JP2019210340A - Method for producing polyvinyl alcohol molding - Google Patents

Abstract

To provide a method for producing a polyvinyl alcohol molding which is excellent in water solubility and has a reduced methyl acetate content.SOLUTION: There is provided a method for producing a polyvinyl alcohol molding obtained by melt-kneading a polyvinyl alcohol composition which contains: a polyvinyl alcohol having a viscosity-average degree of polymerization of 100-800 and a degree of saponification of 70-99.9 mol%; and methyl acetate. The content (a) of the methyl acetate in the polyvinyl alcohol composition before melting is 0.3-5 mass%. The ratio of the content (b) of the methyl acetate in the polyvinyl alcohol molding after melt-kneading to the content (a) satisfies the following formula (I): 0.001≤(b)/(a)≤0.25.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a molded product of polyvinyl alcohol having excellent water solubility and having a reduced methyl acetate content.

  Polyvinyl alcohol (hereinafter sometimes abbreviated as “PVA”) is known as a water-soluble synthetic polymer, and a raw material of vinylon which is a synthetic fiber, a paper processing agent, a fiber processing agent, an adhesive, an emulsification Widely used in applications such as stabilizers for polymerization and suspension polymerization, inorganic binders, films, pharmaceutical coating agents, cosmetics and the like.

  Especially for pharmaceutical coatings and cosmetics, the reduction of residual organic volatiles contained in PVA is strongly demanded from the viewpoint of impact on the human body. Among the residual organic volatiles, methyl acetate dissolves various plastics. For this reason, reduction is particularly required in many applications.

  As a method for solving the above problem, Patent Document 1 proposes a PVA purification method in which PVA is placed in a low-toxic ethanol solution, heated and stirred, and residual organic volatiles in PVA are replaced with low-toxic ethanol. Has been. However, there is a problem that flammable ethanol remains in the PVA, and problems still remain from an industrial point of view, such as newly requiring an ethanol recovery step in the production process.

Japanese Patent Laid-Open No. 2006-138232

  This invention is made | formed based on the above situations, and it aims at providing the manufacturing method of the polyvinyl alcohol molded object which was excellent in water solubility and content of methyl acetate was reduced.

  The above-mentioned problem is a method for producing a polyvinyl alcohol molded article containing a specific amount of methyl acetate and obtained by melt-kneading a polyvinyl alcohol composition having a specific polymerization degree and saponification degree, and the content of methyl acetate before and after melting It is solved by providing a manufacturing method in which the ratio meets a specific range.

That is, the present invention includes the following inventions.
[1] A polyvinyl alcohol molded article obtained by melt-kneading a polyvinyl alcohol composition containing a polyvinyl alcohol and methyl acetate having a viscosity average polymerization degree of 100 to 800 and a saponification degree of 70 to 99.9 mol%. In the production method, the content (a) of methyl acetate in the polyvinyl alcohol composition before melting is 0.3 to 5% by mass, and the content (b) of methyl acetate in the molded polyvinyl alcohol product after melt-kneading And the ratio of content (a) satisfy | fills following formula (I), the manufacturing method of a polyvinyl alcohol molded object.
0.001 ≦ (b) / (a) ≦ 0.25 (I)
[2] The production method of the above [1], wherein the melt kneading temperature is 155 to 235 ° C.
[3] The production method of the above [1] or [2], wherein the melt kneading time is 20 to 500 seconds.
[4] The method according to any one of [1] to [3], wherein the polyvinyl alcohol composition before melting is in the form of a powder having an average particle size of 50 to 2000 μm.

  According to the production method of the present invention, it is possible to easily obtain a polyvinyl alcohol molded article having excellent water solubility and having a reduced methyl acetate content.

