DESCRIPTION
PARTLY ORIENTED CORE-SHEATH POLYESTER COMPOSITE FIBER,
CHEESE-FORM PACKAGE, AND FALSE-TWISTED FIBER
TECHNICAL FIELD
The present invention relates to a partly oriented core-sheath polyester composite fiber which has good false twisting properties, stability in dyeing, and soft feeling and is suitable for mass production, a cheese-form package, and a false-twisted fiber suitable for producing textiles excellent in bulking properties and stretching properties.
BACKGROUND ART
When fibers of polytrimethylene terephthalate (hereinafter sometimes referred to as PTT) are produced, they have characteristics in that the elongation recoverability is high, the initial tensile resistance is low, and thus soft properties are excellent. In addition, the polyethylene terephthalate (hereinafter sometimes referred to as PET) fiber has been recently examined as an attractive polyester fiber which can cover the disadvantage of the polyethylene terephthalate fiber by dyeable properties thereof.
Soft properties are further improved by false-twisting the PTT fiber. Therefore, the partly oriented fiber suitable for false-twisting has been actively examined. As for the

partly oriented PTT fiber (hereinafter sometimes referred to as PTT-POY), physical properties are changed with time since the shrinkage is large. When it is formed into the cheese-form package, the package shape is deteriorated and the false twisting process ability is poor. Particularly, the disadvantage has been largely examined.
For example, in order to keep the cheese-form package in good shape and improve the false twisting process ability, a method including a step of winding while cooling has been proposed (e.g., refer to Patent document 1) . However, although the shape of the cheese-form package can be maintained at some level by the method, it is essential to cool it. When the package is left at room temperature after collecting the package, changes with time are increased and the package is gradually deteriorated. It is found that the method cannot be employed practically. Then, a method including the steps of performing a heat treatment at the time of collecting the partly oriented fiber to increase the degree of crystallinity and winding after reducing the heat shrinkage has been proposed (e.g., refer to Patent documents 2 and 3). The package shape is dramatically improved by the method and the false twisting processability is also improved. Considering practical use, when the package is kept at room temperature for long periods, the package shape is deteriorated. When the package is kept for three months in a stockroom, the false twisting processability is deteriorated.

This shows that there is a problem in mass production. Further, production equipment of the partly oriented fiber needs to have heat treatment equipment. Therefore, the conventional production equipment of PET-fiber which does not need heat treatment cannot be used and investments in mass production are necessary.
On the other hand, as for a composite fiber of polylactic acid (hereinafter sometimes referred to as PLA) and polyester, a core-sheath composite fiber in which PTT is used as a sheath component has been proposed (e.g. , refer to Patent document 4) . However, the proposal aims at improving wear resistance, moisture-resistant, thermal-decomposition properties which are disadvantages of PLA. In addition, it is a fiber which is based on PLA and the solution of problems of the partly oriented PTT fiber is not mentioned. Further, it is quite inferior in soft properties. Although the core-sheath composite fiber in which PTT is used as the sheath component and PLA is used as a core component is produced in Examples, it is a drawn yarn. Problems unique to PTT-POY, such as problems related to prolonged storage or problems of false-twisting are not solved.
As described above, there is a need for the false-twisted fiber to produce the partly oriented fiber which takes advantage of soft properties which are advantages of PTT and suppresses changes with time and a good quality textile. Despite the examination being performed, practically effective techniques

have not been proposed.
Patent document 1: Japanese Patent Application Laid-open (JP-A)
No. 2001-254226 (Claims)
Patent document 2: JP-A No. 2001-020136 (Claims)
Patent document 3: JP-A No. 2003-129328 (Claims)
Patent document 4: JP-A No. 2004-353161 (Claims and Examples)
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
An objective of the present invention is to solve the conventional problems and to provide the partly oriented fiber which changes little in package shape even after practically necessary long-term storage in the stockroom, is excellent in false twisting properties, further has stability in dyeing and soft feeling, and is suitable for mass production, the cheese-form package, and further the false-twisted fiber suitable for producing textiles excellent in bulking properties and stretching properties.
MEANS FOR SOLVING THE PROBLEMS
In order to achieve the above-described objective, the present invention employs the following structures. That is, according to the present invention, there is provided the partly oriented core-sheath polyester composite fiber which includes polylactic acid as a core component and polytrimethylene

terephthalate as a sheath component, where the elongation is from 60 to 130%, the 70°C-water shrinkage is from 0.5 to 7.0%, and the initial tensile resistance is from 20 to 40 cN/dtex.
In the core-sheath polyester composite fiber, it is preferable that the weight average molecular weight of polylactic acid is in the range of 200,000 to 300,000 and the composite ratio is in the range of 20 to 50 wt%.
According to the present invention, there is provided the cheese-form package formed by winding the partly oriented core-sheath polyester composite fiber, where the bulge of the cheese-form package is from -5 to 5% and the saddle of the cheese-form package is from 0 to 5% when measured after storage in an atmosphere of 35°C and 60% RH for 90 days after winding the package.
According to the present invention, there is provided the false-twisted core-sheath composite fiber which includes polylactic acid as a core component and polytrimethylene terephthalate as a sheath component, where the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction is from 0 to 5%, the initial tensile resistance is from 20 to 40 cN/dtex, and the stretch recovery is from 25 to 60%.
EFFECT OF THE INVENTION
The present invention can provide the partly oriented

core-sheath polyester composite fiber which changes little in package shape even after practically necessary long-term storage in the stockroom, is excellent in false twisting properties, further has stability in dyeing and soft feeling, and is suitable for mass production and the cheese- form package. It could not be achieved by the conventional technologies. Further, there can be provided the false-twisted fiber from which textiles excellent in bulking properties, stretching properties, and soft properties with stable quality can be produced. The present invention can provide the partly oriented core-sheath polyester composite fiber, the cheese-form package, and the false-twisted fiber in an environmentally friendly way by using polylactic acid which is a plant-derived raw material and PTT whose part is the plant-derived raw material.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram explaining the bulge and the saddle, i.e., indicators of a package and a package form.
Fig. 2 is a diagram showing an example of preferable yarn-making equipment of the partly oriented core-sheath composite fiber.
Fig. 3 is a diagram showing the yarn-making equipment of partly oriented single PTT fiber produced in Comparative example 5 and core-sheath composite fibers produced in

