JP5353028B2 - Polylactic acid resin composition and method for producing polylactic acid fiber using the same - Google Patents

Description

  The present invention relates to a polylactic acid resin composition excellent in suppressing decomposition gas generation and a method for producing polylactic acid fiber using the same.

  Fibers made of polyamides typified by nylon 6 and nylon 66, and fibers made of polyesters typified by polyethylene terephthalate, polybutylene terephthalate and polylactic acid are excellent in strength, mechanical properties and dimensional stability. Widely used in interiors, vehicle interiors, and industrial applications. In addition, fibers made of polyolefins such as polyethylene and polypropylene are widely used for industrial applications taking advantage of their lightness.

  However, while these polymers made from petroleum resources have excellent properties, they consume large amounts of petroleum resources, which are finite resources. Since it will be released into the atmosphere, it has a great impact on global warming, which is a serious problem on a global scale.

  As an approach to such problems, active efforts are being made to suppress global warming due to the circulation of carbon dioxide by using polymers made from plant resources that grow by taking in carbon dioxide from the atmosphere. Attention has been focused on biomass polymers such as.

  Since polylactic acid has excellent mechanical properties among biomass polymers, it attracts attention as a material that can replace conventional polymers that use petroleum resources as raw materials, and studies on industrialization technology by melt molding are actively conducted. . These industrialization efforts range from improving the properties of resins (polymers) to melt molding processes, and developing applications that make use of the characteristics of polylactic acid. The common problem is the keyword of heat resistance. It is done.

  Polylactic acid has the property that it is easily hydrolyzed at high temperatures and high humidity in terms of molecular structure, so it causes thermal degradation such as easy molecular weight reduction during melt molding, making it difficult to select melt molding conditions. There are many technical proposals for improving the heat resistance of polylactic acid.

  As a proposed technique, for example, there is a technique for improving heat resistance by adding, to polylactic acid, an additive having an effect of trapping organic radicals generated in the course of decomposition in order to make it possible to maintain molecular weight. is there. In this technology, additives can be easily blended into polylactic acid using a melt-kneader, etc., and many of the technologies are effective by allowing the additives to remain in the resin composition. Special equipment is essential. Therefore, it is an industrially effective means.

  As a proposal regarding an additive effective for improving the heat resistance of polylactic acid, there is a technical proposal regarding so-called heat resistance improvement such as retention of molecular weight by adding a phosphorus compound and / or a hindered phenol compound to polylactic acid (patent) Reference 1 and Patent Reference 2). However, although any of the technical proposals can maintain the molecular weight and improve the color tone, there is a problem that the effect of suppressing the decomposition gas generated during the melt processing is low.

  The cracked gas that polylactic acid is generated during melt molding contains lower fatty acids, and the generation of this cracked gas during melt molding not only creates a unique odor in the production site and surrounding environment, but also Since the lower fatty acids are mainly composed of acetic acid, propionic acid, acrylic acid, and the like, if a large amount of cracked gas containing these is generated, an exhaust facility is required to protect workers. Furthermore, all the components of the lower fatty acids have strong metal corrosive properties, which may corrode the pipes and measuring sections of the melt molding equipment and cause the parts of the melt molding equipment to be deformed and damaged if continued for long-term production. Therefore, there is a problem that the frequency of parts replacement increases and eventually the parts need to be made of a special material that has been treated with acid resistance, resulting in increased costs and the need to dedicate the melt molding equipment. there were.

For this reason, attention has been focused on polylactic acid from the viewpoint of environmental protection, and the production volume has been expanding. Recently, development of a polylactic acid resin composition in which generation of decomposition gas during melt molding, especially generation of lower fatty acids is suppressed is eagerly desired. It was.
JP, 2007-23081, A Claims Patent 3532850 Claims

  An object of the present invention is to provide a resin composition comprising a polylactic acid resin in which the generation of decomposition gas during melt processing is suppressed, and a method for producing polylactic acid fiber using the same.

In order to solve the above problems, the present invention has the following configuration. That is, the polylactic acid resin composition of the present invention is a resin composition containing 95% by weight or more of polylactic acid as a resin component (but does not contain a carbodiimide compound) , and has a phosphoric acid structure and a phosphine structure in one molecule. And a decomposition inhibitor having a molecular structure including one phosphorus compound structure selected from phosphite structures and one hindered phenol structure, and 0.01 to 1 mol% of the entire resin is added. A polylactic acid resin composition.

  According to a preferred embodiment of the polylactic acid resin composition of the present invention, the melting inhibitor has a melting point of 70 to 170 ° C., and the polylactic acid resin composition has suppressed decomposition gas generation, The amount of lower fatty acid in the cracked gas generated when held at 250 ° C. for 30 minutes in an inert gas atmosphere is 15 mg / kg or less.

  From the polylactic acid resin composition of the present invention, a polylactic acid fiber can be produced by melt spinning it, and a polylactic acid fiber structure such as a woven or knitted fabric can be obtained from the polylactic acid fiber.

  Moreover, the method for producing the polylactic acid fiber of the present invention comprises polylactic acid obtained by melt spinning using a resin composition containing polylactic acid and a decomposition inhibitor having a molecular structure containing a phosphorus atom and a hindered phenol structure simultaneously in one molecule. A method for producing a polylactic acid fiber, characterized in that the decomposition inhibitor is kneaded with polylactic acid in an amount of 0.01 to 1 mol% based on the entire resin, and then subjected to melt spinning. Is the method.

  In a preferred embodiment of the method for producing the polylactic acid fiber of the present invention, a resin composition containing 95% by weight or more of the polylactic acid as a resin component is used.