The present invention relates to a PVA composition containing polyvinyl alcohol having a viscosity average polymerization degree of 100 to 800 and a saponification degree of 70 to 99.9 mol% (hereinafter sometimes abbreviated as “PVA”) and methyl acetate. A method for producing a PVA molded product obtained by melt-kneading a product, wherein the content (a) of methyl acetate in the PVA composition before melting is 0.3 to 5% by mass, and PVA molding after melt-kneading It is related with the manufacturing method of a PVA molded object with which the ratio of content (b) and content (a) of methyl acetate in a body satisfy | fills following formula (I).
0.001 ≦ (b) / (a) ≦ 0.25 (I)

  As will be described later, PVA is preferably applied to a production method that uses vinyl acetate as a raw material and undergoes a polymerization process, a saponification process, a washing process, and a drying process. As methyl acetate used as a residue remains in the PVA after drying, a PVA composition containing PVA and methyl acetate is obtained as a result. The content (a) of methyl acetate in the PVA composition can be adjusted, for example, by changing the drying conditions, but the methyl acetate incorporated into the composition is less likely to volatilize, so that the conventional drying process requires sufficient methyl acetate. It was difficult to reduce it. As in the present invention, a PVA molded article having a reduced methyl acetate content can be easily obtained by melt-kneading a PVA composition having a viscosity average polymerization degree, a saponification degree, and a methyl acetate content in specific ranges. Can be obtained.

<PVA composition>
The PVA composition used in the production method of the present invention contains PVA and methyl acetate, the viscosity average polymerization degree of PVA is 100 to 800, the saponification degree is 70 to 99.9 mol%, and the content of methyl acetate (A) is 0.3-5 mass%.

  Although the shape of a PVA composition is not specifically limited, It is preferable that it is a powder form with an average particle diameter of 50-2000 micrometers. The average particle size of the powdered PVA composition is determined by the method of JIS-K6726 (1994).

[PVA]
It is important that the PVA viscosity average polymerization degree in the PVA composition is 100 to 800, preferably 200 to 600, and more preferably 200 to 450. PVA having a viscosity average degree of polymerization of less than 100 is difficult to produce. On the other hand, if it is 800 or more, the viscosity when melted becomes too high, and it becomes difficult to reduce the content of methyl acetate. The viscosity average degree of polymerization is a value obtained by measurement according to JIS-K6726 (1994). Specifically, when the saponification degree is less than 99.5 mol%, the intrinsic viscosity [η] (liter / liter) measured in water at 30 ° C. is used for the saponified PVA until the saponification degree is 99.5 mol% or more. The viscosity average degree of polymerization (P) was determined by the following formula using g).
P = ([η] × 10 ⁴ /8.29) ^{(1 / 0.62)}

  It is important that the saponification degree of PVA in the PVA composition is 70 to 99.9 mol%, and 78 to 95 mol% is preferable. When the degree of saponification is less than 70 mol%, the solubility in water is lowered, whereas PVA having a degree of saponification exceeding 99.9 mol% is difficult to produce. The degree of saponification is a value obtained by measurement according to JIS-K6726 (1994).

[Methyl acetate]
It is important that the content (a) of methyl acetate in the PVA composition is 0.3 to 5% by mass, preferably 0.4 to 4% by mass, and more preferably 0.5 to 3% by mass. A PVA composition having a methyl acetate content (a) of less than 0.3% by mass is difficult to produce. When a PVA composition of more than 5% by mass is melt-kneaded, a large amount of foaming occurs, and the PVA composition There is a risk of splashing. The content (a) of methyl acetate in the PVA composition can be measured using headspace gas chromatography as in Examples described later.

<Method for producing PVA composition>
A preferred method for producing the PVA composition used in the present invention comprises a polymerization step for polymerizing vinyl acetate to obtain polyvinyl acetate, a saponification step for saponifying the polyvinyl acetate, a washing step as necessary, and a remaining solvent. Including a drying step to be removed. Methyl acetate can be generated when methanol is used as a solvent in the saponification step, and is contained in the PVA composition due to the use of methyl acetate as a solvent in the saponification step and washing step, but can be removed to some extent in the drying step.

