JP2004124351A - Method for production of latent crimpable polyester conjugated short fibers, and fiber assembly, and nonwoven fabric - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide latent crimpable polyester conjugated fibers excellent in crimpability in heat processing, high-speed carding property in production of nonwoven fabric and high-speed productivity in heat processing property or the like. <P>SOLUTION: The latent crimpable polyester conjugated fibers are obtained by conjugating and spinning a first component and a second component, and comprises the first component with 120-145°C melting point Tf<SB>1</SB>after spinning and comprises α-olefin-propylene copolymer with ≥ 95 mass.% of propylene content and the second component with a thermoplastic resin which has of a melting point Tf<SB>2</SB>≥15°C higher than that of Tf<SB>1</SB>, and at least one in the total percentage of crimp and ratio of the incidental percentage of crimp to the total percentage of crimp is less than 15%, and the temperature exhibiting maximum peak of the heat crimping force is less than 145°C and has ≥75% of dry heating percentage of crimp of the monofilament. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a latently crimpable conjugate short fiber having excellent crimp development during thermal processing. More specifically, the present invention relates to high-speed cardability and thermal processability when producing a nonwoven fabric at a speed of 90 m / min or more. And a latently crimpable conjugate short fiber having excellent high-speed productivity. The present invention also relates to a fiber aggregate using the latently crimpable conjugate short fiber and having excellent shrinkage or stretchability.

Hitherto, as a latently crimpable conjugate fiber used for producing a stretchable nonwoven fabric, for example, in JP-A-2-191720 (Patent Document 1), a Q value is less than 5 and a melt flow rate is 15 or less. ~ 200g / 10min polypropylene as the first component, ethylene-propylene with a melting point of 133 ~ 145 ° C as the second component, parallel type or eccentric core-sheath type with the first component as the core and the second component as the sheath Arranged composite fibers have been proposed. In JP-A-3-167314 (Patent Document 2), a crystalline polypropylene is used as a high melting point component, a copolymer containing polypropylene as a main component and having a melting point of 125 ° C. or more is used as a low melting point component, and the spinning temperature is made relatively high. By making the spinning speed as low as possible, making the stretching temperature relatively high, and making the stretching ratio relatively low, the true heat shrinkage at 120 ° C. is 25% or less, and the apparent heat shrinkage is Stretch conjugate fibers that are 55% or more have been proposed. Further, in JP-A-6-184823 (Patent Document 3), the core component is made of crystalline polypropylene, the sheath component is made of a propylene copolymer having a melting point of 125 ° C. or more, and the total crimp ratio is 18 to 66%. We have proposed an eccentric sheath-core composite fiber with natural crimp. Further, JP-A-5-71057 (Patent Document 4) and JP-A-5-78916 (Patent Document 5) disclose an ethylene-propylene random copolymer having an ethylene content of 3 to 8% by weight and an ethylene-propylene random copolymer. An ethylene-propylene random copolymer having an amount of 0 to 3% by weight, a melt flow rate of 15 to 45 g / 10 min, a dry heat shrinkage of 35% or more at a temperature of 120 ° C. and an initial load of 2 mg, A polypropylene-based composite short fiber having a number of crimps at 120 ° C. of 60/25 mm or more has been proposed. In Japanese Patent Application Laid-Open No. 2001-32139 (Patent Document 6), an eccentric sheath-core conjugate fiber containing polypropylene having a melting point of 160 ° C. or more as a sheath component and a propylene copolymer having a melting point of 120 to 147 ° C. as a core component is disclosed. Proposed.

On the other hand, as a composite fiber in which an ethylene-propylene copolymer polymerized using a metallocene catalyst is exposed on at least a part of the fiber surface, for example, JP-A-10-219521 (Patent Document 7) and JP-A-10- Japanese Patent Application Laid-Open No. 298824 (Patent Document 8) and Japanese Patent Application Laid-Open No. 2001-254256 (Patent Document 9) have been proposed.

JP-A-2-191720 JP-A-3-167314 JP-A-6-184823 JP-A-5-71057 JP-A-5-78916 JP 2001-32139 A JP-A-10-219521 JP-A-10-298824 JP 2001-254256 A

However, the above-mentioned conjugate fiber has the following problems. For example, latent crimps proposed in JP-A-2-191720, JP-A-3-167314, JP-A-5-71057, JP-A-5-78916, and JP-A-6-184823. With regard to the composite conjugate fiber, an attempt has been made to heat-treat the fibrous web at a low temperature of 120 to 140 ° C. and to develop a highly crimp to obtain a stretchable nonwoven fabric excellent in elongation recovery. However, in general, when the stretching ratio at the time of fiber production is increased, the shrinkage force (stretching force) of the nonwoven fabric tends to be improved, but three-dimensional crimping occurs at the fiber production stage (raw cotton stage), and the crimping ratio is increased. But the crimp becomes tight (crisp). When a nonwoven fabric is manufactured using such fibers, poor opening, winding around a cylinder, and formation unevenness (cloudy) occur in the carding process. These problems become significant when the card speed is 50 m / min or more. On the other hand, when importance is placed on cardability, the draw ratio at the time of fiber production is suppressed (that is, lowered), and adjustment is performed so that three-dimensional crimping does not occur. However, in such a case, the shrinking force (stretching force) becomes insufficient, or the shrinking speed is slow, and sufficient shrinkage (stretching) performance cannot be obtained by heat treatment in a short time, and the heat treatment zone becomes large. May be forced and inefficient. Japanese Patent Application Laid-Open No. 2001-32139 discloses an attempt to improve cardability by using a polypropylene having a melting point of 160 ° C. or higher as a sheath component and a propylene copolymer having a high metal friction resistance as a core component. The degree of freedom of the propylene copolymer is low, and the shrinkage may be insufficient.

On the other hand, various fibers have been proposed as conjugate fibers in which an ethylene-propylene copolymer polymerized using a metallocene catalyst is exposed on at least a part of the fiber surface. However, studies on latently crimpable conjugate short fibers having excellent crimp development during thermal processing have not been sufficiently made. Therefore, the fact is that latently crimpable conjugate short fibers which are excellent in crimp development and high-speed productivity have not been obtained.

The present invention has been made in view of the above problems, and has excellent crimp development during thermal processing, and particularly when producing a nonwoven fabric at a speed of 90 m / min or more, such as high-speed carding and thermal processing. An object of the present invention is to provide a latently crimpable conjugate short fiber having excellent productivity. Another object of the present invention is to provide a fiber aggregate and a nonwoven fabric which are excellent in elasticity or shrinkage and have a good texture by using latently crimpable conjugate short fibers.

The present inventors have developed a crimped conjugate short fiber composed of a first component containing an α-olefin-propylene copolymer and a second component containing a thermoplastic resin having a melting point T ₂ of 15 ° C. or more higher than T _1. It is necessary to adjust the total crimp rate and / or the ratio of the natural crimp rate to the total crimp rate, the temperature at which the heat shrinkage stress exhibits the maximum peak, and the single fiber dry heat shrinkage rate to a desired range, and By adjusting the heat shrinkage stress and / or the elongation of a single fiber to a desired range according to the above, or by using a specific α-olefin-propylene copolymer, it is excellent in crimp development and high-speed productivity. The present inventors have found that latently crimpable conjugate short fibers can be obtained, and have reached the present invention.

