JP2012167399A - Polylactic acid-based nonwoven fabric - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic acid-based nonwoven fabric which comprises continuous fibers and is obtained with excellent spinnability and openability, and which can sufficiently retain hydrolysis resistance and strength after a certain period of time has passed, thereby being applicable to practical use.SOLUTION: In the polylactic acid-based nonwoven fabric comprising continuous fibers, the continuous fibers have a core-sheath conjugate form, in which a core part comprises a polylactic acid-based polymer containing a carbodiimide compound and hydrotalcite, and a sheath part comprises a thermoplastic polymer containing no carbodiimide compound.

Description

  The present invention relates to a polylactic acid-based nonwoven fabric.

  Conventionally, various nonwoven fabrics made of thermoplastic polymers such as polyolefins, polyesters, polyamides, etc. are known as materials for daily life, industrial / civil engineering materials, agricultural materials and the like. However, these non-woven fabrics are manufactured from petroleum-derived raw materials, and need to be reviewed from the viewpoint of protecting the natural environment, such as high combustion heat during incineration and generated greenhouse gases.

  Among them, polylactic acid, which is a biodegradable plastic, is a biomass that uses corn as a raw material, and its carbon source is carbon dioxide taken from the atmosphere, and thus has attracted attention as a carbon neutral material. In addition, among biodegradable plastics, mechanical properties and heat resistance are excellent, and mass production is progressing, so the problem of cost is being solved, and various developments of molded products such as fibers using this are being carried out. Yes.

  The development of polylactic acid fibers is preceded by agricultural materials and civil engineering materials that make use of biodegradability. Subsequent large-scale applications are expected to be used for clothing, interiors such as curtains and carpets, and vehicle interiors.

  On the other hand, since polylactic acid has a high hydrolyzability, even in normal use, hydrolysis may progress in some cases, resulting in a strong decrease. For this reason, when used as a general-purpose product, there is a problem that the product life may be short. In addition, when polylactic acid fibers are dyed, hydrolysis proceeds rapidly because they are exposed to a high temperature state (110 ° C. or higher) at the time of dyeing, and the tear strength does not meet the practical level in the fabric using the dyed fibers. There is also. The carboxyl terminal generated by hydrolysis of polylactic acid generates free protons. This free proton serves as a catalyst for hydrolysis of the ester bond and further accelerates the decrease in the molecular weight of polylactic acid, thereby accelerating the deterioration of strength.

  As a method for solving this problem, Patent Document 1 discloses a technique for improving hydrolysis resistance by blocking the carboxyl terminal of a polylactic acid polymer with a carbodiimide compound.

JP 2001-261797 A

The present invention, when obtaining a non-woven fabric composed of continuous fibers, has good spinning properties and spreadability, and can sufficiently retain hydrolysis resistance and strength after a certain period of time that can be put to practical use. It is a technical problem to provide a polylactic acid-based nonwoven fabric.

  As a result of studies to achieve the above-mentioned problems, the present inventor has added the above-mentioned problems by adding a hydrotalcite to a polylactic acid polymer in combination with a carbodiimide compound known as an agent for blocking the carboxyl end. The present invention has been found. Furthermore, if a yarn is formed in a form in which a polylactic acid-based polymer to which a carbodiimide compound or the like is added is disposed in the core and the periphery thereof is coated with a thermoplastic polymer to which no carbodiimide compound is added, It has been found that the generation of irritating odors can be suppressed, and the present invention has been achieved.

  That is, the present invention is a nonwoven fabric constituted by continuous fibers, the continuous fibers are in a core-sheath composite form, and a polylactic acid-based polymer is disposed in the core, and the polylactic acid-based polymer has a carbodiimide compound. And the hydrotalcite, and the sheath is a polylactic acid-based non-woven fabric characterized in that a thermoplastic polymer not containing a carbodiimide compound is arranged.

  Hereinafter, the present invention will be described in detail.

  Examples of the polylactic acid polymer in the present invention include poly (D-lactic acid), poly (L-lactic acid), a copolymer of D-lactic acid and L-lactic acid, a copolymer of D-lactic acid and hydroxycarboxylic acid, Any polymer selected from a copolymer of L-lactic acid and hydroxycarboxylic acid, a copolymer of D-lactic acid, L-lactic acid and hydroxycarboxylic acid, or a blend thereof can be used. . Examples of the hydroxycarboxylic acid copolymerized with lactic acid include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxyheptanoic acid, and hydroxycaprylic acid. Of these, hydroxycaproic acid and glycolic acid are particularly low. This is preferable in terms of cost.

