JPH07316248A - Production of polycarbodiimide - Google Patents

Abstract

PURPOSE:To provide an industrially advantageous process for producing a powdery polycarbodiimide, whereby the amounts of a reaction solvent, a catalyst, etc., used in the polycondensation reaction can be markedly reduced. CONSTITUTION:This production process comprises the steps of condensing an aromatic diisocyanate in the presence of a carbodiimidation catalyst in an alicyclic ether solvent, precipitating the polycarbodiimide from the obtained reaction solution by mixing it with a poor solvent having a boiling point lower than that of the alicyclic ether solvent, recovering the polycarbodiimide from the suspension obtained in the precipitation step, and recirculating the residue obtained by distilling off the poor solvent component from the residual solution obtained in the recovery step into the reaction step.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polycarbodiimide, and more particularly to an improvement in a method for producing a powdery polycarbodiimide.

[0002]

2. Description of the Related Art Since polycarbodiimide, especially aromatic polycarbodiimide, is a thermosetting resin having excellent heat resistance, powdery materials are used as molding materials for heat resistant moldings such as hot press molding. There is. Polycarbodiimide is prepared by treating an organic diisocyanate such as 2,4-tolylene diisocyanate with 3-methyl-1 in an inert solvent.
It is generally obtained by a decarboxylation condensation reaction in the presence of a carbodiimidization catalyst such as -phenyl-2-phospholen-1-oxide. For example, JP-A-51-61599 describes a method of using a hydrocarbon such as benzene, toluene, xylene, decalin, or chloroform, methylene chloride, o-dichlorobenzene, monochlorobenzene, etc. as an inert solvent. In addition, Japanese Patent Laid-Open No. 4-
279618 describes a method using an alicyclic ether such as tetrahydrofuran or dioxane.

In JP-A-51-61599, an inert solvent in which a raw material organic diisocyanate is soluble but a polymer produced by a condensation reaction is insoluble is used, and the reaction mixture is cooled or if necessary. A method is disclosed in which another inert solvent in which the polymer is insoluble is added to the reaction mixture to precipitate the polymer to obtain the desired polycarbodiimide as a fine powder. However, in this method, since the reaction solvent has a low solubility in the polymer, the condensation reaction is carried out in a heterogeneous system, so that inconvenience such as gelation of the reaction system occurs from the initial stage of the reaction, and it can be said that it is a preferable method Absent. Japanese Patent Laid-Open No. 4-279618 discloses a method for obtaining a high-molecular-weight polycarbodiimide solution having good storage stability by using an inert solvent having sufficient solubility for both the raw material organic diisocyanate and the polymer produced by the condensation reaction. Is disclosed. However, JP-A-4-279618 does not disclose any method for separating and recovering powdery polycarbodiimide from the polycarbodiimide solution.

[0004]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems of the prior art, in which an aromatic diisocyanate is subjected to a condensation reaction in the presence of a carbodiimidization catalyst in an inert solvent to give a homogeneous solution. It is an object of the present invention to provide an industrially advantageous method for producing a carbodiimide, which is capable of obtaining a reaction solution as a different solution phase and obtaining a powdery polycarbodiimide from the reaction solution.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have used an alicyclic ether as a reaction solvent in the condensation reaction and obtained the reaction solution and According to the method of precipitating a polymer by mixing a poor solvent having a lower boiling point than an alicyclic ether, the target powdery carbodiimide is easily obtained, and from the residual liquid from which the powdery carbodiimide is recovered, It was found that the active carbodiimidization catalyst can be easily recovered together with the reaction solvent by simply distilling off the poor solvent, and that the recovered catalyst and reaction solvent can be effectively recycled in the condensation reaction step. The present invention has been completed based on this.

Therefore, the gist of the present invention is as follows.
Aromatic diisocyanate, a reaction step of a condensation reaction in the presence of a carbodiimidization catalyst in an alicyclic ether solvent, a reaction solution obtained in this reaction step and a poor solvent having a lower boiling point than the alicyclic ether solvent are mixed And a precipitation step of precipitating polycarbodiimide, and a recovery step of recovering polycarbodiimide from the suspension obtained in this precipitation step, and distilling the poor solvent from the recovery residual liquid obtained from the recovery step. The residual liquid thus obtained is circulated and used in the above reaction step, which is a method for producing a polycarbodiimide.