According to the present invention, a resin composition containing 95% by weight or more of a polylactic acid resin (but not containing a carbodiimide compound) , which is selected from a phosphoric acid structure, a phosphine structure, and a phosphite structure in one molecule. Occurs at the time of melt molding by forming a polylactic acid resin composition containing 0.01 to 1 mol% of a decomposition inhibitor having a molecular structure including one of each phosphorus compound structure and one hindered phenol structure. The generation amount of lower fatty acids in the cracked gas is suppressed, and the odor drifting in the surrounding environment as well as the production site can be reduced. Further, as the amount of lower fatty acid generated decreases, corrosion of the piping and measuring section of the melt processing apparatus is suppressed, so that continuous production with stable quality is possible without requiring special equipment.

The polylactic acid resin composition of the present invention includes at least a polylactic acid which is a resin component, and any one phosphorus compound structure and hindered phenol structure selected from a phosphoric acid structure, a phosphine structure and a phosphite structure in one molecule. The decomposition inhibitor which has the molecular structure which contains each one is contained (however, the carbodiimide compound is not contained) .

  The polylactic acid used in the present invention is a resin mainly composed of L-lactic acid and / or D-lactic acid. However, it is necessary to use a polylactic acid having a high optical purity of the lactic acid component. This is a preferred embodiment because the properties can be improved. Specifically, the polylactic acid preferably contains 80% or more of L-form or 80% or more of D-form among the total lactic acid components of polylactic acid, more preferably 90% of L-form. Polylactic acid containing at least 90% or more of D-form, more preferably 95% or more of L-form or 95% or more of D-form.

  As a method for producing polylactic acid, known polymerization methods can be used, and examples thereof include a direct polymerization method from lactic acid and a ring-opening polymerization method via lactide.

  The melting point of polylactic acid is preferably 120 ° C. or higher, and more preferably 150 ° C. or higher in view of workability after melt processing. The melting point of polylactic acid is usually increased by increasing the optical purity of the lactic acid component, and polylactic acid having a melting point of 120 ° C. or higher contains 90% or more of L-form or 90% or more of D-form. Polylactic acid having a melting point of 150 ° C. or higher can be obtained by containing 95% or more of L-form or 95% or more of D-form.

  The polylactic acid used in the present invention may contain other copolymer components, and examples of the other copolymer components include glycol compounds, dicarboxylic acids, hydroxycarboxylic acids and lactones. These copolymerization components may cause a melting point drop by copolymerization, and conversely may promote decomposition gas generation, but the copolymerization amount is about 0 to 30 mol% with respect to the total monomer components. If so, it can be used without problems.

  Polylactic acid is biodegradable and is easily decomposed into water and carbon dioxide by bacteria, etc., so that it decomposes over time even when left in the natural environment, and as a resin composition, Since it does not remain, it can be said that it is an effective material for environmental conservation. In order to effectively use such characteristics, it is necessary that the resin composition is substantially composed of polylactic acid. Therefore, in the polylactic acid resin composition of the present invention, the composition ratio of the polylactic acid as the resin component is required to be 95% by weight or more when the resin component is 100% by weight. Considering the amount of the inhibitor that acts effectively, the practical upper limit of the composition ratio is 99.9% by weight.

Thus, in the polylactic acid resin composition of the present invention substantially composed of polylactic acid, in order to suppress the amount of lower fatty acids in the cracked gas, a phosphoric acid structure, a phosphine structure and a phosphite structure are contained in one molecule. It is important that a decomposition inhibitor having a molecular structure containing one selected phosphorus compound structure and one hindered phenol structure is added.

  The decomposition inhibitor as used herein means an additive having an effect of efficiently capturing organic radicals and the like generated during decomposition and suppressing generation of decomposition gas, particularly lower fatty acids.

  In general, when a polymer is melted, if the heat resistance of the polymer is low, an organic radical is generated by thermal decomposition of the polymer and the oligomer contained therein, and once the organic radical is generated, it becomes a new radical or a radical initiator that becomes a radical initiator. Things are generated in a chain. Since the organic radical has an unstable structure, the polymer is further decomposed and a new organic radical is generated. Once the organic radicals are generated in this way, the decomposition of the polymer proceeds in a chain and the molecular weight is lowered, so that a volatile decomposition gas is generated in some cases. Further, when the decomposition product stays in a high temperature atmosphere or the like, the reaction further proceeds to form a peroxide, and when oxidized, a corrosive gas such as a lower fatty acid is generated.

In the case of polylactic acid, the decomposition mechanism caused by the radicals described above tends to proceed, and the conventional thermal decomposition suppression prescription is insufficient to suppress the generation of this decomposition gas, and it is more highly heated. It is required to suppress decomposition. As a result of intensive studies on this point, the present inventors have found that each molecule contains one phosphorous compound structure selected from a phosphoric acid structure, a phosphine structure and a phosphite structure, and a molecular structure containing one hindered phenol structure. It has been found that a decomposition inhibitor having the above is very effective.

  The hindered phenol structure has the function of suppressing or stopping the radical chain reaction by supplying electrons to radicals generated by thermal decomposition of polymers and oligomers. It is to suppress. Thereby, the progress of the thermal decomposition of the polymer can be suppressed, and the generation of decomposition gas can also be suppressed.

  However, when the above radical is an organic peroxide radical (R—O—O), R—O, which is an organic peroxide when hydrogen becomes a counter cation after electrons are donated in the hindered phenol structure. In some cases, -OH is generated, and an organic acid (ROOH) is generated from the -OH. Even if this is less than the case where there is no hindered phenol structure, the above-mentioned problems may not be sufficiently solved by the generation of organic acid. Therefore, it is necessary to suppress the generation of peroxide radicals themselves, but organic radicals that are the basis of peroxide radicals may be generated by catalyst residues as well as heat. This is suppressed by a phosphorus compound structure containing a phosphorus atom.

