Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR FORMING TABLETED HIGH-CAUSTIC DETERGENT
Background of the Invention
The institutional detergent market distributes a variety of
products for washing silverware, pots and pans, dishes, floors, walls,
stainless steel surfaces, tile and other areas.
Unlike products used in the home, institutional
detergents are often sold in bulk and dispensed from mechanical
dispensers. There are a variety of different physical forms these can
take, including liquids, powders, solidified bricks, granules and
tablets. Several factors enter into the determination of which
particular physical form is most suitable for the desired application.
Feed rate is a very important consideration. With a
liquid, where the product is directly injected for use, use
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concentration is easy to control. Unfortunately with liquids, the
concentration of active components in the product is generally relatively low
and therefore the container size can be prohibitively large. DE 3326459
discloses a liquid detergent for dishwashing which contains bicarbonate,
metasilicates, phosphate, chlorine, tensides, acoustic source and water. EP
0297273 discloses a solid alkali cleaning material which contains alkali
phosphate, silicates, carbonates and phosphoric partial ester. With solid
forms, which are dissolved with water, the rate of dissolution will influence
dispensing rate.
Delivering consistent feedstock is very important. With a brick
formulation, the product consistency can be maintained to a certain extent,
but dissolution rate can be slow and, as with many forms, there may also be
problems with disposing of the container.
Another very important factor in distributing institutional detergents is
packaging. For environment reasons, it is preferable to minimi~e packaging.
U.S. Patent 5,078,301 discloses a bag of detergent tablets wherein the bag is
a water soluble material. This product is apparently designed to minimi~e
packaging, but has several significant disadvantages, Primarily, with a water
soluble bag, the water will act to dissolve the plastic bag. However, the
undissolved residue of such bags tend to clog the dispenser. Also with a
water soluble bag, there is the requirement of an exterior overwrap to prevent
AMENDED SHEET
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humidity or extraneous water from destroying the water soluble bag during
shipping and storage.
All of these problems are compounded with highly hygroscopic
(highly caustic) and/or hydratable materials. Of course, with the caustic
materials, the operators should never physically handle the detergent.
Powdered cleaning compounds are typically
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dispensed with water. Given that premature exposure to water tends
to increase the caking tendency of powders, clogging of the dispenser
and uniform dispensing from powder systems, especially those prone
to prolonged periods of inactivity, may be a problem.
Many detergents, particularly highly caustic detergents,
dissolve in water and liberate a great deal of heat. It is therefore
preferable to control the dissolution rate of these detergents to avoid
temperature peaks in the dispensing equipment.
With tableted, high-caustic detergent, a further problem
can be encountered. Anhydrous sodium hydroxide and potassium
hydroxide are, of course, very hygroscopic. Typical detergent
formulations generally include some free water, and certainly water
of hydration from sources such as sodium tripolyphosphate
hexahydrate. When tableting, the caustic comes into very close
physical proximity to the water. The water is necessary for the
tableting to occur at reasonable pressures. But once combined
together, the caustic will exothermically react with the free water.
For tableted high caustic detergents, if this reaction occurs after
compression, the mechanical strength of the tablet will be reduced.
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Summary of the Invention
Accordingly, it is an object of the present invention to provide a
method of forming a tableted detergent which includes phosphate
sequestrants, free water, and high levels of caustic. Further, it is an object
of
the present invention to provide such a product wherein the formed tablets do
not deteriorate quickly after formation.
According to one aspect of the invention there is provided a
method of forming a tableted detergent from a partially hydrated phosphate
mixture, anhydrous caustic, 0.5% to 5% by weight free water and 0 to 40% by
weight filler comprising:
adding said free water to said phosphate mixture without adding
said filler, and allowing said water to be absorbed by said phosphate mixture;
and subsequently adding 20% to 70% by weight of the caustic to
said phosphate mixture to form a second mixture whereby the temperature of
said second mixture is maintained at less than 75 C;
compressing said second mixture to form tablets.
Preferably, the filler is present in an amount of at least 5% by
weight, for example 5% to 40% or 5% to 20%. When the temperature of the
second mixture is maintained at less than 50 C the amount of free water may
be 1% to 3% by weight. Caustic may be present in an amount of 40% to 70%
by weight.
