Elastic polyurethane yarn and method of manufacturing the same

The present invention relates to melt-spun polyurethane elastic fiber having a degree of luster of 70 or less, the degree of luster being defined as (I/Io).times.100 where the amount of light reflecting off the surface of the fiber is I and the amount of light reflecting off a standard white plate is Io. On the surface of preferable polyurethane elastic fiber, 10 or more mountain-like protrusions of 0.2 to 5.05 to 110 parts by weight of 5 to 110 parts by weight of .mu.m in height are present every 10 .mu.m fiber in the axial direction. Also, the present invention relates to a process for producing polyurethane elastic fiber, comprising melt-spinning butylene terephthalate-based crystalline polyester (A) and thermoplastic polyurethane (B) wherein before spinning, the compound (A) is melt-mixed with thermoplastic polyurethane (B-1) having isocyanate groups in an amount of 150 to 500 .mu.mol/g. Further, the present invention relates to covered fiber comprising the polyurethane elastic fiber as a core. Even if stockings, tights, sox etc. are produced using the covered fiber of the present invention, the luster phenomenon as the drawback of particularly melted spun urethane does not occur, so it is possible to obtain products with excellent appearance.

FIELD OF THE INVENTION 
The present invention relates to polyurethane elastic fiber and a process 
for producing the same. 
BACKGROUND OF THE INVENTION 
The polyurethane elastic fiber has excellent stretching properties and is 
widely used in the fields of hosiery, underwear, sportswear etc. 
Known processes for producing the polyurethane elastic fiber include a wet 
spinning method where a polyurethane solution is extruded and coagulated 
by passage through a coagulation bath, a dry spinning method where solvent 
is vaporized with hot air, or a melt spinning method where thermoplastic 
polyurethane is melted and extruded followed by solidification by cooling 
with air. Among these spinning processes, the melt spinning process is 
particularly advantageous in that organic solvent with strong possibility 
of polluting the human body and the environment is not used, so this 
process recently has attracted considerable attention as a spinning 
process which is not detrimental to the environment. 
The melt spinning process is a process in which melted polyurethane is 
extruded through a spinning nozzle into air, solidified by cooling and 
wound as described above, so unlike the dry or wet spinning process, no 
volatiles are contained from the melting step to the cooling and 
solidification step. Accordingly, this melt spinning process is 
characterized in that the surface of the resulting fiber is frat and free 
of the uneven surface generated upon removal of volatiles from the inside 
of the fiber. Because of these characteristics, the polyurethane elastic 
fiber produced by the melt-spinning process is superior in wear resistance 
and further possesses the property of glistening. 
However, relatively thin knitted goods such as stockings, tights, sox etc. 
have the disadvantage of too high glistening due to the above surface 
property of polyurethane elastic fiber. For example, black knitted goods 
generate glossy black luster. In stockings, tights, sox etc. made of 
covered fiber having nylon fiber etc. wound around the polyurethane 
elastic fiber, this luster phenomenon occurs very significantly due to 
relatively low degrees of coverage on the polyurethane elastic fiber. 
To reduce the luster phenomenon, there is a method of increasing the number 
of twisting in the covering step in order to increase degrees of coverage. 
However, there is the disadvantage that the fiber is felt hard in 
proportion with an increase in the number of twisting for coverage. 
Further, there is also a method of dyeing the polyurethane elastic fiber 
darkly (e.g. black). However, the reduction in luster attained in this 
method is slight so significant improvements cannot be achieved. 
There is also a known method of decreasing the luster phenomenon by 
roughening the surface of fiber. For example, there is a general method of 
roughening the surface of polyethylene terephthalate fiber by mixing 
inorganic fine particles with a polymer to form fiber and then dissolving 
and removing the surface of the fiber with a chemical such as alkali etc. 
to cause the inorganic fine particles to be removed therefrom so that the 
surface of the fiber is roughened. 
Although this method is effective for polyethylene terephthalate fiber, it 
cannot be applied to polyurethane elastic fiber because there is no 
suitable chemical which can dissolve and remove the fiber surface. 
Further, there is a method in which a large amount (e.g. about 30 to 40% by 
weight) of inorganic fine particles are previously mixed with a 
polyurethane polymer and melt-spun, and the surface of the resulting fiber 
is roughened in the step of solidifying the fiber by cooling. In this 
method, however, because a large amount of inorganic particles are 
contained in the polymer, the melt fluidity of the polymer is lowered, and 
in melt spinning, the polymer clogs a spinning nozzle, or fiber cutting 
frequently occurs to make spinning substantially infeasible. Even if 
spinning is feasible, the physical properties of fiber, such as strength, 
elongation etc. are significantly deteriorated. 
In production of polyurethane elastic fiber by the dry spinning process, 
concave portions are generated after solvent is removed by heating for 
removal of volatiles. Further, there may occur cracking etc. in fiber by 
thermal deterioration, but there are a small number of concave portions, 
cracking is not significant, thus making the state of luster high. 
However, in polyurethane elastic fiber produced by the dry spinning 
process, upon being formed into knitted goods and then subjected to a 
dyeing step, a large number of concave portions and a large number of 
cracks are generated on the surface of the fiber because of removal of 
volatiles from the inside of the elastic fiber through the surface of the 
fiber to the outside, so the actual product has few problems resulting 
from the luster phenomenon. 
However, knitted goods produced without undergoing a wet-heating step, for 
example tights etc. produced by previously dyeing nylon fiber as covering 
fiber, have high degrees of luster because volatiles in the inside of the 
polyurethane elastic fiber are not discharged to the outside. 
Japanese Patent Publication No. 45684/1993 discloses a method of producing 
polyurethane elastic fiber by compounding aliphatic saturated dicarboxylic 
acid in an amount of 0.1 to 5 weight-% with polyurethane followed by dry 
spinning to produce polyurethane elastic fiber having a large number of 
uneven portions on the surface of the fiber. That is, this method is 
different from the present invention in that the aliphatic saturated 
dicarboxylic acid is compounded and the dry spinning method is used. The 
effect of the invention is also different between the present invention 
and this prior art method in that the former is directed to reduction in 
luster while the latter to improvements in stretching properties and 
traveling smoothness. 
