JP2008274086A - Method for producing polyamide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently and stably produce a polyamide having a low content of cyclic oligomers. <P>SOLUTION: The method for producing the polyamide is a method for producing a polyamide mainly consisting of capramide units and comprises subjecting an aqueous caprolactam solution of a water content of 2-20 wt.% to polymerization while feeding the solution to a normal pressure polymerization apparatus to form a thin film of the solution at the upper part of the apparatus. Alternatively, the method comprises subjecting a polyamide prepolymer of an amino group content of 0.03 mmol/1 g or more and a cyclic oligomer content of 0.6 wt.% or less obtained by heating an aqueous caprolactam solution of a water content of 2-20 wt.% at 200-330°C under the elevated pressure for 1-60 min to polymerization while feeding it to a normal pressure polymerization apparatus to form a thin film of the solution at the upper part of the apparatus. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a polyamide having a caproamide unit as a main constituent. More specifically, when a caprolactam aqueous solution or a polyamide prepolymer is supplied to an atmospheric pressure polymerization apparatus, a thin film is formed at the upper part of the atmospheric pressure polymerization apparatus, thereby having a high degree of polymerization and containing a cyclic oligomer, especially a cyclic dimer. The present invention relates to a method for efficiently and stably producing a polyamide having a small amount and suitable as a raw material for fibers and resins.

  Polyamide, which uses caprolactam as the main raw material, is used for textile fibers and industrial fibers by taking advantage of its superior properties. Furthermore, it is used as an injection-molded product in the automotive, electrical and electronic fields, and mainly for food packaging applications. Also widely used as extruded film and stretched film.

  Polyamides based on caprolactam are usually produced by heating caprolactam in the presence of a small amount of water. This manufacturing method is a relatively simple process, and is a manufacturing method widely used in the world. An outline of a general polymerization method for polyamide 6 described in pages 63 to 65 of “Polyamide resin handbook” (Shu Fukumoto, Nikkan Kogyo Shimbun) will be described below.

  Caprolactam is melted and supplied to an atmospheric polymerization tower heated to about 260 ° C., and after staying in this polymerization tower for about 10 hours, it is formed into a strand form from the lower part of the tower and discharged into a water tank to be pelletized. The polymerized pellets contain oligomers such as monomers and cyclic dimers, which are supplied to a hot water extraction tower to remove them, and the monomers and oligomers are extracted countercurrently with hot water sent from the bottom of the tower. And then removed from the bottom. Since the pellet after extraction contains a large amount of water, it is dried at about 100 ° C. in a vacuum or an inert gas atmosphere.

  Thus, since the polyamide after polymerization contains monomers remaining due to polymerization equilibrium and oligomers such as cyclic dimers, when used as it is as raw materials for fibers, films, and injection molded products, the monomers and oligomers are formed during the molding process. It volatilizes and causes many problems, such as the production of fibers, films, and injection-molded products as final products. In particular, the cyclic dimer has a high melting point among the monomers and oligomers, and the adverse effect in the subsequent process is extremely large.

  Therefore, it is necessary to remove these monomers and oligomers, and extraction is generally performed with hot water as described above. This hot water extraction process requires a lot of energy to obtain hot water, and the monomer, oligomer from the hot water containing the extracted monomer and oligomer, concentration process, distillation process, or monomer from the oligomer Much energy is also required in the depolymerization step to be obtained and the purification step to remove impurities.

  In order to reduce the load in the extraction step to the purification step, attempts have been made to reduce the monomers and oligomers contained in the polyamide after polymerization. For example, Patent Document 1 has been proposed. In Patent Document 1, a polyamide prepolymer is obtained by treating a caprolactam aqueous solution for a short time at a high temperature and a high pressure, and is carried out in the low temperature range of the melting point of the polyamide + 10 ° C. or less, which can obtain the polymerization temperature of subsequent atmospheric polymerization. A method for reducing the amount of oligomer contained in the polyamide is disclosed, and it is shown that a polyamide having a cyclic oligomer amount of 0.9% by weight or less was obtained in a region where the degree of polymerization was relatively low. However, in order to reduce the amount of oligomers, it is necessary to perform polymerization at a temperature near the melting point, and very delicate temperature control is required to prevent solidification, and there is a problem in stability in industrial production. Furthermore, since the polymerization is performed in a low temperature range, there is a problem that the degree of polymerization of the obtained polyamide is difficult to increase.

