 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to bleaching agents in granulated form containing a
solid aliphatic peroxycarboxylic acid as the bleaching component.
2. Description of Related Art
Bleaches based on peroxygen compounds are widely used in the bleaching of
fabrics. Commonly used bleaches of this type include, in particular,
hydrogen peroxide and its inorganic derivatives, such as sodium perborate
and sodium percarbonate, which on the one hand represent mild oxidizing
agents that are very safe to handle and, on the other hand, show good
bleaching power at sufficiently high temperatures. By contrast, bleaching
at relatively low temperatures requires stronger oxidizing agents, such as
peroxycarboxylic acids for example, in order to obtain bleaching in a
sufficiently short time. However, peroxycarboxylic acids (also referred to
in short as percarboxylic acids or simply per-acids) are very aggressive
oxidizing agents which show a tendency towards exothermic decomposition
and explosion and cannot be handled in pure form without precautionary
measures. Accordingly, it has been proposed inter alia--with a view to
overcoming these disadvantages--to produce these compounds in situ from
the non-dangerous inorganic per compounds and certain acylating agents, so
called activators, which as such do not undergo exothermic decomposition
or oxidation reactions, although they are sensitive to hydrolysis. This
process is complicated by the use of two components which have to be
separately metered, in addition to which the activation reaction between
the inorganic per compounds and the activators requires an undesirably
long induction time in some cases, above all at very low working
temperatures.
For these reasons, attempts have long been made to find suitable measures
to enable percarboxylic acids to be used as such for bleaching fabrics,
despite their instability and aggressive chemical properties. In this
connection, attention has been focused on the solid percarboxylic acids,
particularly for use in combination with washing processes.
Thus, Belgian Patent 560 389 describes the stabilization of solid
peroxycarboxylic acids using hydratable inorganic salts, in which the
product may also be granulated. Conversion into the granulated form is
particularly desirable when the percarboxylic acids are to be mixed with
other components which, for example because of their sensitivity to
oxidation, must not come into direct contact with the per-acids. DE-OS
2422 691 (British 1456591) mentioned one particular form of stabilization
with salts in which mixtures of magnesium sulfate with a little sodium or
potassium sulfate are used.
Another measure for preventing undesirable interactions between
peroxycarboxylic acids and other components is the coating of per-acid
particles. In FR-PS 1 262 475 (Canadian Patent 615,777), hydrophilic film
forming agents, such as gelatin, are used for this purpose. According to
GB-PS 1 387 167, water-impermeable materials, such as fats and waxes, are
used for coating. Another variant is described in DE-OS 27 37 864 (U.S.
Pat. No. 4,126,573) in which surfactants are used as coating materials.
In addition, numerous proposals have been made to combine desensitization
by salt hydrates with the coating process, as for example in DE-OS 24 22
735 (British 1456592) which describes a mixture of two granulates of which
one consists of percarboxylic acid particles containing salt hydrates and
coated with fatty alcohol. Similar granulates are described in U.S. Pat.
Nos. 3,770,816 and 4,170,453 and in DE-OS 26 52 424 (U.S. Pat. Nos.
4,225,451 and 4,288,388). U.S. Pat. No. 4,259,201 provides an example of
the use of salt-containing, surfactant-coated per-acid granulates in
detergents.
Although numerous problems involved in the use of peroxycarboxylic acids
have been solved by the described measures, a percarboxylic acid
formulation which satisfies all requirements in regard to safe handling,
mechanical and chemical stability, solubility and economic production is
still a long way off. Thus, although the granulates of per-acids and
inorganic salts are sufficiently desensitized, they lack abrasion
resistance so that, in many cases, it is not possible to prevent release
of the peroxycarboxylic acids from the granulates during storage and,
hence, oxidation of other sensitive components of the bleach preparations
containing these granulates. Although the use of coating materials
improves the mechanical properties, it does give rise to disadvantages,
such as poor chemical stability in the case of certain hydrophilic coating
materials or the prevention of dissolution in water in the case of
hydrophobic coatings or those of anhydrous surfactants.
