JP2003082095A - Method for producing polyamide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of producing a high quality polyamide including reduced amount of caprolactam content and polyamide oligomer content advantageously in an industrial scale with low cost, in a method of production of polyamide using recovered lactam as raw material or a part of the raw material. SOLUTION: This invention includes the method for producing polyamide using recovered lactam obtained by a melt volatilization as raw material or a part of the raw material, the method for producing polyamide which uses the recovered lactam obtained by the melt volatilization as raw material or a part of the raw material, by treating at 200-330 deg.C for 1-30 min in a pressurized condition to produce a polyamide prepolymer and then polymerizing the polyamide prepolymer, or the method for producing polyamide using the lactam recovered by the melt colatilization preferably from a vented twin-screw extruder, as raw material or a part of the raw material by treating at 200-330 deg.C for 1-30 min in a pressurized condition to produce a polyamide prepolymer and then polymerizing the polyamide prepolymer in a normal pressure.

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, the present invention relates to a method for producing polyamide with high yield and low energy, which enables reuse of unreacted caprolactam and by-produced polyamide oligomer in polyamide produced using caprolactam as a main raw material.

[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 the fields of automobiles, electric and electronic fields, 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,
Then, it is supplied to the hot water extraction tower, subjected to countercurrent extraction with hot water sent from the lower part of the tower, and then taken out from the lower part. Since the extracted pellet contains a large amount of water, it is dried at about 100 ° C. in a vacuum or an inert gas atmosphere. Further, as a method for removing unreacted caprolactam and polyamide oligomer, a method of treating the polyamide after polymerization in a molten state at high temperature and high vacuum can be mentioned (US Patent 35).
58567 specification).

[0005]

Thus, in the polyamide polymerization step, unreacted monomer and polyamide oligomer are present, and the polyamide oligomer is not removed from the recovered lactam obtained by recovering the monomer and used as it is as a raw material for polymerization. In such a case, the amount of polyamide oligomer after polymerization is larger than that in the case of carrying out the polymerization using only caprolactam as a raw material, which leads to a decrease in the efficiency of the monomer / polyamide oligomer removal step such as hot water extraction and a decrease in the 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.

[0006] In US Pat. No. 6,093,788, the recovery rate of caprolactam is obtained by adding phosphoric acid as a catalyst to the recovered lactam and heating it with steam to hydrolyze the polyamide oligomer in the recovered lactam and regenerate it into caprolactam. Have been proposed. 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.

Japanese Patent Publication No. 9-188758 discloses a method of concentrating a dilute solution of recovered lactam recovered by hot water extraction and supplying it to a polymerization apparatus. An extraction solution having a water content of 92% by weight is described. Water content 1.3-10
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 The inventors of the present invention have conducted extensive studies in order to solve the above-mentioned problems, and as a result, using a recovered lactam, a polyamide having a low monomer content and a low polyamide oligomer content in the produced polymer. Was industrially advantageously produced, and further, by heat-treating the recovered lactam under pressure at a specific temperature for a short time to produce a polyamide prepolymer with a large amount of amino end groups and a small content of cyclic polyamide oligomer. Further, they have found that a polyamide having both a low monomer content and a low polyamide oligomer content in the produced polymer can be produced by polymerizing the polyamide prepolymer, and have reached the present invention.

That is, the present invention is (1) a method for producing a polyamide, characterized in that the recovered lactam obtained by melt volatilization is polymerized as a part or the whole of a raw material.

Further, according to the present invention, (2) a raw material containing a part or all of the recovered lactam obtained by melt volatilization is treated under pressure at 200 to 330 ° C. for 1 to 30 minutes to form a polyamide prepolymer. Then, the polyamide prepolymer is polymerized to produce a polyamide, and (3) the recovered lactam is used as a raw material in an amount of 1 to 20% by weight based on the total weight of the raw material. ) Or (2) the method for producing a polyamide,
(4) The amount of amino end groups of the polyamide prepolymer is 0.
(2) above, which is 1 mmol / g or more
Alternatively, (3) the method for producing a polyamide, (5) the polyamide prepolymer has a cyclic oligomer content of 1.6% by weight or less, and the polyamide according to any one of (2) to (4) above. Production method, (6) Polyamide prepolymer polymerization is atmospheric pressure polymerization, The method for producing polyamide according to any one of the above (2) to (5), (7) Maximum ultimate temperature of atmospheric pressure polymerization is 222 ° C. or less, the method for producing a polyamide according to (6) above, and (8) the water content of the polyamide prepolymer when supplied to an atmospheric pressure polymerization apparatus is 4% by weight or less. The method for producing a polyamide according to any one of (6) and (7) above, (9) an atmospheric pressure polymerization apparatus for feeding the polyamide prepolymer before the atmospheric pressure polymerization apparatus for performing atmospheric pressure polymerization of the polyamide prepolymer (6) The method for producing a polyamide according to any one of (6) to (8), wherein the water is evaporated and removed by flashing at the inlet, and (10) the melt volatilization is melt volatilization using an extruder. 1) to a method for producing a polyamide according to any one of 9), and (11) a method for producing a polyamide according to the above (10), characterized in that the extruder is a vented twin-screw extruder. Is.

