Note: Descriptions are shown in the official language in which they were submitted.
W094/19526 PCT/AU94100066
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WOOL AND WOOL-BLEND FABRIC TREATMENT
The present invention relates to wool and wool blend
fabric treatments and in particular to novel methods of
treating fabrics to give good colour yields when printed
and/or to reduce pilling.
Backqround
Wool and wool-blend fabrics have been processed and
treated for many years to improve and/or enhance a wide
range of characteristics. For example, the pre-treatment
of fabrics, such as wool, before printing is essential to
achieve good colour yields, levelness and brightness.
Similarly a range of processes and treatments have been
proposed to reduce or eliminate pilling.
Traditionally, chlorination has been used and
several variants of the chlorination process are still
used almost exclusively to prepare wool fabrics for
printing. Dichloroisocyanuric acid (DCCA) is the most
common chlorination reagent currently in use, and can be
applied by both batch (the most common) and continuous
processes. The batch method involves chlorination with
3-4% DCCA on mass of fibre (omf), at pH 3.5-4.5 and a
temperature of 20-40C for about 1 hour, followed by an
antichlor aftertreatment with sodium bisulphite and acetic
acid. The continuous process involves padding DCCA (35-50
gl 1), followed by a dwell time of 2-5 minutes before
rinsing and an antichlor treatment similar to the batch
process. The alternative to DCCA is Kroy chlorination,
originally introduced for treatment of wool tops, which
uses a solution of chlorine gas in water in a continuous
fabric treatment process. Chlorine reacts with water to
give a mixture of hypochlorous and hydrochloric acids,
which is sprayed directly onto the fabric with a wetting
agent. The reaction is more rapid than DCCA, but a
rinsing and antichlo treatment are still nècessary.
Processing speeds of 10-15 m min 1 at a chlorine dose
rate of 4% omf are typical and give similar performance to
fabrics treated with 4% DCCA.
Typical problems with fabric chlorination include:
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yellowing, achieving an even application, and fibre
damage. It is also very often necessary to bleach
chlorine-treated fabrics, usually with hydrogen peroxide,
to remove yellowness before printing. However, it is the
environmental pressure on processes involving chlorine,
particularly when absorbable organohalogens (AOX) are
present in the plant effluent, which is leading to the
replacement of chlorination by alternative technologies.
Other methods used to treat fabrics prior to
printing are not common. Two polymer treatment routes,
one for top and one for fabric are currently known, they
are:
l. Hercosett 125 (trade name)
This polymer is applied to wool top after a
prechlorination staqe. Fabrics produced from treated top
have an increased affinity for anionic dyes. The further
mechanical processing which occurs during gilling,
spinning and weaving results in a level preparation.
However the colour yields tend to be lower since less
chlorine is used. Further, care must be taken in washing
off since treated wool has a high affinity for loose
anionic dyes.
2. Synthappret BAP (trade name)
This polymer may be applied to a fabric without the
need for a prechlorination step. The treatment of fabrics
with this polymer prior to printing provides the fabric
with a high affinity for hydrophobic dyes. However, the
lack of a chlorination step reduces the penetration of
printing paste into the fibres, and control over the
steaming conditions is critical. This method has been
used to print wool/cotton blends, but not pure wool
fabrics to date.
Other methods avoiding the use of chlorine have been
developed but are not considered to be commercially viable
despite their reduced environmental impact. To summarise,
the only prior art methods widely used commercially for
pretreating wool fabrics for printing involve
chlorination, followed by rinsing and an antichlor
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treatment, which then may require a bleaching treatment to
remove yellowness.
Pilling is a term used to describe the formation of
small, tight balls of fibre on a fabric surface. Pilling
is highly detrimental to garments, resulting in a worn and
unkempt appearance, and is a particular problem for
knitwear.
The pilling process is complex but can be described
as four successive stages:
(i) Fuzz Formation. The mild rubbing action which
occurs during wear teases some surface fibres from their
parent yarns, resulting in a fuzzy surface.
(ii) Fuzz Entanglement. Areas of the garment which are
subjected to more frequent rubbing develop the higher fuzz
densities. Fibres in such areas become entangled at some
stage to form loose balls.
(iii) Pill Formation and Growth. Continued rubbing on
loose entanglements causes some to roll into tighter
balls. These tight balls resist further rubbing forces,
and some of the weaker fibres in the pills break. The
stronger fibres remain intact and anchor the pills to the
fabric surface. Pills grow as they pick up loose fibres
from the fabric surface.