Further, the method described in the above-described patent publication is 
different from the present invention in that uneven portions on the 
surface of the fiber in the former are wavy (mountain range-like) while 
those in the latter are independent mountain-like protrusions. If the 
fiber is stretched for use, the uneven portions on the fiber surface 
disappear in the case of the wavy shape. On the other hand, the 
independent mountain-like protrusions such as those in the present 
invention maintain the uneven portions on the fiber surface. From this 
difference, the fiber of the present invention brings about significant 
reduction in the luster phenomenon. This difference in the effect is 
brought about by adopting the above constitution of the present invention. 
A mixture of crystalline polyester based on polybutylene terephthalate and 
polyurethane is disclosed in Japanese Laid-Open Patent Publication Nos. 
53448/1975, 50350/1977, 102365/1977, 9851/1978, 263457/1991, 275364/1992, 
275365/1992, 313093/1994, 3135/1995 and 3136/1995 respectively. However, 
none of these publications disclose that the isocyanate group content in 
polyurethane is the range of the present invention. 
Further, any of these publications are directed to molded articles which 
are not to be formed into fiber. Although the present inventor attempted 
to form these particles by spinning into fiber, fiber cutting was 
significant, thus making winding-up difficult or even if it could be 
wound, innumerable nodal defects occurred and adequate elongation could 
not be obtained. Further, mountain-like protrusions were observed on the 
surface of the wound fiber but the majority of them had a height exceeding 
5.0 .mu.m to fail to achieve the effect of preventing luster. 
The present invention is to provide polyurethane elastic fiber which is 
free of the luster phenomenon as well as a process for producing the same. 
According to the process of the present invention, high-melting butylene 
terephthalate-based crystalline polyester (A) is first solidified and then 
stretched in draft and cooling steps where a melted polymer, discharged 
from a nozzle in a spinning step, is stretched in high draft and 
solidified. Hence, a large amount of mountain-like protrusions are 
generated on the surface of the fiber, and the polyurethane elastic fiber 
of the present invention can thereby be produced. 
DISCLOSURE OF THE INVENTION 
The present invention relates to (1) melt-spun polyurethane elastic fiber 
having a degree of luster of 70 or less, the degree of luster being 
defined as (I/Io).times.100 where the amount of light reflecting off the 
surface of the fiber is I and the amount of light reflecting off a 
standard white plate is Io. A preferred embodiment is (2) polyurethane 
elastic fiber according to item (1) above wherein 10 or more mountain-like 
protrusions of 0.2 to 5.0 .mu.m in height are present every 10 .mu.m fiber 
in the axial direction. A further preferred embodiment is (3) polyurethane 
elastic fiber according to item (2) above wherein 15 to 60 mountain-like 
protrusions are present. 
Also, the present invention relates to: (4) a process for producing 
polyurethane elastic fiber, comprising melt-spinning butylene 
terephthalate-based crystalline polyester (A) and thermoplastic 
polyurethane (B) wherein before spinning, the compound (A) is melt-mixed 
with thermoplastic polyurethane (B-1) having isocyanate groups in an 
amount of 150 to 500 .mu.mol/g; (5) a process for producing polyurethane 
elastic fiber according to item (4) above wherein (A) and (B-1) are mixed 
at a ratio of 100 parts by weight of (B-1) to 5 to 110 parts by weight of 
(A); (6) a process for producing polyurethane elastic fiber according to 
item (4) or (5) wherein another thermoplastic polyurethane (B-2) is added 
such that the weight ratio of (A), that is, (A)/{(A)+(B-1)+(B-2)} is in 
the range of 0.05 to 0.2; (7) a process for producing polyurethane elastic 
fiber according to any one of items (4) to (6) wherein thermoplastic 
polyurethane (B-1) having isocyanate groups in amount of 150 to 500 
.mu.mol/g is produced by compounding the isocyanate compound with polyols 
in such amounts that the ratio of the number of moles of isocyanate groups 
to the number of moles of hydroxyl groups is 1.07 to 1.28; (8) covered 
fiber comprising the polyurethane elastic fiber of item (1), (2) or (3) 
above as a core; and (9) stockings, tights or sox comprising the covered 
fiber of item (8) above. 
BEST EMBODIMENT FOR CARRYING OUT THE INVENTION 
Polyurethane elastic fibers were spun by the above methods or under other 
conditions than those of the above-described methods and used to produce 
panty stockings, which were further dyed and finished or not dyed, and the 
panty stockings thus produced were worn and evaluated visually for the 
state of luster outdoors i.e. under sunlight. Then, the panty stockings 
were divided into a permissible group and an impermissible group in terms 
of the degree of luster. Further, the degree of luster of each 
polyurethane elastic fiber corresponding to each panty stocking was 
determined in the method described in the Examples. 
The results indicated that the degrees of luster of all polyurethane 
elastic fibers corresponding to the panty stockings in the permissible 
group were 70 or less, while the degrees of luster of all polyurethane 
elastic fibers corresponding to the panty stockings in the impermissible 
group exceeded 70. 
If the degree of luster exceeds 70, the amount of sunlight reflecting off 
the polyurethane elastic fiber is substantially high, and the resulting 
panty stockings glisten to cause the luster phenomenon. If the degree of 
luster is 70 or less, the reflection of light is less, so the visual 
impression of luster is not bring about. That is, the boundary at which 
luster is substantially felt or not lies in the degree of luster of 70. 
The polyurethane elastic fiber of the present invention is polyurethane 
elastic fiber with a degree of luster of 70 or less and has preferably 
fine mountain-like protrusions with a height of 0.2 to 5.0 .mu.m, more 
preferably 0.2 to 3.0 .mu.m on the surface of the fiber. If the height of 
the protrusion is less than the above-described lower limit, the effect of 
lowering fiber luster is inadequate, while the height exceeds the 
above-described upper limit, the effect of preventing luster cannot be 
obtained. 
In addition, 10 or more, preferably 15 to 60 and more preferably 19 to 50 
protrusions are present every 10 .mu.m fiber in the axial direction. Given 
protrusions less than the above-described lower limit, fiber luster cannot 
be reduced. 
The polyurethane elastic fiber of the present invention is produced by the 
melt spinning process. Preferably, the polyurethane elastic fiber can be 
produced by the process for producing polyurethane elastic fiber, 
comprising melt-spinning butylene terephthalate-based crystalline 
polyester (A) and thermoplastic polyurethane (B) wherein before spinning, 
the compound (A) is melt-mixed with thermoplastic polyurethane (B-1) 
having isocyanate groups in an amount of 150 to 500 .mu.mol/g. 