[0014]

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, 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 a polyamide production step and at least one polyamide chain oligomer or polyamide cyclic oligomer.

The recovered lactam of the present invention is a recovered lactam recovered from a polyamide containing an unreacted monomer 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. For the volatilization removal in this molten state, after the polymerization reaction product is made into a solid such as pellets, it may be melted and heated under reduced pressure in an extruder, thin film evaporator, etc. The polymerization reaction product may be directly supplied to an extruder, a thin film evaporator, or the like for melt volatilization.

Although caprolactam is mainly used as a raw material used in the method for producing a polyamide of the present invention, one kind or two or more kinds of other lactams are contained in an amount not exceeding 20 mol% of the total amount of the monomers within a range not impairing the object of the invention. You can use it together with. 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, enantolactam, capryllactam, undecalactam, laurolactam and the like, among which undecaractam and laurolactam are preferable.

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

Since the recovered lactam is used in the method for producing a polyamide of the present invention, the raw material mixture to be subjected to 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 quantified by the residual amount obtained after vacuum drying at 80 ° C. for 8 hours. The preferable composition of the raw material is such that the lactam is 75 to 98.99% by weight and the content of the polyamide oligomer is 0.01 to 5% by weight, based on 100% by weight of the entire raw material. Further, it is preferable that the raw material contains water, and the amount thereof is 1 to 20% by weight based on 100% by weight of the entire raw material.

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.

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 them, a polyamide prepolymer having a small amount of cyclic oligomers, in particular, has a small content of polyamide oligomer in the polyamide produced after the polymerization reaction.
A preferable example is a method of performing heat treatment for 0 minutes. .

The pressure is not particularly limited as long as it is under pressure, but it is 0.111 to 6.08 MPa (1.1 to 60).
atm, 1.14 to 62.00 kg / cm ² ) is preferable, and 0.152 to 5.065 MPa (1.5 to 50 a).
tm, 1.55 to 51.67 kg / cm ² ) is more preferable. The pressure is preferably 1.1 MPa or more in order to suppress the amount of cyclic oligomer formed during prepolymerization and improve the amino group formation efficiency. On the other hand, when it exceeds 5.065 MPa, it is not preferable in terms of productivity and economy.

The processing temperature for preparing the polyamide prepolymer of the present invention is 200 to 330 ° C. The lower limit is preferably 230 ° C. or higher, and particularly preferably 26.
It is 0 ° C or higher. When the temperature is lower than 200 ° C, the cyclic oligomer content is large at the time when the necessary amino group is obtained, and the upper limit is preferably 330 ° C or lower, and particularly preferably 32.
It is 0 ° C or lower. This is because when the temperature exceeds 330 ° C., it is difficult to control the amount of amino groups in the reaction product and the industrial stability is lacking.

The treatment time for preparing the polyamide prepolymer of the present invention is 1 to 30 minutes, and the upper limit is preferably 25 minutes or less, particularly preferably 20 minutes or less. If it exceeds 30 minutes, the cyclic oligomer content in the reaction product increases, which is not preferable. If it is less than 1 minute, the amino group content fluctuates, and it becomes difficult to control the polymerization degree of the polyamide in the polymerization step.

The amount of amino terminal groups of the polyamide prepolymer of the present invention is preferably 0.1 mmol / 1 g or more of the reaction product, and more preferably 0.15 mmol / g.
1 g or more of reaction product, particularly preferably 0.2 mmol / 1 g
That is all. This is because if it is less than 0.1 mmol / 1 g of the reaction product, the content of the polyamide oligomer in the polyamide increases when the polyamide is produced from the obtained polyamide prepolymer. Although there is no upper limit to the amount of amino groups, it is usually employed in the range of 1.0 mmol / g or less in terms of productivity.

The content of cyclic oligomer in the polyamide prepolymer is preferably 1.6% by weight or less, more preferably 1.0% by weight or less, and particularly preferably 0.6% by weight or less. This is because when it exceeds 1.6% by weight, the content of the polyamide oligomer in the polyamide polymer increases when the polyamide polymer is produced from the obtained polyamide prepolymer. The lower limit of the cyclic oligomer content is not particularly limited, but is usually 0.01% by weight.
Is.

