Note: Descriptions are shown in the official language in which they were submitted.
1340008
Title
Pr~cess of Treating Shrinkable Fibers
Background of the Invention
Field of the Invention
The field of art to which this invention pertains is
shrinkable materials and, more particularly, it is directed to
processes for treating a tow of shrinkable fibers.
Specifically such invention is a process of treating
a tow of aromatic polyamide fibers by moving the tow in folds
through a chamber having a plug section which is operatively
connected by a restricted opening to a treatment section and by
heating the tow with steam in the treatment section.
Sufficient steam migrates into the plug section to
cause shrinkage of the tow in this section. The cross-sectional
area of the tow is substantially the same as the cross-sectional
area of the entrance opening of the plug section as it enters
such opening but it has a smaller cross-sectional area, due to
shrinkage, as it leaves this section and moves through the re-
stricted entrance opening of the treatment section. By making
this opening smaller so that the cross-sectional area of the
shrunken tow as it enters such restricted opening is sub-
stantially the same as the cross-sectional area of such opening,
loss of steam through the entrance opening of the plug section
15 mlnlmlzed.
More specifically, this invention is a process for
dyeing a fiber structure of poly(meta-phenylene isophthalamide)
fibers with a water-soluble dye by heating the amorphous, shrink-
able fibers, as spun and prior to drying, with steam, in a
specifically designed chamber, at a temperature from about
110~C. to about 140~C., and preferably at about 120~C., for a
time sufficient to diffuse substantially all of the dye into
the minute pores in the fibers, throughout the fiber structure.
An organic water-insoluble material, such as an ultra-
violet light screener, may also be mixed with the water-soluble
dye and padded onto the water-swollen fibers prior to heating.
*
~"-~ q 1~
While the dye is effectively d;i'~sed into the fiber structure
at temperatures between 110~(. and 140~C., 6uch structure
must also be heGted with steam at a sublimation temperature be-
low the glass transition temperature of the fibers in order to
sublime the screener into the pores of the fibers. The fibers
are then, preferably, further. heated with steam at about 165~C.
for a time sufficient to collapse the pores in the fibers and
lock the dye therein. At thi.s temperature the fibers also will
crystalli~e and the fiber struc~ure is thereby stabilized
against progressive laundry shrinkage.
Description of the Related Art
Aromatic polyamide fibers are well known to the art.
They have high tensile strength, are flame and heat resistant,
possess good flex life, and have high melting points which make
them particularly suited to be formed into fabrics usable as
protective clothing, and for many other uses.
It further is kno~. that while aromatic polyamide
fibers possess many desired properties as manufactured they al-
so require, for given uses, t.hat various steps be taken to im-
prove a property or properties of the fikers to meet a specific
end use. As an example, various additives such as dyes, ultra-
violet light screeners, flame retardants, antistatic agents or
wa.er repellents, may be incorporated into the fibers during
basic manufacture or in subse~uent proces,ing steps to improve
their performance levels.
This invention is specifically directed to aromatic
polyamide fibers of a poly(meta-phenylene isophthalamide) poly-
mer, hereinafter referred to as "MPD-I fibers". Such fibers,
which are descri_ed in greater detail in U. S. patent 3,287,324
to Sweeny, for example, pos5ess many useful properties. It is
well known to the art, however, that these fibers are difficult
to dye.
Various techniques have evolved to solve this dyeing
problem.
~ r~ 2
Surprisingly it has been found that by heating as-spun,
never-dried, water-swollen, or still moist to the touch, MPD-I
fibers with steam, heated withi~ certain temperature ranges, it
is possible effect:ively to dye the fibers. Specifically, it has
been found that such fibers may be dyed, using a water-soluble
dye, by heating the fibers with steam heated at a temperature
from about 110~C. to 140~C. for a time suf icient to diffuse the
dye into the pores of the fibers.
It further has been found that after this diffusion
step has taken place that such fibers may be subsequently heated,
again with ste~m, at a temperature of about 165~C. to collapse
the fibers and lock the dye in place. This latter step will al-
so crystallize the fibers and stabilize them against progressive
laundry shrinkage.
In practicing the invention just: described, the treat-
ment or dyeing or the fibers is accomplisrled by moving such
fibers, in tow form, through a treatment chamber having one or
more treatment sections. It has been found difficult to main-
tain the steam temperatures at the critical limits required,
within these sec'ions, since 1he steam tends to migrate toward
the chamber openings. This problem is partially solved
by supplying the tow to the chamber in foLds. ~hile
this is an effective means of controlling the loss of s'e~m,
the problem still remains tro~lesome, particularly in the case
of shrinkable tcws because their cross-sections vary due to
shrinkage as they move through the ch~mber.
