JPH06271662A - Method for drying polycarbonate powder - Google Patents

Abstract

PURPOSE:To obtain a method for removing residual solvent, effective for remarkably decreasing the residual organic solvent in granular polycarbonate, enabling the elimination or remarkable shortening of drying process and useful for improving the quality, decreasing the labor and reducing the production cost. CONSTITUTION:A granular polycarbonate containing an organic solvent is heated to a temperature above the glass transition point of the polycarbonate by internal heating to evaporate the organic solvent and obtain dried polycarbonate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drying polycarbonate powder granules containing an organic solvent. More specifically, it relates to a method for efficiently and sufficiently removing an organic solvent from a polycarbonate powder containing an organic solvent.

[0002]

2. Description of the Related Art Polycarbonate is usually produced by a so-called solution method in which an alkaline aqueous solution of a dihydric phenol and phosgene are reacted in the presence of a solvent such as methylene chloride.
The solvent is removed from the obtained polycarbonate solvent solution, and the powder is subjected to a granulation process to obtain a powder, and then subjected to a drying process. As a method of removing the solvent from the solvent solution of the polycarbonate to obtain a granular material, for example, a method of contacting the solvent solution of the polycarbonate with hot water to granulate, a method of gelling into particles by concentrating or cooling, etc. It has been known.
However, many solvents still remain in the powders and granules obtained by these methods, and this residual solvent cannot be sufficiently removed by ordinary drying by heating to a temperature below the glass transition point of polycarbonate. is there. There is also known a method (Japanese Patent Laid-Open No. 4-189834) for drying in an atmosphere having a drying temperature of not less than the glass transition point of polycarbonate. However, in such a high-temperature drying method using an external heating method, a large amount of heat is required to bring the temperature of the polycarbonate powder or above to its glass transition point, and if the temperature of the heating medium is raised, the wall surface of the dryer is increased. Trouble is likely to occur due to fusion of polycarbonate powder particles. Therefore, the drying temperature is actually limited, and even with such a method, it takes a very long time to remove the solvent and it is difficult to sufficiently remove the residual solvent. Moreover, if the drying is strengthened in this way, operational troubles will occur, the molecular weight of the product will decrease, the hue will deteriorate, and foreign matter will be mixed.

As a method for producing a polycarbonate powder granule having a small amount of residual solvent, a method of adding a non-solvent or a poor solvent to a solvent solution of the polycarbonate powder obtained by the reaction or a slurry of the polycarbonate powder granule in which the solvent remains, followed by a drying treatment, Alternatively, a method has been proposed in which a polycarbonate powder or granular material in which a solvent remains is subjected to an extraction treatment with a poor solvent. In these methods, the solvent is sufficiently removed, but a large amount of the non-solvent and the poor solvent remain, and the residual non-solvent and the poor solvent should be sufficiently removed not only by ordinary drying but also by drying at high temperature for a long time. It is difficult. Further, in the manufacturing process of the solid-state polymerization reaction, a method of introducing the pre-condensed prepolymer into a non-solvent or a poor solvent to crystallize it and then conducting the condensation reaction is used. Is difficult to remove sufficiently.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for efficiently and sufficiently removing an organic solvent from a polycarbonate powder granule containing the organic solvent.

The inventors of the present invention have made extensive studies as to how to heat the polycarbonate powder granules in order to achieve the above object. As a result, if the internal heating method by microwave irradiation is used as the heating method, the polycarbonate powder granules have a glass transition point. It was found that the temperature can be easily increased to the above high temperature, fusion does not occur even at such high temperature, the drying time can be significantly shortened, and the organic solvent remaining in the polycarbonate can be significantly reduced. The present invention has been completed.

[0006]

The present invention is characterized in that a polycarbonate powder containing an organic solvent is heated to a temperature not lower than the glass transition point of the polycarbonate by an internal heating method to remove the organic solvent. It is a method for drying a polycarbonate powder.