Comparative examples 9 to 10.
DESCRIPTION OF THE SYMBOLS
1 : Cap
2: Cooling apparatus
3: Oiling apparatus
4: First roller
5: Second roller
6: Contact roller
7: Package
8: First heating roller
9: Second heating roller
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The partly oriented fiber of the present invention is the core-sheath composite fiber. The core component consists of polylactic acid (PLA) and the sheath component consists of polytrimethylene terephthalate (PTT). In order to allow all of the components to deliver performance equal to that of the partly oriented fiber consisting of PTT (single PTT fiber) (hereinafter, sometimes referred to as the partly oriented single PTT fiber), it is preferable that the core-sheath composite form is concentric. The concentric form allows the

partly oriented fiber to be a straight fiber without crimp. Thus, it can be treated in the same manner as the partly oriented single PTT fiber.
The core component of the partly oriented fiber of the present invention is PLA. FLA to be used in the present invention is a polymer containing 90 mol% or more of a repeating unit of - (0-CHCH3-C0)n- and it is obtained by polymerizing lactic acid and oligomer thereof. In this regard, a copolymerization component and a polyfunctional compound may be added thereto in the range of 10 mol% or less. The copolymerization component is an aliphatic compound which is easily biodegraded from the view point of biology. Preferable examples thereof include diols such as ethylene glycol, butanediol, hexanediol, or octanediol; succinic acid, hydroxyalkyl carboxylic acid; and aliphatic lactones such as pivalolactone or caprolactone. As for the polyfunctional compound, a compound in which an suitable cross-linkage or a weak cross-linkage is formed in the polymer by reacting glycerin, pentaerythritol, trimellitic acid, pyromellitic acid, or the like can be used. Further, inorganic particles such as titanium dioxide may be added. However, taking into consideration the use thereof as the core component, it is most preferable not to add inorganic particles such as titanium dioxide from the viewpoint of producing a stable composite form. Lactic acid includes two optical isomers: D-lactic acid and L-lactic acid.

Therefore, the polymer thereof includes poly (D-lactic acid) consisting of only D-isomer, poly (L-lactic acid) consisting . Of only L-isomer, and polylactic acid consisting of both of them. As the optical purity of D-lactic acid or L-lactic acid in polylactic acid becomes lower, the crystallinity decreases and the melting point depression becomes larger. Therefore, it is preferable that the optical purity is 90% or more in order to improve the heat resistance. The optical purity is more preferably 93% or more, further preferably 97% or more , In this regard, a strong correlation between the optical purity and the melting point is shown as described above. When the optical purity is about 90%, the melting point is about 150°C. When the optical purity is 93%, the melting point is about 160°C. When the optical purity is 97%, the melting point is about 170°C. When, in addition to a system in which two types of optical isomers are simply mixed as described above, the two types of optical isomers are blended, which is molded into a fiber, followed by performing heat treatment at 140°C or more to form a stereo complex with racemic crystals, the melting point can be increased dramatically. Thus, it is more preferable. PLA with a weight average molecular weight of 100,000 to 300,000 can be used. The weight average molecular weight has a relationship with changes with time of the partly oriented fiber to be obtained. Inhibitory effects on changes with time are increased by using PLA with a weight average molecular weight

of 200,000 or more, which is preferable. When the weight average molecular weight is set to 300,000 or less, soft properties can be ensured. Thus, it can be said that it is preferable. When polylactic acid is used as the core component, the shrinkage of the partly oriented fiber can be suppressed, changes with time can be reduced, and the deterioration of false twisting processability with time which is the disadvantage of the conventional partly oriented single PTT fiber can be suppressed. In the partly oriented PTT fiber which is obtained by the process of winding after the heat treatment, i.e., a conventional technology, a certain amount of shrinkage can be surely suppressed. However, changes with time in consideration of practical use cannot be suppressed. Thus, problems that the package form with time is deteriorated and the quality of the false twisted textured yarn is lowered could not be solved. However, the significance of the present invention is great from the viewpoint that shrink characteristics which are not reduced in a PLA element and a PTT element can be significantly suppressed by compositing PLA and PTT. Further, polylactic acid is a polymer generated from lactic acid which is produced by fermenting sugars from plants typified by corn. Since it is not made from petroleum, it is a very preferable polymer which meets with the carbon-neutral way. It is noteworthy that the polylactic acid is combined. On the other hand, the sheath component is PTT. PTT to

be used in the present invention is polyester obtained by-containing terephthalic acid as a major acid component and 1,3-propanediol as a main glycol component. It is preferable that PTT contains 90 mol% or more of a repeating unit of trimethyleneterephthalate. In this regard, it may include other copolymerization components at a ratio of 10 mol% or less. Examples of a copolymerizable compound include dicarboxylic acids such as isophthalic acid, succinic acid, cyclohexanedicarboxylic acid, adlpic acid, dimeracid, sebacic acid, or 5-sodium sulfoisophthalate; and diols such as ethylene glycol, diethylene glycol, butanediol, neopentyl glycol, cyclohexane dimethanol, polyethylene glycol, or polypropylene glycol. However, it is not limited to thereto. If necessary, titanium dioxide as a delustering agent, silica and alumina particles as lubricants, and hindered phenol derivatives and color pigments as anti-oxidants maybe added. When the limiting viscosity of PTT is from 0.8 to 1.2, it is easy to fiberize PTT, which is preferable.
Subsequently, physical properties of the partly oriented fiber of the present invention will be described. First, the elongation is 60 to 130%. When the elongation is 60% or more, the shrinkage can be suppressed without performing the heat treatment in the yarn-making process and false twisting processability is improved. The elongation is preferably 65% or more, more preferably 80% or more, further preferably 90%

or more. When the elongation is 130% or less, the change with time can be suppressed. Even if the fiber is stored for a long period of time, excellent false twisting procesaability can be maintained. It is preferably 125% or less, further preferably 120% or less. In the case of the partly oriented fiber, the process does not involve drawing. Therefore, the elongation can be adjusted by spinning speed. The elongation varies depending on the polymer to be used even if the spinning speed is the same speed. When the spinning speed is in the range of 2600 to 3700 m/min, it is easy to obtain the elongation of the present invention.
Subsequently, the 70°C-water shrinkage is from 0.5 to 7%. In the case where the 70°C-water shrinkage is 0.5% or more, the partly oriented fiber is apparently shrunk without being elongated when heat is given, and thus it can be treated in the same manner as the PET fiber. When the 70°C-water shrinkage is 7% or less, the deterioration of the package is suppressed even after prolonged storage in the stockroom and the processability at the time of false twisting becomes good. The 70°C-water shrinkage is more preferably 6% or less, further preferably 3% or less. The 70°C-water shrinkage is mainly determined by the spinning speed, the composite ratio of PLA which is a core polymer, and the presence or absence of heat treatment. In order to obtain the specified elongation, the spinning speed is preferably in the range of 2600 to 3700 m/min