  The melting point of the polylactic acid polymer in the present invention is preferably 150 ° C. or higher. Since the polylactic acid polymer having a melting point of 150 ° C. or higher has high crystallinity, it becomes a non-woven fabric that has good heat resistance, low heat shrinkage, and can be stably heat-processed. Poly-L-lactic acid and poly-D-lactic acid, which are homopolymers of polylactic acid, have a melting point of about 180 ° C. However, when a copolymer is used instead of a homopolymer, the melting point of the monomer should be 150 ° C. or higher. It is necessary to determine the copolymerization ratio. Specifically, in a copolymer of L-lactic acid and D-lactic acid, the molar ratio of L-lactic acid to D-lactic acid is (L-lactic acid) / (D-lactic acid) = 5/95 to 0/100 or ( L-lactic acid) / (D-lactic acid) = 95/5 to 100/0 may be used. If the copolymerization ratio deviates from this value, the melting point is less than 150 ° C. and the amorphous property becomes high, and the object of the present invention may not be achieved.

  The nonwoven fabric of the present invention is composed of continuous fibers in a core-sheath composite form, and the above-mentioned polylactic acid polymer is arranged in the core of the continuous fibers, and the carbodiimide compound and hydrotalcite are contained in the polylactic acid polymer. include.

  Examples of the carbodiimide compound used in the present invention include monocarbodiimide and polycarbodiimide, and those synthesized by a generally well-known method may be used. However, unless it can withstand the high temperature conditions during melt spinning and heat degradation is not likely to occur, the spinnability and operability are deteriorated, and the effects of the present invention cannot be expected. In the present invention, the content of the carbodiimide compound is preferably 0.1 to 1.5 parts by mass when the polylactic acid polymer is 100 parts by mass, and the hydrolysis resistance required within this range. What is necessary is just to determine content suitably according to property. When the content of the carbodiimide compound is less than 0.1 parts by mass, the target polylactic acid-based nonwoven fabric cannot be sufficiently improved in hydrolysis resistance. On the other hand, when the amount is more than 1.5 parts by mass, the spinning property is deteriorated, and a large amount of decomposition gas is generated from the carbodiimide compound, so that the operability deteriorates. For these reasons, a more preferable range is 0.5 to 1 part by mass.

  The hydrotalcite used in the present invention is contained in the polylactic acid polymer in the range of 0.1 to 3 parts by mass with respect to 100 parts by mass of the polylactic acid polymer. By containing hydrotalcite in the polylactic acid polymer, it is possible to have a function of promoting crystallization of the polylactic acid polymer in melt spinning. Further, it is presumed that the inclusion of hydrotalcite together with the carbodiimide compound in the polylactic acid-based polymer has an effect of suppressing a decrease in molecular weight due to hydrolysis. Therefore, by using a polylactic acid-based polymer containing hydrotalcite, the spinning property is improved, and the resulting nonwoven fabric can be imparted with hydrolysis resistance that can be put to practical use. When the content of hydrotalcite is less than 0.1 parts by mass, the effect of containing hydrotalcite cannot be sufficiently achieved, while when it exceeds 3 parts by mass, the strength of the yarn tends to decrease. .

  As a method of incorporating a carbodiimide compound or hydrotalcite into a polylactic acid polymer, a polylactic acid polymer chip and a carbodiimide compound or hydrotalcite are mixed with a kneader to create a master chip once, Chip blending (chipbatch method) and polyspinning of polylactic acid polymer chips, melt powder spinning, and dry powdered carbodiimide compound and hydrotalcite are directly added to polylactic acid polymer chips and mixed ( A method of melt spinning using a dry blending method), and a method in which a polylactic acid polymer chip and a carbodiimide compound or hydrotalcite are mixed in advance by melt kneading to form a chip and melt spinning using the chip. (Compound method).