According to another aspect of the invention there is provided a
method of forming a compressed detergent tablet, said tablet comprising:
from 20% to 70% by weight caustic;
from 20% to 60% by weight of a sequestering agent consisting
of a combination of sodium tripolyphosphate and sodium tripolyphosphate
hexahydrate;
from 1 to 4% by weight polycarboxylic acid having a molecular
weight of 2,000 to 20,000;
from 0 to 5% by weight of a defoaming agent, and from 0 to 4%
by weight propylene glycol and from 5% to 40% by weight filler;
and free water;
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said method comprising combining said propylene glycol, said
poiycarboxylic acid and said free water to form a liquid mixture, combining
said liquid mixture with said sequestering agents, and permitting said liquid
mixture to be absorbed by said sequestering agents to form a first detergent
mixture;
subsequently combining said filler and said caustic to said first
detergent mixture to form a second detergent mixture and compacting said
second detergent mixture to form tablets whereby the order of addition of he
detergent components prevents the second detergent mixture from reaching a
temperature in excess of 50 C.
In summary, the invention is based on combining the individual
components of the detergent, including the phosphate along with free water
and caustic, in such a manner and/or order of addition that the overall
temperature of the product at no time exceeds 75 C and preferably never
exceeds 50 C and most preferably never exceeds 40 C. Careful blending,
selection of raw materials and proper order of addition which factors in the
hygroscopic nature of the materials and the lability of water, once absorbed,
combine to achieve this result.
In one preferred embodiment of the present invention wherein
fillers are included in the detergent formulation, the phosphate sequestrants,
i.e., sodium tripolyphosphate, anhydrous and hexahydrate, are combined
together with any liquid components including all free water. After the liquid
components are absorbed into the sequestrants, caustic, filler and any
bleaching agent are added. The product can then be compressed to form
tablets. In this manner, the hydration reaction is adequately controlled, i.e.
the free-----------------------------------------------------------------------
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water is absorbed by the species most capable of retaining it in the
presence of caustic, thus reducing the potential for an exothermic
reaction and subsequent deterioration of the tablet.
In an alternate embodiment of the present invention,
cooling can be employed to physically control the temperature of the
mixture, thereby preventing an undesirable excessively exothermic
reaction. This, however, requires significant cooling time.
The objects and advantages of the present invention will
be further appreciated in light of the following detailed description.
Detailed Description
The present invention is a method of making a high
caustic tableted detergent, particularly a ware washing detergent.
This ware washing detergent will include a source of caustic, a
hardness sequestering system including a hydrated phosphate, low
molecular weight water-soluble polymers, non-ionic defoaming
surfactants, processing aids and optionally bleaching sources.
The caustic source can be sodium or potassium
hydroxide with sodium hydroxide preferred. Generally, for use in the
present invention, this will include from about 20 to about 70%
caustic with about 45% to about 57% caustic being preferred. The
caustic will be less than fully hydrated and is preferably substantially
anhydrous.
The hardness sequestering system can be a variety of
different chemical components. The primary sequestrants are alkali
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metal salts of polyphosphates. Optional sequestrants include alkali
metal salts of phosphonic acid and of gluconic acid, alkali metal salts
of ethylene diamine tetraacetic acid (EDTA), alkali metal salts of
nitrilotriacetic acid (NTA) and alkali metal salts of polycarboxylic acids
such as polyacrylic acid, polymaleic acid and mixtures thereof.
Phosphates are commonly available in anhydrous or
hexahydrate forms. For purposes of the present invention, a mixture
of anhydrous and hydrated phosphates is preferred. The composition
should include at least 10% hydrated phosphate sequestrant, based
on total formulation.
Generally, the hardness sequestering system of the
present invention will form 20 to about 80% of the overall mass of
the detergent composition, and preferably about 35 to 40%. A
mixture of hydrated (hexahydrate) and anhydrous sodium
tripolyphosphate in the mass ratio of 3:1 to about 1:3, and preferably
1:1 to 2:1. In areas where the amount of phosphates is regulated, it
may be necessary to supplement the water hardness control ability of
the product by adding other sequestrants such as the alkali metal
salts of NTA or EDTA.
