JPS6141923B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for saponifying polyvinyl acetate (hereinafter abbreviated as PVAc), and more specifically, the present invention relates to a method for saponifying polyvinyl acetate (hereinafter abbreviated as PVAc). When producing polyvinyl alcohol (hereinafter abbreviated as PVA) of mol% or less, the water content of methanol is maintained at 0.05 to 0.8% by weight, and the amount of methanol is adjusted to a predetermined degree of saponification.
This is a PVAc saponification method characterized by controlling the degree of saponification by adjusting the weight to be 2 to 3.5 times the stoichiometric amount required to obtain PVA.

Traditionally, the industrial method for producing PVA has generally been to prepare an anhydrous or hydrous alcohol solution of PVAc at least four times the weight of the stoichiometric amount required to obtain PVA with a predetermined degree of saponification, and then add an alkaline catalyst to this solution. The method used is to saponify it, then separate it and dry it. However, in this case, it is extremely difficult to control the degree of saponification of the product in the saponification process of PVAc, and it is especially difficult to stably produce PVA with a low saponification degree with good reproducibility. This is what was most desired to be improved. In other words, the method of controlling the saponification degree of PVA is to adjust the amount of alkali used as a saponification catalyst and the reaction time, but it is difficult to obtain PVA with a low saponification degree of 80 mol% or less. However, if the amount of alkali is reduced in the process, the reaction time becomes extremely long and production cannot be increased, which is not only disadvantageous industrially, but also in this case, if more than 4 times the weight of alcohol is present, the quenching after gelation will occur. The reaction rate gradient from around 50 mol% to around 10 mol% is quite steep, and therefore it is extremely difficult to reproducibly obtain PVA with any saponification degree between this range. In addition, as another method to control the degree of saponification, a method of adding acid or water during the reaction has been proposed, but as mentioned above, the reaction rate gradient is steep in the presence of 4 times the weight or more of alcohol. If the timing of addition of acid or water is slightly incorrect, the degree of saponification will deviate significantly from the specified value.
It is difficult to prevent this even with extremely precise control equipment. In addition, the method of adding water is complicated, as is the case with acids, and if the added water exceeds 0.8% by weight based on the alcohol, PVA will dissolve in the added water, so PVA as a final product
It becomes extremely difficult to dry the polymer, and this tendency is particularly remarkable when the degree of polymerization and saponification is low.

The present inventors have overcome the above-mentioned disadvantages in PVA production, and developed a method for stably producing PVA with a low saponification degree of 80 mol% or less with good reproducibility.
In the method of producing PVA by adding an alkaline catalyst to an anhydrous methanol solution of PVAc and saponifying PVMc, methanol is added to the same weight or twice the weight of the stoichiometric amount required to obtain PVA with a predetermined degree of saponification. It was discovered that the degree of saponification could be easily controlled by dissolving and saponifying PVAc, and an application has already been filed (Japanese Patent Application Laid-Open No. 87593/1983).

However, while this method allows the degree of saponification to be adjusted extremely accurately and reproducibly, the
The disadvantage was that the melt viscosity of PVAc was relatively high. This is considered to be because the saponification is carried out in a substantially anhydrous state, so that the intramolecular distribution of residual acetic acid groups becomes more collective. Furthermore, the second drawback is that the polymer concentration during saponification becomes too high, making it difficult to mix the alkali catalyst and PVAc uniformly, and perhaps because of this, the intermolecular distribution of the degree of saponification becomes too wide. I found out.

In order to overcome these drawbacks, the present inventors continued to conduct intensive research and found that, in particular, when producing PVA with a degree of saponification of 80 mol% or less, the water content is 0.05 to 0.05.
Dissolve PVAc in methanol kept at 0.8% by weight,
By adjusting the amount of methanol to 2 times to 3.5 times the weight of the stoichiometric amount required to obtain a predetermined degree of saponification, the degree of saponification can be accurately adjusted while solving such quality problems. They have found that it can be well adjusted and have completed the present invention.

Alkali catalysts are mainly used in the industrial saponification reaction of methanol solutions of PVAc. For example, when sodium hydroxide is used in anhydrous methanol, the reaction mechanism is mainly the transesterification reaction described below.