Accorcingly, this invention provides i.~proved proc-
esses for treati.g aromatic polyamide fibers, using ste~~ to cye
a water-swollen fiber structure of poly(meta-phenylene isoph-
thalamide) fibers with a water-solu~le dye, before they are
h~ A ~
gi1~3
dried, or to add an organic water-insoluble material to the
fibers, either mixed with the dye or alone, and to lock the dye
and/or other impregnant into the pores of the fibers. This is
accomplished by maintaining the steam wi~hin certain critical
temperature ranges (e.g., 110~C. to 140~C.) in a specially de-
signed chamber to diffuse the dye into the fiber pores and up to
165~C. to sublime the water-insoluble material into such pores.
At this latter temperature the dye is also locked into the fibers~
while stabilizing such fibers against progressive laundry shrink-
age.
Summary of the Invention
Briefly described, this invention is a process for
treating synthetic fibers including the steps of:
moving a tow of shrinkable fibers in folds through a
treatment section having an entrance opening and an exit opening
smaller than the entrance opening and
heating the tow with steam in the treatment section.
In this process, the tow has a cross-sectional area
substantially the same as the cross-sectional area of the en-
trance opening as it enters that opening whereby loss of steam
through such opening is minimized and a smaller cross-sectional
area as it leaves the section, due to shrinkage. This latter
area is only slightly smaller, or substantially the same size
as, the exit opening whereby loss of steam is minimized through
this opening as well.
In a more specific embodiment, this invention is a
process of treating a tow of shrinkable fibers which includes
the steps of:
moving the tow in folds through a plug section
operatively connected by a restricted opening to a treatment sec-
tion, with the plug section having an entrance opening larger
than the restricted opening of the treatment section, and
heating the tow with steam in the treatment sec-
tion.
) O ~
Sufficient steam migrates throu~h the restric~ed open-
ing from the treatment section to the plug 8ection to ~ u~e
shrinkage of the tow in the plug section. The tow has a cross-
sectional area substantially the same as the cross-sectional
area of the entrance opening of the plug section as it moves
through this opening and has a smaller cross-sectional area as
it leaves the plug section and moves through the entrance open-
ing of the treatment section, due to shrinkage. The cross-
sectional area of the shrunken tow as it enters the smaller
entrance opening of the treatment section is substantially
the same as the cross-sectional area of this opening and, along
with the tow moving in folds in the plug section, this sub-
stanially prevents loss of steam through the entrance opening
of the plug section,
Preferably the tow is an amorphous aromatic poly-
amide and, more specifically the aromatic polyamide is poly
(meta-phenylene isophthalamide). Such tow has a second order
glass transition temperature in steam of above about 150~C.
The processes just described further may include the
steps of padding a water-soluble dye onto the tow prior to the
treatment section and heating the tow with steam in the treat-
ment section at a temperature of from about 110~C. to 140~C.
for a time sufficient to diffuse the dye into pores in the fibers
of the tow. Still further steps may include moving the tow into
a second treatment section and heating the tow with steam in
this section at a temperature above its glass temperature from
about 150~C. to 165~C, for a time sufficient to collapse the
pores and lock the dye within the fibers and to crystallize such
fibers and thereby stabilize the tow against progressive laundry
shrinkage.
In still another embodiment, the process of this in-
vention includes the steps of:
moving the tow through first and second treatment sec-
tions,
contacting the fibers of the tow prior to the first
treatment section with an aqueous mixture containing a water-
soluble dye and an organic water-insoluble material which
'13~000g
sublimes in steam at a temperature below the glass transition
temperature of the fibers,
heating the water-swollen fibers with steam in the
first treatment section at a temperature from about 110~C. to
140~C. for a time sufficient: to diffuse substantially all of the
water-soluble dye into the pores of such fibers throughout the
fiber structure,
heating the water-swollen fibers with steam at a sub-
limation temperature below the glass transition temperature of
the fibers for a time sufficient to sublime the water-insoluble
material into the pores of such fibers throughout the fiber
structure, and thereafter
heating the water-swollen fibers with steam in the
second treatment section at a temperature above the glass
transition temperature of the fibers for a time sufficient to
collapse the pores and irreversibly lock the dye within the
fibers and to stabilize the fibers against progressive laundry
shrinkage.
