Note: Descriptions are shown in the official language in which they were submitted.
2144371
HOECHST AKTIENGESELLSCHAFT HOE 94/F 063 J Dr.KI/PP
Description
Bleaching synthetic fibers
The production process of numerous everyday products
includes a treatment known as bleaching. Bleaching has
the function of effecting a change in color of a material
toward a lighter shade. The ultimate aim is a pure white.
The treatment should change the material itself only
insignificantly, if at all. Bleaching plays a significant
role in relation to textile fibers. Textile fibers are
subdivided into natural fibers and man-made fibers. The
former are subdivided in respect of their origin into
natural fibers of animal origin (wool, silk) and natural
fibers of vegetable origin (cotton, flax). The man-made
fibers include the subgroup of synthetic fibers. These
include polyamide fibers, polyester fibers, poly-
acrylonitrile fibers and polyurethane fibers. In the
textile industry it is generally customary to bleach
textile fibers with oxidizing agents. Known chemicals for
this purpose include hydrogen peroxide, ~odium chlorite
and peracids. Hydrogen peroxide is chiefly used on the
abovementioned natural fibers and also in the case of
textile blend fabrics.
DE-A-2 249 062 relates to the bleaching of cellulose-
containing textiles, for example cotton/polyester, by
means of a bleaching agent consisting of an aqueous
hydrogen peroxide solution, an alkali metal hydroxide, an
alkali metal borate and an organic complexing agent. The
bleaching agent preferably contains the equivalent of 0.2
to 1.8 percent by weight of 100 percent strength hydrogen
peroxide, based on the textile material, and preferably
has a pH of 9.5 to 11.5. This bleaching agent is used to
impregnate the textile material, preferably in a
proportion of 50 to 125 percent by weight, based on the
textile material.
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DE-A-0 022 929 mentions a process for bleaching textile
materials, especially polyester-cotton fabrics, by
applying to the textile material an emulsion or suspen-
sion of a bleaching agent, for example the emulsion of an
aqueous hydrogen peroxide solution in a hydrocarbon or
halogenated hydrocarbon solvent, substantially removing
the solvent from the textile material, and then washing
the textile material.
US-A-3 649 164 describes a process for bleaching cellu-
lose-cont~;n;ng textiles, for example polyester-cotton
textiles, by means of an aqueous alkaline hydrogen perox-
ide solution which generally contains from 0.5 to 1.5% of
hydrogen peroxide, based on the weight of the textile
material, 0.05 to 0.5% of a water-soluble peroxydi-
phosphate, based on the weight of textile material, andhas a pH of 9 to 14. To bleach the textile material, it
is pretreated with a bleaching solution at 140 to 160F
and then heated in the impregnated state to the boiling
point of the bleaching solution.
The above-described bleaching processes all concern the
bleaching of polyester blend fabrics.
DE-A-3 002 726 describes a process for bleaching fiber
material with hydrogen peroxide by bleaching a fiber
material with hydrogen peroxide in a weakly acid medium
at a pH of 5 to 7, then ad~;Y; ng the bleaching system
with an alkaline bleaching agent, setting a pH of 8.5 to
11, and continuing the bleaching with hydrogen peroxide
in a weakly basic medium.
The fiber material to be bleached includes for example
natural, synthetic or cellulosic fibers. The examples
show the use of the process for bleaching cotton, wool-
cotton blend fabrics and polyester-cotton blend fabrics.
It is stated in the reference that bleaching with hydro-
gen peroxide in the aforementioned weakly acid pH range
from 5 to 7 produces a whiteness which is achieved by
bleaching with sodium chloride alone. Referring to the
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customary multi-stage bleaching processes involving
~odium chlorite dechlorination or antichlorination and
additional bleaching with hydrogen peroxide in a weakly
alkaline medium, simply bleaching with hydrogen peroxide
in a weakly acid medium is said to be unpracticable.
It is true that hydrogen peroxide, as a bleaching agent,
is considered to have some usefulness in relation to
synthetic fibers, but inadequate bleaching effect is not
achieved (cf. Ullmann's Encyklopadie der technischen
Chemie, 4th edition, volume 23, page 25, 1984).
The only bleaching agent suitable for polyester is
considered to be sodium chlorite, since other bleaching
agents are said to produce an inadequate white effect
(cf. BASF-Handbuch, volume 363d, 8/74, page 81; R.
Lindner, Tenside-Textilhilfsmittel-Waschrohstoffe III,
page 2749, 1971).
Surprisingly, it has been found that even synthetic
fibers, for example polyester fibers, can be adequately
bleached with a bleaching solution comprising an aqueous
hydrogen peroxide solution. Yet more surprising by far is
that an improved bleaching effect can be achieved by
including polyphosphates in such a bleaching solution.
