JP2005162890A - Aliphatic polyester resin and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an aliphatic polyester resin affecting no human health and high in quality/storage stabilities, and to provide a method for producing the same. <P>SOLUTION: The aliphatic polyester resin is such one that the volatiles content thereof is 1 wt.% or less. The method for producing the aliphatic polyester resin comprises the following process: A polycondensation reaction is carried out between an aliphatic diol component and a dicarboxylic acid component, the resultant polymer is then made into pellets or a molded form, which, in turn, is washed with a relevant solvent, and the resultant pellets or molded form thus washed is subjected to drying treatment so that the volatiles content of the final aliphatic polyester resin comes to 1 wt.% or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an aliphatic polyester resin and a method for producing the same, and more particularly to an aliphatic polyester resin in which the content of a volatile component in the aliphatic polyester resin is within a predetermined range and a method for producing the same.

  The aliphatic polyester resin is a resin having an ester bond in the main chain and a skeleton mainly composed of a chain or cyclic aliphatic compound. This aliphatic polyester resin is attracting attention as a plastic that has biodegradability and can provide flexibility not found in aromatic polyester resins, and as a molded product such as films, fibers, and containers, various packaging materials, agricultural materials, fishery materials Etc. are used in all fields.

  When an aliphatic polyester resin is produced, a low molecular weight oligomer remains because the polymerization reaction is insufficient, or a cyclization reaction inevitably occurs to form a cyclic oligomer. Further, such an oligomer is also generated at the time of melt molding in which an aliphatic polyester resin is melted to form an aliphatic polyester resin molding. When the aliphatic polyester resin is melt-molded to form an aliphatic polyester resin molding without removing the generated cyclic oligomer, the cyclic oligomer bleeds out on the surface of the molded body and becomes cloudy on the surface of the molded body (bleed, whitening). Synonymous with phenomenon.) Occurs. Moreover, since the cyclic oligomer contaminates a molding apparatus such as a mold during melt molding, there is a problem in that the surface smoothness of the resulting molded article is impaired and the transparency is lowered. Furthermore, since the contaminated molding apparatus has to be cleaned, there is a problem that the production efficiency is poor.

In order to reduce the amount of cyclic oligomers contained in the aliphatic polyester resin, for example, an aliphatic polyester resin obtained by reacting the aliphatic polyester resin after polymerization or further with a polyvalent isocyanate is used. There has been proposed a method (see Patent Document 1) in which a washing treatment is performed by contacting with water or / and alcohol at a temperature of 10 to 60 ° C. or less from the melting point of the aliphatic polyester resin. In addition, in order to suppress a decrease in the molecular weight of the aliphatic polyester resin in this method, the aliphatic polyester resin after polycondensation, or an aliphatic polyester resin further reacted with a polyvalent isocyanate, an aliphatic ketone, a cycloaliphatic There has also been proposed a method (see Patent Document 2) in which a cleaning treatment is performed by contacting one or more solvents selected from ethers and aliphatic monoesters at a temperature below the melting point of the polyester and below the boiling point of the solvent.
JP 7-316276 A Japanese Patent Laid-Open No. 2002-3606

  However, since these washing treatment methods include a step of washing the aliphatic polyester resin itself with water or an appropriate organic solvent in order to remove the cyclic oligomer in the aliphatic polyester resin, the water or organic solvent used for washing is used. If sufficient removal is not carried out, water and organic solvent remain in the aliphatic polyester resin. If such water or organic solvent remains in the aliphatic polyester resin, volatile components derived from the water or organic solvent volatilize when the aliphatic polyester resin is handled, causing odors and May cause adverse effects. Further, this volatile component may cause foaming and flow unevenness when the aliphatic polyester resin is melt-molded, and may cause a serious problem in the quality of the aliphatic polyester resin.

  In addition, the present inventors are prone to hydrolysis of a water-rich resin, for example, during storage of an aliphatic polyester resin product, and the viscosity of the aliphatic polyester resin product decreases. I encountered a storage stability problem.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an aliphatic polyester resin that does not affect health and has high quality and storage stability, and a method for producing the same. .

  The aliphatic polyester resin of the present invention for solving the above problems is characterized in that the content of a volatile component in the aliphatic polyester resin is 1% by weight or less.

  According to this invention, since the content of the volatile component in the aliphatic polyester resin is limited to 1% by weight, volatilization of the volatile component that adversely affects health can be suppressed. Further, when the aliphatic polyester resin is melt-molded, foaming and flow unevenness do not occur. Further, the aliphatic polyester resin can be prevented from being hydrolyzed, and the viscosity of the aliphatic polyester resin can be prevented from being lowered.

  The aliphatic polyester resin of the present invention is characterized in that the content of the volatile component is measured as a weight loss after heating the aliphatic polyester resin at 120 ° C. for 30 minutes.

  According to this invention, the content of volatile components in the aliphatic polyester resin can be easily estimated.

