Note: Descriptions are shown in the official language in which they were submitted.
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DETERGENT COMPOSITIONS
The invention relates to detergent compositions in the form
of tablets, for use in fabric washing.
Detergent compositions in tablet form are described, for
example, in GB 911204 (Unilever) and US 3953350 (Kao).
They are sold commercially in Spain. Tablets have several
advantages over powdered products: they do not require
measuring and are thus easier to handle and dispense into
the washload, and they are more compact, hence facilitating
more economical storage. These detergent tablets are
intended to be consumed completely when washing a single
load. Thus they should disperse/dissolve completely when
added to water.
Detergent tablets are generally made by compressing or
compacting a detergent powder, which includes 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.
Such tablets can be manufactured by stamping a chosen
quantity of the detergent composition using a press with
steel dies (also referred to as punches) which contact the
powder and apply pressure so as to compact the powder into
a tablet. Such a press may for example have two dies which
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move together within a surrounding sleeve, or one die which
is driven towards a fixed anvil, again within a surrounding
sleeve.
When making tablets, with any kind of material not
necessarily detergent, a problem which can arise is
adhesion of the composition to the steel mould parts.
Adhesion of material to mould parts is disadvantageous,
because the accumulated material spoils the surface finish
of articles compacted in the mould. The traditional
approaches to this problem have been to provide a low
friction surface on the mould parts, e.g. a conventional
non-stick coating of polytetrafluoroethylene, or else to
apply a release agent, for example magnesium stearate.
US-A-3081267 teaches that the dies should rotate relative
to each other while compressing the composition, so as to
prevent the composition from adhering to them.
GB-A-2276345 teaches the stamping of articles, including
tablets of compacted detergent powder, using mould parts
surfaced with an elastomeric material of some thickness.
This is stated to reduce unwanted adhesion to mould parts
provided that the elastomer-surfaced mould exhibits a -
suitable overall modulus of elasticity. The document
explains that a suitable modules of elasticity can be
achieved with a surface coating of elastomer which is at
least 0.5mm thick. A range of 0.5 to 7mm is disclosed.
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The thicknesses which are exemplified are about 4mm.
In WO 97/20028 published in June 1997, we have disclosed
the stamping of tablets using dies which carry a thin
elastomer coating, which has a thickness not exceeding
0.5mm over much or all of its area. This overcomes the
problem of adhesion to the dies, and produces tablets, with
a smooth surface.
By contrast, by using dies which carry a thicker elastomer
coating, we have found that the penetration of water into
the tablets on immersion is increased, thereby accelerating
the dispersion/dissolution of the tablets at the time of
use.
Therefore, in one aspect, the present invention provides
the use of an elastomeric layer, more than 0.5mm thick, on
a surface area of at least one mould part in a press for
compacting particulate detergent composition into tablet
form, which surface area contacts the -composition during
compaction;
in order to enhance the penetration of water through
the tablet surface on immersion.
It is envisaged that the use of such an elastomeric layer
will in particular be applied to the compaction of
particulate detergent compositions having a bulk density of
at least 650g/litre. Starting from a particulate
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composition of relatively high bulk density diminishes void
space within particles relative to void space between
particles. This is desirable because inter-particle '
porosity is more accessible to water on immersion.
The step of compacting the particles reduces the porosity
of the composition. Porosity is conveniently expressed as
the percentage of volume which is air.
The air content of a tablet can be calculated from the
volume and weight of the tablet, provided the air-free
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.
The percentage air content of the tablet varies inversely
with the pressure applied to compact the composition into
tablets while the strength of the tablets varies with the
pressure applied to compact them into tablets. Thus the
greater the compaction pressure, the stronger the tablets
but the smaller the air volume within them.
We have preferred to make tablets with a cylindrical shape
in which the height of the cylinder is generally less than
its diameter. A test of the strength of such tablets is
the diametral fracture stress (DFS) determined using a
testing machine which can urge a pair of confronting faces
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together with a measured force. An example is an Instron
Universal Testing Machine. The test is carried out by
placing the cylindrical tablet between the platens
(confronting planer faces) of the Testing Machine, so that
5 the platens contact the curved surface of the cylinder at
either end of a diameter through the tablet. The sample
tablet is then compressed diametrically, suitably by
advancing the platens of the machine towards each other at
a slow rate such as lcm/min until fracture of the tablet
l0 occurs at which point the applied load required to cause
fracture is recorded. The diametral fracture stress is
then calculated from the following equation:
2P
so ~r Dt
where 8o 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).
