Title: Lyocell multi-filament for tire cord and method of producing the same
Abstract: Disclosed is a lyocell multi-filament for a tire cord and a method of producing the same. The method includes i) dissolving mixed powder of cellulose and polyvinyl alcohol in a mixed solvent of N-methyl morpholine N-oxide and water to prepare a dope, ii) extruding the dope using a spinning nozzle including orifices through air gaps into a conical upper coagulation bath to solidify the dope to produce a multi-filament, iii) feeding the multi-filament through a lower coagulation bath to a washing bath, and washing the multi-filament, and iv) drying and oiling the washed multi-filament and winding the resulting multi-filament. At this time, the orifices each have a diameter (D) of 100 to 300 .mu.m, a length (L) of 200 to 2400 .mu.m, and a ratio of the length to the diameter (L/D) of 2 to 8, and are spaced apart from each other at intervals of 2.0 to 5.0 mm. The method provides a lyocell multi-filament having excellent physical properties useful as a tire cord, thereby producing a tire for an automobile having improved driving stability, dimensional stability, and uniformity using the tire cord.
Patent Number: 6,852,413 Issued on 02/08/2005 to Lee, et al.
| Inventors:
|
Lee; Tae-jung (Anyang-si, KR);
Choi; Soo-myung (Anyang-si, KR);
Wang; Young-soo (Pusan-kwangyeok-si, KR);
Han; Seok-jong (Suwon-si, KR);
Kim; Cheol (Anyang-si, KR);
Kim; Myung-woo (Masan-si, KR);
Kwon; Ik-hyon (Seoul, KR);
Kim; Sung-ryong (Daejeon-kwangyeok-si, KR);
Choi; Jae-shik (Seoul, KR)
|
| Assignee:
|
Hyosung Corporation (Seoul, KR)
|
| Appl. No.:
|
735735 |
| Filed:
|
December 16, 2003 |
Foreign Application Priority Data
| Dec 26, 2002[KR] | 2002-0084310 |
| Jun 30, 2003[KR] | 2003-0043260 |
| Current U.S. Class: |
428/393; 152/451; 428/364; 536/56; 536/57 |
| Intern'l Class: |
D01F 002/00; B60C009/08 |
| Field of Search: |
428/364,393
152/451
536/56,57
|
References Cited [Referenced By]
U.S. Patent Documents
| 4416698 | Nov., 1983 | McCorsley, III | 106/200.
|
| 6013367 | Jan., 2000 | Nakagawa et al. | 428/393.
|
| 6701989 | Mar., 2004 | Choi et al. | 152/451.
|
Primary Examiner: Edwards; N.
Attorney, Agent or Firm: Nath & Associates PLLC, Nath; Gary M., Meyer; Jerald L.
Claims
What is claimed is:
1. A lyocell multi-filament having tenacity of 5 to 10 g/d, elongation of 3
to 13%, modulus of 200 to 400 g/d, birefringence of 0.038 to 0.050,
crystallinity of 40 to 52%, shrinkage of -0.5 to 3%, strength maintenance
after a high 15 temperature and saturated vapor treatment of 90% or
higher, and fineness of 1000 to 2500 deniers.
2. The lyocell multi-filament as set forth in claim 1, wherein elongation
is 0.5 to 4.0% at a load of 4.5 kg.
3. The lyocell multi-filament as set forth in claim 1, wherein a load at
break is 5.0 to 25.0 kg.
4. A tire cord comprising the lyocell multi-filament according to claim 1.
5. A dip cord for tire cords produced using the tire cord according to
claim 4.
6. The dip cord as set forth in claim 5, having fineness of 3000 to 6000
deniers, twist constant of 0.67 to 0.85, and a load at break of 14.0 to
28.0 kg.
7. A tire for automobiles comprising the lyocell multi-filament according
to claim 1.
8. A tire comprising the dip cord according to claim 5.
9. A tire cord comprising the lyocell multi-filament according to claim 2.
10. A tire cord comprising the lyocell multi-filament according claim 3.
11. A tire for automobiles comprising the lyocell multi-filament according
to claim 2.
12. A tire for automobiles comprising the lyocell multi-filament according
to claim 3.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a lyocell multi-filament for a tire cord,
a method of producing the same, the tire cord and a tire for an automobile
using the same. More particularly, the present invention relates to a
lyocell multi-filament for a tire cord, which has excellent physical
properties for the tire cord, thereby providing a tire with improved
driving stability, dimensional stability, and uniformity for an
automobile, a method of producing the same, the tire cord and a tire for
an automobile using the same.
2. Description of the Related Art
As well known to those skilled in the art, a material of a tire cord used
as a framework constituting a tire is selected from the group consisting
of polyester, nylon, aramid, rayon, and steel. In this regard, it is
required that the material of the tire cord has the following excellent
physical properties: 1) high strength and initial modulus, 2) excellent
heat resistance, and no degradation under dry and wet heat, 3) excellent
fatigue resistance, 4) excellent dimensional stability, 5) excellent
adhesiveness to rubbers (refer to Fukuhara, Fiber & Industry, 1980, Vol.
36, pp 290). However, the above materials cannot have all the above
excellent physical properties as described above, so the material of the
tire cord depends on the intended use of the tire cord.