The relative viscosity of butylene terephthalate-based crystalline 
polyester (A) ranges preferably from 1.7 to 3.0, more preferably from 1.8 
to 2.4. When the relative viscosity exceeds the upper limit, the viscosity 
of the resulting melt is too high, thus causing inadequate mixing with 
polyurethane, and if the relative viscosity is less than the lower limit, 
the melt viscosity of the resulting melt is too low, thus making 
production of pellets (particularly by cutting) difficult after mixed with 
polyurethane. 
Here, the above relative viscosity was measured in the following manner. As 
the solvent, phenol/1,1,2,2-tetrachloroethane=6/4 (ratio by weight) was 
used. 0.500.+-.0.0001 g polymer was added to 50 ml of the solvent and 
dissolved at 120.degree. C. for 50 minutes to prepare a sample solution. 
Then, the sample solution and the solvent were measured respectively for 
passage time (sec.) at a temperature of 20.degree. C. with an Ostwald 
viscometer. The relative viscosity is a value calculated using the 
following equation: 
EQU Relative viscosity=[sample solution passage time (sec.)/solvent passage 
time (sec.)] 
Further, a copolymer of polybutylene terephthalate can also be used as 
component (A). In this case, the copolymer when melted is preferably 
incompatible with thermoplastic polyurethane (B). A copolymer with a high 
content of butylene terephthalate is not preferable because it is 
compatible with thermoplastic polyurethane (B). Here, incompatibility 
refers to be judged to be opaque in visual evaluation. If component (A) 
has a melting point of 210.degree. C. or more as determined by DSC, it is 
incompatible with (B) though depending on copolymer components to some 
degrees. 
Examples of components copolymerizable with component (A) include diol 
components e.g. polyalkylene glycols such as dihydroxy polycaprolactam and 
polytetramethylene diol and acid components e.g. aromatic dicarboxylic 
acids such as isophthalic acid etc. and aliphatic dicarboxylic acids such 
as adipic acid etc. 
Thermoplastic polyurethane (B-1) has isocyanate groups preferably at the 
terminal thereof and in an amount of 150 to 500 .mu.mol/g, more preferably 
200 to 470 .mu.mol/g. With an amount of less than the above-described 
lower limit, dispersion between the crystalline polyester component and 
the thermoplastic polyurethane component (i.e. B-1 and arbitrary B-2) is 
worse, and at the time of spinning, fiber cutting occurs frequently to 
make winding-up difficult. Even if the fiber can be wound, innumerable 
nodal defects occur in the polyurethane elastic fiber and sufficiently 
stretchable fiber cannot be obtained. Further, fine mountain-like 
protrusions such as those in the present invention are not generated on 
the surface of the fiber. In an amount exceeding the above-described upper 
limit, the phenomenon of gelation of the polymer becomes significant, and 
fiber cutting occurs frequently to make spinning difficult. By adjusting 
the isocyanate groups in the above range, micro-dispersion between the 
crystalline polyester component and the thermoplastic polyurethane 
component rapidly proceeds to enable significantly superior melt spinning 
whereby the fiber of the present invention can be obtained. 
The thermoplastic polyurethane (B-1) having isocyanate groups in amount of 
150 to 500 .mu.mol/g can be produced by compounding and reacting the 
isocyanate compound with polyols in such amounts that the ratio of the 
number of moles of isocyanate groups to the number of moles of hydroxyl 
groups (hereinafter, also called R ratio) is 1.07 to 1.28, more preferably 
1.09 to 1.25. 
The conventional thermoplastic polyurethane is produced by compounding and 
reacting the isocyanate compound with polyols at an R ratio in the range 
of 0.95 to 1.05. Accordingly, the amount of isocyanate groups in the 
thermoplastic polyurethane thus produced is lower than the lower limit of 
isocyanate groups possessed by component (B-1) of the present invention, 
and there are generated the disadvantages of fiber cutting etc. at the 
time of spinning. 
Here, the thermoplastic polyurethane per se is known, and for example, 
thermoplastic polyurethane described in Japanese Patent Publication No. 
46573/1983 can be used. That is, it -includes known segment polyurethane 
copolymers, for example polymers obtained by reacting polyols with a 
molecular weight of 500 to 6,000, such as dihydroxy polyether, dihydroxy 
polyester, dihydroxy polylactone, dihydroxy polyester amide, dihydroxy 
carbonate and block copolymers thereof, organic diisocyanates with a 
molecular weight of 500 or less, such as p,p'-diphenylmethane 
diisocyanate, tolylene diisocyanate, hydrogenated p,p'-diphenylmethane 
diisocyanate, tetra-methylene diisocyanate, hexamethylene diisocyanate, 
isophorone diisocyanate, p,5-napthylene diisocyanate etc., and 
chain-elongating agents with a molecular weight of 500 or less, such as 
water, hydrazine, diamine, glycol, triol etc. Among these, particularly 
preferable polymers are those using a polyol such as polytetramethylene 
ether glycol, or polycaprolactone polyester, or polybutylene adipate, 
poly-hexamethylene adipate, or polycarbonate. The organic diisocyanate is 
preferably p,p'-diphenylmethane diisocyanate. A particularly preferable 
chain-elongating agent is glycol, and 1,4-bis(.beta.-hydroxyethoxy)benzene 
and 1,4-butanediol are preferable. 
For polymerization of the thermoplastic polyurethane (B), conventional 
methods can be used. Such methods include e.g. a melt polymerization 
method of reacting an isocyanate compound and a polyol in a melted state 
at a temperature of 190.degree. C. or more and a belt polymerization 
method of mixing an isocyanate compound with a polyol sufficiently, 
pouring the mixture onto a heated belt conveyer, and reacting and 
solidifying it at relatively low temperature of 100 to 150.degree. C. In 
polymerization of (B-1) in the present invention, the latter belt 
polymerization method is preferably used whereby abnormal polymerization 
can be prevented. In the present invention, because (B-1) contains a large 
number of isocyanate groups after the polymerization is completed, the 
thermoplastic polyurethane (B-1) is stored preferably in a nitrogen stream 
or dry air so that the isocyanate groups therein do not react with water. 