(iv) Pill Wear-Off. The anchor fibres finally succumb to
the steadily increasing forces acting on the pill and
undergo fatigue failure. As each anchor fibre breaks,
those remaining have to withstand larger forces and the
rate of anchor failure thus accelerates. Pill removal
occures when the rate of anchor fibre breakage exceeds the
rate of pill growth.
The nature of the fibres (origin, processing
history, physical dimensions), the yarn (type, twist) and
the fabric structure are all important factors in
pilling. In wear there are other variables which can
influence the rate of pilling. It is well known that some
wearers produce more rapid and extensive pilling than
others. Laundering can substantially alter pilling
performance. Subjective differences between individuals
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also exist over how objectionable a given amount of
pilling is.
Several chemical treatments are known to reduce
pilling, although as yet no process can guarantee zero
pilling in wear. For example, the oxidative chlorination
processes commonly used for shrinkproofing have some
beneficial effect. Chlorine/Hercosett and certain other
polymer treatments which inhibit fibre migration by
forming inter-fibre bonds, are also beneficial. More
damaging dyeing conditions (i.e. long boiling times, high
temperatures, extremes of pH) also tend to reduce pilling.
Similar to printing pretreatments there is currently
a great deal of environmental pressure against the use of
processes which use chlorine, particularly when adsorbable
organohalogens (AOX) are produced in plant effluent.
Hence it is likely that the partially-effective
ant`i-pilling treatments and printing pre-treatments which
involve chlorine compounds will be phased out within the
next ten years or so.
Applicant has now surprisingly found that the
combination of subjecting a fabric to W radiation
followed by oxidative bleaching provides a synergistic
mechanism to effectively increase the ability of the
fabric to give good colour yield when printed and reduce
the likelihood of pilling.
Extensive investigations involving the use of either
W radiation or oxidative bleaching alone established that
the single steps were ineffective in increasing colour
yields or reducing pilling significantly. It was also
established that the oxidative bleaching step must follow
the irradiation, and cannot be applied first or during
irradiation while wet. It was found that high, even
colour yields, better than those produced by 4% DCCA, were
achieved using the two-step procedure over a range of
classes of dye.
Most research on the effects of W on wool has been
aimed at limiting the long-term negative effects such as
photoyellowing, phototendering and the fading of dyed
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wool. Previous work on the positive application of W
radiation (~ < 400 nm) in the treatment of wool fabrics
appears to be limited to two commercial patents.
U.K. Patent 811702 describes the use of ultraviolet
radiation for modifying the rate of dye uptake of wool
fabrics. This increases the colour yields of exposed
fabric, depending on the nature of the dye used. Use of
suitable stencils during irradiation, followed by use of a
dye resist agent to partially protect unirradiated areas
of fabric during dyeing, can produce good tone-on-tone
effects. This document also discloses that in the
interest of shortening the period of irradiation it is
advantageous to treat the fabric with an oxidising agent
during W exposure. However, this document does not
describe or suggest the possible application of
irradiation to fabric printing, or the method of oxidative
bleaching of the fabric after subjecting the fabric to
irradiation. In fact, the U.K. patent stresses the use of
an oxidising agent during W exposure to shorten the
period of irradiation rather than as an essential,
discrete step in a synergistic process to increase the
affinity of the fabric to dyes.
Japanese Patent H4-41768 claims that W exposure
alone is an effective shrinkproofing treatment for wool
fabrics. However the claimed large reductions in fabric
area shrinkage have not been reproduced in our studies.
This could be due to the nature of the wool fabric used by
the Japanese workers, or because their felting procedure
was less severe than ours.
Summary of the Invention
In particular, the present invention provides a
method of modifying the surface of a fabric which
comprises the successive steps of:
(i) exposing the fabric surface to W radiation;
and
(ii) oxidative treatment of the fabric.
In the first step of the method of the invention the
fabric may be irradiated by ultraviolet light from any
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suitable source. Preferably the fabric is subjected to
ultraviolet radiation in the preferred range of 400-180
nm. More preferably the fabric is subjected to
short-wavelength W radiation (W-C) having a wavelength
of 280-200 nm and yet even more preferably having a
wavelength near the absorption masimum of the disulphide
bonds in wool (approximately 254 nm).
The W radiation may be provided by any suitable
source. The source selected will depend on the intensity
and wavelength of irradiation to be used in the method.
Preferred sources of radiation for ultraviolet radiation
include low; medium-and high-pressure mercury arcs, and
senon discharge tubes. In a preferred embodiment of the
invention a low-pressure mercury arc, producing 85% of
emitted W at 254 nm, may be used.
