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
2004-04-13
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...
C162S157200, C162S157400, C162S157500, C210S348000, C428S364000, C442S327000, C442S060000, C442S361000, C442S365000, C602S041000, C602S042000, C602S045000, C604S367000, C604S372000, C604S373000
Reexamination Certificate
active
06720388
ABSTRACT:
The present invention relates to polypropylene fibres and to fabrics produced from polypropylene fibres.
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 Wj 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.
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.
U.S. Pat. No. 5,648,428 discloses a process for producing a polymer blend in a single reactor, specifically a polymer blend of isotactic polyolefin and syndiotactic polyolefin which may comprise polypropylene. The single reactor is provided with a catalyst system comprising a combination of at least one metallocene catalyst and at least one conventional supported Ziegler-Natta catalyst.
These known polypropylenes suffer from the disadvantage that the processability of the iPP/sPP blends needs to be improved, particularly for spinning fibres, so that higher spinning speeds can be employed before fibre breakage occurs or the incidence of breakage at any given spinning speed is reduced.
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.
WO-A-96/35729 discloses a process for preparing and using a supported metallocene-alumoxane catalyst which is used for the polymerisation or copolymerisation of olefins to produce an olefin polymer or copolymer having a broad and bimodal molecular weight distribution.
It is an aim of the present invention to produce a blend of iPP and sPP which has improved processability, particularly when forming spun fibres. It is a further aim of the present invention to provide fibres, and fabrics in particular non-woven fabrics made from those fibres, which have been produced from that blend.
The present invention provides a polypropylene blend including from 0.3 to 50% by weight of a syndiotactic polypropylene having a multimodal molecular weight distribution and at least 50% by weight of an isotactic polypropylene.
The SPP is typically bimodal.
The isotactic polypropylene (iPP) may have been produced using a Ziegler-Natta catalyst and may be a homopolymer or copolymer and may have a monomodal or multimodal molecular weight distribution.
Preferably, the syndiotactic polypropylene (sPP) concentration in the sPP/iPP blend is from 0.3 to 15 wt %, more preferably from 1 to 10 wt %. The fibre may be a two component sPP/iPP blend.
Preferably, the iPP is a homopolymer, copolymer, being either a random or block copolymer, or terpolymer of isotactic polypropylene.
Typically, the isotactic polypropylene has a melting temperature in the range of from 159 to 169° C., more typically from 161 to 165° C. The iPP employed in accordance with the invention has a molecular weight distribution typically having a dispersion index D of from 3.5 to 9, more preferably from 3.5 to 6.5. The dispersion index D is the ratio Mw/Mn, where Mw is the weight number average molecular weight and Mn is the number average molecular weight of the polymer. The iPP typically has a peak in the molecular weight distribution of around 35,000 to 60,000 kDa. The isotactic polypropylene may have an Mn of from 35,000 to 45,000 kDa.
The isotactic polypropylene preferably has a melt flow index (MFI) of from 1 to 90 g/10 mins, more preferably from 10 to 60 g/10 mins. In this specification the MFI values are those determined using the procedure of ISO 1133 using a load of 2.16 kg at a temperature of 230° C.
The properties of two typical iPP resins for use in the invention are specified in Table 1.
The multimodal sPP, preferably bimodal sPP, is preferably a homopolymer or a random copolymer with a comonomer content of from 0.1 to 1.5 wt %, more preferably from 0.1 to 1 wt %. The multimodal sPP may however be a block copolymer with a higher comonomer content or a terpolymer. If the comonomer content is a
Atofina Research S.A.
Jackson William D.
Nutter Nathan M.
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