Conjugate fiber for air-laid nonwoven fabric manufacture and method for manufacturing a high-density air-laid nonwoven fabric

Inactive Publication Date: 2011-04-21
FIBERVISIONS LP +2
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  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0012]There have been thus attempts at obtaining a nonwoven fabric having excellent stretchability, cushioning characteristics and liquid absorbing ability, by using latently crimp able conjugate fibers, attempts at using latently crimp able fibers in air laying processes, and attempts at obtaining high-basis weight nonwoven fabrics, having small property differences in the machine direction and the width direction, by way of an air laying process. However, such attempts have failed hitherto to achieve simultaneously high fiber existence density through web shrinking, coupled with air laying process processability and productivity. This underscores the need for further improvement.
[0013]Therefore, it is an object of the present invention to provide a conjugate fiber for manufacturing a high-density air-laid nonwoven fabric, the conjugate fiber having a planar zig-zag crimp shape before a thermal treatment, such that a uniform web is obtained by air laying with high processability and productivity, and the conjugate fiber develops a spiral crimp when the web is subjected to a thermal treatment to thereby enable the web to shrink significantly, as a result of which a nonwoven fabric can be obtained in which fibers are amassed to a high density.
[0015]As a result of diligent research directed at solving the above problems, the inventors found that a uniform air-laid web, excellent in air-laying processability and productivity, can be obtained by using a conjugate fiber obtained by conjugating an olefinic thermoplastic resin of low melting point, and an olefinic thermoplastic resin having a melting point higher than that of the low-melting point olefinic thermoplastic resin, such that the centers of gravity of the conjugate components are mutually different in the fiber cross section. The inventors found also that the crimp develop ability of such a conjugate fiber is excellent during thermal treatment of the web, as a result of which the web shrinks significantly, affording a high-density nonwoven fabric in which fibers are amassed to a high density. The inventors found that yet better results are achieved, in particular, when using homopolypropylene having a molecular weight distribution (number-average molecular weight / weight-average molecular weight) not smaller than 3.5 as the high-melting point olefinic thermoplastic resin. The inventors achieved the present invention on the basis these findings.
[0024]Although the conjugate form of the conjugate fiber for air-laid nonwoven fabric manufacture of the present invention is a form in which the centers of gravity of the components are different in the fiber cross section, the crimp shape of the fiber is a completely planar zig-zag crimp shape, with a crimp shape index ranging from 1.05 to 1.60, and a crimp count no greater than 14 crimps / 2.54 cm, at a stage before a thermal treatment. Therefore, the bulkiness of the fiber is small, and in consequence, the conjugate fiber of the present invention exhibits excellent fiber spreadability and dispersibility, as well as dischargeability from a drum screen or a screen mesh, when processed in an air laying process. The conjugate fiber of the present invention allows thus obtaining a web of good texture with high productivity.
[0025]When the obtained web is subjected to a thermal treatment, the fibers develop a spiral crimp, with a remarkable shortening of apparent fiber length, derived from the cross-sectional shape of the fiber and the thermal shrinkage differences between components. This spiral crimp development causes the web to shrink significantly and the fibers to become amassed to a high density. The spiral crimp elicits also adequate entanglement between fibers, as a result of which there is obtained a high-density air-laid nonwoven fabric having excellent stretchability, cushioning characteristics as well as liquid absorption and release characteristics.
[0026]This high-density air-laid nonwoven fabric is obtained by way of an air laying process, and hence a high-basis weight nonwoven fabric of, for instance, 500 g / m2 or more can easily obtained. Moreover, differences in fiber arrangement in the machine direction and the width direction are very small, and thus differences in the properties of the nonwoven fabric in the two directions are likewise small. In such an air-laid web laid to a high basis weight, furthermore, there is an appreciable number of fibers arranged at a certain angle in the vertical direction. During web shrinking through a thermal treatment, these fibers arranged in the vertical direction become bulked up and raised in the vertical direction through the opposing effect of contractile forces in the horizontal direction, while shrinking by developing their own spiral crimp. As a result there is effectively achieved a high-density air-laid nonwoven fabric having high bulkiness and good stretchability and cushioning in the thickness direction of the nonwoven fabric, and exhibiting little property differences in the three spatial directions, i.e. the machine direction, the width direction and the thickness direction. When the air-laid nonwoven fabric is used, for instance, as a liquid absorbing material, it is found that the nonwoven fabric exhibits little differences in liquid absorption and release characteristics in the three spatial directions, while when the nonwoven fabric is used as a cushioning material, it is found that the nonwoven fabric exhibits high compression recovery characteristics in all directions.

Problems solved by technology

However, such attempts have failed hitherto to achieve simultaneously high fiber existence density through web shrinking, coupled with air laying process processability and productivity.

