JP5050367B2 - Process for producing polycaproamide - Google Patents

Description

  The present invention relates to a method for producing polycaproamide. More specifically, the present invention relates to a method for efficiently and stably producing a polycaproamide having a small content of a caprolactam cyclic dimer suitable as a raw material for fibers, injection molded articles and films.

  Polycaproamide resin mainly made of caprolactam is used for textile fibers and industrial fibers by taking advantage of its excellent characteristics. Furthermore, it is used as injection-molded products in the automotive and electrical / electronic fields, and for food packaging applications. It is widely used as an extruded film and stretched film.

  A polycaproamide 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 polycaproamide polymerization method 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 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.

  Generally, polycaproamide after polymerization contains polycaproamide oligomers such as unreacted caprolactam monomer and caprolactam cyclic dimer which remain in the equilibrium of polymerization. Therefore, when used as it is as a raw material for fibers, films and injection molded products Monomers and oligomers volatilize during the molding process, and when obtaining final products such as fibers and films, injection molded products, it causes base stains, thread breakage, and appearance defects, and the mechanical properties and appearance of the resulting products also deteriorate. Cause a number of problems. In particular, caprolactam cyclic dimer has a high melting point of 347 to 348 ° C. among monomers and oligomers (page 61 of “Polyamide resin handbook” (Fukumoto Osamu, 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 with hot water has generally been performed so far. In this hot water extraction process, hot water is usually used in an amount of about 1.5 to 3.0 parts by weight per part by weight of polycaproamide. Cost. Also, much energy is required for extracted monomers, monomers from hot water containing oligomers, concentration operations for separating oligomers, distillation operations, depolymerization operations for obtaining monomers from oligomers, and purification operations for removing impurities. .

  Thus, for example, Patent Document 1 and Patent Document 2 are methods for efficiently performing the extraction operation. Moreover, there exists patent document 3 as a means which abbreviate | omits the extraction process by hot water, for example.

  Patent Document 1 aims to provide a method for efficiently extracting monomers and oligomers by preventing liquid mixing in an extraction tower, and is a funnel type opened upward in a countercurrent contact area in the extraction tower. By providing the cylinders in multiple stages and partially narrowing the section of the tower with the funnel-shaped cylinders, the extraction tanks are separated into stages with different liquid concentrations, such as being connected in multiple stages in series. It has been shown that a high flow rate of extracted water from the bottom prevents downflow of highly concentrated liquid from the top. The amount of hot water specifically disclosed in Patent Document 1 is 1.0 part by weight per 1.0 part by weight of polyamide, but polycaproamide polymerized by the usual method as described above is used as it is in the method of Patent Document 1. Even if it is applied, it is difficult to sufficiently reduce the caprolactam cyclic dimer content.

  Patent Document 2 discloses a method of increasing the oligomer extraction rate by supplying caprolactam as a solvent into the extraction column in order to increase the oligomer extraction rate. However, the amount of hot water used in the examples was 1.3 parts by weight per 1.0 part by weight of polyamide, and not only required a lot of energy as described above, but also polymerized by the usual method as described above. Even if polycaproamide is applied as it is to the method of Patent Document 2, it is difficult to sufficiently reduce the caprolactam cyclic dimer content.

Patent Document 3 discloses a method for suppressing oligomers produced during polymerization and removing mainly monomers from a molten state or a solid phase state. However, in order to suppress oligomer formation, the polymerization temperature needs to be lower than the melting point, and advanced production management technology is required for stable continuous production. Furthermore, since the polymerization of polycaproamide proceeds when the monomer is removed from the molten state or solid phase state, this production method is limited when obtaining polycaproamide having a relatively high degree of polymerization. In addition, the above production method still has problems in stable continuous production.
Japanese Patent Publication No. 47-28918 Japanese Examined Patent Publication No. 63-40445 Japanese Patent Laid-Open No. 11-343341

  An object of the present invention is to efficiently and stably produce a polycaproamide having a small content of a caprolactam cyclic dimer suitable as a raw material for fibers, injection-molded articles, and films.