For any given tablet composition, tablet strength varies
inversely to the air volume expressed as percentage of the
whole volume. If tablets have a shape which is not
cylindrical, their diametral fracture stress is defined as
the diametral fracture stress of cylindrical tablets having
the same composition and percentage air volume and hence
the same density.
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The present invention proves particularly useful when
compacting tablets with sufficient pressure to achieve a
diametral fracture stress or equivalent parameter of at
least BKPa, better at least lOKPa, and preferably not more
than 60KPa. A value not exceeding 25 or 30KPa will often
be adequate, but higher values in a range from 20 or 25 KPa
up to 60 KPa may be used.
In a second aspect this invention provides a process for
the manufacture of tablets of detergent composition,
comprising compacting a particulate composition in a mould
consisting of a plurality of mould parts which are movable
relative to each other, wherein at least one of the mould
parts has an elastomeric coating on a surface area which
contacts the composition, which elastomeric layer has a
thickness of more than 0.5mm, and wherein compaction is
carried out with sufficient pressure to form tablets with a
DFS in the range 8 to 60KPa.
The amount of compaction pressure needed to attain a
desired value of diametral facture stress can be found by
making tablets of the chosen composition using varying
amounts of applied force, and then measuring the strength
of the resulting tablets.
As mentioned above, the tableting press may conveniently
have one or two movable dies which are driven into a
cavity. The elastomeric layer is, suitably, applied to the
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faces of the movable dies which apply pressure to the
composition, and/or to a stationary counter member towards
which a die is driven.
It is conceivable, but not preferred, that the elastomeric
layer could be provided on only one die of a pair, or on a
stationary counter member facing a single die, yet not on
the die. Such arrangements would be expected to lead to
asymmetric tablets in which one face was more permeable
than the opposite face. This would still give the benefit
of enhanced water penetration into the tablet, albeit
through one, not both, faces.
An example of a tableting press used in accordance with the
invention will now be described, with reference to Figs. 1
to 4 of the accompanying drawings in which:-
Fig. 1 is a vertical cross-section through a tablet
press illustrating its general arrangement; and
Figs. 2, 3 and 4 are similar cross-sections showing
stages in the cycle of operations of the tablet press.
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.
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A suitable arrangement, as illustrated in GB-A-2276345 is
shown in Figs. 1 to 4 of the accompanying drawings. The
apparatus is a tabletting press, whose structure
incorporates a tubular sleeve 10 into which fit a lower
punch 12 and an upper punch 14. The sleeve 10 defines a
mould cavity 16 closed at its bottom by the lower punch 12.
In use a particulate composition is supplied to this cavity
by means of a filling shoe 18 which slides on the upper
surface 20.
Initially the filling shoe advances to the position shown
in Fig. 2 with the upper punch 14 raised. A particulate
composition falls from the filling shoe to fill the cavity
16 above the lower punch 12.
Next as seen in Fig. 3 the filling shoe withdraws and the
upper punch 14 is pressed down into the cavity 16 thus
compacting the particulate composition in the cavity to
form a shaped article such as a tablet. Next, as shown in
Fig. 4, the upper punch 14 is raised and the lower punch 12
is also raised until the tablet 22 lies at a level with the
surface 20. After this the filling shoe 18 advances,
pushing the tablet 22 away as it does so while the lower
punch descends to the position shown in Fig. 2 for the
cycle of operations to be repeated.
In accordance with this invention, the upper punch 12 and
the lower punch 14 each have an elastomeric layer over
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their faces which come into contact with the detergent
composition.
The sleeve 10, which also forms part of the mould, is made
of steel and is not surfaced with elastomer. The punches
12,14 and also tablets compacted in the mould make sliding
contact with this sleeve.