The present invention will be described in detail below. In the reaction step of the production method according to the present invention, an aromatic diisocyanate is used as a raw material, which is subjected to a condensation reaction in an alicyclic ether solvent in the presence of a carbodiimidization catalyst to give a polycarbodiimide as a reaction product in a uniform liquid state. This is a step for obtaining a reaction solution contained as a phase. The reaction solution obtained in this step is treated in the subsequent precipitation step.

As the raw material aromatic diisocyanate that can be used in this reaction step, various compounds represented by the following general formulas (I) to (III) can be mentioned.

[0009]

[Chemical 2] [Wherein, X represents an oxygen atom or a methylene group, and R ¹ ,
R ² represents a hydrogen atom, a lower alkyl group or a lower alkoxy group. ]

[0010]

[Chemical 3] [In the formula, R ³ and R ⁴ represent a hydrogen atom, a lower alkyl group or a lower alkoxy group. ]

[0011]

[Chemical 4] [In the formula, R ⁵ represents a hydrogen atom, a lower alkyl group or a lower alkoxy group. ]

The above general formulas (I) to (II)
In I), the lower alkyl group has a carbon number of 1 to
6 straight-chain or branched alkyl groups,
The lower alkoxy group means a linear or branched alkoxy group having 1 to 6 carbon atoms. Examples of the compound represented by the general formula (I) include 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyl ether diisocyanate, and 3,3′-dimethyl-4,4′-diphenyl ether diisocyanate. Examples of the compound represented by the general formula (II) include 4,4′-biphenyl diisocyanate, and 3,3′-dimethyl-4,4′-biphenyl diisocyanate, which are represented by the general formula (III). Examples of compounds represented are 2,4-tolylene diisocyanate,
2,6-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, and the like can be mentioned. And the said aromatic diisocyanate can be used individually or as a mixture of 2 or more types. Among these, the compound represented by the above general formula (I) is preferable, and 4,4′-diphenylmethane diisocyanate is particularly preferable.

The solvent which can be used in the reaction step is an alicyclic ether, which is preferably a liquid at room temperature. Specific examples thereof include tetrahydrofuran, 1,4-dioxane,
Tetrahydropyran and the like can be mentioned, but among these, tetrahydrofuran is particularly preferable. The carbodiimidization catalyst that can be used in the reaction step is preferably phospholene oxide, and specific examples thereof include 1-phenyl-2-
Phosphorene-1-oxide, 3-methyl-2-phospholen-1-oxide, 1-ethyl-3-methyl-2-phospholen-1-oxide, 1-ethyl-2-phosphorene-
Examples thereof include 1-oxide, 3-methyl-1-phenyl-2-phospholen-1-oxide, and phospholene oxides of these 3-phosphorene isomers. These may be used alone or in combination of two or more. In the method of the present invention, in this reaction step, as the whole or a part of the alicyclic ether solvent and the carbodiimidization catalyst, a poor solvent mixed in the precipitation step described below from a recovery residual liquid obtained in the recovery step described below is used. It is necessary to recycle the residual liquid obtained by distilling off (see paragraph number [0025]).

Next, the reaction conditions in the reaction step will be described. The amount of the alicyclic ether solvent used is usually 200 to 1 with respect to 100 parts by weight of the raw material aromatic diisocyanate.
10,000 parts by weight, more preferably 500 to 2,
It is preferable to select in the range of 000 parts by weight. The amount of the carbodiimidization catalyst used is usually 50 to 5,000 ppm, preferably 100 to 3,000 ppm, based on the weight of the starting aromatic diisocyanate.

The reaction temperature is preferably selected in the range of 50 to 140 ° C, preferably 60 to 120 ° C. When the reaction temperature is lower than 50 ° C., the reaction time required to obtain a polycarbodiimide having a desired molecular weight becomes long and the productivity is deteriorated, which is not preferable. On the other hand, when the temperature exceeds 140 ° C, it becomes difficult to control the molecular weight of polycarbodiimide,
When it is remarkable, the entire reaction system may gel, or side reactions such as a crosslinking reaction may occur, which is not preferable.

The reaction pressure is not particularly limited as long as the reaction system can maintain the liquid phase, and is usually a reflux condition of the alicyclic ether solvent used, that is, a pressure equal to the vapor pressure of the solvent at the reaction temperature. Generally, the pressure may be higher than this. When making the reaction pressure higher than the vapor pressure of the alicyclic ether solvent at the reaction temperature,
It is preferable to use an inert gas such as nitrogen gas or argon gas. When the pressure of the reaction system rises above the carbon dioxide gas generated by the condensation reaction, it is preferable to purge this out of the reaction system and maintain the pressure of the reaction system constant.