Method used

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  • Conjugate fiber for air-laid nonwoven fabric manufacture and method for manufacturing a high-density air-laid nonwoven fabric
  • Conjugate fiber for air-laid nonwoven fabric manufacture and method for manufacturing a high-density air-laid nonwoven fabric
  • Conjugate fiber for air-laid nonwoven fabric manufacture and method for manufacturing a high-density air-laid nonwoven fabric

Examples

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example 1

[0131]High-density polyethylene having a melting point of 130° C. and an MFR of 26 g / 10 min, as the first component, and polypropylene having a melting point of 162° C., an MFR of 16 g / 10 min, and a molecular weight distribution of 4.2, as the second component, conjugated at a ratio first component / second component of 50 / 50 wt %, were melt spun using a side-by-side nozzle at a first component extrusion temperature of 240° C., a second component extrusion temperature of 270° C. and a nozzle temperature of 260° C. The cross-sectional shape of the obtained undrawn yarn was a half-moon-like side-by-side shape. The undrawn yarn was drawn 2.0-fold at a drawing temperature of 50° C., and was imparted crimp in a stuffing box crimper. The crimp shape of the fibers coming out of the crimper was a planar zig-zag crimp shape. The same crimp shape was retained even after drying at 70° C. in a circulation drier. The crimp shape index was 1.28. The single-yarn fineness was 3.3 dtex and the crimp c...

example 2

[0133]A propylene-ethylene-butene-1 copolymer (weight ratio of propylene / ethylene / butene-1=93 / 2.5 / 4.5) having a melting point of 136° C. and an MFR of 18 g / 10 min, as the first component, and polypropylene having a melting point of 162° C., an MFR of 11 g / 10 min, and a molecular weight distribution of 4.9, as the second component, conjugated at a ratio first component / second component of 50 / 50 wt %, were melt spun using a side-by-side nozzle at a first component extrusion temperature of 290° C., a second component extrusion temperature of 270° C. and a nozzle temperature of 260° C. The cross-sectional shape of the obtained undrawn yarn was a side-by-side shape in which the second component was imperfectly enfolded in the first component. The undrawn yarn was drawn 3.0-fold at a drawing temperature of 60° C., and was imparted crimp in a stuffing box crimper. The crimp shape of the fibers coming out of the crimper was a planar zig-zag crimp shape. The same crimp shape was retained eve...

example 3

[0135]The same resin combination of Example 2 was melt-spun at a first component extrusion temperature of 240° C., a second component extrusion temperature of 290° C. and a nozzle temperature of 260° C. The cross-sectional shape of the obtained undrawn yarn was a side-by-side shape in which the second component pushed into the first component. The undrawn yarn was drawn 2.2-fold at a drawing temperature of 60° C., and was imparted crimp in a stuffing box crimper. The crimp shape of the fibers coming out of the crimper was a planar zig-zag crimp shape. The same crimp shape was retained even after drying at 70° C. in a circulation drier. The crimp shape index was 1.18. The single-yarn fineness was 2.2 dtex and the crimp count 10.2 crimps / 2.54 cm. The fiber was cut to 5 mm using a rotary cutter, to yield the conjugate fiber for air-laid nonwoven fabric manufacture. The short fiber bulkiness was 140 cm3 / 2 g.

[0136]A web formed by an air laying process using the obtained conjugate fiber h...

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Abstract

Provided is a conjugate fiber for air-laid nonwoven fabric manufacture having a planar zig-zag crimp shape before a thermal treatment, such that a uniform web is obtained by air laying with high processability and productivity, and the conjugate fiber develops a spiral crimp when the web is subjected to a thermal treatment to thereby enable the web to shrink significantly, as a result of which a nonwoven fabric can be obtained in which fibers are amassed to a high density. The conjugate fiber for air-laid nonwoven fabric manufacture is a heat-fusible conjugate fiber in which a first component comprising an olefinic thermoplastic resin is conjugated with a second component comprising an olefinic thermoplastic resin having a melting point higher than that of the first component. The conjugate form is such that the centers of gravity of the conjugate components are mutually different in the fiber cross section, the fiber has a single-yarn fineness of 1 to 10 dtex, a fiber length of 3 to 20 mm, and a planar zig-zag crimp whose crimp shape index (actual length of short fiber / distance between both ends of short fiber) ranges from 1.05 to 1.60, and the web shrinkage upon thermal treatment at 145° C. of a web obtained by an air-laid method is not lower than 40%.

Description

TECHNICAL FIELD[0001]The present invention relates to a conjugate fiber that allows obtaining a high-density and high-basis weight air-laid nonwoven fabric. More particularly, the present invention relates to a conjugate fiber excellent in air-laying processability and productivity, having only planar crimp, so-called zig-zag crimp, before a thermal treatment, such that when an air-laid web manufactured using the conjugate fiber is subjected to a thermal treatment, latent crimp is brought out as a spiral crimp that allows the web to shrink significantly, as a result of which there is obtained a high-density and high-basis weight air-laid nonwoven fabric.[0002]The present invention further relates to a method for manufacturing a high-density air-laid nonwoven fabric using such a conjugate fiber.BACKGROUND ART[0003]Conjugate fibers having latent crimp that is developed into a spiral crimp, on account of shrinkage differences during a thermal treatment, are used, for instance, in stret...

Claims

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Application Information

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IPC IPC(8): D02G1/20D02G3/34D04H1/4291D04H1/50
CPCD01D5/32D01F8/06D04H1/06Y10T428/2924D04H1/4391D04H1/50D04H1/541D04H1/4382D04H1/732D06C7/00D10B2321/022
InventorMIYAUCHI, MINORUNISHITANI, TAKAYUKITERANAKA, MASASHI
OwnerFIBERVISIONS LP