The present invention accordingly provides a process for
bleaching synthetic fibers with hydrogen peroxide, which
comprises bleaching the synthetic fiber with a hydrogen
peroxide bleaching solution at a bleaching solution pH
from 3 to 7 and a bleaching solution temperature between
100 and 135C.
Examples of synthetic fibers are polyester fibers,
polyamide fibers, polyurethane fibers and acetate fibers.
Preference is given to using polyester fibers. It has
been found that the process of the present invention
gives excellent bleaching not only on conventional
polyester fibers, but also on specialty polye~ter fibers,
such as flame retardant polyester fibers (see Chemie fur
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Textilindustrie, 43-95, pages 65-68, 1993) and polyester
microfibers.
The bleaching solution iB usually used in the form of an
aqueous hydrogen peroxide solution. Although, in theory,
hydrogen peroxide solutions of any concentrations can be
used for preparing the bleaching solution, safety consid-
erations dictate a preference for hydrogen peroxide
solutions of less than 65 percent by weight. Those with
from 20 to 35 percent by weight are generally preferred.
For instance, the concentration of the 35 percent
strength aqueous hydrogen peroxide iB preferably 1.0 to
20 ml/l of bleaching solution. Higher amounts of hydrogen
peroxide are possible, but do not yield significant
advantages.
To obtain an improved bleaching effect, it is advanta-
geous to include in the bleaching solution a certain
amount of polyphosphates. These polyphosphates are
preferably compounds of the formula Men+2PnO3n+l and also
MenPnO3n, where Me is an alkali metal ion, alkaline earth
metal ion or G onium ion and n is from 1 to 6. Me i8
preferably an alkali metal ion, especially a sodium ion.
Examples of such polyphosphates are compounds of the
formula Na5p3olo and Na6P60l8. Especially these poly-
phosphates ensure particularly high bleaching effects.
Usually the bleaching solution contains from 0.5 to
10 g/l, preferably from 2 to 3 g/l, of polyphosphate.
The bleaching solution of the present invention custom-
arily contains further suitable ingredients. These
include stabilizers which prevent the decomposition of
hydrogen peroxide and render ineffective any catalyst~
present which favor this decomposition. Customary stabi-
lizers are alkaline earth metal salts. Of the alkaline
earth metal salts, magnesium silicate has particular
importance. Also suitable are soluble magnesium or
calcium salts, such as magnesium sulfate or calcium
chloride. The bleaching solution preferably contains less
than 0.5 percent by weight, especially less than
214~371
0.3 percent by weight, of the alkaline earth metal salt.
The bleaching solution of the present invention may
contain an organic complexing agent, for example an amino
carboxylic acid or its alkali metal or ammonium salt.
Preferably the aminocarboxylic acid contains more than
one amino group, and at least one amino group should be
substituted by 2 carboxylic acid groups, especially an
acetic or substituted acetic acid group. Examples of
preferred complexing agents are ethylenediaminetetraace-
tic acid, N-(2-hydroxyethyl)ethylenediaminetriacetic
acid, diethylenetriaminepentaacetic acid, triethylene-
tetraaminehexaacetic acid or one of these compounds in
which one or more acetic acid groups has or have been
replaced by (2-hydroxyphenyl)acetic acid. The preferred
complexing agent is diethylenetriaminepentaacetic acid or
its alkali metal salt. Further suitable complexing agents
are suitable carboxylic acids, for example gluconic acid,
and suitable phosphonic acids or their alkali metal salts
or ammonium salts, as indicated in Chwala-Anger, Handbuch
der Textilhilfsmittel, pp. 1003-1008, 1972.
The complexing agent content of the bleaching solution is
usually 0.1-5 g/l, preferably 0.2-1 g/l. The amount of
complexing agent depends on the concentration of the
hydrogen peroxide-decomposing metals or on the purity of
the water and on the quality of the synthetic fiber.
The bleaching solution of the present invention may in
addition contain 0.1 to 1 g/l of one or more bleaching
aids, such as protein degradation products or organic
phosphates, e~pecially alkyl and alkylaryl phosphate
esters. Specific examples of phosphate ester~ are alkyl
and alkylaryl esters of poly(ethyleneoxy) phosphates.
The bleachinsr solution of the present invention may
include a~ a further additive a surface-active agent,
preferably a foam-free wetting agent, to facilitate the
washing of the synthetic fiber following the bleaching.
It is possible to use anionic or nonionic surface-active
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agents. Examples of suitable compounds are the conden-
sates of alkylphenols, e.g. nonylphenol, with ethylene
oxide, salts of alkylarylsulfonic acids, e.g. the amine
salts of dodecylbenzenesulfonic acid, and long-chain
alkyl sulfates. The concentration of the surface-active
agent is usually 0.5 to 3 g/l, preferably 1 to 2 g/l.