The polycarbonate as referred to in the present invention is produced by reacting an alkaline aqueous solution of a dihydric phenol (for example, an aqueous solution of a strongly basic hydroxide such as sodium hydroxide or potassium hydroxide) with phosgene in the presence of a solvent. It may be a polyester carbonate mainly composed of a copolymer of aromatic or aliphatic dicarboxylic acid components, or a branched polycarbonate prepared by copolymerizing a trifunctional or higher polyfunctional aromatic compound. It may be a mixture of a normal molecular weight polycarbonate and an ultrahigh molecular weight polycarbonate. The molecular weight thereof is not particularly limited, and a usual polycarbonate having a viscosity average molecular weight of 12,000 to 50,000 or a viscosity average molecular weight of 80,000 is used.
Even the above-mentioned ultra-high molecular weight polycarbonates include halogenated carbonate oligomers obtained from halogenated dihydric phenols and used as flame retardants having an average degree of polymerization of 2 or more, and prepolymers used in the solid-state polymerization method.
In addition, for example, a prepolymer obtained by a so-called transesterification method in which a dihydric phenol and diphenyl carbonate are reacted in a molten state is put into a non-solvent or a poor solvent to be crystallized before being subjected to solid phase polymerization.

As the dihydric phenol used here,
2,2-bis (4-hydroxyphenyl) propane is mainly used, but some or all of it may be replaced with other dihydric phenol. Other dihydric phenols include, for example, bis (4-hydroxyphenyl) methane, 1,1
-Bis (4-hydroxyphenyl) ethane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2
-Bis (4-hydroxy-3-methylphenyl) propane, 2,2-bis (4-hydroxyphenyl) butane,
Bis (4-hydroxyphenyl) sulfone, bis (4-
Examples thereof include hydroxyphenyl) ether, bis (4-hydroxyphenyl) ketone, 4,4'-dihydroxydiphenyl, hydroquinone, and 2,6-dihydroxynaphthalene. Further, it may be a divalent phenol in which a phenyl group is substituted with a lower alkyl group or a halogen atom.

The above-mentioned polycarbonate powder or granule to be used in the present invention may be produced by any method, its shape is arbitrary, and its size is such a size that is usually called a powder or granule. There is no need to limit it in any way, and it is a polycarbonate powder containing one or more organic solvents. The content of the organic solvent is not particularly limited, but is preferably 50% by weight or less, and particularly preferably in the range of 0.1 to 50% by weight because the effect of the present invention is great.

The organic solvent referred to in the present invention is a good solvent used in the production of polycarbonate, a non-solvent or a poor solvent used in a powder granulation process, a crystallization process, etc. Examples of the good solvent include methylene chloride, chloroform, Examples thereof include halogenated aliphatic hydrocarbons such as 1,2-dichloroethane, 1,1,2-trichloroethane, tetrachloroethane, and chlorobenzene, and nonsolvents and poor solvents include, for example, n-heptane, n-hexane, and cyclohexane. Examples thereof include aliphatic hydrocarbons, aromatic hydrocarbons such as benzene, toluene and xylene, esters such as butyl acetate, ketones such as acetone and methyl isobutyl ketone.

As a typical internal heating method used in the present invention, there is a heating method using microwave irradiation. The microwave has a frequency of 300 to 30,000 MHz, and a microwave of 2,450 MHz is usually used. The temperature of heat generated by microwave irradiation is above the glass transition point of polycarbonate. At a temperature lower than the glass transition point, the effect of desolvation is small and the object of the present invention cannot be achieved. Further, if the temperature is too high, the polycarbonate powder particles will be melted, so a temperature higher by 10 to 40 ° C. than the glass transition point of the polycarbonate is preferable, and a temperature higher by 15 to 20 ° C. than the glass transition point is particularly preferable. The microwave irradiation time varies depending on the amount and type of the organic solvent contained in the polycarbonate powder and the amount of water, and cannot be unconditionally limited, but usually about 6 hours is sufficient. According to the microwave irradiation, the polycarbonate powder granules themselves generate heat so that the temperature can be raised efficiently, and even if the temperature of the polycarbonate powder granules is raised above its glass transition point, the atmosphere in the dryer and the temperature of the wall surface are Since the temperature does not exceed the temperature of the granular material, fusion on the wall surface or the like is unlikely to occur, but the wall surface may be cooled to an appropriate temperature from the outside.