Here, n is any positive number representing the number of moles, a is 0
≦a≦1, and the degree of saponification is expressed as a×100 (mol%). Therefore, the stoichiometric amount of anhydrous methanol to produce PVA with saponification degree a x 100 mol% is an mole, and it is theoretically good if this amount of anhydrous methanol exists. Become. However, if an excess of anhydrous methanol is present in the system, it becomes difficult to stop the reaction at a predetermined degree of saponification. This tendency becomes particularly strong when (an+m)/an>2, assuming that the amount of excess anhydrous methanol is mmol. Industrially (an+
m)/an is often 4 or more, and for this reason, the above-mentioned obstacles are very large.
The reaction cannot be stopped with good reproducibility at a predetermined low degree of saponification.

When the present inventors use anhydrous methanol 1
It was discovered that the degree of saponification can be easily controlled within the range of ≦(an+m)/an≦2, and was previously published in JP-A-51-087593.
As mentioned above, the application was filed under No.

However, as mentioned above, this method has two drawbacks: the melt viscosity of PVA increases and the intermolecular distribution of saponification degree widens. These are major obstacles when using PVA as a hot melt adhesive. It has an unfavorable property.

The method of the present invention overcomes these drawbacks and makes it possible to control the degree of saponification with good reproducibility. In other words, when saponification is carried out in the presence of water, the dielectric constant of the system increases, and the alkali of the catalyst spreads along the polymer molecular chain and becomes able to attack. A PVA with uniform internal distribution is obtained, which has a lower melt viscosity than one without. In addition, adding water slows down the saponification reaction rate, so even if the amount of methanol is increased to a certain extent, the degree of saponification can be adjusted with good reproducibility. As a result of decreasing
PVA with a narrow intermolecular distribution of degree of saponification is obtained, probably due to lower solution viscosity and improved miscibility with alkali.

In this way, when producing PVA with a saponification degree of 80 mol% or less, we skillfully utilize the effects of water.
Furthermore, by adjusting the amount of methanol, it became possible for the first time to precisely control the degree of saponification while maintaining a high level of quality. However, if the amount of water is too small, it will not be effective, and if it is too large, not only will drying become difficult, but a larger amount of alkaline catalyst will be required to obtain the desired degree of saponification, resulting in acetate being produced as a by-product. The thermal stability of PVA deteriorates due to the influence of Therefore, the amount of water has its own limitations and needs to be in the range of 0.05 to 0.8% by weight based on methanol.

FIG. 1 shows the relationship between the PVAc concentration and the degree of saponification when PVAc having an average degree of polymerization of 120 is saponified with a 0.5% by weight aqueous methanol solution. In Figure 1, curve 1 indicates that the amount of methanol that is twice the stoichiometric amount required to obtain PVA with the degree of saponification indicated on the vertical axis is
This graph shows the relationship between the PVAc concentration in a solution and the degree of saponification when PVAc is dissolved, and curve 2 is a relationship curve when PVAc is similarly dissolved in 3.5 times the stoichiometric amount of methanol. Therefore, the adjustment range of PVAc/methanol in the saponification method of the present invention is the area surrounded by curve 1 and curve 2.

In addition, in Figure 1, curve 3 is the relationship curve when 5 milli equivalents of sodium hydroxide is added and saponification is carried out at a temperature of 40°C, and curve 4 is the relationship curve when 10 milli equivalents of sodium hydroxide is added. This is the relationship curve for the case. The reaction time under the conditions of curves 3 and 4 is 60 minutes or more after gelation, and indicates that the reaction does not proceed further even if left for any longer, that is, the saturation point of the reaction.

Figure 2 shows PVAc with a degree of polymerization of 120 (an+m)/an
This figure shows the change over time in the degree of saponification when PVAc was dissolved in methanol with various water contents such that PVAc = 3, and saponified by adding 5 milli equivalents of sodium hydroxide to PVAc at a temperature of 40°C. Figure 2 shows that when the water content is 0.02% by weight, the saponification reaction continues even after gelation, and the degree of saponification increases with time, but when the water content is 0.05% by weight or more, more than 60 minutes have passed after gelation. It can be seen that the increase in the degree of saponification was small, indicating that the reaction had almost stopped. It can be seen that when the water content reaches 0.8% by weight, the saponification reaction almost completely stops 60 minutes after gelation.

