Note: Descriptions are shown in the official language in which they were submitted.
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DETERGENT COMPOSITIONS
This invention relates to the manufacture of detergent
compositions in the form of tablets intended to be consumed
when washing a single load of laundry.
When manufacturing a detergent composition for fabric
washing there are a number of possible options. Such
compositions have for many years been manufactured in
particulate form, commonly referred to as powders.
Detergent compositions can also be manufactured as liquids.
Tablets, to which this invention relates, are yet another
possibility.
When formulating a detergent composition there is scope to
make both qualitative and quantitative choices concerning
the ingredients. Anionic detergent actives are the most
commonly used, usually together with nonionic detergent
actives. Amongst the anionic detergent actives which are
commercially available, linear alkylbenzene sulphonate and
primary alkyl sulphate are commonly used. There has been a
trend for particulate detergent compositions to be
manufactured with a bulk density higher than 650 g/litre
which is a departure from older practice when bulk
densities were customarily lower.
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Detergent compositions in tablet form have, potentially at
least, several advantages over powder products. They do
not require the user to measure out a volume of powder or
liquid. Instead one or several tablets provide an
appropriate quantity of composition for washing a single
load in a washing machine or possibly by hand. They are
thus easier for the consumer to handle and dispense.
Detergent compositions in tablet form are generally made by
compressing or compacting a detergent powder which includes
both detergent active and detergency builder. It is
desirable that tablets have adequate strength when dry, yet
disperse and dissolve quickly when added to wash water.
Detergent tablets for fabric washing typically contain at
least 5% by weight of detergent active. This serves as a
binder, but can also retard disintegration and dissolution
of a tablet. (By contrast, tablets for use in automatic
dishwashing machines typically contain 2o by weight or less
of detergent active, customarily a low-foaming nonionic
detergent, as in W096/23053 for instance). There have been
a number of disclosures relating to the manufacture of
detergent tablets for fabric washing which have both
strength and rapidity of disintegration in water, for
example EP-A-522766.
GB-A-1080066 teaches that tablets should have void space
between particles in order to allow penetration of water
into the tablet at the time of use. The teaching of this
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document is that the void volume should be from 35 to 600
of the total tablet volume. US-A-3081267 teaches that void
space within a tablet and communicating with external air
should be from 40 to 60% by volume of the tablet.
Both of these documents teach that after the tablets are
made by compaction of the particulate detergent composition
the tablets should be sprayed on their exterior with water,
which is then allowed to dry. The effect of this is to
cause partial hydration and dissolution at the exterior of
the tablets thus cementing material together at the tablet
exterior and enhancing tablet strength.
These documents date from 1963-1966. In more recent
documents there has been disclosure of tablets of lower
void volume and in Example 6 of EP 711828 tablets are
disclosed which contain aluminosilicate as builder and have
porosities corresponding to 30% or 20% of air in the tablet
volume.
When making tablets from particulate detergent composition,
it is desirable that the tablets should
dissolve/disintegrate rapidly when added to water for use,
yet have a good mechanical strength prior to use. These
properties are antagonistic. As more pressure is used when
a tablet is compacted, so the tablet density and strength
m
rise, but the speed of disintegration/dissolution goes
down.
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This invention is concerned with tablets compacted from a
detergent composition containing a substantial portion of
water-soluble phosphate builder.
Unexpectedly, we have found that in such tablets, the
combination of tablet strength and speed of disintegration
is affected by the choice of material incorporated as
peroxygen bleach. Sodium percarbonate and sodium perborate
tetrahydrate both give properties which are better than
those obtained with sodium perborate monohydrate.
Consequently, in a first aspect the present invention
provides a detergent tablet compacted from a particulate
composition containing:
from 2% preferably 5o up to 50% by weight of detergent
active,
from 20 to 60% by weight of water-soluble inorganic
phosphate builder, and
other ingredients,
wherein the tablet has a density of at least 1040
gm/litre and contains from 8 to 30% by weight of peroxygen
bleach which is sodium percarbonate or sodium perborate
tetrahydrate or a mixture thereof.
Sodium percarbonate has been found to give even better
strength than perborate tetrahydrate and is therefore
preferred.
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The amount of peroxygen bleach is preferably at least l00
by weight of the composition. The amount may be not more
than 25% or even 20% by weight.