as described above. However, when the spinning speed becomes higher, the 70°C-water shrinkage tends to become higher. In the partly oriented single PTT fiber, even when the spinning speed is set to lower values, the 70°C-water shrinkage is increased to 40% or more. Therefore, in the conventional technologies, the heat treatment is performed to reduce the shrinkage when the partly oriented fiber is produced. However, the false twisting processability after prolonged storage is deteriorated by the method as previously described above. Therefore, it is important that the partly oriented core-sheath composite fiber in which PTT is used as the sheath component and PLA is used as the core component is produced in the present invention. Stable false twisting can be carried out after prolonged storage by compositing PLA as the core component. Additionally, it is not necessary to perform the heat treatment when the partly oriented fiber is produced and conventional equipment of partly oriented single PET fiber can be diverted, which suitable for mass production.
As the composite ratio of PLA is larger, the 70°C-water shrinkage can be reduced. When the composite ratio is 20 wt% or more, it is easy to reduce the shrinkage. Thus, it is preferable. The composite ratio of PLA is more preferably 30 wt% or more. However, attention needs to be paid to the composite ratio of PLA. It is important that the partly oriented core-sheath composite fiber of the present invention

has performance equal to the partly oriented single PTT fiber, and can be treated in the same manner as the partly oriented single PTT fiber, and can be substituted with the partly oriented single PTT fiber. Therefore, it is necessary to maintain soft properties, i.e., major characteristics of PTT. Soft properties of PTT can be represented as the initial tensile resistance, which will be described in the next section. In order to maintain the soft properties, the composite ratio of PLA is preferably 50 wt% or less, more preferably 45 wt% or less, most preferably 40 wt% or less.
The initial tensile resistance of the partly oriented fiber of the present invention is from 20 to 4 0 cN/dtex. As described above, it is important that the partly oriented fiber of the present invention can be used in the same manner as the false-twisted single PTT fiber. It is necessary to have soft properties which are important characteristics of PTT. The initial tensile resistance of the partly oriented single PET fiber is about 90 cN/dtex. On the other hand, the initial tensile resistance of the partly oriented single PTT fiber is from 20 to 40 cN/dtex. When it is 40 cN/dtex or less, textiles exhibiting sufficient soft properties are produced. The initial tensile resistance can be achieved when the partly oriented single PTT fiber is used. As previously described above, there is a problem in the false twisting processability after prolonged storage, which is not preferable. In the partly

oriented core-sheath composite fiber in which PLA is used as the core component, when the composite ratio of PLA is 50 wt% or less, it is easy to make the initial tensile resistance 40 cN/dtex or less. Soft properties equal to those of the partly oriented single PTT fiber can be achieved by using PTT as the sheath component. The initial tensile resistance is preferably 34 cN/dtex or less, more preferably 32 cN/dtex or less.
The strength of the partly oriented fiber of the present invention may be set to the range with no problem when producing textiles. When the strength is 1.5 cN/dtex or more, yarn breakage does not occur easily at the time of false twisting. Thus, it is preferable. Further, when the strength is 3.1 cN/dtex or less, it is easy to obtain the elongation of the present invention. Thus, it is preferable.
The polyester fiber of the present invention is wound on a paper tube and supplied as the cheese-form package shown in Fig . 1. With reference to the shape of the cheese- form package, it is preferable that the bulge is from -5 to 5% and the saddle is from 0 to 5%. As shown in Fig. 1, the maximum diameter (Dmax) , the minimum diameter (Dmin) , the maximum width (Wmax) , and the minimum width (Wmin) of package are measured and then the saddle and the bulge are calculated by the equation below. Saddle(%) - {(Dmax-Dmin)/Dmin} x 100 Bulge(%) - {(Wmax-Wmin)/Wmin} x 100

In this regard, the saddle and the bulge need to show the shape after prolonged storage and are measured after storage in an atmosphere of 35°C and 60% RH for 90 days after winding the package.
When the saddle and the bulge are large, the unevenness of the fiber hardness in the package is caused. Particularly, when the saddle is large, the fiber is hard at the maximum diameter portion. On the other hand, the fiber becomes soft easily at the minimum diameter portion. When there is unevenness in the fiber hardness, variations in the processing tension are caused and yarn breakage is caused at the time of false twisting using it. Additionally, variations in dyeing of the obtained textured yarn are caused, and thus the uniformity of textiles is impaired and the quality is lowered. When the saddle and the bulge are within the ranges, the unevenness of the fiber in the package is suppressed and the processability is improved. Further, this results in suppressing a decrease in the quality of the surface of textiles. The bulge is more preferably in the range of -4 to 4% and the saddle is more preferably in the range of 0 to 3%.
In order to make the saddle and the bulge within the preferable ranges, generally, the package shape immediately after winding can be made good by setting the tension at the time of winding to an appropriate range. There is no problem in the partly oriented single PTT fiber immediately after

winding the package. However, the fiber deteriorates after the prolonged storage at 35°C and thus it is difficult to keep it in good condition. In the present invention, a good package after prolonged storage can be obtained by producing the partly oriented core-sheath composite fiber in which PLA is used as the core component and PTT is used as the sheath component. In this regard, when the composite ratio of PLA is from 20 to 50 wt%, a good package shape can be obtained.
Further, the delayed shrinkage of the partly oriented core-sheath composite fiber obtained from the package is preferably from 0 to 1.8%. Here, in the case where 1 m of the partly oriented fiber is obtained within 15 minutes after winding the package, the length is L3 when a load of 5.4x10-^ cN/dtex is applied to the fiber, the length is L4 when a load of 5.4x10-^ cN/dtex is applied to the fiber in an atmosphere of 25°C and 60% RH and left for 48 hours, the delayed shrinkage is calculated by the equation below. Delayed shrinkage(%) - {{L3-L4)/L3} x 100
When the delayed shrinkage is 1.8% or less, the roll firmness of the package can be easily suppressed after winding the package. Thus, it is easy to suppress the temporal change ratio in the swelling ratio. More preferably, the delayed shrinkage is 1.5% or less.
Subsequently, a preferable method for producing the partly oriented core-sheath composite fiber of the present

invention will be described.
The method includes the steps of melting FTT, melting PLA, allowing two melting polymers to join in the form of a core-sheath with a cap, discharging the joined polymer from the cap, pulling out the discharged polymer, and winding up the pulled-out fiber as a cheese-form package without drawing. This method may be the same as the method for producing the conventional partly oriented single PTT fiber. Since it is the same method, the fiber can be inexpensively produced in large quantities. Thus, it is preferable. The heat treatment process was essential for the conventional partly oriented single PTT fiber. Thus, the equipment of the partly oriented single PET fiber could not be used.
However, the heat deterioration of PTT is more severe than that of PET. Therefore, it is preferable to fuse and spin PTT at the lowest possible temperature. The temperature is preferably in the range of 235 to 250°C. On the other hand, the melting point of PLA is further lower and thus the temperature for melting and spinning is preferably in the range of 190 to 245°C. In order to suppress the heat deterioration, it is preferable that the melting time of both PTT and PLA is set to the shortest possible time. Therefore, it is preferable to melt with an extruder. As for melting and spinning, the temperatures for PTT and PLA are separately set. Most preferably, the temperatures are set to the range of 240 to 265°C