That is, the first aspect of the latently crimpable conjugate short fiber of the present invention is that the first component and the second component are conjugate spun, and the melting point Tf ₁ after spinning is in the range of 120 ° C. or more and 145 ° C. or less. And a second component containing a thermoplastic resin having a melting point Tf ₂ higher than Tf ₁ by 15 ° C. or more after spinning, and a first component containing an α-olefin-propylene copolymer having a propylene content of 95 mass% or more. The composite staple fiber having a crimp comprising the components, wherein at least one of the total crimp rate and the ratio of the natural crimp rate to the total crimp rate is 15% or less, and the following (1) and ( It is characterized by satisfying the physical property value of 2).
(1) In the heat shrinkage stress measurement, a maximum peak is shown at a temperature lower than 145 ° C.
(2) According to JIS-L-1015 (dry heat shrinkage), the single fiber dry heat shrinkage at an initial load of 0.018 mN / dtex (2 mg / d) at a temperature of 120 ° C. for 15 minutes is 75% or more. .

The second invention in the latently crimpable conjugate short fiber of the present invention are within the melting point _{T 1} is a 140 ° C. or less 115 ° C. or higher, the propylene content is accounted for more than 95mass%, JIS-K-7210 (Condition: 230 ° C, load: 21.18 N (2.16 kg)) Melt flow rate is in the range of 10 g / 10 min or more and 60 g / 10 min or less, and is determined from a DSC curve measured according to JIS-K-7121. When the total heat of fusion of the α-olefin-propylene copolymer is ΔHm, the α-olefin-propylene copolymer has a temperature of 125 ° C. or less when the heat of fusion calculated from the low temperature side becomes 50% of ΔHm. a first component, an eccentric sheath-core type cross-melting T ₂ is obtained by conjugate spinning and a second component comprising 15 ℃ or higher thermoplastic resin than T ₁ or crimpable multiple having parallel section, A short fibers, of the proportion of natural crimp ratio to the total percentage of crimp and the total crimp ratio, wherein at least 15% or less.

The third invention in the latently crimpable conjugate short fiber of the present invention, the first component and the second component is made is conjugate spinning, the melting point Tf ₁ after spinning is within the range of 120 ° C. or higher 145 ° C. or less A first component containing an α-olefin-propylene copolymer having a propylene content of 95 mass% or more, and a second component containing a thermoplastic resin having a melting point Tf ₂ after spinning of 15 ° C. or more higher than Tf _1. And a crimped conjugate short fiber comprising a web having a basis weight of 30 g / m ² formed from the conjugate short fiber and heat-treated at 120 ° C. for 4 seconds to have a web area shrinkage of 85% or more. It is characterized by the following.

Latently crimpable conjugate short fiber of the present invention, the melting point _{T 1} is in the range of less than 140 ° C. 115 ° C. or higher, the propylene content is accounted for more than 95mass%, JIS-K-7210 ( condition: 230 ° C. Α-olefin-propylene having a melt flow rate at a load of 21.18 N (2.16 kg) within a range of 10 g / 10 min to 50 g / 10 min and obtained from a DSC curve measured according to JIS-K-7121. Assuming that the total heat of fusion of the copolymer is ΔHm, the first component is a resin containing an α-olefin-propylene copolymer having a temperature of 125 ° C. or less when the heat of fusion calculated from the low temperature side becomes 50% of ΔHm. and then, a resin having a melting point T ₂ comprises a high thermoplastic resin 15 ℃ or higher than T ₁ as the second component, the spun filaments were conjugated spinning so that Henshinsaya-core or side-by-side cross-section Stretching at a temperature within the range of 30 ° C. or more and 90 ° C. or less by a factor of 2 or more; imparting mechanical crimping within a range of 11 crimps / 25 mm or more and 18 crimps / 25 mm or less; It can be manufactured by a manufacturing method including performing an annealing treatment at a temperature in the range of not less than 80 ° C. and not more than 80 ° C.

The fiber aggregate of the present invention contains the latently-crimpable conjugate short fiber or the latently-crimpable conjugate short fiber obtained by the production method in an amount of 20 mass% or more. Characterized by the expression of By expressing latent crimp, a fiber aggregate having excellent stretchability or shrinkage and good texture can be obtained.

The nonwoven fabric of the present invention contains at least 20% by mass of the latently crimpable conjugate short fibers or the latently crimpable conjugate short fibers obtained by the production method, and the latently crimpable conjugate short fibers exhibit crimp. And is substantially not thermally fused. Here, the term "substantially" is used in view of the fact that when heated for the development of latent crimping, in practice, a small amount of some fibers are heat-sealed. In the latently crimpable conjugate short fibers of the present invention, the temperature at which latently crimps are developed is lower than its melting point by 5 ° C. or more. Therefore, when a web is produced using these fibers and is shrunk, the web can be shrunk at a high area shrinkage ratio without substantially thermally fusing the fibers to obtain a nonwoven fabric. Therefore, this nonwoven fabric has a high elasticity and a soft texture.

In the latently crimpable conjugate short fiber of the present invention, the first component is a component containing an α-olefin-propylene copolymer, and the total crimp rate and / or the ratio of the natural crimp rate to the total crimp rate, By adjusting the temperature at which the shrinkage stress reaches the maximum peak and the dry heat shrinkage of the single fiber to the desired ranges, excellent three-dimensional crimp development and excellent high-speed productivity can be obtained.

Further, the latently crimpable conjugate short fiber of the present invention has a high crimp at a low temperature despite the low heat shrinkage stress by using a specific α-olefin-propylene copolymer polymerized by a metallocene catalyst. Is expressed. Thereby, it is possible to easily obtain a crimped state represented by the total crimp rate and the ratio of the natural crimp rate to the total crimp rate, which is optimal for realizing high-speed cardability.

The fiber aggregate using the latently crimpable conjugate short fibers, when subjected to heat treatment, exhibits a high degree of contraction due to high shrinkage, and also exhibits a good texture, so that sanitary materials such as diapers, cataplasms It is suitable for medical (use) materials such as wraps and bandages, wet tissues, wipers, cushioning materials, packaging materials, sponge-like nonwoven fabric materials, and the like.

In the latently crimpable conjugate short fiber of the present invention, the first component is an α-olefin having a melting point Tf ₁ after spinning in the range of 120 ° C. or more and 145 ° C. or less and a propylene content of 95 mass% or more. It is a component containing a propylene copolymer (hereinafter, referred to as a propylene copolymer). The melting point after spinning here is determined from the melting peak of the latently crimpable conjugate short fiber obtained according to JIS-K-7121 (DSC method). The lower limit of the melting point Tf ₁ after spinning preferred propylene copolymer is 125 ° C.. The upper limit of the melting point Tf ₁ after spinning preferred propylene copolymer is 140 ° C.. When the melting point Tf ₁ after spinning propylene copolymer is conjugate spinning selects the first component such that less than 120 ° C., there is a fear that spinning becomes poor. On the other hand, the resin such as the melting point Tf ₁ after spinning propylene copolymer exceeds 145 ° C. When the composite-spinning to select as the first component, there is a fear that adhesion yarn occurs.

好 ま し い The lower limit of the preferable propylene content in the propylene copolymer is 96 mass%. The preferred upper limit of the propylene content is 98 mass%. If the propylene content is less than 95% by mass, the rubbery elasticity of the propylene copolymer tends to increase, and the high-speed cardability may be reduced.

Examples of the α-olefin monomer constituting the propylene copolymer include ethylene, butene-1, and the like. Among them, ethylene-propylene copolymer, butene-propylene copolymer and ethylene-propylene-butene terpolymer It is preferable to use at least one member selected from the group, since desired shrinkability can be easily obtained. The content of ethylene and / or butene in the propylene copolymer is preferably 5 mass% or less. A more preferred content of ethylene and / or butene is in the range of 2 mass% to 4 mass%. If the content of ethylene and / or butene is too small, sufficient shrinkage may not be obtained after processing into a fiber aggregate, and if the content of ethylene and / or butene exceeds 5 mass%, high-speed cardability may be obtained. Not only is it inferior, but sometimes the texture of the fiber aggregate becomes sticky.

