Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HOECHST A~-L1 N~SELLSCHAFT HOE 94/F 092 Dr.Rl/rh
Description
Bleaching of textiles
Textile raw material is bleached to prepare it for dyeing
or finishing. Hitherto it was customary to use bleaching
agents such as hydrogen peroxide, sodium hypochlorite or
sodium chlorite.
It has been found that the use of hypochlorites in
bleaching processes gives rise to org~noh~logen compounds
which can be harmful. This leads to an ever increasing
renunciation of this bleaching agent.
The sodium chlorite bleach, which is carried out in the
acid pH range, gives rise to the formation of chlorine
dioxide, which is harmful and represents an odor nuis-
ance. In addition, this bleaching agent can be used onlyon selected textile machines, made of special materials.
Owing to these disadvantages, bleaching with hydrogen
peroxide is increasingly preferred.
The review "Activators and stabilizers for the peroxide
bleach" by Dr. W. Ney in Textilpraxis international 1974,
October and November, pages 1392 - 1565, reveals that
hydrogen peroxide is today the most common bleaching
agent for all natural fibers of vegetable and ~n;~-l
origin.
To achieve a bleaching effect with hydrogen peroxide, it
first has to be activated. Also, the bleaching solution
needs to be stabilized in order that the 1088 of active
oxygen may be m;n;mi zed.
It i~ generally customary and best known to activate with
bases. In the bleaching of cellulose fibers, the base
used for cotton is almost exclusively sodium peroxide
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while sodium carbonate is preferred for bast fibers,
especially linen. The disadvantage with the use of bases
is the alkali sensitivity of animal fibers.
In addition to bases, hydrogen peroxide can be activated
in other ways, for example by chemical conversion of the
hydrogen peroxide into organic and inorganic per-acids.
G. Rosch, Deutsche Textiltechnik 10 (1960), No. 4, pages
191-195, discloses the use of peracetic acid in textile
bleaching. Peracetic acid is inflammable. The concen-
trated solution, which has a pungent odor, is corrosiveand burns the skin. The biggest disadvantage of peracetic
acid is its high explosivity. The use of acetic anhydride
in its preparation may, under adverse conditions, give
rise to the formation, as a by-product, of diacetyl
peroxide which likewise tends to decompose spontaneously.
This behavior is probably the reason why peracetic acid
has never found the expected success as bleaching agent.
In addition to the aforementioned methods of activation,
there are also a number of chemical compounds which come
into consideration for use as activators for hydrogen
peroxide with the formation of per-acids.
According to W. Ney, particularly effective compounds
combine a very small molecular weight with a large number
of reactive acyl groups, such as tetraacetylethylene-
diamine (TAED) and tetraacetylglycoluril (TAGU).
DE-A-l 695 219 discloses the use of acylated glycolurils,
especially TAGU, as a bleaching agent especially in the
bleaching of fibers of any kind.
EP-A-125 641 and US-A-4 544 503 disclose the use of
acyloxybenzenesulfonic acid salts (AOBS) as activators
for the peroxide bleach of fabrics and as dyeing assist-
ant in the dyeing of acrylic fibers.
EP-A-442 549 mentions the use of phthalimidoperoxy-
carboxylic acids as bleaching agents for fabrics and hard
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surfaces.
DE-A-l 291 317 describes a bleaching process which is
suitable for removing stains from textiles and involves
peroxide baths which include organic N-acyl compounds.
The activators mentioned for the inorganic per-salts
used, such as sodium perborate tetrahydrate, sodium
perborate and sodium percarbonate, also include N-acetyl-
caprolactam. The disadvantage with these processes is the
mandatory use of inorganic per-salts.
EP-A-0 584 710 discloses a process for bleaching textile
raw material with the aid of organic per-acids and
hydrogen peroxide wherein the bleaching liquor includes
as bleach activator a carboxamide, a carboxylic ester or
a sulfonic acid salt. The solid bleach activators
described have the disadvantage that they cannot be used
for the liquid metering systems employed in the textile
industry.
It is an object of the present invention to provide
liquid bleach activators suitable for bleaching textile
raw material.
The present invention accordingly provides a process for
bleaching textile raw material with the aid of hydrogen
peroxide by treating the textile raw material with an
aqueous bleaching liquor including hydrogen peroxide and
a bleach activator, which comprises using as the bleach
activator an N-acyllactam of the formula I
,~,0
-C O
(CH2)n ¦ 11 ( I )
N C R
where
n is from 3 to 5, and
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Rl i 8 C~ - C5-alkyl.
The preferred bleach activator is N-acetylcaprolactam.
The textile materials used are preferably cellulo8ei
especially unpretreated natural cellulose, such as hemp,
linen, jute, cotton, regenerated cellulose fibers, such
as staple viscose, viscose acetate, rayon, animal fiber,
such as wool and silk, and also synthetic fibers, such as
polyamide, polyacrylonitrile or polyester fiber
materials, and also fiber blends, for example those of
polyacrylonitrile-cotton or polyester-cotton.