In this latter process, the fibers preferably are
heated with steam at a sublimation temperature from about 110~C.
to 150~C. The water-insoluble material may be an ultraviolet
light screener and the water-insoluble material may be a dis-
perse dye. Further the fibers may be heated with steam in the
second treatment section at a temperature of about 165~C. to
stabilize the fibers.
In more precise detail, this invention is a process
of treating a tow of shrinkable material including the steps of:
moving the tow at a first speed through an entrance
opening at one end of a funnel-shaped, fold-forming section hav-
ing converging walls which define a discharge opening at the
other end of the section, with the entrance opening being larger
than the discharge opening;
moving the folded tow through a restricted entrance
opening of a chamber defined by walls and having a plurality of
sections including a plug section and first and second steam
treatment sections, with the chamber being connected to the dis-
charge opening of the fold-forming section and the chamber
139 D~08
entrance opening being smaller than the entrance opening of
fold-forming section, and the chamber further having a tow
exit opening
wherein the dual action of the converging walls of
the fold-forming section and the tow pushing through the re-
stricted entrance opening of the chamber forms a plurality of
folds in the tow,
wherein steam is introduced into the second steam
treatment section, which is positioned between the entrance
and exit openings of the chamber, whereby such steam flows,
in one direction into and through the second steam
treatment section and into t,he first steam treatment section,
and from there into the plug section and toward the entrance
opening of the fold-forming section and
in the other direction into and through the second
steam treatment section and toward the exit opening of the cham-
ber,
engaging the folds of the tow as it is moved in the
fold-forming section and through the entrance opening of the
chamber with pins on an endless chain moving at a second speed
slower than the first speed
moving the tow in folds through the plug section at
the second speed and
wherein the plurality of folds of the tow are in sub-
stantial contact with the walls of chamber defining the plug sec-
tion during a substantial portion of their movement through this
section whereby to help substantially eliminate loss of steam
through the entrance opening of the fold-forming section and
wherein the steam flowing into this plug section
shrinks the tow so that it has a cross-sectional area smaller
than that at which it entered this section
moving the tow in folds through a restricted entrance
opening of the first treatment section, with such entrance open-
ing being smaller than the entrance opening of the chamber
1 3400~8
moving the tow through the first treatment section at
the second speed and wher,ein the plurality of folds of the tow,
as shrunken in the first plug ~section, are substantially in
contact with the walls defining the first treatment section
through much of their movlement through this section whereby to
further help prevent any losls of steam flowing though this sec-
tion and through the plug section from escaping through the en-
trance opening of the fold-forming section.
In such process, preferably, the chain engages two
tows, one on each side, and moves them at the second speed
through the chamber and the entrance opening of the chamber is
connected to discharge op,ening of the fold-forming section by
a tapered surface. A taplered surface also preferably connects
the plug section to the entrance opening of the treatment sec-
tion.
Finally, in its broadest terms, this invention
matches the shrinking profile of the tow with the profile of the
chamber walls, during treatment of such tow in the chamber.
Brief Description of the Drawing
Fig. 1 is a sch~matic view of an apparatus, including
a treatm,nt chamber suita~ble for practicing the process of this
invention.
Figs. 2 and ~A are schema~ic:views showing the chamber
in greater detail.
Fig. 3 is a cross-sectional view taken along lines
A-A of Fig. 1, which highlights a significant feature of this
invention, in showing the substantial contact of the tow with
the walls defining the restricted opening of the treatment sec-
tion of the chamber as it is moved through that opening.
Description of th~e Preferred Embodiments
This invention is an improved process for treating
shrinkable materials, such as aromatic polyamide fibers.
More Ispecifically,in the processes of this invention,
a water-soluble material, and, if desired, a water-insoluble
material are diffused or sublimed into a fiber structure of
MPD-I amorphous synthetic fibers to improve their properties.
13~0008
During the diffusion and sublimation steps, the fibers are
water-swollen or damp to the touch, with open pores. Steam
controlled at critical temperatures in a chamber, is used
to perfect the process~
Briefly, the fibers of this invention are prepared
from aromatic polyamide polymers such as are disclosed in U. S.
patent 3,063,966 to Kwolek, Morgan and Sorenson; 3,094,511 to
Hill, Kwolek and Sweeny; and 3,287,324 to Sweeny, for example.