The propylene copolymer of the first component, the resin melting point T ₁ is preferably used to be within the scope of 115 ° C. or higher 140 ° C. or less. With such a resin, the melting point Tf ₁ of the first component when the composite short fibers may be 120 ° C. or higher 145 ° C. or less. The lower limit of the melting point T ₁ of the preferred propylene copolymer is 120 ° C.. The upper limit of the melting point T ₁ of the preferred propylene copolymer is 135 ° C.. If the melting point T ₁ of the propylene copolymer is lower than 115 ° C., spinnability may be deteriorated. If the melting point T ₁ of the propylene copolymer exceeds 140 ° C., cohesive yarn may be generated.

The propylene copolymer has a melt flow rate (hereinafter, referred to as MFR) according to JIS-K-7210 (condition: 230 ° C., load: 21.18 N (2.16 kg)) of 10 g / 10 min to 60 g / 10 min. It is preferably within the range. A more preferred lower limit of the MFR is 20 g / 10 min. A more preferred upper limit of the MFR is 50 g / 10 min. When the MFR of the propylene copolymer is less than 10 g / 10 min, the resin itself is hard and may cause thread breakage. When the MFR exceeds 60 g / 10 min, the resin itself may be soft and a cohesive yarn may be generated. .

When the total heat of fusion of the propylene copolymer in the propylene copolymer determined by a DSC curve according to JIS-K-7121 is ΔHm, the temperature at which the heat of fusion calculated from the low temperature side becomes 50% of ΔHm is: , 125 ° C. or lower. A more preferable temperature at which the heat of fusion becomes 50% of ΔHm is 120 ° C. or less. A preferred lower limit of the temperature at which the heat of fusion becomes 50% of ΔHm is 110 ° C. Here, the temperature at which the heat of fusion becomes 50% of ΔHm is determined by drawing a straight line perpendicular to the temperature axis so that the integral area of the DSC curve becomes 50%. Refers to the temperature at the intersection. The temperature at which the amount of heat of fusion becomes 50% of ΔHm is an index indicating the shrinkage behavior accompanying the melting of the resin. When the amount of heat of fusion increases as the temperature rises and reaches about 50% of ΔHm, It is an index defined assuming that it exhibits a sufficient shrinkage force to express latent crimps to a high degree. When using a propylene copolymer having a temperature of 125 ° C. or less when the heat of fusion becomes 50% of ΔHm, a fiber web or the like containing latently crimpable conjugate short fibers is heat-treated to develop latent crimp. Not only is the thermal processing property at a low temperature improved, but the thermal processing speed can be increased with an increase in the thermal processing temperature, and the high-speed productivity is improved, which is preferable.

The difference between the temperature at which the melting point T ₁ and the heat of fusion of the propylene copolymer is 50% of the ΔHm is preferably 7 at ° C. or higher, more preferably 10 ° C. or higher. This temperature difference affects the processing temperature and the area shrinkage rate when the web is surface shrunk when producing a nonwoven fabric from the latently crimpable conjugate short fibers of the present invention. If the temperature difference is less than 7 ° C., it is necessary to raise the processing temperature to near the melting point in order to obtain a high area shrinkage. If the processing temperature is set to such a high temperature, the texture of the nonwoven fabric may be impaired, such as the hardness of the finally obtained nonwoven fabric.

比 The ratio (Q value) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the propylene copolymer is preferably in the range of 1.5 or more and 3.5 or less. A more preferred lower limit of the Q value is 2. A more preferred upper limit of the Q value is 3. The Q value of the propylene copolymer is a factor that affects the shrinking force (stretching force) of the conjugate fiber, and the shrinkage increases when the above range is satisfied.

In the range melting point _{T 1} is a 115 ° C. or higher 140 ° C. or less of the, MFR is in the range of less than 10 g / 10min or more 60 g / 10min, temperature of 125 ° C. or less when the heat of fusion is 50% of the ΔHm Specific examples of the propylene copolymer satisfying the above condition include a propylene copolymer polymerized by a metallocene catalyst, and more specifically, XK1167 and XK1183 manufactured by Nippon Polychem Co., Ltd. Examples of the method for producing a propylene copolymer suitably used in the present invention include a method in which polymerization is carried out using a metallocene catalyst in which a metallocene compound and an alumoxane are combined (Japanese Patent Application Laid-Open No. 2-173014, JP-A-2-173015, JP-A-2-255812, JP-A-3-234710, and JP-A-4-96908.

The propylene copolymer is preferably contained in the first component in an amount of 50 mass% or more. The content of the propylene copolymer is more preferably 80 mass% or more, and it is most preferable that the propylene copolymer is used alone and used as the first component. If the content of the propylene copolymer is less than 50 mass%, sufficient shrinkage during thermal processing cannot be obtained. As the other thermoplastic resin mixed with the first component, for example, polypropylene and / or polybutene-1 is used in consideration of the melting point, MFR, Q value, and the like of the propylene copolymer.

The second component used in the latently crimpable conjugate short fiber of the present invention, the melting point Tf ₂ after spinning is a resin comprising 15 ℃ or higher thermoplastic resin than Tf _1. As the thermoplastic resin, for example, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyester resins such as copolymers thereof, nylon 6, nylon 66, polyamide resins such as copolymers thereof, and polypropylene, And polyolefin resins such as polymethylpentene. In particular, polypropylene, shrinkable polyester, or polyamide is preferably used in terms of spinnability, crimp development, shrinkage, and the like. The thermoplastic resin is preferably contained in the second component in an amount of 50% by mass or more, more preferably 80% by mass or more.

The thermoplastic resin is preferably a polyolefin resin having an MFR in the range of 10 g / 10 min to 100 g / 10 min. A more preferred lower limit of the MFR is 20 g / 10 min. A more preferred upper limit of the MFR is 80 g / 10 min. When the MFR is less than 10 g / 10 min, there is a possibility that only a fiber having low stretchability and a small single fiber elongation may be obtained, and when the MFR exceeds 100 g / 10 min, the spinnability may be deteriorated.

The thermoplastic resin is a polyolefin resin, and the ratio (Q value) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) is preferably 4 or less. A preferred lower limit of the Q value is 2. More specifically, when an α-olefin-propylene copolymer polymerized using a metallocene catalyst is used as the first component, it is preferable to use a polyolefin resin having a Q value of 4 or less. When an α-olefin-propylene copolymer polymerized using a Ziegler-Natta catalyst is used as the first component, it is preferable to use a polyolefin resin having a Q value of 3.3 or less. When the Q value exceeds 4, the crimp development and shrinkage of the conjugated short fibers tend to decrease.

As the polyolefin resin having an MFR in the range of 10 g / 10 min or more and 100 g / 10 min or less and a Q value of 4 or less, a polypropylene resin is preferable. As the polypropylene resin, for example, a trade name of Nippon Polychem Co., Ltd. SA03D.

The cross-section of the latently crimpable conjugate short fiber of the present invention is such that the first component is a sheath component, the second component is a core component, and the center of gravity of the second component (core component) is shifted from the center of gravity of the fiber. An eccentric sheath-core section or a parallel section in which the first component is exposed at a length of 20% or more of the length of the peripheral surface of the fiber is preferable. By using a conjugate fiber having such a fiber cross section, it is possible to obtain a conjugate short fiber having excellent shrinkage and excellent crimp development, which is preferable.

