JP2003261677A - Polyamide prepolymer and method for producing polyamide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To industrially advantageously produce a polyamide of high quality at a low cost which reduces the content of caprolactam and the content of polyamide oligomers in the method for producing the polyamide by using recovered lactams as the raw material or the part of the raw material. <P>SOLUTION: The method for producing a polyamide comprises polymerizing recovered lactams to be obtained by melt volatilization as the part of the raw material or the entire raw material, and the method for producing a polyamide comprises adding 2 mmol to 500 mmol, based on 1 g of the raw material composition, carboxylic acid to the raw material partially or entirely having recovered lactams to be obtained by melt volatilization to treat the resulting mixture under pressure at 200-330°C for 1-60 min to produce a polyamide prepolymer, and then polymerizing the prepolymer to produce a polyamide. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing polyamide using caprolactam as a main raw material. More specifically, in a polyamide produced using caprolactam as a main raw material, unreacted caprolactam and a by-produced polyamide oligomer can be reused, resulting in a high yield,
It relates to a method for producing polyamide with low energy.

[0002]

2. Description of the Related Art Polyamides containing caprolactam as a main raw material are used for textile fibers and industrial fibers by taking advantage of their excellent properties. Furthermore, they are used as injection molded products in automobile fields, electric / electronic fields, etc., and as food products. It is widely used as an extruded film and a stretched film mainly for packaging applications.

Polyamides containing caprolactam as a main raw material are usually produced by heating and melt-polymerizing caprolactam in the presence of a small amount of water. This manufacturing method is a relatively simple process and is widely adopted in the world. An outline of a general-purpose polyamide polymerization method described in items 63 to 65 of "Polyamide Resin Handbook" (edited by Osamu Fukumoto, Nikkan Kogyo Shimbun) is described below.

[0004] Caprolactam was melted and supplied to an atmospheric pressure polymerization tower heated to about 260 ° C, and after staying for about 10 hours in this polymerization tower, it was made into a strand form from the lower part of the tower and discharged into a water tank to be pelletized. It Since the polyamide resin pellets thus obtained contain the caprolactam monomer and the polyamide oligomer generated in the equilibrium of the polymerization,
If it is used as a product in this state, the monomers and oligomers volatilize during the molding process, causing stains on the spinneret, thread breakage, and appearance defects when obtaining the final product such as fibers, films, and injection molded products. It causes many problems such as deterioration of mechanical properties and appearance. Therefore, it is necessary to remove these monomers and oligomers in the polyamide containing caproamide as the main raw material. As a method for removing monomers and oligomers, pellets immediately after polymerization are supplied to a hot water extraction tower and subjected to countercurrent extraction with hot water sent from the lower part of the tower, and then the hot water extraction method taken out from the lower part and removal of monomers and oligomers. Examples of the method include a method in which the polyamide after polymerization is treated in a molten state at high temperature and high vacuum (US Pat. No. 3,558,567 etc.).

[0005]

As described above, in the process of polymerizing a polyamide containing caprolactam as a main component, an unreacted monomer and a polyamide oligomer are present, and a process for removing them is essential. As a method of effectively utilizing the recovered lactam, which is a component from which it has been removed, studies are being made to use these as all or part of the raw material for polyamide polymerization. However, when the polyamide oligomer is used as it is as a raw material for polymerization without being removed, the amount of polyamide oligomer after polymerization is larger than that in the case of performing polymerization using only caprolactam as a raw material, and removal of monomers and polyamide oligomers such as hot water extraction. This leads to a reduction in process efficiency and polymer quality. Therefore, it is necessary to separate and purify only caprolactam from the recovered lactam by distillation or the like for polymerization, but enormous energy is required for this recovery / purification process.

Regarding a method of depolymerizing the recovered lactam to convert it into a monomer caprolactam for reuse, US Pat. No. 6,093,788 discloses that recovered lactam is obtained by adding phosphoric acid as a catalyst to the recovered lactam and heating it with steam. There has been proposed a method for improving the recovery rate of caprolactam by hydrolyzing the polyamide oligomer therein to regenerate it into caprolactam. However, this method has a problem in that the process is complicated and phosphoric acid may be mixed in the raw material to deteriorate the quality of the produced polymer.