The peroxygen bleach is preferably distributed throughout
5 the tablet, although it may be present as a multiplicity of
granules distributed throughout the tablet. Notably,
sodium percarbonate may be utilised in the form of granules
with a water-soluble coating of a protective material
serving to keep moisture away from the percarbonate until
the time of use.
Tablet density preferably lies in a range from 1040 or
1050gm/litre up to 1300gm/litre. The tablet density may
well lie in a range up to 1250 or even 1200gm/litre.
Tablet density is inversely related to tablet porosity,
which is conveniently expressed as the percentage of its
volume which is air (i.e. empty space).
The air content of a tablet can be calculated from the
volume and weight of the tablet, provided the true density
of the solid content is known. The latter can be measured
by compressing a sample of the material under vacuum with a
very high applied force, then measuring the weight and
volume of the resulting solid object.
The true density of a detergent composition is often about
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1.6, in which case a tablet density range from 1040 to
1300g/litre is approximately 19 to 35o air by volume.
Ranges of 1040 to 1250 or 1200g/litre approximates to 22 or
25% to 35o air by volume. A preferred range of 1070 to
S 1250g/litre approximates to 22 to 33o air by volume.
Preferably, part or all of the detergent active is anionic.
We have found that satisfactory strength and speed of
disintegration can be obtained using a detergent active
mixture in which anionic and nonionic detergent are in
proportions from 1.5:1 to 4:1, better 1.8:1 to 3:1 or 4:1.
These proportions give good cleaning. Therefore, in a
second aspect the invention provides a detergent tablet
compacted from a particulate composition containing:
from 2% preferably at least 5% up to 50% by weight of
detergent active,
from 20 to 60o by weight of water-soluble inorganic
phosphate builder, and
other ingredients,
wherein the tablet has a density of at least
1040gm/litre and the detergent active contains anionic and
nonionic detergent in proportions of 1.5:1 to 4:1.
It is preferred that the nonionic detergent active is a
mixture of an ethoxylated fatty alcohol with HLB value over
11.0 and an ethoxylated fatty alcohol with HLB value below
9.5 better below 9Ø
t ,. ~ ,.."
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The particulate composition which is compacted may be a
mixture of particles of individual ingredients, but usually
will comprise particles which themselves contain a mixture
of ingredients. Such particles containing a mixture of
ingredients may be produced by a granulation process and
may be used alone or together with particles or single
ingredients.
The composition will contain detergent active and detergent
builder. Other ingredients are optional, but usually there
will be some other ingredients in addition to the detergent
active and detergency builder.
The amount of detergent active in a tablet is suitably from
5 or 8wto up to 40 to 50wto. Detergent-active material
present may be anionic (soap or non-soap?, cationic,
zwitterionic, amphoteric, nonionic or any combination of
these.
Anionic detergent-active compounds may be present in an
amount of from 0.5 to 40 wto, preferably from 20, 40 or 50
up to 30 or 40 wt%.
Synthetic (i.e. non-soapy anionic surfactants are well
known to those skilled in the art. Examples include
alkylbenzene sulphonates, olefin sulphonates; alkane
sulphonates; dialkyl sulphosuccinates; and fatty acid ester
sulphonates.
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Primary alkyl sulphate having the formula
ROS03- M+
in which R is an alkyl or alkenyl chain of 8 to 18 carbon
atoms especially 10 to 14 carbon atoms and M+ is a
solubilising cation especially sodium, is commercially
significant as an anionic detergent active. Linear alkyl
benzene sulphonate of the formula
R ~ - +
S03 M
where R is linear alkyl of 8 to 15 carbon atoms and M+ is a
solubilising cation, especially sodium, is also a
l0 commercially significant anionic detergent active.
Frequently, such linear alkyl benzene sulphonate or primary
alkyl sulphate of the formula above, or a mixture thereof
will be the desired anionic detergent and may provide 75 to
100wto of any anionic non-soap detergent in the
composition.
In some forms of this invention, the amount of non-soap
anionic detergent lies in a range from 5 to 30 wt% of the
composition, better 5 to 20 wto.
It may also be desirable to include one of more soaps of
fatty acids. These are preferably sodium soaps derived
. r..... , , ~ ,.. ...
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from naturally occurring fatty acids, for example, the
fatty acids from coconut oil, beef tallow, sunflower or
hardened rapeseed oil.