The bleaching solution may also include optical brighten-
ers. The amount used is generally 0.1-5 g/l of bleaching
solution. This ensures optimum white effects in a single-
stage bleaching and brightening process. Compared withthe existing bleaching processes involving sodium chlo-
rite, this also eliminate~ the need for a chlorite-stable
optical brightener.
The use of small amounts of alkali metal carbonates, e.g.
sodium carbonate, is likewise possible.
The bleaching solution has a weakly acid to neutral pH,
preferably a pH within the range 3.0-7.0, especially
within the range 5.0-7Ø The pH required for a maY;~l~m
bleaching effect depends for example on the nature and
quality of the textile material and can also be set or
adjusted for example by altering the acid concentration,
for example via adding acetic acid.
Synthetic fibers are bleached in a liquor ratio generally
from 3:1 to 40:1, preferably 10:1 to 20:1. Synthetic
fibers are bleached in the high temperature (HT) range at
a temperature within the range from 100 to 135C, prefer-
ably within the range from 120 to 130C. At these
temperatures, the steam pressure required is preferably
1 to 3.5 atmospheres, especially 2 to 3 atmospheres. The
time required at a c:ertain temperature to achieve a
certain bleaching effect depends on the temperature: at
100C it is preferably 80 to 120 minutes and at 135C it
is preferably 10 to 30 minutes. Having regard to the
total temperature range, the treatment time there is from
10 to 120 minutes.
21~4371
Following the bleaching operation, the bleached textile
material is preferably washed neutral with hot water.
The process of the present invention is usually carried
out in conventional HT bleaching apparatus.
The ~rocess of the present invention makes it possible to
obtain a white which corresponds to the white of conven-
tionally bleached, e.g. chlorite-bleached, fiber6. In
addition, the process of the present invention proceeds
in a single stage and requires only one bleaching appara-
tus. The avoidable use of hitherto customary bleachingagents such as ~odium chlorite is of considerable benefit
to the environment. Compared with the previous bleaching
processes involving sodium chlorite, there is no need
either for a chlorite-stable brightener. Nor are the
machines of apparatus used exposed to the corroding
conditions which occur in this process.
Use examples:
The whiteness achieved was determined by the method of
Ganz (see R. Griesser, Rev. Prog. Coloration, Vol. 11, p.
25, 1981).
Example 1:
A polyester textile fabric is bleached with a bleaching
solution comprising 5 ml/l of 35% strength by weight
aqueous hydrogen peroxide solution with a pH of 6-7 and
a temperature of 130C over a period of 45 minutes. The
liquor ratio is 20:1. A whiteness of 80 is obtained.
Example 2:
A polyester textile fabric is bleached with a bleaching
solution comprising 5 ml/l of 35% strength by weight
aqueous hydrogen peroxide solution and 3 g/l of sodium
polyphosphate with a pH of 6-7 (set with acetic acid) and
a temperature of 130C over a period of 45 minutes. The
liquor ratio is 20:1. A whiteness of 85 is obtained.
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Example 3:
A polyester textile fabric is bleached with a bleaching
solution comprising 5 ml/l of 35% strength by weight
aqueous hydrogen peroxide solution, 3 g/l of sodium
polyphosphate and 0.5 g/l of an optical brightener
(~Hostalux ERE) with a pH of 6-7 (set with acetic acid)
and a temperature of 130C over a period of 45 minutes.
The liquor ratio is 20:1. A whiteness of 215 is obtained.
Comparative Example 1:
(as described in DE-A-30 02 726)
A polyester textile fabric is bleached with a bleaching
solution comprising 5 ml/l of 35% strength by weight
aqueous hydrogen peroxide solution in a weakly acid
medium with a pH of 6.9, at a temperature of 90C, over
a period of 60 minutes. The bleaching system is then
admixed with an alkaline agent (aqueous sodium hydroxide
solution comprising sodium silicate) and the textile
fabric is bleached in a weakly alkali medium with a pH of
11, at a temperature of 80C over a period of 60 minutes.
The liquor ratio is 10:1. A whiteness of 81 is obtained.
Comparative Example 2:
(sodium chlorite bleach)
A polyester textile fabric is bleached with a bleaching
solution comprising 1.5 g/l of sodium chlorite, 1.0 g/l
of a bleaching aid and 0.5 g/l of a wetting agent
(~Hostapal FA) at a temperature of 130C over a period of
45 minutes. The liquor ratio is 20:1. A whiteness of 86
is obtained.
