JP3173741B2 - Method for producing polyvinyl alcohol-based spherical fine particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for obtaining spherical polyvinyl alcohol (hereinafter abbreviated as PVA) resin fine particles by saponifying a vinyl acetate polymer by a specific method.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a fine-particle PVA-based resin, coarse particles of a PVA-based resin obtained by a known method such as saponification of a vinyl acetate-based polymer are roll-milled or jet-milled. A method of mechanically pulverizing and pulverizing with an alcohol, or a method in which an alcohol solution of a vinyl acetate-based polymer is hardly compatible with any of the polymer and the PVA-based resin and the alcohol, for example, liquid paraffin There is a method in which saponification is carried out in a state of being dispersed inside to obtain a spherical PVA-based resin having a small particle diameter.

[0003]

However, in the former mechanical pulverization method, the pulverization step becomes indispensable and the number of steps is increased, and the particle size distribution of the obtained PVA-based resin fine particles has large variation and large loss. . More spherical PVA
Fine resin particles cannot be obtained by a mechanical grinding method. In the latter case, it is relatively easy to obtain spherical PVA-based resin fine particles, but it is not easy to wash and remove the liquid paraffin attached to the PVA-based resin fine particles, and furthermore, it is necessary to collect the liquid paraffin. And the process becomes complicated. Also P
The degree of saponification of the VA resin is also limited, and the degree of saponification is 65.
If the amount is less than mol%, separation from liquid paraffin becomes difficult, and the particle diameter of the PVA-based resin is limited to about 80 μm.

[0004]

The inventors of the present invention have conducted intensive studies to produce PVA resin fine particles having a sharp particle size distribution and a spherical shape in an industrially advantageous manner. An alcohol solution of a vinyl polymer is spray-dried, subjected to saponification and pulverization to obtain a fine powder containing 50% by weight or more of fine particles having an average particle diameter of 50 μm or less.
According to the method for producing the A-based resin, saponification and pulverization can be performed simultaneously, and a spherical PVA-based resin having a particle size of 50 μm or less has been found, and the present invention has been completed. Less than,
The present invention will be described in detail.

[0005] In carrying out the method of the present invention, a composition is prepared by dissolving a vinyl acetate polymer in an alcohol together with a saponification catalyst. Examples of the saponification catalyst include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, and potassium methylate, and alkali catalysts such as alcoholate. The amount of the catalyst used is 1 to 1 with respect to 1 mol of vinyl acetate.
2,000 mmol, more preferably 5-20.
0 mmol is preferred. If the amount of the catalyst is less than the above range, saponification is not sufficiently performed, and if the amount is too large, the amount of the remaining catalyst is increased, which affects the quality of the final product and requires a washing step, which is not preferable.

Examples of the vinyl acetate polymer include homopolymers of vinyl esters such as vinyl acetate, vinyl propionate, vinyl formate, vinyl stearate, vinyl benzoate and vinyl persatic acid, copolymers of vinyl esters, and the like. These vinyl esters as a main component and other copolymerizable monomers with them, such as unsaturated monocarboxylic acids or salts thereof, alkyl esters, amides, nitriles, unsaturated polycarboxylic acids or salts thereof, partial alkyl esters, complete Alkyl esters, anhydrides, amides, imides, nitriles, unsaturated sulfonic acids or salts thereof, vinyl ethers, ethylene, α-olefins having 3 to 30 carbon atoms,
Copolymers with vinyl chloride, cationic alkyl ethers / polyoxyalkyl allyl ethers, and the like are included. Particularly, a homopolymer of vinyl acetate or a copolymer containing vinyl acetate as a main component is industrially important. In the production of such a polymer, a small amount of an aldehyde, a ketone, a mercaptan derivative or the like can be used as a polymerization degree regulator.

Examples of the alcohol used in the present invention include lower aliphatic alcohols such as methanol, ethanol and propanol, and methanol is usually used industrially. Such alcohols can be used alone or as a mixture of two or more alcohols, but methyl acetate may be used in combination. When methyl acetate is used in combination, the ratio of alcohol / methyl acetate is 0.5 or more by weight,
In particular, the ratio should be 1.5 or more. If the ratio of methyl acetate alone or methyl acetate is too large, the saponification reaction of the polyvinyl ester itself will not proceed smoothly. The concentration of the vinyl acetate polymer in the alcohol solution can vary widely, but is preferably determined in the range of 5 to 50% by weight. More preferably, it is 5 to 35% by weight. If the concentration is less than the above range, it becomes difficult to remove the alcohol, or the particle shape becomes non-uniform, and a spherical particle cannot be obtained.
Conversely, when the amount is too large, the viscosity of the solution becomes too high, so that uniform spraying from a nozzle or the like during spray drying becomes impossible, which is inappropriate.