Regarding the method of using the recovered lactam as a raw material for polymerization, Japanese Patent Publication No. 9-188758 describes a method of concentrating a dilute solution of recovered lactam recovered by hot water extraction and supplying it to a polymerization apparatus. , Water content of 92 to 10% by weight of the extract solution 1.3 to 10
It is industrially disadvantageous because it requires a huge amount of energy because it needs to be concentrated to a weight percentage.

Therefore, there has been a demand for the development of a method for producing a polyamide which uses recovered lactam and consumes little energy and has high productivity.

That is, in the method for producing a polyamide using the recovered lactam as a raw material or a part of the raw material as described above, a high-quality polyamide having a low content of caprolactam (monomer) and a low content of polyamide oligomer in the produced polyamide is used. A method that can be manufactured at low cost has hitherto been unknown.

[0010] Therefore, the present inventors intend to solve the above-mentioned problems of the prior art, and to provide a method for industrially advantageously producing a polyamide having a low polyamide oligomer content, which uses a recovered lactam. To do.

[0011]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that the recovered lactam is heat-treated at a specific temperature for a short time by adding carboxylic acid, under pressure, By hydrolyzing the cyclic oligomer to produce a polyamide prepolymer having many amino end groups and a small cyclic polyamide oligomer content, and further polymerizing the polyamide prepolymer, both the monomer content and the polyamide oligomer content in the produced polymer are The inventors have found that low polyamides can be produced and have reached the present invention.

That is, according to the present invention, (1) a carboxylic acid is added to a raw material composition obtained by melting and volatilizing a part or all of the recovered lactam, and 1 g of the raw material composition
2mmol-500mmol is added to the above and treated at 180-330C under pressure for 1-60 minutes.

(2) The method for producing a polyamide prepolymer according to (1) above, wherein the recovered lactam is used in an amount of 1 to 20% by weight based on the total raw material composition.

(3) Water content is 10 to 5 relative to the total raw material composition.
The method for producing the polyamide prepolymer according to any one of (1) and (2) above, wherein the content is 0% by weight.

(4) The method for producing a polyamide prepolymer according to any one of (1) to (3) above, wherein the melt volatilization is melt volatilization using an extruder.

(5) The method for producing a polyamide prepolymer according to the above (4), wherein the extruder is a vented twin-screw extruder.

(6) The carboxylic acid is a monocarboxylic acid or a dicarboxylic acid, and the above (1) to
(5) The method for producing a polyamide prepolymer according to any one of the items.

(7) The method for producing a polyamide prepolymer according to (6) above, wherein the dicarboxylic acid is terephthalic acid or adipic acid.

(8) The method for producing a polyamide prepolymer as described in (6) above, wherein the monocarboxylic acid is acetic acid or benzoic acid.

(9) The method for producing a polyamide prepolymer according to any one of the above (1) to (8), wherein the amount of amino terminal groups of the polyamide prepolymer is 0.1 mmol or more per 1 g of the raw material composition. .

(10) A carboxylic acid is added in an amount of 2 mmol to 500 mmol to 1 g of the raw material composition to the raw material composition obtained by melt volatilization and containing a part or all of the recovered lactam, and 1 to 1 at 180 to 330 ° C. under pressure. A method for producing a polyamide, which comprises treating for 60 minutes to produce a polyamide prepolymer and then polymerizing a reaction product containing the polyamide prepolymer.

(11) The method for producing a polyamide according to the above (10), wherein the recovered lactam is used in an amount of 1 to 20% by weight based on 100% by weight of the total raw material composition.

(12) The method for producing a polyamide according to (10) or (11) above, wherein the amount of amino terminal groups of the polyamide prepolymer is 0.1 mmol or more per 1 g of the raw material composition.

(13) The method for producing a polyamide according to any one of (10) to (12) above, wherein the content of cyclic oligomer in the polyamide prepolymer is 1.6% by weight or less.

(14) The above-mentioned (10) to (1), wherein the polymerization of the polyamide prepolymer is pressureless polymerization.
3) The method for producing a polyamide according to any one of the above.

(15) The maximum temperature reached in atmospheric polymerization is 180
℃ or more and 222 ℃ or less above (1
The method for producing a polyamide according to any one of 0) to (14).