The reaction solution obtained in the reaction step contains polycarbodiimide in approximately the same concentration as the aromatic diisocyanate used as the raw material. And 2 as raw material
When a mixture of organic diisocyanates consisting of more than one species is used, the polycarbodiimide formed by the condensation reaction has the corresponding repeating units.

The molecular weight of the above polycarbodiimide can be controlled by adjusting the reaction time and other reaction conditions. Generally, it is preferable to adjust the number average molecular weight (in terms of polystyrene) by GPC method (gel permeation chromatography) to be 5,000 to 30,000 as an index.

Further, when the condensation reaction is carried out in the reaction step, an inert gas such as nitrogen gas or argon gas is passed through the reaction system to purge the carbon dioxide gas generated with the progress of the condensation reaction out of the reaction system. As a result, the time required for the reaction can be shortened. The specific method of aeration is either a method of introducing an inert gas into the gas phase of the reaction system and purging it outside the reaction system, or a method of introducing it into the liquid phase and purging it outside the reaction system via the gas phase. Although it is good, a method is preferred in which a nitrogen gas, which is the same amount as or slightly larger than the amount of carbon dioxide gas generated by the reaction, is introduced into the liquid phase and then purged out of the reaction system through the gas phase. The aeration of the inert gas is preferably carried out continuously over the entire reaction period, but it is not always necessary to perform the reaction, and it may be intermittent.

The precipitation step of the production method according to the present invention is a step for precipitating polycarbodiimide in the reaction solution by mixing the reaction solution obtained in the above reaction step with a specific poor solvent. From the process, a suspension having polycarbodiimide as a solid phase is obtained. In this precipitation step, it is necessary to use a poor solvent having a lower boiling point than the alicyclic ether solvent used in the reaction step as the poor solvent mixed with the reaction solution. The suspension obtained in this step is treated in the subsequent recovery step.

The poor solvent that can be used in this precipitation step is not particularly limited as long as it can effectively precipitate the polycarbodiimide formed in the reaction solution and its boiling point satisfies the above requirements. . However, considering the easiness of the separating operation in the subsequent step of recovering the polycarbodiimide from the obtained suspension and then distilling the poor solvent component from the recovery residual liquid, the poor solvent to be used is It is preferable to select from those having a boiling point lower than that of the cyclic ether solvent by 10 ° C. or more. Specific examples of such a poor solvent include:
Examples thereof include methyl formate, diethyl ether, cyclopentane, acetone, dichloromethane, and a mixture thereof, all of which can be particularly preferably used when tetrahydrofuran is used as the alicyclic ether solvent in the reaction step.

The amount of the poor solvent used in this precipitation step is preferably as small as possible within the range in which the polycarbodiimide dissolved in the reaction solution can be precipitated in a good yield, and is usually based on the reaction solution. It is used in the range of 1 to 3 times the volume. If the amount of the poor solvent to be mixed is too small, the precipitation of polycarbodiimide will be insufficient, and conversely if it is too large, the yield of polycarbodiimide cannot be increased,
This is not preferable because it only increases the processing volume in this step and the subsequent recovery step. The method of mixing the reaction solution and the poor solvent in the precipitation step may be the method of adding the poor solvent to the whole amount of the reaction solution, or the method of adding the reaction solution to the whole amount of the poor solvent, or the total amount of the reaction solution and the poor solvent. It may be carried out by any method such as a method of combining with the total amount of the solvent, and is not particularly limited.

In this precipitation step, a method is used in which the total amount of either the poor solvent or the reaction solution is stirred according to a conventional method, while the other, that is, the reaction solution or the poor solvent is added continuously or intermittently. Is common, but at this time,
When the reaction solution or the poor solvent is continuously added little by little,
Polycarbodiimide can be deposited as a solid phase in the form of uniform granules, which is preferable. From the suspension in which polycarbodiimide is deposited in a uniform granular form, not only polycarbodiimide can be easily recovered by the solid-liquid separation operation, but also by drying the filter cake and the like obtained by this separation operation, A powdery polycarbodiimide can be easily obtained, which is preferable. The preferable addition rate of the reaction solution or the poor solvent varies depending on various conditions such as stirring conditions, handling volume, temperature and the like in this step, and is set individually according to these conditions.