  The technology of the present invention is a general stable polymerization method in which the production of a polyamide prepolymer is not essential, and the polymerization temperature is not limited to a low temperature. Since this is a method for efficiently and stably producing a small amount of polyamide, stable operation is possible even when applied to industrial production, and productivity is significantly improved as compared with the conventional technology. Further, the degree of polymerization of the obtained polyamide can be easily increased.

  In Patent Document 2, a polyamide resin with a small amount of oligomer is produced by polymerization at a temperature below the melting point of the resulting polyamide in the presence of a dicarboxylic acid and a diamine, and the obtained polyamide resin is heated under reduced pressure to produce caprolactam, A method for removing the oligomer has been proposed, but in this method, addition of dicarboxylic acid and diamine, that is, copolymerization is essential, which has a problem of affecting the properties of the resulting polyamide.

The technique of the present invention does not require a complicated reaction of adding a dicarboxylic acid and a diamine, and achieves a reduction in the amount of oligomers by a simple method of forming a thin film on the upper part of the atmospheric pressure polymerization apparatus.
JP 2003-82096 A Japanese Patent Laid-Open No. 11-343341

  Accordingly, the present invention solves the above-mentioned problems of the prior art, and efficiently uses polyamide having a high degree of polymerization and having a low cyclic oligomer content, especially a low cyclic dimer content, and suitable as a raw material for fibers and resins. And it is providing the method of manufacturing stably.

  As a result of diligent studies to solve the above problems, it was found that a polyamide having a low oligomer content can be efficiently and stably produced by polymerizing while forming a thin film at the top of the atmospheric pressure polymerization apparatus, and the present invention. Reached.

That is, the present invention is as follows.
1. A process for producing a polyamide, characterized in that when a polyamide having a caproamide unit as a main constituent is produced, polymerization is carried out while forming a thin film at the upper part of the atmospheric pressure polymerization apparatus.
2. 2. The method for producing a polyamide according to 1, wherein an aqueous caprolactam solution having a water content of 2 to 20% by weight is supplied to an atmospheric pressure polymerization apparatus.
3. 3. The method for producing a polyamide according to 2, wherein a plate for forming a thin film is provided on the upper portion of the atmospheric pressure polymerization apparatus, and the thin film is formed by dropping a lactam aqueous solution onto the plate.
4). 2. The method for producing a polyamide according to 1, wherein a polyamide prepolymer having an amino group content of 0.03 mmol / 1 g or more and a cyclic oligomer content of 0.6% by weight or less is supplied to an atmospheric pressure polymerization apparatus.
5. 5. The method for producing a polyamide according to 4, wherein the polyamide prepolymer is obtained by heat-treating an aqueous caprolactam solution having a water content of 2 to 20% by weight at a temperature of 200 to 330 ° C. for 1 to 60 minutes.
6). 6. The method for producing a polyamide according to 4 or 5, wherein a plate for forming a thin film is provided on the upper part of the atmospheric pressure polymerization apparatus, and the thin film is formed by dropping a polyamide prepolymer on the plate.
7). 7. The method for producing a polyamide according to 3 or 6, wherein the plate for forming the thin film is a perforated plate.
8). 8. The method for producing a polyamide according to 7, wherein the area of the plate for forming the thin film satisfies the following formula (I).
0.05 ≤ V / A ≤ 0.20 (I)
V = Caprolactam aqueous solution or polyamide prepolymer supply amount (m ³ / h)
A = area of the plate (m ² )

  By the method of the present invention, it is possible to efficiently and stably produce a polyamide having a high degree of polymerization and having a low cyclic dimer content among cyclic oligomers, which is suitable as a raw material for fibers and resins. Become.

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

  In the method for producing a polyamide of the present invention, polymerization is performed while forming a thin film in the upper part of the atmospheric pressure polymerization apparatus. Although there is no restriction | limiting in particular in the mechanism in which a thin film is formed, Usually, a thin film is formed in the site | part which the dripped caprolactam aqueous solution or polyamide prepolymer contacts with a polymerization apparatus. In order to achieve the object of the present invention, a plate for forming a thin film is provided on the upper part of the atmospheric pressure polymerization apparatus, and a caprolactam aqueous solution or a polyamide prepolymer is dropped on the plate to form a thin film on the plate. Is preferred.

  Although there is no restriction | limiting in particular in the shape of the plate used with the manufacturing method of the polyamide of this invention, It is preferable that the said plate is a plate shape which has a plane, and it is preferable to form a thin film in the said plane. When the surface on which the thin film is formed is not a flat surface, the caprolactam aqueous solution or the polyamide prepolymer is partially distributed, and a sufficient oligomerization effect may not be obtained.