  The aliphatic polyester resin of the present invention is characterized in that the content of water in the aliphatic polyester resin is 2000 ppm (0.2%) or less of the weight of the aliphatic polyester resin (synonymous with mass; the same shall apply hereinafter). .

  A water-rich aliphatic polyester resin is susceptible to hydrolysis, and the hydrolyzed aliphatic polyester resin has a reduced viscosity. According to the present invention, this aliphatic polyester resin can be prevented from being reduced in viscosity. can do.

  The method for producing an aliphatic polyester resin of the present invention for solving the above-described problems is obtained by polymerizing an aliphatic diol component and a dicarboxylic acid component, and then forming an aliphatic polyester resin pellet or molded body to obtain a pellet or molded body. After the aliphatic polyester resin is washed with a washing solvent, the pellet or molded body is dried so that the content of volatile components in the aliphatic polyester resin is 1% by weight or less.

  According to the method for producing an aliphatic polyester resin of the present invention, the pellet or molded body is dried so that the content of the volatile component in the aliphatic polyester resin is 1% by weight or less. Volatilization of volatile components can be suppressed. Moreover, there is provided an aliphatic polyester resin that is free from foaming and flow unevenness and does not cause a decrease in viscosity.

  In the method for producing an aliphatic polyester resin of the present invention, it is preferable that the pellet or molded body of the aliphatic polyester resin to be dried is 1 ton or more per time.

  According to the aliphatic polyester resin and the method for producing the same of the present invention, it is possible to suppress the volatilization of volatile components that adversely affect health. Therefore, when handling the aliphatic polyester resin, work can be performed without any health problems. Further, when the aliphatic polyester resin is melt-molded, foaming and flow unevenness do not occur, so that a high-quality aliphatic polyester resin can be obtained. Furthermore, since the viscosity reduction due to hydrolysis of the aliphatic polyester resin can be prevented, the storage stability of the aliphatic polyester resin product is increased.

  Hereinafter, the aliphatic polyester resin of the present invention and the production method thereof will be described in detail.

1. Aliphatic polyester resin;
The aliphatic polyester resin of the present invention is characterized in that the content of a volatile component in the aliphatic polyester resin is 1% by weight or less of the weight of the aliphatic polyester resin. The aliphatic polyester resin of the present invention can be obtained by polycondensation of the raw materials for the aliphatic polyester resin shown below.

  Hereinafter, the raw material, polycondensation and volatile components of the aliphatic polyester resin will be described in detail.

(Raw material for aliphatic polyester resin)
An aliphatic polyester resin is a polyester resin in which the skeleton forming the polyester is mainly composed of a linear or cyclic aliphatic compound. Such an aliphatic polyester resin can be obtained, for example, by a general method such as melt polycondensation in which an aliphatic diol component and a dicarboxylic acid component are esterified and / or transesterified and then polycondensed under reduced pressure. It can also be obtained by copolymerization of a dicarboxylic acid component and an alkylene oxide.

  Examples of the aliphatic diol component include aliphatic diols and both terminal hydroxy polyethers. These may be used alone or in combination with each other.

  Examples of the aliphatic diol include ethylene glycol, 1,3-propylene glycol, neopentyl glycol, 1,6-hexamethylene glycol, decamethylene glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. They may be used alone or as a mixture of two or more. Of these, it is preferable to use one or more selected from ethylene glycol, 1,4-butanediol, 1,3-propylene glycol, and 1,4-cyclohexanedimethanol. It is preferable to use one or both of 4-butanediol, and it is particularly preferable to use 1,4-butanediol.

  As the both-end hydroxy polyether, a hydroxy polyether having 4 to 1000 carbon atoms is preferably used, one having 10 to 200 carbon atoms is more preferably used, and one having 20 to 100 carbon atoms is particularly preferably used. . Specific examples of both terminal hydroxy polyethers include diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly 1,3-propanediol, and poly 1,6-hexamethylene glycol. In addition, a copolymerized polyether of polyethylene glycol and polypropylene glycol can be used. These may be used alone or as a mixture of two or more.

  As the dicarboxylic acid component, an aliphatic dicarboxylic acid or a derivative thereof is used. These may be used alone or in combination with each other. Moreover, you may use what added aromatic dicarboxylic acid or its derivative to aliphatic dicarboxylic acid or its derivative as a dicarboxylic acid component.

  Examples of the aliphatic dicarboxylic acid include linear or alicyclic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, and cyclohexanedicarboxylic acid. Examples of the aliphatic dicarboxylic acid derivatives include lower alkyl esters such as methyl esters, ethyl esters, propyl esters, and butyl esters of the above aliphatic dicarboxylic acids. These aliphatic dicarboxylic acids or derivatives thereof may be used alone or as a mixture of two or more.

  Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and diphenyldicarboxylic acid. Examples of the aromatic dicarboxylic acid derivative include the lower alkyl esters of the above-mentioned aromatic dicarboxylic acid, specifically, Examples include methyl ester, ethyl ester, propyl ester, and butyl ester. These aromatic dicarboxylic acids or their derivatives may be used alone or as a mixture of two or more thereof in addition to the above aliphatic dicarboxylic acids or their derivatives. Of these, terephthalic acid and isophthalic acid are preferably used for the aromatic dicarboxylic acid, and dimethyl terephthalate and dimethylisophthalate are preferably used as the derivative of the aromatic dicarboxylic acid.

  The aliphatic polyester resin in the present invention is produced using an aliphatic dicarboxylic acid or a derivative thereof as an essential component, and such an essential component (aliphatic dicarboxylic acid or a derivative thereof) is 20 mol% as a proportion of the total amount of the dicarboxylic acid component. It is preferably contained in an amount of 40 mol% or more, more preferably 70 mol% or more. An aliphatic polyester resin can be obtained by containing an aliphatic dicarboxylic acid or a derivative thereof as an essential component in such a ratio.

  Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, and the like.

  In the present invention, other copolymer components may be introduced in addition to the above aliphatic diol component and dicarboxylic acid component, or other copolymer components may be introduced in addition to the dicarboxylic acid component and alkylene oxide. Good.

  Specific examples of the copolymer component include bifunctional oxycarboxylic acids. Further, in order to form a branched structure, at least one or two selected from the group consisting of a trifunctional or higher polyhydric alcohol, a trifunctional or higher polyvalent carboxylic acid or an anhydride thereof, and a trifunctional or higher oxycarboxylic acid The above polyfunctional compound is mentioned.

  Examples of the bifunctional oxycarboxylic acid include lactic acid, glycolic acid, hydroxybutyric acid, hydroxycaproic acid, 2-hydroxy3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, and 2-hydroxyisocaproic acid. These may be mentioned, but these may be oxycarboxylic acid esters or lactones or oxycarboxylic acid derivatives. In addition, these oxycarboxylic acids may be used alone or as a mixture of two or more. When optical isomers are present in these, any of D-form, L-form and racemic form may be used, and the form may be any of solid, liquid or aqueous solution. Among these bifunctional oxycarboxylic acids, lactic acid or glycolic acid, which has a particularly remarkable increase in polymerization rate at the time of use and is easily available, is particularly preferably used, and its form is an aqueous solution of 30% to 95%. Is preferably used because it can be easily obtained. In this case, the lower limit of the amount of the bifunctional oxycarboxylic acid used is usually 0.02 mol%, preferably 0.5 mol%, more preferably 1.0 mol%, based on the total amount of raw material monomers. The upper limit of the amount of the functional oxycarboxylic acid used is usually 30 mol%, preferably 20 mol%, more preferably 10 mol%, based on the total amount of raw material monomers.

  Examples of the trifunctional or higher polyhydric alcohol include glycerin, trimethylolpropane, pentaerythritol, and the like, and these may be used alone or as a mixture of two or more.

  Examples of the tri- or higher functional polycarboxylic acid or anhydride thereof include trimesic acid, propanetricarboxylic acid, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, cyclopentatetracarboxylic anhydride, and the like. And may be used alone or as a mixture of two or more.

  Examples of the tri- or higher functional oxycarboxylic acid include malic acid, hydroxyglutaric acid, hydroxymethylglutaric acid, tartaric acid, citric acid, hydroxyisophthalic acid, hydroxyterephthalic acid, and the like. It may be used as a mixture. In particular, malic acid, tartaric acid, and citric acid are preferably used because of easy availability.

  The above trifunctional or higher polyfunctional compound is used in a total range of 0.1 mol% or more and 5 mol% or less with respect to 100 mol% of the dicarboxylic acid component.

  A chain extender such as diisocyanate, diphenyl carbonate, or dioxazoline may be added as necessary, or a small amount of peroxide may be added to increase the melt tension.

(Polycondensation)
Next, polycondensation of aliphatic polyester resin will be described.

  The aliphatic polyester resin of the present invention is produced by polycondensing the above-mentioned aliphatic polyester resin raw material in the presence of a polycondensation catalyst through an esterification reaction and / or a transesterification reaction.

  Specifically, the above-mentioned aliphatic diol component and dicarboxylic acid component together with the above-described copolymer component used as necessary, in an esterification reaction tank under normal pressure or under pressure, while heating, the esterification reaction and / Or transesterification. Next, the polyester low molecular weight product obtained as an esterification reaction product or a transesterification reaction product is transferred to a polycondensation tank, and is gradually reduced from normal pressure in the presence of a polycondensation catalyst and melted while heating. Polycondensate. Furthermore, if necessary, the aliphatic polyester resin is produced by continuously transferring to a solid-phase polycondensation apparatus and solid-phase polycondensation while heating. These reactions are performed continuously or batchwise, and the esterification reaction tank, the polycondensation tank, and the solid phase polycondensation apparatus may each be one stage or multistage.

  The ratio of the amount of the aliphatic diol component and dicarboxylic acid component used is such that the lower limit of the aliphatic diol component is usually 0.5 mol, preferably 0.8 mol, and the upper limit is 1 mol of the dicarboxylic acid component. Usually 2 moles, preferably 1.5 moles.

