JPH0257057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In recent years, aromatic polyimides have played a major role as highly functional heat-resistant materials.

Manufactured by a polycondensation reaction between an aromatic tetracarboxylic acid dianhydride having one or more aromatic rings in the molecule and an aromatic diamine having one or more aromatic rings in the molecule. Aromatic polyimides generally have the following structure, and from the viewpoint of the strength of the formed film, the logarithmic viscosity measured at 50°C using P-chlorophenol as a solvent is 2.0 or more, especially 2.0 or more. Polymers polycondensed to about 4.0 are in practical use.

(However, R and R' are residues containing an aromatic ring.) However, since aromatic polyimide is a material that requires high functionality, aromatic There are strict requirements for the performance of polyimide, and a considerable amount of polyimide is discarded as non-standard products due to the presence of a small amount of gel or minute pinholes in the formed film. Also, during film production, both ends of the film serve as gripping margins for the machine, so they are later cut and discarded, but both aromatic tetracarboxylic dianhydride and aromatic diamine, which are raw materials for aromatic polyimide, are extremely These are expensive chemicals, and these discarded parts have a large impact on the manufacturing cost of aromatic polyimide.

It is known that these aromatic polyimides are decomposed by heating in the presence of an alkali, but they are completely decomposed into monomer units of aromatic tetracarboxylic acid and aromatic diamine, which can then be reused. There is no known method for using it as a condensation raw material that can be subjected to a polycondensation reaction.

The reason for this is that when imide bonds are dissociated by hydrolysis, an elimination reaction of carboxyl groups accompanies, and under mild decomposition conditions that do not cause elimination of carboxyl groups, imide bonds are The dissociation of bonds is not completed completely and polyimide oligomers remain, and furthermore, the recovered aromatic tetracarboxylic acid and aromatic diamine are significantly colored (brown). The presence of polyimide oligomers can be confirmed as methanol-insoluble components of the recovered material.

Decarboxylation components such as aromatic tetracarboxylic acid and aromatic dicarboxylic acid, which are generated by the elimination of carboxyl groups mixed into the recovered raw material, and polyimide oligomers are inhibitors of the polycondensation reaction, and these are substances that inhibit the polycondensation reaction. If recovered raw materials containing more than % of the raw materials are used, it is impossible to produce an aromatic polyimide with a logarithmic viscosity of 2.0 or more through a polycondensation reaction.

The present inventors completed the present invention as a result of intensive research into a method for recovering aromatic tetracarboxylic dianhydride and aromatic diamine, which have high polycondensation reactivity and can be reused as raw materials for aromatic polyimide.

That is, the present invention provides a method for simultaneously recovering an aromatic tetracarboxylic dianhydride and an aromatic diamine by hydrolysis from an aromatic polyimide that can no longer be used as a molded product. Aromatic polyimide is hydrolyzed at a temperature of 150 to 230°C in the presence of 4.0 to 4.8 times the mole of alkali to the extent that substantially no imide bonds remain, and the resulting reaction product is filtered to obtain aromatic tetracarboxylic acid. After separating into an alkaline aqueous solution (liquid A) and an aromatic diamine as a filter cake, an acid aqueous solution is further added to the filter cake to form an acid aqueous solution of aromatic diamine (liquid B), and the liquids A and B are respectively separated. The aromatic tetracarboxylic acid and the aromatic diamine are precipitated by contacting with activated carbon, and then the aromatic tetracarboxylic acid and the aromatic diamine are precipitated by adding acid and alkali in an amount equal to or more than the neutralization equivalent.The aromatic tetracarboxylic acid is further heated and dehydrated to precipitate the aromatic tetracarboxylic acid and the aromatic diamine. The present invention relates to a method for recovering aromatic tetracarboxylic dianhydrides and aromatic diamines, which is characterized in that they are recovered as anhydrides.

The aromatic polyimide used in this invention is not limited as long as it has heat resistance.

To specifically explain the method of the present invention, an alkali such as caustic soda, caustic potash, or ammonia, and water in an amount of 4.0 to 4.8 times the mole of aromatic polyimide and polyimide units are charged into a pressure-resistant reactor such as an autoclave, and the air is heated. After replacing the phase with an inert gas such as nitrogen or carbon dioxide, the polyimide is hydrolyzed by heating to a temperature in the range of 150 to 230°C until substantially no imide bonds are present.