(16) The reaction product containing the polyamide prepolymer is flushed at the inlet of the atmospheric pressure polymerization apparatus before the atmospheric pressure polymerization apparatus for carrying out the atmospheric pressure polymerization of the polyamide prepolymer to evaporate and remove water. (15) The method for producing a polyamide according to any one of (15). It is composed of

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below.

In the method for producing a polyamide of the present invention, the recovered lactam is used as a part or all of the raw material. The recovered lactam refers to a mixture containing an unreacted monomer recovered in the polyamide production step and at least one of a polyamide chain oligomer and a polyamide cyclic oligomer.

The recovered lactam of the present invention is a recovered lactam recovered from a polyamide containing unreacted monomers and a polyamide oligomer by melt volatilization. Melt volatilization is a method in which a polymerization product containing unreacted monomers and a polyamide oligomer is melted by an extruder or a thin film evaporator and heated under reduced pressure to remove the unreacted raw material and the polyamide oligomer. Although there is a method of using an extruder or a thin film evaporator for melt volatilization, an extruder is preferable, and a twin-screw extruder with a vent connected to a vacuum system is particularly preferable. Volatilization removal in this molten state, after the polymerization reaction product into a solid such as pellets,
It may be melted and heated under reduced pressure in an extruder or thin film evaporator, and the molten polymerization reaction product discharged from the polymerization tower is directly supplied to the extruder or thin film evaporator for melt volatilization. May be.

The cyclic oligomer content in the recovered lactam in the present invention is quantified by analyzing the methanol solution of the recovered lactam by high performance liquid chromatography.

The raw material used in the method for producing a polyamide prepolymer of the present invention is mainly composed of caprolactam,
One kind or two or more kinds of other lactams may be used in combination within a range not exceeding 20 mol% of the total amount of the monomers as long as the object of the invention is not impaired. In order to maintain the crystallinity of polyamide, it is desirable that the content of other lactam is 20 mol% or less.

Specific examples of such lactams include valerolactam, enanthlactam, capryllactam, undecalactam, laurolactam and the like, among which undecaractam and laurolactam are preferable.

The ratio of the recovered lactam used as a part or all of the raw materials in the present invention is not limited as long as the recovered lactam is used, but preferably 1 to 20 when the total raw material composition is 100%. %, More preferably 2 to 15% by weight.

Since the recovered lactam is used in the method for producing a polyamide of the present invention, the polyamide prepolymer used for the polymerization is a mixture of lactam and polyamide oligomer. Here, the polyamide oligomer is a mixture of a cyclic oligomer and a linear oligomer of polyamide. The amount of polyamide oligomer in the raw material composition is 80
It is quantified by the residual amount obtained after vacuum drying at 8 ° C. for 8 hours. The preferable composition of the raw material is 45 to 89.99% by weight of lactam, based on 100% by weight of the entire raw material.
The content of the polyamide oligomer is 0.01 to 5% by weight,
Is. Further, it is preferable that the raw material contains water, and the amount is 1 to 50% by weight based on 100% by weight of the entire raw material.
Is.

The reaction product after the heat treatment of the present invention contains water and a polyamide prepolymer. The polyamide prepolymer is a composition obtained by heat-treating a polyamide raw material, and refers to a mixture of polyamide chain oligomers having amino terminal groups, cyclic oligomers, and unreacted caprolactam. Among these, a polyamide prepolymer having a small amount of cyclic oligomer is particularly preferable because the polyamide oligomer content in the polyamide produced after the polymerization reaction is small.

The method of preparing the polyamide prepolymer requires a method of performing heat treatment under pressure in the presence of a carboxylic acid compound. The pressure is not particularly limited as long as it is under pressure, but the range of 0.111 to 6.08 MPa is preferable, and the range of 0.152 to 5.065 MPa is more preferable. The pressure is preferably 1.1 MPa or more in order to suppress the amount of cyclic oligomer generated during prepolymerization and improve the amino group generation efficiency. On the other hand, when it exceeds 6.08 MPa, it is not preferable in terms of productivity and economical efficiency.