  To the polylactic acid polymer used in the present invention, additives such as known antioxidants, ultraviolet absorbers, pigments, flame retardants, lubricants, stabilizers and the like may be added as long as the object of the present invention is not hindered. Good. However, since the carbodiimide compound used in the present invention is a condensing agent, when a drug having a substituent such as a hydroxyl group, an amino group, or a carboxyl group is added, the side reaction will increase. Since the drug is consumed, the effects of the additive, including the effects of the present invention, may not be sufficiently obtained, so care should be taken in selecting and adding the drug.

  In the continuous fiber in the present invention, as described above, a polylactic acid polymer containing a carbodiimide compound and hydrotalcite forms a core, and the core is coated with a thermoplastic polymer not containing a carbodiimide compound. The cross-sectional shape of the core-sheath composite form is exhibited. In addition, as long as the core-sheath composite form is used, the cross-sectional shape may be any cross-sectional shape such as a circular shape, an elliptical shape, a polygonal shape, a multileaf shape, and a hollow shape.

  In the present invention, a polylactic acid-based polymer containing a carbodiimide compound is spun in such a manner that a thermoplastic polymer not containing a carbodiimide compound is completely covered by making the continuous fiber form a core-sheath composite. Therefore, since the polylactic acid polymer is not exposed on the fiber surface except for the end of the fiber due to the core-sheath composite form and the continuous fiber, it is caused by the carbodiimide compound at the time of production. Generation of an irritating odor can be suppressed, and hydrolysis of the polylactic acid polymer in the core can be effectively suppressed.

The thermoplastic polymer disposed in the sheath portion of the continuous fiber in the present invention is not particularly limited as long as it has yarn-making properties, and examples thereof include polyester polymers, polyamide polymers, polyolefin polymers, and the like. It is done. If the melting point of the thermoplastic polymer in the sheath is too higher than the melting point of the polylactic acid polymer disposed in the core, the polylactic acid polymer is liable to undergo thermal decomposition in the melt spinning process, and the polylactic acid heavy polymer. The melting point of the thermoplastic polymer in the sheath is preferably 230 ° C. or lower, and more preferably 200 ° C. or lower, since there is a risk that the operability may be impaired, such as contamination of the spinneret surface due to thermal decomposition of the coalescence. Preferably there is.
Especially, since it has high durability and flexibility can be added to continuous fibers, the thermoplastic polymer in the sheath is preferably a polyolefin polymer, and particularly preferably polyethylene or polypropylene. .

  As the polyethylene, polyethylene having a melt index (hereinafter abbreviated as MI) measured in accordance with the method described in ASTM D 1238 (E) in the range of 5 to 90 g / 10 min is preferably used. Polyethylene with an MI of less than 5 g / 10 min is difficult to melt-spin when melt spinning unless the melt temperature is extremely high. In melt spinning at such an extremely high temperature, the thermal decomposition of the raw material is accelerated. It is not preferable because dirt is easily attached to the spinneret surface and the operability is remarkably impaired. On the other hand, when MI exceeds 90 g / 10 minutes, it is difficult to obtain a fiber having high strength. For the reasons as described above, it is preferable to use polyethylene of 20 to 80 g / 10 min.

  As the polypropylene, a polypropylene having a melt flow rate (hereinafter abbreviated as MFR) measured according to the method described in ASTM-D-1238 (L) is preferably used in an amount of 5 to 90 g / 10 min. Use of polypropylene having an MFR of less than 5 g / 10 minutes is not preferable for the same reason as in the case of the above-mentioned polyethylene having an MI of less than 5 g / 10 minutes. On the other hand, the case where the MFR of polypropylene exceeds 80 g / 10 min is also not preferable for the same reason as the case where the MI of polyethylene exceeds 90 g / 10 min. For the above reasons, it is preferable to use polypropylene of 20 to 80 g / 10 min.

  The polyolefin polymer may be polymerized using either a Ziegler-Natta catalyst or a metallocene catalyst. Polyolefins polymerized using a metallocene catalyst can easily control the molecular weight of the polymer and can sharpen the molecular weight distribution. Therefore, when the nonwoven fabric is heat-treated, it is easy to determine the heat treatment temperature.