Elastomers are polymers which are deformable, but return to
approximately their initial dimensions and shape upon
release of the deforming force. Generally they are
polymers with long flexible chains, with some cross-linking
between chains so as to form a cross-linked network
structure. The network structure restrains the movement of
the macro-molecular chain molecules and as a result
recovers rapidly after deformation.
The term "elastomeric" as used in defining this invention
includes materials as defined in ISO (International
Standard Organisation) 1982 as an "elastomer", or "rubber".
Also included in the definition of "elastomeric" materials
according to the invention are thermoplastic elastomers and
copolymers and blends of elastomers, thermoplastic
elastomers and rubbers.
At low temperature, elastomers are hard and brittle. Then
with increasing temperature an elastomer goes through a
rubbery phase after softening and retains its elasticity
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and elastic modulus until its decomposition temperature is
reached. The material should of course be in its rubbery
state at the operating temperature of the press. '
Preferably the elastomeric material according to the
5 invention is selected from those classes described in
American Society for Testing and Materials D1418 which
include:-
1. Unsaturated carbon chain elastomers (R Class)
including natural rubbers and butadiene acrylonitrile
10 copolymer, e.g. "Perbunan" ex Bayer.
2. Saturated carbon chain elastomers (M Class) including
ethylene-propylene types, e.g. "Nordel" ex DuPont and
fluorine containing types, e.g. "Viton" ex DuPont.
3. Substituted silicone elastomers (Q Class), e.g. as
available from Dow Corning.
4. Elastomers containing carbon, nitrogen and oxygen in
the polymer chain (U Class), e.g. polyurethane ex
Belzona.
Additional materials, for example fillers, can be
incorporated in the elastomeric material to modify its
mechanical and processing properties. The effects of
filler addition depends on the mechanical and chemical
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interaction between the elastomeric material and the
filler.
Fillers can be used to improve tear resistance for example.
Suitable fillers include carbon blacks; silicas; silicates;
and organic fillers such a styrene or phenolic resins.
Other optional additives include friction modifiers and
antioxidants.
Materials suitable for the elastomeric layer in the present
invention will preferably have a modulus of elasticity, in
the range 0.1 to 50MPa, most preferably 1 to 35MPa. The
layer thickness is preferably at least 0.7mm, and will
often lie in the range 0.7 to about 2.Omm, although thicker
layers can be employed, eg up to about 3mm thickness.
The elastomeric layer may be a piece, such as a disc, cut
from a sheet of elastomer and secured to the die surface
with adhesive. Some elastomers can be applied as a coating
on the die, but this is not preferred-as--awroute for
producing layers more than 0.5mm thick.
Mould parts, to which an elastomeric layer is applied in
. 20 accordance with this invention, will generally be metallic,
most usually steel. Other rigid materials such as ceramics
may possibly be used.
A mould surface may be subjected to pre-treatment to
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improve the bond strength between the surface and the
elastomeric layer. The aim of pre-treatment is to remove
weak boundary layers, for example weak oxides on metals;
optimise the degree of contact between surface and coating
and/or alter the surface topography such that the bondable
surface area is increased, and to protect the surface
before bonding to it.
Notably a surface may be treated by mechanical abrasion -
techniques include wire brushing abrasion papers, and
blasting techniques such as water, grit, sand or glass bead
blasting.
The application of elastomer layers to dies will generally
involve removing the dies from the press, and it may be
convenient to maintain a stock of dies in readiness for use
- which is reasonably practicable for industrial
production.
Adhesives suitable for securing an elastomer layer to a
rigid mould surface include two-part epoxy resin and one-
part cyanoacrylate types. Two-part epoxy resin adhesive is
sold under the trade mark "Araldite" by Ciba-Geigy
Plastics, Duxford, England.
The particulate composition which is compacted may be a
mixture of particles of individual ingredients, or may
comprise particles which themselves contain a mixture of
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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.
A detergent composition which is to be made into tablets
will normally 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 bar or tablet is
suitably from 2 to 60wto and is preferably from 5 or 8wto
up to 40 to 50wt%. 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 wt%, preferably from 2 or 4% to 30
or 40 wt%,- yet more preferably from 8 to 30 wt%.
Synthetic (i.e. non-soap) 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 ~ - +
~~3 M
where R is linear alkyl of 8 to 15 carbon atoms and M+ is a
solubilising cation, especially sodium, is also a
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 c~ non-soap
anionic detergent lies in a range from 0.5 to 15 wt% of the
composition.