In order to solve the above problems, the present invention has the following configuration.
1) Step 2) 1) of obtaining a polycaproamide prepolymer having an amino group content of 0.05 mmol / 1 g or more by heat-treating an aqueous caprolactam solution having a water content of 2 to 14% by weight at a temperature of 220 to 300 ° C. for 5 to 60 minutes. The polycaproamide prepolymer obtained in the process is polymerized in the liquid phase at a polymerization temperature of 240 to 270 ° C. for 5 to 12 hours, and the caprolactam cyclic dimer is 0.3% by weight or less and the caprolactam is 6 to 10% by weight. Step 3) to obtain polycaproamide of 0.5 to 1.2 parts by weight of water with respect to 1 part by weight of polycaproamide and polycaproamide obtained in step 2) and water at 90 to 130 ° C. A process for producing polycaproamide, comprising a step of obtaining a polycaproamide having a caprolactam cyclic dimer content of 0.04% by weight or less by continuously countercurrent-contacting at a ratio of

  By the method of the present invention, it is possible to efficiently and stably produce polycaproamide having a small content of caprolactam cyclic dimer suitable as a raw material for fibers, injection molded articles and films.

  The present invention is described in detail below.

In the method for producing polycaproamide of the present invention,
First, a caprolactam aqueous solution having a water content of 2 to 14% by weight was heat-treated at a temperature of 220 to 300 ° C. for 5 to 60 minutes to obtain a polycaproamide prepolymer having an amino group content of 0.05 mmol / 1 g or more, and the polycaproamide prepolymer Is polymerized in a liquid phase at a polymerization temperature of 240 to 270 ° C. for 5 to 12 hours to obtain a polycaproamide having a caprolactam cyclic dimer of 0.3% by weight or less and a caprolactam of 6 to 10% by weight.

  The polycaproamide 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. The amino 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. is there.

  In the method for producing polycaproamide of the present invention, an aqueous caprolactam 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 water content is less than 2% by weight, a large amount of caprolactam cyclic dimer is produced when a polycaproamide prepolymer having an amino group content of 0.05 mmol / 1 g or more is obtained, and the amount of cyclic dimer after polymerization is 0.3. It becomes difficult to efficiently obtain polycaproamide containing a cyclic dimer in excess of wt% and 0.01 wt% or less after hot water extraction. Moreover, since the energy which heats a raw material becomes large when a moisture content exceeds 14 weight%, it is unpreferable.

  The lower limit of the treatment temperature for obtaining a polycaproamide prepolymer having an amino 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 addition, the processing temperature in this invention refers to the system temperature at the time of obtaining a polycaproamide prepolymer. 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. When the treatment temperature is less than 220 ° C., it takes time to obtain a polycaproamide prepolymer having an amino group content of 0.05 mmol / 1 g or more, so that it is inferior in productivity and unsuitable for industrial production.

  In addition, if the treatment temperature exceeds 300 ° C., the treatment can be performed in a short time, but the pressure for retaining the moisture is high, so that the equipment needs to have high pressure resistance, and the equipment cost is high. The production rate of the amount and the production rate of the caprolactam cyclic dimer become too fast, so that it lacks industrial stability.

  The processing time for preparing the polycaproamide 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 dimer is formed in the polycaproamide prepolymer, and the amount of cyclic dimer after polymerization exceeds 0.3% by weight, and 0.01% by weight after hot water extraction described later It becomes difficult to efficiently obtain polycaproamide containing the following cyclic dimer. If an attempt is made to obtain a polycaproamide prepolymer having an amino group content of 0.05 mmol / 1 g or more in less than 5 minutes, the production rate of the amino group and the production rate of the caprolactam cyclic dimer increase. Lack.