The length of time for which the fabric is
irradiated will depend upon the intensity and wavelength
characteristics of the radiation source and the desired
result. Depending on the source of radiation, the length
of time required may range from a few seconds to 2 hours.
For esample, with a low intensity W source, such as a low
pressure mercury arc, irradiation times of 30-50 minutes
may be required. With a suitable medium or high-pressure
mercury arc of high W intensity (typically 120W cm 1),
irradiation times of a few seconds may be sufficient.
Using a suitable elliptical or parabolic reflector to
focus the W radiation from a tube into a narrow strip or
parallel beam allows fabric to be treated continuously,
and this is clearly the most suitable commercial method
for exposing large pieces of fabric. Alternatively a
continuous irradiation process could be used to treat
individual garments or lengths of fabrics for dyeing.
After W esposure, the colour of the wool or
wool-blend fabrics change from pale cream to pale
olive-green, and this colour changes over an hour or so in
room air to a pale yellow. Measurement by any
conventional method of the yellowness of fabrics
irradiated with W-C after standing for 24 hours can be
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used to assess the degree of surface modification.
In the second step of the invention the fabric may
be oxidised by any suitable treatment. For example, it
may be oxidised by using any suitable oxidant such as
hydrogen peroxide or permonsulphuric acid (PMS). In a
preferred embodiment, the fabric is bleached using
hydrogen peroxide. Preferably a solution of approximately
0.75% w/w hydrogen peroxide having a pH in the range 8-9
is used. The time period required for bleaching will be
dependent upon the type of fabric and oxidant used and the
desired result. The oxidant may be stabilised by any
suitable stabiliser. For example, if a hydrogen peroxide
solution is used then this may be stabilised by a
tetrasodium pyrophosphate.
In a preferred embodiment of the invention only the
W exposure is carried out continuously, followed by a
batch bleaching treatment. The W -irradiated fabric can
be stored for several months before bleaching without any
reduction in colour yields or anti-pilling properties.
In another embodiment of the invention a fully
continuous process using a more rapid oxidant such as PMS
may be used. It is also possible to undertake continuous
bleaching by use of hydrogen peroxide pad/steam methods.
It is possible to create fine-detailed tone-in-tone
effects on prints by placing a suitable stencil between
the radiation source and the fabric surface. After
bleaching, the stencil design is invisible, but after
print paste is applied irradiated areas take up more dye
and show higher colour yields. Fine meshes, small
repeating motifs or stripes can be used effectively to
give the impression that a larger number of colours have
been used to produce the finished design.
It is also possible to transfer tone-in-tone designs
from a compouter to a wool fabric. By using suitable
graphic arts software, a complex design or caption can be
cut into a thin adhesive PVC film which is opaque to W
radiation. The design is transferred either directly onto
the wool fabric or onto a clear polyethylene or
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polypropylene film (which is transparent to W down to
220 nm). After exposing the fabric to W and bleaching,
the design can be developed by overprinting a large area
with a suitable dye paste.
ExamPles
The invention will now be described with reference
to some specific examples. Whilst the e~amples are
limited to the treatment of wool fabrics prior to
printing, this has been done for convenience and in no way
is meant to limit the scope of the invention.
E~ample 1
Pieces of scoured undyed shirting fabric were
exposed to short wavelength W using a low pressure
mercury arc (30W) for periods ranging from 2-30 minutes by
wrapping the fabrics around the W tube. The fabrics were
then bleached for one hour at 60C using 0.75% w/w
hydrogen peroxide solution stabilised by tetrasodium
pyrophosphate (0.6% w/w) at pH 8-8.5. After rinsing,
drying and steam pressing, the fabric was printed using
20 pastes of the following composition:
Indalca PA3, 10% stock solution 50%
dye (e.g. Lanaset Blue 2R) 2%
water 38%
urea 10%
Print pastes were prepared using Lanasol Black 5055,
Lanasol Scarlet 3G and Drimarene Turquoise R-BLD dyes.
Test strips were printed using a Johannes Zimmer
Sample Printing Machine Type MDK, using two passes of a
magnetic squeegee bar.
After printing, fabric was dried at room
temperature, steamed at 100C for 30 minutes in an
autoclave, washed off in warm water and dried. All prints
made on irradiated/bleached fabric were visibly more
intense than those carried out using untreated, bleached
only and W -e~posed only fabric. The reflectance spectra
of printed samples was measured, and the reflectance
values at the centre of the strongest absorption band were
recorded. These were converted to colour yield (K/S)
WO94/19526 ~ 5 ~ 1 7 8 PCT/AU94/00066
values, which are related to the dye concentration at the
surface, using the Kubelka-Munk equation.
