JP4733004B2 - Method for polymerizing aliphatic vinyl ester and method for producing polyvinyl alcohol resin - Google Patents

Description

  The present invention relates to a method for polymerizing an aliphatic vinyl ester and a method for producing a polyvinyl alcohol resin, which can industrially advantageously produce a polyvinyl alcohol resin having a high degree of polymerization.

  Polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) resin is industrially produced by polymerizing an aliphatic vinyl ester in an alcohol solvent at atmospheric pressure and saponifying the resulting aliphatic polyvinyl ester. . Polyvinyl alcohol resins are used in many applications such as fiber processing, paper processing, films, adhesives, binders of various inorganic materials, and emulsion stabilizers, and their applications are expanding.

  In recent years, there has been an increase in applications that require higher viscosity when a polyvinyl alcohol-based resin is used as an aqueous solution and applications that require higher coating strength when it is used as a film. In order to satisfy these requirements, one method is to increase the degree of polymerization of the polyvinyl alcohol-based resin.

  In general, as a method for increasing the degree of polymerization of a polyvinyl alcohol-based resin, it is known that polymerization at a low temperature is most effective when a vinyl ester such as vinyl acetate is polymerized to form a polyvinyl ester. It has been. As specific methods for polymerizing vinyl acetate at low temperatures, photopolymerization at low temperatures and low-temperature photoemulsion polymerization (for example, see Non-Patent Document 1) are well known. When relying on, there is a limit to the amount of heat removal, and in most cases, sufficient productivity cannot be obtained.

  Further, a method has been proposed in which emulsion polymerization of a vinyl ester is performed at a low temperature while boiling a monomer as a raw material under reduced pressure (see, for example, Patent Document 1). In addition, as a method for polymerizing an acrylate ester or the like, a method is also proposed in which suspension polymerization is performed while evaporating at least one liquid substance from a reaction solution under reduced pressure (see Patent Document 2). The reason why emulsion polymerization or suspension polymerization is adopted in these methods is considered to be advantageous in that the viscosity of the reaction solution does not increase, but on the other hand, the polyvinyl ester obtained by emulsion polymerization or suspension polymerization. It is very disadvantageous industrially to take out from water as a dispersion medium and to saponify it into polyvinyl alcohol.

  Therefore, in the conventional technology, it is difficult to produce polyvinyl alcohol having a high degree of polymerization industrially, and industrial polyvinyl alcohol currently on the market usually has a degree of polymerization of up to about 4500. However, the present situation is that the demand for high-polymerization polyvinyl alcohol, which has been increasing in recent years, has not been fully answered.

Japanese Patent Laid-Open No. 05-117307 (see paragraphs [0009] to [0010]) JP-A-10-158310 (refer to claim 1) Naoki Fujiwara, Toshiaki Sato, Ken Yuuki, Shinnosuke Yamauchi, Takuji Okaya; Record of the 102nd Poval Society, 22 (1993)

  In view of the current situation, the present invention provides a novel polymerization method of aliphatic polyvinyl ester and a novel production method of polyvinyl alcohol in order to enable efficient industrial production of polyvinyl alcohol having a high degree of polymerization. Is an issue.

  As a result of intensive studies to achieve the above-mentioned object, the inventors of the present invention conducted solution polymerization while boiling the reaction solution under reduced pressure when polymerizing the aliphatic vinyl ester. As a result, it has been found that a polyvinyl alcohol resin having a high degree of polymerization can be efficiently produced, and further studies have been made, and the present invention has been completed.