and the range of 190 to 220°C, respectively.
According to another present invention, the false-twisted fiber is the false-twisted core-sheath composite fiber in which PLA is used as the core component and PTT is used as the sheath component, where the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction is from 0 to 5%, the initial tensile resistance is form 20 to 40 cN/dtex, and the stretch recovery is from 25 to 60%.
As described above, PLA is the polymer containing 90 mol% or more of a repeating unit of - (O-CHCH3-CO) n- and it is obtained by polymerizing lactic acid and oligomer thereof, in this regard, the copolymerization component and the polyfunctional compound may be added thereto in the range of 10 mol% or less. Further, inorganic particles such as titanium dioxide may be added. However, taking into consideration the use thereof as the core component, it is most preferable not to add inorganic particles such as titanium dioxide from the viewpoint of producing a stable composite form. Lactic acid includes two optical isomers: D-lactic acid and L-lactic acid. Therefore, the polymer thereof includes poly (D-lactic acid) consisting of only D-isomer, poly (L-lactic acid) consisting of only L-isomer, and polylactic acid consisting of both of them. As the optical purity of D-lactic acid or L-lactic acid in polylactic acid becomes lower, the crystallinity decreases and

the melting point depression becomes larger. Therefore, it is preferable that the optical purity is 90% or more in order to improve the heat resistance. The optical purity is more preferably 93% or more, further preferably 97% or more. In this regard, the strong correlation between the optical purity and the melting point is shown as described above. When the optical purity is about 90%, the melting point is about 150°C. When the optical purity is 93%, the melting point is about 160°C. When the optical purity is 97%, the melting point is about 17 0°C. When, in addition to a system in which two types of optical isomers are simply mixed as described above, the two types of optical isomers are blended, which is molded into a fiber, followed by performing heat treatment at 140°C or more to form a stereo complex with racemic crystals, the melting point can be increased dramatically. Thus, it is more preferable. PLA with a weight average molecular weight of 100,000 to 300,000 can be used. The weight average molecular weight has a relationship with the thermal stability of the false-twisted fiber to be obtained. Inhibitory effects on continuous wet-heat shrinkage in the longitudinal direction to be described hereinafter are increased by using PLA with a weight average molecular weight of 200, 000 or more, which is preferable. When the weight average molecular weight is set to 300,000 or less, soft properties can be ensured. Thus, it can be said that it is preferable. When polylactic acid is used as the core

component, the shrinkage of the false-twisted fiber can be stabilized and the disadvantage of the conventional false-twisted single PTT fiber can be improved. When the core-sheath compositing process is properly performed, the stretch recovery is easily kept at a high level while the initial tensile resistance to be described hereinafter is maintained. Preferably, the composite ratio is 20 wt% or more, which allows the stability of shrinkage and stretching properties to be easily satisfied. It is preferably 30 wt% or more. When the composite ratio is 50 wt% or less, the stretch recovery is kept high and soft properties become equal to those of the false-twisted single PTT fiber. Thus, it is preferable. It is more preferably 45 wt% or less. The stretch recovery has a convex relationship with the composite ratio of PLA. When the composite ratio is from 20 to 50 wt%, high stretch recovery can be easily obtained. The false-twisted PTT fiber which satisfies all of them could not be obtained by the conventional technologies. Thus, textiles with soft properties, bulking properties, and stretching properties could not be practically obtained. Further, polylactic acid is the polymer generated from lactic acid which is produced by fermenting sugars from plants typified by corn. Since it is not made from petroleum, it is a very preferable polymer which meets with the carbon-neutral way. It is noteworthy that the polylactic acid is combined.

On the other hand, the sheath component is PTT. PTT to be used in the present invention is polyester obtained by containing terephthalic acid as a major acid component and 1,3-propanediol as a main glycol component. It is preferable that PTT contains 90 mol% or more of a repeating unit of trimethyleneterephthalate. In this regard, it may include other copolymerization components at a ratio of 10 mol% or less. If necessary, titanium dioxide as a delustering agent, silica and alumina particles as lubricants, and hindered phenol derivatives and color pigments as anti-oxidants may be added. When the limiting viscosity of PTT is from 0.8 to 1.2, it is easy to perform the false twisting process of PTT, which is preferable.
In order to obtain the false-twisted fiber of the present invention, it is most preferable to use the partly oriented fiber of the present invention. As for the partly oriented fiber of the present invention, the shrinkage as a partly oriented fiber is suppressed to low levels while soft properties are maintained and the fiber has a proper elongation. In addition, the fiber changes very little with time and thus it is easy to false-twist the fiber even after practically unavoidable storage in the stockroom. Therefore, soft properties, bulking properties, stretching properties, and shrinkage of the false-twisted fiber to be obtained can be stabilized.

The percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction is the percent coefficient of variation of wet-heat shrinkage at 100°C which is calculated by the measuring method as described below. The percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction is 5% or less. That is, this means that the shrinkage unevenness caused by change with time in a large shrinkage and a poor package form is small and the unevenness of textile due to the shrinkage unevenness, soft properties, and smooth properties are good. In the false-twisted core-sheath composite fiber in which PLA is composited as the core, the deterioration of the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction after prolonged storage which has been a problem in the conventional false-twisted single PTT fiber can be suppressed and it is highly advantageous in this respect. In this regard, the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction is preferably 4% or less, most preferably 3 .5% or less . In order to suppress the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction, the weight average molecular weight of PLA to be used as the core component is set to 200,000 or more, which is effective. Further, when the elongation of the partly oriented fiber is about 70%, the processing ratio in false twisting is set to 1.2 times,

preferably 1. 3 times or more . When the elongation is about 100%, the processing ratio is set to 1.3 times or more, preferably 1.4 times or more. When the elongation is about 120%, the processing ratio is set to 1.45 times or more, preferably 1. 5 times or more. In this case, the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction is easily suppressed. When the elongation of the partly oriented fiber to be used is 65%, the processing ratio can be maintained. Thus, it is preferable.
As for the initial tensile resistance, it is important that the false-twisted core-sheath composite fiber of the present invention can be used in the same manner as the false-twisted single PTT fiber. It is necessary to have soft properties which are important characteristics of PTT. The initial tensile resistance of the false-twisted single PET fiber is about 90 cN/dtex. On the other hand, the initial tensile resistance of the false-twisted single PTT fiber is from 20 to 40 cN/dtex. When it is 40 cN/dtex or less, sufficient soft properties can be exhibited as textiles are produced. The initial tensile resistance can be achieved when the false-twisted single PTT fiber is used. However, the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction is deteriorated after prolonged storage. Thus, it is not preferable. In the false-twisted core-sheath composite fiber in which PLA is used as the core