Butylene terephthalate-based crystalline polyester (A) and thermoplastic 
polyurethane (B-1) are melt-mixed in such amounts that the upper limit of 
(A) is preferably 110 parts, more preferably 100 parts by weight and the 
lower limit of (A) is preferably 5 parts by weight, more preferably 7 
parts by weight relative to 100 parts by weight of (B-1). Given an amount 
exceeding the above-described upper limit, mixing of the two components 
becomes poor, while given an amount of less than the above-described lower 
limit, mountain-like protrusions on the surface of the fiber are 
decreased, so the effect of preventing luster cannot be achieved. 
The polyurethane elastic fiber of the present invention can contain the 
other thermoplastic polyurethane (B-2) such that the ratio of 
(A)/{(A)+(B-1)+(B-2)} is preferably in the range of 0.05 to 0.2, more 
preferably 0.075 to 0.2. With a ratio of less than the above-described 
weight ratio, the number of mountain-like protrusions on the surface of a 
fiber is less than the range of the present invention, so the effect of 
preventing luster cannot be achieved. With a ratio exceeding the 
above-described weight ratio, the physical properties of the resulting 
fiber after spinning are inadequate. Here, there is no particular limit to 
the thermoplastic polyurethane (B-2), and the aforementioned (B-1) can 
also be used. 
The method of melt-mixing the butylene terephthalate-based crystalline 
polyester (A) with the thermoplastic polyurethane (B-1) is not 
particularly limited, and for example, the respective components are 
mechanically mixed, then melt-kneaded in a conventional apparatus such as 
extruder etc. at a temperature of preferably 220 to 250.degree. C., 
extruded and formed into pellets. A twin-screw extruder in which the two 
components can be mixed sufficiently at high speed is preferably used. 
It is estimated that this mixing involves not only mere mixing of 
components (A) and (B-1) but also some chemical reaction between the two 
components. It is considered that by this chemical reaction, 
micro-dispersion of components (A) and (B-1) is achieved to improve 
dispersibility. 
Further, thepolyisocyanate compound (D) with a molecular weight of 400 or 
more can be compounded preferably as a cross-linking agent when materials 
containing a product preparedbymelt-mixing component (A) and (B-1) and 
arbitrarily containing (B-2) are melt-spun. It is considered that by this, 
thermostability of the polyurethane elastic fiber can improved, and 
dispersibility can further be improved by reaction with component (A). 
Thepolyisocyanate compound may be that described in Japanese Patent 
Publication No. 46573/1983. 
That is, the above-described polyisocyanate compound is a compound having 
at least 2 isocyanate groups in the molecule and can be synthesized for 
example by allowing the polyol with a molecular weight of 300 to 2,500 to 
react with at least 2-fold excess moles of the organic diisocyanate with a 
molecular weight of 500 or less. Alternatively, a compound having at least 
3 hydroxyl groups can also be used as polyol. As the polyisocyanate 
compound, an organic diisocyanate dimer or 
carbodiimide-modifiedpolyisocyanate can also be used preferably. 
The number of isocyanate groups in one molecule of the polyisocyanate 
compound ranges preferably from 2 to 4, and particularly the diisocyanate 
compound is preferable. If there are too many isocyanate groups, 
thepolyisocyanate compound becomes too viscous and difficult to handle. 
The molecular weight of thepolyisocyanate compound is 400 or more, 
preferably 800 to 3,000. This molecular weight is an apparent molecular 
weight calculated from the amount of isocyanate groups as determined by an 
amine titration method. If the molecular weight of the polyisocyanate 
compound is less than 400, it is denatured due to its high activity during 
storage, and the lower molecule weight decreases a predetermined amount 
thereof, thus making its handling difficult. On the other hand, if its 
molecular weight is too high, the amount of polyisocyanate to be added is 
increased, so spinning after mixing is often unstable. 
Suitable polyisocyanate compounds includes polyols with amolecular weight 
of 300 to 2,500, e.g. isocyanate-terminated compounds having organic 
diisocyanate with a molecular weight of 500 or less added to at least one 
polyol selected from the group consisting of polyether, polyester, 
polyester amide and polycarbonate. A particularly preferably polyol is 
polytetramethylene ether glycol, polycaprolactone polyester or 
polybutylene adipate. The organic diisocyanate is preferably 
p,p'-diphenylmethane diisocyanate. 
The amount of thepolyisocyanate compound added is preferably 3 to 30% by 
weight, more preferably 5 to 20% by weight relative to the total amount of 
the above-described polyisocyanate and materials containing a product 
prepared by melt-mixing component (A) and (B-1) and arbitrarily containing 
(B-2). 
The melt-spinning in the present invention can be practiced using a 
spinning apparatus including a part where materials containing a product 
prepared by melt-mixing component (A) and (B-1) and arbitrarily containing 
(B-2) is melt-extruded, a part where the polyisocyanate compound is added 
and mixed, and a spinning head. 
The part where the polyisocyanate compound is added to and mixed with 
polyurethane in a melted state may be a kneading apparatus having a 
rotating part, but a mixing unit with a stationary kneading element is 
more preferable. 
The mixing unit having the stationary kneading element may be conventional 
one. The shape of the stationary mixing element and the number of elements 
vary depending on the conditions used, but it is essential that these are 
selected such that adequate mixing of the polyurethane elastic body with 
the polyisocyanate compound has been completed before the mixture is 
discharged from the spinning nozzle. 
One embodiment of spinning is described. The product prepared by 
melt-mixing component (A) with component (B-1), and arbitrarily (B-2), are 
chip-blended, fed through a hopper, heated and melted in an extruder. The 
melting temperature is preferably in the range of 190 to 230.degree. C. 
Separately, the polyisocyanate compound is melted at a temperature of 
100.degree. C. or less in a feeding tank and previously defoamed. The 
polyisocyanate compound is easily denatured at too high melting 
temperature, so it is preferable to use a lower temperature within the 
range where the compound can be melted, and a temperature between room 
temperature and 100.degree. C. can be used as necessary. 
The melted polyisocyanate compound is metered in a metering pump, filtered 
if necessary, and added to the above-described material which is melted at 
an association part provided at the top of the extruder. The 
polyisocyanate compound and the material are kneaded in a kneading unit 
having a stationary kneading element. This mixture is metered by a 
metering pump and introduced into a spinning head. 