The processing temperature for preparing the polyamide prepolymer of the present invention is 180 to 330 ° C. The lower limit is preferably 200 ° C. or higher, and the upper limit is preferably 300 ° C. or lower. If the temperature is lower than 180 ° C, the content of the cyclic oligomer at the time when the necessary amino group is obtained is large, and if the temperature exceeds 330 ° C, it is difficult to control the amount of the amino group in the reaction product and the industrial stability is lacking. .

The processing time for preparing the polyamide prepolymer of the present invention is 1 to 60 minutes, and the upper limit is preferably 45 minutes or less, particularly preferably 40 minutes or less. If it exceeds 60 minutes, the cyclic oligomer content in the polyamide prepolymer increases, which is not preferable.
This is because if it is less than the minute, the amino group content fluctuates, and it becomes difficult to control the degree of polymerization of the polyamide in the polymerization step.

The carboxylic acid compound used when preparing the polyamide prepolymer of the present invention is not limited as long as it is a carboxylic acid that does not impair the polymer properties such as coloring and gelation, but a monocarboxylic acid or a dicarboxylic acid is used. It is preferable.

Examples of the monocarboxylic acid compound used in the present invention include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, myristolein. Aliphatic monocarboxylic acids such as acids, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, cycloaliphatic monocarboxylic acids such as cyclohexanecarboxylic acid and methylcyclohexanecarboxylic acid, toluic acid benzoic acid And aromatic monocarboxylic acids such as ethylbenzoic acid, naphthalenecarboxylic acid, anthracenecarboxylic acid, and phenylacetic acid. Of these, acetic acid and benzoic acid are preferable.

Examples of the dicarboxylic acid used in the present invention include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, Aliphatic dicarboxylic acids such as tetradecanedioic acid, pentadecanedioic acid and octadecanedioic acid, aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid and anthracene dicarboxylic acid. Of these, adipic acid and terephthalic acid are preferred.

The amount of the carboxylic acid compound used in the present invention may be an amount necessary to promote the hydrolysis of the cyclic oligomer and promote the consumption of the oligomer, but 2 mmol to 500 mmol per 1 g of the raw material composition is used. It is necessary to be in the range, preferably 3 mmol to 300
It is in the range of mmol, more preferably 4 mmol to 1
It is in the range of 00 mmol.

The method of adding the carboxylic acid used in the present invention is not particularly limited, and a method of blowing carboxylic acid vapor into the heat treatment apparatus can be applied, but the method of adding it as an aqueous solution to the raw material is industrially advantageous.

The amount of amino terminal groups of the polyamide prepolymer of the present invention is determined from the viewpoint of effectively reducing the oligomer content in the polyamide when producing a polyamide from the obtained polyamide preblend polymer. It is preferably 0.1 mmol or more, more preferably 0.15 mmol or more, and particularly preferably 0.2 mmol or more based on 1 g of the product. Although there is no upper limit to the amount of amino groups, it is usually adopted in the range of 1.0 mmol or less in terms of productivity.

The amount of amino terminal groups of the polyamide prepolymer is determined by dissolving the polyamide prepolymer in a phenol ethanol solution and then titrating it with an aqueous hydrochloric acid solution.

The content of the cyclic oligomer in the polyamide prepolymer is 1. From the viewpoint of effectively reducing the content of the oligomer in the polyamide when producing a polyamide from the obtained polyamide preblend polymer. It is preferably 6% by weight or less, more preferably 1.0% by weight or less, and particularly preferably 0.6% by weight.
It is the following. The lower limit of the cyclic oligomer content is not particularly limited, but is usually 0.01% by weight.

The cyclic oligomer content in the polyamide prepolymer in the present invention is quantified by extracting the polyamide prepolymer with methanol and analyzing the extract by high performance liquid chromatography.

In the method for producing a polyamide in the present invention, caprolactam can be further added to the prepolymer at the start of the polymerization for polymerization. The additional amount of caprolactam is preferably such that the amount of amino groups in the raw material composition comprising the polyamide prepolymer and the additional caprolactam is 0.1 mmol or more per 1 g of the raw material composition.

In the method for producing a polyamide of the present invention, it is also a preferable method to produce a polyamide prepolymer and then polymerize the polyamide prepolymer to produce a polyamide.