In preparing the basic water-swollen MPD-I fibers
which are treated by the procless of this invention, aromatic
polyamides which have been prepared by procedures shown in the
above-mentioned patents are combined with various solvents to
form a spinning solution as shown, for example, in U. S. patent
3,063,966 and the fibers or filaments are formed by extruding
the spinning solution through orifices in a spinneret. Such
fibers may be dry-spun or wet-spun to form a water-swollen fiber
structure. In elther case, the fibers as spun are substantially
amorphous.
The fibers whether dry-spun or wet-spun contain a
substantial amount of solvent after having been solidified in
a dry-spinning e-a~oration cell or coagulated in a wet-spinning
precipitation bath. To remove the solvent such fibers are
brought into contact with an aqueous extraction bath, as is
known in the art~ As a result the fibers become "water-swollen"
with a water content of around 35% or more.
The above-described steps of forming amorphous water-
swollen fibers of an aromatic polyamide polymer are known to
the art and these fibers are all suitable for being further
treated or processed in accordance with the process of this in-
vention.
Specifically, in a preferred process, these water-
swollen fibers, which have not been dried, are contacted with
an aqueous solution c~ntaining a water-soluble material and
heated with steam at a temperature from about 110~C. to 140~C.
1340008
for a time sufficient to diffuse substantially all of the water-soluble
material into the pores of the fibers throughout such fiber
structure. The material diffused into the fibers preferably is a dye.
It may also be a surfactant.
In another preferred embodiment, when the material is dyed,
the water-swollen, dye-containing fibers are then further heated
with steam at a temperature above the glass transition temperature
of the fibers for a time sufficient to collapse the pores and
irreversibly lock the dye within the fibers and to crystallize such
fibers and stabilize them against progressive laundry shrinkage.
Temperatures in the range from 150~C to 165~C will accomplish
these objectives.
In still anther embodiment, never-dried, amorphous MPD-I
fibers of the type described are contacted with an aqueous mixture
containing both a water-soluble material, such as a dye, and an
organic water-insoluble material which sublimes in steam at a
temperature below the glass transition temperature of the fibers.
The water-swollen fibers are then heated with steam at a
temperature from about 110~C to 140~C for a time sufficient to
diffuse substantially all of the water-soluble dye into the pores of
such fibers and at a sublimation temperature below the glass
transition temperature of the fibers to sublime the water-insoluble
material into the open pores of such fibers. After the diffusion an
sublimation steps have been completed, the fibers may be further
heated with steam at a temperature above the glass transition
temperature of the fibers for a time sufficient to collapse the pores
and irreversibly lock the material within the fibers and to stabilize
the fibers against progressive laundry shrinkage.
The term "fiber", as used herein, includes both staple fibers
and continuous filaments. The continuous filaments may be in the
form of a tow containing a large number of filaments or in the form
of a yarn.
Referring specifically to Figure 1 of the drawing, a fiber
structure of never-dried, shrinkable fibers, as spun, in large
bundles called tow, as indicated by the reference
I
13~0008
numeral 1, is supplied from a ~upply ~ource 2 and passed over
guide rolls 3 to nip rolls 4 and 4'.
An aqueous bath 5 of constant level is maintained at
the entrance to the nip rolls. The tow 1 of moist to th~ touch
fibers is brought into contact with the bath 5 which contains
the material (e.g., a water-soluble dye, or surfactant, or
ultraviolet light screener, for example) to be diffused or sub-
limed into the fibrous tow. The pick-up of material on the
never-dried tow may be adjusted by suitably controlling the
speed of the tow and the pressure applied between the nip rolls.
The tow 1 coated with the desired amount of material
is then moved by feed rolls 6 into a treatment chamber 7, which
is suitably an elongated tube having two or more treatment
sections to which steam under appropriate pressure can be sup-
plied, as will be explained in greater detail.
The tow is heated in these treatment sections at the
required critical temperatures to diffuse the water-soluble
material and to sublime the insoluble material into the fibers,
after which such fibers may be further heated to stabilize the
fiber structure against progressive laundry shrinkage.
The processed tow is then moved out of the chamber 7
and onto a conveyor 8, and then through squeeze rolls 9 to help
remove water from the treated tow. The tow is then fed by feed
rolls 10 into a dryer 11, which includes upper and lower con-
veyors 12 and 13 which move the tow at a speed which is adapted
to form folds in the tow in the dryer. Such conveyors move the
tow through the dryer 11 for a time sufficient to remove sub-
stantially all of the water from the tow. The dried and proc-
essed tow is then moved over transfer rolls 14 and into a
storage container 15.
The treatment process will now be described in detail.
.