It may also be desirable to include one of more soaps of
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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
5 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.
10 Specific nonionic detergent compounds are alkyl (C$-22)
phenol-ethylene oxide condensates, the condensation
products of linear or branched aliphatic Cs_2o primary or
secondary alcohols with ethylene oxide, copolymers of
ethylene oxide and propylene oxide, and products made by
15 condensation of ethylene oxide with the reaction products
of propylene oxide and ethylene-diamine. Other so-called
nonionic detergent compounds include long-chain amine
oxides, tertiary phosphine oxides, and dialkyl sulphoxides.
Especially preferred are the primary and secondary alcohol
ethoxylates, especially the Clo-15 Primary and secondary
alcohols 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 2 to 400, better 3, 4 or 50
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to 30o by weight of the composition, yet more preferably
from 3, 4 or 5% up to 10 or 15% by weight of the
composition.
Since the nonionic detergent compounds are generally
liquids, these may be absorbed on a porous carrier.
Preferred carriers include zeolite, sodium perborate
monohydrate and Burkeite (spray-dried sodium carbonate and
sodium sulphate as disclosed in EP 221776 (Unilever).
Products of this invention also include detergency builder
and this may be provided by water-soluble salts or by
water-insoluble material.
Examples of water-soluble builders are sodium
tripolyphosphate, pyrophosphate and orthophosphate; soluble
carbonates, e.g. sodium carbonate; and organic builders
containing up to six carbon atoms, e.g. sodium tartrate,
sodium citrate, trisodium carboxymethyloxysuccinate.
In particular phosphate or polyphosphate detergency builder
may provide at least 5% by weight, often at least 10% by
weight of the overall composition.
Alkali metal (preferably sodium) aluminosilicates are
water-insoluble builders. They may be incorporated in
amounts of up to 60a by weight (anhydrous basis) of the
composition, and may be either crystalline or amorphous of
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composition, and may be either crystalline or amorphous of
mixtures thereof, having the general formula:
0.8 - 1.5 Na20.A12O3. 0.8 - 6 Si02
These materials contain some bound water and are required
to have a calcium ion exchange capacity of at least 50 mg
Ca0/g. The preferred sodium aluminosilicates contain 1.5-
3.5 Si02 units (in the formula above).
Suitable crystalline sodium aluminosilicate ion-exchange
detergency builders are described, for example, in GB
1429143 (Procter & Gamble). The preferred sodium
aluminosilicates of this type are the well known
commercially available zeolites A and X, and mixtures
thereof. Also of interest is the novel zeolite P described
and claimed in EP 348070 (Unilever). Zeolite P of this
type is supplied by Crosfields, Warrington, UK under the
designation "Zeolite A24".
Another category of water-insoluble material which can
function as a water-softening agent and detergency builder
is the layered sodium silicate builders disclosed in US-A-
4464839 and US-A-4820439 and also referred to in EP-A-
551375.
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These materials are defined in US-A-4820439 as being
crystalline layered sodium silicate of the general formula
NaMSi02x+1 ~ YH20
where M denotes sodium or hydrogen,
x is from 1.9 to 4 and y is from 0 to 20.
Other builders may also be included in the detergent
composition as necessary or desired. Water-soluble
builders may be organic or inorganic. Inorganic builders
that may be present include alkali metal (generally sodium)
carbonate; while organic builders include polycarboxylate
polymers, such as polyacrylates, acrylic/maleic copolymers,
and acrylic phosphonates, monomeric polycarboxylates such
as citrates, gluconates, oxydisuccinates, glycerol mono-
di- and trisuccinates, carboxymethyloxysuccinates,
carboxymethyloxymalonates, dipicolinates,
hydroxyethyliminodiacetates; and organic precipitant
builders such as alkyl- and alkenylmalonates and
succinates, and sulphonated fatty acid salts.
Especially preferred supplementary builders are
polycarboxylate polymers, more especially polyacrylates and
acrylic/maleic copolymers, suitably used in amounts of from
0.5 to 15 wt%, especially from 1 to 10 wt%; and monomeric
polycarboxylates, more especially citric acid and its
salts.
