Note: Descriptions are shown in the official language in which they were submitted.
- 1 - 21~1813
"Bleaching jeans"
DESCRIPTION
The present invention concerns a process for brightening
or blP~rh;n~ dyed cotton fabrics in the absence of added
hypochlorites, pP~-n~n~tes and enzymes as well as a
brightening bath suitable for carrying out this process.
For several years there has been an increased need for
dyed cotton fabrics in particular for cotton jeans dyed
with indigo or other dyes which are brightened or
partially decoloured in further procP~; n~ steps either
by mechanically supported washing processes or/and by
chemical processes.
It is known that the overall colour tone of j eans
fabrics can be toned down or brighten~d with
hypochlorites such as NaOCl. This process has, however,
the disadvantage that large amounts of waste water
pol luted with AOX result, which have to be subsequently
treated in order to comply with the limits for waste
water which are bPc~m; n~ increasingly stringent. In
addition public criticism of the use of products
containing chlorine as well as of processes for
manufacturing consumer products using ~hpm;~
containing chlorine is increasing due to the
physiological risks of these substances. Manufacturers
of dyed cotton fabrics in particular of jeans fabrics,
therefore attempt to develop brightening processes which
are less critical, in order to save disposal costs or
additional production costs due to subse~uent expensive
effluent processing methods.
- 2 - ~1~181~
It is known inter alia that dextrose as a reducing agent
can be used as an alternative to hypochlorite bleaching
which, however, has the disadvantage that the treatment
temperature has to be at least 80C and the pH value of
the brightening bath has to be adjusted to 13.
Furth. ~ the use of ozone as an oxidizing agent for
brightening dyed cotton fabrics is known, but this
process has, however, the disadvantage that the hRnrll in~
of ozone in technical production processes is quite
difficult. In addition the cotton fibre is heavily
damaged by treatment with ozone. Furth~ ~ ketone
derivatives are known as reducing agents for brightening
cotton fabrics. These substances allow normal conditions
with regard to the 1 eat 1 temperature, pH value of
the brightening bath and duration of treatment, but they
have the disadvantage that the values f or the biological
and chemical oxygen demand of the waste water (BOD5 and
COD) are increased due to organic pollution by the
washing liquor. In addition the white-blue contrast of
cotton f abrics that are dyed with indigo is increased
when uEing ketone derivatives as brightening agents
which is undesired for the application.
In order to avoid the disadvantages of hypochlorite
bleaching, cotton materials have recently been treated
with potas6ium p~rrqn~RnRte to partially oxidize dyes in
the cotton fabric in order to brighten cotton materials.
The disadvantage of this process is that the waste water
from the brightening process is polluted with large
amounts of heavy metals. Moreover the use of
permanganates considerably in~:L ~ases operating costs . In
addition the f ibres are coloured brown through MnO2 .
The use of hydrogen peroxide or peracetic acid to
brighten dyed cotton fabrics i~ known. However, these
_ 3 _ 2 1 ~:L 813
substances are not used themselves to carry out the
brightening step but to neutralize cotton fabric which
has already been brightened by hypochlorite or potassium
pPr---n~;-nslte (cf. e.g. GB-A-2 213 842, US-A-5,205,835,
JP-A-31027174; US-A-5,238,463; JP-A-3027173). However,
as already described above these processes have the
disadvantage of using hypochlorites or p~rr~n~n~tes.
Furth~ the brightening of dyed textiles in the
presence of an enzyme such as peroxidase or oxidase and
H2O2 as an oxidizing agent is known (WO-A-921867). This
process is, however, expensive due to the use of enzymes
and is theref ore not suitable f or large-scale processes .
The object of the present invention was therefore to at
least partially eliminate the disadvantages of the state
of the art and to provide a process for brightening dyed
cotton fabrics which is comparable to the use of
hypochlorite with respect to the achieved effect and
costs but which has the advantage of lower BOD5 and COD
values in the waste water.
DE-OS-27 36 560 discloses a bl~hinq agent composition
which is essentially composed of 50-99 . 9 % by weight of
an inorganic peroxide which is capable of forming
hydrogen peroxide in an aqueous solution and of a
special complexing agent. There is no mention of
peroxodisulf ates .
EP-A-0 531 849 discloses a process for bleaching
materials made of cellulose dyed with direct or reactive
dyes by treatment in a bleaching and retreatment bath
which contains a bleaching agent, stabilizers, cationic
_ '- and optionally non-ionic surfactants. Hydrogen
peroxide is named as the bleaching agent.