Figure 3 shows PVAc in methanol with a moisture content of 0.5% by weight.
This graph shows the time course of the degree of saponification of PVA produced when PVA is dissolved at a ratio of (an+m)/an of 5 to 2 and saponified using 5 milliquivalents of sodium hydroxide at a temperature of 40°C. It is. From Figure 3 (an
+m)/an=5, it can be seen that the saponification reaction continues even after 60 minutes have passed after gelation. On the other hand, when (an+m)/an=3.5 and 2.0, it is clear that the saponification reaction has almost completely stopped after 60 minutes.

From Figures 2 and 3, the amount of methanol (an
+m)/an≧2 and the water content is low, i.e. PVAc in an anhydrous methanol solution with a water content of 0.02%.
When saponifying aqueous methanol with a water content of 0.5% (an+m)an≧4, for example, if you try to control the degree of saponification at 60 mol%, the reaction time will be instantaneous at about 20 minutes. Although it is clear that the reaction must be stopped immediately, it is actually very difficult to control this reaction during production on an industrial scale. However, 2≦
Since the saponification reaction of PVAc dissolved in methanol with a water content of 0.05 to 0.8% by weight in the range of (an+m)/an≦3.5 can be easily stopped at a predetermined degree of saponification, the method of the present invention It is very effective in producing PVA with a low degree of saponification.

The method of the present invention is useful for controlling the degree of saponification and is effective for producing PVA with various degrees of polymerization and saponification. However, if the viscosity of a solution of PVAc dissolved in methanol becomes too high, the reaction may be uneven. This is especially true at low polymerization degrees of 50 to 700.
It is also suitable for obtaining PVA with a low saponification degree of 80 mol% or less.

Effective saponification devices for carrying out the method of the present invention include a kneader type in the case of a batch type, and a belt type, pipe type, twin screw type, etc. in the case of a continuous type. Good results can be obtained using any of these known devices.

EXAMPLES Next, the present invention will be explained in further detail by way of examples. In addition, in the examples, all parts simply refer to parts by weight.

Example 1 In order to obtain PVA with a saponification degree of 60.0 mol%, 69.1 parts of PVAc with an average degree of polymerization of 120 was dissolved in 27.86 parts of methanol with a water content of 0.5% by weight, and the temperature was adjusted to 40°C.
3.37 parts of a 5% by weight methanol solution of sodium hydroxide was added thereto, and after stirring for 5 minutes, the mixture was left to stand. Gelation occurred 15 minutes after the addition of sodium hydroxide.

60 minutes after gelation, a part of the gel was taken out, crushed, and dried under reduced pressure at 80°C and 5 mmHg for 2 hours to measure the degree of saponification.
It was 60.5 mol%. Further, after the gel was left to stand for an additional 60 minutes, ie, 120 minutes after gelation, a portion of the gel was taken out and operated in the same manner, and no progress in the degree of saponification was observed.

Amount of methanol under these conditions (an+m)/an
is twice as high, and sodium hydroxide is 5.25 milliequivalents to PVAc.

For comparison, 52.8 parts of the same PVAc was dissolved in 44.99 parts of methanol with a water content of 0.5% by weight, and 2.45 parts of a 5% by weight methanol solution of sodium hydroxide was saponified at 40°C. After 18 minutes, gelation occurred. It happened. After 20 minutes had elapsed after gelation, a portion of the gel was taken out and treated in the same manner to measure the degree of saponification, which was found to be 59.5 mol%. However, when a gel that was left for 10 minutes (30 minutes after gelation) was processed, the degree of saponification was 65.0 mol%, and when a gel that was left for another 10 minutes (40 minutes after gelation) was processed, the degree of saponification was 68.4. It was mol%. In this case, the amount of methanol (an+m)/an was 4.0, and the amount of sodium hydroxide was 5.25 meq.