The recovery step of the production method according to the present invention is a step for recovering polycarbodiimide dispersed as a solid phase from the suspension obtained in the precipitation step, and from the recovery step, At the same time, a recovery residual liquid which is a liquid component of the suspension is obtained. The method for recovering the polycarbodiimide from the suspension obtained in the precipitation step and obtaining the recovery residual liquid is not particularly limited, and a conventionally known solid-liquid separation method can be used. Specific examples include filtration separation such as pressure filtration, vacuum filtration and centrifugal filtration, and sedimentation separation. Usually, it is preferable to collect the polycarbodiimide as a cake by filtration and obtain the residual liquid as a filtrate. The powdery polycarbodiimide can be easily obtained by drying the cake. The recovery residual liquid obtained in this step is mainly an alicyclic ether solvent from the reaction step,
It consists of a carbodiimidization catalyst, a small amount of low molecular weight polycarbodiimide, and a poor solvent mixed in the precipitation step.

In the method of the present invention, it is indispensable to distill the poor solvent which is a low boiling point component from the recovery residual liquid obtained in the above recovery process and circulate and use the residual liquid in the reaction process. . Evaporation of the poor solvent can be easily carried out by ordinary distillation methods such as atmospheric distillation and vacuum distillation.
By distilling off the poor solvent, an alicyclic ether solvent containing a carbodiimidization catalyst and a small amount of a low molecular weight polycarbodiimide can be obtained as a residual liquid (distiller residue, etc.). Since the carbodiimidization catalyst in this distillation residual liquid retains sufficient catalytic activity, it can be circulated in the reaction step together with the alicyclic ether solvent. In the method of the present invention, it is most preferable to circulate and use all of the distillation residual liquid, but when impurities accumulate due to repeated circulation, a part of the distillation residual liquid is purged to remove impurities from the reaction system. The residue will be removed, the residue will be recycled, and the deficiency will be supplemented by the addition of a new alicyclic ether solvent, a carbodiimidization catalyst.

According to the method of the present invention, the distillate residual liquid is circulated in the reaction step, so that the amount of the carbodiimidization catalyst and the alicyclic ether solvent used in the reaction step can be significantly increased as compared with the case where the distillate is not circulated. In addition to being able to reduce the amount, the low molecular weight polycarbodiimide, which was not precipitated in the precipitation step and was dissolved in the recovery residual liquid, can be reused as one of the reaction raw materials in the reaction step. The poor solvent distilled from the recovery residual liquid can also be circulated and used in the precipitation step, and a little alicyclic ether solvent may be mixed therein.

[0027]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the examples described below as long as the gist thereof is not exceeded. In each of the following examples, the number average molecular weight (polystyrene conversion) of polycarbodiimide was measured by gel permeation chromatography.

Example 1 [First Production] 2 equipped with a stirrer and a reflux condenser
In a liter three-necked flask, 100 g of 4,4′-diphenylmethane diisocyanate (hereinafter abbreviated as “MDI”) and tetrahydrofuran (hereinafter, “TH
Abbreviated as "F". ) 560 g, and 3-methyl-1-
Phenyl-2-phosphorene-1-oxide (carbodiimidization catalyst, abbreviated as "MPPO" hereinafter) 0.2
00 g (2000 ppm relative to the weight of MDI) was charged and reacted at a temperature of 67 ° C. (under reflux of THF) for 6 hours to obtain a reaction solution. The number average molecular weight of the polycarbodiimide in this reaction solution (in terms of polystyrene, the same applies hereinafter) was 8,700. Then, to the above reaction solution, 40
While stirring at a rotation speed of 0 rpm, methyl formate 1359
g (1400 ml) was continuously added dropwise over 200 minutes at a constant rate to obtain a polycarbodiimide-precipitated suspension, which was suction filtered to separate a filter cake and a filtrate. Then, the filter cake was dried under reduced pressure to obtain 66 g of white granular polycarbodiimide powder. Next, the filtrate obtained as described above was transferred to a 5-liter flask equipped with a stirrer and a 10-stage Oldershaw type distillation column, and this was subjected to atmospheric distillation to obtain 1310 g of methyl formate from the top of the column. Was recovered. When this was analyzed by gas chromatography, the purity of the recovered methyl formate was 97% by weight. Further, 508 g of a distillate residual liquid (pot residue) was recovered from the atmospheric distillation, and the purity of THF was 96% by weight when analyzed by gas chromatography.

