Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2002-05-21
2003-11-11
Edwards, N. (Department: 3765)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S395000, C264S103000, C264S210500, C264S210800
Reexamination Certificate
active
06645621
ABSTRACT:
The present invention relates to PTT staple fibres [where PTT equals poly(trimethylene terephthalate)] and to a process for the production thereof by a two-stage spinning and stretching process.
Staple fibres made from polyethylene terephthalate and melt-spinning plants for their production are known (Fourné, Synthetische Fasern [Synthetic Fibres], Hanser Verlag [1995] pages 460-462). Owing to the different crystallization behaviour, these processes cannot readily be applied to PTT.
Processes for the production of PTT continuous filaments have also been described. Thus, Journal of Polymer Science, Part A-1, Vol. 4, 1851-1857 (1966) mentions, inter alia, PTT fibres. The high stretching ratios specified indicate an uneconomically low spinning speed. The fibre properties listed do not meet today's market requirements.
EP 0 547 553 A1 describes the production of monofilaments at a spinning speed of 20 m/min and a production speed of 100 m/min.
EP 0 754 790 A2 describes the production of textile filaments, inter alia from PTT, by means of heating surfaces heated to high temperatures as stretching aids. There are no specific working examples.
WO 99/11845 A1 describes fibres made from PTT with a birefringence of at least 0.030. The parameters given indicate low elongation at break values of ≦90%, which do not facilitate a stretching ratio that is sufficiently high for further conversion into staple fibres and are therefore unsuitable.
WO 99-27168 A1 discloses a high-speed spin-stretch process for the production of PTT filaments which are wound onto yam spools. High throughputs and tow baling for the production of staple fibres cannot be derived therefrom.
CA 86:122866 regarding JP 52-08124 A relates to the treatment of PTT multifilaments with heating devices, where the stretching ratio of 33% to be applied is unsuitable for the production of staple fibres.
CA 86:122865 regarding JP 52-08123 A describes the use of a high stretching ratio of 300%, which is desired per se, in the production of PTT fibres. However, the spinning speed of 360 m/min which is practised to this end is so low that the economic efficiency of the process is put in doubt.
CA 86:122856 regarding JP 52-05320 A describes the spinning of PTT, where the stretching ratio practised indicates uneconomically low spinning speeds.
The object of the present invention is to provide PTT staple fibres, where these and the textiles and home textiles, in particular carpets, produced therefrom should have a high aesthetic level and service quality compared with conventional fibres and should have environmentally friendly dyeing properties. These PTT staple fibres should be produced in a two-stage process of melt spinning and stretching which has higher economic efficiency than the above-mentioned processes for continuous filaments.
This object is achieved in accordance with the invention by PTT staple fibres and by a process for the production of PTT staple fibres having an intrinsic viscosity of at least 0.70 dl/g as described in the patent claims.
The term PTT here is taken to mean a polyester comprising at least 90 mol% of trimethylene terephthalate units. Suitable comonomers are isophthalic acid, 2,6-naphthalenedicarboxylic acid, ethylene glycol, diethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol. Preference is given to poly(trimethylene terephthalate) homopolymer, particularly preferably with a low proportion of ether groups derived from 1,3-propanediol which are formed during the production process. The intrinsic viscosity of the PTT staple fibres is in the range from 0.7 to 1.3 dl/g and particularly preferably from 0.75 to 1.15 dl/g.
The process commences from PUT melt, which is either taken directly from the polycondensation reactor in the preparation of PTT or is obtained by melting PTT granules. The polymer melt may comprise conventional additives, such as dyes, matting agents, stabilisers, antistatics, lubricants and branching agents, in total amounts of from 0 to 5.0% by weight, or the additives can be added to the melt on its way to the spinnerets. Additives which significantly affect structural parameters (for example elongation at break of the strand) are excluded.
In accordance with the invention, PTT staple fibres are produced, preferably with a titre of from 0.8 to 20 den, by a two-stage spinning and stretching process which comprises the following steps:
1. The PTT melt, having a polymer melting point T
m
, is fed to the spinning system at a melt temperature T
S
=T
m
+k (° C.), where 7≦k≦63, preferably 2 ≦k≦41. The transport and distribution of the melt as far as the spinning beam take place here in jacketed product lines, which are heated with liquid and/or vapour-form heat transfer medium in the outer jacket of the lines at a temperature in the range from 234 to 290° C. Other types of heating are possible. The wall shear rates of the melt in the line system are from 2 to 128 sec
−1
, preferably from 3.5 to 16 sec
−1
, in the pipelines and from 12 to 128 sec
−1
in static mixing elements installed within certain line sections. The shear rate &ggr; here is defined by the empty pipe shear rate times the mixer factor m, where the mixer factor is a characteristic parameter of the mixer type and is about 3.5-4 for Sulzer SMXL models. The shear rate &ggr; in sec
−1
is calculated from
γ
γ
=
4
·
10
3
·
G
π
·
δ
·
R
3
·
60
·
m
where G=polymer transport rate (g/min),
&dgr;=nominal density of the polymer (g/cm
3
),
R=empty pipe radius [mm].
The mean residence time of the melt in the product line as far as entry into the spinning beam is a maximum of 30 minutes, preferably a maximum of 25 minutes. The line temperature T
1
is preferably set within the above limits in such a way that it is in the range T
1
=T
S
±15° C. The product line optionally includes at least one booster pump, at least one polymer filter, at least one polymer heat exchanger and at least one shut-off and distribution valve.
2. In the spinning beam, the PTT melt is fed to at least one spinning pump, fed at a constant transport rate, set through the choice of the pump speed, to at least one spin pack by means of the pressure built up by the pump and forced through distributor devices, filter and shear media within the spin pack and spun through the holes of the spinneret plate to give melt strands. The spinneret holes may be circular or designed in any desired other geometry.
The spin pack can be inserted into the spinning beam from below and can have a cylindrical geometry, with the holes in the spinneret plate being distributed symmetrically over an annular area.
The spinneret plates have a hole density of from 0.3 to 20 holes/cm
2
. The spinneret hole diameter D is selected as a function of the hole throughput in accordance with
F
(
g
/
min
)
ζ
(
g
/
cm
3
)
·
π
·
2
2
≥
D
(
mm
)
≥
F
(
g
/
min
)
ζ
(
g
/
cm
3
)
·
π
·
7
2
where &zgr; is the density of the melt and, for homo-PTT, is 1.11 g/cm
3
.
The flow rate F per spinneret hole, based on the fibre titre, is in the range F(g/min)/titre(dtex)=(0.14 to 0.66).
The residence time of the melt in the spin pack is at most 4 minutes. The spinning draft is selected between 1:30 and 1:160 and is determined in a known manner from the ratio of the take-off rate to the injection rate at the spinneret holes.
The heating of the spinning beam is selected in the range 234-290° C. in such a way that the following relationship applies: T
B
(° C.)=T
S
+dT
W
+4/100 dp(bar)±15, where dT
W
=change in the melt temperature in the heat exchanger, which is set positive for heating and negative for cooling and is equal to 0 in the case of plants with no heat exchanger, dp(bar)=total pressure drop of the melt as far as the exit from the spinne
Cordes Ingo
Kellner Christian
Mirwaldt Ulrich
Wandel Dietmar
Edwards N.
Lurgi Zimmer AG
Norris & McLaughlin & Marcus
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