde, acetaldehyde, propionaldehyde and butyraldehyde is used. When producing a resin for a laminated glass interlayer film, butyraldehyde is generally used. As a reactor, in general,
A tank reactor equipped with a stirrer, or a reactor in which a loop reactor and a tank reactor equipped with a stirrer are connected,
A stainless steel product is used. These reactors are well known. A stainless steel reactor is preferable because it has a relatively low equipment cost, but a special reactor lined with glass, titanium alloy, Hastelloy, or zirconium alloy can also be used. However, these special reactors have excellent corrosion resistance and the elution amount of metal ions such as iron ions and chromium ions is extremely small, so that they can be used without adding a reducing agent. . The reaction is carried out by a precipitation method using an aqueous medium or a solution method using an alcohol solvent. In the precipitation method, the resin particles are precipitated and the reaction product is obtained as a slurry. In the solution method, the reaction product is obtained in the form of a solution, but then water is added to precipitate the resin particles and the reaction product is converted into a slurry. Usually, a precipitation method using an industrially advantageous aqueous medium is adopted. A polyvinyl alcohol solution and an aldehyde are supplied to the reactor, and the acetalization reaction is performed in the presence of an acid catalyst. The amount of aldehyde charged (supply amount) is generally supplied in excess of 2 to 10 times the theoretical amount necessary to obtain the desired degree of acetalization. The reaction temperature is generally set in the range of 0 to 95 ° C. The reaction and aging time is generally 1 to 4 hours. Although the degree of acetalization of the resin varies depending on the use, it is generally 56 to 75 mol%, preferably 60 to 70 mol% in terms of average degree of acetalization.
It is defined as mol%. The slurry of the reaction product of the polyvinyl alcohol and the aldehyde thus formed exhibits acidity with an acid catalyst, and in order to neutralize this, an alkali such as caustic soda or baking soda is added and mixed under stirring to the reaction product slurry. It In order to prevent the aldol condensation, these alkalis are generally added in an appropriate amount so that the pH of the slurry liquid becomes 7 to 10 after removing the excess aldehyde. After the reaction for a certain period of time, the reaction is stopped by adding an alkali so that the pH of the slurry liquid becomes about 5, and then the excess aldehyde is removed, and then the pH of the slurry liquid becomes 7 to 10. You may add a suitable amount so that it may become. In this way the slurry is stabilized. When the alkali concentration of the slurry liquid is too high, the aldol condensation due to the residual aldehyde occurs and causes deterioration of the resin. In addition, alkali remains in the resin, and when the resin is dissolved in a solvent, insoluble matter remains, which causes a problem. In the present invention, the reducing agent is added to the slurry of the reaction product stabilized by neutralization. As the reducing agent, any compound having a reducing action can be used, but formic acid, oxalic acid, and hydroquinone having a strong reducing action are particularly preferably used. By the action of this reducing agent, the metal ions eluted from the reactor are finally converted into a water-soluble compound, which is dissolved in water and removed by washing with water. The amount of these reducing agents used is
Depending on the amount of metal ions eluted from the reactor, these metal ions are mainly iron ions and other chromium ions,
The elution amount of these is at most several tens of ppm. Therefore, it is suitable to add the reducing agent so that it is generally contained in the reaction solution in the range of 0.05 to 0.1% by weight, but not limited to this range. The slurry of the reaction product thus treated is dehydrated by a conventional method, washed with water and dried. In this way, a polyvinyl acetal resin having improved coloring to the extent that quality problems do not occur is produced.

In the reaction, a water-soluble compound (for example, iron chloride, chromium chloride, etc.) formed by the reaction of an acid (for example, hydrochloric acid, sulfuric acid) used as a catalyst and a metal ion such as iron ion or chromium ion during the reaction Iron sulfate, chromium sulfate) becomes a water-insoluble compound (for example, iron hydroxide or chromium hydroxide) by subsequent neutralization with alkali. However, as in the present invention, if a reducing agent (for example, formic acid) is added to the slurry after alkali neutralization, the above water-insoluble compound becomes a water-soluble compound (for example, iron formate). .. And
This water-soluble compound is dissolved in water and removed by subsequent washing with water and does not remain in the resin.

