Water-dispersible synthetic fiber of cruciform cross-section to promote dispersibility, and so better uniformity, more opacity, good permeability and an attractive flannel-like hand to the resulting wet-laid fabrics.

TECHNICAL FIELD 
This invention concerns new water-dispersible synthetic polymer fiber, 
particularly of poly(ethylene terephthalate), and its preparation. 
BACKGROUND OF INVENTION 
There has been increased interest in recent years in water-dispersible 
synthetic fiber, especially of polyester. Such water-dispersible fiber is 
used in various non-woven applications, including paper-making and 
wet-laid non-woven fabrics, sometimes as part of a blend, often with large 
amounts of wood pulp, or fiberglass, but also in applications requiring 
only polyester fiber, i.e., unblended with other fiber. This use, and the 
requirements therefor, are entirely different from previous more 
conventional use as tow or staple fiber for conversion into textile yarns 
for eventual use in woven or knitted fabrics, because of the need to 
disperse this fiber in water instead of to convert the fiber into yarns, 
e.g., by processes such as carding, e.g. in the cotton system. It is this 
requirement for water-dispersibility that distinguishes the field of the 
invention from previous, more conventional polyester staple fiber. 
Most such water-dispersible polyester fiber is of poly(ethylene 
terephthalate), and is prepared in essentially the same general way as 
conventional textile polyester staple fiber, except that most 
water-dispersible polyester fiber is not crimped, whereas any polyester 
staple fiber for use in textile yarns is generally crimped while in the 
form of tow, before conversion into staple fiber. Thus, waterdispersible 
polyester fiber has generally been prepared by melt-spinning the polyester 
into filaments, combining the filaments to form a tow, drawing, applying a 
suitable coating to impart water-dispersible properties, generally in the 
same way as a finish is applied to a tow of conventional textile 
filaments, and then, generally without any crimping (or with imparting 
only some mild wavy undulations in some cases to provide extra bulk and a 
three-dimensional matrix), converting the tow into staple. Some prior 
polyester staple fiber has been prepared in uncrimped form, e.g. for use 
as flock in pile fabrics, but for such use, water-dispersibility has not 
been required. 
Polyester fibers are naturally hydrophobic, so it is necessary to apply to 
the polyester a suitable coating, as disclosed by Ring et al. in U.S. Pat. 
No. 4,007,083, Hawkins in U.S. Pat. Nos. 4,137,181, 4,179,543 and 
4,294,883, and Viscose Suisse in British Pat. No. 958,350, to overcome the 
inherent hydrophobic character of the polyester fiber without creating 
foam or causing the fibers to flocculate. It is this coating that has 
distinguished water-dispersible polyester fiber from more conventional 
polyester staple fiber, rather than any inherent characteristic feature of 
the polyester itself, or of its shape, such as the cross-section. 
Heretofore, so far as is known, the cross-section of all commercial 
water-dispersible polyester fiber has been round. Indeed the cross-section 
of most commercial polyester staple fiber for other uses has generally 
been round, because this has been preferred. 
Although, hitherto, most synthetic polymeric water-dispersible fiber has 
been formed of polyester, being inexpensive and plentiful, increasing 
amounts of polyolefins and polyamides are beginning to be used for 
water-dispersible fibers, and so the invention is not limited only to 
polyesters, but covers other synthetic polymers. 
SUMMARY OF INVENTION 
According to the present invention, there is provided new synthetic polymer 
water-dispersible fiber, especially polyester fiber, characterized in that 
the fibers are of cruciform cross-section. 
A cruciform cross-section has been used heretofore for other polyester 
fibers, as described herein. Other than the cross-section, the 
water-dispersible fiber of the invention may be essentially similar to 
prior water-dispersible polyester or other synthetic polymer fibers, 
although the advantages described hereinafter may provide the opportunity 
for additional modifications. The invention will be described hereinafter 
with special reference to polyester fiber, although it will be recognized 
that other synthetic polymers, such as polyamides and polyolefins, may 
also be used. 
The fibers of the invention may be made conveniently by melt-spinning and 
drawing polyester filaments of appropriate denier per filament (dpf), and 
applying thereto a suitable coating to impart water-dispersible 
characteristics. The filaments are then generally cut into staple of 
whatever length is desired for the end-use contemplated. 