[Polymerization process]
Polyvinyl acetate can be produced by polymerizing vinyl acetate by a conventionally known method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, or a dispersion polymerization method. A solution polymerization method in which a lower alcohol is used as a solvent is preferred. Although there is no limitation in particular in a lower alcohol, C3 or less alcohols, such as methanol, ethanol, propanol, isopropanol, are preferable, and methanol is more preferable. As the polymerization operation, any of a batch method, a semi-batch method and a continuous method can be adopted.

  In the polymerization, other monomers than vinyl acetate may be copolymerized within a range not detracting from the spirit of the present invention. Examples of other monomers include α-olefins such as ethylene, propylene, n-butene, and isobutylene; (meth) acrylic acid and salts thereof; methyl (meth) acrylate, ethyl (meth) acrylate, (meth) N-propyl acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate , (Meth) acrylic acid esters such as dodecyl (meth) acrylate and octadecyl (meth) acrylate; (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl ( Meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propane sulfonic acid and , Methacrylic compounds such as (meth) acrylamidopropyldimethylamine and its salts or quaternary salts thereof, N-methylol (meth) acrylamide and its derivatives; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether Vinyl ethers such as n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene chloride Vinylidene halides such as vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid and fumaric acid and salts thereof; Examples thereof include vinyl silyl compounds such as vinyltrimethoxysilane, and isopropenyl acetate. These may be used alone or in combination of two or more. The copolymerization amount of other monomers is usually 10 mol% or less. In the present specification, “(meth) acryl” is a general term for methacryl and acryl.

  There is no limitation in particular in superposition | polymerization temperature, 0-180 degreeC is preferable, 20-160 degreeC is more preferable, and 30-150 degreeC is further more preferable. When polymerizing below the boiling point of the solvent used in the polymerization process, either vacuum boiling polymerization where the solvent is boiled under reduced pressure or normal pressure non-boiling polymerization where the solvent is not boiled under normal pressure is selected it can. In addition, when polymerizing above the boiling point of the solvent used in the polymerization step, pressure non-boiling polymerization that performs polymerization under conditions that do not boil the solvent under pressure, and pressure boiling polymerization that performs polymerization while boiling the solvent under pressure Either of these can be selected.

[Saponification process]
Alcohololysis or hydrolysis reaction using a saponification catalyst can be applied to the resulting solution containing polyvinyl acetate. As a saponification catalyst, an alkali catalyst or an acidic catalyst is preferable, and among them, a catalyst having an alkali metal, particularly a sodium atom is particularly preferable. Examples of the catalyst having a sodium atom include sodium hydroxide and sodium methoxide. As a solvent used in the saponification step, a liquid containing methanol is preferably used. It may contain alcohols such as ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene; It is usually less than 10% by mass with respect to methanol. It is convenient and preferable to carry out the saponification reaction in the presence of sodium hydroxide as a catalyst. The amount of the catalyst used is preferably 0.001 or more and 0.5 or less, more preferably 0.002 or more and 0.4 or less, and more preferably 0.004 or more and 0.3 or less in terms of a molar ratio to vinyl acetate units in the vinyl acetate polymer. Is more preferable.

  The mechanism of methyl acetate formation in the saponification process is that a catalyst is added to a methanol solution of polyvinyl acetate, so that the oxygen atom in the hydroxyl group of methanol nucleophilically attacks the carbon atom of the ester in the side chain of polyvinyl acetate. As a result, it is considered that polyvinyl alcohol and methyl acetate are produced.

[Washing process]
A washing step may be provided as necessary after the saponification step. Examples of the solvent used for washing include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate. The conditions for the washing step are not particularly limited, but it is preferable to wash at a temperature of 20 ° C. to the boiling point of the solvent for about 30 minutes to 10 hours.