The total amount of detergency builder will generally lie
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in a range from 5 to 80wt% of the composition. The amount
may be at least 10 or l5wt% and may lie in a range up to 50
or 60wt%.
Tablets for addition to a washing machine preferably
include a binder material which is water-soluble and also
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.
Preferred is that at least some of the particles of the
detergent composition are individually coated with the
binder material. Then, when the composition is compacted,
this coating serves as a binder distributed within the
composition.
Use of a binder helps to hold the tablet together, thus
enabling it to be made using a lower compaction pressure
and making it inherently more likely to disintegrate well
in the wash liquor. If the binder is also a material that
causes disruption when contacted with water, even better
disintegration properties may be achieved.
It is preferred that the binder material should melt at a
temperature of at least 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
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above the ambient temperature.
For convenience the melting temperature of the binder
material should be below 80°C.
Preferred binder materials are synthetic organic polymers
5 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 glycol of higher molecular weight, notably
4000 or 6000, can also be used.
10 Other possibilities are polyvinylpyrrolidone, and
polyacrylates and water-soluble acrylate copolymers.
The binder may suitably be applied to the particles by
spraying, e.g. as a solution or dispersion. The binder is
preferably used in an amount within the range from 0.1 to
15 10% by weight of the tablet composition, more preferably
the amount is at least to or even aL least 3% by weight of
the tablets. Preferably the amount is not over 8% or even
6% by weight.
Detergent compositions which are compacted into shaped
20 articles according to the invention may contain a bleach
system. This preferably comprises one or more peroxy
bleach compounds, for example, inorganic persalts or
organic peroxyacids, which may be employed in conjunction
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with activators to improve bleaching action at low wash
temperatures. If any peroxygen compound is present, the
amount is likely to lie in a range from 1 to 30% by weight
of the composition.
Perphthalimido perhexanoic acid and perdodecanoic acid are
two examples of organic peroxyacids. Typically these can
be used as 1 to 60 of the composition.
Preferred inorganic persalts are sodium perborate
monohydrate and tetrahydrate, and sodium percarbonate,
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 persalt is used as 5
to 30% by weight of a composition, while activator is 1 to
10% by weight of the 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
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compaction.
The starting particulate composition which is compacted in
accordance with this invention may in principle have any
bulk density. However, we have preferred to utilise
powders of relatively high bulk density. Thus the starting
particulate composition may suitably have a bulk density of
at least 500 g/litre, preferably at least 600 g/litre, and
advantageously at least 700 g/litre.
Granular detergent compositions of high bulk density
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), are inherently suitable for use
in the present invention.
Most preferred are granular detergent compositions prepared
by granulation and densification in the high-speed
mixer/granulator (Fukae mixer), as described in the above-
mentioned EP 340013A (Unilever) and EP 425277A (Unilever).
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EXAMPLE 1
A detergent powder with the following composition was
prepared:
Granulated
Components % by weight
coconut primary
alkyl sulphate 1.4
coconut alcohol 3E0 7.6
coconut alcohol 6E0 4.8
zeolite A24 29.3
soap 2,9
sodium carboxymethyl cellulase 0.8
sodium carbonate 0.3
water 5,3
Postdosed
Components
PEG 1500 4.3
sodium percarbonate
(borosilicate coated) 19.5
TAED granule 4.2
perfume 0.6
antifoam, fluorescer and
heavy metal sequestrant 4.0
sodium citrate 15.0
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The materials listed as "granulated components" were mixed
in a Fukae (Trade Mark) FS-100 high speed mixer-granulator.
(Continuous granulation equipment could also be used, as
could other machinery for granulating in batches.) The
soap was prepared in situ by neutralisation of fatty acid
with sodium hydroxide. The mixture was granulated and
densified to give a powder of bulk density greater than 750
g/litre and a mean particle size of approximately 650~.m.
The powder was sieved to remove fine particles smaller than
180~,m and large particles exceeding 1700~m. The remaining
solids were then mixed with the powder in a rotary mixer,
after which the perfume was sprayed on, followed by the
PEG. The PEG was sprayed at about 80°C onto the powder
which was at about 22-26°C (slightly above ambient because
of frictional heating during granulation).