Suitable nonionic detergent compounds which may be used
include in particular the reaction products of compounds
having a hydrophobic group and a reactive hydrogen atom,
for example, aliphatic alcohols, acids, amides or alkyl
phenols with alkylene oxides, especially ethylene oxide
either alone or with propylene oxide.
Specific nonionic detergent compounds are alkyl (Ce-2z~
phenol-ethylene oxide condensates, the condensation
products of linear or branched aliphatic C8-2o primary or
secondary alcohols with ethylene oxide, copolymers of
ethylene oxide and propylene oxide, and products made by
condensation of ethylene oxide with the reaction products
of propylene oxide and ethylene-diamine.
Especially preferred are the primary and secondary alcohol
ethoxylates, especially the Clo-is Primary and secondary
alcohals ethoxylated with an average of from 5 to 20 moles
of ethylene oxide per mole of alcohol.
In certain forms of this invention the amount of nonionic
detergent lies in a range from 1 to 200, better 2o up to
15% or 20o by weight of the composition.
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Preferred is to use from 5 to 20% of non-soap anionic
detergent, especially linear alkyl benzene sulphonate or
primary alkyl sulphate, together with 2 to 15% of nonionic
detergent, especially ethoxylated fatty alcohol, where the
5 ratio of anionic to nonionic is in the range from 1.5:1 to
4:1.
Products of this invention also include phosphate
detergency builder, which may be ari alkali metal
orthophosphate, pyrophosphate or tripolyphosphate.
10 Preferred is sodium tripolyphosphate.
Examples of other water-soluble builders which may be
present are carbonates, e.g. sodium carbonate; and organic
builders containing up to six carbon atoms, e.g. sodium
tartrate, sodium citrate, trisodium
carboxymethyloxysuccinate.
The amount of phosphate or polyphosphate detergency builder
is at least 20o by weight, often at least 26% or even-at
least 33% by weight of the overall composition.
The total amount of detergency builder will generally lie
in a range from 5 to 80wto of the composition. The amount
may be at least 10 or l5wto and may lie in a range up to 50
or 60wto.
The sodium perborate tetrahydrate or sodium percarbonate is
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advantageously employed together with an activator. Bleach
activators, also referred to as bleach precursors, have
been widely disclosed in the art. Preferred examples
include peracetic acid precursors, for example,
tetraacetylethylene diamine (TAED), now in widespread
commercial use in conjunction with sodium perborate; and
perbenzoic acid precursors. Typically activator used as 1
to 10o by weight of a composition.
Other ingredients may also be present in the overall
composition. These include sodium carboxymethyl cellulose,
colouring materials, enzymes, fluorescent brighteners,
germicides, perfumes and bleaches. Sodium alkaline
silicate may be included, although the amount of this or at
least the amount added as an aqueous liquid, is preferably
restricted so as to keep to a particulate mixture prior to
compaction.
The detergent composition may incorporate a binder which is
water-soluble and serves as a disintegrant by disrupting
the structure of the tablet when the tablet is immersed in
water, as taught in our EP-A-522766.
Such a binder material should melt at a temperature of
35°C, better 40°C or above, which is above ambient
temperatures in many temperate countries. For use in
°
hotter countries it will be preferable that the melting
temperature is somewhat above 40°C, so as to be above the
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ambient temperature.
For convenience the melting temperature of the binder
material should be below 80°C.
Preferred binder materials are synthetic organic polymers
of appropriate melting temperature, especially polyethylene
glycol. Polyethylene glycol of average molecular weight
1500 (PEG 1500) melts at 45°C and has proved suitable.
Polyethylene glycols of molecular weight 4000 and 6000 melt
at about 55°C and 62°C respectively.
Other possibilities are polyvinylpyrrolidone, and
polyacrylates and water-soluble acrylate copolymers.
We have found it desirable that the particulate composition
which is compacted should have a bulk density of at least
650 g/litre, preferably at least 700 g/litre, and
advantageously at least 750 g/litre.
Granular detergent compositions of high bulk density can be
prepared by granulation and densification in a high-speed
mixer/granulator, as described and claimed in EP 340013A
(Unilever), EP 352135A (Unilever), and EP 425277A
(Unilever), or by the continuous granulation/densification
processes described and claimed in EP 367339A (Unilever)
and EP 390251A (Unilever).
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The invention can be put into effect using a conventional
stamping press. A suitable press will generally have a pair
of mould parts which move relatively towards and away from
each other to compact particulate material between
them. They may move within a surrounding sleeve or similar
structure.
