JPH0678380B2 - Method for producing polyvinyl alcohol-based polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for producing a polyvinyl alcohol (hereinafter abbreviated as PVA) polymer. Specifically, in obtaining a polyvinyl alcohol-based polymer from a polyvinyl ester-based polymer obtained by emulsion polymerization, the polyvinyl ester-based polymer emulsion having a particle diameter of 5 μm or less is 2 times or more the weight of the polyvinyl ester-based polymer. , To obtain a substantially uniform solution by mixing with 100 times by weight or less of methanol, after removing unreacted vinyl ester monomer and water, if necessary, saponified by a known method polyvinyl The present invention relates to a method for producing an alcohol-based polymer.

B. Prior art PVA-based polymers have excellent interfacial properties and strength properties as a few crystalline water-soluble polymers, so they are used as stabilizers for paper processing, fiber processing, emulsions, etc. First of all, it is well known that it has an important position as a raw material for vinylon film and vinylon fiber.

However, the conventional PVA-based polymer has a polymerization degree of 2000, which is an upper limit because it is difficult to obtain a polyvinyl ester-based polymer having a high degree of polymerization as a raw material, in terms of processing characteristics and handleability. Only about 3000 items can be seen.

On the other hand, rapid progress in processing technology in recent years has enabled processing of polymers in the ultra-high degree of polymerization region, and thereby succeeding in bringing out previously unknown physical properties. With respect to PVA-based polymers as well, by increasing the degree of polymerization, not only the physical properties in conventional applications are improved, but also new possibilities are expected in new fields such as high-strength fibers.

On the other hand, such a PVA polymer can be obtained by saponifying a polyvinyl ester polymer, especially a polyvinyl acetate polymer. The outline of the production process is [production of polyvinyl acetate polymer → adjustment of polyvinyl acetate polymer in methanol solution → saponification reaction → PVA], and as the saponification reaction, saponification rate, saponification degree control, by-produced salt, In consideration of the physical properties of the obtained PVA and the like, the methanol decomposition reaction with a basic catalyst is usually adopted.

At the time of saponification, the most attention is paid to the problem of residual monomer and water. The former causes coloration of PVA, and the latter causes difficulties such as a decrease in saponification rate and an increase in the amount of required catalyst, resulting in an increase in the amount of salt produced as a by-product.

Incidentally, the saponification reaction of the polyvinyl acetate polymer is started by adding a basic catalyst to a methanol solution of the polyvinyl acetate polymer except in a very special case. This is because the saponification rate and degree of saponification cannot be controlled until the catalyst is evenly distributed throughout the catalyst, and the desired PVA can be obtained without uneven saponification. Therefore, when a polymerization method in a system in which a polymer is precipitated, for example, suspension polymerization or emulsion polymerization method is adopted, when the polyvinyl acetate polymer is taken out, it may be washed or dried for the above-mentioned reason. After sufficiently removing water and unreacted monomers, they are dissolved in methanol and flow into the process after saponification. However, the dissolution of a polyvinyl acetate polymer in methanol becomes extremely difficult as the molecular weight increases, and it takes a lot of time to dissolve, which is a big problem.

On the other hand, when the polymerization is carried out in bulk or in a homogeneous system of a methanol solution, a methanol solution of the polyvinyl acetate polymer can be obtained only by removing the residual monomer, which is a very excellent method.

However, in the case of producing a polymer having a large molecular weight by the bulk or methanol solution polymerization method, especially when it is necessary to perform the polymerization at a low temperature at a low speed, the polymerization system becomes extremely high in viscosity, which makes stirring difficult and heat removal control is possible. It is difficult to obtain the intended polymer. Therefore, PV with high polymerization degree
In the case of synthesizing A, a system in which a polymer such as suspension polymerization or emulsion polymerization is precipitated as a polymerization method, and in particular, emulsion polymerization is advantageous in terms of the polymerization rate, but the above-mentioned difficulties in the process after the polymerization do not occur. is there.

C. Problems to be Solved by the Present Invention The present invention overcomes the above-mentioned difficulties existing in producing a polyvinyl alcohol-based polymer from a polyvinyl ester-based polymer obtained by an emulsion polymerization method, and on an industrial scale. It is intended to provide a novel manufacturing method which can be easily carried out.