` 21 1 13
_ 4 _ ~3 ~
Chemical Abstracts 92: 60299J and 60289A disclose a
process for blea~hin~ dyed cotton fabrics using a
bleaching lye which contains a peroxy ~ , ul.d and an
oxime or peroxy ~ , .u.-d, a complexing agent and a sugar
alcohol or an aldonic acid. Sodium perborate is
disclosed as the peroxo ~ u--d.
The object according to the invention is achieved by a
one-step process for brightening dyed cotton fabrics
which is characterized in that dyed cotton fabrics are
treated with an aqueous bath which contains a peroxo
compound as the active ~, s~t but no added
hypochlorites, p~ n~n~tes and enzymes under
conditions which are suitable for brightening the
colours of the cotton fabrics.
Surprisingly it turned out that the use of peroxo
compounds as brightening agents has a very good effect
on dyed cotton fabrics in particular jeans fabrics. The
process according to the invention has the advantage
compared to known processes that waste water pollution
is avoided since there is no AOX pollution by
hypochlorites and other environmentally harmful
chemicals do not have to be used at all or only to a
slight extent. The COD and BOD5 values as measures of
waste water pollution are not increased by the peroxo
and opposite effects can even occur since
peroxo compounds introduce additional oxygen and thus
decrease the oxygen demand of waste water.
For reasons of waste water and air pollution, the
process according to the invention is preferably carried
out using a brightening bath which contains minimal
amounts of chlorine and in particular less than
_ 5 _ 2~8 1813
5000 ppm, especially preferably less than 1000 ppm and
most preferably less than 200 ppm chlorine (in the form
of elemental chlorine, chlorite, hypochlorite etc. ) .
Suitable conditions f or brightening or bleaching the
colours of the cotton fabrics are understood as those
conditions of concentration of the brightening bath,
temperature and duration of treatment under which the
desired brightening of the colours is achieved without
damaging the cotton f ibres .
A pern~o~ fate is used as the suitable peroxo
_~.d for the process according to the invention.
Among the peroxo-disulfates an i~llk~l ino-earth te.g. Ca),
alkali (e.g. Li, Na, K, Rb, Cs) or ammonium
peroxodisulfate and in particular potassium, sodium
or/and ammonium peroxodisulfate is in turn preferred.
The concentration of the peroxo compound can be varied
tl~r~n~9;nq on the reaction conditions and the desired
degree of brightening of the cotton fabrics. In general
the peroxo ~_ ~ ' can be varied within a concentration
of about 21 mmol/l (~;oLLe~ol~ding to ca. 5 g/l in the
case of sodium peroxodisulfate) up to the solubility
limit of the compound or up to a concentration above
which the cotton f ibre is damaged . The concentration of
the peroxo compound in the brightening bath is
preferably in the range of 21 mmol/l to 2.1 mol/l,
particularly preferably in the range of 42 mmol/l to
1.7 mol/l and most preferably 42 mmol/l to 1.3 mol/l.
The process according to the invention is preferably
carried out at a temperature in the range of 15 to 90C,
preferably of 40 to 80C and most preferably of 50 to
~ 81813
-- 6 --
65C.
The time period f or carrying out the brightening process
according to the invention depends on the desired degree
of brightness, the temperature of the brightening bath
and the concentration of the brightening reagent. This
time period can be easily detF~rm;n-~cl by a person skilled
in the art by routine experiments. When carrying out the
process according to the invention on a terhn;c~l scale
the reaction period is usually 2 minutes to 20 hours,
preferably 5 minutes to 5 hours and particularly
preferably 15 minutes to 1 hour.
The pH value of the brightening bath can be from 0 to
12, pH values in the range from 1 to 10 being preferred
and in the range from 4 to 7 being especially preferred.
In order to adjust the pH range the brightening bath can
contain a buffer system e.g. a phosphate buffer.
Further optional components of the brightening bath are
surface-active agents e.g. surfactants, complexing
agents and further agents which are known in the
respective technical f ield.
The process according to the invention can be carried
out in the usual devices and with the usual required
amounts of the cotton fabrics such as those which are
also used to carry out a bleaching process with
hypochlorite. The dyed cotton fabrics are preferably
treated with the brightening bath according to the
invention in a washing drum.
In a particularly preferred on~horl;r L of the process
according to the invention the brightening bath
~ X181813
-- 7 --
additionally contains an activator which is selected
from transition metal compounds or/and halogenide
compounds. Examples of ~typical transition metals are
titanium, vanadium, chromium, manganese, iron, cobalt,
nickel, copper, zinc, palladium, tin, molybdenum,
silver, cerium, ruthenium, tungsten and rhenium.