Example 2 In order to obtain PVA with a saponification degree of 60.0 mol%, 64.2 parts of PVAc with an average degree of polymerization of 250 was dissolved in 29.58 parts of methanol with a water content of 0.5% by weight, and the mixture was kept at a temperature of 40°C and dissolved in 5% by weight water. sodium oxide methanol solution
6.74 parts were added, stirred for 5 minutes, and left as it was. Gelation occurred 12 minutes after the addition of sodium hydroxide. The gel was treated in the same manner as in Example 1 at 60 minutes and 90 minutes after gelation, and the degree of saponification was measured. As a result, the degree of saponification was 60.3 mol% and 60.0, respectively.
It was mol%. At this time, the amount of methanol is (an
+m)/an=2.5, and sodium hydroxide was 11.3 milliequivalents to PVAc.

In addition, after 90 minutes had passed after gelation, the gel was taken out and dried at 105°C under normal pressure for 60 minutes.
When melted at 180°C, the melt viscosity was 35,000 centipoise.

For comparison, when 64.2 parts of the same PVAc was dissolved in 29.47 parts of methanol with a moisture content of 0.02% by weight and treated in the same way, gelation occurred 10 minutes after adding sodium hydroxide, and 5 minutes after gelation. The degree of saponification was 59.6 mol%, but when the gel was left to stand for an additional 10 minutes, the saponification degree was 72.0 mol%.

In addition, after 5 minutes had passed after gelation, the gel was taken out and neutralized with acetic acid to suppress the progress of gelation.
The melt viscosity was measured at 180°C after drying at 105°C for 60 minutes under normal pressure and found to be 68,000 centipoise.

Example 3 In order to obtain PVA with a saponification degree of 40.0 mol%, 65.7 parts of PVAc with an average degree of polymerization of 490 was dissolved in 31.27 parts of methanol with a water content of 0.5% by weight, and the mixture was kept at a temperature of 40°C and dissolved in 5% by weight water. sodium oxide methanol solution
3.37 parts were added, stirred for 5 minutes, and left as it was.
Gelation occurred 14 minutes after the addition of sodium hydroxide, but at 60 minutes and 120 minutes after gelation.
After a few minutes had elapsed, the gel was treated in the same manner as in Example 1 and its saponification degree was measured, and the saponification degree was 39.5 mol% and 41.2 mol%, respectively.
It was mol%. The amount of methanol at this time (an
+m)/an was 3.5, and sodium hydroxide was 5.51 milliequivalent to PVAc.

For comparison, 59.9 parts of the same PVAc was dissolved in 37.4 parts of methanol with a moisture content of 0.5% by weight, and the mixture was heated to 5% by weight at 40°C.
When 3.07 parts of sodium hydroxide methanol solution was added and treated in the same way, gelation occurred 12 minutes after adding sodium hydroxide.The gel was taken out 5 minutes after gelation, treated in the same way, and measured. The degree is 50.6 mol%, which is already the target
It far exceeded 40.0 mol%. In this case, the amount of methanol (an+m)/an was 4.5, and the amount of sodium hydroxide was 5.51 milliequivalent to PVAc.

Example 4 In order to obtain PVA with a degree of saponification of 75.0 mol%, 65.7 parts of PVAc with an average degree of polymerization of 300 was dissolved in 37.3 parts of methanol with a water content of 0.06% by weight, and the mixture was kept at a temperature of 40°C and dissolved in 5% by weight of water. sodium oxide methanol solution
1.22 parts were added, stirred for 5 minutes, and left to stand. Gelation occurred 20 minutes after addition of sodium hydroxide, but at 60 minutes and 120 minutes after gelation.
When the gels were treated in the same manner as in Example 1 after a few minutes had elapsed, the degree of saponification was 75.2.
and 76.5 mol%. At this time, when the gel was cut out from three arbitrary parts of the gel and treated in the same manner for each of the above points, the dispersion in the degree of saponification was 75.0, 75.3, and 75.3 mol% in the former case, and 76.4, 76.5 in the latter case. and 76.7 mol%, which was substantially uniform, and the intermolecular distribution of the degree of saponification was small. At this time, the amount of methanol (az+m)/an is 2.1, and the amount of sodium hydroxide is PVAc.
The amount was 2.0 milliequivalent.