That is, the present invention
[1] A method for polymerizing an aliphatic vinyl ester, wherein the temperature inside the polymerization machine is reduced, and the polymerization reaction liquid is boiled under the reduced pressure, while the temperature is lower than the boiling temperature of the polymerization reaction liquid at atmospheric pressure. A method of polymerizing an aliphatic vinyl ester, characterized by performing solution polymerization in
[2] The method for polymerizing an aliphatic vinyl ester according to [1] above, wherein the aliphatic vinyl ester is vinyl acetate,
[3] The polymerization method as described in [1] or [2] above, wherein a double helical ribbon blade without a stirring shaft is used as a stirring blade for stirring the polymerization reaction solution;
[4] A polyvinyl alcohol-based resin having a 1,2-glycol bond amount of less than 1.9 mol% by saponifying an aliphatic polyvinyl ester obtained by the method according to any one of [1] to [3] It is related with the manufacturing method of the polyvinyl alcohol-type resin characterized by manufacturing this.

  By using the polymerization method of the present invention, polyvinyl alcohol having a high degree of polymerization can be produced industrially advantageously. Further, by subjecting the vinyl ester to solution polymerization under reduced pressure, the amount of 1,2-glycol bonds in the main chain of the finally obtained polyvinyl alcohol resin is reduced, and a polyvinyl alcohol resin having improved heat resistance is obtained. can get.

  In the polymerization method of the present invention, it is easy to remove the monomer after completion of polymerization because of solution polymerization. In this respect, in the method using emulsion polymerization, it is difficult to remove the monomer due to the influence of the emulsifier residue, and the emulsifier may become an impurity. The present invention is therefore advantageous.

  In emulsion polymerization, scale (dirt) is likely to adhere to the inner wall of the polymerization machine. However, in the present invention, scale is not attached due to the presence of a polymerization solvent because of solution polymerization, and dilution is further performed by adding a polymerization solvent at the end of polymerization. This is advantageous because the work can be easily performed.

  Emulsion polymerization is usually carried out by batch polymerization, and continuous polymerization is also possible, but in order to efficiently polymerize those having a high degree of polymerization, sophisticated equipment in which a plurality of polymerizers are arranged in series is required, resulting in high costs. Become. In this respect, the present invention is advantageous because continuous polymerization is easy because of solution polymerization, and efficient polymerization can be achieved by continuous polymerization even from one polymerization machine.

  In emulsion polymerization, it is necessary to use a water-soluble polymerization initiator (water-soluble initiator). However, water-soluble initiators, particularly non-halogen-based water-soluble initiators are generally low in activity and are sufficient. In order to obtain the reaction rate, it is necessary to use a photopolymerization initiator. In this respect, in the present invention, an oil-soluble polymerization initiator (oil-soluble initiator) can be used for solution polymerization, and there are many non-halogen-based and highly active oil-soluble initiators. In halogen-based polymerization initiators, chlorine is generally used as the halogen, and it has recently been considered unfavorable for environmental protection to add chlorine to the reaction system during the production of polyvinyl ester or PVA. .

Hereinafter, the present invention will be described in detail.
The polymerization method of the present invention is a method of polymerizing an aliphatic vinyl ester. By this polymerization method, an aliphatic polyvinyl ester having a high degree of polymerization is obtained, and by saponifying it, a polyvinyl alcohol resin having a high degree of polymerization is obtained. can get.

  Examples of the aliphatic vinyl ester (monomer) used in the present invention include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl stearate. desirable.

  In addition, the unsaturated monomer copolymerizable with the aliphatic vinyl ester may be copolymerized with the aliphatic vinyl ester within a range not impairing the effects of the present invention, and an embodiment involving such copolymerization is also possible. Are included in the category of “polymerization of aliphatic vinyl ester” in the present invention.

