Note: Descriptions are shown in the official language in which they were submitted.
W095/00697 21 6 ~ ~ ~ 9 PCT/Gsg4/01342
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FA~3RIC TREATMENT
Bachy ~u~d of the In~ention
1. Field of the In~ention
This invention is concerned with methods of reducing ~he
5 degree of fibrillation and fibrillation tendency of fa_ric
made from solvent-spun cellulose fibre, also known as lyocell
fibre.
2. De~cription of Related Art
It is known that cellulose fibre can be made by extrusion
10 of a solution of cellulose in a suitable solvent into a
coagulating bath. This process of extrusion and coagulation
is referred to as "solvent-spinning", and the cellulose fibre
produced thereby is referred to as ~solvent-spun" cellulose
fibre. One example of such a process is described in US-
15 A-4,246,221, the contents of which are incorporated herein by
way of reference. Cellulose is dissolved in a solvent such as
a tertiary amine N-oxide, for example N-methylmorpholine N-
oxide. The resulting solution is extruded through a suitable
die to produce filaments, which are coagulated, washed in
20 water to remove the solvent, and dried. The filaments are
generally cut into short lengths at some stage after
coagulation to form staple fibre. It s also known that
cellulose fibre can be made by extrusion of a solution of a
cellulose derivative into a regenerating and coagulating bath.
25 One example of such a process is the viscose process, in which
the cellulose derivative is cellulose xanthate. Both such
types of process are examples of wet-sp; nn; ng processes.
Solvent-spinning has a number of advantages over other known
processes for the manufacture of cellulose fibre such as the
30 viscose process, for example rP~llc~ environmental emissions.
As used herein, the term "lyocell fibre" means a
cellulose fibre obtained by an organic solvent-spinning
process, in which the organic solvent essentially comprises
a mixture of organic chemicals and water, and in which
35 solvent-spinning involves dissolving cellulose and spinning
W095/00697 PCT/GB94/01342
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without formation of a derivative of the cellulose. As used
herein, the terms "solvent-spun cellulose fibre" and "lyocell
fibre" are synonymous. As used herein, the term "lyocell
fabric" means a fabric woven or knitted from a plurality of
5 yarns, at least some of which yarns contain lyocell fibre,
alone or in blend with other type(s) of fibre.
Fibre may exhibit a tPn~ency to fibrillate, particularly
when subjected to mechanical stress in the wet state.
Fibrillation occurs when fibre structure breaks down in the
10 longit~ n~l direction so that fine fibrils become partially
detached from the fibre, giving a hairy appearance to the
fibre and to fabric containing it, for example woven or
knitted fabric. Dyed fabric containing fibrillated fibre
tends to have a "frosted" appearance, which may be
15 aesthetically undesirable. Such fibrillation is believed to
be caused by mechanical abrasion of the fibres during
treatment in a wet and swollen state. Wet treatment processes
such as scouring, bleaching, dyeing and washing inevitably
subject fibres to mechanical abrasion. Higher temperatures
20 and longer times of treatment generally tend to produce
greater degrees of fibrillation. Lyocell fabric appears to
be particularly sensitive to such abrasion and is consequently
often found to be more susceptible to fibrillation than fabric
made from other types of cellulose fibre. In particular,
25 cotton fabrics have an inherently very low fibrillation
tendency.
EP-A-538,977 discloses that fibrils can be LeuLoved from
fibrillated woven lyocell fabric by treatment with a solution
of a cellulase. Cellulases are enzymes which catalyse the
30 hydrolysis of cellulose. However, such treatment is not as
effective as could be desired, and disposal of used solutions
of the enzyme may pose enviLo~ tal problems.
It has been known for many years to treat cellulose
fabric with a crosslinking agent to improve its crease
35 resistance, as described for example in Kirk-Othmer's
W095l00697 ~ PCT/GB94/01342
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Encyclopaedia of Chemical Technology, third edition, Volume
22 (1983), ~iley-Interscience, in an article entitled
Te~tiles (Finishing)" at pages 769-790, and in an article by
H. Petersen in Rev. Prog. Coloration, Vol 17 (1987), pages
5 7-22. Crosslinking agents may sometimes be referred to under
other names, for example crosslinking resins, chemical
finishing agents and resin finishing agents. Crosslinking
agents are smal'~ molecules cont~;n;ng a plurality of
functional groups capable of reacting with the hydroxyl groups
10 in cellulose to form crosslinks. In the conventional type of
finishing process, a cellulosic fabric is first treated with
a crosslinking agent, for example by application from a pad
bath, dried, and then heated to cure the resin and induce
crosslinking (pad-dry-cure). It is known that crease-
15 resistant finishing treatments embrittle cellulose fabric withconsequent loss of abrasion resistance, tensile strength and
tear strength.