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

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.

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 not particularly limited as long as the amount of amino groups in the raw material composition of the polyamide prepolymer and the additional caprolactam is 0.1 mmol / 1 g or more.

In the method for producing a 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 of the present invention, there is no limitation on the water content of the polyamide prepolymer when it is supplied to the atmospheric pressure polymerization apparatus, but it is preferably 4% by weight or less. This is because if it exceeds 4% by weight, a large amount of heat is required for heating when producing the polyamide, and the productivity is reduced.

In the method for producing a polyamide polymer of the present invention, when 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 flushed to the inlet of the atmospheric pressure polymerization apparatus. A method of removing the water by evaporation is preferably adopted. 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.

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 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. In order to express mechanical properties, it is desirable that the relative viscosity is 2.2 or more,
Further, it is preferably 8.0 or less for ease of molding.

In the method for producing a polyamide of the present invention, the end can be blocked with a carboxylic acid compound, if necessary.
When the terminal is blocked by adding the monocarboxylic acid, the terminal group concentration of the obtained polyamide is lower than that when the terminal blocking agent is not used. On the other hand, when the end groups are blocked with dicarboxylic acid, the total amount of end groups does not change, but the ratio of amino end groups to carboxyl end groups can be changed.
As the carboxylic acid compound, acetic acid, propionic acid, butyric acid,
Like valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, myristoleic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid. Aliphatic monocarboxylic acids such as aliphatic monocarboxylic acid, cyclohexanecarboxylic acid, methylcyclohexanecarboxylic acid, benzoic acid toluic acid, ethylbenzoic acid, naphthalenecarboxylic acid, anthracenecarboxylic acid, phenylacetic acid, etc. Acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, pentadecanedioic acid, octadecanedioic acid Aliphatic dicarboxylic acids such as acids , Phthalic acid, isophthalic acid, terephthalic acid, naphthalene dicarboxylic acid, and aromatic dicarboxylic acids such as anthracene dicarboxylic acid.

As the end-capping agent, a polyamide prepolymer may be charged with a raw material such as caprolactam at the beginning of the heat treatment, a method of adding it during the heat treatment, a method of charging after the heat treatment and before charging the polymerization apparatus, or polyamide. A method of adding when removing unreacted caprolactam and polyamide oligomer in a molten state is adopted. The terminal blocking agent may be added as it is, or may be dissolved in a small amount of solvent and added.

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-based compounds, etc.), weathering agents (resorcinol-based, benzotriazole-based, benzophenone-based, hindered amine-based, etc.), mold release agents and lubricants (aliphatic alcohols, aliphatic amides, aliphatic bisamides, bisurea, polyethylene wax, etc.) , Pigments (cadmium sulfide, phthalocyanine, carbon black, etc.), dyes (nigrosine, aniline black, etc.), crystal nucleating agents (talc, silica, kaolin, clay, etc.), plasticizers (octyl p-oxybenzoate, N-butylbenzene) Sulfonamide, etc., antistatic agent (alkyl sulfate type ani Antistatic agents, quaternary ammonium salt type cationic antistatic agents, nonionic antistatic agents such as polyoxyethylene sorbitan monostearate, betaine amphoteric antistatic agents, etc., flame retardants (melamine cyanurate, Magnesium hydroxide, hydroxide such as aluminum hydroxide, ammonium polyphosphate, brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate, brominated epoxy resin or a combination of these brominated flame retardants and antimony trioxide, etc. ), Filler (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.

[0040]

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) Amino end group content in polyamide prepolymer About 0.2 g of the substance to be measured was precisely weighed, dissolved in 25 cc of phenol-ethanol mixed solvent (83.5: 16.5, volume ratio), and then 0 Titrated with 0.02N hydrochloric acid solution.

(2) Content of Cyclic Oligomer in Polyamide Prepolymer The object to be measured was crushed and passed through JIS standard sieve 24 mesh, and 124 mesh did not pass, powder of the object to be measured was collected, and 20 g of the powder was mixed with 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 60
0E 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 was measured using 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 soaked with 200 ml of methanol for 3 hours in 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
ector 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 is crushed and JIS standard sieve 24 mesh is used. After passing through and passing through 124 mesh, the powder of the measured substance was collected, 20 g of the powder was extracted with 200 ml of methanol for 3 hours using a Soxhlet extractor, and caprolactam contained in the extract was quantified by the above method. After evaporation to dryness with an evaporator and further vacuum drying at 80 ° C. for 8 hours, the residual amount obtained was determined, and the amount of caprolactam determined in the above (4) was subtracted to obtain the polyamide oligomer content.