In the method for producing polyamide of the present invention, the polymerization apparatus used is not particularly limited, and an apparatus generally used for polymerization of caprolactam can be used. Specific examples thereof include liquid layer polymerization apparatuses such as a continuous atmospheric polymerization apparatus, a pressure polymerization apparatus, and a batch polymerization apparatus. Of these, a continuous atmospheric polymerization apparatus is preferable from the viewpoint of productivity.

In the method for producing a polyamide of the present invention, the maximum value of the polymerization temperature is the melting point of the obtained polyamide + 1
It is preferable to polymerize under a temperature condition of 0 ° C. or lower,
Particularly, the temperature condition of 222 ° C. or lower is preferable. When the maximum temperature reached during the polymerization is higher than the melting point of the polyamide + 10 ° C, the content of the polyamide oligomer increases, and when the polymerization temperature is too low, the time required for the polymerization increases and the production efficiency decreases. Therefore, the polymerization temperature is preferably 160 to 232 ° C, more preferably 170 to 222 ° C, particularly preferably 180 to 220 ° C.
The melting point is obtained by removing caprolactam, polyamide oligomer and the like from the obtained polyamide by hot water extraction,
It is defined as the peak top temperature of the endothermic peak based on crystal melting measured by a differential scanning calorimeter (DSC) at a temperature rising rate of 20 ° C./min using a sample obtained by melting the polyamide and then quenching.

If the above conditions are satisfied, the polymerization temperature profile can be arbitrarily set according to a conventional method. In the method for producing a polyamide of the present invention, the polymerization time is usually within 20 hours.

In the method for producing a polyamide polymer of the present invention, when the reaction product containing the water and the polyamide prepolymer obtained by the heat treatment under pressure is fed to the atmospheric pressure polymerization apparatus, the reaction product after the heat treatment under pressure is usually treated. A method of flashing the inlet of the pressure polymerization device to remove water by evaporation is preferably used. Flushing is to discharge a low boiling point component by discharging a reactant placed under heating and pressurization into a container whose pressure is kept low. By evaporating and removing water, the amount of heat required for heating when producing a polyamide can be reduced, and the polymerization temperature control can be facilitated. At this time, it is preferable that the water content in the reaction product after water removal by flashing is small, and it is preferable that the water content is 4% or less.

The degree of polymerization of the polyamide obtained by the method for producing a polyamide of the present invention has a sample concentration of 0.01 g / mL.
The relative viscosity of a 98% sulfuric acid solution of
It is desirable that it is 2.2 to 8.0. Further, it is preferably 2.2 to 7.0, particularly preferably 2.2 to 6.5, and most preferably 2.2 to 6.0. The relative viscosity is preferably 2.2 or more in order to exhibit mechanical properties, and is preferably 8.0 or less in terms of easiness of molding.

The polyamide obtained by the method for producing a polyamide of the present invention has a melting point lower than that of the polyamide so as to obtain a suitable viscosity for applications such as extrusion molding where the polyamide is required to have a high viscosity. It is preferable to adjust to a desired degree of polymerization by solid-state polymerization in which heat treatment is performed under reduced pressure or an inert gas atmosphere at a temperature.

The production method of the present invention includes, for example, antioxidants and low heat stabilizers (hindered phenol type, hydroquinone type, phosphite type and their substitution products, copper halides, chromium salts, manganese salts) depending on the use. , Iodine compounds, etc.), weathering agents (resorcinol-based, benzotriazole-based, benzophenone-based, hindered amine-based, etc.), release agents and lubricants (aliphatic alcohols, aliphatic amides, aliphatic bisamides, bisurea and polyethylene wax) , Pigments (cadmium sulfide, phthalocyanine,
Carbon black), dyes (nigrosine, aniline black, etc.), crystal nucleating agents (talc, silica, kaolin, clay, etc.), plasticizers (octyl p-oxybenzoate, N-)
Butylbenzenesulfonamide, etc., antistatic agents (alkyl sulfate type anionic antistatic agents, quaternary ammonium salt type cationic antistatic agents, nonionic antistatic agents such as polyoxyethylene sorbitan monostearate, betaine type) Amphoteric antistatic agents, etc., flame retardants (hydramines such as melamine cyanurate, magnesium hydroxide, aluminum hydroxide, ammonium polyphosphate, brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate, brominated epoxy resin or Combinations of these brominated flame retardants with antimony trioxide), fillers (graphite, barium sulfate, magnesium sulfate, calcium carbonate, magnesium carbonate, antimony oxide, titanium oxide, aluminum oxide, zinc oxide,
Iron oxide, zinc sulfide, zinc, lead, nickel, aluminum, copper, iron, stainless steel, glass fiber, carbon fiber, aramid fiber, bentonite, montmorillonite, synthetic mica particles, fibrous, needle-like, plate-like filler) , Other polymers (other polyamide, polyethylene, polypropylene, polyester, polycarbonate, polyphenylene, polyphenylene sulfide, liquid crystal polymer, polysulfone, polyether sulfone, ABS resin, SAN resin, polystyrene, etc.) may be added at any time. it can.

