JP5098187B2 - Method for producing polyamide - Google Patents

Description

  The present invention relates to a method for producing a polyamide using caprolactam as a main raw material. More specifically, caprolactam cyclic oligomer suitable for simplifying the removal process and purification process of monomers and oligomers contained in the polymer after polymerization, and energy saving, especially polyamide with low cyclic dimer content is efficient. In addition, the present invention relates to a stable manufacturing method.

  Polyamide resin mainly composed of caprolactam is used for clothing fibers and industrial fibers by taking advantage of its excellent characteristics. Furthermore, it is used as an injection-molded product in the automotive field, electrical / electronic field, etc. and for food packaging applications. It is widely used as an extruded film and stretched film in the center. A polyamide resin mainly composed of caprolactam is 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-purpose polyamide polymerization method described in pages 63 to 65 of "Polyamide resin handbook" (Fukumoto Osamu, 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 bottom of the tower and discharged into a water tank to be pelletized. Next, the pellets are supplied to a hot water extraction tower for removing oligomers such as monomers and cyclic dimers, and the monomers and oligomers are extracted countercurrently with hot water sent from the lower part of the tower and then taken out from the lower part. 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.

  In general, the polyamide after polymerization contains polyamide ligoma such as unreacted caprolactam monomer and caprolactam cyclic dimer remaining in the equilibrium of polymerization. Therefore, when used as it is as a raw material for fibers, films and injection molded products, Oligomer volatilizes during molding processing, and when producing final products such as fibers and films, injection molded products, it causes base stains, thread breakage, and poor appearance, resulting in a decrease in mechanical properties and appearance of the resulting product. Cause a problem. In particular, caprolactam dimer has a melting point of 347 ° C. to 348 ° C. among monomers and oligomers (“Polyamide Resin Handbook” (page 61 of Fukumoto, Nikkan Kogyo Shimbun)), and the adverse effect in the subsequent process is extremely large. Therefore, it is necessary to remove these unreacted monomers and oligomers, and as described above, extraction has generally been performed with hot water. This hot water extraction process requires a lot of energy to obtain hot water, and the extracted monomer, the monomer from the hot water containing the oligomer, the concentration operation to separate the oligomer, the distillation operation, or the monomer from the oligomer. A lot of energy is also required in the depolymerization operation to be obtained and the purification operation to remove impurities.

  In order to reduce the load of these extraction and purification steps, attempts have been made to reduce the monomers and oligomers contained in the polyamide after polymerization. For example, Patent Document 1 proposes.

That is, 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 a low temperature range of the melting point of the polyamide polymer + 10 ° C. or less, which can obtain the polymerization temperature of subsequent atmospheric pressure polymerization. A method for reducing the amount of monomers and oligomers contained in a polyamide polymer immediately after polymerization is disclosed. Here, it is shown that a polyamide polymer having a cyclic oligomer amount of 0.9% by weight or less was obtained. However, the polymer obtained by this method has a relatively low degree of polymerization, and therefore, there is a problem that applicable varieties are limited. was there. In addition, since the polymerization is performed at a temperature near the melting point, very delicate temperature control is required to prevent solidification, and there is a problem in stability in industrial production.
JP 2003-82096 A

  The present invention relates to the content of monomers and oligomers, particularly caprolactam cyclics, which can simplify or save energy in removing the monomers and oligomers from the polymer after polymerization in the production process of polyamides mainly composed of caproamide units. An object is to efficiently and stably produce a polyamide having a low oligomer content.

In order to solve the above problems, the present invention has the following configuration.
1) A method for producing a polyamide comprising a caproamide unit as a main constituent, wherein a caprolactam aqueous solution having a water content of 2 to 14% by weight is treated under a treatment temperature of 220 to 300 ° C. and a pressure equal to or higher than the vapor pressure at the treatment temperature. A polyamide prepolymer having an amino end group content of 0.05 mol / 1 g or more and a cyclic oligomer content of 0.6% by weight or less obtained through the heating step of ˜60 minutes or less is supplied to an atmospheric pressure polymerization apparatus, and a polymerization temperature is obtained. The relative value of sulfuric acid is 2.0 or more, the caprolactam content is 10% by weight or less, and the oligomer content is 2.0, characterized in that liquid phase polymerization is performed at a temperature of 250 to 270 ° C. for 5 to 12 hours. A process for producing a polyamide having a caprolactam cyclic dimer or tetramer content of 1.2% by weight or less.
2) The process for producing a polyamide as described in 1), wherein the content of caprolactam cyclic dimer in the polyamide is 0.3% by weight or less.