  Examples of unsaturated monomers copolymerizable with aliphatic vinyl esters include unsaturated monobasic acids such as acrylic acid or salts thereof, unsaturated dibasic acids such as maleic acid, itaconic acid, fumaric acid, or salts thereof. Or unsaturated dibasic acid monoalkyl esters such as monomethyl maleate and monomethyl itaconate, (meth) acrylic esters, acrylamide, diacetone acrylamide, dimethyl acrylamide, N-methylol acrylamide, N-vinyl-2-pyrrolidone Amide group-containing monomers such as lauryl vinyl ethers, alkyl vinyl ethers such as stearyl vinyl ether, hydroxyl group-containing monomers such as allyl alcohol, dimethylallyl alcohol, isopropenyl allyl alcohol, allyl acetate, dimethylallyl acetate, isopropene Acetyl group-containing monomers such as ruaryl acetate, sulfone group-containing monomers such as sodium vinyl sulfonate, sodium allyl sulfonate, sodium acrylamide-2-methylpropane sulfonate, and halogen-containing monomers such as vinyl chloride and vinylidene chloride. Examples thereof include aromatic monomers such as styrene and styrene, but are not limited thereto.

  In the present invention, solution polymerization is performed in the polymerization of the aliphatic vinyl ester. In the present invention, solution polymerization means polymerization in a homogeneous system in which an aliphatic vinyl ester is completely dissolved in a polymerization solvent. Therefore, in the following, the polymerization reaction liquid may be referred to as a polymerization solution.

  As the polymerization solvent, for example, alcohols such as methanol, ethanol, and propanol, benzene, acetone, glycerin, polyethylene glycol, and the like are used, but methanol is preferred industrially. As a usage-amount of a polymerization solvent, 1-50 mass parts is preferable with respect to 100 mass parts of aliphatic vinyl ester. When the amount is less than 1 part by mass, the scale easily adheres to the inner wall of the polymerization machine. On the other hand, when the amount exceeds 50 parts by mass, the high-polymerization degree polyvinyl alcohol resin or the high-polymerization degree aliphatic polyvinyl ester targeted by the present invention is obtained. This is not preferable because it tends to be difficult to be obtained.

  There is no restriction | limiting in particular as a polymerization initiator of the solution polymerization in this invention, Usually, an azo type compound, a peroxide, etc. are used.

  In the solution polymerization, an organic acid such as tartaric acid, citric acid, and acetic acid may be added for the purpose of preventing hydrolysis of the aliphatic vinyl ester.

  In order to adjust the degree of polymerization, a chain transfer agent such as 2-mercaptoethanol, 1-dodecanethiol, or acetaldehyde may be used, but it should not be added as much as possible when producing a highly polymerized polyvinyl alcohol resin. Is preferred.

  In the present invention, it is important to carry out the polymerization in a state where the pressure in the polymerization machine is reduced, that is, the pressure in the polymerization machine is maintained at a pressure lower than the atmospheric pressure during the solution polymerization. The pressure in the polymerization machine at that time is not particularly limited as long as it is lower than atmospheric pressure, but is preferably 10 to 70 kPa. If it is less than 10 kPa, since the boiling temperature of the reaction solution is too low, it is difficult to obtain a sufficient polymerization rate because the polymerization temperature is too low. On the other hand, if it exceeds 70 kPa, Since it tends to be difficult to obtain a highly polymerized aliphatic polyvinyl ester, it is not preferred.

  There is no particular limitation on the method for maintaining the pressure in the polymerization machine at a pressure lower than the atmospheric pressure. Generally, a suction device such as a vacuum pump is provided on the open side of the reflux condenser attached to remove reaction heat. This can be realized.

  Further, the temperature at the time of solution polymerization (polymerization reaction temperature) needs to be lower than the boiling temperature of the reaction solution under atmospheric pressure. In the present invention, the temperature during solution polymerization specifically means the temperature of the polymerization solution during the polymerization reaction.

  The boiling temperature of the polymerization reaction liquid means a temperature at which vaporization starts from the inside of the polymerization reaction liquid in addition to evaporation from the surface of the polymerization reaction liquid at a predetermined pressure. In this case, the boiling temperature is kept substantially constant.