The spinning head may be a usual synthetic fiber spinning device, but it is 
preferably designed to have a shape with less retention of the mixture. 
After foreign matter is removed if necessary by a filter material such as 
a wire gauze or glass beads in a filter layer provided in the spinning 
head, the mixture is discharged from the spinning nozzle, air-cooled, 
given a lubricant, and wound up. The take-up speed is usually 300 to 1,500 
m/min. 
The strength of the urethane fiber wound around a spinning bobbin may be 
inferior just after spinning, but as it is left at room temperature, its 
strength is increased and its recovery characteristics from elongation at 
high temperature are also improved. After spinning, thermal treatment is 
conducted in a suitable manner to promote improvements in fiber properties 
and thermal performance. 
The polyurethane elastic fiber of the present invention produced in this 
manner can be used as such or preferably covered with polyamide fiber etc. 
to be used as thin knitted goods etc. such as stockings, panty stockings, 
tights, sox etc. 
The covering fiber for use in stockings, panty stockings etc. includes 
nylon multi-filament fiber of 5 to 30 deniers with which the polyurethane 
elastic fiber is covered at a twisting number of 500 to 4,000 T/m. A 
preferable example of covering fiber is nylon multi-filament fiber of 8 to 
20 deniers with which the polyurethane elastic fiber is covered at a 
twisting number of 1,000 to 2,500 T/m. 
The covering fiber for use in tights includes nylon-processed fiber of 30 
to 150 deniers with which the polyurethane elastic fiber is covered at a 
twisting number of 200 to 2,000 T/m. A preferable example of covering 
fiber include nylon-processed fiber of 40 to 110 deniers with which the 
polyurethane elastic fiber is covered at a twisting number of 400 to 800 
T/m. 
The covering method can be either single-covering or double-covering by a 
generally known covering machine, or a covering method using air can also 
be adopted. 
Hereinafter, the present invention is described in more detail with 
reference to the Examples, which however are not intended to limit the 
present invention.

EXAMPLES 
Examples 1 to 6 and Comparative Examples 1 to 4 
The following materials were used as components (A), (B-1) and (B-2). 
&lt;Component (A)&gt; 
After adequately drying at 110.degree. C. for about 24 hours, polybutylene 
terephthalate was used. The relative viscosity was 1.85, and the melting 
point as determined by DSC (DSC-7 type, made by Perkin-Elmer) was 
224.degree. C. 
&lt;Component (B-1)&gt; 
Thermoplastic polyurethane produced in the following manner was used. 
Materials used in preparation thereof and their compounding amounts are as 
follows: 
Polybutylene adipate diol with a molecular weight of 2,000 having hydroxyl 
groups at both ends: 67 parts by weight (0.035 mol) 
1,4-Butanediol: 5.3 parts by weight (0.0589 mol) 
p,p'-Diphenylmethane diisocyanate (MDI): 27.7 parts by weight (0.1108 mol) 
The ratio (R) of the number of moles of isocyanate groups to the number of 
moles of hydroxyl groups=1.20 
First, after polybutylene adipate diol and 1,4-butanediol were sufficiently 
mixed at 100.degree. C., MDI heated at 45.degree. C. was added to the 
mixture and mixed sufficiently at 100.degree. C. for 1 minute. Then, the 
mixture was continuously poured onto a conveyer heated at 100.degree. C. 
to conduct polymerization reaction. After the reaction product was cooled 
until it could be easily removed from the conveyer, the reaction product 
was removed from the conveyer, then cooled to room temperature and cut 
into small pieces. The small pieces as component (B-1) were stored in a 
nitrogen stream. 
The isocyanate groups in component (B-1) were determined in the following 
method. The result indicated the amount of the isocyanate groups was 360 
.mu.mol/g. 
Method of measuring the amount of isocyanate groups: 
(1) 20 ml solution containing 3.25 g dibutylamine/1-liter toluene is mixed 
with 15 ml dimethylacetamide, and 1 g of the polymer is dissolved in the 
mixture to give a sample. 
(2) 0.04 weight-% bromophenol blue reagent in isopropyl alcohol is prepared 
as an indicator. 
(3) 0.4 ml of the indicator is added to the sample, and the mixture is 
titrated with 0.05 N hydrochloric acid. The point at which the color of 
the solution turned from blue to green is regarded as the end point. Here, 
X ml is assigned to the amount of hydrochloric acid used in titration. 
(4) As a blank, the mixture in item (1) above is prepared, and 0.4 ml of 
the indicator is added thereto, and the mixture is titrated with 0. 05 N 
hydrochloric acid. Here, Y ml is assigned to the amount of hydrochloric 
acid used in titration. 
(5) The amount of isocyanate (NCO) groups is calculated using the following 
equation: 
EQU Amount of NCO groups (.mu.mol/g)=[(Y-X) xhydrochloric acid normality 
(N).times.1000]/[polymer weight (g)] 
In the measurement method described above, the concentration of the 
dibutylamine solution and the concentration of hydrochloric acid for 
titration are suitably varied depending on the amount of the isocyanate 
groups in the polymer. 
&lt;Component (B-2)&gt; 
Thermoplastic polyurethane prepared in the following manner was used. 
Materials used in preparation thereof and their compounding amounts are as 
follows: 
Polytetramethylene diol with a molecular weight of 1,000: 210 parts by 
weight (0.420 mol) 
1,4-Butanediol: 18.1 parts by weight (0.402 mol) 
p,p'-Diphenylmethane diisocyanate (MDI): 105parts byweight (0.840 mol) 
The ratio (R) of the number of moles of isocyanate groups to the number of 
moles of hydroxyl groups=1.02 
Polytetramethylene diol heated at 50.degree. C. and MDI heated at 
45.degree. C. were sufficiently mixed and passed through a reaction 
cylinder having a stationary mixing element heated at 55.degree. C. to 
give a prepolymer. Then, 1,4-butanediol was sufficiently mixed with the 
above-described prepolymer and then melt-polymerized at a polymerization 
temperature of 240.degree. C. at a screw revolution of 150 rpm in a 45 
mm.phi. twin-screw mixing machine to produce polyurethane pellets of 1.5 
mm.phi. in diameter. 