Accordingly, efforts are still being made to find new per-acid formulations
having better all-round properties. In this connection, attempts are being
made inter alia to fathom the dependence of stability on the type of
auxiliaries added. Thus, many complexing agents capable of masking heavy
metals have proved effective stabilizers against catalytic decomposition
in almost all peroxycarboxylic acids, whereas with certain
peroxycarboxylic acids, for example, surfactants promote decomposition, as
mentioned in U.S. Pat. No. 3,639,285. With other peroxycarboxylic acids,
certain coating compositions have a destabilizing effect, as can be seen
from EP-OS 74 730 (Canada 190441). On the strength of these and other
similar results, current opinion would appear to be that experience with
one type of per-acid can rarely be applied to another type. Accordingly,
optimal formulations can only be achieved by measures that are
individually tailored to the particular type of percarboxylic acid.
SUMMARY OF THE INVENTION
The object of the present invention in this connection is to provide an
improved formulation for solid aliphatic peroxycarboxylic acids in
relation to the prior art.
According to the invention, this object is achieved by forming or building
up a bleaching agent in the form of a granulate of uniform composition
which contains solid aliphatic peroxycarboxylic acid and hydratable
inorganic salt and which is characterized in that it contains an organic
polymer compound soluble in alkaline-aqueous medium as granulating aid,
wherein all the components are uniformly distributed in the individual
granules of the granulate and which granulate alone, in water, gives a
pH-value in the mildly acidic range. The term "granulate" as used herein
is intended to mean the granulated form of the composition containing a
plurality of individual particles or granules.
This peroxycarboxylic acid formulation represents a sufficiently
desensitized, abrasion resistant, dust free and, hence, easy to handle
form of the solid aliphatic per-acids. Despite their mechanical stability,
the granulates dissolve rapidly in water or alkaline-aqueous medium, so
that the per-acids present are immediately available as bleaches in the
solution. In this form, the per-acids show unusual chemical stability and,
accordingly, may be stored for long periods, even under adverse
conditions. In addition, the granulates may readily be produced by
build-up granulation in a one-step process.
In general, the per-acid granulates according to the invention may be used
in any application where the percarboxylic acids present may be used with
advantage as oxidizing, bleaching or disinfecting agents. However, they
are preferably used in the bleaching of fibers and fabrics and, more
particularly, in the bleaching of fabrics during washing. One particular
advantage of the granulates in this respect is their compatibility with
other detergent ingredients, particularly alkaline reacting substances and
oxidation sensitive components, which enables the per-acids to be mixed
with the detergents without further measures and to be stored in this
form.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS
The peroxycarboxylic acids present in the bleaching agents according to the
invention are solid aliphatic compounds containing from 4 to 36 carbon
atoms which contain the group --CO.sub.3 H attached to carbon once or
repeatedly in the molecule. They may optionally contain the
groups--CO.sub.2 H, --CO.sub.2 Me, --SO.sub.3 H and --SO.sub.3 Me as
substituents or ether oxygen, where Me is an equivalent of a metal cation
from the group comprising Na.sup.+, K.sup.+, Mg.sup.2+ and Ca.sup.2+.
Preferably the per-acids are unsubstituted compounds corresponding to the
formula C.sub.(n-x) H.sub.(2n+2-3x) (CO.sub.3 H).sub.x where n=4 to 36
and x=1 to 3. Particular preference is attributed to monoperoxycarboxylic
acids containing from 10 to 18 carbon atoms and to diperoxycarboxylic
acids containing from 6 to 22 carbon atoms, of which the unbranched
.alpha.,.omega.-diperoxycarboxylic acids containing from 9 to 13 carbon
atoms are particularly important by virtue of their particularly good
bleaching effect. It is possible to use chemically uniform peracids as
well as mixtures of two or more peracids. The peroxycarboxylic acids as
pure compounds should be solid at room temperature and more especially at
temperatures of up to 50.degree. C. Particularly preferred per-acids are
those which are solid at temperatures of up to 50.degree. C. even in
technical quality, i.e. with a distinct content of the parent carboxylic
acid. The per-acid content of the granulates is from 3 to 50% by weight,
preferably from 5 to 30% by weight and more preferably from 7 to 20% by
weight.
Suitable hydratable inorganic salts for the granulates according to the
invention are salts of sodium, potassium, magnesium, calcium and aluminum
with oxidation stable anions of mineral acids, providing these salts are
capable of forming defined hydrates and do not show an alkaline reaction
in water. Examples of salts such as these are NaH.sub.2 PO.sub.4 and KAl
(SO.sub.2).sub.2. Sodium sulfate and magnesium sulfate are preferably
used, a mixture of sodium sulfate and magnesium sulfate in a ratio of from
2:1 to 40:1 and preferably in a ratio of from 5:1 to 25:1 (based on the
anhydrous forms) being particularly preferred. The inorganic salt content
of the granulates is from 40 to 95% by weight, preferably from 70 to 92%
by weight and more preferably from 75 to 90% by weight, again calculated
as, based on, the anhydrous form of the salt.