The tow 1 carrying the dye or other treatment m~terial
from the bath 5 is fed by feed rolls 6 at a first speed through
an entrance opening 17 at one end of a funnel-shaped, fold--
forming section 18 having converging walls 19 which define a
discharge opening 20 at the other end of the section.
134~0~8
The tow is then moved through a restricted entrance
opening 21 of the treatme!nt chamber 7 defined by walls 22 and
having a plurality of sections including a plug ~ection 23 and
first and second steam treatment sections 24 and 25. The
chamber 7 is connected, preferably by a sharply tapered surface
22' to the discharge opening 20 of the fold-forming section 18
and the chamber entrance opening 21 is smaller than the en-
trance c,pening 17 of the fold-forming section 18. The dual
action of the converging walls of the fold-forming section 18
and the tow 1 pushing through the restricted entrance opening
21 of the chamber 7 formci a plurality of folds in the tow. The
chamber 7 further has a tow exit opening 26.
Steam in introduced into the second steam treatment
section 25 which is posit:ioned between the entrance and exit
openings 21, 26 of the chamber 7. The steam flows in one
direction into the seconcl steam treatment section 25, then
through this section and into the first steam treatment section
24, and from there into t:he plug section 23 and toward the en-
trance opening 17 of the fold-forming section 18 and in the
other direction into and through the second steam treatment sec-
tion 25 and toward the e~cit opening 26 of the chamber 7.
As best seen in Figure 3, the folds of the tow 1 are
engaged by pins 27 on an endles~ chain 28 as the tow is moving
in fold~-forming section ]L8 and through the entrance opening 21
of the chamber 7. The chain 28 moves at a second speed slower
than the first speed at which the tow is fed into the fold-
forming section 18, by feed rolls 6.
The tow is moved in folds through the plug section 23
at this second speed. In this section 23 the plurality of folds
of the l:ow are in substantial contact with the walls of chamber
7 during a-substantial portion-of-their movement through_such
section whereby to help ;ubstantially eliminate loss of steam
through the entrance opening 17 of the fold-forming section 18.
The ste~m flowing into this plug section 18 shrinks the tow so-
that it has a cross-sectional area smaller than that at which
it enteced the section. The tow is then moved from the plug
1340008
section 23 and a restricted entrance opening 29 of the first
treatment section 24. The restricted entrance opening 29 i8
smaller than the restricted entrance opening 21 of the chamber
7.
The tow is moved through the first treatment section
24 at the second speed and the plurality of folds of the tow,
as shrunken in the plug section 23, are substantially in con-
tact with the walls defining the first treatment section 24
through much of their movement through such section whereby to
further help prevent any loss of steam flowing through this sec-
tion 24 and through the plug section 23 from e~caping through the
entrance opening 17 of the fold-forming section 18. Thi6 inven-
tion provides better control of steam temperatures in the criti-
cal treatment sections of the chamber.
The substantial contact of the folded tow with the
walls of the chamber 7, pushing through the restricted entrance
opening 21 of the plug section 23 and hence through the re-
stricted opening 29 of the first treatment section 24, along
the contact of the folds with the walls 22 in these sections,
substantially prevents escape of steam through the entrance
opening of the chamber.
In this same connection, it frequently is desirable
to wash the treated fibers in a wash section 30 of the chamber
7 prior to discharge of the tow from such chamber. The wash
water along with the folded tow, further combine to substantial-
ly prevent loss of steam through the exit opening 26 of the cham-
ber, as well.
By controlling loss of steam through the chamber open-
ings, it is possible to maintain better control of the critical
temperatures required in the first and second treatment sec-
tions, to effectively treat the fibers, as-previously described.
The treatment of the tow in the manner just de-
scribed provides MPD-I fibers having the improved properties
sought in the treatment.
The following example will further illustrate this
invention .
Examp~e
A. Preparation of Never-Dried Filaments of Poly(meta-
phenylene isophthalamide) ~MPD-I).
Filaments of MPD-I having an inherent viscosity of
1.5 were dry spun from a filtered solution containing 19%
MPD-I, 70~ dimethylacetamide (DMac), 9% calcium chloride, and
2% water. On leaving the drying tower the as-spun filaments
were given a preliminary wash with water so that they contained
about 60% DMac, 15% calcium chloride, and 100-150% water, based
on the weight of dry polymer. The filaments were washed and
drawn 4X at 90~C. in a counter-current extraction-draw process
in which the calcium chloride determined as chloride content
and DMac content were reduced to about 0.1% and 0.5%, re-
spectively. The wet filaments were gathered together to form
a tow, a conventional antistatic finish was applied to the tow,
and the tow was crimped in a stuffer box crimper at a tempera-
ture of about 80~C. in the presence of steam. The tow was then
collected, still moist to the touch, in a plastic-lined card-
board box. The individual filaments had a linear density of
about 1.55 decitex ~dtex) (1.7 dpf). The linear density of the
never-dried filaments here and elsewhere herein is based on the
weight of dry filaments.