  The plate is preferably in the form of a perforated plate. The perforated plate in this patent refers to a plate having a plurality of holes in a flat plate. There is no restriction | limiting in particular in the shape of the hole drilled in the perforated plate, A polygon, a circle, an ellipse etc. are selected. Although there is no restriction | limiting in particular in the magnitude | size per hole, Usually, the thing of the hole of the range of 10 square mm-20 square cm is used. Further, the ratio of the area of the hole to the total area of the plane of the porous plate, that is, the opening ratio is not particularly limited, but a value of 5 to 40% is preferable, and a value of 10 to 30% is more preferably selected.

  Although there is no restriction | limiting in the installation angle in case the said plate is a plane, It is preferable to install horizontally. In the case where it is not horizontal, the dropped caprolactam aqueous solution or polyamide prepolymer does not stay on the plate, and thin film formation may be insufficient.

Although there is no restriction | limiting in particular about the area of the plate of this invention, It is preferable to satisfy | fill the following formula (I).
0.05 ≤ V / A ≤ 0.20 (I)
V = Caprolactam aqueous solution or polyamide prepolymer supply amount (m ³ / h)
A = area of the plate (m ² )

  The value of V / A in the above formula (I) is preferably in the range of 0.06 to 0.19, and more preferably in the range of 0.07 to 0.18. It is preferable that the value of V / A is 0.20 or less because the effect of reducing oligomers is sufficiently exhibited. Moreover, it is preferable to make it 0.05 or more because not only a low oligomerization effect can be sufficiently obtained, but also the occurrence of abnormal staying on the plate can be prevented.

  The aforementioned hole portion is not included in the plate area.

  One or a plurality of the plates can be installed. There is no particular limitation on the number of the installed sheets, but it is preferable to set the number so as to satisfy the above formula (I). When installing a plurality of plates, the total area is A.

  In the polyamide production method of the present invention, the caprolactam aqueous solution can be supplied to the atmospheric polymerization apparatus as it is, and the polyamide prepolymer obtained by heat-treating the caprolactam aqueous solution under pressure is applied to the atmospheric polymerization apparatus. It can also be supplied. When a polyamide prepolymer is supplied, a higher oligomerization effect can be obtained.

  The polyamide prepolymer referred to in the present invention is a composition obtained by heat treatment of caprolactam, and refers to a mixture containing a chain oligomer, a cyclic oligomer and an unreacted monomer.

  In the polyamide production method of the present invention, when a polyamide prepolymer is supplied, a caprolactam aqueous solution having a water content of 2 to 20% by weight is maintained at a pressure equal to or higher than the vapor pressure of the caprolactam aqueous solution at the heat treatment temperature. What was obtained by heat treatment at 1 ° C. for 1 to 30 minutes is preferred, and a polyamide prepolymer having an amino group content of 0.03 mol / 1 g or more and a cyclic oligomer content of 0.6 wt% or less is obtained. Is preferably fed to an atmospheric pressure polymerization apparatus.

  In the method for producing a polyamide of the present invention, it is preferable to use a caprolactam aqueous solution having a water content of 2 to 20% by weight as a raw material.

  The lower limit of the water content is preferably 2% by weight, more preferably 2.2% by weight, particularly preferably 2.4% by weight, based on the total amount. Further, the upper limit of the moisture content is preferably 20% by weight, more preferably 16% by weight, and particularly preferably 13% by weight with respect to the total amount. By using a caprolactam aqueous solution having a water content of 2% by weight or more, the progress rate of the polymerization can be set to an appropriate rate, and when obtaining a polyamide prepolymer having an amino group content of 0.03 mmol / 1 g or more, a cyclic dimer is obtained. Is preferable because the amount of cyclic dimer contained in the resulting polyamide can be suppressed. Moreover, it is preferable to use a caprolactam aqueous solution having a water content of 20% by weight or less because it is not necessary to increase the energy necessary for heating the raw material more than necessary.