  The esterification reaction and / or transesterification reaction is carried out at normal pressure to slightly reduced pressure, and the reaction temperature has a lower limit of usually 50 ° C., preferably 120 ° C., and an upper limit of usually 300 ° C., preferably 260 ° C. . The lower limit of the reaction time is usually 20 minutes, preferably 30 minutes, and the upper limit is usually 5 hours, preferably 3 hours. In the transesterification reaction, a transesterification catalyst may be used. Transesterification catalysts include polycondensation catalysts described later, mineral acids such as sulfuric acid, hydrochloric acid and phosphoric acid, organic acids such as acetic acid and paratoluenesulfonic acid, Lewis acids such as boron fluoride etherate, tin octylate and dibutyltin. Examples thereof include organic tin compounds such as oxide and dibutyltin laurate, stannous halides such as stannous chloride and stannous bromide, activated clay, and acidic ion exchange resins.

  The melt polycondensation is carried out in the presence of a polycondensation catalyst, and the reaction temperature has a lower limit of usually 100 ° C., preferably 150 ° C., and an upper limit of usually 350 ° C., preferably 300 ° C. The lower limit of the pressure at this time is usually 1 Pa, preferably 10 Pa, and the upper limit is usually 1300 Pa, preferably 700 Pa. The lower limit of the reaction time is usually 1 hour, and the upper limit is 15 hours, preferably 6 hours.

  As the polycondensation catalyst, a catalyst commonly used as a polyester polycondensation catalyst is used. For example, germanium dioxide, germanium tetroxide, germanium hydroxide, germanium oxalate, germanium tetraethoxide, germanium tetra-n-butoxide, etc. Germanium compounds, antimony compounds such as antimony trioxide, antimony pentoxide, antimony acetate, methoxyantimony, tetra-n-propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, titanium oxalate, potassium titanium oxalate, etc. A titanium compound etc. are mentioned, The 1 type (s) or 2 or more types chosen from these groups can be used. Further, in combination with the above compounds, one or more selected from magnesium compounds such as magnesium oxide, magnesium hydroxide, magnesium alkoxide, magnesium acetate, magnesium carbonate, cobalt compounds, and the like can be used. Among these, a germanium compound or a titanium compound is particularly preferable in the present invention.

  The amount of the polycondensation catalyst used is usually 0.001 parts by weight, preferably 0.005 parts by weight, with the upper limit being usually 100 parts by weight based on the total amount of the aliphatic diol component and dicarboxylic acid component described above. 3 parts by weight, preferably 1.5 parts by weight.

  In addition, at the time of melt polycondensation, metal compounds other than the above-mentioned compounds may be present within a range that does not interfere with polycondensation. In this case, the metal compounds include zirconium, hafnium, chromium, molybdenum, tungsten, iron, nickel. , Gold, silver, copper, zinc, aluminum, tin, antimony, lanthanum, cerium, and other oxides, hydroxides, alkoxides, carbonates, phosphates, carboxylates, halides, and the like. 1 type (s) or 2 or more types chosen from a compound can be used.

  As the stabilizer, together with the polycondensation catalyst, one or two selected from phosphorus compounds such as orthophosphoric acid, tris (triethylene glycol) phosphate, ethyl diethylphosphonoacetate, ethyl acid phosphate, triethylene glycol acid phosphate, phosphorous acid More than seeds can be used.

  The aliphatic polyester resin thus obtained is usually extracted in the form of a strand from the outlet provided at the bottom of the polycondensation tank, and is cooled with water or cooled with water, and then cut with a cutter and pellets. It becomes.

  In the solid phase polycondensation, the pellets are usually heated at a pressure in the range of 130 Pa to normal pressure, at a temperature in the range of 60 ° C. to 220 ° C., for a time in the range of 30 minutes to 50 hours. Is done.

  The resulting aliphatic polyester resin has a polystyrene-equivalent number average molecular weight of usually 10,000 or more, preferably 30,000 or more, and preferably 200,000 or less. When the number average molecular weight in terms of polystyrene is less than the above range, the mechanical strength may be inferior. On the other hand, when it exceeds the above range, melt moldability may be deteriorated.

(Volatile component)
Here, the volatile component in the present invention refers to a component that volatilizes in the air when the aliphatic polyester resin is left at room temperature or under heat, and refers to water, an organic solvent, or a mixture thereof.

  Examples of the organic solvent include alcohols such as methanol, ethanol, propanol, isopropyl alcohol, butanol, 2-butanol, t-butanol, pentyl alcohol, hexanol, cyclohexanol, and ethylene glycol, and ketones such as acetone, methyl ethyl ketone, and cyclohexanone. , Ethers such as dimethyl ether, diethyl ether, 1,4 dioxane and tetrahydrofuran, esters such as ethyl acetate, methyl acetate, propyl acetate, butyl acetate, methyl butyrate and ethyl butyrate, aromatics such as benzene, chlorobenzene, toluene and xylene Examples include hydrocarbons, aliphatic hydrocarbons such as hexane, heptane, octane and cyclohexane, substances with relatively low boiling points such as N, N-dimethylacetamide and dimethylformamide. It can, it is possible to use one or more selected from these groups.