  The polymerization reaction temperature is not particularly limited as long as it is lower than the boiling temperature of the reaction solution under atmospheric pressure, and is preferably about 10 to 56 ° C. depending on the composition of the reaction solution. In the present invention, since a high degree of polymerization is obtained by solution polymerization, it may be difficult to stir when the viscosity of the solution becomes extremely high at low temperatures. Therefore, the polymerization reaction temperature should be 0 ° C. or higher industrially. Is preferred. Therefore, a particularly preferable polymerization temperature is about 0 to 56 ° C.

  In the present invention, in order to perform solution polymerization at a temperature lower than the boiling temperature of the polymerization reaction solution under atmospheric pressure, solution polymerization is performed while boiling the polymerization reaction solution under the above-described reduced pressure. By carrying out the boiling of the polymerization reaction liquid under reduced pressure, it becomes easy to keep the temperature of the reaction liquid at a substantially constant temperature lower than the boiling temperature of the polymerization reaction liquid under atmospheric pressure. Therefore, the polymerization reaction temperature can also be adjusted by the pressure in the polymerization machine. In addition, what is necessary is just to attach the reflux condenser to a superposition | polymerization machine, and to evaporate the evaporation material by this boiling.

  The polymerization machine for solution polymerization of the aliphatic vinyl ester used in the present invention is not particularly limited as long as the pressure in the polymerization machine can be maintained at a pressure lower than atmospheric pressure. The polymerization method may be any of batch polymerization, semi-continuous polymerization, and continuous polymerization. From the viewpoint of excellent productivity, continuous polymerization is preferable, and batch polymerization is preferable from the viewpoint of increasing the degree of polymerization.

  A well-known stirrer can also be used, and the stirring blade for stirring the polymerization reaction liquid is not particularly limited. A double helical ribbon wing with no blade is preferred. In the solution polymerization in the present invention, as the polymerization proceeds, the viscosity of the polymerization reaction solution increases, and in a formulation in which the polymerization yield is relatively increased by polymerization at a low temperature, the viscosity becomes considerably high, but a double helical ribbon without a stirring axis. By using a blade, even in such a case, stirring can be performed without any problem, and the object of the present invention can be sufficiently achieved.

  Double helical ribbon blades without stirring shafts are known per se (see, for example, Kazutaka Takada et al., Nagare 22 (2003) 201-207 “Development of High-Efficiency Stirring Blades”). Examples include “Logbone (registered trademark)” manufactured by Shinko Environmental Solution. In addition, by using a double helical ribbon blade without a stirring shaft, bulk polymerization can be performed as an application of the present invention.

  In the polymerization solution when the polymerization reaction is completed, the unreacted aliphatic vinyl ester monomer usually remains in addition to the obtained aliphatic polyvinyl ester. In the present invention, this unreacted monomer is removed. Demonomerization is preferably performed. Since the polymerization method of the present invention is based on solution polymerization, the demonomer can be easily performed by a conventional method. For example, the monomer removal can be performed by dropping the polymerization solution from the upper part of the multistage tower and blowing methanol vapor from the lower part of the tower.

  By the polymerization method of the present invention as described above, an aliphatic polyvinyl ester having a high degree of polymerization is obtained, and a polyvinyl alcohol resin having a high degree of polymerization can be produced by saponifying the aliphatic polyvinyl ester. Such a method for producing a polyvinyl alcohol-based resin is also one aspect of the present invention.

  In the present invention, the method for saponifying the aliphatic polyvinyl ester may be carried out in accordance with a known method. For example, in a mixed solvent of alcohols such as methanol, esters such as methyl acetate and ethyl acetate, and alcohols. Thus, a method of using an alkali metal hydroxide such as sodium hydroxide or an alcoholate such as sodium methylate as a saponification catalyst can be employed. Moreover, there is no restriction | limiting in particular also in the drying and grinding | pulverization method of a saponification thing, What is necessary is just to perform by a well-known method.

  As a polymerization degree of the aliphatic polyvinyl ester thru | or polyvinyl alcohol-type resin obtained by this invention, 4500 or more are preferable and 5000-8000 are more preferable. If the degree of polymerization is less than 4500, it is difficult to say that the object of the present invention can be sufficiently achieved.

