Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric
Reexamination Certificate
2000-05-31
2003-04-15
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
C442S361000, C442S362000, C442S364000, C442S382000, C442S389000, C442S400000, C442S401000
Reexamination Certificate
active
06548432
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyethylene nonwoven fabric and a laminate comprising the same. More particularly, the present invention relates to a polyethylene nonwoven fabric having a small diameter of fibers making up the nonwoven fabric and good formation as well as to a nonwoven fabric laminate having excellent softness, water impermeability and interlaminar bond properties obtained using the polyethylene nonwoven fabric.
TECHNICAL BACKGROUND
It is known that nonwoven fabrics prepared using polyethylene fibers are soft and comfortable to the touch. However, due to general difficulty in spinning of polyethylene fibers, polyethylene nonwoven fabrics prepared by the conventional meltblowing process have a larger fiber diameter and poor formation. In order to reduce the fiber diameter of polyethylene fibers, it was necessary to elevate a spinning temperature but in this case, gel formation tends to occur sometimes.
It was then attempted to form fibers using a polyethylene of a lower molecular weight than that of a general-purpose polyethylene resin, e.g., a polyethylene wax. However, it was difficult to produce a web continuously, since such a low molecular weight polyethylene had a poor single yarn strength and caused serious fuzzing though its spinnability was good.
Japanese Patent Laid-Open Publication No. 63-165511 discloses a method for preparing polyethylene fibers which comprises blending a linear low density polyethylene having a melt index of less than 40 with a low molecular weight polyethylene having a melt index of 40 or more and one or two members selected from liquid paraffin and then melt-extruding the blend at a particular temperature, thereby to allegedly obtain nonwoven fabrics having a fine fiber in size and soft touch. However, the fiber diameter of the nonwoven fabric produced by the method is at best up to 2 denier (approximately 18 &mgr;m), which is not fine enough.
Therefore, an object of the present invention is to provide a polyethylene nonwoven fabric, which has a very small diameter of fibers and excellent uniformity. Another object of the present invention is to provide a nonwoven fabric laminate having excellent softness, water impermeability and interlaminar bond properties, using the polyethylene nonwoven fabric.
DISCLOSURE OF THE INVENTION
To achieve the foregoing objects, the present invention provides a polyethylene nonwoven fabric produced from a resin composition comprising a polyethylene (A) and a polyethylene wax (B) by the meltblowing process.
To achieve the foregoing objects, the present invention also provides a nonwoven fabric laminate comprising a plurality of nonwoven fabric layers, in which at least one of the nonwoven fabric layers is a layer comprising the above-mentioned polyethylene nonwoven fabric.
BEST EMBODIMENT OF THE INVENTION
The polyethylene nonwoven fabric of the invention (hereinafter referred to as “nonwoven fabric of the invention”) and the nonwoven fabric laminate comprising the same will be described below in more detail.
The nonwoven fabric of the invention contains the fibers comprising a resin composition comprising a polyethylene (A) and a polyethylene wax (B).
The polyethylene (A) in accordance with the present invention which is the essential component for forming the fibers to constitute the nonwoven fabric of the invention includes a homopolymer of ethylene and a copolymer of ethylene and other monomer(s). The copolymer may be a random copolymer or a block copolymer. The other monomers include &agr;-olefins having 3 to 20 carbon atoms such as propylene, 1-butene, 1-pentene, 1-hexene, 4-metyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene. Specific examples of this polyethylene are copolymers of ethylene with &agr;-olefins such as 4-methyl-1-pentene and 1-hexene. In the copolymers, the ethylene monomeric unit content is generally at least 80 mol %, preferably in the range of 90 to 99.5 mol % as determined by
13
C-NMR.
As the fibers making up the nonwoven fabric of the invention, these polyethylenes may be employed alone or in combination of two or more.