For any chosen composition, the density and strength of
tablets varies with the pressure applied to compact the
composition into tablets.
to The amount of pressure needed to obtain a density in the
required range can be found by making tablets with varying
amounts of applied force, and determining the density of
the tablets obtained.
The tablets may be made without any spray on of water after
stamping the tablets.
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Example 1
Tablets for use in fabric washing were made, starting with
a base powder of the following composition:
parts by weight
S Sodium linear alkylbenzene sulphonate 9.62
C13-is fatty alcohol 7E0 1 . 07
X13-is fatty alcohol 3E0 3 . 21
Soap 0.27
Sodium tripolyphosphate, type lA 1 24.31
Sodium silicate 5.88
Sodium carboxymethyl cellulose 0.21
Acrylate/maleate copolymer 1.15
Salts, moisture and minor ingredients 8.9
54.60
1. This tripolyphosphate contained less than 30%
of
the phase I form of anhydrous sodium tripolyphosphate.
Three powders were made by mixing this base powder with
persalts, sodium tripolyphosphate specified to contain 700
phase I form and contain 3.5o water of hydration (Rhodia-
Phos HPA 3.5 available from Rhone-Poulenc) and other
detergent ingredients as tabulated below.
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The compositions thus contained the following percentages
by weight:
a by weight
C
Base powder 54
60
. 54.60 54.60
HPA sodium tripolyphosphate 21
22
. 21.22 20.12
5 TAED granules 3
35
. 3.35 3.35
Sodium carbonate 3
20
. 4.95 --
Sodium percarbonate 15.00 -_
Sodium perborate monohydrate
-- 13.25 --
Sodium perborate tetrahydrate --
-- 19.30
10 Anti-foam granule 1
.16 1.16 1
16
Enzymes, phosphonate, perfume 1 .
47
. 1.47 1.47
The amounts of persalt were chosen to give the same amounts
of available oxygen. The sodium percarbonate was in the
form of granules with a water-soluble coating.
15 35g portions of each composition were made into cylindrical
tablets of 44 mm diameter, using a Carver hand press. The
force applied to make the tablets was the same (300kg) in
each case.
The tablets were weighed and measured to determine their
density which was found to be 1117gm/litre ~ 5% in each
case.
The strength of the tablets was determined by the following
test of their diametral fracture stress. The test
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procedure was carried out using a testing machine with flat
faces which were urged together by a measured force, such
as an Instron Universal Testing Machine.
The cylindrical tablet was placed between the platens of an
Instron machine, so that the platens contact the curved
surface of the cylinder at either end of a diameter through
the tablet. The sample tablet was then compressed
diametrically, by advancing the platens of the machine
towards each other at a slow rate such as lcm/min until
fracture of the tablet occurred, at which point the applied
load required to cause fracture was recorded. The
diametral fracture stress was then calculated from the
following equation:
2P
bo=
~t Dt
where bo is the diametral fracture stress in Pascal (Pa), P
is the applied load in Newtons (N) to cause fracture, D is
the tablet diameter in metres (M) and t is the tablet
thickness, also in metres (M).
we have found it desirable in this invention that tablets
should have a DFS of at least 6KPa, better at least BKPa.
DFS will usually not need to exceed 40KPa, and a range from
10 to 40KPa is particularly preferred. Values of DFS up to
at least 60KPa may be used, however.
.,.w. ~......_ . ,
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The break-up, dispersion and dissolution of tablets was
measured by a test procedure in which a tablet is placed on
a plastic sieve with 2mm mesh size which was immersed in 9
litres of demineralised water at ambient temperature of
22°C and rotated at 200 rpm. The water conductivity was
monitored until it reached a constant value.
The time for break up and dispersion of the tablets was
taken as the time (T9o) for change in the water conductivity
to reach 900 of its final magnitude. This was alter,
l0 confirmed by visual observation of the material remaining
on the rotating sieve.
The results obtained were:
C
percarbonate perborate perborate
mono- tetra-
h drate h drate
Tablet strength 32 20 27
(kPa)
Tablet dissolution 3,5 5_2 3.8
T9o (min)
This shows that tablets made with percarbonate and with
perborate tetrahydrate had unexpectedly greater strength
than tablets made with perborate monohydrate. They also
' 20 dissolved more quickly, in spite of their greater strength.