For comparison, the same 65.7 parts of PVAc with a moisture content of 0.06%
When dissolved in 25.2 parts of methanol and treated in the same manner with 2.44 parts of 5% by weight sodium hydroxide methanol solution at 40°C, gelation occurred 19 minutes after the addition of sodium hydroxide, and 60 minutes and 120 minutes after gelation. When the gel was cut out from any part of the gel at the time point and treated in the same manner, the degree of saponification was 72.3, 75.1 and 78.0 mol% in the former case, and 78.0 mol% in the latter case.
73.4, 76.6, and 78.9 mol%, and although the degree of saponification did not progress much, the intermolecular distribution of the degree of saponification at each time point was considerably broader than that of the example. At this time, the amount of methanol (an+m)/an was 1.5, and the amount of sodium hydroxide was 4.0 milliequivalent to PVAc.

Example 5 In order to obtain PVA with a saponification degree of 60 mol%, 65.7 parts of PVAc with an average degree of polymerization of 120 was dissolved in 43.3 parts of methanol with a water content of 0.7% by weight, and the mixture was kept at a temperature of 40°C and dissolved in 5% by weight water. sodium oxide methanol solution
4.29 parts were added, stirred for 5 minutes, and left to stand. Gelation occurred 15 minutes after addition of sodium hydroxide, but 60 minutes after gelation
After 120 minutes, the gel was treated in the same manner as in Example 1, and its saponification degree was measured to be 60.0 mol% and 60.1 mol%, respectively.
Therefore, no progress in the degree of saponification was observed. Furthermore, when the gel after 120 minutes was dried at 105° C. under normal pressure for 60 minutes, the volatile content was 2.5%. Furthermore, when this dried PVA was melted at 180°C, the melt viscosity was 33,000 centipoise, and the melt was only slightly colored pale yellow.
The amount of methanol (an+m)/an at this time is 3.2,
Sodium hydroxide was 7 meq to PVAC.

For comparison, 65.7 parts of the same PVAc was dissolved in 40.4 parts of methanol with a water content of 1.1% by weight, and through trial and error we determined the conditions under which PVA with a degree of saponification of 60 mol% could be obtained with good reproducibility. 5% by weight when
The amount of sodium hydroxide methanol solution is 7.35
12 milliequivalents of sodium hydroxide per part of PVAc was required. When the thus obtained gel with a degree of saponification of 60.3 mol% was similarly dried, the volatile content was 4.3%. Furthermore, when this dried PVA was melted at 180℃, the melt viscosity was
Although the temperature was 31,000 centipoise, the molten material was colored brown and had a strong PVA decomposition odor. The amount of methanol (an+m)/an at this time is also 3.2
It was hot.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the PVAc concentration and the degree of saponification in a methanol solution of PVAc with an average degree of polymerization of 120. Figure 2 shows PVAc with an average degree of polymerization of 120 in methanol with different moisture contents (an+m)/an=
This figure shows the change over time in the degree of saponification when PVAc was dissolved at a temperature of 3.0 and saponified by adding 5 milli equivalents of sodium hydroxide to PVAc at a temperature of 40°C.
Figure 3 shows that PVAc with an average degree of polymerization of 120 was dissolved in methanol with a moisture content of 0.5% by weight while changing the ratio of (an+m)/an, and the mixture was saponified by adding 5 milliquivalents of sodium hydroxide to PVAc at a temperature of 40°C. This figure shows the change over time in the degree of saponification.

Claims (1)

[Claims] 1. When saponifying a methanol solution of polyvinyl acetate by adding an alkali catalyst to produce polyvinyl alcohol with a degree of saponification of 80 mol% or less, the water content of methanol is maintained at 0.05 to 0.8% by weight, and the amount of methanol is The degree of saponification of polyvinyl acetate is controlled by controlling the degree of saponification so that the weight is 2 to 3.5 times the stoichiometric amount required to obtain polyvinyl alcohol with a predetermined degree of saponification. Saponification method.