  Specifically, the pentavalent phosphorus structure includes a phosphoric acid structure, a phosphonate structure, a phosphinate structure, and a phosphine oxide structure, and the trivalent phosphorus structure includes a phosphite structure, a phosphonite structure, a phosphinite structure, a phosphine structure, and the like. Although the residue can be deactivated and the generation of organic radicals itself can be suppressed, a phosphine structure is particularly preferable from the viewpoint of coordination ability to the catalyst residue. In addition, phosphorus compounds are also effective from the viewpoint of changing R—O—OH, which is a peroxide, to an alcohol instead of an organic acid. In this case, it is important that the phosphorus compound acts as a reducing agent, and trivalent phosphorus such as a phosphine structure or a phosphite structure is preferable.

  That is, if the hindered phenol structure is not present, the radical chain reaction cannot be stopped, and the reaction proceeds steadily, resulting in oxidation of low-molecular organic substances that are finally produced, resulting in the generation of a large amount of lower fatty acids. On the other hand, without the phosphorus compound structure, the generation of the original organic radical cannot be suppressed, or the reaction for generating the organic acid from the organic peroxide cannot be suppressed.

  Generation of organic radicals due to thermal decomposition of the polymer and generation reaction of cracked gas (especially lower fatty acids) due to this proceed in the above-mentioned reaction, and the reaction rate may be fast, so the phosphorus atom and the hindered phenol structure It is important to prepare in the same molecule so that generation suppression of organic radicals, radical deactivation, and peroxide reduction can be performed in cooperation.

  Of these three mechanisms, the radical deactivation by the hindered phenol structure and the remaining two mechanisms or both may be combined, but the hindered phenol structure and the phosphate structure ( Molecules equipped with three of pentavalent phosphorus) and phosphine structure (trivalent phosphorus) or phosphite structure (trivalent phosphorus) are difficult to obtain industrially and are expensive even if available. A decomposition inhibitor having a structure and any one phosphorus compound structure selected from a phosphoric acid structure (pentavalent phosphorus), a phosphine structure (trivalent phosphorus), and a phosphite structure (trivalent phosphorus) is preferable. In particular, from the viewpoint of suppressing the generation of organic radicals themselves, it is preferable to use a decomposition inhibitor composed of a hindered phenol structure and a phosphate structure.

  Aiming at the same effect, for example, it is conceivable to use a phosphorus compound structure and a hindered phenol compound in combination as described in Patent Document 1, but in this case, the phosphorus atom and the hindered phenol structure are contained in one molecule. Because it does not have, it is difficult to efficiently suppress the reaction of fast radical chain reaction and reaction from organic radicals to organic acids, and each additive has a different melting point, so reaction due to temperature Since the properties are also different, the effect of suppressing the generation of the cracked gas targeted by the present invention is reduced. Needless to say, when a phosphorus compound or a hindered phenol compound is used alone, the effect of suppressing the generation of cracked gas is reduced.

  The cracked gas generated at the time of melt molding of polylactic acid has a unique odor derived from lower fatty acids, and if this gas is generated in a large amount, exhaust equipment is required to protect workers.

  In addition, this cracked gas has lower fatty acids, that is, acidic components such as acetic acid, propionic acid and acrylic acid. Especially, acetic acid and propionic acid are corrosive to metals, so that they can be produced continuously for a long time. In the worst case, the apparatus may be damaged because the pipe part and the measuring part of the melt forming apparatus exposed to the generation of cracked gas are corroded and the metal part is deteriorated every moment. In particular, melt spinning equipment often has complicated piping, and the residence time is long, so the effect of this corrosion is significant, especially when the spinning machine is frequently stopped due to product type switching, etc. In this case, the cracked gas adhering to the piping and measuring section liquefied at the place where it stayed while the equipment was stopped, and it entered between the joints of the piping and the parts of the measuring section, and stayed due to heating during restarting. Since the corrosion of the part is rapidly advanced, the piping and the measuring part are forced to be exchanged, which has a serious impact on the production plan and cost. As a countermeasure, it may be possible to change the surface of the pipe or metering section to a special material with acid-resistant treatment. However, in addition to enormous costs, it may be necessary to dedicate the equipment. In this case, since the cracked gas drifting in the production environment is not suppressed, this is not a fundamental solution, and the effect of suppressing cracked gas generation according to the present invention is very large.

  It is important that the addition amount of the decomposition inhibitor used in the present invention is in the range of 0.01 to 1 mol% with respect to the entire resin. By suppressing the generation amount of lower fatty acids, the working environment is improved and melted. Effective in suppressing metal corrosion of forming equipment.

  The whole resin as used herein refers to the amount of polylactic acid, and it is important that the decomposition inhibitor of the present invention is contained in an amount of 0.01 to 1 mol% relative to this.

The decomposition inhibitor used in the present invention has a molecular structure in which one phosphorous compound structure selected from a phosphoric acid structure, a phosphine structure and a phosphite structure and a hindered phenol structure are included in each molecule. When the addition amount is 0.01 mol% or more based on the whole resin, it acts on the organic radicals generated by the decomposition and is effective in suppressing the generation of lower fatty acids. The larger the amount of the decomposition inhibitor added, the more effective the suppression of the lower fatty acid generation amount. By making the addition amount of the decomposition inhibitor 1 mol% or less, it is possible to suppress deterioration of melt characteristics such as the melt viscosity of polylactic acid accompanying the increase of the addition amount. Moreover, if it is the range of said addition amount, it can be used without a problem for the use which considered the biodegradability of polylactic acid. Moreover, the addition amount of a decomposition inhibitor has the preferable range of 0.1-0.5 mol% from a viewpoint that an excessive decomposition inhibitor does not remain in a polylactic acid resin composition after melt molding.