  In the present invention, in order to obtain a polyamide prepolymer having an amino group content of 0.03 mmol / 1 g or more, the treatment temperature is preferably 200 ° C. or more, more preferably 205 ° C. or more, particularly preferably 210 ° C. or more. . The treatment temperature is preferably 300 ° C. or lower, more preferably 290 ° C. or lower, particularly preferably 280 ° C. or lower. By setting the treatment temperature to 200 ° C. or higher, the time for obtaining a polyamide prepolymer having an amino group content of 0.03 mmol / 1 g or more can be set in an appropriate range, which is preferable from the viewpoint of productivity. In addition, by setting the treatment temperature to 300 ° C. or lower, the pressure for retaining moisture does not become too high, which is preferable in terms of equipment costs. Furthermore, it is preferable also from the point of the production | generation speed | rate of the amount of amino groups, and the production | generation speed | rate of a cyclic oligomer.

  In addition, in order to maintain the moisture content of caprolactam aqueous solution in the range of this invention mentioned above in this process temperature, it is preferable to maintain the pressure at the time of a process more than the vapor pressure in process temperature. Although there is no restriction | limiting in such a pressure control method, Usually, it can carry out using a pressure control valve etc. Further, in order to maintain the pressure at the time of treatment at or above the vapor pressure at the treatment temperature, there is no gas phase inside the reactor that performs the heat treatment.

  In the present invention, the lower limit of the treatment time for obtaining the polyamide prepolymer is preferably 1 minute, more preferably 5 minutes, and particularly preferably 10 minutes. The upper limit is preferably 60 minutes, more preferably 50 minutes, and particularly preferably 40 minutes. In order to obtain a polyamide prepolymer having an amino group amount of 0.03 mmol / 1 g or more by setting the treatment time to 1 minute or more, the production rate of the amino group amount and the production rate of the cyclic dimer are not too fast. This is preferable because the polyamide prepolymer can be produced industrially stably. Moreover, the production | generation amount of the cyclic dimer in a polyamide prepolymer can be decreased by setting it as 60 minutes or less, and the amount of cyclic dimers contained in the polyamide after superposition | polymerization shall be 0.30 weight% or less. This is preferable.

  In the present invention, when the polyamide prepolymer is supplied, the amount of amino groups of the polyamide prepolymer is preferably 0.03 mmol / 1 g or more. More preferably, it is 0.05 mmol / 1g or more, Most preferably, it is 0.07 mmol / 1g or more. When the amount of amino groups is 0.03 mmol / 1 g or more, the rate of addition of remaining caprolactam to amino groups, that is, the consumption rate of caprolactam, is increased when the polyamide is polymerized from the polyamide prepolymer. It is preferable that the cyclic oligomer is prevented from being generated via the chain oligomer by the reaction with and the cyclic dimer content contained in the polymerized polyamide can be 0.30% by weight or less. There is no upper limit to the amount of amino groups, but if the amount of amino groups is large, it tends to solidify when fed to the polymerization tower, and therefore a range of 0.4 mmol / 1 g or less is usually adopted in terms of productivity. The cyclic oligomer content in the polyamide prepolymer is preferably 0.60% by weight or less. More preferably, it is 0.50 weight% or less, Most preferably, it is 0.40 weight% or less. The content of 0.60% by weight or less is preferable because the cyclic oligomer content in the polyamide produced from the polyamide prepolymer can be kept low. Although there is no restriction | limiting in particular in the minimum of cyclic oligomer content in this polyamide prepolymer, Usually, it is 0.01 weight%.

  In the polyamide production method of the present invention, when supplying the polyamide prepolymer obtained by the heat treatment under pressure to the atmospheric pressure polymerization apparatus, it is possible to evaporate and remove moisture by flushing at the upper part of the atmospheric pressure polymerization apparatus. Preferably employed. By removing the water by transpiration, the amount of heat required for heating when producing the polyamide can be reduced and the polymerization temperature can be easily controlled.

  There is no particular limitation on the relative viscosity of the polyamide obtained in the method for producing a polyamide of the present invention, but the relative viscosity at 25 ° C. of a 98% sulfuric acid solution having a sample concentration of 0.01 g / mL is preferably 2.2 or more. Preferably, it is 2.25 to 7.0, and particularly preferably 2.3 to 6.0. If the relative viscosity is less than 2.2, the mechanical properties may be insufficiently expressed. If the relative viscosity exceeds 8.0, the melt viscosity may be too high and molding may be difficult.

  Although there is no restriction | limiting in particular in the monomer content in the polyamide obtained in the manufacturing method of the polyamide of this invention, Preferably it is 10 weight% or less, More preferably, it is 9 weight% or less, More preferably, it is 8 weight% or less. .

  Although there is no restriction | limiting in particular in the oligomer content in the polyamide obtained in the manufacturing method of the polyamide of this invention, Preferably it is 2.0 weight% or less, More preferably, it is 1.9 weight% or less.