[Drying process]
A drying step for removing the solvent by heating after the saponification step or washing step may be provided, and the temperature and time are not particularly limited, but are usually 40 to 130 ° C. and 1 to 20 hours in consideration of productivity. PVA composition whose methyl acetate content (a) is 0.3 to 5% by mass can be easily obtained by performing drying at.

<Method for producing PVA molded body>
In the method for producing a PVA molded body of the present invention, when the PVA composition is melt-kneaded to obtain a PVA molded body, PVA molding after melt-kneading with respect to the content (a) of methyl acetate in the PVA composition before melting. It is important that the proportion of the content (b) of methyl acetate in the body satisfies the following formula (I).
0.001 ≦ (b) / (a) ≦ 0.25 (I)

  Although there is no particular limitation on the technique for melt-kneading the PVA composition, known kneading apparatuses such as a kneader ruder, a single-screw or twin-screw extruder, a mixing roll, a Banbury mixer, and a plast mill can be used. Among these, a melt kneading method using a single or twin screw extruder having a sufficient kneading force and a plast mill is preferable.

  The kneading apparatus may be provided with a vapor removal vent. Further, the number of vents is not particularly limited.

The shape of the opening of the vent is usually a circle; an ellipse; a polygon such as a triangle, a quadrangle, a pentagon, etc., preferably a circle or a quadrangle. The size of the opening is usually 1～150Cm ^2, preferably 2～80Cm ^2, particularly preferably 3 to 10 cm ^2. If the opening is too large, the unmelted PVA composition tends to be ejected, and if it is too small, the unmelted PVA composition is clogged and the vapor cannot be removed, or the pressure in the kneading apparatus tends to be too high. is there.

  Although there is no restriction | limiting in particular in melt kneading | mixing temperature, 155-235 degreeC is preferable and 170-220 degreeC is more preferable. When the melt kneading temperature is less than 155 ° C, removal of methyl acetate tends to be insufficient, and when it exceeds 235 ° C, the water solubility of the resulting PVA molded product tends to deteriorate.

  Although there is no restriction | limiting in particular in melt-kneading time, 20-500 second is preferable, 35-400 second is more preferable, and 50-300 second is further more preferable. If the melt kneading time is less than 20 seconds, removal of methyl acetate tends to be insufficient, and if it exceeds 500 seconds, the water solubility of the resulting PVA molded product tends to deteriorate.

  A cooling step may be provided after melt-kneading the PVA composition. The cooling method is not particularly limited, and a conventionally known method such as air cooling or air cooling can be used. However, since the PVA molded body is water-soluble, cooling by a water bath or shower cannot be adopted.

  Methyl acetate contained in the composition can be efficiently removed by melt-kneading the PVA composition as in the present invention. Conventionally, the PVA composition is generally dried as a powder by a hot air drier or steam heating, and in these methods, methyl acetate in the vicinity of the surface layer of the PVA composition can be removed to some extent, but is taken into the interior. It is difficult to efficiently remove the generated methyl acetate, and the drying requires a long time for the removal, resulting in a decrease in productivity.

It is important that the content (b) of methyl acetate in the PVA molded article obtained by the production method of the present invention satisfies the following formula (I) with respect to the content (a) of methyl acetate in the PVA composition before melting. is there.
0.001 ≦ (b) / (a) ≦ 0.25 (I)
A PVA molded article having (b) / (a) of less than 0.001 is difficult to produce, and if (b) / (a) exceeds 0.25, the amount of methyl acetate to be reduced is insufficient. (B) / (a) is preferably 0.005 to 0.2, and more preferably 0.01 to 0.15. In addition, content (b) of the methyl acetate in a PVA molded object can be measured using head space gas chromatography as the Example mentioned later.

  The viscosity average polymerization degree and saponification degree of PVA in the PVA molded product obtained by the production method of the present invention are the same as those of the PVA composition described above.

