Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-01-24
2003-11-11
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000, C526S290000, C526S351000
Reexamination Certificate
active
06646051
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polypropylene fibres and to fabrics produced from polypropylene fibres.
DESCRIPTION OF RELATED ART
Polypropylene is well known for the manufacture of fibres, particularly for manufacturing non woven fabrics.
EP-A-0789096 discloses such polypropylene fibres which are made of a blend of syndiotactic polypropylene (sPP) and isotactic polypropylene (iPP). That specification discloses that by blending from 0.3 to 3% by weight of sPP, based on the total polypropylene, to form a blend of iPP-sPP, the fibres have increased natural bulk and smoothness, and non-woven fabrics produced from the fibres have an improved softness. Moreover, that specification discloses that such a blend lowers the thermal bonding temperature of the fibres. Thermal bonding is employed to produce the non-woven fabrics from the polypropylene fibres.
The specification discloses that the isotactic polypropylene comprises a homopolymer formed by the polymerisation of propylene by Ziegler-Natta catalysis. The isotactic polypropylene typically has a weight average molecular weight Mw of from 100,000 to 4,000,000 and a number average molecular weight Mn of from 40,000 to 100,000, with a melting point of from about 159 to 169° C. However, the polypropylene fibres produced in accordance with this specification suffer from the technical problem that the isotactic polypropylene, being made using a Ziegler-Natta catalyst, does not have particularly high mechanical properties, particularly tenacity.
WO-A-96/23095 discloses a method for providing a non-woven fabric with a wide bonding window in which the non-woven fabric is formed from fibres of a thermoplastic polymer blend including from 0.5 to 25 wt % of syndiotactic polypropylene. The syndiotactic polypropylene may be blended with a variety of different polymers, including isotactic polypropylene. The specification includes a number of examples in which various mixtures of syndiotactic polypropylene with isotactic polypropylene were produced. The isotactic polypropylene comprised commercially available isotactic polypropylene, which is produced using a Ziegler-Natta catalyst. It is disclosed in the specification that the use of syndiotactic polypropylene widens the window of temperature over which thermal bonding can occur, and lowers the acceptable bonding temperature.
WO-A-96/23095 also discloses the production of fibres from blends including syndiotactic polypropylene which are either bi-component fibres or bi-constituent fibres. Bi-component fibres are fibres which have been produced from at least two polymers extruded from separate extruders and spun together to form one fibre. Bi-constituent fibres are produced from at least two polymers extruded from the same extruder as a blend. Both bi-component and bi-constituent fibres are disclosed as being used to improve the thermal bonding of Ziegler-Natta polypropylene in non-woven fabrics. In particular, a polymer with a lower melting point compared to the Ziegler-Natta isotactic polypropylene, for example polyethylene, random copolymers or terpolymers, is used as the outer part of the bi-component fibre or blended in the Ziegler-Natta polypropylene to form the bi-constituent fibre.
EP-A-0634505 discloses improved propylene polymer yarn and articles made therefrom in which for providing yarn capable of increased shrinkage syndiotactic polypropylene is blended with isotactic polypropylene with there being from 5 to 50 parts per weight of syndiotactic polypropylene. It is disclosed that the yarn has increased resiliency and shrinkage, particularly useful in pile fabric and carpeting. It is disclosed that the polypropylene blends display a lowering of the heat softening temperature and a broadening of the thermal response curve as measured by differential scanning calorimetry as a consequence of the presence of syndiotactic polypropylene.
U.S. Pat. No. 5,269,807 discloses a suture fabricated from syndiotactic polypropylene exhibiting a greater flexibility than a comparable suture manufactured from isotactic polypropylene. The syndiotactic polypropylene may be blended with, inter alia, isotactic polypropylene.
EP-A-0451743 discloses a method for moulding syndiotactic polypropylene in which the syndiotactic polypropylene may be blended with a small amount of a polypropylene having a substantially isotactic structure. It is disclosed that fibres may be formed from the polypropylene. It is also disclosed that the isotactic polypropylene is manufactured by the use of a catalyst comprising titanium trichloride and an organoaluminium compound, or titanium trichloride or titanium tetrachloride supported on magnesium halide and an organoaluminium compound, i.e. a Ziegler-Natta catalyst.
EP-A-0414047 discloses polypropylene fibres formed of blends of syndiotactic and isotactic polypropylene. The blend includes at least 50 parts by weight of the syndiotactic polypropylene and at most 50 parts by weight of the isotactic polypropylene. It is disclosed that the extrudability of the fibres is improved and the fibre stretching conditions are broadened.
EP-A-0894875 discloses bicomponent fibres of isotactic and syndiotactic polypropylene in which an isotactic polypropylene component and a syndiotactic polypropylene component are each fused to the other along the fibre axis. This specification does not address the problem of the manufacture of non-woven fabrics by thermal bonding.
EP-A-0832924 relates to a polyolefin moulding composition for producing high strength non-woven fabric.
WO-A-97/10300 discloses polypropylene blend compositions comprising propylene copolymer having a broad molecular weight distribution. The first and second propylene polymers of the blend are preferably isotactic.
EP-A-0870779 discloses a metallocene catalyst system for producing a polypropylene blend of iso- and syndiotactic polypropylene.
EP-A-0284707 discloses a hafnium metallocene catalyst for the polymerisation of olefins, in particular to make isotactic polypropylene.
EP-A-0427696 discloses a process and catalyst for producing syndiotactic polymers, in particular syndiotactic polypropylene using metallocene catalysts.
It is further known to produce syndiotactic polypropylene using metallocene catalysts as has been disclosed for example in U.S. Pat. No. 4,794,096.
Recently, metallocene catalysts have also been employed to produce isotactic polypropylene. Isotactic polypropylene which has been produced using a metallocene catalyst is identified hereinafter as miPP. Fibres made of miPP exhibit much higher mechanical properties, mainly tenacity, than typical Ziegler-Natta polypropylene based fibres, hereinafter referred to as znPP fibres. However, this gain in tenacity is only partly transferred to non-woven fabrics which have been produced from the miPP fibres by thermal bonding. Indeed, fibres produced using miPP have a very narrow thermal bonding window, the window defining a range of thermal bonding temperatures through which, after thermal bonding of the fibres, the non-woven fabric exhibits the best mechanical properties. As a result, only a small number of the miPP fibres contribute to the mechanical properties of the non-woven fabric. Also, the quality of the thermal bond between adjacent miPP fibres is poor. Thus known miPP fibres have been found to be more difficult to thermally bond than znPP fibres, despite a lower melting point.
SUMMARY OF THE INVENTION
It is an aim of the present invention to broaden the thermal bonding window of miPP fibres. It is a further aim of the invention to provide non-woven fabrics of miPP fibres exhibiting improved mechanical properties, in particular tenacity.
It is known that polypropylene fibres, and non-woven fabrics made of polypropylene fibres, tend to feel rough to the touch. It is also an aim of the present invention to improve the softness of miPP polypropylene fibres.
The present invention provides a polypropylene fibre including a polypropylene blend comprising up to 15% by weight of sPP, at least 10% by weight of a first isotactic polypropylene produced
Atofina Research
Jackson William D.
Nutter Nathan M.
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