  Although there is no restriction | limiting in particular in cyclic dimer content in the polyamide obtained in the manufacturing method of the polyamide of this invention, Preferably it is 0.30 weight% or less, More preferably, it is 0.28 weight% or less.

  Although there is no restriction | limiting in particular in the polymerization temperature of this invention, Preferably it is 200-270 degreeC, More preferably, it is 205-260 degreeC. The polymerization temperature of 200 ° C. or higher is preferable because the polymerization rate can be made economical and the amount of oligomer generated during the polymerization can be kept low. If the amount of the cyclic dimer contained in the obtained polyamide can be 0.3% by weight or less, the oligomer removal and purification steps in the subsequent steps are facilitated, which is preferable. Moreover, it is preferable to set the polymerization temperature to 270 ° C. or lower because the production rate of the cyclic oligomer can be suppressed. By performing the polymerization in this temperature range, the amount of oligomer contained in the polyamide after polymerization can be 2.0% by weight, and the amount of cyclic dimer can be 0.3% by weight or less. The polymerization temperature here is the maximum temperature of the polyamide or its precursor in the polymerization apparatus.

  The polymerization time of the present invention is not particularly limited, but the monomer amount may exceed 10% by weight in less than 5 hours. Therefore, the polymerization temperature may exceed 270 ° C. in order to keep the monomer amount to 10% by weight or less. There is a problem that the generation rate of the cyclic oligomer is increased. Moreover, when it exceeds 25 hours, the amount of the cyclic dimer exceeds 0.30% by weight and it is not economical. In the present invention, a preferable polymerization time is 8 to 20 hours.

  In the production method of the present invention, the amount of the cyclic dimer in the polyamide is not particularly limited, but in a preferred embodiment, it is 0.30% by weight or less, and in a more preferred embodiment, it is 0.25% by weight or less. Become. Since the cyclic dimer has a sublimation property and a high melting point, it is a main causative substance of the base stain at the time of film production and spinning, so that the amount of the cyclic dimer is reduced as described above. It is extremely useful in practice.

  In the method for producing a polyamide of the present invention, when the polyamide prepolymer is supplied to an atmospheric pressure polymerization apparatus, caprolactam can be further added to the polyamide prepolymer at the start of 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 comprising the polyamide prepolymer and the additional caprolactam is 0.03 mmol / 1 g or more.

  Caprolactam is mainly used as the raw material used in the method for producing a polyamide of the present invention, but one or two or more other lactams and derivatives thereof are used in an amount of 10 mol% of the total polyamide raw material within a range not impairing the object of the invention. It may be used in combination as long as it does not exceed. If it exceeds 10 mol%, the crystallinity of the resulting polyamide may be lowered. Specific examples of such combined lactams and derivatives thereof include valerolactam, enantolactam, capryllactam, undecalactam, laurolactam and the like.

  In the method for producing a polyamide of the present invention, at least one additive selected from 5 mol% or less of dicarboxylic acid, diamine, and salts thereof with respect to caprolactam is supplied to the raw material before heat treatment or to the polymerization stage. Can be polymerized. This makes it possible to further shorten the required polymerization time. However, the addition amount is preferably 4 mol% or less, more preferably 3 mol% or less. If the additive amount exceeds 5 mol%, the melting point and crystallinity of the resulting polyamide may be lowered, and the moldability and physical properties of the molded product may be lowered.

  Dicarboxylic acids constituting the additive include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassic acid, tetradecanediic acid. Acids, aliphatic dicarboxylic acids such as pentadecanedioic acid, octadecanedioic acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, etc. Can be mentioned.

  Examples of the diamine constituting the additive include 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,13-diaminotridecane, 1,14-diaminotetradecane, 1,15-diaminopentadecane, 1,16-diaminohexadecane, Aliphatic diamines such as 1,17-diaminoheptadecane, 1,18-diaminooctadecane, 1,19-diaminononadecane, 1,20-diaminoeicosane, diethylaminopropylamine, cyclohexanediamine, bis- (4-aminohexyl) ) Alicyclic diamines such as methane, xylylene diamine And aromatic diamines such as emissions and the like.

  The additive is preferably a dicarboxylic acid and diamine salt, more preferably a salt derived from an aliphatic and / or aromatic dicarboxylic acid and an aliphatic diamine, most preferably adipic acid and 1, A salt derived from 6-diaminohexane and / or a salt derived from terephthalic acid and 1,6-diaminohexane.