component, when the composite ratio of PLA is 50 wt% or less, it is easy to make the initial tensile resistance 40 cN/dtex or less. Further, PTT is used as the sheath component. This allows for the achievement of soft properties equal to those of the false-twisted single PTT fiber. The Initial tensile resistance is preferably 34 cN/dtex or less, more preferably 32 cN/dtex or less.
The stretch recovery is to evaluate the flattening of false twist crimp. As the value of the stretch recovery is higher, it has crimp opposed to the binding force when textiles are produced and bulking properties. When the stretch recovery is 25% or more, textiles excellent in bulking properties and flexibility can be obtained. When the false-twisted fiber is obtained from the partly oriented core-sheath composite fiber in which PLA is placed in the core, it is easy to obtain a fiber with high stretch recovery. This is considered to be due to the fact that polymer is easily softened by applying heat at the time of false twisting since PLA has a low melting point and crimp can be applied without impairing soft properties of PTT. When the weight average molecular weight of PLA is 200, 000 or more, the effect becomes higher. When the stretch recovery is 3 0% or more, much better textiles can be obtained. Most preferably, it is 35% or more. When the stretch recovery is 60% or less, flexible textiles can be obtained without impairing soft properties of PTT. Generally, it is known that high

stretch recovery causes crude curing of textiles. However, when the weight average molecular weight of PLA to be blended with the core is 200,000 or more, the false twisting process can be performed in the range that does not impair soft properties of PTT even if the stretch recovery is high. Thus, it is particularly preferable.
Usable examples of the method of false twisting may include known methods such as pin-type false twisting, friction-type false twisting, or belt nip-type false twisting methods and the like. For example, in the case of the friction-type false twisting method, the processing is carried out using a draw false twisting machine having a false twisting heater (a first heater) with a temperature of 100 to 160°C or preferably a contact type heater with a temperature of 100 to 150°C. Further, a so-called false twisting method with two heaters which includes a step of reducing the torque of the textured yarn which has been heat-set with the first heater using a second heater to produce yarn with low crimps and low torque may be used. In this case, the second heater may be either the contact or non-contact type. The temperature of the second heater is in the range of 100 to 150°C, preferably in the range of 100 to 140°C. The working speed is usually from 400 to 800 m/min. A urethane disk and a ceramic coated disk are suitable as a false twist tool. The processing ratio varies depending on the elongation of the partly oriented fiber to be

used. When the partly oriented fiber has an elongation of about 70%, the processing ratio is set to 1.2 times or more, preferably 1.3 times or more. When the elongation is about 100%, the processing ratio is set to 1.3 times or more, preferably 1.4 times or more. When the elongation is about 120%, the processing ratio is set to 1.45 times or more, preferably 1.5 times or more. In this case, the orientation of PLA to be combined to the core is increased. This makes easy to suppress the percent coefficient of variation of continuous shrinkage in the longitudinal direction and increase the stretch recovery. Further, the stretch recovery can be increased by setting a ratio of a circumferential speed D of the false twisting tool to a working speed Y (hereafter sometimes referred to as a D/Y ratio) to 1.4 to 1.8, preferably 1.5 to 1.8. In the false-twisted fiber of the present invention having a core-sheath structure of the combination of PLA and PTT, the maintenance performance of mechanically and thermally applied crimp is high. Since the fiber has no a so-called flattening, particularly, the stretch recovery is easily maintained.
A textile having soft properties and a good quality can be produced by forming the false-twisted core-sheath composite fiber of the present invention into a woven knitted fabric including clothing materials. Clothing materials which can suppress the shrinkage caused by heat of a dryer can be provided. Particularly, it is preferable to use the fiber as a vehicle

interior material from the viewpoint of a small change with time and durability in a severe environment in a vehicle. Since the fiber can contribute to the promotion of carbon-neutral in auto industries, it can be said that it is the best material. Examples
Hereinafter, the present invention will be specifically described with reference to Examples. In this regard, the main measured values in Examples were measured by the following methods.
(1) Limiting viscosity
The limiting viscosity (r\) is a value obtained by using orthochlorophenol as a solvent, measuring the viscosity at 30°C, and calculating by the following definitional equation. Here, C represents the concentration of solution and ŋr represents the relative viscosity (the ratio of the solution viscosity in a certain concentration C to the solvent viscosity).

(2) Weight average molecular weight
µwith Gel permeation chromatography 2690 (manufactured by Waters). In this regard, measurement conditions are as follows:
Solvent: chloroform (manufactured by Wako Pure Chemical Industries, Ltd., for HPLC)

Temperature: 40°C
Flow rate: 1 mL/min
Sample concentration: 10 mg/4 mL
Filtration: Maishori-disk 0.5 |.µ
-TOSOH
Injector: 200 ^1
Detector: differential refractometer RI (Waters 2410)
Standard: polystyrene (concentration: 0.15 mg of sample/1 mL
of solvent)
Measuring time: 40 minutes.
(3) Strength, elongation, initial tensile resistance
The measurement was performed in accordance with JIS L1013 (1999) . The strength and the elongation were measured at a grip interval of 20 cm and at a tension rate 50%/mln in accordance with JIS L1013 (1999), Section 8.5, "Tensile strength and percentage of elongation". The initial tensile resistance was measured at a grip interval of 20 cm and at a tension rate 50%/min in accordance with JIS L1013 (1999), Section 8.10. In this regard, as for measurement samples, samples which do not change with time ranging from 12 to 48 hours after collecting packages are used. In the measurement of the false-twisted fiber, the initial load was 0.088 cN/dtex.
(4) 70°C-water shrinkage
Fiber is subjected to hank-to-bobbin operation at 1 m x 10 times. The hank length is LO when a load of 29 x 10'^ cN/dtex

is applied to the hank. The hank length is LI when the hank
is treated with warm water at 70°C for 10 minutes in a state
that a load of 0.29 x 10'^ cN/dtex is applied thereto, is
air-dried for 12 to 24 hours, and then a load of 29 x 10'^ cN/dtex
is applied. The 70°C-water shrinkage is calculated by the
equation below,
70°C-water shrinkage (%) - {(L0-L1)/L0} x 100
In this regard, as for measurement samples, samples which do
not change with time ranging from 12 to 48 hours after collecting
packages are used.
(5) Saddle and bulge of package
When the partly oriented fiber is wound in each of Examples and Comparative examples, the fiber is wound on the paper tube having a diameter of 134 mm at a winding width of 114 mm to form 8 kg of package (wound diameter: about 34 0 mm) . The obtained package was left in an atmosphere of 35°C and 60% RH for 90 days and then the shape of package was measured. As shown in Fig. 1, the maximum diameter (Dmax), the minimum diameter (Dmin), the maximum width (Wmax), and the minimum width (Wmin) of package were measured and then the saddle and the bulge were calculated by the equation below. The resulting value was rounded to the whole number. Saddle(%) - {(Dmax-Dmin)/Dmin} x 100 Bulge(%) - {{Wmax-Wmin)/Wmin} x 100