  Moreover, in this invention, the polyvinyl alcohol-type resin excellent in heat resistance with few amounts of 1, 2- glycol bonds can be manufactured. The amount of 1,2-glycol bonds is preferably less than 1.9 mol%, more preferably 1.8 mol% or less.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these Examples.
In addition, the characteristic evaluation of obtained PVA was performed with the following method.
(1) Degree of polymerization;
It calculated | required according to JISK6726 (1994).
(2) Saponification degree;
It calculated | required according to JISK6726 (1994).
(3) 1,2-glycol bond amount;
The ¹ H-NMR spectrum was measured with a DMSO-d6 solvent using an NMR measurement apparatus (Varian, UNITY INOVA600), and calculation was performed by a conventional method.

Example 1
A stirrer (medium to high viscosity flat blades as shown in FIG. 1) is used with 950 parts by weight of vinyl acetate, 50 parts by weight of methanol, and 0.09 parts by weight of 2,2′-azobis (2,4-dimethylvaleronitrile). ), A polymerization condenser equipped with a reflux condenser, a decompressor, and a pressure gauge, and with the internal pressure of the polymerizer reduced to 61 kPa, the temperature was raised until boiling, and solution polymerization was started. The boiling temperature of the polymerization solution was 52.2 ° C. The polymerization reaction was performed while maintaining the above reduced pressure and boiling, and the polymerization was terminated when the polymerization yield was 36.1%.
Subsequently, after demonomerization by a conventional method, the obtained polyvinyl acetate was alkali saponified to obtain polyvinyl alcohol having a saponification degree of 100 mol%. The degree of polymerization of this polyvinyl alcohol was 5130, and the amount of 1,2-glycol was 1.7 mol%.

(Example 2)
980 parts by weight of vinyl acetate, 20 parts by weight of methanol, 0.001 part by weight of citric acid, and 7.0 parts by weight of di-n-propyl peroxydicarbonate were charged into the same polymerization machine used in Example 1 and polymerized. In a state where the internal pressure of the machine was reduced to 14 kPa, the temperature was raised until boiling, and solution polymerization was started. The boiling temperature of the polymerization solution was 16.8 ° C. The polymerization reaction was carried out while maintaining the above reduced pressure and boiling, and the polymerization was terminated when the polymerization yield was 20%.
Subsequently, after demonomerization by a conventional method, the obtained polyvinyl acetate was alkali saponified to obtain polyvinyl alcohol having a saponification degree of 100 mol%. The degree of polymerization of this polyvinyl alcohol was 7840, and the amount of 1,2-glycol bonds was 1.2 mol%.

(Example 3)
990 parts by weight of vinyl acetate, 10 parts by weight of methanol, and 0.28 parts by weight of 2,2′-azobisisobutyronitrile were charged into the same polymerization machine used in Example 1, and the internal pressure of the polymerization machine was adjusted to 51 kPa. In a state where the pressure was reduced to 0, the solution was heated to boiling and solution polymerization was started. The boiling temperature of the polymerization solution was 48.9 ° C. The polymerization reaction was carried out while maintaining the above reduced pressure and boiling, and the polymerization was terminated when the polymerization yield was 25.5%.
Subsequently, after demonomerization by a conventional method, the obtained polyvinyl acetate was alkali saponified to obtain polyvinyl alcohol having a saponification degree of 100 mol%. The degree of polymerization of this polyvinyl alcohol was 6900, and the 1,2-glycol bond amount was 1.6 mol%.

(Comparative Example 1)
Polymerization was carried out in the same manner as in Example 1, except that the inside of the polymerization machine was carried out under atmospheric pressure without reducing the pressure, and that the polymerization yield of polyvinyl acetate was 33.7%. The boiling temperature was 66.2 ° C.
Subsequently, after demonomerization by a conventional method, the obtained polyvinyl acetate was alkali saponified to obtain polyvinyl alcohol having a saponification degree of 100 mol%. The degree of polymerization of this polyvinyl alcohol was 3650, and the amount of 1,2-glycol bonds was 1.9 mol%.