  The composite ratio of the core part and the sheath part in the core-sheath composite form of continuous fibers may be appropriately selected according to the use of the nonwoven fabric, but the core / sheath is 1/5 to 5/1 in terms of mass ratio. More preferably, it is in the range of 1/3 to 3/1. In particular, as the ratio of the core / sheath exceeds 5/1, the thickness of the portion covered by the sheath becomes thinner, so that it is difficult to sufficiently achieve effects such as improvement in durability due to the core-sheath structure.

  The single yarn fineness of the fibers constituting the polylactic acid-based nonwoven fabric of the present invention is preferably 1 to 10 dtex. Furthermore, it is preferable that it is 1.5-8 decitex. When the single yarn fineness is less than 1 dtex, the operability tends to deteriorate, for example, yarn breakage occurs in the spinning process. On the other hand, if it exceeds 10 dtex, the spinning yarns are poorly cooled, and thus the spun yarns tend to be in close contact with each other, and the opening property tends to be inferior.

The basis weight of the polylactic acid-based nonwoven fabric of the present invention may be appropriately selected according to the use and purpose, and is not particularly limited, but is generally preferably 10 g / m ² or more. When the basis weight is 10 g / m ² or less, although it is excellent in flexibility, it tends to be inferior in mechanical strength and is easily broken. The upper limit is not particularly limited, but is about 800 g / m ² .

  Examples of the non-woven form of the polylactic acid-based nonwoven fabric of the present invention include a heat-bonded nonwoven fabric in which constituent fibers are bonded to each other by heat, an entangled nonwoven fabric in which constituent fibers are mechanically entangled by a needle punch method, a spunlace method, or the like. Can be mentioned. Further, various bonding methods may be used in combination. In consideration of productivity and mechanical strength, it is preferably a heat-bonded nonwoven fabric in which constituent fibers are bonded together by heat.

Specifically, the method of thermal bonding includes a heated embossing roll and a flat roll having a smooth surface, a pair of heated embossing rolls, or a fiber web between a pair of heated flat rolls, In this method, part of the fibers are softened or melted by heat to bond the constituent fibers. The pattern of the embossing roll directly becomes the shape of the heat bonding part, but the shape is not particularly limited, and may be a linear shape such as a dotted shape, a linear shape, or a lattice shape. In the case of a scattered dot shape, any shape such as a round shape, an oval shape, a rhombus shape, a triangle shape, a T shape, a well shape, a rectangular shape, and a square shape may be used. The size and density of the adhesion points may be appropriately selected depending on the purpose, but the size of the adhesion points is preferably 0.1 to 1.0 mm ² and the density of adhesion points is ² to 80 / cm ² . If the size of each bonded portion is less than 0.1 mm ² or the bond point density is less than 2 pieces / cm ² , the bond strength is small and the mechanical strength tends to be inferior. In addition, when the size of the bonded portion exceeds 1.0 mm ² or when the bonding point density exceeds 80 pieces / cm ² , the flexibility and bulkiness of the resulting nonwoven fabric are reduced because the area of the bonding point is large. It becomes a trend.

  Next, the preferable manufacturing method of the polylactic acid-type nonwoven fabric of this invention is demonstrated. The polylactic acid-based nonwoven fabric of the present invention can be efficiently produced by a spunbond method in which the spinning process and the nonwoven fabric forming process are performed in a continuous process. First, prepare a core component in which a carbodiimide compound and hydrotalcite are mixed with a polylactic acid polymer to be a core part, while preparing a thermoplastic polymer for a sheath part so that a predetermined mass ratio is obtained. These components are individually weighed, melted, and spun from a core-sheath compound spinneret. The spun yarn is cooled by a known cooling device such as a cooling air flow, and is pulled and thinned to a target fineness by a known take-up means such as air soccer. The continuous and refined continuous fiber group is opened by a known opening device, and then spread and deposited on a movable collection surface such as a screen conveyor to form a continuous fiber web. The obtained continuous fiber web is passed through a thermal bonding apparatus to thermally bond the fibers to obtain a target polylactic acid-based nonwoven fabric.

  The towing speed by air soccer is preferably in the range of 3500 to 7000 m / min. If the pulling speed is too slow, the molecular orientation of the polymer does not proceed sufficiently, resulting in poor mechanical performance and dimensional stability of the resulting nonwoven fabric. On the other hand, if it is too fast, the spinning stability is poor, yarn breakage tends to occur, and the operability tends to deteriorate.