The textile material to be treated can be present in the
various processing states, for example the cellulose-
containing material as loose material, staple, slubbing,
yarn, knitted fabric or woven fabric. The textile
material i8 treated continuously (for example by impreg-
nation) or batchwise (for example by means of exhaust
processes in a bleaching apparatus) in aqueous liquor.
The aqueous bleaching liquor, in addition to the bleach
activators mentioned, hydrogen peroxide and optionally
peroxide stabilizers, includes w~h;ng and wetting
agents, additives, such as defoamers and dissolution
improvers, buffer systems, such as phosphate salts and
citric acid, and basic salts, such as sodium bicarbonate,
disodium carbonate and/or sodium hydroxide. The pH of the
bleaching liquor iB within the range from 5 to 13,
preferably 7 to 9.
The molar ratio of hydrogen peroxide to bleach activator
i8 1.0 - 5 : 1, preferably 1.1 - 1.5 : 1, based on the
active carbonyl group of the bleach activator.
The liquid bleach activators of the invention permit
preparation of the bleaching liquor in the liquor makeup
vessel in the above-described manner or direct metering
by metering means together with the other liquid
ingredients of the bleaching liquor directly into the
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bleaching apparatus or the impregnating beck.
In the bleaching apparatus, the textile material is
wetted and saturated with the bleaching liquor 80 that
the weight of the liquor is usually 3 - 50 times that of
the textile material. The textile raw material is treated
cold with the bleaching liquor or heated together with
the bleaching liquor to temperatures from 40 to 130C and
treated at these temperatures. Customary treatment times
range from 30 minutes to 3 hours.
In the impregnating processes, the textile raw material
is impregnated, i.e. wetted and saturated, with the
bleaching liquor in the impregnating beck. After impreg-
nation, the textile raw material i8 either stored cold
for a period from 0.5 to 24 hours, usually at room
temperature, or heated in atmospheric steamers with steam
at temperatures from 95C to 120C. The residence time at
this temperature is 1 minute to 2 hours.
Usually, but not mandatorily, the bleach with the bleach
activators of the invention is followed by a further
bleaching process, for example the alkaline peroxide
bleach.
It has been found that precisely the combination of
activator bleach with alkaline peroxide bleach results in
good whiteness of the textile material. Following the
bleach, the textile material is washed.
The examples which follow illustrate the process of the
invention.
Example l
Bleaching of knitwear and desized woven cloth in 100%
cotton.
The first step involves the activated peroxide bleach: -
8 g/l of N-acetylcaprolactam
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-
5 g/l of H22 (35% strength aqueous solution)
5 g/l of calcined sodium carbonate
3 g/l of 3Lastabil TGS (peroxide stabilizer, trade-
mark of Hoechst AG, mixture of organic carboxylic
acid and phosphonic acid salts)
3 g/l of ~9Eostapal FA (washing and wetting agent,
trademark of Hoechst AG, mixture of various fatty
alcohol ethoxylates)
The liquor is made up in the liquor makeup vessel. The
textile material is cold-padded and steamed under satu-
rated steam at 97 - 102C for 15 - 30 minutes. This is
followed by a wash.
In the second step, the material is impregnated wet-on-
wet with an alkaline peroxide bleaching liquor.
25 g/l of H22 (35% strength aqueous solution)
4 g/l of caustic soda
3 g/l of ~'Lastabil TGS
3 g/l of ~Hostapal FA
The impregnated material is steamed with saturated steam
for 15 - 20 minutes and then washed.
Example 2
Bleaching of knitwear and desized woven cloth in 100%
cotton by exhaust method.
The liquor ratio of bleaching liquor to textile material
is 10:1.
The bleaching liquor includes
1 g/l of ~Hostapal FA
1 g/l of ~ Lastabil TGS
2 g/l of calcined sodium carbonate
2 g/l of H202 (35% strength aqueous solution)
3 g/1 of N-acetylcaprolactam
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The liquor i8 heated together with the textile material
to 60C and held at that temperature for 1 hour. Then
hydrogen peroxide and caustic soda are added 80 that the
concentrations in the bleaching bath are as follows:
6 g of 35% ~trength aqueous H22 solution/l of
bleaching bath
1 g/l of caustic soda.
The bleaching liquor is heated up to 95C and held at
that temperature for 1 hour. The liquor is then dis-
charged and the textile material is rinsed with hot water
(60C)
Example 3
Bleaching of woven cloth in 100% viscose fiber.
The cloth has been predesized.
The bleaching liquor includes:
8 g/l of N-acetylcaprolactam
5 g/l of H202 (35% strength aqueous solution)
5 g/l of calcined sodium carbonate
3 g/l of ~Lastabil TGS
3 g/l of ~Hostapal FA
The cloth is impregnated with the bleaching liquor and
batched at room temperature (20 - 30C) for 18 hours.
Then the cloth is washed with hot water.