Particular importance is attributed to the granulation aid. Suitable
granulation aids are organic polymer compounds soluble in alkaline-aqueous
medium, such as soluble cellulose or starch derivatives or soluble, fully
synthetic polymers. Examples are methyl cellulose, solid polyethylene
oxides, polyvinyl pyrrolidone and polymeric carboxylic acids. It is
preferred to use homopolymers of acrylic acid, maleic acid and crotonic
acid and copolymers thereof with one another and with other monomers,
particularly polyacrylic acid, maleic acid-acrylic acid copolymers (molar
ratio 1:5 to 5:1) and crotonic acid-vinyl acetate copolymers (1:10 to
1:80), which give per-acid granulates of particularly high quality.
Polymers containing carboxyl groups are preferably present in the acid
form, although they may even be partially used as salts, providing those
salts do not show an alkaline reaction. The polymeric granulation aid is
preferably used in a quantity of from 0.2 to 10% by weight and more
preferably in a quantity of from 0.5 to 4% by weight, based on the
bleaching agent as a whole.
By using the above-mentioned granulation aids, it is possible to convert
the mixtures of per-acids and salts into mechanically stable granulates
using small quantities of these additives without the granules having to
be coated. This simplifies the production of stable per-acid granulates
and, at the same time, avoids the disadvantages of coated products, above
all the slow disintegration of the granules in the bleaching solution. In
addition, the uniform distribution of all the components in the individual
granules and the presence of the granulation aids would appear even to
promote the dispersion and dissolution of the per-acid particles present
in the granulates in the solution. The use of granulation aids dissolving
only in alkaline medium, for example crotonic acid/vinyl acetate
copolymers, is particularly advantageous here.
In the quantities used, the granulation aids surprisingly do not affect the
chemical stability of the per-acids, so that the products largely retain
their bleaching activity, even in the event of prolonged storage. However,
the stability of the products may often be further increased by various
additives. Thus, it has been found that chelate complexing agents for
heavy metals, particularly in quantities of up to 2% by weight and
preferably in quantities of from 0.1 to 1% by weight, can have a
beneficial effect on retention of the active oxygen during storage and/or
during the bleaching process in solution. Any of the complexing agents
normally used for stabilizing peroxycarboxylic acids are suitable,
although it is preferred to use polyphosphonic acids, such as
1-hydroxyethane-1,1-diphosphonic acid, or ethylene diamine tetramethylene
phosphonic acid and salts thereof.
In addition, it has surprisingly been found that certain surfactants do not
adversely affect the stability of the granulates in storage, even when
they are uniformly incorporated in the granules. The surfactants in
question are certain anionic surfactants, namely the salts of long-chain
(C.sub.6 -C.sub.22) monoalkyl sulfuric acid esters (alcohol sulfates),
more especially fatty (C.sub.8 -C.sub.18) alcohol sulfates and the salts
of sulfuric acid semi-esters of the reaction products of long-chain
alcohols, particularly fatty alcohols, with ethylene oxide, hereinafter
EO, (ether sulfates). On the contrary, these surfactants appear in some
cases further to improve stability in storage and to have a positive
effect upon the bleaching results obtainable with the granulates. These
surfactants may be present in the granulates in quantities of up to 10% by
weight and preferably in quantities of from 1 to 5% by weight.
The ready-formulated bleaching agents mayt contain water as a further
optional constituent in quantities of up to 20% by weight and preferably
in quantities of from 0.5 to 5% by weight. The quantity of water present
is always smaller than the quantity which may be calculated as the maximum
possible proportion of water of hydration from the salt content of the
granulates. The water content of the granulates emanates from their
production. The presence of water has a beneficial effect on the
desensitization of the per-acids, although it mot absolutely essential for
that purpose.
In addition to the components mentioned above, other components may be
incorporated in the granulates providing they do not adversely affect the
positive properties of the basic composition. Components such as these
are, for example, additional desensitizing agents, flow or solubility
modifiers and buffers. At all events, it is important to ensure that no
alkaline-reacting materials are used and that the granulates show a mildly
acidic reaction. They should have a pH value of from 3 to 7 and preferably
of from 4 to 6 in water (0.5%). Keeping to these limits is crucial to the
chemical stability of the granulates.
