Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric
Reexamination Certificate
1999-07-09
2003-08-19
Mullis, Jeffrey (Department: 1711)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
C442S334000, C442S361000, C442S414000
Reexamination Certificate
active
06607996
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a biodegradable filament nonwoven fabric which is degradable by microorganisms and the like in natural environments, and to a method of producing the same. Particularly, the invention relates to a biodegradable filament nonwoven fabric which is obtainable from a polylactic acid based polymer under specific conditions, and to a method of producing the same.
BACKGROUND OF THE INVENTION
Hitherto, nonwoven fabrics which are degradable by microorganisms and the like have been known, examples thereof including degradable nonwoven fabrics composed of natural or regenerated fibers or filaments such as of cotton, flax, hemp, ramie, wool, rayon, chitin and alginic acid.
However, such degradable nonwoven fabrics, which are generally hydrophilic and water absorptive, are not suitable for use in such an application as disposable diaper top sheet which should have hydrophobic and less water absorptive properties and provide a dry tactile feeling even in a wet or moistened state. These nonwoven fabrics are much liable to deterioration in strength and dimensional stability under wet and moistened environmental conditions and, hence, find limited application in the general industrial material field. Further, the nonwoven fabrics are not thermoformable because of their non-thermoplastic property and, hence, are inferior in processability.
Therefore, positive research and development have recently been made on microbially degradable filaments which are obtainable by the melt spinning technique from microbially degradable polymers having thermoplastic and hydrophobic properties, and on microbially degradable nonwoven fabrics composed of such filaments. In particular, a group of polymers generally called aliphatic polyesters are attracting high attention because they are microbially degradable. Specific examples of such polymers include poly-&bgr;-hydroxyalkanoates as typical microbially degradable polyesters, poly-&ohgr;-hydroxyalkanoates such as polycaprolactone, polyalkylene alkanoates such as polybutylene succinate which are polycondensates of a glycol and a dicarboxylic acid, and copolymers of these polymers. In recent development of a new polymerization process which ensures efficient production of polymers of high polymerization degree, various attempts have been made to produce filaments from poly-&agr;-oxyacids such as poly-L-lactic acid and nonwoven fabrics composed of such filaments of the aforesaid aliphatic polyesters, polylactic acid in particular has a relatively high melting point, so that nonwoven fabrics composed of polylactic acid filaments are possibly useful in applications which require heat resistance. Therefore, much expectation is now directed toward practical application of the polylactic acid nonwoven fabrics.
For example, JP-A-7-126970 (1995) discloses a staple fiber nonwoven fabric composed principally of polylactic acid, and JP-A-6-212511 (1994) discloses a polylactic acid staple fibers useful for production of polylactic acid staple fiber nonwoven fabrics. However, the production of these staple fiber nonwoven fabrics involves many production steps from filament melt-spinning to nonwoven fabric formation, thereby posing a limitation to reduction in the production costs.
Further, JP-A-7-48769 (1995), JP-A-6-264343 (1994), International Nonwovens Journal, Vol. 7, No. 2, pp 69 (1995), and EP-A-0637641 suggest filament nonwoven fabrics produced from polylactic acid by a so-called spun-bond technique in which filaments are melt-extruded and deposited on a screen to form a web.
In JP-A-7-48769, however, a suggestion is simply made that a nonwoven fabric can be produced from a lactic acid polymer through the spun-bond technique, with no specific description given to the production process and the physical properties of the resulting nonwoven fabric. In JP-A-6-264343, which pertains to a microbially degradable filament aggregate for agricultural use, there is no detailed statement about critical production conditions such as a filament drafting speed and the like, nor any teaching on the physical properties of the resulting nonwoven fabric. The teaching of International Nonwovens Journal, Vol. 7, No. 2, pp 69 (1995) is merely such that a hard and brittle plate-like polylactic acid spun-bonded fabric was obtained. In EP-A-0637641, there is no teaching that a polylactic acid spun-bonded fabric excellent in flexibility and mechanical strength was produced.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a polylactic acid based filament nonwoven fabric which is degradable by microorganisms and the like in natural environments and excellent in mechanical strength and flexibility for practical use.
In accordance with a first aspect of the present invention to accomplish this object, there is provided a nonwoven fabric composed of monocomponent filaments of a polylactic acid based polymer, the polylactic acid based polymer being selected from the group consisting of poly-D-lactic acid, poly-L-lactic acid, copolymers of D-lactic acid and L-lactic acid, copolymers of D-lactic acid and a hydroxycarboxylic acid, and copolymers of L-lactic acid and a hydroxycarboxylic acid which have melting points of not lower than 100° C., and blends of any of these polymers which have melting points of not lower than 100° C., the polylactic acid based filaments having a birefringence of 10×10
−3
to 25×10
−3
, a degree of crystallinity of 12 to 30 wt % and a crystal size of not greater than 80 Å as measured axially of the filaments, the nonwoven fabric having a boiling water shrinkage percentage of not higher than 15%.
In accordance with a second aspect of the present invention, there is provided a nonwoven fabric composed of modified cross-section or composite filaments of a polylactic acid based polymer, the polylactic acid based polymer being selected from the group consisting of poly-D-lactic acid, poly-L-lactic acid, copolymers of D-lactic acid and L-lactic acid, copolymers of D-lactic acid and a hydroxycarboxylic acid, copolymers of L-lactic acid and a hydroxycarboxylic acid, copolymers of D-lactic acid, L-lactic acid and a hydroxycarboxylic acid, which have melting points of not lower than 100° C., and blends of any of these polymers which have melting points of not lower than 100° C., the polylactic acid based filaments having a degree of crystallinity of 12 to 30 wt % and a crystal size of not greater than 80 Å as measured axially of the filaments, the nonwoven fabric having a boiling water shrinkage percentage of not higher than 15%.
In accordance with a third aspect of the present invention, there is provided a method of producing a nonwoven fabric composed of polylactic acid based filaments, the method comprising the steps of: melting a polylactic acid based polymer at a temperature of (Tm+20)° C. to (Tm+80)° C. (wherein Tm is the melting point of the polylactic acid based polymer) and extruding the resulting melt through a spinneret into filaments; drafting the resulting filaments at a drafting speed of 3,000 to 6,500 m/min by means of a suction device; spreading open each other and accumulating the drafted filaments on a movable collector surface thereby to form a web; and heat-treating the web; wherein the polylactic acid based polymer is selected from the group consisting of poly-D-lactic acid, poly-L-lactic acid, copolymers of D-lactic acid and L-lactic acid, copolymers of D-lactic acid and a hydroxycarboxylic acid, copolymers of L-lactic acid and a hydroxycarboxylic acid, and copolymers of D-lactic acid, L-lactic acid and a hydroxycarboxylic acid, which have melting points of not lower than 100° C., and blends of any of these polymers which have melting points of not lower than 100° C., and has a melt flow rate of 10 to 100 g/10 min as measured at 210° C. in conformity with ASTM-D-1238.
The polylactic acid based filament nonwoven fabrics according to the present invention are degradable by microorganisms and the like in natural environments, and excelle
Matsunaga Atsushi
Matsunaga Mamiko
Nagaoka Koichi
Harness & Dickey & Pierce P.L.C.
Mullis Jeffrey
Tomoegawa Paper Co. Ltd.
LandOfFree
Biodegradable filament nonwoven fabric and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Biodegradable filament nonwoven fabric and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Biodegradable filament nonwoven fabric and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3094406