Method and apparatus of transferring a packet and generating an error detection code therefor

Fibers and yarns of polyethylene terephthalate (PET) and PET copolymers with a sheath/filamentous core microstructure are formed from unoriented and non crystalline "as spun" source fibers and yarns by drawing to high draw ratios in one step. Fibers and yarns with the sheath/filamentous core microstructure are stiffer than commercial PET fibers. Fibers and yarns with the sheath/filamentous core microstructure may be annealed and relaxed to increase their dimensional stability without loss of the sheath/filamentous core microstructure.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to a process for producing fibers and yarns of 
polyethylene terephthalate (PET) and PET copolymers which have a unique 
morphology. Unoriented and non-crystalline PET yarn, when drawn in 
accordance with the process of the invention, is formed into a yarn in 
which each fiber of the yarn has a sheath/fibrillar core (s/fc) 
microstructure. Because of this unique microstructure the yarn exhibits 
unique physical properties. 
PET fibers and yarns are known and utilized in many industrial 
applications. Industrial PET fiber and yarns, are differentiated from 
other PET filaments by their higher tenacity (strength) and higher modulus 
(stiffness). These high strength polymer fibers are particularly suitable 
for such applications as tire cords, conveyor belts, hosing, threads, 
carpets and the like. However, in the past, high stiffness PET fibers have 
suffered from substantial shrinkage when subjected to heat, which may 
render them unusable for many applications for which they are otherwise 
well suited, such as for tire cords. In order to reduce heat shrinkage 
while retaining high stiffness U.S. Pat. Nos. 4,101,525 and 4,195,052 are 
directed to processes for producing PET fibers which have high stiffness 
and reduced shrinkage and greater dimensional stability. These improved 
tensile properties result from the high degree of polymer extension and 
alignment along the fiber axis and by the distribution of fine, uniformly 
distributed, oriented, stabilizing crystallinity in the filaments that is 
produced in the spinning a drawing process. PET yarns produced in 
accordance with these processes are known as High Modulus Low Shrinkage 
(HMLS) yarns and have received commercial acceptance. Nevertheless, the 
art desires fibers and yarns of even greater tenacity and modulus, reduced 
heat shrinkage, and greater dimensional stability. The present invention 
is directed towards providing such improved PET fibers and yarns. 
The starting fiber used for carrying out the present invention is 
molecularly unoriented and non-crystalline PET fiber or yarn. When drawn 
according to the invention such that a draw ratio of greater than 5.7:1 is 
achieved in one step then each fiber in such a drawn yarn will have a 
sheath/fibrillar core (s/fc) distribution of microstructure that is 
visible in optical photomicrographs of the fiber. By this is meant that 
the core of each fiber has a multitude of long crystalline fibrils with a 
diameter of about 0.1 um that are aligned with the fiber axis. The polymer 
in the sheath of each fiber does not have long fibrils but is comprised of 
oriented and crystalline PET. 
PET fibers having the s/fc morphology exhibit a higher modulus than that of 
HMLS PET fibers and yarns, but exhibit higher heat shrinkage when 
heat-treated. In order to reduce the degree of shrinkage on heating in 
fibers with the s/fc microstructure, the fibers may be subjected to 
additional processing. These additional processing steps are 1) Annealing 
(heat treating under high line tension to further develop crystallinity) 
and 2) Relaxing (heat treating under reduced line tension to allow a 
degree of shrinkage). The s/fc microstructure is retained throughout the 
annealing and relaxation steps. 
PET fibers and yarns that have a s/fc microstructure and which have been 
annealed and relaxed have higher stiffness, lower heat shrinkage, and 
higher dimensional stability than that of the commercially available HMLS 
fibers and yarns. Accordingly PET yarns and fibers processed in accordance 
with the present invention are higher performance substitutes for the 
applications for which HMLS yarns and fibers are suited.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In order to achieve a PET yarn or fiber having the desired s/fc 
microstructure and physical characteristics it is necessary that the feed 
PET fiber or yarn be molecularly unoriented and non-crystalline. The 
presence of either orientation or crystallinity will prevent the formation 
of the s/fc microstructure in the drawing process. Fibers that are 
unoriented and non-crystalline have low birefringence, so that a 
birefringence test may be used to determine if a fiber is suitable for use 
in this process. Generally speaking unoriented and non-crystalline PET 
fibers result when the fibers are spun at low speed, that is spinning 
speeds in the area of 1-300 mpm (meters per minute). Fibers spun at higher 
rates (1000 mpm) will be partially aligned and those spun at even higher 
rates (&gt;2000 mpm) will be highly aligned and partially crystalline. Either 
of these conditions will not allow the desired s/fc microstructure to be 
formed. 
