PROCESS FOR TABLET PRODUCTION

PROCEDE POUR LA FABRICATION DE COMPRIMES

English Abstract

The use of complex phosphates in phosphate containing water
treatment chemical tablets results in tablets having superior hardness
and integrity for a given tableting pressure.

French Abstract

L'utilisation de phosphates complexes dans des comprimés à base de phosphates pour le traitement chimique des eaux permet d'obtenir une dureté et une uniformité supérieures pour une pression donnée de production de ces comprimés.

Claims

What is claimed is:
1. In a process for making water treatment chemical tablets wherein
compression is used to form the water treatment chemical tablets wherein
phosphate is used in formulating the tablets, the improvement which
comprises using an effective amount of a complex phosphate therein,
thereby reducing the amount of energy necessary to form the tablets
compared to orthophosphate.
2. The process of claim 1 wherein said complex phosphate is
selected from the group consisting of pyrophosphates, polyphosphates,
and metaphosphates.
3. The process of claim 1 wherein said complex phosphate is
selected from the group consisting of tetrapotassium pyrophosphate and
potassium tripolyphosphate.
4. A tableted water treatment formulations formed by compression of
a mixture comprising a powdered treatment chemical, a complex
phosphate and a liquid release agent.
5. The tableted water treatment formulation of claim 4 wherein said
complex phosphate is selected from the group consisting of
pyrophosphates, polyphosphates, and metaphosphates.
6. The tableted water treatment formulation of claim 4 wherein said
complex phosphate is selected from the group consisting of
tetrapotassium pyrophosphate and potassium tripolyphosphate.

7. The tableted water treatment formulation of claim 4 wherein said
liquid release agent is silicone.

Description

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M-1070
PROCESS FOR TABLET PRODUCTION
FIELD OF THE INVENTION
The present invention relates to tableting of water treatment
chemicals and more specifically to an improved process for producing
water treatment chemical tablets which contain phosphates.
BACKGROUND OF THE INVENTION
The implementation of a water treatment program which employs
dry, powdered or granular treatment chemicals is simplified if the
treatment chemicals are formed into tablets, bricks or blocks (hereinafter
referred to as tablets). The primary advantages of tablets is their ease of
handling and simplification of dosing or chemical feed operations. A
typical mechanical tablet preparation process includes material
preparation, granulation, compression, quality control and storage. The
most critical part of such operations is compression, which directly effects
the physical qualities (hardness, friability), chemical qualities
(preservation of active ingredients) and efficacy of the tablets. In addition
to the active ingredients, tablets may include fillers, binders, lubrication
agents, disintegration agents, etc.

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Tablets are compressed from blends of particulate solid material
with good flow and compressibility characteristics. In many cases, the
materials have been pregranulated to promote compressibility into
tablets. Normally, the tablets are made using a tableting press in which
s preblended components are compressed to form the tablets. This is
normally a dry process. Wet granulation may also be employed to form
tablets. A wet process entails preparation of a blend, wetting the blend
with a binder solution, milling the wet mass into moist granules
agglomerated with a binder and drying the granules, followed by further
milling and blending prior to compression.
In the wet or dry process, a certain amount of energy is extended
in order to form a tablet. Energy is used, not only to compress the
ingredients into a tablet, but also to eject or expel the tablet from the
press once the tablet is formed. Although the amount of energy needed
to both form a tablet and eject a formed tablet from the press is small on a
per tablet basis, the energy is substantial given the large number of
tablets that are manufactured over a period of time. A reduction in the
amount of energy needed for production of an acceptable tablet
translates into a cost savings.
In the water treatment area where corrosion and/or scale control
chemicals are added to aqueous systems, tableting of dry, powdered, or
granular materials eases handling and feeding operations. When
tableting water treatment chemicals containing orthophosphates such as
mono, di or trisodium phosphate and mono, di or tripotassium phosphate,
the resulting tablets typically have poor hardness and experience a high
rate of breakage and dusting.