  In the present invention, the polycaproamide prepolymer is prepared so that the amount of amino groups is 0.05 mmol / 1 g or more. Furthermore, it is preferably 0.07 mmol / 1g or more, particularly preferably 0.09 mmol / 1g or more. When the amount of amino groups is less than 0.05 mmol / 1 g, the rate of addition of caprolactam remaining to amino groups, that is, the consumption rate of caprolactam, when polymerizing polycaproamide from the obtained polycaproamide prepolymer is slow, so caprolactam Tends to produce a caprolactam cyclic dimer via a caprolactam chain dimer by reaction with water, the amount of caprolactam cyclic dimer after polymerization exceeds 0.3% by weight, and 0. It becomes difficult to efficiently obtain polycaproamide containing 01% by weight or less of cyclic dimer. Although there is no upper limit to the amount of amino groups, the effect does not change even if the amount exceeds 0.4 mmol / g, and thus a range of 0.4 mmol / g or less is usually adopted in terms of productivity.

  In the present invention, the polycaproamide prepolymer obtained as described above is polymerized in a liquid phase at a polymerization temperature of 240 to 270 ° C. for 5 to 12 hours, and a caprolactam cyclic dimer is 0.3% by weight or less, A polycaproamide with 6-10% by weight of caprolactam is obtained. The polymerization temperature here refers to the average temperature in the system during the polymerization. The average temperature in the system is obtained from an average value obtained by setting at least three thermometers in the polymerization system as evenly as possible (that is, the temperature in the first half of polymerization, the middle of polymerization, and the second half of polymerization can be measured) Refers to temperature.

  There is no restriction | limiting in particular in the polymerization apparatus used in order to superpose | polymerize the said polycaproamide prepolymer, The apparatus generally used for superposition | polymerization of a 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 apparatus for performing the polymerization is preferably provided separately from the reaction tank for performing the step of obtaining the polycaproamide prepolymer from the viewpoint of easy temperature control.

  The polymerization temperature and polymerization time are such that the caprolactam cyclic dimer after polymerization is 0.3% by weight or less, preferably 0.2% by weight or less, and caprolactam is 6 to 10% by weight, preferably 7 to 9% by weight. The polymerization temperature may be selected from the above range, but a preferable polymerization temperature is 250 to 265 ° C., and a preferable polymerization time is 6 to 10 hours. The polymerization temperature profile can be arbitrarily set according to a conventional method.

  If the cyclic dimer after polymerization exceeds 0.3% by weight, it becomes difficult to efficiently obtain polycaproamide containing 0.04% by weight or less of the cyclic dimer after hot water extraction. In addition, when caprolactam is less than 6% by weight, the oligomer extraction rate in the hot water extraction operation decreases, and it is difficult to efficiently obtain polycaproamide containing a cyclic dimer of 0.04% by weight or less after hot water extraction. It becomes. Moreover, in order to make caprolactam less than 6 weight%, the process of removing a monomer is needed after normal superposition | polymerization. If caprolactam exceeds 10% by weight, the yield of polycaproamide is low, which is not economical. The content of the cyclic dimer can be reduced by lowering the polymerization temperature or the polymerization time, and the caprolactam content can be reduced by increasing the polymerization time.

  If the polymerization temperature is less than 240 ° C, the polymerization rate is slow and it takes a long time to polymerize, which is not economical, and caprolactam cyclic dimer is produced in excess of 0.3 wt% during the polymerization. Later, it becomes difficult to efficiently obtain polycaproamide containing 0.04% by weight or less of a cyclic dimer, and the original purpose cannot be achieved. In addition, when the temperature exceeds 270 ° C., the production rate of caprolactam cyclic dimer increases, so that the amount of cyclic dimer after polymerization exceeds 0.3% by weight and 0.04% by weight or less after hot water extraction. It becomes difficult to efficiently obtain polycaproamide containing a cyclic dimer. When the polymerization time is less than 5 hours, caprolactam exceeds 10% by weight or the polymerization temperature needs to exceed 270 ° C. in order to make caprolactam less than 10% by weight, and the production rate of caprolactam cyclic dimer increases. There's a problem. On the other hand, if it exceeds 12 hours, the caprolactam cyclic dimer content exceeds 0.3% by weight and it is not economical.