For example, a radial tire, requiring excellent initial modulus
(elasticity), heat resistance, and dimensional stability, for high-speed
driving of an automobile comprises a tire cord mostly consisting of a
rayon fiber with low shrinkage and excellent dimensional stability. At
this time, the initial modulus is usually expressed as load per unit
stretch for a certain fiber denier, in other words, as a slope of an
elongation-load curve in a strength and elongation test. The higher the
initial modulus of the tire cord is, the less the tire will be deformed,
so the high initial modulus contributes to improving fatigue resistance,
heat resistance, and durability of the tire. Particularly, the high
initial modulus improves transverse-strength of the radial tire, thus
excellent driving stability of the radial tire is secured. Additionally,
the rayon tire cord has excellent driving stability in comparison with
various tire cords consisting of other materials because its physical
properties are rarely degraded at a temperature of 80 to 100.degree. C.
during driving of the automobile.
However, the rayon tire cord has relatively low tenacity and its modulus is
greatly degraded by moisture, so it is difficult to control moisture and
quality of the tire during the production of the tire including the rayon
tire cord. Additionally, even if the tire including the rayon tire cord is
manufactured, when a surface of the tire is damaged and moisture
penetrates into the damaged tire, strength and modulus of the tire are
reduced, thus being poor in terms of its performance. Accordingly, there
is a need to develop a tire cord having excellent strength and modulus
against moisture, in addition to having excellent tenacity.
Meanwhile, an artificial lyocell fiber consisting of cellulose is
advantageous in that elongation is low and tenacity is high, so its
dimensional stability is excellent, and its strength preservation
proportion is 80% or higher when the lyocell fiber absorbs water because
of its low moisture regain. Accordingly, in comparison with rayon (60%),
the lyocell fiber is competitive in terms of low reduction of modulus and
low deformation. However, the lyocell fiber has not been used as the tire
cord because of the spinning related problems.
A commercial value of fibers used in the tire cord or other industrial
materials depends on their physical properties such as tenacity and
modulus while the commercial value of fibers for clothes depends on
dyeability for vivid or bright colors and ease of care.
Accordingly, each textile maker continuously improves each textile's
qualities using various fiber production technologies according to use of
the fibers. Various technologies have been developed to improve physical
properties of the fibers. For example, when molecular chains constituting
a polymer are desirably oriented along a fiber axis, the fibers have
excellent physical properties useful to be applied to clothes and various
industrial fields. In this regard, orientation is conducted during the
drafting process, so the drafting process is one of the most important
processes capable of improving physical properties of the fibers.
Furthermore, the drafting process is conducted under a thermoplastic state
in which fluidity of molecules is good according to a melt-spinning
process. Additionally, according to a solution-spinning process, after a
solution including three components, that is, a solvent, a non-solvent,
and a polymer is prepared, the solution is spun using a wet spinning or
dry spinning method. The drafting process is conducted while vaporizing
the solvent in the case of the dry spinning method, but in the case of the
wet spinning methods, drafting of the fibers is conducted during the
coagulation process, so depending on a concentration and temperature of a
coagulation liquid.
Further, in the case of producing the lyocell fiber, when a solution
including NMMO (N-methyl morpholine N-oxide), water, and cellulose at
relatively high temperature of 80 to 130.degree. C. is spun in such a way
that a spinning nozzle is dipped in a coagulation bath according to the
traditional wet spinning method, the solution is too quickly coagulated to
secure desirable physical properties. Additionally, it is difficult to
sufficiently vaporize the solvent from a high viscous cellulose solution
of about 10000 poises using only the dry spinning method.
Meanwhile, a dry-wet method may be used to improve physical properties of
the fibers and spinning efficiency by properly utilizing air gaps
positioned between the spinning nozzle and the coagulation bath.
For example, EP. Pat. A-259,672 discloses a process of producing an aramid
fiber, in which the drafting and coagulation process are conducted using
air gaps to improve physical properties of the aramid fiber, and U.S. Pat.
No. 4,501,886 suggests a process of spinning cellulose triacetate using
air gaps. Additionally, Japanese Pat. No. 81,723 by Mitsubishi Rayon Co.
describes a high-speed spinning process of a PAN (polyacrylonitrile) fiber
using air gaps, East German Pat. No. 218,124 discloses a process of
spinning a cellulose solution using a tertiary aminoxide-based aqueous
solution, in which air gaps are used to prevent a plurality of filaments
from adhering to each other, and U.S. Pat. No. 4,261,943 discloses a
process of spraying water acting as a non-solvent to air gaps each having
a space of 50 to 300 mm to prevent a plurality of filaments from adhering
to each other.
The processes as described above contribute to improving orientation of the
fibers using the air gaps. However, they are not useful to be directly
applied to the production of a lyocell multi-filament, because filaments
are apt to adhere to each other because of a great number of filaments, so
desired spinning efficiency is not obtained. As well, the lyocell fiber
produced by the above processes has inadequate tenacity and elongation for
use as a tire cord.
Further, H. Chanzy et al. (Polymer, 1990 Vol.31, pp 400-405) propose a
process of producing a fiber using air gaps, in which salts such as
ammonium chloride or calcium chloride are added to a solution of cellulose
with the degree of polymerization (DP.sub.w) of 5000 in NMMO and the
resulting mixture is then spun to produce the fiber with tenacity of 56.7
cN/tex and elongation at break of 4%. However, it is difficult to
commercialize this process because of various disadvantages, for example
the recovery of the coagulation solution containing salts.
Further, U.S. Pat. No. 5,942,327 describes a process of producing a fiber
with tenacity of 50 to 80 cN/tex, elongation of 6 to 25%, and monofilament
fineness of 1.5 dtex using air gaps, in which a solution of cellulose with
the degree of polymerization (DP.sub.w) of 1360 in NMMO hydrate is spun.