CA 02203284 1997-04-21
SUMMARY OF THE INVENTION
It was discovered that in tableting phosphate containing water
treatment chemicals, substitution of complex phosphates for
orthophosphates greatly improved the tablets' properties. In addition to
improving the properties of the tablets, the use of complex phosphates
was found to reduce the energy needed to form a tablet of a given
hardness.
10 DESCRIPTION OF THE PREFERRED EMBODIMENT
In accordance with the present invention, a formulation and
method has been discovered to make phosphate containing water
treatment tablets with improved properties. It was discovered that the
use of complex phosphates as opposed to orthophosphates in water
treatment tablets resulted in harder tablets with improved integrity for a
given tableting pressure. To produce tablets of a given hardness, the
use of complex phosphates was found to require a lower tableting
pressure than orthophosphates.
As used herein, complex phosphates refers to phosphates such as
pyrophosphates, polyphosphates and metaphospates. Preferred
complex phosphates within the scope of the present invention include but
are not limited to tetra potassium pyrophosphate and potassium
tripolyphosphate.
Water treatment tablets which incorporate complex phosphates in
accordance with the present invention may also incorporate conventional
binders, disintegration components and/or lubricants. Suitable binders

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include, but are not limited to: gums, starch, modified starch, cellulose
and cellulose derivatives, copolymers or homopolymers of vinyl acetate
and vinyl pyrollidone. Suitable disintegration components includes, but
are not limited to: silicones, crosslinked carboxymethylcellulose, sodium
starch gycolate, starch, microcrystalline cellulose and alginic acid and its
salts. Suitable lubricants include, but are not limited to: stearic acid,
stearate salts, colloidal silica, talc, silicones and combinations thereof.
A water treatment tablet incorporating the improvement of the
o present invention is typically prepared by initially mixing one or more
water treatment chemicals, one or more complex phosphates, a binder,
and optionally a disintegrant and a lubricant. The resultant blend is fed
to a tableting press.
The following examples illustrate the present invention.
The efficacy of the present invention was evaluated by tableting
two commercial water treatment formulations conventionally sold in tablet
form. The water treatment formulations included nitrite/nitrate,
20 molybdate, phosphate and optionally borate and silicate along with
conventional defoamers, surfactants and release agents. The
formulations tested are available as CW-1332 and CW-1331 from
BetzDearborn Inc. The commercial formulations as well as powder
premixes of the commercial formulations without phosphate or release
25 agents (CW-1331 base and CW-1332 base) were tested. The effect of
various potassium phosphate salts on tableting strength was examined
using the following steps:

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1. Measure, premix water treatment formulation and add
34.4% (wt.) phosphate to be tested and 0.25% (wt.) silicon release agent
to the "base" premixes and mix. A control run which employed CW-1332
with a conventional othrophosphate was also tableted.
s
2. Tablet using a Stokes B2,20 station laboratory press
equipped with pressure sensors to measure compaction and ejection
forces. Compaction forces were varied from about 1500 kg to about 2800
kg and the tablet properties were observed and measured.
3. Measure hardness using a hardness tester after at least 24
hour"cure" time.
The following phosphates were tested: (a) dipotassium phosphate
(DKP); (b) tetrapotassium pyrophosphate (TKPP), and (c) potassium
tripolyphosphates (KTPP).
Table I summarizes the formulation tested.
Table I
Formulation Composition (wt. %)
A B C D E F
Component
CW 1332 100
CW 1332 base 63.35 65.35 65.35
CW 1331 base 82.9 82.9
DKP 34.40 18.85
TKPP 34.40 18.85
KTPP 34.40
Silicone 100 0.25 0.25 0.25 0.25 0.25 0.25

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Each formulation was run through three trials at increasing
compression forces. Tablet hardness after a 24-hour curing period was
measured. Table appearance was also rated. Table ll summarizes the
results.
Table ll
Compress Hardness
Composition Set Appearance Force(kg) (kp)
A 1 poor 1093 6.9
2 poor 2003 10.1
3 poor 3383 13.2
B 1 poor 1097 3.3
2 picking 1760 5.3
3 good 3192 7.4
C 1 fair 1127 5.2
2 good 1838 10.4
3 excellent 3220 15.6
D 1 fair 1086 5.4
2 good 1804 9.3
3 excellent 3078 13.2
E. 1 fair 1010 1.5
3 fair 1238 2.7
4 fair 1858 3.9
good 3507 6.4
F 1 excellent 2147 3.6
2 excellent 2764 3.7
3 excellent 3386 5.4
4 fair 1134 1.5
The data in Table ll shows that when a complex phosphate is used
to replace an orthophosphate in a water treatment chemical tablet, there
is a desirable increase in tablet hardness for a given compression force.
It was also found that when a liquid lubricant, silicone in this case, was

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employed, compressibility improved with an aging period. This is
believed to be a result of allowing time for distribution of the liquid
lubricant into the tablet matrix.
While the present invention has been described with respect to
particular embodiments thereof, it is apparent that numerous other forms
and modifications of the present invention will be obvious to those skilled
in the art. The appended claims and this invention generally should be
construed to cover all such obvious forms and modifications which are
o within the true spirit and scope of the present invention.