  On the other hand, the content of the volatile component in the aliphatic polyester resin is measured as the weight loss after heating the aliphatic polyester resin at 120 ° C. for 30 minutes. Specifically, the aliphatic polyester resin is heated for a predetermined time, the weight of the aliphatic polyester resin before and after the heating is measured, and the difference in the weight of the aliphatic polyester resin before and after the heating, that is, the weight By calculating the decrease, the content of the volatile component in the aliphatic polyester resin can be estimated. The heating temperature at this time is preferably lower than the decomposition temperature of the aliphatic polyester resin, and is usually in the range of 50 ° C. or higher and 200 ° C. or lower. As a simple specific example, the aliphatic polyester resin is heated at 120 ° C. for 30 minutes, and the weight loss at that time can be estimated as the content of volatile components. Here, the decomposition temperature of the aliphatic polyester resin is a temperature at which the main chain or side chain of the aliphatic polyester resin starts to be cut by heat, and when the temperature is gradually raised, the aliphatic polyester resin This is the temperature at which weight loss begins. Weight loss occurs because low molecular weight components are generated and volatilized by cleavage of the main chain or side chain of the aliphatic polyester due to oxidation or dissociation.

2. A method for producing an aliphatic polyester resin;
Next, the manufacturing method of the aliphatic polyester resin of this invention is demonstrated.

  The method for producing the aliphatic polyester resin of the present invention is the method of using the above-mentioned raw material and the aliphatic polyester resin obtained by the polycondensation method using the raw material as pellets or a molded body, and then washing the pellet or molded body. The volatile component in the aliphatic polyester resin is characterized in that the drying treatment is performed so that the content of the volatile component is 1% by weight or less of the weight of the aliphatic polyester resin after the drying treatment. Hereinafter, the cleaning process and the drying process will be described.

(Cleaning process)
First, the washing treatment of the aliphatic polyester resin will be described.

  In addition to the polymer, monomers and oligomers remain in the aliphatic polyester resin after polycondensation. If a molded body is formed by melt molding without removing the remaining monomers and oligomers, a phenomenon occurs in which this oligomer, particularly a cyclic oligomer, bleeds out on the surface of the molded body. For this reason, the surface of the molded body may become cloudy or a molding apparatus such as a mold may be contaminated during molding.

  In the present invention, in order to remove this cyclic oligomer, a washing treatment using water, an organic solvent, or a mixture thereof as a washing solvent is performed.

  As the cleaning treatment, for example, a low molecular weight component containing a cyclic oligomer in the aliphatic polyester resin is prepared by filling a container with aliphatic polyester resin pellets or molded articles (hereinafter referred to as pellets) and contacting with a cleaning solvent. Extract. Specifically, aliphatic polyester resin pellets or the like are filled in a container, and water, an organic solvent, or a mixture thereof is added to the container as a cleaning solvent to perform a cleaning process. The molded product as used herein refers to a product obtained by melt-molding pellets into a film, sheet, container, molded piece, casing, or the like.

  As the organic solvent, for example, alcohols such as methanol, ethanol, isopropyl alcohol and butanol, ketones such as methyl ethyl ketone, ethers such as dimethyl ether and tetrahydrofuran, esters such as methyl acetate, ethyl acetate and butyl acetate are preferable. Used. These may be used singly or in combination of two or more, and may be used by mixing with water.

  Although there is no restriction | limiting in particular about the usage-amount of a washing | cleaning solvent, Usually, it uses in the range of 0.5 times or more and 10 times or less with respect to the weight of an aliphatic polyester resin. Although there is no restriction | limiting in particular also about the temperature of a cleaning solvent, Usually, it exists in the range below 10 degreeC or more and the boiling point of a cleaning solvent.

  The cleaning treatment is usually performed at normal pressure, but cleaning in a pressurized state is possible if necessary. In the case of cleaning in a pressurized state, cleaning may be performed at a temperature exceeding the boiling point of the cleaning solvent. In this cleaning treatment, the inside of the container filled with the pellets of the aliphatic polyester resin or the like may or may not be stirred. You may circulate the water used for washing | cleaning, an organic solvent, or mixtures thereof using a pump etc. The washing time is usually in the range of 10 minutes to 100 hours.

  After completion of the cleaning treatment, the aliphatic polyester resin from which the low molecular weight component including the cyclic oligomer has been removed is obtained by removing only the cleaning solvent from the container. The removal efficiency of low molecular weight components including cyclic oligomers can be controlled by the temperature of the cleaning solvent, the amount of cleaning solvent used, and the cleaning time. The amount of the cyclic oligomer in the aliphatic polyester resin after the washing treatment is preferably 4000 ppm (0.4%) or less, more preferably 3000 ppm (0.3%) or less.