When the latently crimpable conjugate short fiber is an eccentric sheath-core conjugate fiber, the eccentricity of the second component is preferably in the range of 20% or more and 60% or less. A more preferable lower limit of the eccentricity is 30%. A more preferred upper limit of the eccentricity is 50%. The eccentricity here is defined by the following equation.

(4) If the eccentricity of the second component is less than 20%, sufficient shrinkage during low-temperature processing cannot be obtained, and crimp development cannot be obtained. When the eccentricity exceeds 60%, the balance in the resin ratio of the first component and the second component becomes extremely poor, and a crimp suitable for high-speed cardability cannot be obtained.

(4) When the latently crimpable conjugate short fibers are side-by-side conjugate fibers, the exposure ratio of the first component to the fiber peripheral surface length is preferably 20% or more. A more preferable lower limit of the exposure rate is 30%. If the exposure ratio is less than 20%, the shrinkage may be insufficient. When the exposure ratio is 100%, the composite staple fiber has substantially the eccentric cross section.

複合 The composite ratio of the first component and the second component is preferably in the range of 3: 7 to 7: 3 in volume ratio. A more preferable range of the volume ratio is 4: 6 to 6: 4. If the ratio of the first component is less than 3, shrinkage may be insufficient, and if the ratio of the first component exceeds 7, high-speed cardability may deteriorate, and productivity may decrease.

The latently crimpable conjugate short fiber of the present invention is a conjugate short fiber having a crimp consisting of a first component containing the propylene copolymer and a second component containing the thermoplastic resin, At least one of the ratio of the natural crimp ratio to the total crimp ratio and the natural crimp ratio satisfies 15% or less, and satisfies the following physical property values (1) and (2).
(1) In the heat shrinkage stress measurement, a maximum peak is shown at a temperature lower than 145 ° C.
(2) According to JIS-L-1015 (dry heat shrinkage), the single fiber dry heat shrinkage at an initial load of 0.018 mN / dtex (2 mg / d) at a temperature of 120 ° C. for 15 minutes is 75% or more. .

Here, the total crimp rate is based on a crimp rate based on a mechanical crimp given by a crimper or the like and a natural crimp (that is, a three-dimensional crimp) that naturally appears in a fiber by heating or the like in a manufacturing stage. It corresponds to the sum of the crimp rates. The total crimp rate is a crimp rate determined for a fiber manufactured according to a normal manufacturing method described later, and is measured according to JIS-L-1015. The natural crimp rate is determined by producing a fiber under the same conditions as the fiber for which the total crimp rate is obtained, applying a mechanical crimp under the same conditions, and then drying at a low temperature (specifically, about 20 ° C. The fiber manufactured so as to suppress the occurrence of spontaneous crimp (by natural drying at room temperature of about 30 ° C. for 1 to 3 days) was measured for the crimp rate in accordance with JIS-L-1015, and this was machined. The crimp rate is calculated according to the following equation (1).
Natural crimp rate = Total crimp rate-Mechanical crimp rate (1)

Further, the ratio of the natural crimp rate to the total crimp rate is calculated according to the following equation (2).

The latently-crimpable conjugate short fiber of the present invention is specified as a fiber in which at least one of the total crimp ratio and the ratio of natural crimp to the total crimp ratio is 15% or less.
The total crimp rate is an important factor for determining the high-speed cardability of the latently crimpable conjugate short fiber of the present invention, and is adjusted by a draw ratio, a mechanical crimp number, a mechanical crimp rate, and an annealing temperature. It is possible to do. The lower limit of the preferable total crimp rate is 11%. A preferred upper limit of the total crimp rate is 14%. In the case of latently crimpable conjugate short fibers, the total crimp ratio at the raw cotton stage affects the cardability (nep generation, formation unevenness, and card winding), especially when passing through high-speed cards. It becomes remarkable. If the total crimping ratio exceeds 15%, three-dimensional crimping is highly developed at the raw cotton stage, resulting in poor opening, winding around a cylinder, or uneven formation (cloudy) when passing through a high-speed card. There is a tendency.

Since the latently crimpable conjugate short fibers of the present invention hardly exhibit natural crimping at the raw cotton stage, the latently crimpable conjugate short fiber has a ratio of the natural crimping ratio to the total crimping ratio of 15% or less. It is also specified as a composite short fiber. Such a fiber having a small ratio of the natural crimp ratio to the total crimp ratio has good cardability even if the total crimp ratio exceeds 15%, and is suitable for a high-speed card. The ratio of the natural crimp rate to the total crimp rate is preferably 10% or less. It is more preferable that both the total crimp rate and the ratio of the natural crimp rate to the total crimp rate be 15% or less from the viewpoint of cardability.

The heat shrinkage stress is a factor indicating a shrinkage behavior with respect to temperature. When the heat shrinkage stress shows a maximum peak at a temperature lower than 145 ° C., it indicates that a high degree of shrinkage is exhibited even at a low temperature during thermal processing. That is, by satisfying the physical property value of the above (1), it contributes to energy saving of nonwoven fabric production, and high-speed production becomes possible. In the above description, “low temperature” means a temperature lower by 40 ° C. than the melting point Tf ₁ of the first component of the latently crimpable conjugate short fiber of the present invention after spinning. The latently-crimpable conjugate short fibers of the present invention exhibit latent crimping such that the area shrinkage of a web (30 g / m ² ) becomes 70% or more even at such a low temperature. The heat shrinkage stress is measured as described below.

[Heat shrinkage stress]
The measurement is performed by the following procedure using a thermal stress measuring device KE-ZLS manufactured by Kanebo Synthetic Engineering Co., Ltd. as a thermal shrinkage stress measuring device.
(1) Prepare a sample so that the sample length is 50 mm and the fineness of the sample is about 110 dtex in total, and set on a mounting hook. At this time, the number of single fibers required to make the total about 110 dtex is measured in advance.
(2) An initial load of 3.23 cN / 110 dtex (3.3 g / 110 dtex) is applied to the sample.
(3) When the apparatus was heated in a temperature range of 40 ° C. to 170 ° C. at a heating rate of 1.25 ° C./sec with the sample length kept at 50 mm, each temperature and load value were read and the load value was measured. The temperature at which the maximum peak is shown is defined as the maximum peak temperature, and the value obtained by dividing the maximum load value by the number of single fibers required to make the total load about 110 dtex the maximum heat shrinkage stress per single fiber. When the maximum peak covers a temperature range of 2 ° C. or more, it indicates the temperature when the maximum peak is first reached.

潜在 In the latently crimpable conjugate short fibers of the present invention, the temperature range in which the maximum peak of the heat shrinkage stress occurs is less than 145 ° C. A preferred upper limit of the temperature at which the maximum peak of the heat shrinkage stress occurs is 140 ° C. When the temperature at which the maximum peak of the heat shrinkage stress exceeds 145 ° C., the processing temperature tends to be high, and the feel of the nonwoven fabric tends to deteriorate.

潜在 The latently crimpable conjugate short fibers of the present invention preferably have a maximum heat shrinkage stress per single fiber in the range of 0.1 cN or more and 0.25 cN or less. Since the higher the heat shrinkage stress per single fiber is, the higher the shrinkage is, the higher the heat shrinkage stress is, the higher the heat shrinkage stress is in the above range, the higher the productivity in the nonwoven fabric production. A more preferred lower limit of the maximum heat shrinkage stress is 0.12 cN. The preferred upper limit of the maximum heat shrinkage stress is 0.2 cN. When the maximum heat shrinkage stress is less than 0.1 cN, for example, when heat processing is performed at a high speed such that the residence time in the heat processing machine is 5 seconds or less, or when heat processing is performed at a low temperature, sufficient shrinkability is obtained. Tend not to be obtained. If the maximum heat shrinkage stress exceeds 0.25 cN, three-dimensional crimping is likely to occur at the raw cotton stage, and the total crimping ratio tends to increase.