  There is no restriction | limiting in particular in the method of supplying the said additive to an atmospheric pressure polymerization apparatus. A granular solid may be added to the polymerization apparatus, or may be dissolved in a solvent such as water and added as a solution.

  In the polyamide production method of the present invention, monomers and oligomers may be further removed from the obtained polyamide by hot water extraction, may be volatilized and removed by heating under reduced pressure, or heated under reduced pressure, After removing the monomer and oligomer, hot water extraction may be further performed. The volatilization removal of the monomer and oligomer by heating under reduced pressure may be performed in a solid phase or in a molten state after the polymerization reaction product is made into a solid such as a pellet. Volatile removal in the molten state may be performed by making the polymerization reaction product a solid such as a pellet, and then performing melting / depressurization heating with an extruder or a thin film evaporator, etc. The reaction product may be supplied directly to an extruder, a thin film evaporator or the like. Further, by simultaneously performing melt polymerization or solid phase polymerization of polyamide in the volatilization removal by heating under reduced pressure of monomers and oligomers, the polymerization degree can be adjusted to a suitable value according to the application.

  The polyamide obtained by the production method of the present invention is a temperature lower than the melting point of the polyamide so that a suitable viscosity can be obtained for applications where the polyamide is required to have a high viscosity, such as high-strength fibers and extrusion molding. And it is preferable to adjust to a desired polymerization degree by solid-phase polymerization which heat-processes under nitrogen stream or reduced pressure.

  In the polyamide production method of the present invention, the terminal group can be blocked with a carboxylic acid compound or the structure of the terminal group can be controlled as necessary. When end-capping is performed by adding a monocarboxylic acid, the end group concentration of the obtained polyamide is lower than when no end-blocking agent is used. On the other hand, when end-capping with dicarboxylic acid, the total amount of terminal groups does not change, but the ratio of amino groups to carboxyl groups can be changed. Specific examples of the carboxylic acid compound 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, myristic acid, palmitic acid, Aliphatic monocarboxylic acids such as stearic acid, oleic acid, linoleic acid and arachidic acid, cycloaliphatic monocarboxylic acids such as cyclohexanecarboxylic acid and methylcyclohexanecarboxylic acid, benzoic acid, toluic acid, ethylbenzoic acid, phenylacetic acid Aromatic monocarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassic acid, tetradecanedioic acid Aliphatic dica, such as pentadecanedioic acid, octadecanedioic acid Bon acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, and aromatic dicarboxylic acids such as naphthalene dicarboxylic acid. In addition, as a method for adding a terminal blocking agent, a method of simultaneously charging raw materials such as caprolactam in the initial stage of the heat treatment of the polyamide prepolymer, a method of adding before introducing the atmospheric pressure polymerization apparatus, and removing the monomers and oligomers in a molten state of the polyamide The method of adding at the time is adopted. The terminal blocking agent may be added as it is, or may be added after being dissolved in a small amount of solvent.

  In the production method of the present invention, for example, an antioxidant or a heat stabilizer (hindered phenol type, hydroquinone type, phosphite type and substituted products thereof, copper halide, iodine compound, etc.), weathering agent ( Resorcinol, salicylate, benzotriazole, benzophenone, hindered amine, etc.), mold release agents and lubricants (fatty alcohol, aliphatic amide, aliphatic bisamide, bisurea, polyethylene wax, etc.), pigment (titanium oxide, sulfide) Cadmium, phthalocyanine, carbon black, etc.), dyes (nigrosine, aniline black, etc.), crystal nucleating agents (talc, silica, kaolin, clay, etc.), plasticizers (octyl p-oxybenzoate, N-butylbenzenesulfonic acid amide, etc.) ), Antistatic agent (alkyl sulfate type anion) Antistatic agents, quaternary ammonium salt type cationic antistatic agents, nonionic antistatic agents such as polyoxyethylene sorbitan monostearate, betaine amphoteric antistatic agents), flame retardants (melamine cyanurate, (Hydroxides such as magnesium hydroxide and aluminum hydroxide, ammonium polyphosphate, brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate, brominated epoxy resins or combinations of these brominated flame retardants with antimony trioxide) , 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, ara Fiber, bentonite, montmorillonite, particles of synthetic mica, fiber, needle, plate filler, etc.), other polymers (other polyamides, polyethylene, polypropylene, polyester, polycarbonate, polyphenylene ether, polyphenylene sulfide, Liquid crystal polymer, polysulfone, polyethersulfone, ABS resin, SAN resin, polystyrene, etc.) can be added at any time.