Detergent tablets were prepared by compaction of 5og
quantities of the detergent powder formulation using
apparatus as illustrated in Figs. 1 to 4. The tablets were
of circular cross-section having a diameter of 4.5 cm and a
thickness of approximately 2.5 to 3.1 cm.
Compaction of the detergent powder, to make tablets, was
carried out using either plain steel top and bottom
punches, or alternatively punches which had an elastomer
layer on their faces which contact the detergent
composition.
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More specifically, one set of punches was given a
polyurethane coating painted on as a solvent solution and
providing a thickness of approximately 250~m after
evaporation of solvent. Another set of punches was
5 provided with an elastomer layer in accordance with the
present invention, lmm thick and glued on to the steel
punches.
With each set of punches 100 tablets were produced after
which the top punch was inspected.
10 With steel punches, the top punch was found to have 0.3 to
0.6g of powder firmly adhering to it, and producing
indentations in the tablet surfaces.
With both sets of punches bearing an elastomeric layer, the
top punch was found to have only about O.Olg of powder
15 adhering to it. This was a light dusting which was easily
removed. If a larger quantity of tablets was to be made,
it would be possible to run the press for an extended
period without needing frequent stops to clean the punches.
In a comparative experiment, a similar detergent
20 composition was compacted in the same way, but with a self-
adhesive polytetrafluoroethylene coating on the upper and
lower punches. After producing batches of 100 tablets it
was found that 0.1 to 0.6 g of detergent powder had become
firmly adhered to the punch surfaces.
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The flat surfaces of tablets made with these punches were
inspected visually. It was apparent that when tablets were
made with steel punches the first tablets produced had
smooth faces. After running the press for some time the
tablets had rougher surfaces but the roughness was
attributable entirely to material which had become adhered
to the dies. By contrast when tablets were made using dies
surfaced with elastomer lmm thick the surfaces were rougher
than the surfaces of either of the first tablets made with
steel dies and tablets made with dies having a thin
elastomer coating. In the case of tablets made using dies
with the thick elastomer coating in accordance with the
present invention the individual particles of the
composition could still be discerned at the surface of the
tablets.
This result which was apparent from inspection by eye was
also confirmed by laser profilometry.
The strength of tablets made with these various dies was
tested by the test of diametral fracture stress described
earlier.
Capillarv ugtake test
The speed at which the tablets took up water on immersion
was tested by a procedure in which the weight of a tablet '
is checked and then the tablet is placed with one of its
flat faces resting on a horizonal gauze support in a dish.
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Water, coloured with ink, is poured into the dish until the
level of water contacts the lower face of the tablet
resting on the gauze. After 1 minute the tablet is
removed, any superficial water is shaken off and the tablet
is weighed. The increase in weight of the tablet is an
indication of the rate at which water is taken up through
capillary action. The results obtained were:
DFS Capilliary
uptake(gm)
Thick elastomer (lmm) 12.4 4.2
Thin elastomer (250~m) 12.5 3.2
No elastomer 10.3 3.4
Water uptake (partially submersed)
In another test the procedure is similar except that the
water coloured with ink is poured into the dish until it is
nearly at the same level as the top surface of the tablet,
although this top surface is not itself covered by water.
After a period of time, which in this Example was 30
seconds, the tablet is removed from the dish and the gain
in weight is measured. As the water and ink penetrate into
the tablet the tablet takes on the dark colour of the ink.
It is observed whether the dark colour of the ink is
visible over the whole of the top face of the tablet (which
was not wetted directly) or whether a disc of light colour
can still be seen on this top face of the tablet. If such
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a disc can be seen its diameter is measured. The results
of these tests are set out in the following table.
DFS Water Diameter of
uptake(gm) dry core (mm)
Thick elastomer (lmm) 12.4 9.3 11.2
Thin elastomer (250~Cm) 12.5 7.8 20.3
No elastomer 10.3 8.1 17.9
Uptake of water by the tablets made using the dies surfaced
with thick elastomer was calculated to be approximately the
whole of the available porosity (void space) in the
tablets. The porosity was calculated to be approximately
25o by volume.