In the relationship between the total crimp rate and the heat shrinkage stress, when the total crimp rate is large, the heat shrinkage stress also tends to increase, and although the shrinkage itself increases, the high-speed card property is inferior and the card is discharged from the card. Since the fibers are firmly entangled in the card web, there is no degree of freedom between the fibers, and there is a tendency that a sufficient shrinkage rate in the web cannot be obtained.

The single fiber dry heat shrinkage factor is a factor indicating an apparent shrinkage behavior due to the appearance of crimp with respect to temperature. While the conventional latently crimpable conjugate short fibers increase the total crimp ratio to facilitate crimping, the latently crimpable conjugate short fibers of the present invention have high-speed cardability and shrinkage. In order to balance the properties, at least one of the total crimp rate and the ratio of the natural crimp rate to the total crimp rate is 15% or less, and the shrinkage rate is larger than the conventional dry heat shrinkage rate of about 50 to 70%. It has.

The latently crimpable conjugate short fibers of the present invention were measured at a temperature of 120 ° C. for a period of 15 minutes at an initial load of 0.018 mN / dtex (2 mg / d) according to JIS-L-1015 (dry heat shrinkage). The single fiber dry heat shrinkage is 75% or more. The preferable lower limit of the single fiber dry heat shrinkage is 80%. When the single fiber dry heat shrinkage is less than 75%, the three-dimensional crimping property is poor.

潜在 The latently crimpable conjugate short fibers of the present invention preferably have a single fiber elongation of 80% or more and 200% or less measured according to JIS-L-1015. The single fiber elongation is a physical property determined by the crystallinity and fiber orientation of the fiber, and substitutes for shrinkage behavior with respect to temperature. When the single fiber elongation is set to 80% or more and 200% or less, it has appropriate crystallinity and non-crystallinity. Both cardability and shrinkage can be achieved. A more preferable lower limit of the single fiber elongation is 100%. A more preferable upper limit of the single fiber elongation is 150%. If the single fiber elongation is less than 80%, three-dimensional crimping tends to occur easily at the raw cotton stage, resulting in poor high-speed cardability. If the single fiber elongation exceeds 200%, sufficient shrinkage may not be obtained during heat treatment.

The latently crimpable conjugate short fibers of the present invention can be produced, for example, as follows. First, a propylene copolymer having a melting point T _{1 in} the range of 115 ° C. to 140 ° C. and a propylene content of 95 mass% or more, or a mixture containing the propylene copolymer, and a melting point T ₂ of T ₁ A thermoplastic resin higher than 15 ° C. or a mixture containing the thermoplastic resin is prepared. Next, the propylene copolymer or a mixture containing the propylene copolymer is used as a first component, and the thermoplastic resin or a mixture containing the same is used as a second component, and is subjected to composite spinning using a conventional melt spinning machine to have a fineness of 3 dtex or more and 50 dtex or more. A spun filament within the following range is prepared. When the take-up fineness of the spun filament is less than 3 dtex, yarn breakage or the like occurs and fiber productivity is reduced. When the take-up fineness of the spun filament exceeds 50 dtex, sufficient drawing cannot be performed in the drawing step, and a fiber having a uniform fineness cannot be obtained by necking.

Next, the spun filament is drawn using a known drawing machine to obtain a drawn filament. The stretching treatment is preferably performed by setting the stretching temperature to a temperature in the range of 30 ° C. or more and 90 ° C. or less. The stretching ratio is preferably 2 times or more. A more preferred lower limit of the stretching ratio is 3 times. The more preferable upper limit of the stretching ratio is 5 times. The stretching treatment is one factor that determines the obtained single fiber elongation, and the expression of the three-dimensional crimp at the raw cotton stage is suppressed by adjusting the stretching treatment conditions so that the single fiber elongation becomes 80% or more. It becomes possible. If the stretching temperature is less than 30 ° C., sufficient stretching cannot be performed, and the single fiber elongation tends to remain. In addition, voids may be generated and the fiber strength may be significantly reduced. If the stretching temperature exceeds 90 ° C., sufficient shrinkage cannot be obtained during nonwoven fabric processing. If the draw ratio is less than 2 times, the single fiber elongation remains large and the high-speed cardability is poor. Furthermore, sufficient shrinkage cannot be obtained during nonwoven fabric processing. On the other hand, when the stretching ratio exceeds 5 times, three-dimensional crimping is likely to occur at the raw cotton stage, and the total crimping ratio and the ratio of the natural crimping ratio to the total crimping ratio tend to increase, resulting in poor high-speed cardability. May be. The stretching method may be any of a wet stretching method performed in warm water or hot water or a dry stretching method.

(4) A predetermined amount of a fiber treatment agent is attached to the obtained drawn filament, and is mechanically crimped by a crimper (crimp applying device). The number of crimps in the mechanical crimp is preferably in the range of 11 peaks / 25 mm or more and 18 peaks / 25 mm or less. When the number of crimps is less than 11 ridges / 25 mm, high-speed card passage is poor because the card is easily wound around the cylinder and fly is easily generated. Further, the web strength indicating the degree of entanglement between the fibers is low, and a trouble tends to occur in the carding process. If the number of crimps exceeds 18 peaks / 25 mm, uneven formation such as NEP and cloudy due to poor spreading in the carding process occurs.

フ ィ ラ メ ン ト Anneal the filament after crimping at a temperature in the range of 20 ° C. or more and 80 ° C. or less for several seconds to about 30 minutes. When the annealing treatment is performed after the fiber treatment agent is applied, the annealing treatment temperature is set to a temperature within a range of 50 ° C. or more and 80 ° C. or less, the treatment time is set to 5 minutes or more, and the annealing treatment is performed. More preferably, the agent is dried. By setting the annealing treatment in the above temperature range, the crystallization of the conjugate fiber is suppressed, the expression of the three-dimensional crimp at the raw cotton stage is suppressed to a low level, and the total crimp rate and the natural crimp rate with respect to the total crimp rate are reduced. It is possible to adjust the ratio and the single fiber dry heat shrinkage to a desired range.

終了 After the annealing treatment is completed, the filament is cut to a length within a range of 30 mm or more and 100 mm or less, depending on the application.

Next, a specific example of the method for producing a latently crimpable conjugate short fiber of the present invention will be described. As a first component, the melting point T ₁ is in the range of 115 ° C. or more and 140 ° C. or less, the propylene content accounts for 95 mass% or more, the MFR is in the range of 10 g / 10 min or more and 60 g / 10 min or less, and A resin made of a propylene copolymer having a temperature at which the heat of fusion becomes 50% of ΔHm is 125 ° C. or less is prepared. As a propylene copolymer satisfying these conditions, the propylene content is in the range of 96 mass% to 98 mass% and the Q value is in the range of 1.5 to 3.5, and is polymerized by a metallocene catalyst. It is preferably at least one selected from ethylene-propylene copolymer, butene-propylene copolymer and ethylene-propylene-butene terpolymer.

On the other hand, as the second component, a thermoplastic resin having a melting point T ₂ higher than T ₁ by 15 ° C. or more, for example, a polypropylene resin having an MFR in the range of 10 g / 10 min to 100 g / 10 min and a Q value of 4 or less Prepare

An eccentric sheath-core nozzle in which the first component constitutes a sheath component, the second component constitutes a core component, and the center of gravity of the second component is shifted from the center of gravity of the fiber, or Using a parallel type nozzle arranged so as to be exposed at a length of 20% or more with respect to the length of the peripheral surface, the spinning temperature is set to a temperature within a range of 200 ° C or more and 300 ° C or less, and is extruded by melting. At a speed in the range of 150 m / min to 1500 m / min to obtain a spun filament having a fineness in the range of 3 dtex to 30 dtex.