At this time, the number of filaments of the resulting fiber is just 50
filaments. In general, the filament for a tire cord must have fineness of
about 1000 deniers, so hundreds of plies of filaments are needed to secure
fineness of about 1000 deniers. Accordingly, this patent is
disadvantageous in that it is difficult to secure the tire cord with
desired physical properties after twisting or dipping. Practically, it is
difficult to control spinning conditions of quenching in the air-gap,
washing, and drying of the fiber during spinning of the fiber with large
denier in comparison with the spinning process of the fiber with small
denier, so rarely securing desired physical properties of the fiber and
scarcely maintaining uniformity of the filaments. Accordingly, it is
nearly impossible to produce the industrial fiber referring to physical
properties of the fiber with 50 filaments. Furthermore, a process of
spinning the solution to the air gaps requires a new design accompanying
with additional considerations, such as an outer diameter of the spinning
nozzle, a diameter of an orifice, intervals between orifices, a length of
each of the air gaps, feeding conditions of cooling air, and a drying
condition of the filaments depending on a feeding direction of the
coagulation liquid and a spinning speed, because adherence of the
filaments to each other and quenching efficiency are varied according to
an increase of the number of the filaments. In this regard, physical
properties of the fiber depend on the design.
Moreover, U.S. Pat. No. 5,252,284 discloses a process of spinning a fiber
under conditions of air gaps each having a length within about 10 mm and a
winding speed of 45 m/min to produce the fiber consisting of 800 to 1900
filaments. However, this patent is disadvantageous in that elongation is a
relatively high 15.4% and tenacity is at most 47.8 cN/tex, thus securing
insufficient competitiveness of the fiber for use as a tire cord in terms
of tenacity and productivity.
Additionally, some methods of producing a mixture solution of cellulose and
polymer using NMMO are known in the art.
For example, U.S. Pat. No. 3,447,939 discloses a process of producing a
solution containing cellulose and polyvinyl alcohol dissolved in NMMO, and
U.S. Pat. No. 3,508,941 proposes a method of dissolving a mixture of
cellulose and polyvinyl alcohol in NMMO to extract the mixture. Further,
according to U.S. Pat. No. 4,255,300, when a mixing ratio of cellulose and
polyvinyl alcohol is 4:1 to 2:1 and a percent composition ratio of a
polymer to a solvent is 20% or lower, a fiber has excellent elongation.
However, U.S. Pat. No. 4,255,300 does not disclose the fact that the
tenacity of the fiber is improved because polyvinyl alcohol is added to
cellulose.
Meanwhile, U.S. Pat. No. 6,245,837 discloses a process of producing a fiber
with a tenacity of 27 cN/tex, in which a mixture including cellulose,
polyethylene, polyethylene glycol, polymethylmethacrylate, and
polyacrylamide is dissolved in a NMMO solution. However, this patent is
disadvantageous in that the fiber has very poor tenacity to be used as an
industrial filament or a tire cord.
Therefore, there remains a need to develop a cellulose solution for a high
strength cellulose filament.
The present inventors have made an effort to develop the cellulose solution
for the high strength cellulose filament, and found the fact that a
cellulose/polyvinyl alcohol/NMMO solution suppresses the generation of
fibril while a cellulose fiber is formed and the cellulose fiber having
excellent flexibility and tenacity can be produced using the
cellulose/polyvinyl alcohol/NMMO solution, thus the cellulose/polyvinyl
alcohol/NMMO solution is usefully applied to an industrial filament or a
tire cord.
Furthermore, the present inventors have conducted extensive studies into
the method of producing a lyocell filament useful as a tire cord,
resulting in the finding that the lyocell multi-filament for tire cords
with excellent physical properties can be obtained by providing a method
of producing the lyocell multi-filament, comprising the steps of
dissolving mixed powder of cellulose and polyvinyl alcohol in a mixed
solvent of N-methyl morpholine N-oxide and water to prepare a dope,
extruding the dope using a spinning nozzle including orifices through air
gaps into a conical upper solidifying bath to solidify the dope to produce
a multi-filament, feeding the multi-filament through a lower coagulation
bath to a washing bath, washing multi-filament, drying and oiling
multi-filament, and winding the resulting multi-filament, thereby
accomplishing the present invention.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made keeping in mind the above
disadvantages occurring in the prior art, and an object of the present
invention is to provide a method of producing a lyocell filament with
excellent tenacity and modulus for a tire cord in high yield, thereby
producing a tire with improved driving stability, dimensional stability,
and uniformity for an automobile.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and other advantages of the present
invention will be more clearly understood from the following detailed
description taken in conjunction with the accompanying drawings, in which:
FIG. 1 schematically illustrates the spinning process according to the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
Based on the present invention, the above object can be accomplished by
providing a method of producing a lyocell multi-filament for a tire cord,
comprising i) dissolving mixed powder of cellulose and polyvinyl alcohol
in a mixed solvent of N-methyl morpholine N-oxide (NMMO) and water to
prepare a dope, ii) extruding the dope using a spinning nozzle including
orifices through air gaps into a conical upper coagulation bath to
coagulate the dope to produce a multi-filament, iii) feeding the
multi-filament into a lower coagulation bath, changing moving course of
the multi-filament to a washing bath, and washing the multi-filament, and
iv) drying and oiling multi-filament and winding the resulting
multi-filament. At this time, the orifices each have a diameter (D) of 100
to 300 .mu.m, a length (L) of 200 to 2400 .mu.m, and a ratio of the length
to the diameter (L/D) of 2 to 8, and are spaced apart from each other at
intervals of 2.0 to 5.0 mm.
Additionally, the present invention provides the lyocell multi-filament
having fineness of 1000 to 2500 deniers, load at break of 5.0 to 25.0 kg.
The lyocell multi-filament consists of 500 to 1500 filaments each having
fineness of 0.5 to 4.0 deniers.