EXAMPLES Examples and comparative examples of the present invention will be shown below. (1) Description of reaction device The reaction device shown in FIG.
A butyraldehyde tank 3, a first loop reactor 11, a second loop reactor 12, an auxiliary reactor 20 provided in the middle of the second loop reactor 12, and a tank reactor 2. It has and. All of these devices are made of stainless steel (SUS316) (iron content 62 to 69% by weight,
The chromium content is 16 to 18% by weight). The polyvinyl alcohol dissolution tank 1 and the first loop type reactor 11 are connected by a supply pipe 24, the first loop type reactor 11 and the second roux type reactor 12 are connected by a transfer pipe 26, and
A transfer pipe 27 is provided between the loop reactor 12 and the tank reactor 2.
Are connected by. Reference numeral 17 is an extraction valve. Also,
The butyraldehyde tank 3 and the first loop reactor 11 are connected by a supply pipe 25. The first loop type reactor 11 and the second loop type reactor 12 are provided with a circulation pump 7, a pressure gauge 8 and a flow meter 9, and the supply pipes 24 and 25 are provided with a supply pump 14, respectively. Has been. The volume of the polyvinyl alcohol dissolution tank 1 is 100
The capacity of the liter and butyraldehyde tank is 10 liters. The first loop reactor 11 has a diameter of 40 mm.
It has a capacity of 1 liter. The second loop reactor 12 is formed by a pipe having a diameter of 25 mm, and the auxiliary reactor 20 having a volume of 3.5 liters is provided in the middle of the pipe line, and the total volume is 5 liters.
The volume of the tank reactor 2 is 100 liters. The tank reactor 2 is provided with a reflux condenser (not shown) in order to prevent butyraldehyde from flowing out of the system. (2) Production of polyvinyl butyral resin Using the reaction apparatus shown in FIG. 1, a polyvinyl butyral resin was produced by the following method. Polyvinyl alcohol having an average degree of polymerization of 1500 and a saponification degree of 99.5 mol% was dispersed in pure water in a polyvinyl alcohol dissolution tank 1 so as to have a concentration of 10% by weight, and then this was heated to 90 ° C. and dissolved. Then, it cooled to 75 degreeC. This polyvinyl alcohol 1
To 100 parts by weight, 3.1 parts by weight of an aqueous solution of hydrochloric acid having a concentration of 10% by weight was mixed as an acid catalyst. Further, 5.5 parts by weight of butyraldehyde was prepared in the butyraldehyde tank 3.
Further, the first loop type reactor 11 and the second loop type reactor 12 were filled with pure water at 75 ° C., and the circulation pump 7 of each was operated and circulated. In addition, the tank type reactor 2 has a temperature of 85 ° C.
The purified water and the aqueous hydrochloric acid solution were adjusted so that the hydrochloric acid concentration was 0.15% by weight, and the stirring amount was added. The polyvinyl alcohol aqueous solution containing the above acid catalyst and butyraldehyde were supplied to the first loop reactor 11 at a constant ratio so that the total amount of them disappeared in 60 minutes. Both are mixed through the confluence, and the mixed liquid is circulated in the first loop reactor 11 by the circulation pump 7. The flow rate in the first loop reactor 11 is adjusted to 6 m / sec to prevent the particles generated by the reaction from coalescing. An amount of slurry liquid commensurate with the supply of the polyvinyl alcohol aqueous solution and butyraldehyde is transferred into the second loop reactor 12, and is circulated in the second loop reactor 20 by the circulation pump 7.
The flow velocity in the second loop type reactor 12 is adjusted to 3 m / sec,
In addition, withdrawal valve 17 so that the pressure becomes 2 kg / cm ^2.
Was adjusted to prevent the particles from coalescing and the reaction proceeded. When the slurry liquid was sampled from the outlet of the first loop reactor 11 and the butyralization degree of the resin particles was measured, the butyralization degree was 40.0 mol%.
Furthermore, the slurry liquid circulating in the second loop reactor 12 is transferred into the tank reactor 2, the rotation speed of the stirring blade of the tank reactor 2 is 250 rpm, the peripheral speed of the stirring blade is 2 m / sec, and the use efficiency is 1
The reaction and aging were carried out at 85 ° C. for 3 hours while stirring with setting to 0 w / liter. The second loop reactor 1
When the slurry liquid was sampled from the outlet of No. 2 and the butyralization degree of the resin particles was measured, the butyralization degree was 55.0 mol%. Then, baking soda was added to stop the reaction, the pH was adjusted to about 5, and the mixture was cooled to 40 ° C. Extract the cooled slurry into a filter cloth bag, and
After washing with pure water for 0 minutes, this was put into a separately prepared 100-liter stainless steel (SUS316) stirring container, the pH was adjusted to about 8 with sodium bicarbonate, and the mixture was neutralized at 70 ° C. for 3 hours and then a reducing agent. As formic acid, 0.05% by weight was added to the reaction solution, and the mixture was left at 70 ° C. for 2 hours, washed with pure water for 30 minutes, dehydrated and dried. In this way, a white granular polyvinyl butyral resin was produced. The slurry liquid can be neutralized in the tank reactor 2 without using a separately prepared 100-liter stirring container. In this case, after removing excess butyraldehyde, baking soda is charged into the tank reactor 2 to adjust the pH to about 8. (3) Quality of polyvinyl butyral resin Regarding the obtained polyvinyl butyral resin, JIS
When the degree of butyralization was measured by K 6728,
The degree of butyralization was 64.7 mol%. Further, a transparent plate having a thickness of 3 mm was formed using this polyvinyl butyral resin, and the yellowness (YI) of this transparent plate was measured according to JIS K 7103.
Was 0.8. The present inventor has confirmed by experiments that the polyvinyl butyral resin, which has been improved in coloring to the extent that quality problems do not occur, has a yellowness index (YI) of 1.0 or less according to the above measurement method. Therefore, it is understood that the polyvinyl butyral resin obtained in Example 1 has a good quality without coloring. Example 2 In Example 1, 0.05% by weight of oxalic acid as a reducing agent was added instead of 0.05% by weight of formic acid as a reducing agent. Other than that was performed like Example 1. The yellowness index (YI) of the transparent plate is 0.7, and it can be seen that the polyvinyl butyral resin obtained in this Example 2 has a good quality without coloring. Comparative Example 1 In Example 1, formic acid as a reducing agent was not added at all. Other than that was performed like Example 1. in this case,
The yellowness (YI) of the transparent plate is 4.9, and it appears to be colored yellow and has a defect in appearance. Comparative Example 2 In Example 1, 0.022 parts by weight of a tetrasodium salt of ethylenediaminetetraacetic acid as a chelating agent was added in place of 0.05 part by weight of formic acid as a reducing agent. Other than that was performed like the comparative example 1. In this case, the yellowness (YI) of the transparent plate is 4.5, and the transparent plate looks yellow and has a defect in appearance.

As described above, according to the present invention, polyvinyl alcohol and aldehyde are reacted in the presence of an acid catalyst,
In the method of producing a polyvinyl acetal resin by neutralizing the slurry of the reaction product with an alkali, washing with water and drying, a reducing agent is added after the neutralization of the alkali so that a quality problem does not occur. It is possible to produce a polyvinyl acetal resin with improved coloring. Therefore, the polyvinyl acetal resin obtained by the method of the present invention is suitable as a raw material resin for interlayer films for laminated glass, paints, adhesives, binders and the like.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing an example of a reaction apparatus used in the present invention.

[Explanation of symbols]

 1 polyvinyl alcohol dissolution tank 2 tank type reactor 3 butyraldehyde tank 7 circulation pump 11 first loop type reactor 12 second loop type reactor 14 supply pump 17 extraction valve 20 auxiliary reactor 24 supply pipe 25 supply pipe 26 transfer pipe 27 Transfer pipe

Claims (2)

[Claims] 1. A method for producing a polyvinyl acetal resin by reacting polyvinyl alcohol with an aldehyde in the presence of an acid catalyst, neutralizing the slurry of the reaction product, washing with water and drying to produce a polyvinyl acetal resin. A method for producing a polyvinyl acetal resin, which comprises adding a post-reducing agent. 2. The method for producing a polyvinyl acetal resin according to claim 1, wherein formic acid or oxalic acid is used as the reducing agent.