FIG. 1 illustrates drawing apparatus 10 suitable for carrying out the 
various drawing (and relaxing) steps of the present invention. A supply 
spool 11 provides the fiber or yarn 12 to be worked to a feed unit 14 
which comprises a number of driven wheels 16 through which the fiber 12 is 
threaded so that the feeding speed of fiber 12 is controlled by the 
rotation of wheels 16 whose speed is controlled by controller 18. After 
exiting feed unit 14, fiber 12 passes through temperature controlled ovens 
20,22 which act to provide any necessary heating to fiber 12. A tension 
meter 24 senses the tension of fiber 12 and supplies a signal indicating 
the tension of fiber 12 to permit the process to be controlled. Fiber 12 
then passes to take up unit 26 and is threaded through a series of driven 
take up wheels 27 under the control of controller 28 and passes to a take 
up spool 30. 
The speed of rotation of wheels 16 of feed unit 14 is controlled by 
controller 18 which cooperates with controller 28 to control the speed of 
wheels 27 of take up unit 26. When wheels 27 of take up unit 26 are 
rotated at a speed greater than that of wheels 16 of feed unit 14 a 
tension will be applied to fiber 12 so that it can be drawn. Conversely, 
when wheels 27 of take up unit 26 are rotated at a speed lesser than that 
of wheels 16 of feed unit 14 a relaxation will be applied to fiber 12. 
Ovens 20,22 are used to supply any heating to fiber necessary to the 
drawing or relaxing steps. The ratio of speed of rotation of the wheels 27 
of take up unit 26 to the speed of the wheels 16 of feed unit 14 controls 
the "draw ratio" applied to fiber 12. By way of example, if take up unit 
26 is operated at a speed 6 times that of feed unit 14 the draw ratio will 
be 6 to 1, so that the length of fiber 12 will be increased to 
approximately six times its original length in this drawing process. For 
processes requiring multiple drawing (or relaxing) steps a series of 
feeding and take up units, ovens and their associated controllers may be 
used to complete the steps of the process in a continuous manner. 
The s/fc microstructure of the fibers and yarns processed in accordance 
with the present invention is formed by drawing unoriented, 
non-crystalline PET yarns to draw ratios beyond 5.7 to 1 in one step at 
temperatures just above or below the polymer glass transition temperature, 
Tg (approximately 80.degree. C.). To achieve high draw ratios (&gt;5.7:1) in 
one step high, near breaking, tensions must be applied to the draw line. 
When such tensions are applied a so-called "head and shoulders neck" forms 
in the yarn at a point between the feed rolls and the oven. A "head and 
shoulders" neck is characterized by an abrupt transition to narrower 
diameter. In this type of necking the diameter of the fiber undergoes an 
abrupt reduction in diameter in the space of less than a few millimeters. 
(This is not the same as the thinning or extension that occurs in many 
polymer drawing processes where the draw in any one step is at less than 
5.7 to 1 or at draw temperatures well above Tg. (In a thinning, the 
diameter of the drawn fibers gradually reduces over a space of one or more 
centimeters.) Heat and draw line tension are needed to initiate the head 
and shoulders necking of the fibers but it is usually possible to maintain 
the neck at lower temperatures with higher applied tensions. Necking 
initiation temperatures in the range 60 to 120.degree. C. have been used. 
Maintenance temperatures as low as 29.degree. C. are possible. 
In order to assure the formation of the desired s/fc microstructure it is 
necessary to draw the unoriented non-crystalline yarn with a sufficiently 
high line tension so that: a) a head and shoulders neck forms and b) a 
high draw ratio (5.7 to 1 or greater) results in a single step. The 
equipment illustrated in FIG. 1 is useable to carry out this drawing. In 
order to draw to a ratio of 5.7 or greater to one the rotation of speed of 
the take up unit 26 is adjusted by controller 28 so that its wheels 27 
rotate at a speed 5.7 or more times the speed of wheels 16 of feed unit 1. 
Drawing of the fibers or yarns at much above 6 to 1 may cause breakage of 
the fiber or yarn, thus such breaking draw ratios form the upper limit of 
the draw ratio of this process. Ovens 20 (or 22) are used to apply heat to 
the fiber to cause initiation of the head and shoulders neck, after neck 
initiation the temperature of the ovens 20,22 may be reduced, as less 
temperature is required to maintain the neck. Generally speaking in order 
to produce the s/fc microstructure draw throughput rates between 2 and 6 
mpm are required. 