  The surface temperature of the heating roll during thermal bonding is preferably in the range of (Tm-60) to Tm ° C. with respect to the melting point (Tm) of the thermoplastic polymer in the sheath. When the roll surface temperature is too low, the thermal bonding is not sufficiently performed, and the mechanical performance and the dimensional stability tend to be lowered. On the other hand, when the roll surface temperature is too high, the fibers melt and adhere to the roll surface, which may impair operability. If necessary, a binder resin or the like may be applied to the nonwoven fabric obtained by the heat treatment by a method such as a dipping method, a coating method, or a foam impregnation method. Moreover, what is necessary is just to select the binder resin to provide suitably according to the objective.

  According to the present invention, by adding a carbodiimide compound and hydrotalcite to a polylactic acid-based polymer, the spinning property is improved and the hydrolysis resistance is improved. Also, a core-sheath composite in which a polylactic acid-based polymer containing a carbodiimide compound or the like is arranged in the core, and a thermoplastic polymer not containing a carbodiimide compound is arranged in the sheath and coated with a polylactic acid-based polymer containing a carbodiimide compound. By adopting continuous fiber as a form, it is possible to suppress the generation of irritating odors due to carbodiimide compounds at the time of production, and to keep the working environment at the production site normal, and in the obtained nonwoven fabric Can effectively suppress hydrolysis of the polylactic acid polymer in the core. Therefore, according to the present invention, it is possible to provide a highly practical polylactic acid-based non-woven fabric that does not easily cause a decrease in strength with the passage of time.

EXAMPLES Next, although this invention is demonstrated based on an Example, this invention is not limited at all by the Example. Various physical properties described in the examples were determined by the following measuring methods.
(1) Melting point (° C)
Using a differential scanning calorimeter manufactured by Perkin Elma Co., Ltd., the sample mass was measured at 5 mg and the heating rate was 10 ° C./min. The temperature giving the maximum value of the obtained melting endotherm curve was defined as the melting point (° C.).

(2) Weight per unit (g / m ² )
Five sample pieces having a sample length of 20 cm and a sample width of 5 cm in a standard state were prepared, and the mass (g) of the sample piece of each sample was weighed, and the obtained value was converted per unit area to obtain a basis weight (g / m ² ).

(3) Hydrolysis resistance evaluation After putting a sample (nonwoven fabric) in a constant temperature and humidity chamber at a temperature of 60 ± 5 ° C. and a relative humidity of 95 ± 5% and exposing it to a high temperature and high humidity state for a predetermined time, The tensile strength (N / 5 cm width) was measured and obtained. Tensile strength was determined in accordance with JIS L 1906 by preparing five sample pieces with a sample length of 20 cm and a sample width of 5 cm, and a constant speed extension type tensile tester (Tensilon UTM-4-1-100 manufactured by Orientec Co., Ltd.) for each sample. ), And was stretched at a grip interval of 10 cm and a tensile speed of 20 cm / min, and the average value of the resulting breaking load at break (N / 5 cm width) was taken as the tensile strength (N / 5 cm width). When measuring the strength, both the machine direction (MD) of the sample and the direction (CD) perpendicular to the machine direction were measured.
As an evaluation method for hydrolysis resistance, the strength retention was calculated by the following formula, where S0 was the initial tensile strength before the constant temperature and humidity chamber was charged, and S1 was the tensile strength after the predetermined time was charged.
Strong retention rate (%) = (S1 / S0) × 100

Example 1
Melting point: 174 ° C., MFR: 21 g / 10 min (measured according to the method described in ASTM-D-1238 with a melting temperature of 210 ° C. and a load of 2160 gf), L-lactic acid / D-lactic acid = 99.6 / 0.4 ( Mol%) of polylactic acid polymer. 0.5 parts by mass of hydrotalcite (DHT-4A-2, manufactured by Kyowa Chemical Industry Co., Ltd.) and 0.5 parts by mass of carbodiimide compound (EN160, manufactured by Matsumoto Yushi Co., Ltd.) with respect to 100 parts by mass of this polylactic acid polymer. What added the part was made into the core component.

On the other hand, high-density polyethylene having a melting point of 129 ° C., MI of 25 g / 10 min, and a density of 0.95 g / m ³ was prepared as a thermoplastic polymer to be disposed in the sheath.