(Drying process)
Next, the drying process of the aliphatic polyester resin will be described.

  In the washed aliphatic polyester resin, water used as a cleaning solvent, an organic solvent, or a mixture thereof is attached or contained. If such a cleaning solvent remains in the aliphatic polyester resin, when handling the aliphatic polyester resin, an odor of a volatile component derived from the cleaning solvent is generated, which may cause health problems. Further, this volatile component is likely to cause foaming and flow unevenness when the aliphatic polyester resin is melt-molded, and there is a possibility that a large problem in practical use of the aliphatic polyester resin may occur. In addition, aliphatic polyester resins containing a large amount of water are susceptible to hydrolysis. For example, they are subject to hydrolysis during storage of the product, and the product viscosity tends to decrease. Therefore, a drying process for removing these volatile components is necessary.

  Examples of such a drying treatment include a method of heating an aliphatic polyester resin pellet or the like, a method of heating under reduced pressure, a method of irradiating an electromagnetic wave or light, a method of holding under an air stream, a freeze drying method, and the like.

  When drying by heat treatment, the container is filled with aliphatic polyester resin pellets and the like, and the inside of the container is heated with a heater or the like. At this time, the filling portion of the aliphatic polyester resin pellets or the like can be used as a moving bed, or a screw-like one can be provided in the filling portion, and the aliphatic polyester resin pellets can be heated and dried while flowing. . By such a method, partial overheating of aliphatic polyester resin pellets and the like can be prevented, and the drying efficiency can be increased. An air stream can be generated in the container and dried by heating. Further, volatile components in the air stream can be recovered by a condenser or the like. Further, the polyester can be filled with aliphatic polyester resin pellets and the like, and the drying process can be performed by mixing the aliphatic polyester resin pellets and the like while flowing with an air stream. Although there is no restriction | limiting in the temperature at the time of performing these drying processes, Usually, it dries at the temperature below melting | fusing point of aliphatic polyester resin. These drying treatments can be performed batchwise or continuously.

  When drying under reduced pressure, the container to be used can be a general reaction vessel, a double cone type dryer that can flow the contents, a tauter mixer equipped with a stirring screw inside the vessel, or the like. . In general, the temperature at this time is preferably equal to or lower than the melting point of the aliphatic polyester resin. Further, the processing temperature can be changed stepwise as necessary. The operating pressure can be arbitrarily selected within the range of normal pressure to vacuum. In general, the higher the degree of vacuum, the higher the drying efficiency. However, in consideration of the recovery efficiency of volatile components, the operation may be performed at a relatively low pressure.

  In the case of drying using electromagnetic waves, for example, a device that fills a container with aliphatic polyester resin pellets and irradiates the aliphatic polyester resin with electromagnetic waves using a lamp that emits electromagnetic waves can be used. A moving bed or a screw may be provided in the filling portion of the aliphatic polyester resin pellets or the like so that the aliphatic polyester resin pellets are exposed to electromagnetic waves while flowing. Further, an air flow can be generated in the container, or the container can be dried under reduced pressure as a closed system. The temperature at that time is not particularly limited, but is usually dried at a temperature not higher than the melting point of the aliphatic polyester resin. As electromagnetic waves, microwaves, infrared rays, near infrared rays, or the like is used. It is preferable to use near infrared rays from the viewpoint of the cost of equipment and the simplicity of operation.

  The content of the volatile component in the aliphatic polyester resin at the time when the drying treatment is completed is preferably 1% by weight or less with respect to the weight of the aliphatic polyester resin subjected to the drying treatment, and is 0.5% by weight or less. More preferably. When the content of the volatile component exceeds 1% by weight, it may cause odor as described above, and may cause foaming during melt molding and deterioration of storage stability. The lower limit of the content of the volatile component is not particularly limited, but is desirably as small as possible.

  The water content is desirably 2000 ppm (0.2%) or less, and more desirably 1000 ppm (0.1%) or less. If the water content exceeds 2000 ppm (0.2%), hydrolysis proceeds while the aliphatic polyester resin is stored, and the molecular weight of the aliphatic polyester resin may be reduced.

  Conditions such as temperature, time, and pressure in the drying treatment are appropriately adjusted so that the content of volatile components in the aliphatic polyester resin is 1% by weight or less based on the weight of the aliphatic polyester resin after the drying treatment. The Inappropriate temperature, time, and pressure in the drying process will increase the content of volatile components in the aliphatic polyester resin, which will volatilize and cause product odor, foaming during melt molding, deterioration of storage stability, etc. May be invited.

  The drying temperature is usually in the range of 20 ° C. or more and the melting point of the aliphatic polyester resin, and the drying pressure is normal pressure or reduced pressure. The drying time is usually in the range of 1 hour to 100 hours. In addition, it is desirable that the drying time is determined while confirming the content of volatile components as needed during the drying process. Examples of the method for confirming the content of volatile components include a method using an infrared moisture meter, a Karl Fischer method, a headspace gas chromatograph method, and the like. When carrying out a large amount of drying treatment on the premise of industrial production, the drying conditions may differ from the laboratory scale, so it is necessary to set the drying conditions according to the implementation scale.