[0008] The alcohol solution may contain a small amount of water. The amount of water is desirably selected from the range of 0.05 to 10% by weight based on the vinyl acetate polymer. The presence of a small amount of water is considered to play a role in randomizing the distribution of residual acetate groups in the saponified product and controlling the degree of saponification. However, the presence of excess water requires a large amount of catalyst for the saponification reaction and tends to increase the stickiness of the particles. Further, inorganic substances, metals, fine particles such as resins, organic substances such as antibacterial agents and preservatives, surfactants, antioxidants, defoaming agents and the like can be added as long as the effects of the present invention are not impaired. .

As a method for mixing the components, an alcohol solution of a vinyl acetate polymer, a saponification catalyst and, if necessary, the above-mentioned additives are added to a container having a known stirring device under stirring, and the mixture is uniformly mixed. Mix and stir to obtain a mixed solution. It is also possible to carry out mixing and stirring while adjusting the temperature within the range of -80 ° C to 50 ° C as necessary. If the residence time after mixing is long, the mixture may be solidified, so that a method of continuously mixing is industrially preferable. The solution thus obtained is usually in the form of a paste, which is fed to a disk-type or nozzle (pressurized or two-fluid) type spraying machine for 50 to 200 times.
It sprays in the atmosphere of ° C.

The former disk type has a rotation speed of 5000
The solution is dropped onto a disk rotating at about ０００40000 (rpm), and is sprayed by centrifugal force of the disk. The latter nozzle type further includes a pressurized type and a two-fluid type. The pressurized type pressurizes the solution and ejects the solution from a nozzle to form a spray state. The two-fluid type is a specific gas (for example, , Nitrogen gas) while pressurizing, mixing with the solution and jetting it out from a nozzle to form a spray state. In the case of nozzle spray, the shape of the nozzle is a circle,
It is arbitrary such as a square and an ellipse. In this spraying step, the saponification of the vinyl acetate polymer and the PV
The A-based resin is finely divided at the same time.

The saponification degree at this time is not particularly limited, but is preferably 50 mol% or more. When saponification degree decreases, PV
Aggregation of the A-based resin fine particles occurs. Further, the upper limit of the saponification degree is limited to about 90 mol% only in the present spraying step, and when a higher saponification degree product is required, for example, the saponification degree of less than 90 mol% obtained in the present invention is obtained. The degree of saponification can be increased by re-saponifying the PVA-based resin fine particles having the degree of saponification. Specifically, it is possible to re-slurry the obtained fine particles with methanol in the presence of a catalyst, hold the slurry at a constant temperature, and then dry it. Regarding the particle size of the PVA-based resin fine particles, those having a particle size of 50 μm or less must be contained in an amount of 50% by weight or more. To satisfy this, the concentration of the mixed solution (paste) and the size of the sprayed droplets are important so,
You can control this. Specifically, in the case of a disk type sprayer, the amount of dripping, the number of rotations of the disk, etc. are adjusted, and in the case of the nozzle type, the nozzle diameter, pressure, etc. are adjusted.

The PVA-based resin fine particles thus obtained are:
Although it can be used for various applications as it is, if necessary, after a washing step, the above-mentioned re-saponification step, a drying step, etc.
It may be commercialized. Further, a heat treatment can be carried out, if necessary, for the purpose of improving the water dispersibility of the fine particles. When such heat treatment is performed, it is preferable to perform the heat treatment in an inert gas such as nitrogen, carbon dioxide, or argon in order to prevent coloring of the particles.

The PVA-based resin fine particles thus obtained can be used in various applications, for example, moldings such as fibers, films, sheets, pipes and tubes, and adhesives such as wood, paper, aluminum foil and plastics. Adhesives, re-wetting agents, humectants, hot-melt adhesives, pressure-sensitive adhesives, binders for non-woven fabrics, adhesives for cement admixture, etc., coating agents for paper and textiles, additives for molded products, inks And various additives such as additives for paints and the like, suspension polymerization of unsaturated monomers such as vinyl chloride, vinyl acetate and acrylic acid ester, and dispersion stabilizers for emulsion polymerization, but are not necessarily limited to these. Not something.

[0014]

The present invention will be specifically described below with reference to examples. In the examples, “parts” and “%” are based on weight unless otherwise specified. Example 1 Polyvinyl acetate having an average degree of polymerization of 2000 (vinyl acetate 10
0 parts, methanol 16.4 parts and azobisisobutyroni
Tolyl 0.008 mol% polymerized under nitrogen atmosphere
) Of 38.6 parts of a 28.6 methanol solution and 5 parts of sodium hydroxide (10.7 mmol per 1 mol of vinyl acetate) were mixed and stirred in a can equipped with a stirrer.
The temperature was kept at 0 ° C. and sprayed from a nozzle (φ = 0.5 mm) at a spray pressure of 1.0 kg / cm ^{2 into} a nitrogen gas atmosphere at 150 ° C., and simultaneously dried to obtain a polymerization degree of 1700 and a saponification degree of 6
PVA-based resin fine particles having 0 mol% and an average particle diameter of 30 μ were obtained.