The aromatic tetracarboxylic acid produced by hydrolysis is present in the aqueous solution as an alkali salt, and the aromatic diamine is precipitated at the bottom of the autoclave after cooling and is filtered out. After decolorizing the filtrate with activated carbon, add an inorganic acid such as hydrochloric acid or sulfuric acid or an organic acid such as formic acid or acetic acid to acidify the liquid to precipitate aromatic tetracarboxylic acid, filter, wash with water, and dry. collected by. Here, during the precipitation of the aromatic tetracarboxylic acid from the alkaline solution, it is particularly necessary to make the solution acidic by adding an acid in an amount equal to or more than the neutralization equivalent in order to remove the mixed diamine component. The recovered aromatic tetracarboxylic acid is heated and dehydrated in an inert gas stream to form aromatic tetracarboxylic dianhydride, which can then be used as a raw material for aromatic polyimide. A purification operation may be added later.
In this way, from substandard aromatic polyimide,
Aromatic tetracarboxylic dianhydride can be recovered with a high yield of 90% or more.

On the other hand, the precipitate filtered out after hydrolysis is aromatic diamine, and is subjected to the following treatment to remove foreign substances and decolorize it.

First, the precipitate is made into an aqueous acid solution such as hydrochloric acid, sulfuric acid, formic acid, acetic acid, etc., and the solution is decolorized with activated carbon and filtered. Next, an alkali such as caustic soda, caustic potash, or ammonia is added to the filtrate to make the liquid alkaline. The precipitated aromatic diamine is collected by filtration, washing with water, and drying. Here, when the aromatic diamine is precipitated from the acidic solution, it is particularly necessary to make the solution alkaline by adding an alkali equivalent to or more than the neutralization equivalent in order to remove the mixed carboxylic acid component.
In this way, from substandard aromatic polyimide,
Aromatic diamines can be recovered with a yield of over 90%. The recovered aromatic diamine can be used as it is as a raw material for polycondensation, but of course a purification operation such as sublimation purification may be added.

In this invention, the alkali used for hydrolysis may be caustic soda, caustic potash, or ammonia, but the amount used is based on the polyimide unit.
It is necessary to add 4.0 times the mole or more; if it is less than this, the decomposition reaction will not proceed completely and a low molecular weight oligomer having a polyimide bond will be produced. In addition, excessive use is undesirable because it promotes decarboxylation reaction, and 4.0 to 4.0
Approximately 4.8 times the molar amount is optimal. The amount of water during hydrolysis is sufficient as long as it is sufficient to dissolve the alkali salt of aromatic tetracarboxylic acid produced, but generally it is 5 to 20% water based on the weight of the polyimide that has not yet been charged. About twice the amount is sufficient.

In addition, in this invention, when hydrolyzing polyimide, the decomposition time until imide bonds are substantially no longer present varies depending on the hydrolysis temperature: 150°C for 7 hours, 170°C for 5 hours, 200°C at 3.5
Appropriate time is 2.5 hours at 230°C.

Examples and comparative examples are shown below.

Example 1 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter abbreviated as BPDA) and diaminodiphenyl ether (hereinafter abbreviated as DADE)
Aromatic polyimide produced by polycondensation of 30g of gripping margin during film formation [logarithmic viscosity (ηinh) at 50℃ is 3.5], 11.5g of caustic soda
(4.4 times the mole per polyimide unit), 300ml of distilled water
was placed in an autoclave with an internal volume of 430 ml. After the gas phase was purged with nitrogen, the temperature was raised to 190° C. and the mixture was stirred for 4 hours for hydrolysis. After cooling, the contents of the autoclave were filtered. Add 1 g of powdered activated carbon to the filtrate and
After stirring for several minutes, the activated carbon was separated by filtration, and 40 ml of concentrated hydrochloric acid was added to the filtrate. The precipitate was filtered, washed with water, dried under reduced pressure at 60°C overnight, and a portion was methyl esterified. Elemental analysis and gas chromatography analysis revealed that 3,3',4,4'-biphenyltetracarboxylic acid ( (hereinafter abbreviated as BPTA). Furthermore, gas chromatography analysis after esterification revealed that the concentration of the decarboxylated component was as small as 0.014%.
In addition, the recovered BPDA was completely dissolved in methanol and did not contain any insoluble matter, so it was confirmed that it did not contain any oligomers having polyimide bonds. 16 hours at 240℃ in nitrogen flow
The recovery rate after heating and dehydrating BPTA to form BPDA was 92.6% based on the charged aromatic polyimide.
It was hot.

Further, after the hydrolysis, 30 ml of concentrated hydrochloric acid and 270 ml of distilled water were added to the filtered solid to dissolve it, and 1 g of powdered activated carbon was added and stirred for 30 minutes, after which the activated carbon was separated by filtration. 15 g of caustic soda was added to the filtrate and stirred, and the precipitate precipitated was filtered, washed with water, and dried under reduced pressure at 60° C. overnight to obtain a white powder.

Elemental analysis and gas chromatography analysis of a portion revealed that the frame was pure.
It was confirmed that it was DADE. The recovery rate was 91.1%.