Each fiber in such a drawn yarn has a s/fc distribution of microstructure 
that is visible in optical micrographs of the fiber at 1000.times. 
magnification. FIG. 2a and 2b are respectively an optical and a SEM 
photomicrograph of a fiber processed according to the present invention, 
which clearly shows the s/fc microstructure. Typically the fibrillar core 
is contained in the central 17 um of a 28 um diameter fiber. The sheath of 
each fiber is highly oriented (as shown by birefringence) and crystalline 
(as shown by the absence of a "cold crystallization" peak in DSC 
thermograms) but free of the fibrillar filaments which are seen in the 
core. The core of each fiber includes a multitude of long crystalline 
microfibrils (as seen in optical micrographs at 1000.times. magnification) 
that are aligned with the fiber axis and have a diameter of about 0.1 um. 
Typically approximately 700 microfibers can be counted in the core of a 28 
um diameter fiber. It appears that the strain caused by drawing to high 
ratios induces a type of strain-induced crystallization that results in 
the s/fc microstructure. 
As will be discussed in detail below, a fiber or yarn of PET with the s/fc 
microstructure will have a high stiffness (initial modulus or EASL). 
However, the dimensional stability of the "as drawn" yarn can be improved 
by processing that improves the crystallinity (annealing) and reduces its 
heat shrinkage (relaxation). Annealing and relaxing lead to yarns with a 
s/fc microstructure which exhibit an improved dimensional stability. 
In the annealing step fiber that has been drawn to induce the s/fc 
microstructure is subjected to a higher temperature heat treatment under 
high, near breaking, line tensions to improve the crystal structure. The 
annealing is conducted at a temperature above the cold crystalline 
temperature (approximately 140.degree. C.) of PET as determined from DSC 
thermograms. This is believed to result in a growth in crystal size and 
perfection. Annealing is conducted at high, near breaking, line tensions 
so as to prevent any contraction of extended polymer chains. By way of 
example, a drawn PET yarn with a s/fc microstructure can be annealed by 
subjecting it to line tension that produces a slight additional draw (draw 
ratios of 1.05-1.3 to 1) at a temperature of 200.degree. C. for a 
residence time of 30 seconds. Annealing produces an increase in yarn 
stiffness and a reduction in heat shrinkage while retaining the 
sheath/core microstructure. 
If a greater reduction in heat shrinkage is required the heat treating step 
can be followed by a "relaxation" step. In the relaxation step heat is 
applied to the fiber or yarn at a reduced line tension. The lower line 
tension and hence the relaxation are accomplished by running the rollers 
of take up unit at a slower speed than those of the feed unit. Suitable 
exemplary parameters for the relaxation step are an applied temperature of 
200.degree. C. with a draw ratio of from 0.8 to 1 to 0.95 to 1. The 
resulting relaxed PET fibers or yarn exhibit reduced heat shrinkage with 
some loss of stiffness but the dimensional stability which is a balance of 
these two properties can be improved. 
EXAMPLES 
Before discussing the particular examples of the PET yarn processed in 
accordance with the present invention a discussion of the terms used in 
the measurement of the physical properties of the yarn is appropriate: 
Birefringence: Birefringence, or "Bi" is determined by using a Berek 
compensator mounted in a polarizing light microscope, which expresses the 
difference in the light index parallel and perpendicular to the fiber 
axis. The birefringence level achieved is directly proportional to stress 
exerted on the fiber material during melt spinning. When PET is spun under 
relatively low stress conditions, as when spun at low speeds (1-500 mpm) 
birefringences of 0.001 to 0.002 result. When spun under conditions of 
high stress, as when spun at high take-up speeds, higher birefringences 
(0.003 to 0.030) result. 
Tensile Properties: Stress-strain curves for five samples of each yarn were 
measured on an Instron Universal Tester in accordance with ASTM D885-79, 
vol. 03.01. Tensile strength at break, elongation at break, and initial 
modulus properties were derived. Tenacity and initial modulus are reported 
in units of grams per denier at 25 deg. C. Elongation given as percent 
measured at 25 deg. C. 