  Moreover, about content of the volatile component in aliphatic polyester resin, it can estimate by the method similar to the method mentioned above. That is, the aliphatic polyester resin is heated for a predetermined time, the weight of the aliphatic polyester resin before and after the heating is measured, and the difference in the weight of the aliphatic polyester resin before and after the heating is obtained, whereby the volatilization in the aliphatic polyester resin is determined. The content of the component can be estimated. The heating temperature at this time is desirably lower than the decomposition temperature of the aliphatic polyester resin as described above, and is usually in the range of 50 ° C. or higher and 200 ° C. or lower. As a simple specific example, the aliphatic polyester resin is heated at 120 ° C. for 30 minutes, and the weight loss at that time can be estimated as the content of volatile components.

  Moreover, it is preferable that the pellet of the aliphatic polyester resin etc. which are dried is 1 ton or more per time.

  In the case where the drying process is performed with the temperature, pressure, and time fixed, generally, the larger the amount of the aliphatic polyester resin pellets and the like that are subjected to the drying process, the lower the drying efficiency. However, according to the method for producing an aliphatic polyester of the present invention, the aliphatic polyester resin pellets and the like can be efficiently dried even when subjected to a drying treatment of 1 ton or more at a time. Therefore, it is possible to dry the aliphatic polyester resin pellets on an industrial scale.

  Hereinafter, the present invention will be described in more detail with reference to examples.

(Example 1)
In a reaction vessel having an internal volume of 5000 L equipped with a reflux tower, 1336 kg of succinic acid, 1180 kg of 1,4-butanediol, and 72.1 kg of 90% aqueous lactic acid solution containing 720 g of germanium dioxide were placed. The esterification reaction was performed at 220 ° C. for 2 hours. Thereafter, the contents were transferred to a reaction vessel equipped with a decompression device, and the pressure in the vessel was reduced from atmospheric pressure to 0.3 hPa over 1.5 hours while maintaining the temperature of the contents at 230 ° C. The degree of reduced pressure was maintained, and polycondensation was further performed for 3 hours to obtain an aliphatic polyester resin. The inside of the reaction vessel after completion of the polymerization was pressurized with nitrogen, the molten resin of the aliphatic polyester was extruded from the bottom of the reaction vessel into a strand shape, and cut into a pellet shape while cooling to obtain an aliphatic polyester resin pellet. . The reduced viscosity of the aliphatic polyester resin was 2.3 dl / g, and the content of the cyclic dimer oligomer in the aliphatic polyester resin was 7900 ppm (0.79%). The content of the cyclic dimer oligomer was measured using a high-performance liquid chromatograph manufactured by GL Sciences.

  1500 kg of the resulting aliphatic polyester resin pellets were filled into a 5000 L jacketed conical dryer, and 18 kg of water and 1782 kg of acetone were added as washing solvents while maintaining the temperature in the dryer at 50 ° C. Allowed to stand for 12 hours. Thereafter, only the cleaning solvent was extracted from the container, and the inside of the container was decompressed while rotating the dryer. After drying for 30 hours while keeping the pressure in the container at 2.5 hPa or less at a temperature of 80 ° C in the dryer, the aliphatic polyester resin pellets are discharged from the dryer and promptly laminated with aluminum laminate moisture barrier. Sealed in a bag. At this time, the content of water by the Karl Fischer method in the pellets of the aliphatic polyester resin was 570 ppm (0.057%), and the content of the volatile component by the infrared moisture meter was 0.13% by weight. Moreover, the measured value of the content of acetone by the head space gas chromatograph method was 740 ppm (0.074%).

  The reduced viscosity (ηsp / c) was determined from the solution viscosity obtained by measuring the obtained aliphatic polyester resin in phenol / tetrachloroethane (weight ratio 1: 1) at 30 ° C. with a solution concentration (0.5 g / dl). .

  The content of the volatile component is represented by the weight ratio of the content of the volatile component to the weight of the aliphatic polyester resin, and specifically, an infrared moisture meter (FD-240 manufactured by Kett Science Laboratory Co., Ltd.). The pellets of the aliphatic polyester resin were heated at 120 ° C. for 30 minutes, the weights of the pellets before and after the measurement were measured, and the weight loss, which is the difference in the weight of the pellets before and after the heating, was used as the volatile component content.

  The water content was measured with a Karl Fischer moisture meter. The pellets of aliphatic polyester resin were heated to 150 ° C. under a dry nitrogen stream, and the water content in the pellets was calculated from the amount of water in the stream. The water content was expressed as a weight ratio of the water content to the pellet weight.