The present invention can optionally include a chlorine
source. One preferred chlorine source is dichloroisocyanurate. This
is added in amounts of up to 7% by weight. Other bleaching aids
including alkali metal perborates and percarbonates may also be used.
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In addition to the above, the detergent composition may
include defoaming surfactants. One typical class of anionic
defoaming surfactants is the phosphate esters. The defoaming non-
ionic surfactant used herein is selected from the group consisting of
alcohol alkoxylates, alkyl alkoxylates, block copolymers and mixtures
thereof. Generally, these nonionic surfactants are prepared by the
condensation reaction of a suitable amount of ethylene oxide and/or
propylene oxide with a selected organic hydrophobic base under
suitable oxyalkylation conditions. These reactions are well known
and documented in the prior art. Generally, these will have a
molecular weight of 900 to about 4,000. One such surfactant is an
ethylene oxide propylene oxide block copolymer. Commercially
available surfactants include Triton CF32TM, Triton DF12TM, Plurafac
LF131 T"", Plurafac LF132TM, Plurafac LF231 T"", Industrol N3T"" and
Genapol PN30T"". These can be included in an amount from about 0.5
to about 5% with about 1.5% preferred.
In addition to this, low molecular weight (2,000-20,000),
water-soluble polybasic acids such as polyacrylic acid, polymaleic or
polymethacrylic acid or copolymeric acids can be used as
sequestering aids, to inhibit growth of calcium carbonate crystals and
to improve rinseability. Preferably the water-soluble polymer will be
a polycarboxylic acid such as polyacrylic acid having a molecular
weight of around 5000. Generally, the present invention should
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include from about 1 % to about 4% polyacrylic acid on an actives
basis with about 2% preferred.
The detergent formulation may also include 1 % to 5%
of a polyhydric water soluble alcohol. Suitable water soluble
polyhydric alcohols include propylene glycol, ethylene glycol,
polyethylene glycol, glycerine, pentaerythritol, trimethylol propane,
triethanolamine, tri-isopropanol amine and the like. Propylene glycol
is preferred. This acts as both a processing aid and a dissolution aid
for the tablet, as is discussed below.
In order to provide a strong tablet the present invention
will include from about 2 to 10% liquid components, preferably less
than 8%. Generally, this can be provided for by the nonionic
surfactant, the polyalcohols and/or free water. The formulation
should also include 2% to 10% by weight of water of hydration. This
also provides for a stronger tablet. Generally, there will be at least
0.5% up to 5% free water in the composition. This can be the
solvent for the polymer or surfactant. It is preferable to keep the free
water less than 5% and the total liquid at less than 10% to keep the
product flowable and non-tacky during the tableting.
In addition to the above, the detergent formulation can
include optional ingredients commonly referred to as fillers such as
soda ash, the silicates such as sodium and potassium silicate and
polysilicate, and sodium metasilicate and hydrates thereof, alkali
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metal chloride, alkali metal sulfates and alkali metal bicarbonate.
These can be present in an amount of 1 % to 30% by weight.
A preferred formuiation for use in the present invention
includes the following:
Tab/e 1
Solid Components:
10.0% soda ash
21.0% sodium tripolyphosphate
hexahydrate (18% water of
hydration)
16.3% sodium tripolyphosphate powder
0.2% sodium dichloro-isocyanurate
(ACL-6OTM)
45.0% caustic bead
Liquid Components:
4.5% 5000 molecular weight
polyacrylic acid (48% active in
water)
1.5% ethylene oxide propylene oxide
block copolymer non-ionic
surfactant
1.5% propylene glycol
In this formulation, the sodium tripolyphosphate
hexahydrate provides 3.8% water of hydration and the polyacrylic
acid provides about 2.3% free water.
A very high caustic formula includes:
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Table 2
Solid Components:
21.0% sodium tripolyphosphate hexahydrate
(18% water of hydration)
16.3% sodium tripolyphosphate powder
56.7% caustic bead
Liquid Components:
3.0% 5000 molecular weight polyacrylic acid
(48% active in water)
1.5% ethylene oxide propylene oxide block
copolymer non-ionic surfactant
1.5% propylene glycol
A third formulation which includes trisodium NTA is
shown at Table 3.