(6) Delayed shrinkage
1 m of the partly oriented fiber is obtained within 15 minutes after winding the package. The length is L3 when a load of 5.4 X 10'^ cN/dtex is applied to the fiber. The length is L4 when a load of 5.4 x 10'^ cN/dtex is applied to the fiber in an atmosphere of 25°C and 6 0% RH and left for 4 8 hours. The delayed shrinkage was calculated by the equation below. The resulting value was rounded to the second decimal place, which was the first decimal place. Delayed shrinkage(%) - {(L3-L4)/L3} x 100.
(7) Full package ratio of the false-twisted fiber
The friction-type false twisting method based on the urethane disk (in-draw false twist, working speed: 400 m/min, the draw ratio was adjusted so that the elongation of the false-twisted fiber was 40%, the temperature of the first heater: 145°C, the temperature of the second heater: 130°C) was performed by using 8 kg of package of the partly oriented core-sheath composite fiber. Four pieces of a 2 kg spool of false-twisted fibers were collected. One hundred pieces of partly oriented core-sheath composite fibers were divided into 400 pieces of false-twisted fibers, followed by false twisting. The percentage of the 2 kg spool of false-twisted fibers collected in 400 pieces of false-twisted fibers without yarn

breakage was calculated. The resulting value was rounded to the whole number. In this regard, the partly oriented core-sheath composite fiber after storage in an atmosphere of 35°C and 60% RH for 90 days was used.
(8) Knitting test of the false-twisted fiber
A 28 gauge-circular knitting fabric was produced by using 4 pieces of false-twisted fibers collected from the partly oriented core-sheath composite fibers of arbitrary packages among the false-twisted fibers obtained in (7) . In the dyeing method, the fabric was dyed at a bath ratio of 1:100 at 50°C for 15 minutes using 0.275% owf of Tetracil Navy Blue SGL as dye, 5.0% owf of Tetrocine PE-C (manufactured by Seiken Inc.) as an auxiliary agent, and 1.0% owf of Niccasan Salt #1200 (manufactured by NICCA CHEMICAL CO., LTD.) as a dispersant and further dyed at 90°C for 2 0 minutes. The uneven dyeing and the dyeing difference between lines of thread as to the dyed samples were comprehensively evaluated. Three evaluators who had 3 years or more of experience took counsel whether or not to ship them as a product and graded them on a scale of one to three. The acceptable level is indicated by triangle and circular marks.
Circular mark: Very uniform and excellent quality. Triangle mark: Stable quality and suitable for shipping. Cross mark: Significant disadvantage and unsuitable for

shipping.
(9) Soft properties
A sensory test of touching the 28 gauge-circular knitting fabric obtained in (8) was performed. Three evaluators who had 3 years or more of experience took counsel and graded it on a scale of one to two. The acceptable level is indicated by a circular mark.
Circular mark: Very excellent. Cross mark: Hard.
(10) Overall evaluation of the partly oriented fiber
Evaluations (7), (8), and (9) were performed and the overall evaluation was performed. The acceptable level of the full package ratio of the false-twisted fiber is 95% or more. The acceptable level of the knitting test of the false-twisted fiber is indicated by triangle and circular marks. The acceptable level of soft properties is indicated by the circular mark. The standard with acceptable levels in all of the Evaluations is succeeded in the overall evaluation and indicated by the circular mark. The standard with at least one unacceptable level in the three Evaluations is not succeeded in the overall evaluation and indicated by a cross mark.
(11) Percent coefficient of variation of continuous wet-heat

shrinkage in the longitudinal direction
The false-twisted fiber was subjected to wet heat treatment under conditions (yarn feeding rate: 10 m/min, measured yarn length: 30 m, yarn feeding tension: 20 gf, wet heat temperature: 100°C) by using FTA-500 (manufactured by Toray Engineering Co. , Ltd.) and the wet heat shrinkage at 100°C was continuously measured. The percent coefficient of variation thereof was calculated. The resulting value was rounded to the second decimal place and calculated to the first decimal place.
(12) Stretch recovery
The false-twisted fiber is subjected to hank-to-bobbin operation at 1 m x 10 times, left in a no-load state for 15 minutes, treated in boiling water at 100°C, and then air-dried for 24 . hours. A load of 0.00176 cN/dtex and a load of 0.0882 cN/dtex were applied to the heat-treated sample in water in accordance with JIS L1013 (1999), Section 8.13, "Stretch recovery". Two minutes later, the hank length LO was measured. Then, the load of 0.0882 cN/dtex was removed and only the load of 0.00176 cN/dtex was applied to the sample in water. Two minutes later, the hank length LI was measured. The stretch recovery was calculated by the equation below. The resulting value was rounded to the whole number. (Stretch recovery) - (L0-L1)/L0 x 100 (%)

(13) Stretch properties
The 28 gauge-circular knitting fabric was produced in the same manner as described in (8) Knitting test of the false-twisted fiber and the sensory test of stretch properties thereof was carried out. Three evaluators who had 3 years or more of experience took counsel and graded them on a scale of one to three. The acceptable level is the triangle mark or more. Circular mark: Uniform, excellent stretch properties, and good restoring properties were observed.
Triangle mark: Uniform stretch properties were observed, a mesh opening of knitting fabric remained a little, but it was in a satisfactory range from a practical standpoint. Cross mark: Poor stretch properties were observed and a drawn mark was left.
(14) Overall evaluation of the false-twisted fiber
In addition to (8) Knitting test of the false-twisted fiber and (9) Soft properties, (13) Stretch properties were evaluated. The standard with acceptable levels in all of the Evaluations is succeeded in the overall evaluation and indicated by the circular mark. The standard with at least one unacceptable level in the Evaluations is not succeeded in the overall evaluation and indicated by the cross mark.