The first crosslinking systems were based on
formaldehyde, urea-~ormaldehyde and melamine-formaldehyde
20 resins. These suf~ered a number of problems. The treatment
caused temporary stiffening of the fabric because of the
presence of externally adhering resin. Treated fabric was
liable to liberate objectionable odours on storage. These
odorous subst~nces included the amine catalysts used to cure
25 the resin and the toxic chemical formaldehyde. It was
therefore considered necessary to wash the treated fabric to
remo~e external ~ adhering resin and byproducts of resin
formation capable of giving rise to objectionable odours.
Such w~.~h;ng and subse~uent drying of the treated fabric added
30 to the cost of the process.
Such systems have largely been replaced by sysLems
containing the so-called "low-formaldehyde resins" and "zero-
formaldehyde resins" as crosslinking agents. One known class
of such agents consists of the N-methylol resins, that is to
35 say small molecules cont~;n;ng two or more N-hydroxymethyl or
~- al3~o~ymethyl, in particular N-methoxymethyl, groups . N-
W095/00697 PCT/GB94/01342
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methylol resins are generally used in conjunction with acidcatalysts chosen to improve crosslinking performance. In a
typical process, a solution cont~in;ng about 5-9~ by weight
N-methylol resin crosslinking agent and 0.4-3.5~ by weight
5 acid catalyst is padded onto dry cellulosic ~abric to give
60-lO0~ by weight wet pickup, after which the wetted fabric
is dried and heated to cure and fix the crosslinking agent.
Fabrics treated with low-formaldehyde or zero-formaldehyde
resins generally do not exhibit temporary stiffening and do
lO not release objectionable odours. Cured flat fabrics and
finished garments are rarely washed prior to sale to the
consumer.
S~!mmary of the In~ention
According to a first aspect of the invention, a method
15 for reducing the fibrillation t~n~Pncy of lyocell fabric
includes the steps of:
a) treating the ~abric with a low-formaldehye or zero-
formaldehyde crosslinking resin;
b) heating the fabric under conditions effective to
20cause reaction between the resin and the cellulose;
c) washing the fabric; and
d) drying the fabric.
In this and the other aspects of the invention, the
fabric is treated with the crosslinking resin and heated to
25 cause reaction between the resin and the cellulose in the form
of flat fabric. In one embo~;m~nt of this and the other
aspects of the invention, which may be preferred, the fabric
is washed and dried in the form of flat fabric and is
thereafter suitable for cutting into pieces for the
30 manufacture of garments or other textile articles. In another
embodiment of this and other aspects of the invention, the
fabric is first made up into garments or other textile
W095/00697 ~ PCT/GB94tO1342
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articles which are then washed and dried to complete the
method of the invention.
According to a second aspect of the invention, a method
for reducing the degree of fibrillation of lyocell fabric
5 includes the steps of:
a) treating the fabric with a low-formaldehye c~ zero-
formaldehyde crosslinking resin;
b) heating the fabric under conditions effective to
cause reaction between the resin and the cellulose;
.
c) washing the fabric; and
d) drying the fabric.
According to a third aspect of the invention, a method
for providing a lyocell fabric which exhibits a low degree of
fibrillation and has a low fibrillation tendency includes the
15 steps of:
a) scouring and dyeing the fabric, thereby inducing
fibrillation in the fabrici
b) treating the fabric with a low-fo ~aldehye or zero-
formaldehyde crosslinking resin;
c) heating the fabric under conditions effective to
cause reaction between the resin and the cellulose;
d) washing the fabric; and
J
e) drying the fabric.
In this third aspect of the invention, the fabric may
25 optionally be bleached between the scouring and dyeing
proc~sses in step (a) and may optionally be dried between
W095/00697 PCT/GB94/01342
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steps (a) and (b). After step (c), the fabric may exhibit
such a high degree of fibrillation that textile articles made
from it would be commercially unacceptable. After step (e),
the fabric in the form of flat fabric or of textile articles
5 exhibits a very low and commercially desirable degree of
fibrillation.
One class of preferred crosslinking resins consists of
the N-methylol resins. Examples of suitable N-methylol resins
are those described in the abovementioned articles in Kirk-
10 Othmer and by Petersen. Examples of such resins include 1,3-
dimethylolethyleneurea (DMEU), 1,3-dimethylolpropyleneurea
(DMPU) and 4,5-dihydroxy-1,3-dimethylolethyleneurea (DHDMEU).