  The degree of polymerization of the polycaproamide of the present invention is not particularly limited as long as it satisfies the physical properties and processability of the final product, such as fibers, films, and injection molded products. In the present invention, it is also possible to add a solid phase polymerization operation. This solid phase polymerization operation is not particularly limited, but is preferably performed after hot water extraction from the viewpoint that it can be performed simultaneously with drying. To illustrate the degree of polymerization, the relative viscosity at 25 ° C. of a 98% sulfuric acid solution having a sample concentration of 0.01 g / mL is 2.0 or more. Furthermore, it is preferably 2.05 to 7.0, particularly preferably 2.1 to 6.5, and most preferably 2.15 to 6.0. If the relative viscosity is less than 2.0, the mechanical properties may be insufficiently expressed, and if it exceeds 8.0, the melt viscosity may be too high and molding may be difficult.

  In the polycaproamide production method of the present invention, at the start of polymerization, caprolactam can be further added to the polycaproamide prepolymer for polymerization. The additional amount of caprolactam is not particularly limited as long as the amount of amino groups in the raw material composition composed of polycaproamide prepolymer and additional caprolactam is 0.05 mmol / 1 g or more.

  Although caprolactam is mainly used as the raw material used in the method for producing polycaproamide of the present invention, one or two or more other lactams and derivatives thereof are used as a whole in the raw material of polycaproamide as long as the object of the invention is not impaired. It may be used in combination within a range not exceeding 10 mol%. If it exceeds 10 mol%, the crystallinity of the resulting polycaproamide 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 polycaproamide 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 contained in the raw material before heat treatment or in the polymerization stage. It can be fed and 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, with respect to caprolactam. When the amount of the additive exceeds 5 mol%, the melting point and crystallinity of the resulting polycaproamide polymer 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 salt of a dicarboxylic acid and a diamine, more preferably a salt derived from an aliphatic and / or aromatic dicarboxylic acid and an aliphatic diamine, and most preferably an adipic acid and hexamethylene. Salts derived from diamines and / or salts derived from terephthalic acid and hexamethylenediamine.

  There is no restriction | limiting in particular in the supply method of the said additive. It may be added to the raw material before the heat treatment or the polymerization apparatus as it is, or it may be dissolved in a solvent such as water and added as a solution.

  In the method for producing polycaproamide of the present invention, the terminal can be blocked with a carboxylic acid compound and the degree of polymerization can be adjusted as necessary. When end-capping is performed by adding a monocarboxylic acid, the end group concentration of the obtained polycaproamide 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.

  In addition, as a method of adding a terminal blocking agent, a method of charging simultaneously with raw materials such as caprolactam before the heat treatment of polycaproamide prepolymer, a method of adding in the middle of the heat treatment, adding after the heat treatment and before introducing the atmospheric pressure polymerization apparatus Method is adopted. The terminal blocking agent may be added as it is, or may be added after dissolving 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.), release agents and lubricants (fatty alcohol, aliphatic amide, aliphatic bisamide, 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-butylbenzenesulfonamide, etc.), antistatic Agent (alkyl sulfate type anionic antistatic agent, Quaternary ammonium salt type cationic antistatic agent, nonionic antistatic agent such as polyoxyethylene sorbitan monostearate, betaine amphoteric antistatic agent, etc.), flame retardant (melamine cyanurate, magnesium hydroxide, aluminum hydroxide) Such as hydroxide, ammonium polyphosphate, brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate, brominated epoxy resin or a combination of these brominated flame retardants and antimony trioxide), filler (graphite, sulfuric acid) Barium, 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, ben Particles, fibers, needles, platy fillers, etc.), other polymers (other polycaproamide, 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.

  In the method for producing polycaproamide of the present invention, polycaproamide 1 obtained by removing low polymer (hot water extraction) while continuously countercurrently contacting the polycaproamide obtained by the polymerization method with hot water is used. By using 0.5 to 1.2 parts by weight of hot water with respect to parts by weight, it is finally possible to efficiently obtain polycaproamide having a caprolactam cyclic dimer content of 0.04% by weight or less. Become.