Furthermore, the present invention provides a tire cord for an automobile
and a tire for an automobile using the lyocell multi-filament.
In the i) step of the method of producing the lyocell multi-filament
according to the present invention, mixed powder of cellulose and PVA
(polyvinyl alcohol) is dissolved in a mixed solvent of NMMO (N-methyl
morpholine N-oxide) and water to prepare a dope.
Further, a pulp with a highly pure cellulose is used so as to produce a
lyocell multi-filament for a tire cord according to the present invention.
Because lignin has an amorphous structure and hemicellulose has a poor
crystalline structure, it is preferable to use the pulp containing a high
.alpha.-cellulose content and a minimum amount of lignin and hemicellulose
so as to produce a high quality cellulose-based fiber. Additionally, the
cellulose-based fiber is highly oriented and crystallized using cellulose
molecules with the high degree of polymerization, thereby securing
excellent physical properties. In this regard, it is preferable to use a
soft wood pulp with a degree of polymerization (DP.sub.w) of 800 to 1200
containing 93% or higher .alpha.-cellulose content.
PVA is added to cellulose during the preparation of the dope so as to
produce the desirable lyocell multi-filament for the tire cord according
to the present invention, thereby improving fibril resistance,
flexibility, and tenacity of the lyocell multi-filament. At this time, PVA
functions to reduce viscosity of a cellulose solution to increase fluidity
of the cellulose solution to improve homogeneity of the solution.
Additionally, the homogeneous cellulose solution contributes to improving
spinning efficiency thereof and producing the lyocell multi-filament with
excellent physical properties.
Furthermore, useful as a solvent needed during preparing the dope is the
mixed solvent of NMMO and water in the present invention, and NMMO1H.sub.2
O containing 10 to 20 wt % water, and preferably 13 wt % water is used as
NMMO.
Meanwhile, it is necessary to prepare the highly homogeneous and highly
concentrated dope while increasing the penetration of the solvent into the
mixed powder of cellulose and PVA so as to produce the fiber with
excellent physical properties. For this reason, it is needed to secure a
device capable of providing high shear stress to the solution and to
maintain a temperature of the solution at 80 to 130.degree. C. For
example, when the temperature is higher than 130.degree. C., a molecular
weight of cellulose is reduced due to the thermal decomposition of
cellulose, thus undesirably increasing end groups of molecular chains of
cellulose to reduce its physical properties and cause the decomposition of
NMMO. On the other hand, when the temperature is lower than 80.degree. C.,
time and energy consumed to sufficiently dissolve cellulose in the solvent
are increased and there is a disadvantage such that a low concentration of
cellulose solution must be prepared.
Moreover, it is necessary to uniformly mix cellulose and PVA with liquid
NMMO before cellulose is dissolved in the mixed solution of NMMO and water
to sufficiently penetrate liquid NMMO into cellulose powder to swell the
mixture of cellulose and PVA so as to produce the homogeneous dope without
undissolved cellulose particles.
Accordingly, in order to prepare the highly homogeneous cellulose solution,
cellulose powder mixed with PVA and the concentrated NMMO liquid are put
into a kneader at the same time and all of them are mixed with each other
in the kneader. The resulting mixture is repeatedly dispersed, sheared,
compressed, drawn, and folded in the kneader to produce a paste of the
swollen mixture of cellulose and PVA. The paste thus produced is
continuously stuffed into an extruder connected to the kneader and then
dissolved in the extruder, thereby accomplishing the highly homogeneous
cellulose/PVA dope.
In detail, cellulose powder with an average particle size of 500 .mu.m or
smaller is produced by a crusher, and the cellulose powder is mixed with
PVA powder having the degree of polymerization of 1000 to 4000 in a powder
mixer. The mixed powder of cellulose and PVA contains 0.5 to 30 wt % PVA,
and preferably 1 to 10 wt % PVA. When a PVA content in the mixed powder is
less than 0.5 wt %, physical properties such as fibril resistance of the
fiber become poor. On the other hand, when the PVA content is more than 30
wt %, the PVA is extracted in a coagulation bath after the dope is spun,
so undesirably increasing recovery cost of NMMO.
Hereinafter, there will be given a detailed description of the production
of the dope. First of all, 50 wt % NMMO aqueous solution is concentrated
to prepare the NMMO aqueous solution containing 10 to 20 wt % water, and
poured in conjunction with the mixed powder of cellulose and PVA into the
kneader. At this time, NMMO functions to swell the mixed powder, and is
maintained to 70 to 100.degree. C., and preferably 80 to 90.degree. C. in
terms of temperature during feeding NMMO into the kneader. The mixed
powder and concentrated NMMO are injected into the kneader at 65 to
90.degree. C., and preferably 75 to 80.degree. C. to produce the resulting
mixture, and the resulting mixture contains 5 to 20 wt % mixed powder of
cellulose and PVA, and preferably 9 to 14 wt % mixed powder according to
the degree of polymerization of cellulose. The mixed powder of cellulose
and PVA and liquid NMMO are repeatedly compressed, drawn, folded, and
sheared in the kneader to produce the homogeneous cellulose/PVA paste, and
the paste thus produced is fed into the extruder while being maintained at
75 to 80.degree. C. The paste is melted in the extruder at 85 to
105.degree. C. to accomplish the dope.
Furthermore, in the ii) step of the method of producing the lyocell
multi-filament according to the present invention, the dope is extruded
through a spinning nozzle including a plurality of orifices, reaches a
conical upper coagulation bath through air gaps between the fillaments,
and is solidified to obtain the multi-filament. At this time, each of the
orifices has a diameter (D) of 100 to 300 .mu.m, a length (L) of 200 to
2400 .mu.m, and a ratio of the length to the diameter (L/D) of 2 to 8, and
an interval between adjacent orifices is 2.0 to 5.0 mm.