Other examples include compounds based on urones, triazinones
and carbamates. Another example of a preferred class of
15 crosslinking agents consists of compounds based on 1,3-
dialkyl-4,5-dihydroxy(alkoxy)ethyleneurea and its derivatives.
A further example of a suitable crosslinking agent is
melamine. Yet another example of a suitable crosslinking
agent is butanetetracarboxylic acid (BTCA). More than one
20 type of crosslinking resin may be used.
Crosslinking agents for crease-resistant finishing of
cellulose fabric are generally used in conjunction with a
catalyst. The catalyst serves to accelerate the crosslinking
= reaction and curing and fixation of the resin. The method of
25 the invention preferably utilises such a catalyst when
reco~m~n~e~ for use with the chosen crosslinking agent. For
example, N-methylol resins are preferably used in conjunction
with an acid catalyst, for example an organic acid such as
acetic acid or a mineral acid such as zinc nitrate or
30 magnesium chloride. Latent acids such as ~mmn~;um salts, amine
salts and metal salts may be used. Mixed catalyst systems may
be used.
The crosslinking agent and any catalyst are preferably
applied to the fabric from solution, preferably in water. The
; 3S solution may be applied to the fabric in known types of ways,
WO 95/00697 ~ 9 PCT/GB94/01342
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for example the solution may be padded on to the fabric or the
fabric may be passed through a treatment bath of the solution.
The fabric may be a woven or knitted fabric. The solution may
contain at least about 2~, preferably about 3 to about 6~, by
5 weight crosslinking agent. When a catalyst is used, the
solution may contain at least about 1~, preferably abou~ 1 to
about 2~, by weight catalyst.
After treatment with crosslinking resin according to the
invention, the ~abric is hea~ed to fix and cure the
10 crosslinking agent. The fabric may also be dried. The
heating step may precede, be part of, or follow the drying
step. The time and temperature required in the heating step
depend on the nature of the crosslinking agent and optional
catalyst employed. After heating and optionally drying, the
15 fabric may contain at least about 0.5~, preferably at least
about 1.0~, more preferably at least about 2.0~, by weight of
fixed crosslinking agent calculated on the weight of the
cellulose. The fabric generally contains no more than about
4~ by weight of fixed crosslinking agent calculated on the
20 weight of the cellulose. It has generally been found that
about 70 to 90~ of the crosslinking agent in the wet fabric
may become fixed to the cellulose.
The concentration of the resin in the bath is chosen
according to the activity and curing efficiency of that resin,
25 to give the desired value for resin fixed on fabric.
After heating and fixation, the fabric is washed and
dried according to conventional procedures for cellulose
fabrics .
Fabric treated according to the invention exhibits a very
30 low degree o~ ~ibrillation. This is particularly
surprising in that treatment with crosslinking agents is
generally believed to reduce the abrasion resistance of
cellulosic fabrics. The method of the invention requires an
,
W095/00697 PCT/GB94/01342
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additional wet processing step, and as mentioned hereinabove
such wet processing steps are known to cause fibrillation of
lyocell fabric. Fabric treated according to the invention has
excellent resistance to fibrillation compared with untreated
5 fabric. Fabric treated according to the invention is suitable
for the manufacture of textile articles such as garments. Such
textile articles may be laundered with onl~ little or slow
loss of the reduction in fibrillation tendency.
The method of the invention is applicable to fabric which
10 has already been dyed, including fabric dyed by processes such
as rope-dyeing which are known to cause mechanical abrasion.
This is an advantage of the invention, because it is known
that rope-processing of a fabric generally improves bulking
and relaxation of the fabric, leading to superior handle. The
15 method of the invention can be used on fabric which is already
fibrillated, even severely fibrillated. It has surprisingly
been found that when fabric exhibiting a high degree of
fibrillation is treated according to the method of the
invention, the treated fabric generally exhibits a very low
20 level of fibrillation. For most applications, fabric which
exhibits a high degree of fibrillation is considered to be of
subst~n~rd quality, with the consequence that additional
expensive processing steps are not considered to be justified.
It is a particular advantage of the invention that it permits
25 subst~n~rd fabric to be converted into first quality fabric
and textile articles.
Materials were assessed for degree of fibrillation using
the method described below as Test Method 1.