Example 1
PLA (poly-L-lactic acid) having an optical purity of 98 . 0% and a weight average molecular weight of 214, 000 was used as the core component and Homo PTT having a limiting viscosity of 1.1 was used as the sheath component. PLA and PTT were melted by using the extruder at 190°C and 250°C, respectively. The resulting products were measured with a pump so that the composite ratio of PLA was 30 wt% and the composite ratio of PTT was 70 wt%. Thereafter, the core-sheath compositing process was performed with the cap, followed by discharging at 240°C. The discharged polymer was made into partly oriented fiber with a spinning machine shown in Fig. 2. The fiber was pulled by a first roller 4 at a speed of 2700 m/min and wound at a speed of 2650 m/min after passing through a second roller 5 to form a cheese-form package 7. In this regard, the first roller 4 and the second roller 5 are not a heating roller and they are at ordinary temperature.
The obtained partly oriented core-sheath composite fiber exhibited good physical properties: elongation: 120%, 70°C-water shrinkage: 1.8%, initial tensile resistance: 29 cN/dtex. The delayed shrinkage was 0 . 6% . The obtained package was stored in an atmosphere of 35°C and 60% RH for 90 days. Thereafter, the bulge and the saddle were measured and the results were good. The full package ratio of the false-twisted fiber was 97%, which was satisfactory. The knitting test and

soft properties were also good. It was a very excellent package. The results are shown in Table 1.
Examples 2 to 4
The partly oriented core-sheath composite fibers were obtained in the same manner as described in Example 1 except that the composite ratio of PLA and the composite ratio of PTT were changed to those as shown in Table 1. As shown in Table 1, excellent results were obtained. Particularly, in Example 4, all evaluation criteria were well-balanced. Good results which were the same or more than those of Example 1 were obtained.
Example 5
The partly oriented core-sheath composite fiber was obtained in the same manner as described in Example 2 except that the weight average molecular weight of PLA was 165,000. Since the molecular weight of PLA was low, the 70°C-water shrinkage was slightly high. Therefore, although the package form and the knitting test of false-twisted fiber fall short of those of Example 2, good results were obtained.
Comparative examples 1 and 2
The partly oriented core-sheath composite fibers were obtained in the same manner as described in Example 1 except that the composite ratio of PLA and the composite ratio of PTT

were changed to those as shown in Table 1. In Comparative example 1 where the composite ratio of PLA was 10%, the suppression of 70°C-water shrinkage was insufficient and the bulge was also bad, which resulted in inferior processability. In Comparative example 2 where the composite ratio of PLA was 60 wt%, the initial tensile resistance was increased to 48 cN/dtex and only knitting fabrics inferior in soft properties could be obtained.
Comparative example 3
The partly oriented core-sheath composite fiber was obtained in the same manner as described in Comparative example 2 except that the weight average molecular weight of PLA was 165,000. The initial tensile resistance was high, which resulted in inferior soft properties.
Comparative example 4
Homo PTT having a limiting viscosity of 1.1 was used and melted by using the extruder at 250°C. After the measurement with the pump, the core-sheath compositing process was performed with the cap, followed by discharging at 240°C. The discharged polymer was made into partly oriented fiber with the spinning machine shown in Fig. 2. The fiber was pulled by the first roller 4 at a speed of 2700 m/min and wound at a speed of 2650 m/min after passing through the second roller 5 at the

same speed to form the cheese-form package 7. In this regard, the first roller 4 and the second roller 5 are not a heating roller and they are at ordinary temperature. In the obtained partly oriented fiber, the 70°C-water shrinkage was increased to 46%. The bulge, the saddle, and the delayed shrinkage were poor. The full package ratio in false twisting was 65% and the knitting test was also bad, and thus good results were not obtained.
Comparative example 5
Homo PTT having a limiting viscosity of 1.1 was used and melted by using the extruder at 250°C. After the measurement with the pump, the core-sheath compositing process was performed with the cap, followed by discharging at 240°C. The discharged polymer was made into partly oriented fiber with the spinning machine shown in Fig. 3 . A first heating roller 8 was set to 80°C. The fiber was pulled at a speed of 2700 m/min and wound at a speed of 2650 m/min after passing through a second heating roller 9 set to 120°C at the same speed to form the cheese-form package 7 . In the obtained partly oriented fiber, the 7 0°C-water shrinkage was 2.8%, which was good shrinkage. The saddle and bulge of the package immediately after winding were good. However, the package was deteriorated after storage for 90 days and the full package ratio in false twisting was 88%. The results were insufficient. As a further comparison,

when the partly oriented fiber of Comparative example 5 was not stored and false-twisted five days after collecting the package, the full package ratio in false twisting was 96%. The results of Comparative example 5 show that the false twisting processability is reduced by prolonged storage.

Examples 6 to 8, Comparative examples 6 to 8
The partly oriented core-sheath composite fibers were obtained under the same conditions as those of Example 1 except that the speed of the first roller 4 and the second roller 5 and the winding-up speed in Fig. 2 were changed to those shown in Table 1. In Examples 6 to 8, where the elongation, the 70°C-water shrinkage, the initial tensile resistance, the saddle and the bulge of the package in the present invention were used, good false twisting processability and good knitting fabric could be obtained. In Comparative example 6 where the elongation was 143% and Comparative example 7 where the elongation was 133%, it is considered that there are many non-oriented amorphous portions. Therefore, the full package ratio of the false twisted textured yarn after storage for 90 days was insufficient. In Comparative example 8 where the elongation was set to 52%, the 70°C-water shrinkage could not be suppressed. Thus, the bulge of the package after storage for 90 days was deteriorated and the processability was very poor.
Comparative example 9
Homo PET having a limiting viscosity of 0.5 was used as the core component and Homo PTT having a limiting viscosity of 1.1 was used as the sheath component. PET and PTT were melted by using the extruder at 290°C and 250°C, respectively. The

resulting products were measured with a pump so that the composite ratio of PET was 30 wt% and the composite ratio of PTT was 70 wt%, Thereafter, the core-sheath compositing process was performed with the cap, followed by discharging at 270°C. The discharged polymer was made into partly oriented fiber with the spinning machine shown in Fig. 3. The first heating roller 8 was set to 100°C. The fiber was pulled at a speed of 3000 m/min and wound at a speed of 2960 m/min after passing through the second heating roller 9 that was unheated at the same speed to form the cheese-form package 7. The obtained partly oriented core-sheath composite fiber exhibited good physical properties (elongation: 125%, 70°C-water shrinkage: 3.8%, initial tensile resistance: 34 cN/dtex). The saddle and the bulge of the package immediately after winding were good. However, the package was deteriorated after storage for 90 days. The full package ratio in false twisting was 93%, which was insufficient. The result of the knitting test was rejected and thus a satisfactory false-twisted fiber was not obtained.
Comparative example 10
Homo PET having a limiting viscosity of 0.5 was used as the core component and Homo PTT having a limiting viscosity of 1.1 was used as the sheath component. PET and PTT were melted by using the extruder at 290°C and 250°C, respectively. The

resulting products were measured with a pump so that the composite ratio of PET was 30 wt% and the composite ratio of PTT was 70 wt%. Thereafter, the core-sheath compositing process was performed with the cap, followed by discharging at 270°C. The discharged polymer was made into partly oriented fiber with the spinning machine shown in Fig. 3. The first heating roller 8 was set to 55°C. The fiber was pulled at a speed of 1600 m/min and wound at a speed of 3700 m/min after drawing to the second heating roller 9 set to 150°C and 3800 m/min to form the cheese-form package 7. Since the obtained core-sheath composite fiber was drawn, the elongation was 58%. The 70°C-water shrinkage, the initial tensile resistance, the saddle, and the bulge were also good. However, sufficient soft properties could not be obtained.