Next, the spun filament is subjected to a drawing treatment by setting the drawing temperature to a temperature in the range of 40 ° C. or more and 80 ° C. or less, and setting the draw ratio in a range of 2 to 6 times. Is obtained in the range of 1 dtex or more and 15 dtex or less.

Next, a predetermined amount of the fiber treating agent is applied, and mechanical crimping is performed using a crimper (crimping device) in a range of 11 crimps / 25 mm or more and 18 crimps / 25 mm or less. Then, the annealing treatment temperature is set to 50 ° C. or more and 80 ° C. or less, the treatment time is set to 5 minutes or more and 30 minutes or less, and the annealing treatment is performed, and the fiber treating agent is dried. Next, by cutting so that the fiber length becomes 30 mm or more and 100 mm or less, at least one of the total crimp rate and the ratio of the natural crimp rate to the total crimp rate satisfies 15% or less, and the heat shrinkage. A latently crimpable conjugate short fiber that satisfies predetermined physical properties with respect to stress and single fiber dry heat shrinkage is obtained.

The latently crimpable conjugate short fibers of the present invention are different from conventional fibers in the heat shrinkage behavior of the web when the web is formed therefrom, and can be specified by the heat shrinkage behavior. Specifically, the latently crimpable conjugate short fiber of the present invention is formed by conjugate spinning of the first component and the second component, and has a melting point Tf ₁ after spinning in the range of 120 ° C. or more and 145 ° C. or less. A first component containing an α-olefin-propylene copolymer having a propylene content of 95 mass% or more, and a second component containing a thermoplastic resin having a melting point Tf ₂ after spinning of 15 ° C. or more higher than Tf _1. And a crimped conjugate short fiber comprising a web having a basis weight of 30 g / m ² formed from the conjugate short fiber and heat-treated at 120 ° C. for 4 seconds to have a web area shrinkage of 85% or more. Things. That is, the latently-crimpable conjugate short fiber of the present invention is one that expresses latently-crimped at a relatively low temperature and for a short time.

The latently-crimpable conjugate short fiber of the present invention described above is contained in a fiber aggregate in an amount of 20 mass% or more, and by developing latent crimp, the fiber aggregate is excellent in stretchability or shrinkage and has a good texture. Form an object. Examples of the fiber aggregate include a woven and knitted fabric and a nonwoven fabric.

Next, a nonwoven fabric as a specific example of the fiber aggregate of the present invention will be described together with a method for producing the nonwoven fabric. The nonwoven fabric can be obtained by preparing a card web so as to contain the latently crimpable conjugate short fibers in an amount of 20% by mass or more, heat-treating the card web, and developing a latent crimp. The nonwoven fabric may be mixed with other fibers or laminated other than the latently crimpable conjugate short fibers. The other fibers are, for example, natural fibers such as cotton, silk, wool, hemp, pulp, regenerated fibers such as rayon and cupra, and synthetic fibers such as acrylic, polyester, polyamide, polyolefin, and polyurethane. One or more types of fibers may be selected according to the application.

カ ー ド As a card web used in manufacturing the nonwoven fabric, a parallel web, a semi-random web, a random web, a cross web, a criss cross web and the like can be mentioned, and two or more different types of fiber webs may be laminated. Further, in order to entangle the fibers, the fiber web may be subjected to a secondary processing such as a needle punching treatment or a hydroentangling treatment before and / or after the heat treatment, if necessary. In particular, according to a method of three-dimensionally entangled constituting fibers, such as a needle punching process and a hydroentanglement process, when a three-dimensional crimp of a latently crimpable conjugate short fiber is developed by a heat treatment described below, Since the fibers are appropriately restrained, they have a high degree of elongation recovery and are preferable.

The fiber web is subjected to a heat treatment by a known heat treatment means. As the heat treatment means, it is preferable to use at least one heat treatment method selected from a hot air blowing method and a thermocompression bonding method. The heat treatment conditions such as the heat treatment temperature in the heat treatment method are appropriately set according to the heat treatment method to be adopted. For example, when a hot air blowing method (air-through method) is employed, the heat treatment temperature may be set to a temperature at which three-dimensional crimping of the latently crimpable conjugate short fiber is developed, and preferably, Tf ₁ -40 ≦ T ( C.) ≦ Tf ₁ +20, more preferably Tf ₁ −30 ≦ T (° C.) ≦ Tf ₁ −5.

The obtained non-woven fabric has excellent shrinkage and elasticity, and has a soft texture. Therefore, sanitary materials such as diapers, medical (use) materials such as cataplasms and bandages, wet tissues, wipers, cushioning materials, packaging materials, It is suitable for applications such as sponge-like nonwoven fabric materials.

Hereinafter, the contents of the present invention will be specifically described with reference to examples. The melting points T ₁ and T ₂ of the _first and _second components used, the temperature at which the heat of fusion calculated from the low temperature side of the first component becomes 50% of ΔHm, the first and second components after spinning, The melting points Tf ₁ and Tf _{2 of the} components, the strength and elongation of a single fiber, the number of crimps, the ratio of the natural crimp rate to the total crimp rate and the total crimp rate, the dry heat shrinkage rate of the single fiber, the area shrinkage rate of the nonwoven fabric, and High-speed cardability was measured as follows.

[Measurement of T ₁ and T ₂ , and 50% temperature of heat of fusion ΔHm of first component]
Using a Seiko DSC, the sample amount was adjusted to 5.0 mg, held at 200 ° C for 5 minutes, cooled to 40 ° C at a rate of 10 ° C / min, and then melted at a rate of 10 ° C / min. by, give heat of fusion curve for each of the first and second components, the melting heat curve obtained was determined melting point T ₁ and T _2, respectively. Further, from the heat of fusion curve obtained for the first component, the temperature at which the heat of fusion calculated from the low temperature side became 50% of ΔHm was determined.

[Measurement of Tf ₁ and Tf ₂ ]
Using a DSC manufactured by Seiko, the sample amount was 6.0 mg, the temperature was raised from room temperature to 200 ° C. at a temperature rising speed of 10 ° C./min to melt the fibers, and Tf ₁ was obtained from the obtained heat of fusion curve. And Tf ₂ were determined.

[Strength and elongation of single fiber]
According to JIS-L-1015, the load value and elongation at the time of fiber cutting were measured using a tensile tester with a sample gripping distance of 20 mm, and the results were defined as single fiber strength and single fiber elongation, respectively.

[Number of crimps, total crimp rate, mechanical crimp rate, ratio of natural crimp rate to total crimp rate]
The number of crimps and the total crimp rate were measured according to JIS-L-1015. In addition, in each of Examples and Comparative Examples, after spinning and stretching using the same resin and the same manufacturing conditions, a mechanical crimp was applied, and then at room temperature (about 20 ° C. to about 30 ° C.) for 1 to 3 days. The mixture was air-dried to obtain a composite short fiber for measuring a mechanical crimp rate. About this composite short fiber, the crimp rate was measured according to JIS-L-1015, and this was made into the mechanical crimp rate. From the total crimp rate and the mechanical crimp rate, the natural crimp rate was determined according to the above equation (1), and further, the ratio of the natural crimp rate to the total crimp rate was determined according to the above equation (2).