The location and method of microwave irradiation are not particularly limited. For example, a polycarbonate powder containing an organic solvent is irradiated with microwaves to generate heat at a temperature above its glass transition point to remove the solvent, and then the solvent is removed in a conventional drying step, a conventional drying step. After that, a method of irradiating with microwaves, a method of irradiating with microwaves in the same step as an ordinary drying device, etc. These can be performed once or twice or more in a batch system or a continuous system. Also,
In order to efficiently perform microwave irradiation, it is possible to uniformly irradiate the polycarbonate powder or granules with microwaves from several locations, or by irradiating the polycarbonate powder or granules while stirring and flowing the microwaves. . When the temperature of the polycarbonate granules is raised above the glass transition point by microwave irradiation and dried, the desolvation time can be significantly shortened compared to the case of only a normal drying step, and the amount of organic solvent remaining in the granules is also reduced. It can be significantly reduced.

[0013]

EXAMPLES The present invention will be further described with reference to the following examples. In addition,% is% by weight, quantitative analysis of residual solvent was carried out using a gas chromatograph [Type 263 manufactured by Hitachi, Ltd.], and FID or TCD was used as a detector.

[0014]

Example 1 p-te in an amount of 0.030 molar ratio with bisphenol A and bisphenol A as end-capping agent.
An aqueous sodium hydroxide solution of rt-butylphenol and phosgene were reacted by a conventional method in the presence of methylene chloride and triethylamine. After completion of the reaction, the methylene chloride layer was separated, the separated methylene chloride solution was thoroughly washed with water, and then the methylene chloride solution was poured into warm water to remove most of the methylene chloride to obtain a polycarbonate powder. The amount of methylene chloride in the obtained granules was 26.2%, and the viscosity average molecular weight was 23,700. The frequency of this powder is 2, 4
The temperature was raised to 165 ° C. by a microwave of 50 MHz and irradiation was performed for 5 hours. The amount of methylene chloride in the obtained polycarbonate powder was 0.0003%.

[0015]

Example 2 Example 1 was repeated except that the microwave irradiation conditions were 155 ° C. and 5 hours. The amount of methylene chloride in the obtained polycarbonate powder is 0.0007.
%Met.

[0016]

Example 3 After the polymerization reaction and the granulation step were carried out in the same manner as in Example 1, the obtained polycarbonate powder was further put into hot water, mixed and stirred, and then dehydrated. The amount of methylene chloride in the obtained powder and granules was 2.4%. The powder and granules were heated to 165 ° C. by microwave and irradiated for 2 hours. The amount of methylene chloride in the obtained polycarbonate powder is 0.0
It was 010%.

[0017]

[Comparative Example 1] The same procedure as in Example 1 was carried out except that microwave irradiation was not carried out and drying was carried out at 140 ° C for 9 hours using a paddle dryer. The amount of methylene chloride in the obtained polycarbonate powder was 0.023%.

[0018]

[Comparative Example 2] The same procedure as in Example 3 was carried out except that microwave irradiation was not performed and drying was performed at 140 ° C for 9 hours using a paddle dryer. The amount of methylene chloride in the obtained polycarbonate powder granules was 0.010%.

[0019]

[Comparative Example 3] When microwaves were not used and drying was performed at 155 ° C by a paddle type dryer, fusion of powder and granules occurred within the dryer in 3 hours. The results are summarized in Table 1.

[0020]

[Table 1]

[0021]

According to the present invention, the amount of organic solvent remaining in the polycarbonate powder can be significantly reduced,
In addition, the drying process can be omitted or greatly shortened, the quality can be improved, the labor of the process can be saved, and the manufacturing cost can be reduced.

Claims (1)

[Claims] 1. A method of drying a polycarbonate powder or granular material, which comprises heating the polycarbonate powder or granular material containing an organic solvent to a temperature not lower than the glass transition point of the polycarbonate by an internal heating method to remove the organic solvent.