Table 3
21.0% sodium tripolyphosphate hexahydrate
(18% water of hydration)
16.3% anhydrous sodium tripolyphosphate
10.0% Trisodium NTA
1.7% soda ash
45.0% caustic
3.0% 5000 mw acrylic acid (48% active)
1.5% EOPO block copolymer
1.5% propylene glycol
In order to formulate the detergent of the present
invention, the phosphates are combined together and mixed in a
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ribbon or paddle blender. The fillers and other non-hygroscopic
materials are not added at this time. Since a very low concentration
of the liquid components is being added to the formulation, the liquid
components should be combined prior to blending with the
sequestrants. Normally, the ethylene oxide propylene oxide block
copolymer will react with the polyacrylic acid to form a solid or gel.
However, mixing the propylene glycol with these two liquid
components prevents this reaction.
Thus, any liquid components such as polyacrylic acid
dissolved in water, the nonionic surfactant and the propylene glycol,
are thoroughly mixed together and then sprayed evenly on the
phosphate with mixing and allowed to soak into the phosphate. The
caustic is added, then the fillers and finally the dichloroisocyanurate.
If NTA or EDTA are added, these should generally be added with the
fillers, i.e., after the caustic.
It is very important that during all stages of mixing, and
even after formulation, the temperature be kept at less than 75 C,
preferably less than about 50 C and preferably less than 40 C. It
is theorized that hydration of the caustic generates heat which, if
excessive, will cause the STPP hexahydrate to liberate water, most
likely accompanied by the decomposition of the tripolyphosphate
anion, which will generate more heat, weakening the tablet.
However, by allowing the free water to be effectively completely
absorbed by the phosphate, the hydration reaction is sufficiently
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slowed and excessive heat is not generated and the hexahydrate does not
give up water. The phosphate mixture strongly bonds with the free water.
As such when the caustic is combined with the mixture of phosphate and
now bound water, hydration of the caustic is avoided. This prevention of
caustic being hydrated in turns keeps the temperature down. Hence
applicant's process provides a method of temperature control so as to
maintain mixing temperature below 75 C by controlling or preventing the
autocatalytic reaction.
If the free water is instead added to the fillers, or even to a
mixture of filler and sequestrant, then that water which hydrates the filler
is
relatively easily accessed by the caustic and the resulting hydration is so
rapid, generating so much heat, that the hydrated phosphate gives up water
causing the formed tablets to crumble or weaken.
The detergent blend is then pressed to form tablets using a
standard tableting machine. One such machine suitable for use in the
present invention is the Stokes brand tableter. Generally, to form tablets,
the powder is subjected to 4 to 10 tons pressure. Generally, the tablet will
have a thickness of about 12 to 13 mm and a diameter of about 20 mm. The
maximum diameter will be a function of the dispenser/feed water interface
area.
The tablets of the end product after being produced do not
weaken significantly over time. These can then be used in a typical ware
washer apparatus equipped with a water spray detergent dispenser.
There are alternate methods to achieve this same result. An
initial method of achieving this result is to omit fillers and form the
detergent with anhydrous and hydrated sequestrants, along with the
previously mentioned liquid components, as shown in Table 2. The
phosphates are combined with the liquid component so that any free
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water present is adsorbed onto the sequestrants. The caustic is then
added and the mixture tableted. Again, because the phosphates hold
the water relatively tightly, the temperature at all times is maintained
at less than 75 C and generally less than 50 C and therefore the
hexahydrate will not liberate water which can react with the caustic.
The formed tablets do not deteriorate rapidly after formation.
In a second alternate method of practicing the invention,
the fillers can be combined with the phosphates and the water
subsequently added. This can then be blended together with the
caustic, provided sufficient cooling is provided so that the
temperature is kept less than 50 C and preferably less than 40 C.
This temperature is maintained for sufficient time to allow the caustic
to react completely with any labile water prior to the tableting
operation. Of course, this requires added processing time.
By employing the preferred method, the formed tablets
have a drastically improved storage stability and shelf life. The end
products are stronger, which means they are less likely during
shipping to break apart and during use they will dissolve more slowly
and evenly, providing for an even distribution of the detergent
dissolved in water without creating an extreme exotherm. In all, this
system provides many unique advantages and although several
embodiments of the present invention have been disclosed, the
invention itself should be defined only by the appended claims
wherein we claim:
