JP2000351853A - Drying method for polyvinyl alcohol resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drying method for a polyvinyl alcohol resin whereby the discoloration of the resin, decrease in water solubility, and fusion to the wall of a drying vessel during drying are prevented by irradiating a polyvinyl alcohol resin having a specified volatile content with microwaves to dry it. SOLUTION: A polyvinyl alcohol resin (hereunder referred to as PVA) having a volatile content of 0.1-30 wt.% is dried. Though not specifically limited, a microwave generator having an effective output of about 0.1-500 kw/hr is favorable as a production plant. Though the drying time varies with the volatile content, attempted volatile content, and amount of PVA being dried and the effective output of a microwave irradiator used, an irradiation time per 100 kg of PVA is preferably selected from the range of 5 sec to 6 min when, e.g. the effective output of the microwave irradiator used is about 100 kw/hr. The drying treatment can be continuously conducted by irradiating saponified PVA under transport on a belt conveyor or the like with microwaves from the upper side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for drying a polyvinyl alcohol resin (hereinafter abbreviated as PVA).

[0002]

2. Description of the Related Art Conventionally, PVA has been useful as a water-soluble resin, and is generally produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate with an alkali metal as a catalyst. PVA obtained by the
It usually contains a solvent such as methanol used during saponification, and the solvent is removed by heating and drying to produce a PVA powder. That is, PVA after saponification
Is dried into PVA powder, and in this drying process, high-temperature hot air of usually 60 ° C. or higher is usually used.

[0003]

However, in the drying method using the above-mentioned hot air, the PVA is discolored,
The water solubility, which is a characteristic of A, decreases, or when dried (dry)
A phenomenon such as fusion of PVA to the wall of the can has been observed, and new improvement of the drying method is desired.

[0004]

The present inventor has conducted intensive studies in view of the above circumstances, and has found that PVA having a volatile content of 0.1 to 30% by weight is irradiated with microwaves and dried. As a result, the inventors have found that the above-mentioned problems have been solved, and have completed the present invention. Incidentally, the volatile matter referred to in the present invention means a substance which volatilizes at about 100 ° C. under normal pressure, and specifically, alcohols (methanol, ethanol, isopropyl alcohol, etc.) used or by-produced during the production of PVA. , Acetate (methyl acetate, ethyl acetate, etc.),
Water, acetic acid and the like.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. As the PVA to be dried in the present invention, usually,
Examples include those produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate.However, the present invention is not necessarily limited thereto, and not only partially saponified or completely saponified polyvinyl acetate, Vinyl esters and monomers copolymerizable therewith, such as ethylene, propylene, isobutylene, α-octene, α-dodecene,
Olefins such as α-octadecene, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride,
Unsaturated acids such as itaconic acid or salts thereof or mono- or dialkyl esters; acrylonitrile; nitriles such as methacrylonitrile; amides such as acrylamide and methacrylamide; ethylene sulfonic acid, allyl sulfonic acid; Olefin sulfonic acid or its salt, alkyl vinyl ether, N
-Saponified copolymers of acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyldiallylvinylketone, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride and the like.

[0006] The content of volatile matter in PVA to be dried is 0.1 to 30% by weight, and the content of such volatile matter is 0.1 to 30% by weight.
If the amount is less than 1% by weight, the drying efficiency by microwave irradiation deteriorates. On the other hand, if the amount exceeds 30% by weight, an excessive microwave irradiation device is required, which is not practical.

In obtaining PVA before drying as described above, it can be obtained by saponifying polyvinyl acetate by a conventional method. Specifically, for example, an aqueous solution or an alcohol (methanol, ethanol, etc.) solution containing a saponification catalyst such as sodium hydroxide is mixed with polyvinyl acetate formed into a paste with a solvent such as methanol, Saponification is performed, and a solvent such as methanol is added to form a slurry. Then, the PVA is usually powdered or granulated PVA containing alcohol, acetate, etc., by filtration or treatment such as a centrifuge. And Finally, a drying process is performed. Therefore, in the present invention, the pre-dried PVA powder such as dried before drying, hot air drying, jacket heating or the like may be subjected to a drying treatment by microwave.

In the present invention, the most characteristic feature of the above-mentioned method of drying PVA is to irradiate a microwave when drying the PVA. Such a method will be described.

In the present invention, the microwave generator is not particularly limited, but the production plant preferably has an effective output of about 0.1 to 500 kW / hr, and the irradiation time is determined by evaporating the PVA to be dried. Although it cannot be said unconditionally according to minute or target volatile matter, processing amount, and effective output of the microwave irradiation apparatus, for example, when a microwave irradiation apparatus having an effective output of about 100 kW / h is used, per 100 kg of PVA is used. 5 seconds ~
If the irradiation time is less than 5 seconds, a sufficient drying effect cannot be expected. Conversely, if the irradiation time exceeds 6 minutes, there is no particular problem, but energy is wasted, which is not preferable.