  The polyamide obtained by the production method of the present invention can be formed into a molded product by an ordinary molding method as in the case of conventional polyamide. There is no restriction | limiting in particular regarding a shaping | molding method, Well-known shaping | molding methods, such as injection molding, extrusion molding, blow molding, and press molding, can be utilized. The molded product referred to here includes shaped products such as fibers, films, sheets, tubes, monofilaments, etc., in addition to molded products by injection molding or the like.

  Hereinafter, the present invention will be specifically described with reference to examples. In addition, the definition of the characteristic value and the measuring method described in the claims, the specification text, the examples, and the comparative examples are as follows.

(1) Amount of monomer and amount of cyclic dimer in polyamide The polyamide is crushed, passed through JIS standard sieve 24 mesh, and 124 mesh collected non-passed polyamide powder. About 20 g of the powder was extracted with 200 ml of methanol for 3 hours by Soxhray extraction. The caprolactam contained in the extract was quantified using a high performance liquid chromatograph. The measurement conditions are as follows. Prior to the measurement, confirmation of the column retention time and preparation of a calibration curve were performed using standard samples of caprolactam and caprolactam cyclic dimer.
High performance liquid chromatograph: Waters 600E
Column: GL Sciences ODS-3
Detector: Waters 484 Tunable Absorbance Detector
Detection wavelength: 254 nm
Injection volume: 10 μl
Solvent: methanol / water (The composition of methanol / water was a gradient analysis of 20: 80 → 80: 20 (volume ratio))
Flow rate: 1 ml / min.

(2) Oligomer amount in polyamide Polyamide is pulverized, JIS standard sieve 24 mesh is passed, 124 mesh non-passable polyamide powder is collected, about 20 g of the powder is Soxhlet extracted with 200 ml of methanol for 3 hours, and evaporated to dryness with an evaporator Furthermore, the residue amount obtained after removing caprolactam by vacuum drying at 80 ° C. for 8 hours was determined as the oligomer content.

(3) Sulfuric acid relative viscosity (ηr)
The polyamide is pulverized, the JIS standard sieve 24 mesh passes, and the 124 mesh non-passable polyamide powder is collected. About 20 g of the powder is Soxhlet extracted with 200 ml of methanol for 3 hours, and the residue is dried and used as a measurement sample. Measurement was performed using an Ostwald viscometer at a concentration of 0.01 g / ml of a sample in 98% sulfuric acid at 25 ° C.

(4) Amino group content in polyamide prepolymer Weighing about 0.2 g of the substance to be measured and dissolving it in 25 cc of a mixed solvent of phenol and ethanol (83.5: 16.5, volume ratio), 0.02N hydrochloric acid aqueous solution Was titrated using.

(5) Cyclic oligomer content in polyamide prepolymer The object to be measured is pulverized, passed through a JIS standard sieve 24 mesh, and 124 mesh is not passed, and the powder of the object to be measured is collected. Extraction was performed using a time Soxhlet extractor, and cyclic oligomers contained in the extract were quantified using a high performance liquid chromatograph. Prior to the measurement, confirmation of column retention time and preparation of a calibration curve were carried out using standard samples of caprolactam and caprolactam cyclic dimer, caprolactam cyclic trimer, and caprolactam cyclic tetramer. The calibration curve for caprolactam ring having a degree of polymerization of 5 was calculated as the same as the caprolactam ring tetramer. Moreover, in the following examples, cyclic oligomers of 7-mer or higher were not detected. The measurement conditions are as follows.
High performance liquid chromatograph: Waters 600E
Column: GL Sciences ODS-3
Detector: Waters 484 Tunable Absorbance Detector
Detection wavelength: 254 nm
Injection volume: 10 μl
Solvent: methanol / water (The composition of methanol / water was a gradient analysis of 20: 80 → 80: 20 (volume ratio))
Flow rate: 1 ml / min.

Examples 1-3
Heat treatment and polymerization were performed using the apparatus shown in FIG.