  The above polymer is weighed so that the weight ratio of the core part to the sheath part is core / sheath = 1/1, melted at 220 ° C. using an individual extruder type melt extruder, and the core-sheath type spinneret is obtained. The melt spinning was performed at a single hole discharge of 1.3 g / min. The spun yarn was cooled with a known cooling device, and was pulverized with a pulling speed of 4200 m / min using an air soccer ball, and opened with a known fiber opening device. The opened yarn was collected on a moving screen conveyor to obtain a web made of continuous fibers in a core-sheath composite form. The single yarn fineness of the continuous fiber was 2.8 dtex.

The obtained web was hot-pressed with a hot embossing apparatus having a surface temperature set at 120 ° C. to obtain a polylactic acid-based nonwoven fabric having a basis weight of 50 g / m ² . Table 1 shows the results of evaluation of hydrolysis resistance of the obtained polylactic acid-based nonwoven fabric. In the hydrolysis resistance evaluation, the obtained nonwoven fabric had a very small decrease in strength even after being exposed to a high temperature and high humidity state for 600 hours, and was excellent in hydrolysis resistance.

Comparative Example 1
In Example 1, with respect to 100 parts by mass of a polylactic acid polymer, only 0.5 parts by mass of a carbodiimide compound was added, and a polylactic acid polymer without addition of hydrotalcite was used, and high-density polyethylene was used. The melt was melted at 210 ° C. using an extruder-type melt extruder and melt-spun using a single-phase spinneret at a single-hole discharge rate of 1.7 g / min. The yarn spun from the spinneret was hard to be cooled, and even when trying to introduce it into air soccer, the fibers were in close contact with each other and could not be satisfactorily produced, giving up a nonwoven web.

Comparative Example 2
In Example 1, a polylactic acid polymer in which only 0.5 parts by mass of hydrotalcite was added and no carbodiimide compound was added to 100 parts by mass of a polylactic acid polymer, and high-density polyethylene was used. Without melting at 210 ° C. using an extruder-type melt extruder and melt spinning with a single-hole type spinneret at a single-hole discharge rate of 1.7 g / min, and a pulling speed of 5500 m / min. A nonwoven fabric was produced in the same manner as in Example 1 except that the set temperature of the heat embossing apparatus was 130 ° C., and a polylactic acid-based nonwoven fabric having a basis weight of 50 g / m ² was obtained. Table 1 shows the results of evaluation of hydrolysis resistance of the obtained polylactic acid-based nonwoven fabric. In the hydrolysis resistance evaluation, the strength of the obtained nonwoven fabric greatly decreased after being exposed to a high temperature and high humidity state for 400 hours, and almost no strength after 600 hours.

Comparative Example 3
In Example 1, a non-woven fabric was produced in the same manner as in Example 1 except that only 0.5 parts by mass of hydrotalcite was added without adding the carbodiimide compound to 100 parts by mass of the polylactic acid-based polymer. A polylactic acid-based nonwoven fabric having a basis weight of 50 g / m ² was obtained. Table 1 shows the results of evaluation of hydrolysis resistance of the obtained polylactic acid-based nonwoven fabric. In the hydrolysis resistance evaluation, the obtained non-woven fabric was reduced to about 30 to 40% of the initial strength after being exposed to a high temperature and high humidity state for 600 hours.

Claims (3)

  A nonwoven fabric composed of continuous fibers, in which the continuous fibers are in a core-sheath composite form, and a polylactic acid polymer is disposed in the core, and the polylactic acid polymer includes a carbodiimide compound and hydrotalcite. A polylactic acid-based non-woven fabric characterized in that a thermoplastic polymer not containing a carbodiimide compound is arranged in the sheath. The content of the carbodiimide compound and hydrotalcite in the polylactic acid polymer is 0.1 to 1.5 parts by mass of the carbodiimide compound and 0.1% of hydrotalcite with respect to 100 parts by mass of the polylactic acid polymer. It is 1-3 mass parts, The polylactic acid-type nonwoven fabric of Claim 1 characterized by the above-mentioned. The polylactic acid nonwoven fabric according to claim 1 or 2, wherein the thermoplastic polymer in the sheath is a polyolefin polymer.