The isocyanate groups, as determined in the same manner as above, were 40 
.mu.mol/g. 
First, 50 parts by weight of component (A) and 50 parts by weight of 
component (B-1) were chip-blended uniformly in a conventional tumbler, and 
then melt-kneaded in a 45 mm.phi. twin-screw kneader at a cylinder 
temperature of 240.degree. C. at a screw revolution of 150 rpm and 
extruded through a dice whereby pellets of about 1.5 mm in diameter were 
prepared. 
Then, components (A) and (B-1) produced in the above-described manner using 
the amounts (parts by weight) shown in Tables 1 and 2 and component (B-2) 
were chip-blended uniformly in a conventional tumbler and then melt-spun 
to produce polyurethane elastic fiber. 
The melt-spinning was practiced in the following manner. A mixture obtained 
by chip-blending in the manner described above was melted at 220.degree. 
C. Separately, the cross-linking agent (D) melted at 70.degree. C. with a 
molecular weight of 1,250 having isocyanate groups at both ends having 
polycaprolactone diol being reacted at both ends with MDI was mixed in an 
amount of 15% by weight relative to the total amount of the mixture and 
the cross-linking agent. Then, the resulting mixture was introduced into a 
spinning nozzle of 1.0 mm in diameter, extruded into air, wound up at a 
rate of 600 m/min. and spun into a mono-filament of 20 deniers. The degree 
of luster of each spun polyurethane elastic fiber was measured, and the 
heights and the number of mountain-like protrusions thereon were 
determined. The results are shown in Tables 1 and 2. 
Each polyurethane elastic fiber thus obtained was covered with covering 
nylon fiber 10 deniers/5 filaments under the conditions of 2.6-fold 
covering draft and the twisting number of 1,500 T/m to produce covered 
fiber. Then, merely knitted panty stockings consisting of 100% covered 
fiber at the hosiery portion, and further black-dyed and finished panty 
stockings, were respectively produced and worn under sunlight, and the 
state of luster was evaluated. The results are shown in Tables 1 and 2. 
The meanings of the symbols and terms in Tables 1 and 2 are shown below. 
&lt;Degree of luster&gt; 
A 3-dimensional varied-angle photometer MODEL JSG-22 (made by Jonan 
Seisakusho K. K.) was used to measure a light reflecting off a sample 
after a projector and a receptor were positioned at an angle of incidence 
of 30.degree. and an angle of reflection of 30.degree. relative to a 
normal line on a sample stand. In this measurement, a standard white plate 
as an accessory of the photometer was placed on the sample stand, and 
light from the light injector was exposed to the standard white plate. Io 
was assigned to the amount of light which the standard white plate 
received from the projector. Polyurethane elastic fiber of 720 m in total 
wound around a paper tube was re-wound on a square metal plate with a size 
of 60 mm in one side and a thickness of 0.4 to 1.0 mm at a take-up speed 
of 12 m/min., at a take-up angle of 0.09.degree. with a roll width of 42 
mm and a rolling tensile strength of 0.01 g at which the polyurethane 
elastic fiber was not elongated (the resulting roll is referred to 
hereinafter as nuance roll). The nuance roll was placed in the sample 
stand such that an angle between lines formed by projecting the optical 
axis of light from the projector and the take-up direction of the 
nuance-roll polyurethane elastic fiber respectively to a plane 
perpendicular to a normal line of the sample stand was 0.09.degree.. Then, 
the nuance-roll fiber was exposed to the same light as light which the 
standard white plate received from the projector. I was assigned to the 
amount of light which the receptor received from the nuisance-wound fiber. 
(I/Io).times.100, that is, the degree of luster was thus determined. Given 
the above fiber length of 720 m in total, the fiber is not affected by the 
conditions of the surface or color of the metal plate itself, so a 
material other than the metal plate can be used for preparing the sample. 
&lt;State of Luster&gt; 
The state of luster was evaluated visually at the time of wearing panty 
stockings. .circleincircle.: No luster. .largecircle.: Slight luster. 
.DELTA.: Luster. X: Significant luster. 
&lt;Measurement of mountain-like protrusions&gt; 
An electron microscope (JSM5300, made by JEOL Ltd.) was used and a 
photograph of the surface of the fiber (magnification: 1,000) was taken. 
Then, the side of the fiber in the photograph was magnified two thousand 
times by a photocopier (U-Bix-4060AF, made by Konica Corporation) and 
examined. 
The polyurethane elastic fibers in Tables 1 and 2 were determined in the 
following manner. 
&lt;Denier&gt; 
The weight of the fiber cut into 9 cm was determined by a torsion balance 
so that its denier was calculated. 
&lt;Strength, Elongation&gt; 
Strength and elongation were calculated from an S--S curve measured with a 
tensile tester (made by Orientec K. K.) under the following conditions. 
Sample length, 10 cm; tensile rate, 50 cm/min.; room temperature, 
21.+-.2.degree. C.; and room humidity, 65.+-.5% RH. 
&lt;Elongation Restoration&gt; 
Two reciprocating continuous measurements were conducted under the 
conditions of a sample length of 10 cm and a tensile restoration rate of 
50 cm/min. As the elongation restoration, (restoration stress/tensile 
stress).times.100 (%) at the time of 80% elongation in the second tensile 
restoration curve was determined. 
TABLE 1 
__________________________________________________________________________ 
Example 1 2 3 4 5 6 
__________________________________________________________________________ 
Compounding amount of each component 
(A) (parts by weight) 50 50 50 50 50 50 
(B-1) (parts by weight) 50 50 50 50 50 50 
(B-2) (parts by weight) 900 567 400 233 150 942 
(A) (% by weight) 5 7.5 10 15 20 4.8 
Degree of luster 47 42 32 18 9 70 
Protrusions on fiber surface 
Number of protrusions/10 .mu.m 18 19 22 47 58 9 
Height (.mu.m) 0.2-5.0 0.2-5.0 0.2-0.5 0.2-5.0 0.2-5.0 0.2-5.0 
State of luster 
before dyeing 
.smallcircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.smallcircle. 
after dyeing .smallcircle. .circleincircle. .circleincircle. .circleinc 
ircle. .circleincircle. .smallcircle 
. 