  The polycaproamide after polymerization is once pelletized by a usual method. The shape and size of the pellet are not particularly limited, but a cylindrical shape having a diameter of 1.2 mm to 3.0 mm and a length of 2.0 mm to 4.0 mm is preferable. If the diameter is less than 1.2 mm or the length is less than 2.0 mm, the pelletization may require a lot of cost. If the diameter exceeds 3.0 mm or the length exceeds 4.0 mm, The hot water extraction operation may take a long time.

  As a hot water extraction device for continuously counter-contacting the pellets with hot water, the pellet has a pellet supply port and a hot water discharge port at the top of the extraction tower, and a pellet discharge port and hot water at the bottom of the extraction tower. It is a device having a supply port, and the pellets descend from the pellet supply port toward the discharge port, and the hot water introduced from the hot water supply port rises in countercurrent contact with the pellets, from the hot water discharge port. What has the structure discharged | emitted is preferable. Here, the pellets are supplied to the upper part of the extraction device from which hot water is introduced from the lower part and discharged from the upper part, and are discharged from the lower part so that the inside of the extraction apparatus is filled with pellets.

The extraction time is 3 to 40 hours, preferably 5 to 30 hours, and more preferably 7 to 25 hours. If the extraction time is less than 3 hours, the cyclic dimer cannot be sufficiently removed, and if it exceeds 40 hours, it takes a long time and is not economical, and polycaproamide is hydrolyzed during the extraction operation. May occur and the degree of polymerization may decrease.
Here, the shape of the extraction tower of the extraction device is not particularly limited as long as it is an extraction tower used in a normal polycaproamide hot water extraction device. For example, in the case of a cylindrical shape, the length of the tower (L) L / D, which is the ratio of diameter (D), is preferably 5 or more and 50 or less. If it is less than 5, abnormal mixing of hot water tends to occur, and if it exceeds 50, the length of the tower becomes longer and the equipment cost increases.

  The upper limit of caprolactam cyclic dimer content in the final polycaproamide is 0.04% by weight, preferably 0.03% by weight, more preferably 0.02% by weight, still more preferably 0.01% by weight, Particularly preferred is 0.008% by weight, and most preferred is 0.005% by weight. When the caprolactam cyclic dimer amount exceeds 0.04% by weight, the caprolactam cyclic dimer volatilizes a lot when processed into fibers, films, and injection molded products, resulting in spout contamination, thread breakage, and poor appearance. As a result, the mechanical properties and appearance of the resulting product also deteriorate. Although the minimum of caprolactam cyclic dimer content is not specifically limited, 0.001 weight% is preferable. Even if it is less than 0.001% by weight, the effect is small.

  The amount of hot water continuously brought into counter-current contact with the polycaproamide pellets is 0.5 to 1.2 parts by weight, preferably 0.55 to 1.1 parts by weight with respect to 1 part by weight of polycaproamide. Particularly preferred is 0.6 to 1.0 part by weight, and most preferred is 0.65 to 0.95 part by weight.

  By bringing the polycaproamide pellets into countercurrent contact with hot water, oligomers such as caprolactam and caprolactam cyclic dimer migrate from the pellet to the hot water side (ie, oligomers such as caprolactam and caprolactam cyclic dimer are extracted). . Caprolactam hot water extracted from polycaproamide pellets by making the amount of hot water continuously counter-currently contacted with polycaproamide pellets 1.2 parts by weight or less with respect to 1 part by weight of polycaproamide The concentration can be made sufficiently high, and the caprolactam is a good solvent for the caprolactam cyclic dimer, so that the caprolactam cyclic dimer can be extracted efficiently. When the amount exceeds 1.2 parts by weight, the caprolactam cyclic dimer cannot be efficiently removed from the pellet because the hot water concentration of caprolactam, which is a good solvent for the caprolactam cyclic dimer, is not sufficiently high. When the amount of hot water is less than 0.5 parts by weight relative to 1 part by weight of polycaproamide, the concentration of caprolactam in hot water increases and the extraction rate of the amount of caprolactam cyclic dimer itself increases. Since the amount of caprolactam cyclic dimer increases, the caprolactam cyclic dimer does not decrease sufficiently due to the difference in equilibrium concentration between the hot water of the caprolactam cyclic dimer and the polycaproamide pellets.