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

A. Raw materials used Examples 1 to 7 Caprolactam was obtained by melting a special grade reagent of Tokyo Kasei Kogyo Co., Ltd. and drying it with a molecular sieve. This caprolactam was polymerized by heating at 197 ° C. for 7 hours and 220 ° C. for 4 hours. The polymerization reaction product was melted and volatilized under the following conditions using a twin-screw extruder with a 30 mmφ vent manufactured 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. Melt volatilization conditions ・ L / D = 45.5, rotation in the same direction, deep groove type ・ Barrel temperature: The 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.

The caprolactam containing the obtained polyamide oligomer was subjected to heat treatment under pressure in a flow reactor under the conditions shown in Table 1 to obtain a polyamide prepolymer. Then, the obtained polyamide prepolymer was fed to an atmospheric continuous polymerization tower and polymerization was carried out under the conditions shown in Table 1 to obtain a polymerization reaction product. The polymer properties of each polymerization reaction product are shown in Table 1. No possible oligomers of 7-mer or higher were observed in each polymerization reaction product.

[0047]

[Table 1] Comparative Examples 1 to 3 Using the raw material caprolactam used in Example 1, polymerization was carried out in the same manner as in Example 1, and the polymerization reaction product was crushed to obtain JI.
The powder of the substance to be measured, which passed through S standard sieve 24 mesh and was not passed through 124 mesh, was collected, 20 g of the powder was extracted with 200 ml of methanol for 3 hours using a Soxhlet extractor, and evaporated to dryness with an evaporator. The difference was used. The composition of the melt-recovered lactam was 80% by weight of caprolactam and 20% by weight of polyamide oligomer.

The caprolactam containing the obtained polyamide oligomer was heat-treated under pressure in a flow reactor under the conditions shown in Table 2 to obtain a polyamide prepolymer. Next, the obtained polyamide prepolymer was fed to an atmospheric continuous polymerization tower, and polymerization was performed under the conditions shown in Table 2 to obtain a polymerization reaction product. The polymer properties of each polymerization reaction product are shown in Table 2.

[0049]

[Table 2] As can be seen in Examples 1 to 5 using the melt-recovered lactam and Comparative Examples 1 to 3 using the extract-recovered lactam, the production method of the present invention yields a polyamide having a low polyamide oligomer content even when the recovered lactam is used. I found out that

[0050]

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 small content of polyamide oligomer from the recovered caprolactam and 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.

Continued front page    F term (reference) 4J001 DA01 DB01 DB04 DD13 EA05                       EA06 EA07 EA08 EE27C                       EE28C FA03 FA05 FB01                       FC01 GA12 GB02 GB03 GB05                       GB06 GB14 GE02 HA01 HA02                       JA01 JA10 JA12

Claims (11)

[Claims] 1. A method for producing a polyamide, which comprises polymerizing a recovered lactam obtained by melt volatilization as a part or the whole of a raw material. 2. A polyamide prepolymer is produced by treating a raw material partially or wholly recovered lactam obtained by melt volatilization under pressure at 200 to 330 ° C. for 1 to 30 minutes to produce a polyamide prepolymer. A method for producing a polyamide, which comprises polymerizing to produce a polyamide. 3. Recovered lactam is used as a raw material for 1 to 2 of all raw materials.
0% by weight is used, The manufacturing method of the polyamide of Claim 1 or 2 characterized by the above-mentioned. 4. The method for producing a polyamide according to claim 2, wherein the amount of amino terminal groups of the polyamide prepolymer is 0.1 mmol / g or more. 5. The method for producing a polyamide according to claim 2, wherein the polyamide prepolymer has a cyclic oligomer content of 1.6% by weight or less. 6. The method for producing a polyamide according to claim 2, wherein the polymerization of the polyamide prepolymer is pressureless polymerization. 7. The method for producing a polyamide according to claim 6, wherein the highest temperature reached in the atmospheric pressure polymerization is 222 ° C. or lower. 8. The method for producing a polyamide according to claim 6, wherein the polyamide prepolymer has a water content of 4% by weight or less when fed to the atmospheric polymerization. 9. The polyamide prepolymer is flushed at the inlet of the atmospheric pressure polymerization apparatus before the atmospheric pressure polymerization apparatus for performing atmospheric pressure polymerization of the polyamide prepolymer to remove water by evaporation. Method for producing polyamide. 10. The method for producing a polyamide according to claim 1, wherein the melt volatilization is melt volatilization using an extruder. 11. The method for producing a polyamide according to claim 10, wherein the extruder is a vented twin-screw extruder.