[Single fiber dry heat shrinkage]
According to JIS-L-1015, the grip interval is 100 mm, the processing temperature is 120 ° C., the processing time is 15 minutes, and the dry heat at an initial load of 0.018 mN / dtex (2 mg / d) and 0.45 mN / dtex (50 mg / d) Each shrinkage was measured.

[Web area shrinkage]
The web area shrinkage was measured by the following method.
(1) A card web having a basis weight of about 30 g / m ² is prepared using a semi-random card machine and cut into a size of 20 cm × 20 cm. The dimensions (cm) of the web before shrinkage treatment are measured.
(2) Using an air-through heat treatment machine, the card web is heat-treated and shrunk in a free state at a heat treatment temperature of 120 ° C. and a wind speed of 1.5 m / sec. The heat treatment time was set to 4 seconds and 12 seconds, and the web area shrinkage was measured in each case.
(3) Measure the dimensions (cm) of the web after shrinking.
(4) The area shrinkage is calculated from the following equation.

[High-speed card]
Using a roller-type card machine, check the formation of the card web, the generation of fly wool (fly), static electricity, and the presence or absence of winding when the card web with a basis weight of about 15 g / m ² is discharged at a line speed of 120 m / min. And the following criteria.
◎: The texture of the card web, generation of fluff, static electricity, and winding were all excellent.
：: Good texture of card web, generation of fly wool, static electricity, and winding.
Δ: One of the formation of the card web, generation of fluff, static electricity, and winding was defective.
X: Two or more of the formation of the card web, generation of fluff, static electricity, and winding were defective.

[Example 1]
The sheath component (first component) has a melting point of 128 ° C., an MFR of 26 g / 10 min, a temperature of 116 ° C. when the heat of fusion becomes 50% of ΔHm, a Q value of 2.6, and an ethylene content of 2.6 mass%. An ethylene-propylene copolymer having a propylene content of 97.4 mass%, which was polymerized using a metallocene catalyst (manufactured by Nippon Polychem Co., Ltd., test grade name: XK1183) was used. As the core component (second component), crystalline polypropylene (manufactured by Nippon Polychem Co., Ltd., trade name: SA03B) having a melting point of 161 ° C., an MFR of 30 g / 10 min, and a Q value of 3.5 was used. Using an eccentric sheath-core composite nozzle for the two components, setting the composite ratio (volume ratio) of the first component / second component to 5/5, the spinning temperature of the sheath component is 250 ° C, and the spinning temperature of the core component is 230 ° C. To obtain a spun filament having an eccentricity of 40% and a fineness of 6.7 dtex.

(4) The spun filament was drawn 3.3 times in hot water at 60 ° C. to give a drawn filament having a fineness of 2.5 dtex. Next, after applying the fiber treating agent, the drawn filament was subjected to mechanical crimping of about 15 peaks / 25 mm with a stuffing box type crimper. Then, annealing and drying are simultaneously performed in a relaxed state for about 15 minutes in a hot air penetration type dryer set at 65 ° C., and the filament is cut into a fiber length of 51 mm. Short fibers were obtained.

[Example 2]
As a core component (second component), a crystalline polypropylene (trade name: SA03D, manufactured by Nippon Polychem Co., Ltd., trade name: SA03D) having a melting point of 161 ° C., an MFR of 30 g / 10 min, and a Q value of 3, is used. Except that the film was stretched 3.0 times in hot water at 60 ° C., and a mechanical crimp of about 13 peaks / 25 mm was applied with a crimper, and the latent crimpability of the present invention was obtained in the same manner as in Example 1. A composite short fiber was obtained.

[Example 3]
A method similar to that of Example 2 except that a spun filament having a fineness of 6.7 dtex is drawn 3.3 times in warm water at 60 ° C., and a mechanical crimp of about 12 peaks / 25 mm is applied by a crimper. Thus, a latently crimpable conjugate short fiber of the present invention was obtained.

[Example 4]
A method similar to that of Example 2 except that a spun filament having a fineness of 7.4 dtex is drawn 3.6 times in hot water at 60 ° C., and a mechanical crimp of about 15 peaks / 25 mm is applied by a crimper. Thus, a latently crimpable conjugate short fiber of the present invention was obtained.

[Example 5]
The sheath component (first component) has a melting point of 128 ° C., an MFR of 38 g / 10 min, a temperature of 116 ° C. when the heat of fusion becomes 50% of ΔHm, a Q value of 2.6, and an ethylene content of 2.6 mass%. An ethylene-propylene copolymer having a propylene content of 97.4 mass%, which was polymerized using a metallocene catalyst (manufactured by Nippon Polychem Co., Ltd., test grade name: XK1167) was used. As the core component (second component), a crystalline polypropylene (manufactured by Nippon Polychem Co., Ltd., trade name: SA06A) having a melting point of 161 ° C., an MFR of 60 g / 10 min, and a Q value of 3.0 was used. Using these, a latently crimpable conjugate short fiber of the present invention was obtained in the same manner as in Example 1. In this example, a mechanical crimp of about 13 peaks / 25 mm was applied by a crimper.

[Example 6]
The sheath component (first component) has a melting point of 136 ° C., an MFR of 18 g / 10 min, a temperature of 130 ° C. when the heat of fusion becomes 50% of ΔHm, a Q value of 3.5, and an ethylene content of 4.3 mass%. An ethylene-propylene copolymer having a propylene content of 95.7 mass%, which was polymerized using a Ziegler-Natta catalyst (trade name SX02R, manufactured by Nippon Polychem Co., Ltd.) was used. A method similar to that of Example 1 except that a spun filament having a fineness of 6.7 dtex is drawn 3.3 times in hot water at 60 ° C., and a mechanical crimp of about 13 peaks / 25 mm is applied by a crimper. Thus, a latently crimpable conjugate short fiber of the present invention was obtained.

[Comparative Example 1]
A spun filament having a fineness of 7.2 dtex, composed of the first component used in Example 6 and the second component used in Example 1, was drawn 3.6 times in hot water at 60 ° C., and was crimped by a crimper. Latent crimpable conjugate short fibers were obtained in the same manner as in Example 1 except that a mechanical crimp of about 14 peaks / 25 mm was provided.

[Comparative Example 2]
A spun filament having a fineness of 6.7 dtex, composed of the first component used in Example 6 and the second component used in Example 1, is drawn 3.3 times in hot water at 60 ° C., and crimped by a crimper. Latent crimpable conjugate short fibers were obtained in the same manner as in Example 1 except that a mechanical crimp of about 14 peaks / 25 mm was provided.

[Comparative Example 3]
A spun filament having a fineness of 6.0 dtex, composed of the first component used in Example 6 and the second component used in Example 1, was drawn 3.0 times in warm water at 60 ° C., and was crimped with a crimper. Latent crimpable conjugate short fibers were obtained in the same manner as in Example 1 except that a mechanical crimp of about 15 peaks / 25 mm was provided.
Table 1 shows the physical properties of the resulting latently crimpable conjugate short fibers.

The latently crimpable conjugate short fibers of Examples 1 to 6 had a total crimp ratio and a ratio of the natural crimp ratio to the total crimp ratio of 15% or less, a temperature at which the heat shrinkage stress exhibited the maximum peak, and a single fiber dryness. By setting the heat shrinkage in a desired range and further setting the heat shrinkage stress and single fiber elongation in the above-mentioned preferable ranges, the high-speed cardability and the web shrinkability were excellent. In particular, short fibers using the ethylene-propylene copolymer polymerized by the metallocene catalyst of Examples 1 to 5 have a high degree of shrinkage in spite of a small heat shrinkage stress. It was possible to easily adjust the total crimp rate while suppressing the expression.