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EXAMPLE 2
Detergent powder of the following composition was prepared
by the same procedure as in Example 1:
Granulated
Components o by wei~c~ht
coconut primary
alkyl sulphate 1.4
coconut alcohol 5E0 11.7
zeolite A24 27.7
soap 2.7
sodium carboxymethyl cellulase 0.8
sodium carbonate 0.3
water 8.8
Postdosed
Components
PEG 1500 4.0
sodium perborate tetrahydrate 18.5
TAED granule 4.0
perfume 0.4
antifoam, fluorescer and
heavy metal sequestrant 4.0
sodium citrate 14.2
sodium polyacrylate 1.6
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The detergent composition was sieved to remove particles
smaller than 200~m and stamped into tablets using plain
steel dies and (separately) using dies surfaced with
elastomer. Various levels of compaction force were
employed with each set of dies.
Elastomer A was lmm thick and had elastic modulus of
0.72MPa. Elastomer B was lmm thick and had elastic modulus
9.83MPa.
The tablets were tested to determine their density,
porosity, strength and water uptake. The results are
tabulated below. The test of water uptake was the test in
which the tablet was partially submerged, leaving its upper
face exposed to air, as described in the previous example,
but with varying periods of time, as indicated.
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31
cn ~ w "
z 'a-~~ w
o ~' ~-' v --~ v
H w w '-'~ N
v N v
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w v v O U p
~ ~ U U
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'O
'd
~r
H O
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N
W o
''' 0 0 0 0 0 0 0 0 0 'd'~n o 0 0 0 ~n o
w x ~ ~ ~ ~ ~ ~ ~ ~ ~ o ~ ~ ~ M ~ ~ M
O O M
H
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W H
v N N b
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y n ~ ao a n ao .-~oo ~ rn w o0 0~ ~
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47
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v-1 r1 r-Ir~ r-1r-a e~ r1r1 v-Ir1 ei ri ri ~i ri r1
E E E ~ ~ '~ ~C ~C~ ~C ~C W a1 c0 a1 a4 00
E"' O O O O O f.~ 5-afa~r S.a~r S..W., 1~ S-a~ S.a
v v v v v v v v v v v v
O ~ N ~ ~ ~ E E E E E E E E E E E E
tU rtfra rtStoO O O O O O O O O O O O
w .-i~ .-~.-W...iy ~ra ~ i.y..r~ ~",a
w w w w w m u~ m u~ ~n m u, v~ v, cn ro ra
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A o 0 o 0 o ~ r, ~ ,-r,~ r, r, W w
2 2 Z 2 z w W w W w w w W W w
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By comparing results at similar porosity and strength, it
can be seen that tablets with similar density, porosity and
strength had greater water uptake when made with elastomer-
faced dies.
EXAMPLE 3
Tablets for use in fabric washing were made, starting with
a spray-dried base powder of the following composition:
Ingredient PARTS BY WEIGHT
Sodium linear alkylbenzene 11.0
sulphonate
C13-15 fatty alcohol 7E0 2.4
Ci3-15 fatty alcohol 3E0 2.3
Sodium tripolyphosphate* 18.0
Sodium silicate 4.0
Soap 0.21
Acrylate/maleate copolymer 1.5
Sodium sulphate, moisture and balance
minor ingredients to 45
* Added to the slurry as anhydrous sodium
tripolyphosphate containing at least 70% phase II
form.
This powder was then mixed with other ingredients as
tabulated below. These included particles of sodium
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tripolyphosphate specified to contain 70o phase I form and
contain 3.5o water of hydration (Rhodia-Phos HPA 3.5
available from Rhone-Poulenc).
Ingredient % by weight
Base powder 45
Sodium percarbonate granules 15
TAED granules 3.4
Anti-foam granules 3.2
Perfume, enzymes and other 3.5
minor ingredients
Rhodiaphos HPA3.5 30
tripolyphosphate
Sodium carbonate _
40g portions of this particulate composition were made into
cylindrical tablets of 44 mm diameter, using a press fitted
with punches elastomer surface layers about 2mm thick.
The press was set to apply compaction force of
approximately lOKN corresponding to a pressure of about 6
or 7 MPa which was sufficient to produce tablets with a
diametral fracture stress of about 25 KPa.