  The melt molding temperature of polylactic acid is generally 170 to 250 ° C. However, in order to improve the melt-kneading property and make the decomposition inhibitor more effective, the melting point of the decomposition inhibitor used in the present invention is It is preferable that it is below the melt molding temperature of lactic acid. However, if the melting point of the decomposition inhibitor is too low, it may sublime at the same time as it is put into the kneader, and the effect of suppressing decomposition with respect to the added amount may not be obtained. The melting point of the inhibitor is preferably 70 to 170 ° C, more preferably 100 to 170 ° C.

  The melting point mentioned here means the peak top temperature of the melting peak observed by differential scanning calorimetry (DSC). As a specific measuring method, for example, it can be performed as follows. That is, 10 mg of a sample is weighed, sealed in an aluminum pan, placed in a DSC, and measured at a heating rate of 16 ° C./min. Then, at 2nd run, the peak top temperature of the melting peak is obtained as the melting point.

The decomposition inhibitor used in the present invention has a molecular structure containing one phosphorous compound structure selected from a phosphoric acid structure, a phosphine structure and a phosphite structure and a hindered phenol structure in one molecule. are those containing, as specific examples thereof, diethyl [[3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl] methyl] Although etc. phosphonate or a metal salt thereof and the like, handling Considering the property and melting point of the decomposition inhibitor, diethyl [[3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl] methyl] phosphonate is preferably used. Examples of diethyl [[3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl] methyl] phosphonate include “IRGAMOD” (registered trademark) 295 manufactured by Ciba Chemical Specialty Co., Ltd. Since this decomposition inhibitor is a powder, it is easy to handle at the time of blending, and has an appropriate melting point for use in the present invention at 120 ° C., so that it can be suitably used.

  The polylactic acid resin composition of the present invention suppresses the generation of decomposition gas by adding such a decomposition inhibitor, but the amount of lower fatty acid is suppressed among the decomposition gas components. This is very important.

  Lower fatty acid means acetic acid, propionic acid, acrylic acid, etc., and has a unique irritating odor, so if a large amount of cracked gas containing these is generated, exhaust equipment is required to protect workers It becomes. Furthermore, since all the components of lower fatty acids have strong metal corrosive properties, they corrode the piping and measuring section of the melt molding equipment, resulting in deterioration in quality due to contamination and deterioration in quality due to deterioration in discharge lightness. In addition, continuous production may cause serious problems such as deformation and breakage of parts of the melt molding apparatus.

  Since the polylactic acid resin composition of the present invention suppresses the generation of lower fatty acids generated during melt molding by the above-described mechanism, it can reduce the adverse effect on the production environment and prevent deterioration of the melt molding apparatus.

The polylactic acid resin composition of the present invention is characterized by being suppressed even when held for 30 minutes in an excessive temperature condition of 250 ° C., which is a high temperature, relative to the melting point of polylactic acid (generally 170 ° C.). If the amount of the lower fatty acid measured at this time is suppressed, the above-mentioned problems of odor and metal corrosion are greatly improved. Specifically, the amount of lower fatty acid contained in the cracked gas generated when held at a temperature of 250 ° C. for 30 minutes in an inert gas atmosphere is preferably 15 mg / kg or less based on the weight of the resin composition. In this range, the deterioration of the melt molding apparatus due to odors and metal corrosion drifting on the production site is greatly improved as compared with the case of no addition.

  In the case of a melt spinning machine, there are complicated and complicated pipes, and the metering section is also complicated, so this decomposed gas tends to stay between the joints and parts of the pipe, and it liquefies when stopped and corrodes it. Will be expanded. Therefore, the lower fatty acid content is preferably as small as possible, but if it is 13 mg / kg or less, as shown in Example 5 described later, almost no odor is felt even during melt molding, and metal corrosion is hardly confirmed. A more preferable range is mentioned. However, as a feasible range, the lower limit of the lower fatty acid amount is 1 mg / kg.

  The amount of the lower fatty acid in the cracked gas referred to here is measured as follows.

  First, 50 mg of the pelletized polylactic acid resin composition is weighed, heated to a temperature of 250 ° C. in a glass container filled with helium gas, and the decomposition gas generated while being held at this temperature for 30 minutes is activated carbon. Collect in a collection tube. The collection tube in which the cracked gas is collected is heated to a temperature of 300 ° C., the collected components are desorbed, introduced into gas chromatography, and the components are analyzed to analyze the components contained in the cracked gas and the generated amount. And the amount generated per unit weight of the polylactic acid resin composition can be calculated by dividing by the weight of the polylactic acid resin composition.

  The pellets referred to here are those obtained by granulating the polylactic acid resin composition into small spherical shapes, cylindrical shapes, prismatic shapes, plate shapes, etc., each having a diameter or a side of about 1 to 20 mm. The resin composition discharged from the kneader is made into a gut and then cut with a cutter.

The polylactic acid resin composition of the present invention includes polylactic acid and a molecular structure each containing one phosphorous compound structure selected from a phosphoric acid structure, a phosphine structure and a phosphite structure and a hindered phenol structure in one molecule. A method of melting and mixing the decomposition inhibitor with an extruder or kneader, a method of mechanically uniformly mixing solid substances together, and then molding directly at the same time as mixing, and an additive directly into the resin polymerization can It can be produced by a generally known apparatus such as a method of charging and mixing.