The polyamide obtained by the production method of the present invention can be formed into a molded product by a usual molding method, like conventional polyamides. The molding method is not particularly limited, and known methods such as injection molding, extrusion molding, blow molding, and pressing can be used. The term "molded product" as used herein includes molded products in a narrow sense such as injection molding, as well as shaped products such as fibers, films, sheets, tubes, and monofilaments.

[0059]

EXAMPLES The present invention will be specifically described with reference to the following examples. The analysis and measurement described in Examples and Comparative Examples were performed according to the following methods.

(1) Amount of amino end group in polyamide prepolymer About 0.2 g of the substance to be measured was precisely weighed and dissolved in 25 cc of phenol-ethanol mixed solvent (83.5: 16.5, volume ratio). Titrated with 0.02N hydrochloric acid solution.

(2) Content of Cyclic Oligomer in Polyamide Prepolymer The object to be measured is crushed and passed through JIS standard sieve 24 mesh, and 124 mesh does not pass, the object powder is collected, and 20 g of the powder is added to 200 mL of methanol. Was extracted for 3 hours using a Soxhlet extractor, and the cyclic oligomer contained in the extract was quantified using a high performance liquid chromatograph. In the following examples, no cyclic oligomer of 7-mer or more was observed. The measurement conditions are as follows. High Performance Liquid Chromatography: Waters 6
00E Column: GL Science ODS-3 Detector: Waters 484 Tunable Absorbanse Det
Detection wavelength: 254 nm Injection volume: 10 μL Solvent: Methanol / water (Methanol water composition is 20: 8)
Gradient analysis of 0 → 80: 20) Flow rate: 1 mL / min.

(3) Water content of polyamide prepolymer It measured using the Hiranuma trace water content measuring device AQ-6.

(4) Caprolactam polyamide in polyamide was crushed and passed through JIS standard sieve 24mesh, 124mesh was not passed, powders of the measured substance were collected, and 20g of the powder was collected in 200 mL of methanol for 3 hours with a Soxhlet extractor. Was extracted, and caprolactam contained in the extract was quantified using a high performance liquid chromatograph. The measurement conditions are as follows. High Performance Liquid Chromatography: Waters 600E Column: GL Sciences ODS-3 Detector: Waters 484 Tunable Absorbanse Det
Detection wavelength: 254 nm Injection volume: 10 μL Solvent: Methanol / water (20:80 (volume ratio)) Flow rate: 1 mL / min.

(5) Polyamide oligomer content in polyamide Polymerization reaction product was crushed and passed through JIS standard sieve 24 mesh, 124 mesh was not passed. Extraction time using Soxhlet extractor, quantifying the amount of caprolactam contained in the extract by the above method, evaporating to dryness with an evaporator and further vacuum drying at 80 ° C / 8 hours, the residual amount obtained Was calculated, and the amount of caprolactam obtained in the item (4) was subtracted to obtain the polyamide oligomer content.

(6) Sulfuric Acid Relative Viscosity (ηr) The concentration was measured in 98% sulfuric acid at a concentration of 0.01 g / L at 25 ° C. using an Ostwald viscometer.