Preferred transition metals are iron, copper, cobalt,
zinc, silver, r-n~ln~e, chromium, nickel or mixtures
thereof. The transition metals can be used in the form
of metal salts or complex '~, metal salts being
preferred. The transition metals are particularly
preferably used in the form of their sulfate salts. Most
preferred are iron(III) salts, iron(II) salts and
coppertII) salts, in particular iron(III) sulfate,
iron ( I I ) sul f ate and copper ( I I ) sul f ate .
The transition metal ollnr9 used as the activator is
preferably added to the brightening bath according to
the invention in an amount of up to 25 mmol/l in
relation to the metal. The transition metal compound is
preferably used in an amount of 0.05 to 15 mmol/l,
particularly preferably of 0.05 to 8 mmol/l with respect
to the metal.
The use of copper(II) sulfate, iron(II) sulfate or
iron(IrI) sulfate as the activator is particularly
preferred when ammonium peroxodisulfate is used as the
peroxo compound. The use of iron(III) sulfate or
iron(II) sulfate as the activator is also particularly
preferred when sodium peroxodisulfate is used as the
peroxo ~ '.
Examples of halogenide ~ ullds which are suitable a6
the activator are chloride, bromide and iodine _ '~
- 8 - 21 81 81 3
in particular bromide compounds. A illm, alkali metal
and alkaline-earth metal halogenides are preferred and
alkali metal halogenides are particularly preferred.
Most preferred are sodium or/and potassium bromide.
The halogenide - uul.d used as the activator is
pref erably added to the brightening bath according to
the invention in an amount of up to 500 mmol/l with
respect to the halogenide ion. The halogenide compound
is particularly preferably used in an amount of
0.5 mmol/l to 200 mmol/l, most preferably of 1 to
20 mmol/l with respect to the halogenide ion.
In comparison to activation with transition metal
compounds, activation with halogenide ions and in
particular with bromide ions has the advantage that the
concentration of the peroxo compound can be considerably
reduced without impairing the brightening effect. When
bromide ions and persulfates are present simultaneously
in the brightening bath, concentrations in the range of
21 mmol/l to 420 mmol/l persulfate (corresponding to 5
to 100 g/l in the case of sodium peroxodisulfate) and
0.5 to 200 mmol/l, in particular 1 to 20 mmol/l bromide
are particularly preferred and optimal effects are
already achieved at very low bromide concentrations.
When selecting optimal process conditions care should be
taken that the concentrations of the halogenide cul~ ulld
and the peroxo ~ ul-d are inversely proportional
within the specif ied ranges .
A further r~mhorl;-^nt of the present invention comprises
a treatment of the dyed cotton fabrics at an alkaline pH
value. The treatment of the cotton fabrics in AlkAl inf~
conditions has the advantage that an attack by H+ ions,
218:L813
g
which can lead to a reduction in the tear resistance, is
completely excluded. In this P~hQ~ the treatment is
preferably carried out in a pH range of 9 to 13,
particularly preferably of 10 to 12. Since peroxo
c, _ ac, e.g. persulfates, only have a moderate
brightening effect under ~lk 1l ;nP conditions without
added hypochlorite, a suitable activator for Alk 1l ine pH
values is preferably added. Examples of such activators
are transition metal complex, '- soluble at
~lk~l ;n~ pH values, e.g. complex c ul-ds of iron,
copper, cobalt or nickel, and particularly preferably
complex ~ c of iron.
Specif ic examples of suitable activators are complexes
of transition metals with ammonia, polyamines such as
EDTA, thiocyanate, cyanide or fluoride. Cyano complexes
are preferably used, particularly preferably
hexacyanoferrate (II) or hexacyanoferrate (III)
complexes. The hexacyanoferrate complexes are used for
example in the form of alkali metal salts, e.g. sodium
or potassium salts.
The complexes are preferably used in an amount of up to
25 mmol/l with respect to the metal, particularly
preferably in an amount of 0.05 to 15 mmol/l, most
preferably of 0. 05 to 8 mmol/l with respect to the
metal .
nhen transition metal complex c _ ~- are used as an
activator a surprisingly strong brightening is achieved
even at very low concentrations of peroxo compounds.
Therefore when brightening under ~lkll;nP conditions,
the concentration of the peroxo ~ u~lds is in the
range of e.g. 5 mmol/l to 2.1 mol/l, preferably 5 mmol/l
1813
-- 10 --
to 1 mol/l, particularly preferably 5 mmol/l to
250 mmol/l. The treatment temperature is preferably 70
to 90C, particularly preferably ca. 80C. The duration
of treatment depends on the concentration of the peroxo
and activator compounds used, however good results were
achieved with a treatment period in the range of 10 min
to 1 h, particularly of 10 min to 30 min.