Example 9
The partly oriented fiber obtained in Example 1 was stored in an atmosphere of 35°C and 60% RH for 90 days. Thereafter, the friction-type false twisting method based on the urethane disk (in-draw false twist) was performed. In this regard, the false twisting was performed under conditions (working speed: 400 m/min, processing ratio: 1.6 times, D/Y ratio: 1.5, temperature of the first heater: 145°C, temperature of the second heater: 130°C) and a 84 dtex-36 filament false-twisted fiber was obtained. The percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction was 3.4%, the initial tensile resistance was 28 cN/dtex, and the stretch recovery was 3 5%. As shown in Table 3, a textile excellent in the knitting test, soft properties, and stretch properties were obtained.
Examples 10 to 12
The false twisting process was performed under the same conditions as those of Example 9 except that the partly oriented fiber of Example 4 was used as Example 10, the partly oriented fiber of Example 3 was used as Example 11, and the partly oriented fiber of Example 2 was used as Example 12 in order to observe effects on the composite ratio of PTT to PLA and they were respectively used after storage in an atmosphere of 35°C and 60% RH for 90 days. Then, the false-twisted fibers were

obtained. All of the obtained textiles were good. Particularly, in Example 11, the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction was suppressed so as to be lower. Thus, the stretch recovery and the initial tensile resistance were sufficient and the most well-balanced textile was produced.
Example 13
The false twisting process was performed under the same conditions as those of Examplel2 except that the partly oriented fiber of Example 5 was used after storage in an atmosphere of 35°C and 60% RH for 90 days and the false-twisted fiber was obtained. Since the weight average molecular weight of PLA was low, the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction was relatively high. Although the results of the knitting test and stretch properties were inferior to those of Example 12, a good textile could be obtained.
Comparative example 11
The. false twisting process was performed under the same conditions as those of Example 9 except that the partly oriented fiber of Comparative example 1 was used after storage in an atmosphere of 35°C and 60% RH for 90 days and the false-twisted fiber was obtained. Since the composite ratio of PLA was low,

the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction could not be suppressed. Further, the stretch recovery and stretch properties were insufficient, and thus a good textile could not be obtained.
Comparative example 12
The composite ratio of PTT to PLA was set to 45:55 and the partly oriented fiber was obtained in the same manner as described in Example 1. The obtained partly oriented fiber was stored in an atmosphere of 35°C and 60% RH for 90 days. Thereafter, the false twisting process was performed under the same conditions as those of Example 1 and the false-twisted fiber was obtained. It was expected that the initial tensile resistance would be increased because of a high composite ratio of PLA and the stretch recovery would be increased because of the increased composite ratio of PLA. However, the values were not high. This is considered to be due to the fact that the balance of the composite ratio was lowered by the decreased composite ratio of PTT. The obtained textile was inferior in soft properties.

Examples 14 and 15, Comparative example 13
The partly oriented fiber of Example 4 was stored in an atmosphere of 35°C and 60% RH for 90 days, followed by false twisting at the processing ratio described in Table 4. The false twisting was performed under the same conditions as those of Example 10 except for the processing ratio. The percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction and the stretch recovery were varied by the change of the processing ratio. However, good textiles were obtained in Examples 14 and 15 which were within the specified range of the present invention. On the other hand, the percent coefficient of variation of continuous wet-heat shrinkage in the longitudinal direction was increased to 5.3% in Comparative example 13 and thus the texture was rejected in the knitting test. Additionally, it was rejected in the evaluation of soft-properties since shrinkage unevenness of textile was large and it had rough feeling despite a low initial tensile resistance.
Examples 16 and 17, Comparative example 14
The partly oriented fiber of Example 4 was stored in an atmosphere of 35°C and 60% RH for 90 days, followed by false twisting at the D/Y ratio described in Table 4. The false twisting was performed under the same conditions as those of Example 10 except for the D/Y ratio. The percent coefficient

of variation of continuous wet-heat shrinkage in the longitudinal direction and the stretch recovery were varied by the change of the D/Y ratio. However, good textiles were obtained in Examples 16 and 17 which were within the specified range of the present invention. On the other hand, in Comparative example 14, the stretch recovery was 23%, which is insufficient. Therefore, only textile inferior in stretch properties could be obtained..

INDUSTRIAL APPLICABILITY
The present invention can be provided the partly oriented fiber which changes little in package shape even after practically necessary long-term storage in the stockroom, is excellent in false twisting properties, further has stability in dyeing and soft feeling, and is suitable for mass production, the cheese-form package, and the false-twisted fiber from which textiles excellent in bulking properties, stretching properties, and soft properties with stable quality can be produced. Suitable applications of the present invention include common clothing materials and materials typified by vehicle interior materials. Particularly, long-term transportation becomes easier, which makes global operations possible.

CLAIMS

1. A partly oriented core-sheath polyester composite
fiber comprising:
polylactic acid as a core component; and polytrimethylene terephthalate as a sheath component; wherein the following requirements (1) to (3) are satisfied:

(1) Elongation: 60 to 130%;

(2) 70°C-water shrinkage: 0.5 to 7.0%; and

(3) Initial tensile resistance: 20 to 40 cN/dtex.

2. The partly oriented core-sheath polyester composite fiber according to claim 1, wherein the weight average molecular weight of polylactic acid is in the range of 200, 000 to 300, 000.

3. The partly oriented core-sheath polyester composite fiber according to claim 1 or 2, wherein the composite ratio of polylactic acid is from 20 to 50 wt%.

4. A cheese-form package formed by winding the partly oriented core-sheath polyester composite fiber according to any of claims 1 to 3, wherein the bulge of the cheese-form package and the saddle of the cheese-form package when measured after storage in an atmosphere of 35°C and 60% RH for 90 days after

winding the package satisfy the followings (4) to (5):

(4) Bulge of the cheese-form package: -5 to 5%; and

(5) Saddle of the cheese-form package: 0 to 5%.

5. A false-twisted core-sheath polyester composite fiber comprising:
polylactic acid as a core component; and
polytrimethylene terephthalate as a sheath component;
wherein the following requirements (6) to (8) are satisfied:
(6) Percent coefficient of variation of continuous
wet-heat shrinkage in the longitudinal direction: 0 to 5%;
(7) Initial tensile resistance: 20 to 40 cN/dtex; and
(8) Stretch recovery: 25 to 60%.