Examples 2 to 5 According to the composition shown in Table 1, the same operation as in Example 1 was carried out to obtain PV.
A type resin fine particles were obtained. In addition, the polyvinyl acetate of Examples 3-5 was used.
The desired level of methanol is adjusted by adjusting the amount of methanol during polymerization.
A polymer having a degree of homopolymerization was obtained. Example 6 1000 parts of the spherical fine particles obtained in Example 1, 2000 parts of methanol and 5 parts of sodium hydroxide were mixed in a vessel equipped with a stirrer, and the mixed slurry was kept at 40 ° C. for 5 hours to perform re-saponification. Was. After the saponification slurry was dried after solid-liquid separation, PVA-based resin fine particles having a saponification degree of 98.0 mol% were obtained.

Comparative Example 1 2500 parts of a 40% methanol solution of polyvinyl acetate having an average degree of polymerization of 2000 and 3 parts of sodium hydroxide (6.4 mmol per 1 mol of vinyl acetate) were charged into a reactor equipped with a stirrer. Was kept at 25 ° C. and stirred. Subsequently, liquid paraffin (viscosity of 1.6 poise at 20 ° C.) 1600
When the stirring speed was adjusted to 300 revolutions per minute, the polyvinyl acetate was dispersed in liquid paraffin in a spherical shape. The reaction was carried out while maintaining the temperature at 25 ° C., and the reaction was stopped after a lapse of 180 minutes. After that, solid-liquid separation was attempted.
Separation of the VA-based fine particle powder was impossible.

Comparative Example 2 An average degree of polymerization of 17 obtained by alkali saponification by a conventional method.
00, PVA having a degree of saponification of 70 mol% and an average particle size of 430 μm
Resin based on a jet mill [Nippon Pneumatic Industries, Ltd.]
Made, supersonic jet crusher LABO JET LJ]
To obtain PVA-based resin fine particles.

Comparative Example 3 The same operation as in Comparative Example 2 was performed with the composition shown in Table 1 to obtain P
VA resin fine particles were obtained. P obtained in Examples and Comparative Examples
Table 1 shows the particle shape and the like of the VA-based resin fine particles. Also, Coulter Counter (COUNTER MULTIZEZE)
FIG. 1 shows the results obtained by measuring the particle size distribution of the dispersion in 4) using 4% LiCl / isopropyl alcohol. As is clear from Table 1 and FIG. 1, the PV obtained by the present invention was
The A-based resin fine particles have a sharp distribution and are spherical particles.

[0019]

[Table 1]

[0020]

[Outside 1] The shape was confirmed with an optical microscope (500 times).

[0021]

According to the method for producing PVA-based fine particles of the present invention, saponification and fine-particle formation can be performed simultaneously, and the obtained fine particles are spherical and have a sharp particle size distribution. Further, the fine particles can have a high degree of polymerization, and can be used for molding applications, various adhesives, dispersion stabilizing aids, and the like. Further, the fine particles of the present invention have very good dispersibility in water and are very useful for use as an aqueous dispersion of a PVA-based resin.

[0022]

[Brief description of the drawings]

3 shows the particle size distribution of PVA-based resin fine particles obtained in Examples and Comparative Examples.

[Explanation of symbols]

1 ... Particle size distribution curve of Example 1 2 ... Particle size distribution curve of Example 2 3 ... Particle size distribution curve of Example 3 4 ... Particle size distribution curve of Example 4 5 ... Example Particle size distribution curve of 5 6 ... Particle size distribution curve of Example 6 7 ... Particle size distribution curve of Comparative Example 2 (previously passed through a 70-mesh sieve) 8 Particle size distribution curve of Comparative Example 3 ( 〃
)

Claims (3)

(57) [Claims] An alcohol solution of a vinyl acetate polymer containing a saponification catalyst is spray-dried, and saponification and pulverization are performed to obtain a fine powder containing 50% by weight or less of fine particles having a particle size of 50 μm or less. For producing polyvinyl alcohol-based spherical fine particles characterized by the following 2. A polyvinyl alcohol having a saponification degree of 50.
2. The method for producing polyvinyl alcohol-based spherical fine particles according to claim 1, wherein the amount is at least mol%. 3. An alcohol solution having a polyvinyl acetate content of 5 to 50% by weight, a saponification catalyst amount of 1 to 1000 mmol per 1 mol of vinyl acetate, and an atmosphere temperature of 50 to 200 ° C during spraying. 3. The method for producing polyvinyl alcohol-based spherical fine particles according to claim 1, wherein