FIG. 1 schematically illustrates the spinning process according to the
present invention. With reference to FIG. 1, the cellulose solution is
quantitatively fed from a gear pump 1 through the spinning nozzle 2 and
air gaps 3 to a surface of a coagulation liquid. The spinning nozzle 2 has
a circular cross-section, and a diameter of 50 to 160 mm, preferably 80 to
130 mm. When the diameter of the spinning nozzle 2 is smaller than 50 mm,
cooling efficiency of the cellulose solution is reduced and the partially
solidified cellulose filaments are attached to each other because
intervals between the orifices are very short. On the other hand, when the
diameter is larger than 160 mm, auxiliary devices such as a spinning pack
and the spinning nozzle become undesirably large. Moreover, when the
diameter of each of the orifices is smaller than 100 .mu.m, yarn breaking
occurs during spinning the cellulose solution to reduce spinning
efficiency, but when the diameter of each orifice is larger than 300
.mu.m, a solidifying speed of the cellulose solution in the coagulation
bath is slow and it is difficult to wash the multi-filament to remove
NMMO. Additionally, when the length of each orifice is shorter than 200
.mu.m, orientation of the cellulose solution becomes poor to degrade
physical properties of the multi-filament. On the other hand, when the
length is longer than 2400 .mu.m, great expense and effort are undesirably
required to produce the orifices.
Meanwhile, the number of orifices is 500 to 1500, and preferably 800 to
1200 because the multi-filament is industrially used as a tire cord and
the cellulose solution must be uniformly cooled. Efforts have been made to
develop industrial lyocell fibers, but the lyocell multi-filament with
high tenacity for tire cords have not yet been developed because it is
difficult to secure excellent spinning efficiency and sophisticated
technologies are needed due to the great number of filaments. To avoid the
above disadvantages, the spinning nozzle 2 including the above desirable
number of orifices is used in the present invention. When the number of
orifices is less than 500, fineness of each filament becomes large, so
NMMO is not sufficiently removed from the filaments for a short time to
cause incomplete solidification and washing of the filaments. On the other
hand, when the number of orifices is more than 1500, the adjacent
filaments are attached to each other in the air gaps and stability of each
of the filaments is reduced, thus physical properties of the
multi-filament are degraded, and some problems may occur in the twisting
and heat-treatment process which are processes required to apply the
multi-filament to tire cords.
Additionally, when the dope passing through the spinning nozzle 2 is
solidified in the upper coagulation liquid, it is difficult to obtain the
multi-filament with a dense and homogeneous structure because a surface
and an interior of a thick strand of the solidified dope have different
solidifying rates. Accordingly, the cellulose solution, that is, the dope,
is spun through the air gaps 3 with desirable space to produce fine fibers
in the coagulation liquid. When the thickness of each of the air gaps is
thin, the surface solidification of the spun dope is quickly conducted and
occurrence of micropores in the multi-filament is increased in the
solvent-removing process to prevent a draw ratio from being increased and
reduce a spinning speed. On the other hand, when the thickness of each of
the air gaps is thick, the filaments are attached to each other and
affected by a temperature and humidity of each air gap, thus the
production of the multi-filament is unstable. Hence, the width of the air
gap is preferably 20 to 300 mm, and more preferably 30 to 200 mm.
When the dope passes through the air gaps 3, quenching air is supplied to
the filaments so as to properly cool the filaments to prevent them from
being melted and attached to each other and to increase dipping resistance
of the filaments to the coagulation liquid. Additionally, a sensor 5 is
installed between a quenching air supplier 6 and the filaments to monitor
the temperature and humidity of the air gaps and control them. The cooling
air is preferably maintained at 5 to 20.degree. C. For example, when a
temperature of the cooling air is lower than 5.degree. C., the
solidification of the filaments is quickly promoted, so the high-speed
spinning process is not feasible. But, when the temperature is higher than
20.degree. C., yarn breaking may occur because dipping resistance of the
filaments to the coagulation liquid is reduced.
Moreover, a moisture content in the cooling air affects the solidification
of the filaments, and relative humidity (RH) in the air gaps 3 is
preferably 10 to 50%. In detail, dry air with relative humidity (RH) of 10
to 30% is supplied near the spinning nozzle and wet air with relative
humidity (RH) of 30 to 50% is supplied near the coagulation liquid so as
to improve a solidification speed of the filaments and prevent the
filaments from attaching to a surface of the spinning nozzle. The cooling
air is supplied to the filaments in such a way that it flows in parallel
with surfaces of the vertically moving filaments. At this time, a flowing
speed of the cooling air is preferably 1 to 10 m/sec, and more preferably
2 to 7 m/sec. When the flowing speed is less than 1 m/sec, the cooling air
does not sufficiently affect the filaments, a portion of each of the
filaments which the cooling air reaches late is different from another
portion of each of the filaments which the cooling air reaches early in
terms of the solidifying speed, and yarn breaking occurs, thereby the
homogeneous filaments being rarely produced. On the other hand, when the
flowing speed is more than 10 m/sec, the filaments vibrate, so the
filaments may be attached to each other and spinning stability of the
filaments is not secured because the dope is not uniformly spun.
As for a composition in the upper solidifying bath according to the present
invention, it is preferable that a concentration of NMMO in water in the
upper coagulation bath is 5 to 20%.