A. Raw material recovery lactam Caprolactam is obtained by melting a special grade reagent of Tokyo Kasei Kogyo Co., Ltd. and drying it with molecular sieves. This caprolactam is polymerized by heating at 197 ° C for 7 hours and 220 ° C for 4 hours, and then the polymerization reaction. The product was melted and volatilized under the following conditions using a twin-screw extruder with a 30 mmφ vent made by Japan Steel Works, Ltd. in which a trap was provided at the vent portion, and a mixture of caprolactam and polyamide oligomer trapped in the trap was used. The composition of the melt-recovered lactam was 97% by weight of caprolactam and 3% by weight of polyamide oligomer.

Conditions for melt volatilization: L / D = 45.5, rotation in the same direction, deep groove type, barrel temperature: temperature from the raw material supply side is 160/240
/ 250/260/260/260/260/250 /
250 ° C ・ Decompressed deaeration at 133 Pa (1 Torr) from the 2nd, 4th, and 6th zones ・ 200 rpm.

Example 1 The recovered lactam was treated in the flow reactor shown in FIG. The recovered lactam and water were put into the storage tank of 1, the carboxylic acid shown in Table 1 was added, the pressure of the pump of 2 was applied to the reaction vessel of 4, and the reaction product containing the polyamide prepolymer was obtained from the valve of 5. . The pressure was adjusted with the valve of 6 and confirmed with the pressure gauge of 3. Heat treatment was performed under the conditions shown in Table 1 to obtain a polyamide prepolymer. Examples 2 to 5 In the same manner as in Example 1, the carboxylic acid and conditions shown in Table 1 were adjusted and heat treatment was performed to obtain a polyamide prepolymer.

Comparative Example 1 Heat treatment was carried out in the same manner as in the example without adding carboxylic acid to the raw material.

Comparative Example 2 The heat treatment was carried out in the same manner as in the example except that the treatment temperature was lowered to 120 ° C.

Comparative Example 3 1 mol% (1000 mmol%) of benzoic acid was added to the raw material and heat treatment was performed.

Comparative Example 4 A treatment was performed using only the caprolactam used in Example 1 under the conditions shown in Table 1 to obtain a polyamide prepolymer.

[0073]

[Table 1] In Examples 1 to 6 and Comparative Example 1, prepolymers having a low oligomer content were obtained in a short treatment time. In addition, the temperature of Comparative Example 2, the amount of benzoic acid added in Comparative Example 3, the heat treatment time of Comparative Example 4, and the like increase the amount of cyclic oligomers in the polyamide prepolymer, and the reaction does not proceed, resulting in high efficiency and low cost. It can be seen that no polyamide prepolymer can be obtained.

As can be seen in Examples 1-5 using melt recovered lactam and Comparative Example 4 using only caprolactam,
In the production method of the present invention, it was found that a polyamide having a low polyamide oligomer content can be obtained with high efficiency and low energy even if a recovered lactam is used.

Examples 6 to 8 and Comparative Examples 5 to 8 The polyamide prepolymers shown in Examples 1, 2 and 5 and Comparative Examples 1, 3 and 4, or caprolactam were subjected to atmospheric polymerization. In the same manner as in Example 1, the recovered lactam and water were put into the storage tank 1 of the apparatus shown in FIG. 1, the carboxylic acid shown in Table 1 was added, the pressure was increased by the pump 2 and the reaction vessel 4 was charged.
The pressure was adjusted with the valve of and the confirmation was performed with the pressure gauge of 3. The reaction mixture containing the polyamide prepolymer was adjusted to the conditions shown in Table 1 and heated, and the reaction mixture containing the polyamide prepolymer was supplied to the atmospheric continuous polymerization tower indicated by 7 in FIG. 1 to carry out the polymerization under the conditions shown in Table 2 to carry out the polymerization reaction. I got a thing. The polymer properties of each polymerization reaction product are shown in Table 2. No cyclic oligomer of 7-mer or more was observed in each polymerization reaction product.

[0076]

[Table 2] Examples 6-8 and Comparative Example 5 using extractive recovery lactam
As can be seen from ~ 8, in the production method of the present invention, it was found that a polyamide having a low polyamide oligomer content can be obtained with high production efficiency and low cost even if the recovered lactam is used.

[0077]

Industrial Applicability As described above, according to the production method of the present invention, it is possible to industrially advantageously obtain a polyamide having a low polyamide oligomer content from the recovered caprolactam and the polyamide oligomer as raw materials. As a result, the polyamide oligomer, which is a by-product, can be reused, and the polyamide can be produced with high production efficiency and low cost.

