Resin composition for bi-component fiber

1. A resin composition for core-sheath type bi-component fiber comprising:

core component comprising homopolypropylene fulfilling the following requirements (i) to (v):

(i) molecular weight distribution of 2.4 or less,

(ii) residual stress rate of 0.05% or less,

(iii) melt index, measured under load of 2.16 kg at 230° C. according to ASTM D1238, of 20 to 40 g/10 min,

(iv) tacticity of 98% or more,

(v) melting point of 155° C. or less; and

sheath component comprising high density polyethylene having density measured according to ASTM D1505 of 0.930 g/cm 3 or more.

2. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein shear viscosity of the homopolypropylene in the shear rate section of 500 1/s, measured according to ASTM D3835, is 90 to 120 Pa·s.

3. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein the homopolypropylene has total volatile organic compounds content of 30 ppm or less, based on the total weight of the homopolypropylene.

4. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein the molecular weight distribution of the homopolypropylene is 2.0 to 2.4.

5. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein the residual stress rate of the homopolypropylene is 0.005 to 0.05%.

6. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein the melting point of the homopolypropylene is 140 to 155° C.

7. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein the density of the high density polyethylene is 0.930 to 0.970 g/cm 3 .

8. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein melt index of the high density polyethylene, measured under load of 2.16 kg at 230° C. according to ASTM D1238, is 10 to 40 g/10 min.

9. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein melting point of the high density polyethylene is 120 to 135° C.

10. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein the core component and the sheath component are included at a weight ratio of 70:30 to 90:10.

11. A method for preparing core-sheath type bi-component fiber, comprising steps of:

polymerizing propylene while introducing hydrogen gas in an amount of 300 to 500 ppm based on the total weight of propylene, in the presence of a catalyst comprising a transition metal compound of the following Chemical Formula 1, to prepare homopolypropylene fulfilling the following requirements (i) to (v):

(i) molecular weight distribution of 2.4 or less,

(ii) residual stress rate of 0.05% or less,

(iii) melt index, measured under load of 2.16 kg at 230° C. according to ASTM D1238, of 20 to 40 g/10 min,

(iv) tacticity of 98% or more,

(v) melting point of 155° C. or less;

preparing a resin composition for core-sheath type bi-component fiber using the homopolypropylene as a core component, and high density polyethylene having density measured according to ASTM D1505 of 0.930 g/cm 3 or more as a sheath component; and

melt spinning the resin composition for core-sheath type bi-component fiber to prepare core-sheath type bi-component fiber comprising a core comprising the homopolypropylene and a sheath comprising the high density polyethylene,

in the Chemical Formula 1,

A is carbon, silicon or germanium,

X 1 and X 2 are each independently, halogen,

R 1 and R 5 are each independently, C 6-20 aryl substituted with C 1-20 alkyl, R 2 to R 4 and R 6 to R 8 are each independently, hydrogen, halogen, C 1-20 alkyl, C 2-20 alkenyl, C 1-20 alkylsilyl, C 1-20 silylalkyl, C 1-20 alkoxysilyl, C 1-20 ether, C 1-20 silylether, C 1-20 alkoxy, C 6-20 aryl, C 7-20 alkylaryl, or C 7-20 arylalkyl, and

R 9 and R 10 are identical to each other, and are C 2-20 alkyl.

12. The method for preparing a core-sheath type bi-component fiber according to claim 11 , wherein A is silicon(Si), R 1 and R 5 are each independently, a phenyl group substituted with a C 3-6 branched alkyl group, and R 9 and R 10 are identical to each other, and are a C 2-4 linear alkyl group.

13. The method for preparing a core-sheath type bi-component fiber according to claim 11 , wherein the compound of the Chemical Formula 1 is a compound represented by the following Chemical Formula 1a,

14. Non-woven fabric comprising core-sheath type bi-component fiber, wherein the core comprises homopolypropylene fulfilling the following requirements (i) to (v):

i) molecular weight distribution of 2.4 or less,

(ii) residual stress rate of 0.05% or less,

(iii) melt index, measured under load of 2.16 kg at 230° C. according to ASTM D1238, of 20 to 40 g/10 min,

(iv) tacticity of 98% or more

(v) melting point of 155° C. or less, and

the sheath comprises high density polyethylene having density measured according to ASTM D1505 of 0.930 g/cm 3 or more.

15. The non-woven fabric according to claim 14 , wherein the non-woven fabric is spunbond non-woven fabric.

16. The resin composition for core-sheath type bi-component fiber according to claim 1 , wherein the high density polyethylene is ethylene homopolymer or copolymer of ethylene and alpha olefin monomers, and the alpha olefin monomers is one or more selected from the group consisting of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hezene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-eicosene.

17. The resin composition for core-sheath type bi-component fiber according to claim 16 , wherein when the high density polyethylene is the copolymer of ethylene and alpha olefin monomers, the alpha olefin monomers are included in an amount of 0.1 wt % or more and 20 wt % or less.

18. The method for preparing a core-sheath type bi-component fiber according to claim 11 , wherein the melt spinning process is conducted in the sequence of:

Step 1: spinning each of the core component and the sheath component in a molten state to prepare spun filaments;

Step 2: cooling the spun filaments at an air flow of 25 to 35 rpm under 10 to 20° C.; and

Step 3: binding the cooled filaments with each other.