The colour yield of W -treated/peroxide-bleached
fabric was significantly higher than that of unirradiated
fabric. The colour yields increased with irradiation time
as shown in Figure 1, and in all cases exceeded those for
fabric treated with 4~ dichloroisocyanuric acid (DCCA)
after 30 minutes irradiation.
Esample 2
A piece fine glass fibre mesh was placed between a
low pressure mercury arc and a sample of ecru shirting
fabric. The sample was exposed to W for 40 minutes,
followed by pero~ide bleaching as described in Example 1.
The mesh design was not visible after bleaching, but after
printing with Lanasol Black 5055, a fine-detailed
black/grey tone-in-tone effect was observed.
E~ample 3
Scoured ecru wool fabric sampler were placed on a
conveyor system and passed below a medium pressure mercury
arc the W radiation from which was focused at the fabric
surface using an elliptical reflector. The conveyor speed
was varied from 2 to 15 metres per minute, and a single W
source having a power of 120W/cm was used. Samples were
given up to three passes under the W source over a range
of conveyor speeds, to simulate a machine having a series
of W tubes. The fabrics were then bleached, printed with
Lanasol Black 5055 and steamed as per Example 1, and the
colour yields measured. The colour yields of
W -exposed/bleached fabric varied with conveyor speed as
shown in Figure 2.
The example clearly demonstrates that colour yields
better than a 4% DCCA treatment can be achieved using
continuous W irradiation operating at speeds between 2
and 12 metres per minute.
E~ample 4
A company logo was generated using computer graphic
arts software and the design was cut into a thin black
adhesive PVC film. The design was affixed to a sheet of
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polyethylene film held taut on an aluminium frame. The
frame was held firmly over a piece of wool challis fabric
and a bank of low-pressure mercury arcs was positioned
over the frame. The frame and fabric were exposed to W
for 40 minutes. The fabric was removed and bleached as
described in Example 1. The entire area of the logo was
printed with Drimarene Turquoise R-BLD paste, and the
print was dried, steamed and washed off normally.
Irradiated areas of the printed logo were far more
intensely coloured than unexposed areas, and a
high-quality tone-in-tone print was obtained.
Esample 5
Four groups of three standard pilling samples
(double jersey knitted fabric) were prepared. The first
group was exposed to W-C radiation from a bank of eight
low-pressure mercury tubes for 50 minutes on both sides.
The second group was also exposed to W using similar
conditions, but afterwards the samples were bleached for
one hour at 60C with hydrogen peroxide (0.75% w/w)
stabilised with tetrasodium pyrophosphate (6 g/l) at pH
8-8.5. The samples were rinsed well and allowed to dry.
The third group of samples were bleached with peroxide
only, and the fourth group of specimens were untreated
controls. Pilling performance was measured using an Atlas
Random Tumble Pilling Tester (RTPT) using the standard
procedure (ASTM D3512-82), with number of pills counted at
5, 10, 15, 20, 25, 30 and 60 minute intervals. Figure 3
shows the variation in the mean number of pills per sample
throughout the pilling test. It is clear that only those
samples treated with W/peroxide bleachin~ show excellent
anti-pilling performance.
Example 6
Seven groups of three samples of standard double
jersey knitted fabric were prepared. The groups were
exposed to W-C radiation using an irradiator fitted with
eight low-pressure germicidal W tubes for periods of 0,
5, 10, 20, 30, 40 and 50 minutes. All samples were then
bleached for one hour at 60 C with hydrogen peroxide
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(0.75%w/w) stabilised with tetrasodium pyrophosphate (6
g/l) at pH 8-8.5. The samples were rinsed well in water
and allowed to dry. The pilling tests were performed on
each group of samples according to the standard ASTM
random tumble test method (ASTM D3512-82), with number of
pills counted at 5, 10, 15, 20, 25, 30 and 60 minute
intervals. Figure 4 shows the variation of the mean
number of pills observed for samples in each group with
tumbling time. Clearly the extent of W irradiation has a
dramatic effect on the degree of pilling observed; zero
pilling was found throughout the pilling test for all
samples irradiated with W for 50 minutes.
It will be appreciated by persons skilled in the art
that numerous variations and/or modifications may be made
to the invention without departing from the spirit and
scope of the invention as broadly described. The present
embodiments are, therefore, to be considered in all
respects as illustrative and not restrictive.