  By the method of the present invention, it is possible to efficiently and stably produce a polyamide having a low content of monomers and oligomers, particularly a caprolactam cyclic dimer having a large adverse effect on product quality, contained in a polyamide polymer after polymerization, It is possible to simplify or save energy in the subsequent extraction and purification steps. In addition, the polyamide production method of the present invention is capable of stable operation even when applied to industrial production, and productivity is significantly improved as compared with the prior art.

  The present invention is described in detail below.

  In the method for producing a polyamide of the present invention, an aqueous caprolactam solution having a water content of 2 to 14% by weight is first heated under pressure at a temperature of 220 to 300 ° C. for 5 to 60 minutes, so that the amino end group amount is 0.05 mol / 1 g or more. In addition, a polyamide prepolymer having a cyclic oligomer content of 0.6% by weight or less is obtained, the polyamide prepolymer is supplied to an atmospheric pressure polymerization apparatus, and the maximum polymerization temperature is 5 to 12 at a temperature of 250 to 270 ° C. Liquid phase polymerization for a time, sulfuric acid relative viscosity is 2.0 or more, caprolactam content is 10% by weight or less, oligomer content is 2.0% by weight or less, and caprolactam cyclic 2-tetramer content is 1. 2% by weight of polyamide is 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 chain oligomers, cyclic oligomers and unreacted monomers. The cyclic oligomer is one in which the terminal group of the chain oligomer is cyclized by amide bond within the same molecular chain, and has a degree of polymerization of up to 6. The amino terminal group amount is the total amount of one end group of a chain caproamide oligomer in which caprolactam is hydrolyzed and ring-opened by reaction with water or one or more caprolactams are added to aminocaproic acid. It is.

  In the method for producing a polyamide of the present invention, a caprolactam aqueous solution is prepared. The lower limit of the water content at this time is 2% by weight, preferably 2.5% by weight, particularly preferably 3% by weight, based on the total amount. The upper limit of the water content is 14% by weight, preferably 13% by weight, particularly preferably 12% by weight, based on the total amount. When the moisture content is less than 2% by weight, a large amount of caprolactam cyclic oligomer is formed when a polyamide prepolymer having an amino end group amount of 0.05 mmol / 1 g or more is obtained, and the amount of cyclic dimer to tetramer after polymerization is 1.2% by weight. %, The burden of the oligomer removal process increases. On the other hand, if the water content exceeds 14% by weight, the energy required to heat the raw material increases, which is not preferable.

The lower limit of the treatment temperature for obtaining a polyamide prepolymer having an amino end group amount of 0.05 mmol / 1 g or more of the present invention is 220 ° C., preferably 225 ° C., particularly preferably 230 ° C. The upper limit of the treatment temperature is 300 ° C, preferably 290 ° C, particularly preferably 280 ° C. In order to maintain the water content of the caprolactam aqueous solution within the range of the present invention described above at the present treatment temperature, it is necessary to maintain the pressure during the treatment at or above the vapor pressure at the treatment temperature. Can be performed using a pressure control valve or the like. The pressure at this time is not particularly limited as long as it is sufficient to prevent the evaporation of moisture in the system, but 0.111 to
The range of 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 atm, 1.55 to 51.67 kg / cm ^2). ) Is more preferable. Under a pressure of less than 0.111 MPa, the amino group production efficiency during prepolymerization is reduced, so that the amount of oligomer in the polyamide prepolymer increases until the necessary amino group amount is obtained, while 6.08 MPa. If it exceeds, the productivity and economy will be inferior. When the treatment temperature is less than 220 ° C., it takes time to obtain a polymer having an amino end group amount of 0.05 mmol / 1 g or more, so that it is inferior in productivity and unsuitable for industrial production. In addition, when the treatment temperature exceeds 300 ° C., the treatment can be performed in a short time, but the equipment cost becomes expensive due to the increased pressure to retain moisture, the production rate of the amino terminal group amount, caprolactam Since the production rate of the cyclic oligomer becomes too large, it lacks industrial stability.
The processing time for preparing the polyamide prepolymer of the present invention is 5 to 60 minutes. The upper limit is preferably 50 minutes or less, particularly preferably 40 minutes or less. If it exceeds 60 minutes, a large amount of caprolactam cyclic oligomers are produced in the polyamide prepolymer, and the amount of cyclic 2-tetramer after polymerization exceeds 1.2% by weight, resulting in a large burden on the subsequent oligomer removal and purification steps. Become. If an attempt is made to obtain a polyamide prepolymer having an amino end group amount of 0.05 mmol / 1 g or more in less than 5 minutes, the production rate of the amino end group amount and the production rate of the caprolactam cyclic oligomer increase, resulting in lack of industrial stability.

  The polyamide prepolymer of the present invention thus obtained has an amino end group amount of 0.05 mmol / 1 g or more in the polyamide prepolymer. More preferably, it is 0.06 mmol / 1g or more, Most preferably, it is 0.08 mmol / 1g or more. When the amount of amino end groups is less than 0.05 mmol / 1 g, the rate of addition of caprolactam remaining to the amino end groups when polymerizing the polyamide from the obtained polyamide prepolymer, that is, the consumption rate of caprolactam is slow, so caprolactam is mixed with water. In this reaction, a caprolactam cyclic oligomer is likely to be produced via a caprolactam chain oligomer, and the caprolactam cyclic dimer to tetramer after polymerization exceeds 1.2% by weight. growing. Although there is no upper limit to the amount of amino end groups, the effect is not changed even if it exceeds 0.4 mmol / 1 g, and thus a range of 0.4 mmol / 1 g or less is usually adopted in terms of productivity. The cyclic oligomer content in the prepolymer is 0.6% by weight or less. Preferably it is 0.4 weight% or less, Most preferably, it is 0.3 weight% or less. This is because when the amount exceeds 0.6% by weight, the oligomer content in the polyamide polymer increases when the polyamide polymer is produced from the obtained polyamide prepolymer. Although there is no restriction | limiting in particular in the minimum of this cyclic oligomer, Usually, it is 0.01 weight%.

  The polyamide prepolymer thus obtained is polymerized in the liquid phase at 250 to 270 ° C. for 5 to 12 hours to obtain polyamide. The caprolactam content in the polyamide is 10% by weight or less, preferably 9% by weight or less, more preferably 8% by weight or less. Although there is no restriction | limiting in particular in a minimum, Usually, it is 3 weight%. Further, the oligomer content in the polyamide is 2.0% by weight or less, preferably 1.9% by weight or less. Although there is no restriction | limiting in particular in a lower limit, Usually, it is 1.0 weight%. The total of the caprolactam cyclic dimer to tetramer in the polyamide is 1.2% by weight or less, preferably 1.1% by weight or less. Although there is no restriction | limiting in particular in a minimum, Usually, it is 0.3 weight%. The oligomer content in the polyamide referred to in the present invention is the amount of residue obtained after about 20 g of polyamide powder is Soxhlet extracted with 200 ml of methanol for 3 hours, the extract is evaporated to dryness and further vacuum dried to remove caprolactam. From the weight, the ratio is obtained by dividing the weight by the weight of the polyamide powder as a sample.

  In the method for producing a polyamide of the present invention, when the polyamide prepolymer obtained by heat treatment under pressure is supplied to an atmospheric pressure polymerization apparatus, the reaction product after the heat treatment under pressure is flushed to the upper part of the atmospheric pressure polymerization apparatus to remove moisture. It is preferable to remove the transpiration. 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.

  In the method for producing a polyamide of the present invention, the polymerization apparatus to be 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.

  The polymerization temperature and the polymerization time are as described above so that the oligomer contained in the polyamide polymer after polymerization is 2.0% by weight or less, the caprolactam cyclic 2-tetramer is 1.2% by weight or less, and the caprolactam is 10% by weight or less. Choose from a range. If the amount of oligomer contained in the polymer after polymerization exceeds 2.0% by weight or the amount of cyclic dimer to tetramer exceeds 1.2% by weight, the burden on the subsequent oligomer removal and purification process becomes large. Become. If caprolactam exceeds 10% by weight, the yield of polyamide is low, which is economically undesirable.