When the filaments pass through the upper coagulation bath 4, if the
spinning speed is increased by 50 m/min or more, the coagulation liquid
seethes due to friction between the filaments and the coagulation liquid.
This phenomenon functions to reduce stability of the production of the
multi-filament when physical properties of the multi-filament and the
spinning speed are improved by drawing the multi-filament to improve
productivity of the multi-filament. Accordingly, a doughnut-shaped mesh
net 7 is installed on the upper coagulation bath 4 to cause the
solidifying liquid to flow in the same direction as movement of the
filaments to spontaneously draw and orient the multi-filament.
Furthermore, in the iii) step of the method of producing the lyocell
multi-filament according to the present invention, the multi-filament is
fed through a lower coagulation bath 8 to a washing bath. In detail, the
lower coagulation bath 8 functions to recover the coagulation liquid 10
flowing down along the filaments discharged from the upper coagulation
bath 4, and a roller 9 installed in the lower coagulation bath 8 functions
to change the moving direction of the filaments. Additionally, the roller
9 rotates so as to reduce frictional resistance of the roller 9 to the
filaments. Furthermore, a control bath is separately installed so as to
control a concentration of the coagulation liquid in the upper coagulation
bath 4 in such a way that it is the same as a concentration of the
coagulation liquid in the lower coagulation bath 8 or a difference between
concentrations of the upper and lower coagulation bath 4 and 8 is within
0.5%. In this regard, a temperature and concentration of the coagulation
liquid must be constant because the solvent removing and drawing processes
which seriously affect physical properties of the filaments are
simultaneously conducted when the filaments pass through the upper and
lower coagulation bath 4 and 8. The filaments passing through the lower
coagulation bath are rinsed in the rinsing bath. At this time, the
filaments are rinsed according to a traditional rinsing process.
Moreover, in the iv) step of the method of producing the lyocell
multi-filament according to the present invention, the washed
multi-filament is dried, oiled, and wound according to a traditional
process, thereby accomplishing an industrial filament for tire cords.
The lyocell multi-filament according to the present invention has fineness
of 1000 to 2500 deniers and load at break of 5.0 to 25.0 kg. Further, the
multi-filament consists of 500 to 1500 filaments each having fineness of
0.5 to 4.0 deniers. Additionally, the multi-filament has tenacity of 5 to
10 g/d, elongation of 3 to 13%, modulus of 200 to 400 g/d, birefringence
of 0.038 to 0.050, crystallinity of 40 to 51%, shrinkage of -0.5 to 3%,
and strength maintenance of 90% or more after the heat and saturated vapor
treatment at a high temperature, thereby being usefully applied to the
tire cord for an automobile.
According to the present invention, disadvantages occurring in the method
of producing the lyocell multi-filament using a wet spinning process are
desirably overcome, and the maximum spinning speed is 250 m/min. That is
to say, even though the number of orifices of the spinning nozzle is
large, the homogeneous cellulose solution and the cooling air with
desirable temperature and humidity are used, so spinning efficiency is
excellent and friction between the filaments and the solidifying liquid in
the solidifying bath is reduced, thereby accomplishing the high-speed
spinning process.
A better understanding of the present invention may be obtained by reading
the following examples which are set forth to illustrate, but are not to
be construed to limit the present invention.
Dopes and lyocell multi-filaments produced according to examples and
comparative examples as will be described below are evaluated as follows:
(a) Degree of Polymerization (DP.sub.w)
An intrinsic viscosity (IV) of cellulose dissolved in a solvent was
obtained at 25.+-.0.01.degree. C. within a concentration range of 0.1 to
0.6 g/dl by a Ubbelohde viscometer using a 0.5M cupriethylenediamine
hydroxide solution prepared according to ASTM D539-51T. At this time, the
intrinsic viscosity was obtained by extrapolating a specific viscosity
against the concentration, and the intrinsic viscosity thus obtained was
substituted for the Mark-Houwink's equation, as will be described below,
to obtain a degree of polymerization.
[IV]=0.98.times.10.sup.-2 DP.sub.w.sup.0.9
(b) Attachment of the Filaments
Filament was repeatedly cut to lengths of 1 m, and the cut yarn with a
length of 1 m was cut again to produce a sample with a length of 0.1 m.
The above procedure was repeated so as to produce five samples. The
samples thus produced were dried at 107.degree. C. for 2 hours without
load, and then observed by naked eye using an Image Analyzer to determine
whether the filaments were attached to each other or not. If any
attachment between the filaments was found, the filament was evaluated as
"fail (F)", but if no attachment is found, it was evaluated as "pass (P)".
(c) Strength (kgf) and Elongation at Specific Load (%)
After the samples were dried at 107.degree. C. for 2 hours, strength and
elongation of each sample with a length of 250 mm were measured using a
low-speed elongation type of tensile strength tester manufactured by
Instron Co. at a tension speed of 300 m/min and at 80 TPM (twist/m). At
this time, elongation at specific load is measured as elongation at load
of 4.5 kg.
(d) Shrinkage (%)
After each sample was left at a temperature of 25.degree. C. and a relative
humidity of 65% for 24 hours, a first length (L.sub.0) of each of the
samples measured at a load of 20 g and a second length (L.sub.1) of each
of the samples measured after being treated at the load of 20 g at
15.degree. C. for 30 minutes were used to calculate shrinkage of each
sample by the following equation.
S(%)=(L.sub.0 -L.sub.1)/L.sub.0.times.100
(e) Birefringence
Birefringence of each sample was measured using a polarization microscope
adopting a Na-D light source and a Berek compensator.
(f) Crystallinity
Crystallinity of each sample was assessed using a wide angle X-ray
diffractometer (manufactured by Ricaku Co., X-ray source: CuKa (Ni
filter), output: 50 KV and 200 mA, and angle range: 2.theta.=5 to
45.degree.)