The dyed cotton fabrics used in the process according to
the invention are pref erably dyed with dyes selected
from the group comprising vat, direct and sulphur dyes.
Typical vat dyes are indigo, thioindigo and other
indigoid dyes, indanthrene and other anthraquinoid dyes,
phthalocyanine and naphthalene dyes.
All substances that are used to dye cotton fabrics and
in particular jeans fabrics, ~sp~ciAl ly indigo,
thioindigo and other indigoid dyes as well as sulfur
dyes are particular preferred as dyes.
After brightening the dyed cotton or jeans fabrics by
the process according to the invention, these are
cleaned in the usual way e.g. by rinsing or/and
neutralizing the brightening bath. Since the process
according to the invention does not cause any
discolouration e . g . yellowing of the cotton f ibres, an
aftertreatment is generally not ~c~sAry. A further
advantage of the process according to the invention is
that the degree of brightness i . e . the brightening of
the total colour tone of the dyed cotton fabrics can be
very easily controlled by selection of the duration of
treatment and temperature, concentration of the peroxo
c~ ~ and if desired the activator compound.
2181 813
-- 11 --
In particular when using sodium peroxodisulfate and if
desired iron(III) sulfate as the activator, the waste
water does not contain any !h~m;~ which pollute the
environment since sodium peroxodisulfate decomposes to
60dium sulfate and oxygen and iron sulfate also poses no
problem since this substance is for example added in
sewage plants as a f locculant . When peroxo compounds, in
particular persulfates, are used in the brightening
bath, then additional oxygen is even introduced into the
bath and thus the oxygen demand of the waste water is
reduced. The use of halogenide ions, in particular of
bromide ions, at the low concentrations that are
ne, ecsAry to activate the peroxo ~-c _ _I.d also does not
lead to signif icant environmental pollution .
In addition the present invention concerns the use of a
bath which contains 21 mmol/l to 2.1 mol/l of a peroxo
compound as the active ~ ~ A' t and which is free of
added hypochlorites, permanganates and enzymes to
brighten dyed cotton fabrics. The peroxo compound is
preferably selected from the group comprising H202,
perphosphates, perborates, percarbonates, persulfates,
percarbamide, peracetic acid and mixtures thereof. A
peroxodisulfate is particularly preferred as the peroxo
compound, most preferred are potassium, sodium or/and
,n i llm peroxodisulf ate .
In addition the bath can contain an activator selected
from the transition metal compounds at a concentration
of up to 25 mmol/l in relation to the metal or
halogenide compounds at a concentration of up to
500 mmol/ l with respect to the halogenide ion .
The bath particularly preferably contains 21 mmol/l to
- 12 - 21~1813
420 mmol/l of a persulfate as the active component and
0.5 to 200 mmol/l halogenide ions as the activator.
A further subject matter of the present invention is the
use of a bath for brightening dyed cotton fabrics which
has an ;llk;~l inP pH value and contains 5 mmol/l to
2.1 mol/l of a peroxo compound as the active component
and a transition metal complex ~ , ~UII~ soluble at
;~lk~l inP pH values and which is free of added
hypochlorites, pPrr~n~ In~tes and enzymes.
It is intended to elucidate the invention by the
following example
EXA~IPLE
A 4 x 4 cm sample of a blue jeans fabric dyed with
indigo was placed in 100 ml of a brightening bath. Then
the pH value was detPrm;nPd. It was stirred continuously
during the brightening process in order to ensure good
penetration of the fabric with the brightening solution.
Subsequently the piece of textile was rinsed with
distilled water in order to stop the brightening
process. The degree of brightness was judged in the dry
state (dried by hot-air at 50C in a drying chamber)
using a textile sample which had not been brightened as
a reference. The degree of the brightening effect
(decrease in the blue colouration down to white) was
scored in 5 steps as follows:
0 no decrease in blue colouration
slight brightening
2 good brightening (desired effect)
3 stronger brightening
21~1813
-- 13 --
4 6trongly bleached
5 very 6trongly bleached
The brightening effect of ammonium peroxodisulfate
(APS), potassium peroxodisulfate (PPS) and sodium
peroxodisulfate (SPS) was ~Y;~m; ned.
1) Pr~l im;n Iry experiments: comparison of various
per6ulf ate6
No. Bleaching Conc. Addit. Conc. Temp. Time Score Fabric
agent
APS 100 g/l - - RT 20 h 1 ok
2 PPS 45 g/l - - RT 20 h 0 . 5 ok
3 SPS 100 g/l - -- RT 20 h 1 ok
APS (experim. 1) and SPS (experim. 3) show above all a
usable bleaching effect. PPS (experim. 2) has a lower
solubility but is comparable to APS and PPS with regard
to the bleaching effect.