  The polymerization temperature is 250 to 270 ° C, preferably 250 to 267 ° C, more preferably 250 to 265 ° C. When the polymerization temperature is less than 250 ° C., the polymerization rate is slow and it takes a long time for the polymerization, which is not economical. In addition, oligomers are produced in excess of 2.0% by weight during the polymerization, and caprolactam cyclic 2-tetramers. Therefore, the burden of the subsequent oligomer removal and purification steps increases. In addition, when the temperature exceeds 270 ° C., the production rate of caprolactam cyclic oligomer increases, so that the oligomer after polymerization exceeds 2.0% by weight, and the amount of cyclic 2 to tetramer exceeds 1.2% by weight. The burden on the subsequent oligomer removal and purification steps is increased. The polymerization temperature here is the maximum temperature of the polyamide or its precursor in the polymerization apparatus. When the polymerization time is less than 5 hours, caprolactam may exceed 10% by weight, so that the polymerization temperature needs to exceed 270 ° C. in order to make caprolactam 10% by weight or less, and the production rate of caprolactam cyclic oligomer increases. There are problems such as. On the other hand, if it exceeds 12 hours, the caprolactam cyclic dimer to tetramer content is more than 1.2% by weight and it is not economical. In the present invention, a preferable polymerization time is 6 to 10 hours. According to the method of the present invention, the content of caprolactam cyclic dimer in the polyamide polymer is usually 0.3% by weight or less, and in a preferred embodiment, it is 0.25% by weight or less. Since the cyclic dimer is sublimable and has a high melting point, it is a main causative substance of the base stain during film production and spinning, so that the caprolactam cyclic dimer is reduced as described above. It is extremely useful in practice. The lower limit of the cyclic dimer is not particularly limited, but is usually 0.001% by weight.

  The relative viscosity of the polyamide of the present invention is 2.0 or more as the relative viscosity at 25 ° C. of a 98% sulfuric acid solution having a sample concentration of 0.01 g / mL. More preferably, it is 2.05-7.0, Most preferably, it is 2.1-6.5, Most preferably, it is 2.15-6.0. If the relative viscosity is less than 2.0, the mechanical properties may not be sufficiently expressed. If the relative viscosity exceeds 8.0, the melt viscosity is too high and molding becomes difficult.

  In the method for producing a polyamide of the present invention, it is possible to polymerize by further adding caprolactam to the polyamide prepolymer at the start of polymerization. The additional amount of caprolactam is not particularly limited as long as the amino terminal group amount in the raw material composition composed of the polyamide prepolymer and the additional caprolactam is 0.05 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 does not matter if it is used in combination as long as it does not exceed. When it exceeds 10 mol%, the crystallinity of the resulting polyamide polymer 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. When the amount of the additive exceeds 5 mol%, the melting point and crystallinity of the resulting polyamide polymer may decrease, and the moldability and physical properties of the molded product may decrease.

  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 caries 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, caprolactam and oligomer 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 caprolactam and oligomers, hot water extraction may be further performed.

  The volatilization removal of caprolactam 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.

  In addition, the degree of polymerization can be adjusted to a suitable value according to the application by simultaneously performing melt polymerization or solid phase polymerization of polyamide in the volatilization removal of caprolactam and oligomer by heating under reduced pressure.

  The polyamide obtained by the method for producing a polyamide of the present invention is less 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. It is preferable to adjust the degree of polymerization to a desired degree by solid-phase polymerization in which the heat treatment is performed under a nitrogen flow or under 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 resin 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 terminal groups to carboxyl terminal 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.

  The end-capping agent can be added by adding raw materials such as caprolactam at the beginning of the heat treatment of the polyamide prepolymer at the same time, adding it before introducing the atmospheric pressure polymerization apparatus, and adding unreacted caprolactam and oligomer in the molten state to the polyamide resin. A method of adding at the time of removal is employed. 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 (aliphatic alcohol, aliphatic amide, aliphatic bisamide, bisurea, polyethylene wax, etc.), pigments (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 and 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) Amino terminal group amount in polyamide prepolymer About 0.2 g of the substance to be measured was precisely weighed and dissolved in 25 cc of a phenol / ethanol mixed solvent (83.5: 16.5, volume ratio), and then 0.02N hydrochloric acid. Titration with aqueous solution.

(2) Cyclic oligomer content in polyamide prepolymer The object to be measured is pulverized, passed through JIS standard sieve 24mesh, 124mesh does not pass, 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. 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.

(3) Caprolactam amount in polyamide and caprolactam cyclic 2-4 tetramer amount Polyamide was pulverized, passed through JIS standard sieve 24 mesh, 124 mesh collected non-passed polyamide powder, and about 20 g of the powder was collected in 200 ml of methanol for 3 hours. Soxhlet extraction was performed, and 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 carried out using standard samples of caprolactam and caprolactam cyclic dimer, caprolactam cyclic trimer, and caprolactam cyclic tetramer.
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.