D. Means for solving the problem The inventors of the present invention have made diligent studies on a method for producing a polyvinyl alcohol polymer from a polyvinyl ester polymer obtained by emulsion polymerization, and as a result, a polyvinyl ester polymer immediately after polymerization. The polyvinyl ester polymer emulsion having a particle size of 5 μm or less is mixed with 2 times or more and 100 times or less by weight of methanol of the polyvinyl ester polymer without coagulating the emulsion and removing the polymer. To obtain a substantially uniform solution, and after removing the unreacted vinyl ester monomer and water as necessary, a basic catalyst is added and saponification is carried out by a conventional method as described below. The present invention has been completed by finding that the desired PVA polymer can be obtained extremely easily without using any complicated technical means. A.

The manufacturing method of the present invention will be described in detail below.

The greatest feature of the production method of the present invention is that when obtaining PVA from a polyvinyl ester polymer obtained by emulsion polymerization, particularly a polyvinyl acetate polymer emulsion, time and energy are the most problematic. This is where PVA is obtained without going through the process of coagulation, polymer extraction, and polymer dissolution.

The emulsion obtained by emulsion polymerization consists of water, a polymer, a monomer, a stabilizer, etc., but it is generally difficult to dissolve the polymer in a solvent containing a non-solvent, especially when the degree of polymerization is high. In the present invention, surprisingly, the polyvinyl ester polymer emulsion having a particle size of 5 μm or less is 2 times by weight or more, 100 times by weight or less, more preferably 5 times by weight or more, with respect to the polyvinyl ester polymer. By mixing with 50 times by weight or less of methanol,
With very gentle stirring, the emulsion does not agglomerate and agglomerate, and it is extremely easy and within a very short time, a substantially homogeneous methanol solution of the polyvinyl ester polymer (including water in emulsion). I was able to do it.

The particle size of polyvinyl ester polymer emulsion is 5
If it is larger than μ, the disadvantage is that it takes time to dissolve the polyvinyl ester-based polymer, but especially when it is intended to obtain PVA with a high degree of polymerization, the degree of polymerization is also considered. The emulsion particle size should be 5 μm or less.

When the amount of methanol with which the polyvinyl ester polymer emulsion having a particle diameter of 5 μm or less is mixed is less than 2 times the weight of the polyvinyl ester polymer,
The solubility of the polyvinyl ester polymer is poor, and a substantially uniform solution cannot be obtained.

Further, when the amount of the methanol is more than 100 times by weight with respect to the polyvinyl ester-based polymer, there is no problem in the solubility of the polyvinyl ester-based polymer, but since the polymer concentration becomes low, subsequent steps It is not preferable because the passability is poor.

When a mixed medium of water and methanol is used as the medium for emulsion polymerization, the amount of methanol is the total amount of both the methanol in the medium and the methanol in which the polyvinyl ester polymer emulsion obtained is mixed. However, it may be 2 times or more by weight and 100 times or less by weight with respect to the polyvinyl ester polymer.

If the substantially homogeneous methanol solution thus obtained contains unreacted vinyl ester monomer to the extent that it adversely affects saponification, the unreacted monomer is removed by distillation, and then a basic catalyst is added to the solution. The saponification reaction can be carried out by the method. In this case, since water from emulsion is present, the amount of catalyst required is larger and the amount of salt produced as a by-product is increased as compared with the case of saponification in the usual substantially anhydrous state, but washing is performed as necessary. It can be removed. In particular, PVA with a high degree of polymerization and a high degree of saponification can be easily removed by washing with water. Further, it is of course possible to distill the remaining water by utilizing azeotropy by blowing in methanol or adding the third component, and then performing saponification.

As described above, in the present invention, the polymer is separated from the polyvinyl ester-based polymer emulsion, and the emulsion having a specific particle diameter is directly added and dissolved in a specific amount of methanol for saponification, without removing the polymer. There is no particular limitation on the properties and saponification conditions of the emulsion used,
As an emulsion, from the viewpoint of the solubility of methanol,
It is preferable to use a low molecular weight surfactant as a stabilizer, that is, a nonionic surfactant, a nonionic-anionic surfactant, or an anionic surfactant, and the polymerization rate of vinyl ester is 95% or less, preferably 90%. % Or less, more preferably 80% or less. 5 for average particle size
μ or less is essential, but more preferably 2 μ or less,
Particularly, 1 μ or less is desirable.

As the polyvinyl ester-based polymer, vinyl formate,
Vinyl acetate, vinyl propionate, vinyl valerate,
Examples thereof include polymers such as vinyl caprate, vinyl laurate and vinyl stearate, and vinyl acetate polymers are particularly preferable.