  Although the shape of the PVA molded object obtained by the manufacturing method of this invention is not specifically limited, For example, shapes, such as a powder, a pellet, a film, are mentioned.

(Use)
The PVA molded body obtained by the production method of the present invention can be used for various applications. Examples are given below, but are not limited thereto.
(1) Dispersant use: Dispersion stabilizers for organic and inorganic pigments such as paints and adhesives, and dispersion stabilizers for suspension polymerization of various vinyl compounds such as vinyl chloride, vinylidene chloride, styrene, (meth) acrylate, and vinyl acetate. (2) Coating agent: Paper coating agent, sizing agent, textile processing agent, leather finish agent, paint, antifogging agent, metal corrosion inhibitor, galvanizing brightener, antistatic agent (3) Adhesive applications: Adhesives, adhesives, rewet adhesives, various binders, additives for cement and mortar (4) Emulsifier applications: Emulsifiers for emulsion polymerization, post-emulsifiers such as bitumen (5) Flocculant applications: Suspension in water And coagulants of materials and dissolved materials, metal flocculants (6) Paper processing applications: paper strength enhancers, oil and solvent resistance imparting agents, smoothness improvers, surface gloss improvement aids, sealants, barrier agents, light resistance Imparting agent, waterproofing agent, dye / developer dispersant, Adhesion improver, binder (7) Agricultural applications: Agricultural binders, Agrochemical spreading agents, Agricultural coatings, Soil improvers, Erosion inhibitors, Agrochemical dispersants (8) Medical and cosmetic applications: Granulating binders, Coating agent, emulsifier, patch, binder, film preparation substrate, film forming agent (9) Viscosity modifier application: thickener, rheology modifier (10) Film application: water-soluble film, polarizing film, barrier film, Film for packaging fiber products, seed curing sheet, vegetation sheet, seed tape, hygroscopic film (11) Applications: Fiber, pipe, tube, leak-proof membrane, water soluble fiber for chemical lace, sponge (12) Gel application: Pharmaceutical Gels, industrial gels (13) Post-reaction applications: low-molecular organic compounds, high-molecular organic compounds, and inorganic compounds

  Hereinafter, the present invention will be described in more detail with reference to examples. In the following Examples and Comparative Examples, “parts” and “%” represent parts by mass and mass%, respectively, unless otherwise specified.

[Viscosity average polymerization degree of PVA]
The viscosity average degree of polymerization was measured according to JIS-K6726 (1994). Specifically, when the saponification degree is less than 99.5 mol%, the intrinsic viscosity [η] (liter / liter) measured in water at 30 ° C. is used for the saponified PVA until the saponification degree is 99.5 mol% or more. The viscosity average degree of polymerization (P) was determined by the following formula using g).
P = ([η] × 10 ⁴ /8.29) ^{(1 / 0.62)}

[Saponification degree of PVA]
The degree of saponification was measured according to JIS-K6726 (1994).

[Content of methyl acetate in PVA composition and PVA molded article]
<Creation of calibration curve>
Using isopropanol as an internal standard, three types of aqueous solutions having a known methyl acetate content were prepared, and a gas chromatograph (GC-2010, manufactured by Shimadzu Corporation) equipped with a headspace sampler (Turbo Matrix HS40, manufactured by Parkin Elmer) was used. Measurements were made to create a calibration curve.
<Measurement of methyl acetate content>
Distilled water was collected according to the marked line of a 1000 mL volumetric flask, and 0.1 mL of isopropanol as an internal standard solution was added with a measuring pipette and stirred well. This solution is referred to as “dissolved solution”. Next, 500 mg of the PVA composition or PVA compact was weighed into a vial for head space gas chromatography measurement, and a stirrer was introduced. Then, 10 mL of the solution was measured with a whole pipette and placed in the vial. . After the cap was attached to the vial and tightened until it was locked, the vial was placed on a hot stirrer, and the PVA composition or the PVA molded body was heated and dissolved. After visually confirming that the inside of the PVA composition or the PVA molded body was completely dissolved, the headspace gas chromatography measurement was performed, and the methyl acetate in the PVA composition or the PVA molded body was obtained from the calibration curve prepared as described above. The content was determined.