  Specifically, for example, polylactic acid and a decomposition inhibitor are separately weighed and inserted into a twin-screw kneader. When the screw diameter is 37 mmφ and L / D = 48, the kneading temperature is 200 to 240 ° C., The polylactic acid resin composition of the present invention can be stably obtained by setting the discharge rate to 5 to 50 kg / hour and the screw rotation speed to 100 to 400 rpm. At this time, from the viewpoint of suppressing the generation of radicals at the initial stage of kneading and the generation of components that can be radical initiators such as peroxides, it is preferable to first dry-blend the decomposition inhibitor into the polylactic acid resin. .

  Additives other than the decomposition inhibitor used in the present invention can be added to the polylactic acid resin composition of the present invention as long as the object of the present invention is not impaired. For example, molding aids such as crystal nucleating agents and lubricants, ultraviolet absorbers, hydrolysis resistance improvers and colorants such as pigments and dyes, foaming agents, antistatic agents, conductive agents, flame retardants, reinforcing agents, fillers, A plasticizer, a compatibilizer thickener and the like can be optionally contained.

  The polylactic acid resin composition of the present invention can be melt-spun to produce polylactic acid fibers. Specifically, the polylactic acid resin composition of the present invention can be melted and spun again after being once pelletized and melt-mixed by directly connecting an extruder to a spinning machine. Can be melt-spun as it is.

  About this spinning machine, it can be spun by a known melt spinning machine, but the spinning temperature is higher than the melting point of polylactic acid, specifically, a range of 170 to 250 ° C. is preferably used. Considering the spinnability, it is preferable to set the temperature in the range of 200 ° C. or higher. However, since polylactic acid is originally low in heat resistance, a cracked gas is generated in this temperature range, but this becomes longer as the residence time is longer and the spinning temperature is higher. The polylactic acid resin composition of the present invention can be spun without deteriorating the production environment even when the residence time is long, and the progress of corrosion of the piping of the spinning machine during spinning can be suppressed. In addition, the cracked gas generated during spinning oozes out from the piping and measuring section of the spinning machine, corroding the outside of the spinning machine piping, and if it proceeds excessively, the spinning machine is damaged, making continuous operation difficult. However, in the polylactic acid resin composition of the present invention, these influences are remarkably reduced, and the ripple effect is very large considering industrialization.

  The spinning speed at the time of melt spinning the polylactic acid resin composition of the present invention is preferably in the range of 200 to 6000 m / min from the viewpoint of reducing the spinnability deterioration accompanying an increase in spinning tension. Further, after the obtained polylactic acid fiber is wound once for the purpose of reducing the fineness and improving the mechanical properties, or continuously after spinning, it is stretched by a stretching device having a known pair of heating rollers. You can also. As a stretching temperature and a heat treatment temperature, the stretching temperature is 60 to 130 ° C., and the heat treatment temperature is preferably 100 to 150 ° C. as a condition for obtaining good stretchability. The draw ratio needs to be changed with the elongation of the undrawn yarn as a guideline. Considering the handleability of the fiber and the processability in the subsequent process, the drawn yarn has an elongation of 10 to 50%. It is preferable to set the magnification.

  With regard to the cross-sectional shape of the polylactic acid fiber, it is possible to freely select a multi-lobe cross section such as a round cross section, a hollow cross section, a trilobal cross section, and other irregular cross sections. The form of the polylactic acid fiber can be any of long fibers and short fibers, and in the case of long fibers, it may be multifilament or monofilament.

  The polylactic acid fiber structure in the present invention means various fiber products such as nonwoven fabrics such as woven fabrics, knitted fabrics, spun bonds, melt blows and spun laces, and hot compression molded products such as cups and boards. The polylactic acid fiber is made into a polylactic acid fiber structure so that it can be used not only for clothing such as shirts, blousons, pants and coats, but also for clothing materials such as cups and pads, curtains, carpets, mats, furniture, etc. It can be used for various purposes such as interior use, industrial material use such as wiping cloth, polishing cloth and filter, and vehicle interior use.

  It goes without saying that the polylactic acid resin composition of the present invention can be processed and used in various molded products by methods such as injection molding and extrusion molding as well as fibers. The molded product can be used as an injection molded product, an extrusion molded product, a blow molded product, a film, a sheet, and the like.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. The following methods were used as measurement methods in the examples.

A. Melt viscosity of polymer (resin) The melt viscosity of the polymer was measured at a desired speed using a Capillograph 1B manufactured by Toyo Seiki. The polymer storage time from the insertion of the chip to the start of measurement was 4 minutes, and the measurement was performed in a nitrogen atmosphere.

B. Decomposition gas generation amount measurement of polylactic acid resin composition The chip is placed in a glass container filled with helium gas, heated from a temperature of 50 ° C. to a temperature of 250 ° C. at a heating rate of 10 ° C./min, and a temperature of 250 ° C. Hold for 30 minutes. The components generated at this time are collected in an activated carbon collection tube (manufactured by Spelco: carbon trap 400). The collection tube was heated at a temperature of 300 ° C., the collected components were desorbed, and introduced into an Automass SUN-200 GC / MS manufactured by JEOL Ltd., and the components and the amount of generation were analyzed (CG / MS column: GL Science Co., Ltd. CP-WAX52CB 25 m × 0.32 mm). The generation amount (mg / kg) was calculated by dividing the generation amount of each component by the chip weight. The cracking gas suppression effect was judged by (circle) -x as follows according to the amount of lower fatty acids.
・ Lower fatty acid content 15 mg / kg or less: ○
・ Less than 20 mg / kg: △
・ 20 mg / kg or more: ×
○ was accepted and Δ and × were rejected.