B. Dyeing and Shrinka~e Stabili~ation of Tows of Never-Dried
MPD-I Filaments in a Steam Chamber.
Two 120-kilotex (1~000,000 denier) tows of never-dried
MPD-I filaments, prepared as described in Part (A) above, were
creeled through the guides of a continuous tow dyeing apparatus
equipped for high shrinkage tow. The tows were first fed between
nip rolls at a rate of 14 m/min. wherein an aqueous dye solution
was padded onto the tow so that the individual ~ilaments in the
tow were coated with the solution~ The solution contained 40 g/l
of C.I. (Colour Index) No.-Basic Yellow 28 dye (a water-soluble
dye), and 6 g/l of C.I. No. Basic Red 15 (a water-soluble dye),
and 6 g/l cellulosic thickner, and 58 g/l of anionic surfactant,
adjusted to a pH of 7 (adding acetic acid or caustic soda as need-
ed until the desired pH was obtained). The pick-up of the dye
solution on the tow as 30 weight %.
134~ûO~ '
,~
Af~er t~e ~ow~ were ra~Ae~ with the dye ~olution,
they were then passed through the entrance funnel of 4 ch~er,
such as that shown in Figure 2, the rectangular discharge end
of the funnel having a width of 95 mm and a depth of 115 mm.
Within the funnel the tows were turned and then gathered into
fold~ as they were picked up by a chain moving at 1 m/min.,
one tow on each 6ide of the chain. The tow6, carried by the
chain, were then pas6ed into the entrance Gl~ning of a plug
section of the ch~her, which had a rectangular cross 6ection
90 mm in width and 110 mm in depth, the discharge op~ing of
the funnel and the entrance opening of the plug ~ection being
gently tapered into one another to avoid a stair step tr~nsi-
tion. The plug ~ection wa~ 3 m in length, and from it the tows
were carried by the chain into a first treatment section, al~
3 m in length, which had a rectangular cross section 88 mm in
width and 107 mm in depth, the tran~ition from the plug sectiDn
to the first treatment section being gently tapered to avoid
a stair-step transition. From the first treatment section th~e
tows were then carried by the chain into a 6econd treatment
section 6 m in length wherein the tows of filaments coated with
the 601ution were exposed to steam at a pres~ure of 609 kPa
(six bars) and a temperature of 165~C. the ~team being intro-
duced into the chamber through holes in thewalls of ~he cham-
ber. The ~team flowed from the 6econd steam section bac~ inbo
the first treatment section and then lnto the plug sec~tion at
progressively lower pressure~ and temperatures in the direction
of the entrance funnel, the folds of the tow effectively seal-
ing the entrance to the plug section so ~at substantially no
steam flowed back into the entrance funnel. W~thin a zone
begi~ning at about the end of the plug section and exten~g
well into ~he first treatment section the fila~ent~ in the tows
coated with the solution were eYroseA to ~team at a t~mperatyre
of about 120~C. for a contact time of about two minutes. The
temperatur- of the tow- at the end of the first treatment ~eo-
tion, going into the ~_o~.d 6team treatment ~ectlon, was abo~t
1 3 4 ~ J 3 3
,~
165-C. and remained ~t about 165~C. throughout the second treat-
ment section. Upon leaving the treatment s-ctions the tows
were passed into a final wash section, wherein they were was~hed
with water. The water and the wet tows acted together to con-
dense the 6team flowing from the second treatment section and
formed an ef~ective seal to prevent any steam from flowing
from the eXit end of the chamber.
After the tows were washed, they were fed into a f~rced
air dryer, wherein their moisture level was reduced to 7%
moisture. Finish was not added to the tow. me tows were d~ed
to a bright ~hsde of orange. The shrinkage of the tows was
mea~ured and determined to be 0.9~.
In other experiments with similar tows using apparatus
having a steam ch~mher of constant area, it was found to be
dif~icult to maintain the steam at a pressure higher than ab4ut
203 kPa (t~o bars). The shrinkage of the tow when heated with
steam at a pressure of only 203 kPa was 7%.