The use of a cruciform cross-section for the water-dispersible fiber of the 
invention has, surprisingly, been found to promote dispersibility, in 
comparison with a round cross-section, and this imparts to the resulting 
wet-laid fibers better uniformity, more opacity, good permeability, and an 
attractive flannel-like hand as will be seen in the Example.

DISCLOSURE OF THE INVENTION 
As indicated above, a cruciform cross-section has already been used for 
more conventional polyester staple fiber, that has been spun into 
filaments and drawn, cut, converted into spun yarn, and used in woven or 
knitted fabrics. Such fiber has not had the water-dispersible 
characteristics required for this invention. Similarly, polyester 
filaments having a cruciform cross-section are already known from Lehmicke 
U.S. Pat. No. 2,945,739, which discloses a process for melt-spinning 
polyamide and polyester filaments of, inter alia cruciform cross-section, 
and woven and knitted fabrics from staple fibers, and from Jamieson U.S. 
Pat. No. 3,249,669, which discloses a process for making a multifilament 
yarn of polyester filaments of various cross-sections, including a 
cruciform cross-section. Oriented polyester filaments of non-round 
cross-section have also been described by Frankfort et al. in U.S. Pat. 
Nos. 4,134,882 and 4,195,051, having been prepared by spinning at a very 
high speed (6,000 ypm), which high speeds could also be used to prepare 
oriented polyester filaments of cruciform cross-section as a substrate for 
applying thereto a suitable coating to impart water-dispersible 
characteristics, and thereby obtain water-dispersible fiber according to 
the invention. None of this art concerns the field of the present 
invention. However, the polyester filamentary substrates for making the 
water-dispersible fiber of the invention may be prepared by the techniques 
described therein, or by appropriate modifications of these or other known 
techniques of making polyester filaments of non-round cross-section. 
The prior art references disclose parameters for a cruciform cross-section 
and FIG. 1 is essentially as shown therein. 
The preparation of the polyester staple fiber is otherwise conventional, 
involving the steps of melt-spinning polymer into filaments, collecting 
the filaments into a tow, drawing the tow, and applying a suitable coating 
to impart water-dispersible characteristics. If low shrinkage is desired, 
the drawn filaments are generally annealed. 
Selection of an appropriate coating to promote water-dispersibility is 
important, and more of such coating is generally required than for 
comparable weights of fiber of round cross-section of similar dpf, because 
of the larger surface area of the periphery of the cruciform 
cross-section. It is especially important to provide good boundary 
lubrication properties. For this reason, an ethoxylated coating is 
preferred. 
Suitable coatings are disclosed in Hawkins, U.S. Pat. Nos. 4,137,181, 
4,179,543 and 4,294,883 and also in U.S. Ser. No. 842,789, also filed Mar. 
27, 1986 in the names of van Issum and Schluter, disclosing the use of a 
synthetic copolyester of poly(ethylene terephthalate) units and 
poly(oxyalkylene) of groups derived from a poly(oxyalkylene)glycol having 
an average molecular weight in the range of 300 to 6,000, as disclosed, 
e.g. in McIntyre, et al. U.S. Pat. Nos. 3,416,952, 3,557,039 and 
3,619,269, referred to therein; other useful segmented copolyesters are 
disclosed in Raynolds U.S. Pat. No. 3,981,807; all these disclosures are 
incorporated herein by reference. 
Such polyester fiber is generally prepared first in the form of a 
continuous filamentary uncrimped tow or, if extra bulk is required, and a 
more three-dimensional matrix, the filaments may be provided with mild 
wave-like undulations by a mild crimping-type process, and the uncrimped 
or mildly wave-like filaments are cut to the desired cut length, i.e. to 
form the water-dispersible fiber, which is generally sold in the form of 
bales, or other packages of cut fiber. Suitable cut lengths are generally 
from about 5 to about 90 mm (1/4 to 3 inches), generally up to 60 mm (21/2 
inches), and of length/diameter (L/D) ratio from about 100:1 to about 
2000:1, preferably about 150:1 to about 2000:1, it being an advantage of 
the invention that good performance has been obtainable with preferred 
water-dispersible fiber of the invention with an L/D ratio higher than we 
have considered satisfactory with prior art water-dispersible polyester 
fiber. A suitable denier per filament is generally from about 0.5 to about 
20. The coating is generally present in amount about 0.04 to about 1.0% of 
the weight of fiber (OWF%). 
There is also provided a process for preparing such water-dispersible 
polyester fiber, comprising the steps of melt-spinning the polyester into 
filaments of cruciform cross-section, forming a tow of such filaments, 
drawing, and then coating the filaments in the tow with such synthetic 
copolyester, and, at an appropriate time, converting such coated filaments 
into staple fiber. 
The coating is preferably cured on the filaments by heating the coating 
filaments, or the resulting staple fiber, if desired, to a temperature of 
about 100.degree. to about 190.degree. C. to improve durability. 
The invention is further illustrated in the following Example, in which all 
parts and percentages are by weight, unless otherwise indicated, and OWF 
is (solids) "of weight of fiber". Reference is made to several 
measurements of yarn properties, such as tensile properties (tenacity and 
elongation-to break), which are measured according to the methods 
described in Frankfort et al. U.S. Pat. No. 4,134,882. It will be 
understood that other conditions can be used e.g., other designs of 
orifice, such as are shown in the art. 
EXAMPLE 
The following fibers, Fiber A, a comparison of round cross section, and 
Fiber N, a fiber of the invention of cruciform cross section, were both 
spun from poly(ethylene terephthalate) of intrinsic viscosity 0.64, 
containing 0.3% TiO.sub.2 as a delusterant. 
Fiber A was spun at 1600 ypm into filaments with conventional radial air 
quenching using a 900 hole spinneret, with round holes 0.015 inches in 
diameter and capillary length of 0.030 inches, a 270.degree. C. block, and 
polymer throughput 68.2 pounds/hour. Denier per filament was 3.67. Fiber A 
was then oriented by running over a set of feed rools at 29.3 ypm, 
followed by a set of draw rolls at 80.0 ypm, and delivered to a conveyer 
by puller rolls at 80.1 ypm. Between feed roll sections the filaments were 
treated in a 45.degree. C. water bath. Between feed and draw rolls the 
rope was sprayed with water at 98.degree. C. Between draw and puller rolls 
a commercial water-dispersible coating (50/50 mixture of potassium salt of 
mono and diacid phosphate esters of lauryl alcohol/tallow alcohol 
ethoxylated with 25 moles of ethylene oxide) was applied. The filaments 
were then relaxed free in an oven at 150.degree. C. for 6 minutes. 
Fiber N was produced in a similar manner to Fiber A except that 625 
filaments of 3.22 dpf and cruciform cross-section were spun through 
capillaries as shown in FIG. 2, with block temperature 273.degree. C., and 
throughput 42.9 pounds/hour. Roll speeds for the orientation were feed 
rolls 32.1 ypm, draw rolls 80.2 ypm and puller rolls 79.2 ypm, and a 
somewhat higher level of water-dispersible coating was used to offset 
approximately 57% higher surface area of the cruciform cross-section. 
The properties of the drawn coated filaments are compared in Table 1. 
TABLE 1 
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Sample A N 
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Cross-section Round cruciform 
dpf 1.47 1.56 
coating OWF (%) 0.4 0.44 
Boil-off shrinkage (%) 
1.0 0 
Dry heat shrinkage 2.45 3.6 
(196.degree. C.) (%) 
Tenacity at break (g/d) 
4.5 4.8 
Elongation at break (%) 
42 26 
Tenacity at 0.93 0.93 
2% elongation (g/d) 
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Both types were cut to form water-dispersible fiber of 1/4, 3/8, 1/2 and 
3/4 inch cut lengths and were tested on an inclined wire Fourdrinier 
machine. Fibers were dispersed for three minutes in a small pulper at 
0.75% consistency (lbs. fiber per 100 lbs. slurry, or furnish). The 
cylindrical pulper was approximately 3 feet in diameter by 6 feet deep. 