On the other hand, by adjusting the spinning conditions and the drawing conditions, in Comparative Example 1, short fibers having a high heat shrinkage stress and a high single fiber dry heat shrinkage could be obtained, but three-dimensional crimps appeared at the raw cotton stage. Therefore, the total crimp ratio was large, and the ratio of the natural crimp to the total crimp ratio was also large. In addition, cloudy was generated due to the winding around the main cylinder (a phenomenon in which a sudden increase in the number of windings around the main cylinder caused sudden discharge and repeated winding for a while, resulting in uneven weight per unit area), resulting in uneven formation of the card web. In Comparative Example 2, the cardability was better than in Comparative Example 1, and no NEP was confirmed, but cloudy occurred. Furthermore, the area shrinkage of the web at 120 ° C. for 4 seconds was not satisfactory. In Comparative Example 3, the cardability was good, but a sufficient heat shrinkage was not obtained.

The latently crimpable conjugate staple fiber of the present invention suppresses the expression of three-dimensional crimp at the raw cotton stage, and develops a good crimp in a short heat treatment. In addition, the heat treatment time is shortened), and it is useful for producing a fiber aggregate (in particular, a nonwoven fabric) having a soft texture.

Claims (14)

An α-olefin-propylene copolymer comprising a first component and a second component, which is formed by composite spinning, has a melting point Tf ₁ after spinning in the range of 120 ° C. or more and 145 ° C. or less, and has a propylene content of 95 mass% or more. a first component comprising a polymer, the melting point Tf ₂ after spinning a composite short fibers having a crimp and a second component comprising 15 ℃ or higher thermoplastic resin than Tf _1, the total crimp ratio A latently crimpable conjugate short fiber in which at least one of a ratio of a natural crimp ratio to a total crimp ratio is 15% or less and satisfies the following physical property values (1) and (2).
(1) In the heat shrinkage stress measurement, a maximum peak is shown at a temperature lower than 145 ° C.
(2) According to JIS-L-1015 (dry heat shrinkage), the single fiber dry heat shrinkage at an initial load of 0.018 mN / dtex (2 mg / d) at a temperature of 120 ° C. for 15 minutes is 75% or more. . The latently crimpable conjugate short fiber according to claim 1, wherein the maximum heat shrinkage stress per single fiber in the heat shrinkage stress measurement is in the range of 0.1 cN to 0.25 cN. The latently crimpable conjugate short fiber according to claim 1 or 2, wherein the single fiber elongation measured according to JIS-L-1015 is in the range of 80% or more and 200% or less. An eccentric sheath-core cross section in which the first component is a sheath component, the second component is a core component, and the center of gravity of the second component is shifted from the center of gravity of the fiber, The latently crimpable conjugate short fiber according to any one of claims 1 to 3, wherein the component is a parallel-shaped cross section in which the component is exposed at a length of 20% or more with respect to the length of the peripheral surface of the fiber. The first component contains an α-olefin-propylene copolymer in an amount of 50 mass% or more, and complies with JIS-K-7210 (conditions: 230 ° C., load: 21.18 N (2.16 kg)) of the α-olefin-propylene copolymer. The melt flow rate measured according to the method is in the range of 10 g / 10 min or more and 60 g / 10 min or less, and the total heat of fusion of the α-olefin-propylene copolymer determined by the DSC curve in JIS-K-7121 was defined as ΔHm. The latently crimpable conjugate short fiber according to any one of claims 1 to 4, wherein the temperature when the heat of fusion calculated from the low temperature side becomes 50% of ΔHm is 125 ° C or less. α-olefin-propylene copolymer, ethylene-propylene copolymer, butene-propylene copolymer and ethylene-propylene-butene terpolymer having a propylene content of 96 mass% or more and 98 mass% or less. The latently crimpable conjugate short fiber according to any one of claims 1 to 5, which is at least one selected from the group consisting of: The ratio (Q value) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the α-olefin-propylene copolymer is in the range of 1.5 or more and 3.5 or less. The latently crimpable conjugate short fiber according to any one of the above. The latently crimpable conjugate short fiber according to any one of claims 5 to 7, wherein the α-olefin-propylene copolymer is a resin polymerized by a metallocene catalyst. Melting point _{T 1} is in the range of 140 ° C. or less 115 ° C. or higher, the propylene content is accounted for more than 95mass%, JIS-K-7210 ( condition: 230 ° C., a load 21.18 N (2.16 kg)) in the When the melt flow rate is in the range of 10 g / 10 min or more and 60 g / 10 min or less, and the total heat of fusion of the α-olefin-propylene copolymer determined from a DSC curve measured according to JIS-K-7121 is ΔHm. A first component containing an α-olefin-propylene copolymer having a temperature of 125 ° C. or less when the heat of fusion calculated from the low temperature side becomes 50% of ΔHm, and a melting point T ₂ higher than T ₁ by 15 ° C. or more A crimped conjugate short fiber having an eccentric sheath-core type cross section or a parallel type cross section obtained by compound spinning with a second component containing a thermoplastic resin, wherein the total crimp rate and the self crimp rate relative to the total crimp rate are Among percentage of crimp, at least one of 15% or less latently crimpable conjugate short fiber. The said thermoplastic resin contained in a 2nd component is a polyolefin resin, The ratio (Q value) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the said polyolefin resin is 4 or less. 10. The latently crimpable conjugate short fiber according to any one of items 9 to 9. An α-olefin-propylene copolymer comprising a first component and a second component, which is formed by composite spinning, has a melting point Tf ₁ after spinning in the range of 120 ° C. or more and 145 ° C. or less, and has a propylene content of 95 mass% or more. a first component comprising a polymer, the melting point Tf ₂ after spinning a composite short fibers having a crimp and a second component comprising 15 ℃ or higher thermoplastic resin than Tf _1, the composite short fibers A latently crimpable conjugate short fiber which forms a web having a basis weight of 30 g / m ² and heat-treats the web at 120 ° C. for 4 seconds to have a web area shrinkage of 85% or more. Melting point _{T 1} is in the range of 140 ° C. or less 115 ° C. or higher, the propylene content is accounted for more than 95mass%, JIS-K-7210 ( condition: 230 ° C., a load 21.18 N (2.16 kg)) in the When the melt flow rate is in the range of 10 g / 10 min or more and 50 g / 10 min or less, and the total heat of fusion of the α-olefin-propylene copolymer determined from a DSC curve measured according to JIS-K-7121 is ΔHm. A resin containing an α-olefin-propylene copolymer having a temperature at which the heat of fusion calculated from the low temperature side becomes 50% of ΔHm is 125 ° C. or less is used as the first component, and the melting point T ₂ is 15 ° C. higher than T _1. Using a resin containing a high thermoplastic resin as the second component as a second component, to obtain a spun filament by performing composite spinning so as to have an eccentric sheath-core type or side-by-side cross section; Stretching at a temperature within the range of 2 times or more, applying mechanical crimps in a range of 11 crimps / 25 mm or more and 18 crimps / 25 mm or less, and a temperature in a range of 20 ° C. or more and 80 ° C. or less A method for producing a latently crimpable conjugate short fiber, which comprises performing an annealing treatment in step (a). A latently crimpable conjugate short fiber according to any one of claims 1 to 11, or a latently crimpable conjugate short fiber obtained by the production method according to claim 12, which contains at least 20 mass%, A fiber aggregate in which latent crimp is expressed in the conjugate short fiber. A latently crimpable conjugate short fiber according to any one of claims 1 to 11, or a latently crimpable conjugate short fiber obtained by the production method according to claim 12, which contains at least 20 mass%, A nonwoven fabric in which latent crimps have been expressed in the conjugate staple fibers and substantially not heat-sealed.