C. Melting | fusing point of polymer (resin) and additive Using TA Instruments DSC2920 Modulated DSC, the peak top temperature which shows melting | fusing of a polymer by 2nd run was made into melting | fusing point of a polymer. The temperature rising rate at this time was 16 ° C./min, and the sample amount was 10 mg.

D. Strength and elongation of polylactic acid fiber The fineness (dtex) was calculated by making a 100 m small wrinkle with a measuring machine manufactured by Intec Corporation and multiplying the weight by 100. Using a tensile tester “Tensilon” (registered trademark) UCT-100 manufactured by Orientec Co., Ltd., a stress-strain curve is measured under the conditions of a sample length of 20 cm and a tensile speed of 100% / min. The breaking strength is calculated by reading the load at break and dividing the load by the initial fineness. Further, the elongation at break is calculated by reading the strain at break and multiplying the value divided by the sample length by 100. This was repeated 5 times or more, and a simple number average of the obtained results was obtained to obtain the strength and elongation of the fiber.

E. Odor Evaluation during Melt Spinning Using the pellets prepared in Example 1 and Comparative Examples 1 to 4, a spinning temperature of 220 ° C. and a single hole discharge rate of 0.85 g / min, 0.35 mmφ (L / D = 2.0) ) Melt spinning was performed using -36 holes. 6 hours after the start of polymer discharge, fix the tip of the odor sensor (portable monitor OD-85 manufactured by Riken Keiki Co., Ltd.) at a distance of 50 mm from the spinneret surface, measure the odor, and display the value displayed on the odor sensor three times. Measurements were made, simple number averages were calculated, and odor evaluation was performed based on the numerical values. Moreover, the odor around the melt spinning machine was judged by ○ to × as follows.
・ I do not feel: ○
・ We feel weak: △
・ We feel strongly: ○
○ was accepted and Δ and × were rejected.

F. Metal Corrosion Evaluation of Pipe and Metering Section of Melt Spinning Machine Using pellets prepared in Example 1 and Comparative Examples 1 to 4, with a spinning temperature of 220 ° C. and a single hole discharge rate of 0.85 g / min, 0.35 mmφ (L /D=2.0) Melt spinning was carried out continuously for 24 hours using -36 holes. After the completion of melt spinning, the spinning machine is temporarily stopped, cooled and heated again, and then disassembled to check the state of metal corrosion in the piping and metering section of the spinning machine. It evaluated by x.
・ No metal corrosion is seen: ○
・ Metallic corrosion is seen in some places: △
・ Metallic corrosion is seen: ×
○ was accepted and Δ and × were rejected.

(Comparative Example 1)
Lactide prepared from L-lactic acid with an optical purity of 99.5% was mixed with bis (2-ethylhexanoate) tin catalyst (lactide to catalyst molar ratio = 10000: 1) at a temperature of 180 ° C. in a nitrogen atmosphere. Polymerization was performed for 140 minutes to obtain polylactic acid having a melt viscosity of 115 Pa · s (240 ° C., 1216 sec ⁻¹ ) and a melting point of 170 ° C. When the decomposition gas component of this polylactic acid was analyzed, lower fatty acids (acetic acid, propionic acid and acrylic acid) were mainly detected, and the generation amount was 25.7 mg / kg. The results are shown in Table 1.

[Example 1]
The polylactic acid obtained in Comparative Example 1 has a molecular structure including one phosphorous compound structure selected from a phosphoric acid structure, a phosphine structure, and a phosphite structure and a hindered phenol structure in each molecule. As a decomposition inhibitor (additive A), the following chemical formula 1

“IRGAMOD295” (registered trademark) (melting point: 120 ° C.) manufactured by Ciba Chemical Specialty Co., Ltd. is weighed so that the added amount is 0.1 mol% (0.5 wt%) and introduced into a twin-screw kneader. Previously, it was dry-blended with polylactic acid and introduced into a twin-screw kneader. Kneading was carried out with a twin-screw kneader (screw diameter: 37 mmφ L / D: 48) set at a kneading temperature of 220 ° C., a screw rotation speed of 300 rpm, and a discharge rate of 15 kg / hour to obtain a pelletized polylactic acid resin composition.

  When the decomposition gas component of the obtained polylactic acid resin composition was analyzed, lower fatty acids (acetic acid, propionic acid and acrylic acid) were measured in the same manner as in Comparative Example 1, but any of acetic acid, propionic acid and acrylic acid was measured. In comparison with Comparative Example 1, the amount of the component was reduced, and the amount of lower fatty acid was 11.4 mg / kg, which was reduced by 50% or more (decomposition gas suppression effect: ◯). The results are shown in Table 1.

(Comparative Example 2)
Additive B is represented by the following chemical formula 2

Except that it was made “ADEKA STAB AX-71” (registered trademark) (phosphorus compound melting point 70 ° C.) manufactured by Adeka Co., Ltd., and the addition amount was 0.1 mol% (0.7 wt%), all in accordance with Example 1. Carried out.

  Although the obtained polylactic acid resin composition maintained the molecular weight, in the analysis of the decomposition gas component, the amount of generation of any component of acetic acid, propionic acid, and acrylic acid increased on the contrary compared with Comparative Example 1. The lower fatty acid content was 35.8 mg / kg, which was about 40% higher than that of Comparative Example 1 (decomposition gas suppression effect: x). The results are shown in Table 1.