[Water solubility of PVA molded product]
After adding 96 parts of water to 4 parts of the obtained PVA molded body and stirring at 90 ° C. and 300 rpm for 1 hour, the degree of dissolution of the PVA molded body in the aqueous solution was visually observed and evaluated as follows.
A ... Transparent B ... Cloudy

Example 1
Sodium hydroxide was added to a 30% methanol solution of polyvinyl acetate having a viscosity average degree of polymerization of 500 at a molar ratio of 0.008 with respect to polyvinyl acetate as a saponification catalyst at 40 ° C. for 1 hour. went. The obtained polymer was washed by immersing in methanol for 30 minutes. Next, the solvent was removed by centrifugation, followed by drying at 105 ° C. for 3 hours. The viscosity average polymerization degree was 500, the saponification degree was 90 mol%, and the methyl acetate content (a) was 2.1%. A powdery PVA composition having an average particle diameter of 430 μm was obtained. The obtained PVA composition was melt-kneaded at a melt-kneading temperature of 190 ° C. and a melt-kneading time of 60 seconds using “Lab plast mill 4C150” manufactured by Toyo Seiki Seisakusho, cooled by air cooling, and had a viscosity average polymerization degree of 500. A PVA molded article having a saponification degree of 90 mol%, a methyl acetate content (b) of 0.08%, and a value of (b) / (a) of 0.04 was obtained. The aqueous solution of the obtained PVA molded body was transparent, and the evaluation was A.

Examples 2-4, Comparative Examples 1-3
A PVA molded article in the same manner as in Example 1, except that the viscosity average polymerization degree, saponification degree, methyl acetate content (a) and average particle diameter, melt kneading temperature, time, etc. of the PVA composition used were changed. Got. About the obtained PVA molded object, water solubility was evaluated along the above-mentioned method. The results are shown in Table 1.

  In Comparative Examples 1 and 2, the value of (b) / (a) was 0.25 or more, and the removal of methyl acetate was insufficient. In Comparative Example 3, since the saponification degree of the PVA composition was too low, the water solubility of the obtained PVA molded article was insufficient.

Comparative Example 4
When the PVA composition was dried in the same manner as in Example 1 except that no lab plast mill was used and a dryer was used instead, and the mixture was not melt-kneaded, the methyl acetate content (b) was 1. 9%, (b) / (a) was 0.90, and removal of methyl acetate was insufficient.

  As shown in the examples, according to the production method of the present invention, a PVA molded article having excellent water solubility and a reduced methyl acetate content can be easily obtained. If the manufacturing method of this invention is employ | adopted, drying time is short, it is excellent in economical efficiency, and industrial usefulness is very high.

Claims (4)

A method for producing a polyvinyl alcohol molded article obtained by melt-kneading a polyvinyl alcohol composition containing a polyvinyl alcohol and methyl acetate having a viscosity average polymerization degree of 100 to 800 and a saponification degree of 70 to 99.9 mol%. The content (a) of methyl acetate in the polyvinyl alcohol composition before melting is 0.3 to 5% by mass, and the content (b) and content of methyl acetate in the polyvinyl alcohol molded body after melt-kneading. The manufacturing method of the polyvinyl alcohol molded object with which the ratio of (a) satisfy | fills following formula (I).
0.001 ≦ (b) / (a) ≦ 0.25 (I)   The manufacturing method of Claim 1 whose melt-kneading temperature is 155-235 degreeC.   The production method according to claim 1 or 2, wherein the melt-kneading time is 20 to 500 seconds.   The manufacturing method in any one of Claims 1-3 whose polyvinyl alcohol composition before a fusion | melting is a powder form with an average particle diameter of 50-2000 micrometers.