[Brief description of drawings]

FIG. 1 is a schematic view of a polymerization reaction device used in Examples.

[Explanation of symbols] 1: Raw material storage tank 2: Raw material supply pump 3: Pressure gauge 4: Pressurized heat treatment tank 5: Regulator valve 6: Polyamide prepolymer sampling port 7: Atmospheric pressure continuous polymerization tower

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4J001 DA01 DB01 DD13 EA02 EA05                       EA06 EA07 EA08 EA45 EB02                       EB03 EB05 EB06 EB07 EB08                       EB09 EB10 EB35 EB36 EB37                       EB44 EB45 EB46 EB64 EE02E                       EE04E EE06E EE08E EE09E                       EE14E EE18E EE23E EE25E                       EE27C EE28C EE28E EE35E                       EE36E EE43E EE53E EE58E                       EE64E EE72E EE74E GA01                       GA03 GA12 GB02 GB03 GB04                       GB05 GB06 GB12 GC04 GC05                       GD01 HA01 HA02 HA05 JA01                       JA04 JA07 JA10 JA13 JB02                       JB13 JB21 JB27 JC01

Claims (16)

[Claims] 1. A carboxylic acid is added in an amount of 2 mmol to 500 mmol to 1 g of the raw material composition to a raw material composition containing a part or all of the recovered lactam obtained by melt volatilization, and 1 to 1 at 180 to 330 ° C. under pressure. A method for producing a polyamide prepolymer, which comprises treating for 60 minutes. 2. The recovered lactam is contained in an amount of 1 to 2 with respect to the total raw material composition.
0% by weight is used, The manufacturing method of the polyamide prepolymer of Claim 1 characterized by the above-mentioned. 3. The method for producing a polyamide prepolymer according to claim 1, wherein the water content is 10 to 50% by weight based on the total raw material composition. 4. The method for producing a polyamide prepolymer according to claim 1, wherein the melt volatilization is melt volatilization using an extruder. 5. The method for producing a polyamide prepolymer according to claim 4, wherein the extruder is a vented twin-screw extruder. 6. The method for producing a polyamide prepolymer according to claim 1, wherein the carboxylic acid is a monocarboxylic acid or a dicarboxylic acid. 7. The method for producing a polyamide prepolymer according to claim 6, wherein the dicarboxylic acid is terephthalic acid or adipic acid. 8. The method for producing a polyamide prepolymer according to claim 6, wherein the monocarboxylic acid is acetic acid or benzoic acid. 9. The method for producing a polyamide prepolymer according to claim 1, wherein the amount of amino terminal groups of the polyamide prepolymer is 0.1 mmol or more per 1 g of the raw material composition. 10. A carboxylic acid is added in an amount of 2 mmol to 500 mmol to 1 g of the raw material composition to a raw material composition obtained by melt volatilization and containing a part or all of the recovered lactam, and 1 to 60 at 180 to 330 ° C. under pressure. A method for producing a polyamide, which comprises treating the reaction product containing the polyamide prepolymer after the treatment for minutes to generate a polyamide prepolymer. 11. The method for producing a polyamide according to claim 10, wherein the recovered lactam is used in an amount of 1 to 20% by weight based on 100% by weight of the total raw material composition. 12. The method for producing a polyamide according to claim 10, wherein the amount of amino terminal groups of the polyamide prepolymer is 0.1 mmol or more per 1 g of the raw material composition. 13. The method for producing a polyamide according to claim 10, wherein the cyclic oligomer content of the polyamide prepolymer is 1.6% by weight or less. 14. The method for producing a polyamide according to claim 10, wherein the polymerization of the polyamide prepolymer is atmospheric polymerization. 15. The maximum attainable temperature of atmospheric pressure polymerization is 180 ° C. or higher and 222 ° C. or lower, and
The method for producing a polyamide according to any one of the above. 16. A method of flushing a reaction product containing the polyamide prepolymer at the inlet of the atmospheric pressure polymerization apparatus to evaporate and remove water before supplying the atmospheric pressure polymerization apparatus for performing atmospheric pressure polymerization of the polyamide prepolymer. The method for producing a polyamide according to any one of the above.