Fibers were then mixed with unrefined sulphite pulp to form a 50% 
polyester blend and diluted to 0.1% consistency in a 10 cubic meter stock 
tank. This stock was further diluted in the headbox of the machine to 
0.0143% consistency and formed into a 0.5 meter wide wet lay nonwoven 
fabric at 20 meters/minute. A spray of an acrylic binder, Acronyl 240D was 
spray applied at the end of the Fourdrinier wire. The fabric was then 
cured in a through air drier at 150.degree. C. Finished fabric weight 
averaged 40 grams/square meter. 
Dispersion quality can be judged by the uniformity of the fabric produced 
from a given sample. As cut length increases, the uniformity of the fabric 
can generally be expected to suffer significantly. However, great 
advantages can result from using a longer fiber because the fabric tear 
strength increases, for example. In practice, therefore, a fabric producer 
will generally wish to use the longest fiber that will meet his uniformity 
standards. Thus, a longer fiber with improved, or equivalent uniformity 
would be preferred. 
The dispersion quality of fabrics from Fibers A and N were rated as they 
were produced on the machine by observing the fabrics as the water drained 
from them on the Fourdrinier wires. Results of this comarison are in Table 
2 and indicate good dispersion for the cruciform in spite of its 57% 
greater surface area. 
TABLE 2 
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DISPERSION DESCRIPTION 
ROUND CRUCIFORM 
CUT LENGTH ITEM A ITEM N 
______________________________________ 
1/4 inch good dispersion 
good dispersion 
few log defects 
few log defects 
3/8 inch some log defects 
good dispersion 
general quality not 
fair fabric cover 
so good as 1/4 inch 
(opacity) 
1/2 inch fairly good dispersion 
normal dispersion 
3/4 inch dispersion definitely 
very good dispersion 
poor, cover lower 
______________________________________ 
Standard physical properties were measured for the set of fabrics at Herty 
Foundation, Savannah, GA. Compared each time to Fiber A as 100%, Fiber N 
had the following average properties: 
______________________________________ 
Air Permeability, Gurley 
112% 
Opacity, ISO 2471 111% 
Bulk, TAPPI T410 om-83 and T411 om-83 
118% 
Tensile Strength, TAPPI T494 om-81 
100% 
Tensile Stretch, TAPPI T494 om-81 
85% 
Tear Strength, TAPPI T414 om-82 
104% 
______________________________________ 
On balance, Item N exhibited advantages in the important areas of higher 
permeability, opacity, bulk and tear strength compared to the control at 
equivalent tensile strength with a small reduction in stretch. The cover 
advantage is important because less fiber can be used for a nonwoven 
fabric with similar performance characteristics, thereby saving materials 
cost. The fabrics of Item N also have an attractive flannel-like hand. 
When used with the appropriate water-dispersible coating in appropriate 
amount, the cruciform cross-section fiber of the invention has given a 
fabric with surprisingly good dispersion uniformity, and the properties 
indicated. 
From theoretical considerations, water-dispersible fibers of conventional 
round cross-section would have been expected to give more uniform 
dispersions, and, therefore, more uniform wet-laid fabrics. This is 
because the surface energy required to disperse a fiber (or other 
articles) is given by: 
EQU Energy=(Surface Tension).times.(Dispersed surface area-Undispersed surface 
area). 
The undispersed fiber exists in logs or clumps of many hundreds of fibers, 
most of which are on the inside of the logs. Therefore the undispersed 
surface area is negligible compared to the dispersed area, and the energy 
term can be expressed approximately as: 
EQU Energy=(Surface Tension).times.(Number of fibers).times.(Surface area of a 
fiber). 
This energy term describes both the energy required to disperse the fiber, 
and the free energy driving force for reagglomeration. Therefore, for any 
given coating, and fiber dpf, fibers with lower area would be expected to 
provide a more uniform dispersion, hence more uniform fabric. The minimum 
surface area per unit weight for a given fiber occurs when the 
cross-section is round, which would be expected, therefore, to be 
preferred. 
Surprisingly, however, these cruciform fibers, in spite of about 60% 
greater surface area gave more uniform fabrics. Without limiting the 
invention to any theory, this may result from the fiber's hydrodynamic 
shape, which may more effectively use the energy available in the mixer 
shear field.