(g) Strength Maintenance After the Saturated Vapor Treatment
After exposed to high temperature and moisture, each sample was left in an
autoclave (manufactured by the present inventors) at 170.degree. C. for 10
min under a saturated vapor atmosphere so as to evaluate its shape and
physical property stability. The resulting sample was then dried to
measure its strength, and a ratio of the measurements of the strength
before and after the saturated vapor treatment was calculated to evaluate
the strength maintenance of each sample.
EXAMPLE 1
Mixed powder in which pulp with the degree of polymerization (DP.sub.w) of
1200 containing a .alpha.-cellulose content of 97% is mixed with PVA in a
weight ratio of 20:1, NMMO.1H.sub.2 O, and 0.01 wt % propyl gallate were
mixed to produce an 11.5% cellulose solution. Spinning nozzles with a
diameter of 120 mm including 800, 1000, and 1200 orifices were used to
extrude the cellulose solution. At this time, a diameter of each of the
orifices was 150 .mu.m, and a ratio of a length to the diameter (L/D) of
each orifice was 4 for all the spinning nozzles. When the cellulose
solution (head temperature: 110.degree. C.) passed through the spinning
nozzle flew through air gaps at a point spaced apart from the spinning
nozzle by 50 mm, cooling air with a temperature of 20.degree. C. and
relative humidity of 40% blew at a speed of 4 m/sec to the solution, and
an extruding amount and spinning speed of the solution were controlled in
such a way that fineness of the resulting multi-filament was 1500 to 2000
deniers. A temperature of a coagulation liquid was 20.degree. C. and the
coagulation liquid contained 20% NMMO and 80% water, and the coagulation
liquid circulated between an upper and a lower coagulation bath. At this
time, a temperature of the cooling air and a concentration of the
coagulation liquid were continuously monitored using a sensor and a
refractometer. NMMO remaining on the multi-filament discharged from the
upper and lower coagulation bath was rinsed, and the washed multi-filament
was dried and wound. Physical properties of the multi-filament are
described in Table 1.
TABLE 1
Example 1
Spinning conditions 1-1 1-2 1-3 1-4 1-5
Nozzle diameter (mm) 120 120 120 120 120
Number of orifices 800 1000 1200 1000 1000
Orifice diameter (.mu.m) 150 150 150 150 150
Fineness of multi- 1510 1508 1502 1720 2000
filament (d)
.sup.1 Physical properties
Attachment Pass Pass Pass Pass Pass
Tenacity (g/d) 6.5 7.7 9.4 7.5 5.7
Elongation at 2.1 1.9 1.1 1.9 2.7
specific load (%)
Elongation at 8.4 6.7 3.9 9.7 12.5
break (%)
Modulus (g/d) 230 270 350 280 205
Crystallinity (%) 44 48 51 50 42
Birefringence 0.043 0.046 0.048 0.049 0.042
(.DELTA.n .times. 10.sup.3)
.sup.2 Strength 93 94 92 95 95
maintenance (%)
.sup.1 Physical properties: physical properties of the multi-filament
.sup.2 Strength maintenance: Strength maintenance after the saturated vapor
treatment
From the Table 1, it can be seen that the number of the orifices rarely
affects spinning efficiency of the cellulose solution, and when the number
of the orifices is slightly increased, tenacity is increased and
elongations at specific load and at break are decreased. As for modulus,
it is the highest when the number of the orifices is 1200. When the
extruding amount and spinning speed are controlled in such a way that
fineness of the multi-filament is 1500 to 2000, attachment of the
filaments to each other is scarcely affected. Additionally, tenacity is
reduced but elongation is apt to be increased with an increase of fineness
of the multi-filament.
EXAMPLE 2
First mixed powder in which pulp with the degree of polymerization
(DP.sub.w) of 800 containing a .alpha.-cellulose content of 97% is mixed
with PVA in a weight ratio of 20:1, second mixed powder in which pulp with
the degree of polymerization (DP.sub.w) of 1200 containing a
.alpha.-cellulose content of 97% is mixed with PVA in a weight ratio of
20:1, NMMO.1H.sub.2 O, and 0.01 wt % propyl gallate were mixed to produce
two different cellulose solution samples. In this regard, a concentration
of the cellulose solution including the pulp with the degree of
polymerization of 800 was 13.5%, and that of the cellulose solution
including the pulp with the degree of polymerization of 1200 was 11.5%.
Spinning nozzles with a diameter of 120 mm including 1000 orifices with
three types of diameters of 120, 150, and 200 .mu.m were used to extrude
the cellulose solution. At this time, a ratio of a length to the diameter
(L/D) of each orifice was 5 for all the spinning nozzles. Cooling air was
fed to air gaps according to the same procedure as the example 1, and an
extruding amount and spinning speed of the solution were controlled in
such a way that fineness of the resulting multi-filament was 1500 deniers.
Subsequently, the cellulose solution passed through a coagulation liquid,
was washed, dried, and wound to accomplish the multi-filament. Physical
properties of the multi-filament are described in Table 2.
As described above, the spinning nozzle including 1000 orifices was used,
and the pulps each having the degree of polymerization (DP.sub.w) of 800
and 1200 were used to produce the multi-filament and dip cord in example
2. From the Table 2, it can be seen that tenacity is apt to be increased
with an increase of the diameter of the orifice, and much more increased
in the case of using the pulp with DPw of 800 than in the case of using
the pulp with DPw of 1200. Additionally, elongation is reduced but modulus
is increased in accordance with an increase of the diameter of the
orifice. Further, tenacity and modulus are highest when the degree of
polymerization of the pulp is 1200 and the diameter of the orifice is 200.