(Comparative Example 3)
Additive C is represented by the following chemical formula 3

In order to make the OH equivalent equivalent to that in Example 1 using “IRGANOX1010” (registered trademark) (hindered phenol compound melting point 110 ° C.) manufactured by Ciba Chemical Specialty Co., Ltd. All were carried out according to Example 1 except that the content was 4% by weight.

  When the decomposition gas component of the obtained polylactic acid resin composition was analyzed, the generation amount of acetic acid, propionic acid and acrylic acid was slightly reduced as compared with Comparative Example 1, but the lower fatty acid generation amount was 18.8 mg / kg. In addition, the effect of suppressing the amount of lower fatty acid produced was only about 27% (decomposition gas suppression effect: Δ), which was not as good as the resin composition of the present invention (Example 1). The results are shown in Table 1.

(Comparative Example 4)
The phosphorus compound (additive B) used in Comparative Example 2 and the hindered phenol compound (Additive C) used in Comparative Example 3 were used in combination, and the phosphorus compound was 0.1 mol% (0.7 wt%) with respect to the entire resin. %), And hindered phenol compound was added according to Example 1 except that it was added as 0.025 mol% (0.4 wt%).

  When the decomposition gas component of the obtained polylactic acid resin composition was analyzed, the amount of acetic acid, propionic acid, and acrylic acid decreased compared to Comparative Example 1, but conversely, compared to Comparative Example 2, acetic acid was used. The amount of lower fatty acid is 19.8 mg / kg and the suppression effect is about 23% (decomposition gas suppression effect: Δ). The polylactic acid resin composition of the present invention (Example 1) contains The result was far from perfect. The results are shown in Table 1.

<Additives>
Additive A: IRGAMOD295, Ciba Chemical Specialty Co., Ltd. Chemical Formula 1
Additive B: Adeka Corporation ADEKA STAB AX-71 Chemical Formula 2 (phosphorus compound)
Additive C: “IRGANOX” (registered trademark) 1010 manufactured by Ciba Chemical Specialty Co., Ltd. Chemical formula 3 (hindered phenol compound)
<Decomposition gas suppression effect>
-Lower fatty acid amount 15 mg / kg or less: ○ Less than 20 mg / kg: Δ 20 mg / kg or more: ×.

[Examples 2 to 4]
The addition amount of the decomposition inhibitor (additive A) was 0.02 mol% (0.1 wt%) [Example 2], 0.5 mol% (2.5 wt%) [Example 3], and 1 mol% ( 5% by weight) All were carried out in accordance with Example 1, except that [Example 4].

  Table 2 shows the result of analyzing the decomposition gas of the obtained polylactic acid resin composition. Even when the addition amount is 0.02 mol%, even in [Example 2], the amount of the lower fatty acid is reduced to 14.7 mg / kg (decomposition gas suppression effect: ◯) compared to Comparative Example 1, and the decomposition used in the present invention. It can be seen that the inhibitor effectively acts to suppress the generation of lower fatty acids. In addition, the amount of lower fatty acid generated decreased with the increase in the amount of decomposition inhibitor added, and 10.4 mg / kg (decomposition gas inhibitory effect) of the one [Example 3] to which 0.5 mol% of the decomposition inhibitor was added. : ○) With respect to [Example 4] even when 1 mol% was added, the amount of lower fatty acid was significantly reduced as compared with Comparative Example 1 and the amount of lower fatty acid was 9.8 mg / kg (decomposition gas suppression effect: ○). Was. The results are shown in Table 2.

<Additives>
Additive A: “IRGAMOD” (registered trademark) 295 chemical formula 1 manufactured by Ciba Chemical Specialty Co., Ltd.
<Decomposition gas suppression effect>
-Lower fatty acid amount 15 mg / kg or less: ○ Less than 20 mg / kg: Δ 20 mg / kg or more: ×.

(Comparative Example 5)
Using the pellets prepared in Comparative Example 1, melt spinning was performed at a spinning temperature of 220 ° C. It measured so that it might become a single hole discharge amount 0.85g / min, and it discharged from 0.35mm (phi) (L / D = 2.0) -36 hole nozzle | capacitance (residence time until discharge: 25 minutes). The melted and discharged resin was cooled and solidified, and after the oil agent was adhered, it was wound up at a spinning speed of 3000 m / min. When the mechanical properties of the obtained fiber were measured, the strength was 2.2 cN / dtex and the elongation was 97%.

  As a measure of odor generation during melt spinning, when an odor sensor (portable monitor OD-85 manufactured by Riken Keiki Co., Ltd.) using the odor immediately below the base for odor evaluation was evaluated, the displayed numerical value was 666, which is high. Numerical values are shown. In addition, a unique odor caused by lower fatty acids drifted around the melt spinning machine (odor status: x). In order to check the deterioration of the piping and the metering section of the melt spinning machine, spinning was continued for 24 hours under the above-mentioned conditions, the spinning was finished, the melt spinning machine was cooled, the temperature was raised again, and the spinning machine was After disassembling and confirming the piping and measuring section of the spinning machine, it was confirmed that the spinning machine was deteriorated especially due to metal corrosion between pipe joints and parts of the measuring section (spinning machine deterioration evaluation: X). The results are shown in Table 3.

[Example 5]
All were carried out according to Comparative Example 5 except that the pellets prepared in Example 1 were used. When the mechanical properties of the obtained polylactic acid fiber were measured, the strength was 2.3 cN / dtex and the elongation was 99%, and the same mechanical properties were obtained as in Comparative Example 5, and there was also a problem in spinnability. There was no.