According to the present invention, the polyethylene (A) has preferably a weight-average molecular weight (Mw) in the range of 21,000 to 45,000, more preferably 23,000 to 40,000, in terms of spinnability and kneading compatibility with the polyethylene wax (B). In the present invention, the weight-average molecular weight (Mw) was determined by gel permeation chromatography under the following conditions.
Apparatus Used
Measurement apparatus: Gel permeation chromatograph (manufactured by Waters Inc., Model 150-C)
Analyzer: System controller (manufactured by Toso Corporation, Model SC-8010)
Detector: Differential refractometer
Conditions for Measurement
Column: TSK gel GMH
6
-HT×1+TSK gel GMH
6
-HTL×1 (7.8 mm
ID
×60 mm
L
, manufactured by Toso Corporation)
Moving phase: o-Dichlorobenzene (hereinafter abbreviated as ODCB)
Stabilizer for the moving phase: 2,6-di-tert-butyl-p-cresol (5 g/20 kg-ODCB)
Column temperature: 140° C.
Flow rate: 1.0 ml/min
Feeding volume: 500 &mgr;l
Concentration of a sample measured: 30 mg/20 ml-ODCB
Concentration of the standard sample: 15 mg/20 ml-ODCB
Molecular weight calibration: monodispersed 16 polystyrenes (manufactured by Toso Corporation)
It is preferred that the polyethylene (A) has a density preferably in the range of 0.890 to 0.970 g/cm
3
, more preferably 0.910 to 0.960 g/cm
3
, most preferably 0.930 to 0.955 g/cm
3
. In the present invention, the density of the polyethylene (A) is determined by means of a density gradient tube using a strand, which has been obtained at the time of measurement of a melt flow rate (MFR) at 190° C. under a load of 2.16 kg and which is treated by heating at 120° C. for 1 hour and slowly cooling to room temperature over 1 hour.
The melt flow rate (MFR) of the polyethylene (A), which has been determined in accordance with ASTM D1238 under the conditions of a temperature of 190° C. and a load of 2.16 kg is in the range of generally 15 to 250 g/10 mins., preferably 20 to 200 g/10 mins., more preferably 30 to 200 g/10 mins.
The polyethylene wax (B) which is also the essential component of the fibers making up the nonwoven fabric in accordance with the present invention includes a homopolymer of ethylene and a copolymer of ethylene with other polymerizable monomer(s). As the polymerizable monomers there are the same monomers given as &agr;-olefins for the polyethylene (A). Where a copolymer is used as the polyethylene wax (B), the ethylene monomer unit is contained in the range of generally 80 mol % or more, preferably 90 to 99.5 mol % (as determined by by
13
C-NMR).
The softening point of the polyethylene wax (B) is preferably between 110 and 145° C. In view of spinnability and kneading compatibility with the polyethylene (A), the weight-average molecular weight (Mw) of the polyethylene wax (B) is preferably 15,000 or less, more preferably in the range of 6,000 to 12,000.
The polyethylene wax (B) may be prepared either by polymerization of a low molecular weight polymer conventionally used or by reducing the molecular weight of a high molecular weight polyethylene through thermal degradation. There is no particular restriction how to prepare the polyethylene wax (B).
In the resin composition which forms the fibers making up the polyethylene nonwoven fabric of the invention, a weight ratio of the polyethylene (A) to the polyethylene wax (B), namely, (A)/(B) is preferably in the range of 90/10 to 10/90, more preferably 30/70 to 70/30, most preferably 40/60 to 60/40.
The melt flow rate (MFR) of the resin composition above, which has been determined in accordance with ASTM D1238 under the conditions of a temperature of 190° C. and a load of 2.16 kg is in the range of preferably 300 to 600 g/10 mins., more preferably 400 to 550 g/10 mins.
The resin composition of the present invention may further contain, if necessary and desired, optional components such as other polymers, coloring agents, stabilizers,
Hisada Minoru
Motomura Shigeyuki
Birch & Stewart Kolasch & Birch, LLP
Mitsui Chemicals Inc.
Morris Terrel
Wachtel Alexis
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