[Second Production] In the flask used in the first production, 100 g of MDI, and 508 g of the distillate residual liquid recovered from the first production and 72 wt.
A mixed liquid with g (THF content is 560 g) was charged,
The reaction was carried out at a temperature of 67 ° C. (under reflux of THF) for 6 hours,
A reaction solution was obtained. The number average molecular weight of polycarbodiimide in this reaction solution was 8,620. Then, while stirring the above reaction solution at a rotation speed of 400 rpm, a mixed poor solvent of methyl formate 1310 g recovered from the first production and new methyl formate (total amount of methyl formate 1359 g) was added. It took 200 minutes to continuously drop the solution at a constant rate to obtain a polycarbodiimide-precipitated suspension. The suspension was suction-filtered to separate a filter cake and a filtrate. By drying under reduced pressure, 75 g of white granular polycarbodiimide powder was obtained.

Example 2 [First Production] In the example described in Example 1, diethyl ether (999 g, 1400) was used in place of methyl formate.
ml) was used, and a polycarbodiimide-precipitated suspension was obtained in the same manner as in the same example, and this suspension was treated in the same manner as in the same example to give 68 g of white granular polycarbodiimide powder. , And a filtrate were obtained. Next, the filtrate obtained as described above was subjected to atmospheric distillation in the same manner as in Example 1 to obtain diethyl ether 9 having a purity of 97% by weight.
68 g and 501 g of a distillate residual liquid (pot residue) having a THF purity of 95% by weight were recovered.

[Second Production] The flask used in the first production was charged with 100 g of MDI, 501 g of the distillation residue recovered from the first production, and a new THF 84.
A mixed liquid with g (THF content is 560 g) was charged,
The reaction was carried out at a temperature of 67 ° C. (under reflux of THF) for 6 hours,
A reaction solution was obtained. The number average molecular weight of polycarbodiimide in this reaction solution was 8,510. Then, while stirring the above reaction solution at a rotation speed of 400 rpm, 968 g of diethyl ether recovered from the first production
And a novel diethyl ether mixed poor solvent (total amount of diethyl ether is 999 g) was continuously added dropwise at a constant rate over 200 minutes to obtain a suspension in which polycarbodiimide was precipitated. The suspension was suction filtered to separate it into a filter cake and a filtrate, and the filter cake was dried under reduced pressure to obtain 76 g of white granular polycarbodiimide powder.

According to each of the above-mentioned examples, in the production method of the present invention, in the second and subsequent production steps, the reaction solvent recovered from the previous production step and the carbodiimidization catalyst recovered at the same time, and It is clear that the poor solvent can be effectively recycled.

[0033]

EFFECTS OF THE INVENTION According to the production method of the present invention, the reaction solvent used in the reaction step, the carbodiimidization catalyst, and the poor solvent used in the precipitation step are effectively used by effectively utilizing the recovery residual liquid obtained by recovering the polycarbodiimide. Since the amount can be significantly reduced and the amount of the raw material aromatic diisocyanate used can also be reduced, there is a remarkable effect that a powdery polycarbodiimide can be industrially advantageously produced.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ken Takeuchi, 1st Toho-cho, Yokkaichi-shi, Mie Mitsubishi Kasei Co., Ltd. Yokkaichi factory (72) Inventor Satoshi Amano 1-1-18-1, Nishiarai-eicho, Adachi-ku, Tokyo Nisshinbo The Tokyo Research Center

Claims (5)

[Claims] 1. A reaction step of subjecting an aromatic diisocyanate to a condensation reaction in an alicyclic ether solvent in the presence of a carbodiimidization catalyst, the reaction solution obtained in this reaction step having a boiling point higher than that of the alicyclic ether solvent. A precipitation step of mixing a low poor solvent to precipitate polycarbodiimide, and a recovery step of recovering polycarbodiimide from the suspension obtained in this precipitation step, and the recovery residual liquid obtained from the recovery step A method for producing a polycarbodiimide, characterized in that the residual liquid obtained by distilling the poor solvent is reused in the reaction step. 2. The production of polycarbodiimide according to claim 1, wherein the poor solvent distilled from the recovery residual liquid obtained in the recovery step is recovered, and the poor solvent is circulated in the precipitation step. Method. 3. The method for producing a polycarbodiimide according to claim 1 or 2, wherein the aromatic diisocyanate is a compound represented by the following general formula (I). [Chemical 1] [Wherein, X represents an oxygen atom or a methylene group, and R ¹ ,
R ² represents a hydrogen atom, a lower alkyl group or a lower alkoxy group. ] 4. The method for producing a polycarbodiimide according to claim 1, wherein the alicyclic ether solvent is tetrahydrofuran and the poor solvent is methyl formate. 5. The method for producing a polycarbodiimide according to any one of claims 1 to 3, wherein the alicyclic ether solvent is tetrahydrofuran and the poor solvent is diethyl ether.