[0010] The above-mentioned microwave irradiation is performed on P after saponification.
The drying process can be continuously performed by irradiating the microwaves from above while transferring the VA on a belt conveyor or the like, and further, a batch drying method may be used.

Although the drying method in the PVA manufacturing process has been described above, the drying method of the present invention is not limited to the drying in the PVA manufacturing process, but may be applied to the case where volatile components cause processing trouble in the PVA processing process. Is also effective as a method for drying (adjusting volatile components) PVA. Thus, the PVA dried by the drying method of the present invention can obtain PVA with little change in physical properties due to the influence of heat such as discoloration or decrease in water solubility. It is useful for applications such as turbidity agents and fiber sizing agents.

[0012]

The present invention will be specifically described below with reference to examples. In the examples, “parts” and “%” mean on a weight basis unless otherwise specified.

Example 1 PVA containing 3% of methanol and 0.5% of methyl acetate preliminarily dried after saponification [Saponification degree: 99.5 mol%, average polymerization degree: 1700, volatile matter content: 4.5% ] (Average particle diameter: 450 μm), placed on a belt conveyor so as to have a thickness of about 2 cm, and irradiated with microwaves (effective output: 100 kW / h) from a height of about 30 cm above the belt. The drying was performed while moving the belt conveyor so that the time was 60 seconds. The methanol content of the PVA after drying was 0.1%, and no methyl acetate was observed. The dried state was good. The content of methanol and methyl acetate was measured by gas chromatography. Further, the PVA after drying was evaluated for colorability and water solubility in the following manner.

(Coloring property) The color of PVA before and after drying was visually observed and evaluated as follows. ○ −−− No coloring is observed × −−− Yellowing is observed

(Water soluble) 16 g of PVA after drying
and 384 cc of water in a beaker with a magnetic stirrer at 90 ° C. for 2 hours (about 200 rpm).
The state after m) was visually observed and evaluated as follows. ○ −−− Completely dissolved × −−− Undissolved matter is observed

Example 2 The procedure of Example 1 was repeated except that PVA containing 2% of methanol, 2% of water and 1% of methyl acetate [containing 5.3% of volatile matter] was used to dry the PVA. went. The methanol content of the dried PVA is 0.1%, water 0.3
%, No methyl acetate was observed and the dry state was good. The PVA after drying was evaluated in the same manner as in Example 1.

Example 3 After saponification, preliminarily dried PVA containing 3% of methanol, 1% of water and 2% of methyl acetate [degree of saponification 88.
0 mol%, average polymerization degree 2000, 6.3% volatile content]
Was dried in the same manner as in Example 1 except that powder (average particle diameter: 850 μm) was used. The methanol content of the dried PVA was 0.2% and the water content was 0.3%, and no methyl acetate was observed. PV after drying
A was evaluated in the same manner as in Example 1.

Example 4 In Example 1, the microwave irradiation conditions were changed,
Effective power 100kw /
h for 90 seconds to perform drying. The methanol content of the dried PVA was 0.5%, no methyl acetate was observed, and the dried state was good. The PVA after the drying treatment was evaluated in the same manner as in Example 1.

Comparative Example 1 The PVA of Example 1 was dried by leaving it to stand in a hot-air dryer at 80 ° C. for 60 minutes. The methanol content of the dried PVA was 1.2% with 0.1% methyl acetate.
The PVA after drying was evaluated in the same manner as in Example 1.

Comparative Example 2 In Comparative Example 1, the sample was left standing in a hot-air dryer at 120 ° C. for 60 minutes. Drying was carried out in the same manner except for the above. Dried PVA
Had a methanol content of 0.2% and no methyl acetate was found. The PVA after drying was evaluated in the same manner as in Example 1. Table 1 shows the evaluation results of the examples and the comparative examples.

[0021]

[Table 1]

[0022]

According to the drying method of the present invention, the drying time during the drying treatment is greatly reduced, and there is no fusion to the (drying) can, and the obtained PVA is discolored, It is excellent in quality without decreasing water solubility,
Is useful for applications such as films, adhesives, suspending agents, fiber sizing agents, papermaking, fibers, and emulsifiers.

Continued on the front page F term (reference) 4F070 AA26 HA01 HB15 4F073 AA32 BA17 CA42 4J100 AA02Q AA03Q AA06Q AA15Q AA19Q AC03Q AC04Q AD02P AE02Q AF11Q AG04P AJ01Q AJ02Q AJ03Q AJ08 AM AK01Q18 AK01Q13 AQ08Q BA03H BA33Q BA56Q GD02 HA09 JA03 JA11

Claims (1)

[Claims] 1. A method for drying a polyvinyl alcohol resin, which comprises irradiating a microwave to a polyvinyl alcohol resin having a volatile content of 0.1 to 30% by weight.