5.88 g (20 mmol) of BPDA and 4.01 g (20 mmol) of DADE recovered in the manner described above were
When polycondensation was performed at 160°C for 1 hour using 91.6 g of P-chlorophenol as a solvent by the method described in Publication No. 65227, the logarithmic viscosity (ηinh) at 50°C was
An aromatic polyimide having a value of 2.83 was obtained. This value indicates that condensation was sufficiently high.

ηinh.=ln(η/η.)/c where η: Viscosity η of the polyimide solution. : Viscosity of solvent (P-chlorophenol) C: Concentration of polyimide (g/100g) A film with a thickness of 30μ was prepared from the obtained polyimide by the method described in JP-A-55-65227, and When the strength and elongation (at break) were measured, they were 23.9 Kg/mm ² and 83%, respectively.

Example 2 In the same manner as in Example 1, 30 g of a substandard aromatic polyimide film was hydrolyzed at 150°C for 7 hours.
Recovery rates for BPDA and DADE were 91.1% and 93.3%, respectively.
Obtained in %. The concentration of the decarboxylated component in the recovered BPDA was sufficiently low at 0.011%, and it did not contain any polyimide oligomer. When polycondensation was carried out in the same manner as in Example 1 using these recovered raw materials,
The logarithmic viscosity at 50°C was 3.02, which was a fully satisfactory value, and the tensile strength and elongation of the polyimide film were 24.1 Kg/mm ² and 85%.

Example 3 BPDA and DADE were prepared in the same manner as in Example 1, except that aromatic polyimide was hydrolyzed at a temperature of 230°C for 2.5 hours and formic acid was used instead of hydrochloric acid.
were obtained with recoveries of 93.4% and 92.6%, respectively.

The concentration of decarboxylated components in the recovered BPDA is 0.018
%, and contained no polyimide oligomer at all. When polycondensation was carried out in the same manner as in Example 1 using these recovered raw materials, the logarithmic viscosity at 50°C was 2.97, which was a fully satisfactory value, and the polyimide film had a tensile strength of 23.6 Kg/mm ² and an elongation of 82%
It was hot.

Comparative Example 1 The same experiment as in Example 1 was conducted except that 26.2 g of caustic soda (10 times the mole relative to the polyimide unit) was used, and BPTA and DADE were obtained with a recovery rate of 92.4% and 92.1%, respectively. Analysis of the recovered BPTA revealed that polyimide oligomers were not present, but the concentration of decarboxylated components was as high as 0.43%. Furthermore, when polycondensation was carried out in the same manner as in Example 1, the logarithmic viscosity of the polycondensate was as low as 1.63, which was not a satisfactory value. The tensile strength of polyimide film is 13.7
Kg/mm ² and elongation was 45%.

Comparative Example 2 Hydrolysis was carried out at 130° C. for 15 hours using the method of Example 1, and 67.3% of BPTA and 55.1% of DADE were recovered. As a result of BPTA analysis, the concentration of decarboxylated components was 0.00%, but polyimide oligomer
It was also contaminated by 7.3%. The recovered BPTA was anhydrified to form BPDA, and then polycondensed in the same manner as in Example 1, but the viscosity after the reaction did not increase at all.

Comparative Example 3 Hydrolysis was carried out at 250°C for 1 hour in the same manner as in Example 1, and BPTA and DADE were reduced to 94.6% and 94.6%, respectively.
A recovery rate of 94.1% was obtained. Analysis of BPTA revealed that no polyimide oligomer was mixed in, but the concentration of decarboxylated components was 1.65%. As a result of the polycondensation test, the logarithmic viscosity at 50℃ was 1.16, the tensile strength of the polyimide film was 7.6 Kg/mm ² , and the elongation was 23%.
This was a low and unsatisfactory value.

Claims (1)

[Claims] 1 In a method for simultaneously recovering aromatic tetracarboxylic dianhydride and aromatic diamine by hydrolysis from aromatic polyimide that can no longer be used as a molded product, 4.0 to 4.8 times the molar amount per polyimide unit of the aromatic polyimide. in the presence of alkali
Hydrolyzing aromatic polyimide at a temperature of 150 to 230°C to the extent that virtually no imide bonds remain,
After filtering the obtained reaction product and separating it into an alkaline aqueous solution of aromatic tetracarboxylic acid (liquid A) and an aromatic diamine as a filter cake, an acid aqueous solution is further added to the filter cake to separate the aromatic diamine acid. Aqueous solution (B solution)
Then, the A liquid and the B liquid are brought into contact with activated carbon, and then acid and alkali in an amount equal to or more than the neutralization equivalent are added to precipitate aromatic tetracarboxylic acid and aromatic diamine. A method for recovering aromatic tetracarboxylic dianhydride and aromatic diamine, which comprises further heating and dehydrating the tetracarboxylic acid to recover the dianhydride.