Elongation at Specified Load (EASL): EASL is the elongation that a yarn 
sample undergoes when subjected to a load (the specified load). The load 
specified here is 2 g/den. The EASL values reported here are therefore the 
elongation at 25 deg. C. that a yarn exhibits when subjected to a load 
amounting to 2 g/den, expressed as a percent of the original length. EASL 
is an alternative to initial modulus as a measure of fiber stiffness. 
Stiffer fibers elongate less under load. Whereas initial modulus reflects 
the stiffness of the yarn at low applied loads where the stress/strain 
response is linear, EASL is used as a measure of stiffness at higher loads 
where the stress/strain response may or may not be linear. 
Hot Air Shrinkage(HAS): HAS is the reduction in length, measured at room 
temperature, that yarn exhibits when exposed to hot air in an oven at 177 
deg. C. for 30 min under a load of 0.1 g/den.; expressed as a percent of 
its original length. 
In general, as PET fiber becomes more oriented through spinning or drawing 
the polymer chains in the fiber become more extended and aligned with the 
fiber axis. As a result the fiber stiffness increases (initial modulus 
increases, EASL decreases) and the tendency to shrink in hot air increases 
(HAS increases). In applications such as tire reinforcement the 
reinforcing tire cord experiences high tire fabrication temperatures. A 
tire cord with a high stiffness may loose this stiffness if it shrinks 
during fabrication. Thus, in the case of tire reinforcement, high 
stiffness is only useful if it is not accompanied by high shrinkage. In 
HMLS yarns a relatively high stiffness is achieved without proportionate 
increase in hot air shrinkage. This is the result of the formation of a 
distribution of fine crystallites in the fibers of the yarn that 
effectively restrain shrinkage. EASL and HAS values are frequently taken 
as measures of yarn stiffness and shrinkage. 
Dimensional Stability Rating (DSR): The DSR is a calculated figure of merit 
that is a measure of yarn dimensional stability. EASL and HAS values are 
used as measures of stiffness and shrinkage. The DSR is obtained by 
calculating the ratio of the sum of EASL and HAS for a sample yarn to the 
sum for a reference yarn 
DSR=(EASL+HAS).sup.reference * 100/(EASL+HAS).sup.sample 
By this definition, a dimensional stability rating of greater than 100 
indicates that the yarn in question (the sample) has a greater stability 
than the reference and is therefore more desirable as a tire 
reinforcement. 
PET fiber was processed through the various steps of the present process 
and its physical properties were measured after each step so as to 
determine what properties were affected by the process steps. The physical 
properties of the yarns produced by the process steps of the present 
invention are summarized in Table 1 to follow. Table 1 also includes the 
properties of commercially available Hoechst Celanese Trevira (R) D-792 
HMLS tire yarns both as spun and drawn ("D-792 Spun & Drawn" and after 
standard heat treating steps ("D-792 Heat Treated"). 
TABLE 1 
__________________________________________________________________________ 
Yarn Draw 
Ten 
Elong @ 
Init. 
EASL 
HAS EASL 
DSR 
__________________________________________________________________________ 
s/fc - "as drawn" 
6.1 6.8 
10.4 141 1.19 
20.9 
22.1 
29% 
s/fc - annealed 
7.4 9.8 
6.5 173 0.73 
9.4 10.2 
63% 
s/fc - 6.5 5.5 
13.4 129 1.31 
2.0 3.3 193% 
annealed/relaxed 
D-792 7.9 
10 111 2.3 6.4 8.7 74% 
spun & drawn 
D-792 8.9 
9 127 1.7 4.7 6.4 100% 
Heat Treated 
__________________________________________________________________________ 
Ten @ Brk = Tenacity at breakage in grams per denier 
Elong @ Break = Elongation at breakage in grams per denier 
Init Mod = Initial Modulus (Stiffness) in grams per denier 
EASL = Elongation at a Specified Load (2 grams per denier) as a percentag 
HAS = Hot Air Shrinkage at 177.degree. C. as a percentage 
EASL + HAS = Sum of EASL and HAS percentages 
DSR = Dimensional Stability Rating: EASL + HAS!Sample/EASL + HAS!D792 a 
a % 
The feed yarn used herein was a 19 filament, 677 denier, PET yarn melt spun 
from PET resin (iv in OCP=0.68 dL/g) spun at 300.degree. C. at 200 mpm. 
The fiber had a low birefringence (Bi=0.001) and no indications of 
heterogeneity or anisotropy. The Tg of the PET fiber was measured by 
differential scanning calorimetry (DSC) to be=.about.80.degree. C. Three 
packages of the yarn were combined to form a 57 filament, 2030 denier 
yarn. 