Test Method 1 (Assessment of Fibrillation)
There is no universally accepted st~n~rd for assessment
of fibrillation, and the following method was used to assess
Fibrillation Index (F.I.). Samples of fibre were arranged
into a series showing increasing degrees of fibrillation. A
st~n~rd length of fibre from each sample was then measured
woss/oo697 PCT/GB94/0~42
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and the number of fibrils (fine hairy spurs extending from the
main body of the fibre) along the standard length was counted.
The length of each fibril was measured, and an arbitrary
numher, being the product of the number of fibrils multiplied
S by the average length of each fibril, was determined for each
fibre. The fibre exhibiting the highest value of this product
was identified as being the most fibrillated fibre and was
assigned an arbitrary Fibrillation Index of 10. A wholly
unfibrillated fibre was assigned a Fibrillation Index of zero,
10 and the rPm~;n;ng fibres were evenly ranged from 0 to 10 based
on the microscopically measured arbitrary numbers.
The measured fibres were then used to form a standard
graded scale. To determine the Fibrillation Index for any
other sample of fibre, five or ten fibres were visually
15 compared under the microscope with the standard graded fibres.
The visually determined numbers for each fibre were then
averaged to give a Fibrillation Index for the sample under
test. It will be appreciated that visual determination and
averaging is many times quicker than measurement, and it has
20 been found that skilled fibre technologists are consistent in
their rating of fibres.
Fibrillation Index of fabrics can be assessed on fibres
drawn from the surface of the fabric. Woven and knitted
fabrics having F.I. of more than about 2.0 to 2.5 exhibit an
25 unsightly appearance.
Description of Pre~erred Embod~enta
The invention is illustrated by the following Examples.
In each case, the never-dried fibre used was prepared by
extruding a solution of cellulose in N-methylmorpholine N-
30 oxide (NMMO) into an aqueous bath and washing the fibre soformed with water until it was essentially free of NMMO.
~ les
A 100~ lyocell spun yarn woven fabric exhibiting zero
W095/00697 PCT/GB94tO1342
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F.I. was desized, scoured and dyed in a jet dyeing machine.
Desizing was carried out using a 1.5 g/l aqueous solution of
a commercially-available amylase preparation at pH 6.S-7.5 for
45 minutes at 70C. Scouring was carried out using an aqueous
5 solution containing 2 g/l sodium carbonate and 2 g/l anionic
detergent for 60 minutes at 95C. Dyeing was carried out using
an aqueous solution cont~in;n~ 4~ by weight on fabric o~ the
dyestuff Procion Navy HE-R 150 (Procion is a Trade Mark of
Zeneca plc), 80 g/l sodium sulphate and 20 g/l sodium
10 carbonate for 120 minutes at 85C. The fabric was rinsed with
water, first at 70C and then at ambient temperature; soaped
off using an aqueous solution containing 2 g/l Sandopur SR
(Sandopur is a Trade Mark of Sandoz AG) for 20 minutes at
95C; hydroextracted; and dried. This procedure is a typical
15 rope treatment process for cellulosic fabrics. The treated
fabric was severely fibrillated, and exhibited F.I. 4.5.
Samples of dyed fabric were padded with aqueous solutions
cont~;n;ng varying amounts of the low-formaldehyde resin
DHDMEU (supplied under the Trade Mark Arkofix NG conc by
20 Hoechst AG). The solutions contained an acid-liberating
catalyst as recommPn~Pd by the resi~ supplier at 25~ by weight
on weight of Arkofix NG conc. The samples of fabric were then
dried at 110C and the resin flash cured for 30 seconds at
180C. They were then reloaded on the jet dyeing machine and
25 scoured twice as before. The samples were then hydroextracted,
padded wet-on-wet with an aqueous dispersion cont~;nin~ 50 g/l
of a silicone-based softener (available under the Trade Mark
Rucofin A0736 from Rudolf Chemicals Ltd.), and dried at 110C.
The results were as shown in Table 1:
Table 1
Resin in bath ~ w/w 0.0 1.0 2.0 4.0 6.0 8.0
Resin fixed on fabric ~ w/w 0.0 0.5 1.0 2.0 3.0 4.0
F.I. 5.8 1.9 1.5 0.5 0.4 0.3
- The figures for the amount of resin fixed on fabric are
WO 95/00697 ~ PCT/GB94/01342
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estimated figures, based on 70~ active solids in Arkofix NG
conc, 80~ expressed liquor, and 85~ curing efficiency.
It can be seen that the F.I. of the untreated fabric
increased from 4.5 as expected during these additional wet
5 processing steps, whereas in contrast treatment with resin
actu.ally reduced the F.I. of the fabric from 4.5 to a
com~ercially acceptable level of 1.9 or less.