  When the odor just below the spinneret was evaluated in the same manner as in Comparative Example 5, the odor sensor displayed values of 399 and 40% suppressed the odor, and almost no odor was felt even around the melt spinning machine. (Odor status: ○). In addition, as in Comparative Example 5, spinning was performed continuously for 24 hours, and after cooling, the temperature was raised again and the spinning machine was disassembled to check the piping and measuring section of the spinning machine. Almost no metal corrosion was observed (spinning machine deterioration evaluation: ◯). The results are shown in Table 3.

(Comparative Example 6)
All were carried out in accordance with Comparative Example 5 except that the pellets prepared in Comparative Example 2 (phosphorus compound added) were used. The mechanical properties of the obtained polylactic acid fiber were 2.4 cN / dtex in strength and 86% in elongation, which was slightly reduced as compared with Comparative Example 5. When the odor just below the spinneret was evaluated in the same manner as in Comparative Example 5, the displayed value of the odor sensor was 885, and the odor increased by 33% compared to Comparative Example 5. A unique odor caused by lower fatty acids drifts around the spinning machine, and a particularly sour irritating odor was felt (odor status: x). Further, as in Comparative Example 5, spinning was performed continuously for 24 hours, and after cooling, the temperature was raised again, the spinning machine was disassembled, and the piping and metering section of the spinning machine were confirmed. Metal corrosion was confirmed at the joints and the measuring section (spinner deterioration evaluation: x). The results are shown in Table 3.

(Comparative Example 7)
All were carried out in accordance with Comparative Example 5 except that the pellets prepared in Comparative Example 3 (with hindered phenol compound added) were used. The mechanical properties of the obtained fiber were as follows: the strength was 2.2 cN / dtex, and the elongation was 95%. When the odor just below the spinneret was evaluated in the same manner as in Comparative Example 5, the odor sensor display value was 495 and 26% of the odor was suppressed compared to Comparative Example 5, but it was unique around the melt spinning machine. The odor was felt (odor status: Δ). In addition, as in Comparative Example 5, spinning was performed continuously for 24 hours, and after cooling, the temperature was raised again, the spinning machine was disassembled, and the piping and metering section of the spinning machine were confirmed. Although metal corrosion at the joints of the pipes and the measuring section was slightly suppressed, deterioration was advanced as compared with Example 4 (spinning machine deterioration evaluation: Δ). The results are shown in Table 3.

(Comparative Example 8)
All were carried out in accordance with Comparative Example 5 except that the pellets prepared in Comparative Example 4 (combination of phosphorus compound and hindered phenol compound) were used. Regarding the mechanical properties of the obtained polylactic acid fiber, the strength was 2.3 cN / dtex, and the elongation was 90%. When the odor just below the spinneret was evaluated in the same manner as in Comparative Example 5, the odor sensor display value was 512 and 23% of odor was suppressed compared to Comparative Example 5, but as in Comparative Example 5, A unique odor was felt around the melt spinning machine (odor status: Δ). In addition, as in Comparative Example 5, spinning was performed continuously for 24 hours, and after cooling, the temperature was raised again, the spinning machine was disassembled, and the piping and metering section of the spinning machine were confirmed. Although metal corrosion at the joints of the pipes and the measuring section was slightly suppressed, deterioration was advanced as compared with Example 4 (spinning machine deterioration evaluation: Δ). The results are shown in Table 3.

<Additives>
Additive A: “IRGAMOD” (registered trademark) 295 chemical formula 1 manufactured by Ciba Chemical Specialty Co., Ltd.
Additive B: Adeka Corporation ADEKA STAB AX-71 Chemical Formula 2 (phosphorus compound)
Additive C: “IRGANOX” (registered trademark) 1010 manufactured by Ciba Chemical Specialty Co., Ltd. Chemical formula 3 (hindered phenol compound)
<Odor evaluation>
・ Odor status: Not felt: ○ Feel weak: △ Feel strong: ×
<Evaluation of spinning machine deterioration>
Metal corrosion: No metal corrosion is observed: ○ Metal corrosion is observed in some places: Δ Metal corrosion is observed: x.

Claims (7)

A resin composition containing 95% by weight or more of polylactic acid as a resin component (but not containing a carbodiimide compound) , and any one selected from a phosphate structure, a phosphine structure and a phosphite structure in one molecule A polylactic acid resin composition, wherein a decomposition inhibitor having a molecular structure containing one phosphorus compound structure and one hindered phenol structure is added in an amount of 0.01 to 1 mol% based on the entire resin.   The polylactic acid resin composition according to claim 1, wherein the decomposition inhibitor has a melting point of 70 to 170 ° C.   3. The polylactic acid according to claim 1, wherein the amount of lower fatty acid in the cracked gas generated when kept at a temperature of 250 ° C. for 30 minutes in an inert gas atmosphere is 15 mg / kg or less. Resin composition.   A polylactic acid fiber comprising the polylactic acid resin composition according to any one of claims 1 to 3.   A polylactic acid fiber structure comprising the polylactic acid fiber according to claim 4. A resin composition comprising polylactic acid and a decomposition inhibitor having a molecular structure containing one of a phosphorus compound structure selected from a phosphoric acid structure, a phosphine structure and a phosphite structure and a hindered phenol structure in one molecule ( However, it does not contain a carbodiimide compound), and is a method for producing polylactic acid fibers that are melt-spun, and kneaded with polylactic acid in such an amount that the above-mentioned decomposition inhibitor becomes 0.01 to 1 mol% with respect to the entire resin. A method for producing a polylactic acid fiber, which is then subjected to melt spinning.   The method for producing polylactic acid fiber according to claim 6, wherein melt spinning is performed using a resin composition containing 95% by weight or more of polylactic acid as a resin component.