Properties of polyurethane elastic fiber 
Denier (denier) 20 20 20 20 20 20 
Strength (g/denier) 1.95 1.90 1.80 1.40 1.00 1.95 
Elongation (%) 460 450 430 400 370 460 
Elongation restoration (%) 93 91 90 88 85 93 
__________________________________________________________________________ 
TABLE 2 
______________________________________ 
Comparative Example 
1 2 3 4 
______________________________________ 
Compounding amount of each component 
(A) (parts by weight) 
-- 50 50 50 
(B-1) (parts by weight) -- 50 50 50 
(B-2) (parts by weight) 100 3230 1010 1010 
(A) (% by weight) 0 1.5 4.5 4.5 
Degree of luster 98 93 75 80 
Protrusions on fiber surface 
Number of protrusions/10 .mu.m 0 trace 7 11 
Height (.mu.m) -- -- 0.2-5.0 6.0-10.0 
State of luster 
before dyeing 
X X .DELTA. 
X 
after dyeing X X .DELTA. X 
Properties of polyurethane elastic fiber 
Denier (denier) 20 20 20 20 
Strength (g/denier) 2.00 1.98 1.95 1.94 
Elongation (%) 460 460 460 460 
Elongation restoration (%) 93 93 93 93 
______________________________________ 
In Examples 1 to 6, the luster was hardly observed in the panty stockings 
before dyeing or in the panty stockings after dyeing and finishing. The 
degree of luster of the polyurethane elastic fiber in Example 1 was 47, 
and the degree of luster of the polyurethane elastic fiber in Example 5 
was 9. In Example 1, 18 fine mountain-like protrusions were observed on 
the surface of the polyurethane elastic fiber every 10 .mu.m fiber in the 
axial direction. 
In Example 5, 58 fine mountain-like protrusions were observed. The heights 
of all the polyurethane elastic fibers in Examples 1 to 6 were uniform in 
the range of 0.2 to 5.0 .mu.m. As the number of fine protrusions was 
increased, the degree of luster was decreased. 
On the other hand, in Comparative Example 1 where the product prepared by 
melt-mixing components (A) and (B-1) was not contained, the luster was 
significantly observed in the evaluation of wearing the panty stockings. 
The degree of luster of the polyurethane elastic fiber was 98, and 
mountain-like protrusions were not observed on the surface of the fiber. 
Even in Comparative Example 2 where the amount of component (A) was less 
than the range of the present invention, the luster was significantly 
observed in the evaluation of wearing the panty stockings, and the degree 
of luster of the polyurethane elastic fiber was 93, and there was 
generated only a trace of mountain-like protrusion. 
In Comparative Example 3, the luster was observed in the evaluation of 
wearing the panty stockings. The degree of luster of the polyurethane 
elastic fiber was 75, and the number of mountain-like protrusions on the 
surface of the fiber was 7. 
In Comparative Example 4, the number of protrusions on the polyurethane 
elastic fiber was 11, but the heights of the protrusions exceeded 5.0 
.mu.m, and the degree of luster was 80, and the luster was significantly 
observed in the evaluation of wearing the panty stockings. 
FIGS. 1 and 2 are electron microphotographs showing the form of the surface 
of the polyurethane elastic fiber in Example 4. FIGS. 3 and 4 are electron 
microphotographs showing the form of the surface of the polyurethane 
elastic fiber in Comparative Example 1. As is evident from each figure, 
the polyurethane elastic fiber of the present invention possesses a large 
number of mountain-like protrusions on the surface of the fiber. 
Although fiber properties were deteriorated as the content of the product 
obtained by melt-mixing components (A) and (B-1) was increased, its 
properties were satisfactory as the elastic fiber. 
Examples 7 to 11 and Comparative Examples 5 to 6 
The same polybutylene terephthalate as in Example 1 was used as component 
(A). 
Component (B-1) was polymerized and produced in the same manner as in 
Example 1 except that the following materials were used in the amounts 
(parts by weight) shown in Tables 3 and 4. The respective ratios (R) of 
the number of moles of isocyanate groups to the number of moles of 
hydroxyl groups are as shown in Tables 3 and 4. 
The materials used in polymerization are as follows: 
Polytetramethylene diol with a molecular weight of 1,000 
1,4-Butanediol 
p,p'-Diphenylmethane diisocyanate (MDI) 
The amount of isocyanate groups in the resulting component (B-1), as 
determined in the same manner as in Example 1, is shown in Tables 3 and 4. 
Then, components (A) and (B-1) were melt-kneaded in a twin-screw extruder 
in the amounts (parts by weight) shown in Tables 3 and 4, and were 
melted-spun in the same manner as in Example 1 to produce polyurethane 
elastic fiber. 
Then, the properties of the polyurethane elastic fiber were evaluated in 
the same manner as in Example 1. The results are shown in Tables 3 and 4. 
TABLE 3 
______________________________________ 
Example 7 8 9 10 11 
______________________________________ 
Component (B-1) 
Compounding amounts (parts by weight) 
Polytetramethylene diol 
100 100 100 100 100 
MDI 50 50 50 50 50 
1,4-Butanediol 
7.82 7.36 6.65 
6.00 5.40 
R ratio 1.07 1.10 1.15 1.20 
1.25 
Isocyanate groups 150 220 310 390 460 
(.mu.mol/g) 
Compounding amounts (parts by weight) 
(A) 10 10 10 10 10 
(B-1) 90 90 90 90 90 
Degree of luster 
70 30 24 
18 23 
Protrusions on fiber surface 
Number of protrusions/ 
10 28 30 45 42 
10 .mu.m 
Height (.mu.m) 0.2-5.0 0.2-5.0 0.2-5.0 0.2-5.0 0.2-5.0 
State of 
before dyeing 
.largecircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
luster after dyeing .largecircle. .circleincircle. 
.circleincircle. .circleincircl 
e. .circleincircle. 