Further, it may be a copolymer obtained by copolymerizing the above vinyl ester monomers with a copolymerizable monomer, and examples of these monomers include (meth) acrylic acid, (meth) acrylic acid ester, itaconic acid or Examples thereof include esters thereof, maleic acid esters or maleic anhydride, (meth) acrylamide or derivatives thereof, vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride, acrylonitrile, vinylalkoxysilane and the like.

The production method of the present invention can be applied to the production of PVA-based polymer of any polymerization degree, but is particularly effective when obtaining a high-polymerization degree PVA-based polymer from a high-polymerization degree polyvinyl ester-based polymer emulsion, and It is particularly effective in the case of a highly polymerized PVA having a viscosity of 1.5 dl / g or more, preferably 3.2 dl / g or more.

[Here, the intrinsic viscosity of the polyvinyl ester-based polymer is defined by a value measured at 30 ° C. in acetone for polyvinyl acetate re-complexed after saponification of the polyvinyl ester-based polymer, and a polyvinyl alcohol-based polymer. The intrinsic viscosity of a polymer is defined as a value measured at 30 ° C. in acetone for polyvinyl acetate obtained by reacetylating the polyvinyl alcohol polymer. Further, in order to obtain a high degree of polymerization PVA, it is desirable that the polyvinyl ester polymer emulsion be obtained by emulsion polymerization in a mixed medium of water and methanol. The mixing ratio of water and methanol is Is desirable.

E. Action and Effect of the Invention The present invention is the most problematic in terms of time and energy when obtaining PVA from the polyvinyl ester polymer emulsion obtained by emulsion polymerization (coagulation of emulsion → removal of polymer → dissolution of polymer). PV without going through the process
It provides a process for obtaining A, which has a particle size of 5
a polyvinyl ester polymer emulsion of μ or less,
2 times by weight or more with respect to the polyvinyl ester polymer,
It was achieved by mixing with 100 times by weight or less of methanol to obtain a substantially uniform solution, removing unreacted vinyl ester monomer and water, if necessary, and then saponifying by a known method. The production method of the present invention can be applied to the production of a PVA-based polymer having any degree of polymerization, but is particularly effective when obtaining a PVA-based polymer with a high degree of polymerization.

The PVA thus obtained can be used in conventional fields of application, and the high degree of polymerization PVA effectively obtained in the present invention is suitable as a PVA high strength sheet or PVA high strength fiber. Is used.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1, Comparative Examples 1, 2 After stirring 300 parts of ion-exchanged water in a reactor equipped with a stirrer, a thermometer, a nitrogen introducing tube and a cooling tube and boiling for 30 minutes, it was cooled to room temperature while introducing nitrogen. . 12 parts of polyoxyethylene [POE (40)] nonylphenyl ether (Nonipol 400, Sanyo Kasei Co., Ltd.) under a nitrogen flow, FeS
O ₄ · 7H ₂ O 0.05 parts and Rongaritsuto was dissolved with stirring was added 0.50 parts. After the dissolution, a mixed solution of 300 parts of vinyl acetate and 100 parts of methanol, which was separately degassed at 60 ° C. under a stream of nitrogen, was added to the reactor under a stream of nitrogen, and the mixture was stirred at room temperature for 30 minutes. After that, the mixture was cooled under nitrogen flow until the internal temperature reached -20 ° C, and 0.03% hydrogen peroxide solution adjusted with separately degassed ion-exchanged water was added at 12 parts / h.
Polymerization was initiated while uniformly adding continuously at r. During the polymerization, the system was sealed with nitrogen gas to prevent oxygen from entering. After 2 hours, when the polymerization rate reached 48%, the addition of hydrogen peroxide solution was stopped, and 1.0 part of hydroquinone monomethyl ether was added to stop the polymerization.

The emulsion (particle size: 0.2 μm) obtained here was divided into three equal amounts, A (Example 1), B (Comparative Example 1) and C (Comparative Example 2), and the following treatments were carried out for PVA. An attempt was made to obtain a system polymer.

A: 1000 parts of methanol at room temperature (methanol / polymer = 2
0.5 part of hydroquinone monomethyl ether was dissolved in 1.5) and gradually added with stirring to dissolve, to give a substantially homogeneous solution. It took about 2 hours to become substantially uniform.

After that, unreacted vinyl acetate monomer was removed under reduced pressure while adding methanol to obtain a methanol solution of polyvinyl acetate (including water). (Polymer concentration 7.1%) B: 50 parts of methanol at room temperature (methanol / polymer = 1.
While 0.5 part of hydroquinone monomethyl ether was dissolved in 7) and gradually added with stirring, an attempt was made to dissolve it, but a substantially uniform solution was not obtained even after 7 days.