  The acetone content was measured by a headspace gas chromatograph method. After the aliphatic polyester resin pellets were completely dissolved in 1,2,4-trichlorobenzene, the gas in the gas phase of the container was collected, and acetone was quantified by gas chromatography. At this time, the column was polysilane DB-5, 60 m in length, and the column temperature was set to 300 ° C. Further, He was used as a carrier gas, and measurement was performed under the condition of a flow rate of 18 ml / min. The acetone content was expressed as a weight ratio of the acetone content to the pellet weight.

  The resulting aliphatic polyester resin pellets did not smell and did not cause foaming or flow unevenness during melt molding. In addition, viscosity reduction did not occur in the molded product of the obtained aliphatic polyester resin.

(Example 2)
5,000 kg of reaction vessel equipped with a reflux tower with 1024 kg of succinic acid, 330 kg of adipic acid, 1140 kg of 1,4-butanediol, and 71 kg of 90% lactic acid aqueous solution dissolved with 710 g of germanium dioxide The esterification reaction was carried out at 220 ° C. for 2 hours. Thereafter, the contents were transferred to a reaction vessel equipped with a decompression device, and the internal pressure of the vessel was reduced from atmospheric pressure to 0.3 hPa over 1.5 hours while maintaining the temperature of the reaction solution at 230 ° C. The degree of reduced pressure was maintained, and polycondensation was further performed for 3 hours to obtain an aliphatic polyester resin. The inside of the reaction vessel after completion of the polymerization was pressurized with nitrogen, the molten resin of the aliphatic polyester was extruded from the bottom of the reaction vessel into a strand shape, and cut into a pellet shape while cooling to obtain an aliphatic polyester resin pellet. . The reduced viscosity of this aliphatic polyester resin was 2.1 dl / g, and the content of the cyclic dimer oligomer in the aliphatic polyester resin was 4200 ppm (0.42%).

  The resulting aliphatic polyester resin pellets (1500 kg) were filled into a 5000 L jacketed conical dryer, charged with 18 kg of water and 1782 kg of acetone, and kept at a temperature of 30 ° C. for 6 hours. I put it. Thereafter, only the cleaning solvent was extracted from the container, and the inside of the container was decompressed while rotating the dryer. After drying for 40 hours while maintaining the pressure in the container at a temperature of 60 ° C. or less at a temperature of 60 ° C. in the dryer, the pellets of the aliphatic polyester resin are discharged from the dryer and immediately put into an aluminum laminate multilayer moisture-proof packaging bag. Put in and sealed. At this time, the content of water in the pellets of the aliphatic polyester resin was 630 ppm (0.063%), and the content of volatile components was 0.15% by weight. The content of acetone was 800 ppm (0.080%). The resulting aliphatic polyester resin pellets did not smell and did not cause foaming or flow unevenness during melt molding. In addition, viscosity reduction did not occur in the molded product of the obtained aliphatic polyester resin.

  The reduced viscosity, volatile component content, water content, and acetone content were measured in the same manner as in Example 1.

(Comparative Example 1)
1500 kg of the aliphatic polyester resin pellets obtained in Example 1 were filled into a conical dryer with a jacket of 5000 L, and 18 kg of water and 1782 kg of acetone were added, and the temperature in the dryer was maintained at 50 ° C. The mixture was allowed to stand for 12 hours. Thereafter, only the cleaning solvent was extracted from the container, and the inside of the container was decompressed while rotating the dryer. Keeping the pressure inside the dryer at 80 ° C and keeping the pressure in the vessel at 2.5 hPa or less, after drying for 8 hours, drain the aliphatic polyester resin pellets from the dryer and quickly put it into an aluminum laminate multilayer moisture-proof packaging bag Put in and sealed. At this time, the content of water in the aliphatic polyester resin pellets was 570 ppm (0.057%), and the content of volatile components was 2.0% by weight. The content of acetone was 1.5% by weight. The odor of acetone remained in the pellets of the aliphatic polyester resin in this state. Further, when melt molding was performed using pellets of this aliphatic polyester resin, foaming was observed in the molded product, resulting in molding failure. The volatile component content, water content, and acetone content were measured in the same manner as in Example 1.

Claims (5)

  A content of a volatile component in the aliphatic polyester resin is 1% by weight or less.   2. The aliphatic polyester resin according to claim 1, wherein the content of the volatile component is measured as a weight loss after the aliphatic polyester resin is heated at 120 ° C. for 30 minutes.   3. The aliphatic polyester resin according to claim 1, wherein the content of water in the aliphatic polyester resin is 2000 ppm or less of the weight of the aliphatic polyester resin.   After the aliphatic diol component and the dicarboxylic acid component are polymerized, the aliphatic polyester resin is pelletized or molded, and the pellet or molded aliphatic polyester resin is washed with a cleaning solvent. A method for producing an aliphatic polyester resin, comprising drying the pellets or molded body so that the content of a volatile component is 1% by weight or less. 5. The method for producing an aliphatic polyester resin according to claim 4, wherein the pellet or molded product of the aliphatic polyester resin to be dried is 1 ton or more per time.