Properties of polyurethane elastic fiber 
Denier (denier) 
20 20 20 20 20 
Strength (g/denier) 1.85 2.00 2.00 2.10 1.70 
Elongation (%) 
460 475 470 
410 400 
Elongation restora- 93 93 92 92 92 
tion (%) 
______________________________________ 
TABLE 4 
______________________________________ 
Comparative Example 5 6 
______________________________________ 
Component (B-1) 
Compounding amounts (parts by weight) 
Polytetramethylene diol 100 100 
MDI 50 50 
1,4-Butanediol 8.31 4.84 
R ratio 1.04 1.30 
Isocyanate groups (.mu.mol/g) 85 540 
Compounding amounts (parts by weight) 
(A) 10 10 
(B-1) 90 90 
Degree of luster 86 -- 
Protrusions on fiber surface 
Number of protrusions/10 .mu.m 4 -- 
Height (.mu.m) 0.2-5.0 -- 
State of luster 
before dyeing X -- 
after dyeing X -- 
Properties of polyurethane elastic fiber 
Denier (denier) 20 -- 
Strength (g/denier) 1.30 -- 
Elongation (%) 350 -- 
Elongation restoration (%) 92 -- 
______________________________________ 
In Examples 7 to 11, the amount of isocyanate groups in component (B-1) was 
varied within the range of the present invention. On any fiber surface, 10 
or more protrusions of 0.2 to 5.0 .mu.m in height were observed every 10 
.mu.m fiber in the axial direction, and the degree of luster was 70 or 
less. It was found that the number of the protrusions was increased as the 
amount of isocyanate groups in (B-1) was increased. Further, the degree of 
luster was decreased as the number of the protrusions was increased. In 
the evaluation of wearing the panty stockings, the luster was hardly 
observed. Further, the properties of any elastic fibers were good. 
On the other hand, thermoplastic polyurethane with isocyanate groups 
contained in an amount of less than the range of the present invention was 
used in Comparative Example 5. The melted polymer extruded from the nozzle 
was found to possess draft irregularity in the thinning step, and fiber 
cutting frequently occurred. Further, the wound fiber had a large number 
of nodal defects. The number of fine mountain-like protrusions was 
significantly low, and the degree of luster was 86. Further, the luster 
was significantly observed in the evaluation of wearing the panty 
stockings. The properties (strength and elongation) of the elastic fiber 
were lower than in the Examples. 
In Comparative Example 6, the thermoplastic polyurethane with isocyanate 
groups exceeding the range of the present invention was used. The 
phenomenon of gelation of the polymer was significant, and fiber cutting 
occurred at the nozzle to make spinning infeasible. 
Examples 12 to 19 and Comparative Examples 7 to 8 
Components (A), (B-1) and (B-2) were the same as in Example 1. Components 
(A) and (B-1) were melt-kneaded in the amounts (parts by weight) shown in 
Tables 5 and 6 in the twin-screw extruder in the same manner as in Example 
1 to give a product. Then, the product produced by melt-kneading 
components (A) and (B-1), and component (B-2), were chip-blended in the 
weight parts shown in Tables 5 and 6 and mixed uniformly in the same 
manner as in Example 1, and then melt-spun in the same manner as in 
Example 1 to give polyurethane elastic fiber. Then, the polyurethane 
elastic fiber was evaluated in the same manner as in Example 1 for the 
state of luster by wearing the panty stockings. The results are shown in 
Tables 5 and 6. In the tables, the item "spinnability" shows fiber cutting 
at the time of spinning, ".circleincircle." means that fiber cutting 
hardly occurs, ".largecircle." means that slight fiber cutting occurs, and 
"x" means that spinning is not feasible due to fiber cutting. 
TABLE 5 
______________________________________ 
Example 12 13 14 15 16 17 18 19 
______________________________________ 
Compounding amount of each component 
(A) (parts 5 7 15 30 50 70 100 110 
by weight) 
(B-1) (parts 100 100 100 100 100 100 100 100 
by weight) 
(B-2) (parts 0 0 75 170 350 290 330 370 
by weight) 
(A) 4.8 6.5 7.9 10.0 10.0 15.2 18.9 19.0 
(% by weight) 
Spinnability .circleincircle. .circleincircle. .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.largecircle. 
State of luster 
before dyeing .largecircle. .circleincircle. .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
after dyeing 
.largecircle. .circleinc 
ircle. .circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
______________________________________ 
TABLE 6 
______________________________________ 
Comparative Example 7 8 
______________________________________ 
Compounding amount of each component 
(A) (parts by weight) 3 120 
(B-1) (parts by weight) 100 100 
(B-2) (parts by weight) 0 410 
(A) (% by weight) 2.9 19.0 
Spinnability .circleincircle. X 
State of luster 
before dyeing X -- 
after dyeing X -- 
______________________________________ 
In Examples 12 to 19, the amount (parts by weight) of component (A) 
relative to component (B-1) was varied within the range of the present 
invention. The spinnability of any fibers was good. Further, the state of 
luster in evaluation of wearing the panty stockings (stained and finished 
panty stockings) made of the polyurethane elastic fibers in Examples 12 to 
19 was also permissible. 
In Comparative Examples 7 to 8, on the other hand, the amount (parts by 
weight) of component (A) relative to component (B-1) was not in the range 
of the present invention. In Comparative Example 7 where the amount (parts 
by weight) of component (A) relative to component (B-1) was less than the 
range of the present invention, the spinnability was good, but the luster 
was significantly observed in evaluation of wearing the panty stockings. 
Further, in Comparative Example 8 where the amount (parts by weight) of 
component (A) relative to component (B-1), fiber cutting occurred 
frequently because of inadequate mixing of component (A) with component 
(B-1), so the polyurethane elastic fiber cannot be recovered. 
INDUSTRIAL APPLICABILITY 
The polyurethane elastic fiber possesses excellent stretching 
characteristics and is thus used widely in the fields of hosiery, 
underwear, sportswear, corset etc. The urethane elastic fiber of the 
present invention, while maintaining the characteristics of the elastic 
fiber, is free of the luster phenomenon occurring in melt-spun urethane 
fiber, and its product is excellent in appearance. Accordingly, the 
elastic fiber of the present invention can be used preferably In the 
above-described fields. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is an electron microphotograph (magnification: 1,000) showing the 
form of the polyurethane elastic fiber produced in Example 4. 
FIG. 2 is an electron microphotograph (magnification: 3,500) showing the 
form of the polyurethane elastic fiber produced in Example 4. 
FIG. 3 is an electron microphotograph (magnification: 1,000) showing the 
form of the polyurethane elastic fiber produced in Comparative Example 1. 
FIG. 4 is an electron microphotograph (magnification: 3,500) showing the 
form of the polyurethane elastic fiber produced in Comparative Example 1.