  The temperature of the hot water used for the extraction operation is 90 ° C or higher and 130 ° C or lower. When the temperature is lower than 90 ° C., the extraction rate of the caprolactam cyclic dimer is slow and an efficient extraction operation becomes difficult. Moreover, when it exceeds 130 degreeC, there exists a possibility that a polycaproamide pellet may cause a melt | fusion. Preferably, it is 90-110 degreeC, Most preferably, it is 90-100 degreeC. When the temperature is 100 ° C. or lower, a pressurizing equipment with a pressure higher than the atmospheric pressure for maintaining the temperature is unnecessary, and the equipment cost can be reduced.

  The polycaproamide obtained by the production method of the present invention can be used for a drying operation or solid-phase polymerization for further increasing the degree of polymerization, or, for example, an antioxidant or a heat stabilizer (hindered phenol, hydroquinone, depending on the application). , Phosphites and their substitutes, copper halides, iodine compounds, etc.), weathering agents (resorcinols, salicylates, benzotriazoles, benzophenones, hindered amines, etc.), mold release agents and lubricants (aliphatic alcohols) , Aliphatic amides, aliphatic bisamides, bisureas, polyethylene waxes, etc.), pigments (cadmium sulfide, phthalocyanine, carbon black, etc.), dyes (nigrosine, aniline black, etc.), crystal nucleating agents (talc, silica, kaolin, clay, etc.) ), Plasticizer (octyl p-oxybenzoate, N Butylbenzenesulfonamide, etc.), antistatic agent (alkyl sulfate type anionic antistatic agent, quaternary ammonium salt type cationic antistatic agent, nonionic antistatic agent such as polyoxyethylene sorbitan monostearate, betaine type Amphoteric antistatic agents, etc.), flame retardants (melamine cyanurate, magnesium hydroxide, aluminum hydroxide and other hydroxides, ammonium polyphosphate, brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate, brominated epoxy resins or these Combinations of brominated flame retardants and antimony trioxide), fillers (graphite, barium sulfate, magnesium sulfate, calcium carbonate, magnesium carbonate, antimony oxide, titanium oxide, aluminum oxide, zinc oxide, iron oxide, zinc sulfide, Asia , Lead, nickel, aluminum, copper, iron, stainless steel, glass fiber, carbon fiber, aramid fiber, bentonite, montmorillonite, synthetic mica and other particulate, fibrous, needle-like, plate-like fillers), other polymers ( Other polycaproamide, 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 molding method can be performed by an ordinary molding method as in the case of conventional polycaproamide. There is no restriction | limiting in particular about 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 in a narrow sense such as injection molding.

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

(1) Amino group content Approximately 0.2 g of the measurement object was precisely weighed and dissolved in 25 cc of a phenol / ethanol mixed solvent (83.5: 16.5, volume ratio), and then titrated with a 0.02N aqueous hydrochloric acid solution. .

(2) Caprolactam amount and caprolactam cyclic dimer amount polycaproamide in polycaproamide were pulverized, passed through JIS standard sieve 24mesh, 124mesh collected non-passed polycaproamide powder, and about 20g of the powder was methanol Soxhlet extraction was performed with 200 ml for 3 hours, 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 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 (20:80 (volume ratio))
Flow rate: 1 ml / min
(3) Sulfuric acid relative viscosity (ηr)
In the case of polycaproamide before hot water extraction, the polycaproamide is pulverized, the JIS standard sieve 24mesh is passed, the 124mesh non-passable polycaproamide powder is collected, and about 20 g of the powder is soxhrayed with 200 ml of methanol for 3 hours. Extract the residue and use the residue as a measurement sample after drying. In the case of polycaproamide after hot water extraction, it is used as a measurement sample after drying. 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 1-9
Heat treatment and polymerization were performed using the apparatus shown in FIG. FIG. 1 is a schematic view of a heat treatment and polymerization apparatus.