  The caprolactam aqueous solution having the composition shown in Table 1 is charged into the raw material storage tank 1, and then the caprolactam aqueous solution is supplied to the polymerization tower 7 via the pressure heat treatment tank 4 using the raw material supply pump 2 having the pressure gauge 3 on the discharge side. Then, continuous polymerization was performed under the conditions shown in Table 1, and a polyamide as a polymerization reaction product was obtained from the lower part of the polymerization tower 7. At the start of polymerization, 10 L of raw material was retained in the polymerization tower 7 in advance, and then the discharge amount from the polymerization tower was adjusted so that the amount of raw material retained in the polymerization tower was 10 L. The plates listed in Table 1 were installed in the upper space. In addition, a hole with a diameter of 4 mm was made in the plate so as to have the opening ratio shown in Table 1. In this example, polymerization was carried out without performing heat treatment in a pressurized heat treatment tank.

Examples 4-6
A caprolactam aqueous solution having the composition shown in Table 1 is charged into the raw material storage tank 1, and then supplied to the pressurized heat treatment tank 4 using the raw material supply pump 2 having the pressure gauge 3 on the discharge side. The heat treatment was performed. Next, the obtained polyamide prepolymer was supplied to the polymerization tower 7, and continuous polymerization was performed under the conditions shown in Table 1, and a polyamide as a polymerization reaction product was obtained from the lower part of the polymerization tower 7.

  The pressure in the apparatus is maintained and adjusted by the pressure regulating valve 5 so that moisture does not evaporate from the caprolactam aqueous solution during the heat treatment, and after passing through the pressure regulating valve 5, the pressure is released to the atmospheric pressure. The water evaporated from the polymer was discharged out of the system from the upper part of the polymerization tower 7.

  The polyamide prepolymer was sampled for analysis from the sample collection valve 6 before being supplied to the polymerization tower 7. Further, the polyamide after polymerization was collected from the lower part of the polymerization tower 7.

  About others, it implemented similarly to Examples 1-3.

Comparative Examples 1 and 2
The case where no plate is used is shown in Table 2 as Comparative Examples 1 and 2.

  As is apparent from Tables 1 and 2, a polymer having a small number of cyclic oligomers and a high ηr was obtained by using the production method of the present invention. Further, when no plate was used, or when the number of plates was less than the range of the present invention, there were many cyclic oligomers and only a lower value of ηr was obtained.

  The present invention provides a cyclic oligomer, particularly a polyamide having a low cyclic oligomer content, which is suitable as a raw material for fibers and resins by reducing the amount of monomers and oligomers after polyamide polymerization while obtaining the required high degree of polymerization. Can be efficiently and stably produced, and the oligomer removal and purification steps, which are subsequent processes, can be simplified, and polyamide can be produced with high production efficiency and low energy cost.

It is the schematic of the heat processing and the polymerization apparatus which were used in the Example.

Explanation of symbols

1: Raw material storage tank 2: Raw material supply pump 3: Pressure gauge 4: Pressurized heat treatment tank 5: Pressure regulating valve 6: Pressurized and heated reactant collection port 7: 15L atmospheric pressure continuous polymerization tower 8: Plate

Claims (8)

A method for producing a polyamide, characterized in that when a polyamide having a caproamide unit as a main constituent is produced, polymerization is carried out while forming a thin film on the upper part of the atmospheric pressure polymerization apparatus. 2. The method for producing a polyamide according to claim 1, wherein a caprolactam aqueous solution having a water content of 2 to 20% by weight is supplied to an atmospheric pressure polymerization apparatus. 3. The method for producing a polyamide according to claim 2, wherein a thin film is formed by providing a plate for forming a thin film on an upper part of the atmospheric pressure polymerization apparatus, and dropping a lactam aqueous solution onto the plate. 2. The method for producing a polyamide according to claim 1, wherein a polyamide prepolymer having an amino group content of 0.03 mmol / 1 g or more and a cyclic oligomer content of 0.6% by weight or less is supplied to an atmospheric pressure polymerization apparatus. The method for producing a polyamide according to claim 4, wherein the polyamide prepolymer is obtained by heat-treating a caprolactam aqueous solution having a water content of 2 to 20% by weight under pressure at a temperature of 200 to 330 ° C for 1 to 60 minutes. The method for producing a polyamide according to claim 4 or 5, wherein a plate for forming a thin film is provided on the upper part of the atmospheric pressure polymerization apparatus, and the thin film is formed by dropping a polyamide prepolymer on the plate. The method for producing a polyamide according to claim 3 or 6, wherein the plate for forming a thin film is a perforated plate. The method for producing a polyamide according to claim 7, wherein the area of the plate for forming a thin film satisfies the following formula (I).
0.05 ≤ V / A ≤ 0.20 (I)
V = Caprolactam aqueous solution or polyamide prepolymer supply amount (m ³ / h)
A = area of the plate (m ² )

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