C: After adding polyvinyl chloride to a saturated aqueous solution of calcium chloride containing 2.0 parts of hydroquinone to precipitate polyvinyl acetate, washing with water and washing with warm water were repeated to remove unreacted vinyl acetate monomer, and 50 ° C under warm air for 24 hours. Dried. Subsequently, polyvinyl acetate polymer that had been cut into small pieces was added to 600 parts of methanol and dissolved at 40 ° C. with stirring to obtain a methanol solution of polyvinyl acetate. This dissolution took about 72 hours.

Subsequently, both A and C have a polymer concentration of 5%, at 40 ° C., A is [NaoH] / [VAC] (molar ratio) = 0.1, and C is [NaoH] /
When saponification was performed under the condition of [VAC] (molar ratio) = 0.05, no coloring was observed and colorless PVA was obtained.
When the saponification degree was measured for PVA washed with Soxhlet with methanol, A was 98.5% and C was 99.1%. Furthermore, in both A and C, 0.1 part of PVA was recomplexed in a mixed solution of 8 parts of acetic anhydride and 2 parts of pyridine at 105 ° C. for 20 hours with occasional stirring to form acetone-ether, acetone-
When the intrinsic viscosity of polyvinyl acetate which had been repeatedly purified by reprecipitation in an aqueous system was measured in acetone at 30 ° C, the PVA of A was [η] = 3.67 (dl / g) and the PVA of C was [η] = 3.61 (dl /
g) As described above, the manufacturing method of the present invention is extremely effective.

Claims (11)

[Claims] 1. When obtaining a polyvinyl alcohol polymer from a polyvinyl ester polymer obtained by emulsion polymerization, 2 parts by weight of polyvinyl ester polymer emulsion having a particle size of 5 μm or less is added to the polyvinyl ester polymer. It is characterized in that it is mixed with methanol of not less than 100 times and not more than 100 times by weight to obtain a substantially uniform solution, and after removing unreacted vinyl ester monomer and water as necessary, saponification by a known method. A method for producing a polyvinyl alcohol-based polymer. 2. The production method according to claim 1, wherein the polyvinyl ester polymer emulsion has a particle size of 2 μm or less. 3. The intrinsic viscosity of the polyvinyl ester polymer is
The manufacturing method according to claim 1, which is 1.5 dl / g or more. [Here, the intrinsic viscosity of the polyvinyl ester polymer is defined as a value of polyvinyl acetate resaponified after saponification of the polyvinyl ester polymer, measured in acetone at 30 ° C. ] 4. The polyvinyl ester polymer has an intrinsic viscosity
The manufacturing method according to claim 1, which is greater than 3.2 dl / g. [Here, the intrinsic viscosity of the polyvinyl ester polymer is defined as a value of polyvinyl acetate resaponified after saponification of the polyvinyl ester polymer, measured in acetone at 30 ° C. ] 5. The method according to claim 1, wherein the polyvinyl alcohol polymer obtained has an intrinsic viscosity of 1.5 dl / g or more. [Here, the intrinsic viscosity of the polyvinyl alcohol-based polymer is
The polyvinyl acetate obtained by reacetylating the polyvinyl alcohol polymer is defined as the value measured at 30 ° C. in acetone. ] 6. The production method according to claim 1, wherein the polyvinyl alcohol polymer obtained has an intrinsic viscosity of more than 3.2 dl / g. [Here, the intrinsic viscosity of the polyvinyl alcohol-based polymer is
The polyvinyl acetate obtained by reacetylating the polyvinyl alcohol polymer is defined as the value measured at 30 ° C. in acetone. ] 7. The method according to claim 1, wherein the polyvinyl ester polymer emulsion is mixed with 5 times or more and 50 times or less by weight of methanol of the polyvinyl ester polymer. 8. A polyvinyl ester polymer emulsion obtained by emulsion polymerization using any of a nonionic surfactant, a nonionic-anionic surfactant, or an anionic surfactant. Claim 1st
The manufacturing method according to the item. 9. The method according to claim 1, wherein the polyvinyl ester polymer emulsion is obtained by emulsion polymerization in a mixed medium of water and methanol. 10. The mixing ratio of water and methanol in the mixed medium is a weight ratio. The manufacturing method according to claim 9, wherein 11. The production method according to claim 1, wherein the vinyl ester is vinyl acetate.