COMPARATIVE EXAMPLE 1
An 11.5% cellulose solution was produced using a mixture of pulp with the
degree of polymerization (DP.sub.w) of 1200 containing a .alpha.-cellulose
content of 97%, NMMO.1H.sub.2 O, and 0.01 wt % propyl gallate without PVA.
Spinning nozzles with a diameter of 120 mm including 1000 orifices with
two types of diameters of 120 and 150 .mu.m were used to extrude the
cellulose solution. At this time, a ratio of a length to the diameter
(L/D) of each orifice was 5 for all the spinning nozzles. Cooling air was
fed to air gaps according to the same procedure as the example 1, and an
extruding amount and spinning speed of the solution were controlled in
such a way that fineness of the resulting multi-filament was 1500 deniers.
Subsequently, the cellulose solution passed through a coagulating liquid,
was washed, dried, and wound to accomplish the multi-filament. Physical
properties of the multi-filament are described in Table 2.
TABLE 2
Example 2
Comp. Ex. 1
Spinning conditions 2-1 2-2 2-3 2-4 2-5
2-6 1-1 1-2
DP.sub.w of cellulose 800 800 800 1200 1200
1200 1200 1200
.sup.1 Con. of cellulose (%) 13.5 13.5 13.5 11.5 11.5
11.5 11.5 11.5
Orifice diameter (.mu.m) 120 150 200 120 150
200 120 150
.sup.2 Fineness (d) 1510 1505 1511 1500 1508
1507 1502 1505
.sup.3 Physical properties
Attachment Pass Pass Pass Pass Pass
Pass Pass Pass
Tenacity (g/d) 5.7 6.3 7.5 7.9 9.4
9.7 4.5 4.8
.sup.4 Elongation (%) 2.9 1.6 1.0 1.2 1.1
1.0 2.5 2.7
Elongation at break (%) 7.2 5.8 4.9 7.5 3.9
3.8 8.7 6.9
Modulus (g/d) 210 247 266 280 330
368 173 188
Crystallinity (%) 48 48 49 50 50
51 38 39
Birefringence (.DELTA.n .times. 10.sup.3) 0.045 0.045 0.042
0.048 0.049 0.049 0.037 0.037
.sup.5 Strength maintenance (%) 93 94 92 92
95 98 84 88
.sup.1 Con. of cellulose (%): Concentration of cellulose.
.sup.2 Fineness (d): Fineness of multi-filament
.sup.3 Physical properties: physical properties of the multi-filament
.sup.4 Elongation (%): Elongation at specific load (%)
.sup.5 Strength maintenance: Strength maintenance after the saturated vapor
treatment
COMPARATIVE EXAMPLE 2
The cellulose solution was produced according to the same procedure as
comparative example 1, and the physical properties of the multi-filament
were estimated while varying the number of orifices each having a diameter
of 150 .mu.m. When the number of orifices is 400, the spinning efficiency
is not poor but draft (ratio of winding speed of the
multi-filament/extruding speed of the cellulose solution) is reduced
because an extruding speed of the solution was much faster than a winding
speed of the multi-filament, thereby reducing tenacity.
When the number of the orifices is 1000 and fineness of the multi-filament
is 800 and 2300 denier, physical properties of the multi-filament and dip
cord are described in Table 3. If fineness of the multi-filament is 800
denier, strength is too poor to apply the multi-filament to a tire cord.
The multi-filament with fineness of 2300 denier is not useful to be
applied to the tire cord because of excessively high fineness.
Furthermore, the spinning nozzles including orifices having diameters of
90 and 350 .mu.m are insufficiently competitive in terms of spinning
efficiency, causing yarn breaking. Particularly, when the diameter of the
orifice is 350 .mu.m, most of filaments are attached to each other,
thereby greatly reducing the physical properties of the multi-filament.
TABLE 3
Comparative Example 2
Spinning conditions 2-1 2-2 2-3 2-4 2-5
2-6
DP.sub.w of cellulose 1200 1200 1200 1200 1200
1200
Orifice diameter (.mu.m) 150 150 150 90 350
150
Number of orifices 400 1000 1000 1000 1000 1000
Fineness of multi- 1503 800 2300 1511 1510 1508
filament
.sup.1 Physical properties
Attachment F F F F F Pass
Tenacity(g/d) 4.9 4.1 4.8 2.9 4.2 4.7
Elongation at 2.1 1.6 1.3 1.5 1.9 1.1
specific load (%)
Elongation at 6.5 3.4 9.1 6.0 6.3 5.3
break (%)
Modulus (g/d) 173 169 174 119 170 177
Crystallinity (%) 39 36 39 34 36 36
Birefringence 0.044 0.044 0.042 0.045 0.039
0.044
(.DELTA.n .times. 10.sup.3)
.sup.2 Strength 88 89 87 80 85 88
maintenance (%)
.sup.1 Physical properties: physical properties of the multi-filament
.sup.2 Strength maintenance: Strength maintenance after the saturated vapor
treatment
Therefore, the present invention provides a lyocell multi-filament having
excellent physical properties useful as a tire cord, thereby producing a
tire for an automobile having improved driving stability, dimensional
stability, and uniformity using the tire cord.
The present invention has been described in an illustrative method, and it
is to be understood that the terminology used is intended to be in the
nature of description rather than of limitation. Many modifications and
variations of the present invention are possible in light of the above
teachings. Therefore, it is to be understood that within the scope of the
appended claims, the invention may be practiced otherwise than as
specifically described.
*