The granulates are best produced by methods in which thermal and mechanical
stressing, which could lead to decomposition of the per-acids, is avoided
particularly suitable granulation processes are those of the build-up or
agglomeration type, in which small particles are built up or agglomerated
into the desired particle size. Illustrative are processes such as
fluidized-bed granulation, rolling granulation in rotating drums or on
granulation pans, and mixed granulation, of which the mixed granulation
processes, especially in mixers comprising rotating tools, such as for
example Patterson-Kelly mixers, Lodige mixers and Forberg mixers, are
particularly preferred.
Production by the methods mentioned above ensures that, where their
particle size permits, all the constituents are uniformly distributed in
the individual granules and all the granules have the same composition.
In general, the production process itself does not start out from the pure
percarboxylic acids, but instead from safe to handle premixes of the type
which accumulate inter alia in the production of the percarboxylic acids,
for example in accordance with DE-OS 2930 546 (U.S. Pat. No. 4,287,135).
Premixes such as these contain (based on dry matter) from about 10 to 90%
by weight of the solid aliphatic peroxycarboxylic acid and, in addition,
traces of the parent carboxylic acid (due to inadequate reaction during
conversion into the per-acid), traces of hydrogen peroxide, and inorganic
salts, particularly Na.sub.2 SO.sub.4 and MgSO.sub.4. A particular
advantage is that, to produce the granulates according to the invention,
these per-acid premixes do not have to be dried, but instead may be used
in the moist form in which they initially accumulate during production.
The water content of the premixes may even exceed the maximal quantity
fixable as water of hydration in the salts.
In the case of mixed granulation, the solid per-acid or, preferably, the
per-acid premix is introduced into the granulator, for example a
Patterson-Kelly V mixer or a Lodige ploughshare mixer, with other solid
constituents of the granulates and intensively premixed therewith. Water
or a solution or suspension of granulate constituents in water, preferably
an aqueous solution of the granulation aid, is then introduced with
continuous movement of the apparatus, after which the continuous movement
of the apparatus is continued until all the constituents have been
uniformly distributed and the desired grain spectrum of the granulates has
been formed. The quantity of water is preferably selected so that the
moist granulate initially formed has a water content of from 8 to 30% by
weight. If the starting materials already contain enough water, there is
no need for water to be added during the granulation process. The
described mixed granulation may be carried out at room temperature and
even at slightly elevated temperatures of up to about 45.degree. C. and
preferably at a temperature of from 32.degree. to 40.degree. C. If
desired, granulation may be followed by drying of the granulates,
optionally in the same apparatus or even by other careful methods, for
example, of the fluidized-bed type. Dried granulates are preferred above
all in cases where the per-acid formulation is required to be
substantially free from ballast. If the granulates are obtained by a
method which gives a very broad grain size distribution, it may be
advisable to sieve the end product and to recycle unwanted grain sizes,
optionally after grinding.
The resulting per-acid granulates are distinguished by high mechanical
stability and, in particular, by abrasion resistance. They may be produced
in various grain sizes, above all in the 0.1 to 5 mm range. The 0.4 to 1.6
mm range is of particular importance for incorporation in detergents,
whereas coarser granulates with grain sizes in the 1.6 to 4 mm range may
even be preferred for independently used special products. The granulates
according to the invention generally have powder densities of from 400 to
1200 grams per liter and preferably from 500 to 1000 g/l.
It is of course readily possible subsequently to apply inert coatings of
various kinds, whether in the form of continuous films or in the form of
fine powders applied by deposition, to the granulates according to the
invention, although it is precisely the advantage of the invention that
such a measure is not essential.
The particularly preferred field of application for the bleaching agents
according to the invention is in the bleaching of fabrics in conjunction
with a washing treatment. For this purpose, the granulates may be used as
such, i.e. without further additive, although they are preferably made up
as scattering mixtures with other solid active substances required for the
treatment of fabrics. Thus, a bleach based on the granulates according to
the invention may contain, for example, alkalizing agents, per-acid
activators and, optionally, other bleaching agents, such as perborate for
example, as further active substances. In addition, surfactants, builders,
foam inhibitors and optical brighteners are mentioned as active substances
for a combined washing and bleaching preparation. In these made-up forms,
the outstanding mechanical and chemical stability of the granulates and
their compatibility with the surrounding materials are particularly
advantageous, particularly in regard to the | | |