(Comparative Example 2)
It was carried out under atmospheric pressure without reducing the pressure in the polymerization machine, and instead of 7.0 parts by mass of di-n-propyl peroxydicarbonate, 2,8'-azobis (2,4-dimethylvaleronitrile) 0.08 Polymerization was carried out in the same manner as in Example 2, except that parts by mass were used and that the polymerization yield of polyvinyl acetate was 34.9%. The boiling temperature was 70.3 ° C.
Subsequently, after demonomerization by a conventional method, the obtained polyvinyl acetate was alkali saponified to obtain polyvinyl alcohol having a saponification degree of 100 mol%. The degree of polymerization of this polyvinyl alcohol was 4180, and the amount of 1,2-glycol bonds was 1.9 mol%.

(Comparative Example 3)
Polymerization was carried out in the same manner as in Example 3, except that the inside of the polymerization machine was carried out under atmospheric pressure without reducing the pressure, and that the polymerization yield of polyvinyl acetate was 29.1%. The boiling temperature was 72.5 ° C.
Subsequently, after demonomerization by a conventional method, the obtained polyvinyl acetate was alkali saponified to obtain polyvinyl alcohol having a saponification degree of 100 mol%. The degree of polymerization of this polyvinyl alcohol was 4250, and the 1,2-glycol bond amount was 2.0 mol%.

Example 4
990 parts by weight of vinyl acetate, 10 parts by weight of methanol, and 7.0 parts by weight of di-n-propyl peroxydicarbonate were mixed with a stirrer (using a double helical ribbon blade without a stirring shaft) as shown in FIG. Then, the solution was charged into a polymerization machine equipped with a pressure reducer and a pressure gauge, and the temperature was raised to boiling with the internal pressure of the polymerization machine reduced to 14 kPa, and solution polymerization was started. The boiling temperature of the polymerization solution was 18.0 ° C. The polymerization reaction was performed while maintaining the above reduced pressure and boiling, and the polymerization was terminated when the polymerization yield was 39%.
Subsequently, after demonomerization by a conventional method, the obtained polyvinyl acetate was alkali saponified to obtain polyvinyl alcohol having a saponification degree of 100 mol%. The degree of polymerization of this polyvinyl alcohol was 7170, and the amount of 1,2-glycol bonds was 1.2 mol%.

  The polymerization conditions and the properties of the obtained polyvinyl alcohol are summarized in Table 1 below.

It is a figure which shows an example of the superposition | polymerization machine for enforcing the method of this invention. It is a figure which shows another example of the superposition | polymerization machine for enforcing the method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polymerizer 2 Stirrer 3 Pressure control valve 4 Reflux condenser 5 Pressure reducer 6 Pressure gauge 7 Raw material charging port 8 Discharge port

Claims (4)

  A method for polymerizing an aliphatic vinyl ester, in which the pressure in the polymerization machine is reduced, and the polymerization reaction liquid is boiled under the reduced pressure, and solution polymerization is performed at a temperature lower than the boiling temperature of the polymerization reaction liquid at atmospheric pressure. A method for polymerizing an aliphatic vinyl ester, characterized in that:   2. The method for polymerizing an aliphatic vinyl ester according to claim 1, wherein the aliphatic vinyl ester is vinyl acetate.   The polymerization method according to claim 1 or 2, wherein a double helical ribbon blade without a stirring shaft is used as a stirring blade for stirring the polymerization reaction solution.   Saponifying the aliphatic polyvinyl ester obtained by the method according to any one of claims 1 to 3, to produce a polyvinyl alcohol-based resin having a 1,2-glycol bond amount of less than 1.9 mol%. A method for producing a polyvinyl alcohol-based resin.

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