2 ) Inf luence of the concentration
No. Bleaching Conc. Addit. Conc. Temp. Time Score Fabric
agent
4 SPS 100 g/l -- - RT 21 h 2 ok
5 SPS 200 g/l -- -- RT 21 h 4 ok
6 SPS 300 g/l -- -- RT 21 h 4.5 ok
Experiments 4 to 6 show that the bleaching ef f ect can be
regulated by means o~ the concentration.
2~1 813
-- 14 --
3 ) Inf luence of temperature
No. Bleaching Conc. Addit. Conc. Temp. Time Score Fabric
agent
7 SPS 100 g/l - - 60C 40 min 1 ok
8 SPS 100 g/l - - 80C 20 min 2 ok
Experiments 7 and 8 show that the desired degree of
brightness can be adjusted within a 6ignificantly
reduced duration of treatment by selecting a higher
temperature .
4) Effect of PPS with various activators
It turned out that transition metal ~ ullds above all
iron(III) in the form of iron(III) sulfate, iron(II)
sulfate or copper(II) sulfate enhance the attack of
persulfate on the indigo dye. It is remarkable that no
significant damage to the fabric takes place during this
process .
~181~13
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- 16 _ 8 8
Experiments 9 to 16 show that various activators are
suitable for this application. Iron(III) (experiment 9),
chromium (experiment 14) and iron(II) (experiments 15
and 16) showed the strongest effect.
5) Comparison of various activator dosages
No. Bl-~a~h;n~ Conc. Addit. Conc. Temp. Time Score Fabric
agent
17 SPS 250 g/l Fe2(SO4)3 1.25 60C 20 min 2 ok
18 SPS 250 g/l Fe2(S04)3 2.5 60C 20 min 3 ok
19 SPS 300 g/l Fe2(S04)3 2.5 60C 20 min 3.5 ok
Experiments 17 to 19 show that the concentration of the
activator must not be adjusted too high since otherwise
an effect would result which may be too strong. Noreover
the persulfate concentration and iron activator
concentration have to be matched to one another. In this
case values of 200 - 300 g/l SPS and 0.75 - 1.8 mmol/l
iron(III) sulfate prove to be optimal.
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21gl81~
-- 18 --
In contrast to experiment 20 the pH value was adjusted
to 7 ln experiment 21 (preferred pH range 5 - 12) which
shows that the desired degree of brightness of 2 is
achieved even at this pH value. Experiments 22 and 23
show that the bleaching time could be reduced to 20 min
using 300 g/l SPS even at pH 7. Experiment 25 shows that
a degree of brightness of 2 can be achieved at a pH
value of 5 which was adjusted with a buffer mixture
while adhering to the standard conditions.
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21~1813
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21 ~813
-- 22 --
Experiments 34 and 35 show that the optimal effect can
already be achieved using small amounts of bromide and a
further increase of the bromide concentration does not
result in further i~ V~ t. Experiments 36 to 39 show
that in this range the degree of bleaching can also be
regulated by reducing the bromide concentration.
Experiments 4 0 to 4 2 show that the ef f ect can be
increased up to complete decolouration by increasing the
SPS content in the bleaching vat.
In experiments 35, 40 and 41 the mole ratio was adjusted
to 1: 50 (NaBr: SPS) .
`~ 2~81813
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21~813
-- 24 --
Experiments 43 and 44 show that when an activator is not
added there is only a slight ble~hin~ in the RlkRl ;nP
range. Experiments 45 and 46 show that the bleaching
action of persulfate in the RlkRl ;nP range is
c~nqidPrably amplif ied by the addition of an activator .
Experiment 47 shows that there is no detectable effect
of the activator in the neutral range (pH 7.5).
Experiments 48 and 49 show that the ble~rh;nq action is
considerably higher at a bath temperature of 80C than
at a bath t, a~UL~ of 60C.
Experiments 50 and 51 show that the activation with
potassium hexacyanoferrate (III) functions equally as
well as activation with potassium hexacyanoferrate (II).
Experiment 52 shows that the activator concentration can
be reduced further to ca. l mmol/l without wP~kPn; ng the
brightening effect. Experiment 53 shows that a strong
blPR~-h;n~ action is achieved even at a pH value of 12.
Experiment 55 shows that the brightening action can be
regulated by a further reduction of the activator in the
blP~- h; n~ solution .