  The caprolactam aqueous solution having the composition shown in Tables 1 and 2 is charged into the raw material storage tank 1 and then supplied to the heat treatment tank 4 provided with the heating cylinder 5 using the raw material supply pump 2 having the pressure gauge 3 on the discharge side. Were heated and subjected to continuous heat treatment under the conditions shown in Table 1. Next, the obtained polycaproamide prepolymer was supplied to a polymerization tower 9 equipped with a heating cylinder 10, and the contents were heated to carry out continuous polymerization under normal pressure under the conditions described in Table 1, and a polymerization reaction was generated from the lower part of the polymerization tower 9. The product polycaproamide was discharged and pelletized to obtain cylindrical polycaproamide 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 moisture does not evaporate from the caprolactam aqueous solution during the heat treatment, and the water evaporated from the polycaproamide prepolymer by releasing the pressure after the pressure regulating valve to atmospheric pressure. Was discharged from the upper part of the polymerization tower 9 via the packed tower 11 to the outside of the system. The reflux ratio in the packed tower was 1, and caprolactam contained in the evaporated water was recovered. The polymerization temperature was measured with thermometers installed in the upper, middle and lower portions of the polymerization tower, and the average values are shown in Tables 1 and 2.

  Subsequently, the low polymer was removed with hot water using the apparatus shown in FIG. FIG. 2 is a schematic view of a low polymer removal apparatus. Polycaproamide pellets are supplied to the extraction tower 12 from the upper port 13, and a low polymer is continuously removed by hot water under the conditions shown in Tables 1 and 2, and a rotary valve 14 installed at the lower part of the extraction tower 12 is used. I took it out. The residence time of the polycaproamide pellets in the extraction tower 12 was 20 hours. Hot water was supplied from the lower part 15 of the extraction tower 12 and discharged from the upper part 16 at a temperature of 95 ° C. In addition, L / D which is a ratio of the height (L) and the diameter (D) of the cylindrical extraction tower used here was 30.

  When analyzing the polycaproamide prepolymer, before supply to the polymerization tower 9, the valve 7 is opened from the sampling port 8 so that the water in the caprolactam aqueous solution is not evaporated during the heat treatment so that the pressure in the heat treatment tank is maintained. Amide prepolymer was collected.

  Amino group content of polycaproamide prepolymer and content of caprolactam and caprolactam cyclic dimer in polycaproamide after polymerization and before removal of low polymer, and caprolactam cyclic 2 in polycaproamide after removal of low polymer The results of body content analysis are shown in Table 1.

  As is apparent from the results of Tables 1 and 2, in the production method of the present invention, a very small amount of caprolactam cyclic dimer content of 0.01% by weight or less can be obtained.

  The present invention is an efficient and stable production method of polycaproamide having a low caprolactam cyclic dimer content, and the polycaproamide obtained by the method of the present invention is used for fibers, injection molded articles and films. Suitable as a raw material.

It is the schematic of the heat processing and the polymerization apparatus which were used in the Example. It is the schematic of the low polymer removal apparatus 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: Polycaproamide prepolymer sampling port 9: Polymerization tower 10: Heating cylinder 11: Packing tower 12: Extraction tower
13: Extraction tower upper port 14: Rotary valve 15: Hot water supply port 16: Hot water discharge port

Claims (1)

1) Step 2) 1) of obtaining a polycaproamide prepolymer having an amino group content of 0.05 mmol / 1 g or more by heat-treating an aqueous caprolactam solution having a water content of 2 to 14% by weight at a temperature of 220 to 300 ° C. for 5 to 60 minutes. The polycaproamide prepolymer obtained in the process is polymerized in the liquid phase at a polymerization temperature of 240 to 270 ° C. or less for 5 to 12 hours, and the caprolactam cyclic dimer is 0.3% by weight or less and the caprolactam is 6 to 10% by weight. % Of polycaproamide 3) Polycaproamide obtained in the step 2) and water at 90 to 130 ° C. with respect to 1 part by weight of polycaproamide 0.5 to 1.2 parts by weight of water A process for producing polycaproamide, comprising a step of obtaining a polycaproamide having a caprolactam cyclic dimer content of 0.04% by weight or less by continuously countercurrent-contacting at a ratio of

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