The feed yarn was drawn in a manner to produce a s/fc microstructure. The 
57 filament feed yarn was drawn on the unit of FIG. 1; a head and 
shoulders neck was initiated by hot air (100.degree. C.) flowing through 
oven 20 with a load on the line of 650 g. The neck localized at a position 
2 to 4" before (upstream) from the oven. At this load the fiber stretched 
such that the take-up roll ran 6 times faster than the feed roll for a 
calculated draw ratio of 6.0:1. The ratio of feed to product denier was 
6.1, indicating an actual draw ratio of 6.1:1. When a higher load was 
applied to achieve a higher draw ratio, the line would break. Because the 
load produced a very high draw ratio in a single step a s/fc 
microstructure developed in each of the fibers of the yarn that is 
observable via optical microscopy. 
The physical properties of the "as drawn" s/fc yarn are shown in Table 1 in 
the row "s/fc nontreated". It can be seen that the "as drawn" s/fc yarn 
has a higher stiffness than the standard tire yarn ("D-792 Heat Treated") 
with about equal tenacity and elongation. This higher stiffness is 
indicated by both measures of stiffness: a) by higher initial modulus, and 
b) by lower EASL. However, the heat shrinkage (HAS) is greater for the "as 
drawn" s/fc yarn than for the standard D-792 yarn which results in a poor 
Dimensional Stability Rating of 29%. This indicates that the "as drawn" 
s/fc yarn is not as dimensionally stable as either as untreated D-792 
(DSR=63%) or heat treated D-792 (DSR=100%). Nevertheless if heat shrinkage 
is not a consideration in the application for which the yarn is intended, 
the physical properties of the s/fc, non-treated PET yarn are superior to 
that of D-792. 
In order to improve the dimensional stability rating of the "as drawn" s/fc 
yarn, it was annealed. The "as drawn" s/fc yarn was subjected to 
200.degree. C. heat treatment (annealing) for a residence time of 30 
seconds while being drawn at a draw ratio of 1.265 to 1 with an applied 
load of 920 grams. As is seen in the row "s/fc Annealed" of Table 1 the 
annealing step has greatly reduced the heat shrinkage while improving 
modulus and tenacity thus raising the DSR from 29% to 63% which is 
comparable to that of non heat treated D-792. The s/fc microstructure is 
preserved in yarns that have been annealed. 
In order to further reduce the heat shrinkage the annealed s/fc PET yarn 
was further processed in a relaxation step. The annealed yarn was heat 
treated at 200.degree. C. for a residence time of 30 seconds but with a 
draw ratio of less than one, e.g., the take up unit rotates at a lower 
speed than the feed unit. In this case the relaxation ratio was 0.95 to 1 
at a relatively low line tension of 45 grams. The relaxation step will 
cause the more shrink prone components in the annealed yarn to contract 
(relax) while retaining s/fc microstructure. As is shown in the 
row"s/fc-annealed/relaxed" of Table 1, the resulting PET yarn exhibited 
lower heat shrinkage (HAS) while retaining a substantial fraction of the 
stiffness it had after annealing. This results in a DSR of 193%, a 
substantial improvement in dimensional stability compared to D-792. The 
combination of low heat shrinkage and high stiffness is not found in the 
commercially available D-792 PET yarn which when heat treated has a DSR of 
100%. Additional relaxation steps may be undertaken to further reduce heat 
shrinkage. 
In order to determine whether the s/fc microstructure is formed in PET 
copolymers, a yarn comprising 90% by weight PET with a 10% by weight of a 
2,6 naphthalene dioate monomer was used as the feed yarn. This yarn was 
spun at 200 mpm and had a low birefringence. A 57 filament yarn was 
processed on the equipment of FIG. 1. A s/fc microstructure was formed in 
certain of the fibers when the yarn was fed at 4 mpm and necking was 
initiated by heating to 120.degree. C. with a load of 620 grams and a draw 
ratio of 6.6 to 1. A s/fc microstructure was also formed in certain of the 
fibers when the yarn was fed at 6 mpm and necking was initiated by heating 
to 120.degree. C. with a load of 620 grams and a draw ratio of 6.75 to 1. 
Thus the present process is applicable to copolymers having at least 90% 
of the components of PET. 
The invention has been described with respect to preferred embodiments. 
However, as those skilled in the art will recognize, modifications and 
variations in the specific details which have been described and 
illustrated may be resorted to without departing from the spirit and scope 
of the invention as defined in the appended claims.