(4) Amount of oligomers in polyamide Polyamide is crushed, JIS standard sieve 24 mesh passes, 124 mesh collects non-passed polyamide powder, about 20 g of the powder is soxhlet extracted with 200 ml of methanol for 3 hours, and evaporated to dryness with an evaporator. After solidifying and further vacuum drying at 80 ° C. for 8 hours, the amount of residue obtained after removing caprolactam was determined as the oligomer content.

(5) Sulfuric acid relative viscosity (ηr)
The polyamide was pulverized, JIS standard sieve 24 mesh passed, 124 mesh collected non-passed polyamide powder, about 20 g of the powder was Soxhlet extracted with 200 ml of methanol for 3 hours, and the residue was 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.

Examples 1-9, Comparative Examples 1-7 (heat treatment and polymerization)
A. Raw materials used The following raw materials were used in the following Examples and Comparative Examples.

  Caprolactam was prepared by melting a special grade of Tokyo Chemical Industry Co., Ltd. and drying it with molecular sieves.

B. Heat treatment and continuous polymerization at normal pressure Heat treatment and polymerization were carried out using the apparatus shown in FIG.

  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 heat treatment tank 4 equipped with the heating cylinder 5 using the raw material supply pump 2 having the pressure gauge 3 on the discharge side to heat the contents. Then, the heat treatment was continuously performed under the conditions described in Table 1. Next, the obtained polyamide prepolymer was supplied to the polymerization tower 9, the contents were heated, continuous polymerization was performed under normal pressure under the conditions described in Table 1, and the polymerization reaction product was obtained from the lower part of the polymerization tower 9 equipped with the heating cylinder 10. A certain polyamide was discharged and pelletized to obtain cylindrical polyamide pellets having a diameter of about 2 mm and a length of about 3 mm. The pressure in the heat treatment tank is maintained and adjusted by the pressure regulating valve 6 so that water does not evaporate from the caprolactam aqueous solution during the heat treatment, and the water evaporated from the polyamide prepolymer is released by releasing the pressure after the pressure regulating valve to the polymerization tower. 9 It discharged | emitted out of the system via the packed tower 11 from the upper part. The reflux ratio in the packed tower was 1, and caprolactam contained in the evaporated water was recovered.

  When analyzing the polyamide prepolymer, before supplying to the polymerization tower 9, the valve 7 is opened from the sampling port 8 so as to maintain the pressure in the heat treatment tank so that moisture does not evaporate from the caprolactam aqueous solution during the heat treatment. Collected. Table 1 shows the amino end group amount of the polyamide prepolymer and the content analysis results of the caprolactam oligomer and the caprolactam cyclic dimer in the polyamide.

  The present invention is an efficient and stable method for producing a caprolactam cyclic oligomer, particularly a polyamide having a low cyclic dimer content, and the polyamide obtained by the method of the present invention simplifies the subsequent monomer and oligomer removal step. Or energy saving is possible.

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: Heat treatment tank 5: Heating cylinder 6: Pressure regulating valve 7: Valve 8: Polyamide prepolymer sampling port 9: Polymerization tower 10: Heating cylinder 11: Packing tower

Claims (2)

A method for producing a polyamide comprising a caproamide unit as a main constituent, wherein a caprolactam aqueous solution having a water content of 2 to 14% by weight is treated at a treatment temperature of 220 to 300 ° C. and a pressure equal to or higher than a vapor pressure at the treatment temperature. A polyamide prepolymer having an amino end group content of 0.05 mol / 1 g or more and a cyclic oligomer content of 0.6% by weight or less, obtained through a step of partial heating, is supplied to an atmospheric pressure polymerization apparatus, and the maximum polymerization temperature is obtained. Liquid phase polymerization at a temperature of 250 to 270 ° C. for 5 to 12 hours, sulfuric acid relative viscosity is 2.0 or more, caprolactam content is 10% by weight or less, oligomer content is 2.0% by weight Hereafter, the manufacturing method of polyamide whose sum total of caprolactam cyclic | annular 2-tetramer content is 1.2 weight% or less. The method for producing a polyamide according to claim 1, wherein the content of caprolactam cyclic dimer in the polyamide is 0.3% by weight or less.

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