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BACKGROUND OF THE INVENTION
This invention relates to liquid, highly alkaline cleaners having a high
solids content that are useful in such applications as in the production
of finished steel.
For years, many industries have used liquid alkaline cleaners, normally
based on sodium or potassium hydroxide, for various applications such as
laundry, textile, maintenance and metalworking processes. A specific
example of such an application is the alkaline cleaning of steel strip in
the steel industry. Operations such as continuous and batch annealing,
galvanizing and electrolytic plating require the complete removal of cold
rolling lubricant residuals as the first step in their processes. In
general, liquid cleaners have been preferred to powdered formulations for
their ease of handling and inherent safety. Previous to this invention,
the active content of these cleaners has been limited to approximately 50%
by weight, with the balance composed of water. More highly concentrated
versions of this class of cleaners are desirable as it reduces the volume
of concentrate required to obtain a given cleaner bath concentration. This
in turn reduces the end cost of the cleaner by minimizing the
manufacturing, shipping and handling cost components. This invention
permits the manufacture of liquid alkaline cleaners that contain as high
as 80% active ingredients; furthermore, due to the basic chemical and
physical properties upon which they are based, virtually unlimited
combinations of normally employed alkaline cleaner additives can be used
depending upon the intended application and performance specifications.
In addition to percent solids limitations, one of the major problems
previous to this invention was the relatively low concentrations of
inorganic alkaline silicates that could be incorporated into a high
alkalinity liquid formula without destabilizing or gelling the cleaner.
For example, using the conventional preparation procedure for a
concentrated alkaline liquid which involves dissolving the caustic
insoluble ingredients into a water based premix, adding the premix to the
caustic base of the cleaner (normally 50% NaOH), mixing the combination
for a specified time and set of conditions, and then sometimes
homogenizing the final product by various mechanical means, the maximum
amount of silicate that may be included has been approximately 5% on a
SiO.sub.2 basis.
Inorganic alkaline silicates as a general class are important ingredients
for alkaline cleaning for at least two major reasons. First, in all
alkaline cleaning applications, silicates are relatively inexpensive
additives, yet exhibit good detergency, soil-suspension and surface-active
properties. Where permitted, the inclusion of silicates in a formulation
can significantly improve the cost-performance of an alkaline cleaner.
Secondly, in metal cleaning, particularly for electrolytic cleaning,
highly silicated alkaline cleaners deposit a thin layer of silicate onto
the metal surface. This film is important in the cleaning of strip steel
prior to batch annealing, where the silicate layer helps prevent the
welding of adjacent coil laps during batch anneal -- a defect
appropriately called "Stickers" in the industry vernacular.
Prior to this invention any cleaning operation requiring or desiring the
use of a high silicate content, highly alkaline cleaner was forced to use
a powdered form of cleaner. This invention provides a stable, highly
silicated, high solids liquid alkaline cleaner composition and a method
for manufacturing the composition. Using the method of this invention, a
liquid alkaline cleaner can be produced with a SiO.sub.2 content of 0-30%.
By substituting phosphates, borates, carbonates or other cleaning
additives that are insoluble and inert in concentrated liquid caustic
solutions, almost any desired alkaline cleaning formulation can be
produced in a highly concentrated liquid form.
The conventional manufacturing methods for the production of concentrated
liquid alkaline cleaners involve the dissolution of the caustic insoluble
ingredients, such as the organic additives (surfactants, chelating agents,
foam controls, etc.) and the inorganic additives (silicates, phosphates,
borates, etc.), into water as a premix. This conventional method cannot be
used with high levels of the inorganic additives as these additives
precipitate and the entire product then thickens beyond an acceptable
point, sometimes resulting in complete solidification, when the premix is
added to the caustic base and blended. Furthermore, using the quantity of
water required to completely dissolve the additives in the premix severely
limits the maximum attrainable solids content of the formulation. As an
alternative conventional method of preparation, the addition of
commercially available additives to the caustic base prior to premix
addition or to a final blended product has also been largely unsuccessful,
with the resulting blends having been found to be too unstable or thick to
be practical.
SUMMARY OF THE INVENTION
The composition of the invention is defined as a free-flowing, liquid,
highly alkaline, stable cleaner composition having a high total solids
content within the range of about 40 weight percent to about 80 weight
percent, said total solids include from about 20 to about 50 weight
percent caustic based on total composition and a cleaning effective amount
of an inorganic particulate material dispersed and suspended in the
caustic, said inorganic material being both nonreactive and insoluble in
said caustic of the composition.
The inorganic material is preferably present in an amount within the range
of 5 to 30 weight percent of the composition and most preferably is sodium
metasilicate.
The caustic preferably includes both NaOH and KOH with each present up to
an amount sufficient to saturate the composition with NaOH and KOH.
The inorganic material is preferably suspended in the caustic and is made
stable by making the particulate material of a small enough size
preferably colloidal and/or by coating the small particles with a surface
active agent to enable the particles to act as colloidal particles and
remain in suspension, thereby creating a stable solution.
The caustic is preferably formed by mixing solid NaOH with an aqueous
solution of KOH or vice versa. Such a procedure allows high caustic levels
without lowering of the freezing point to unacceptable levels.
The method of manufacture of the invention is defined as the method for
preparing a free-flowing, liquid, highly alkaline, stable cleaner
composition which includes forming a solution of caustic of a
concentration sufficient to provide from about 20 to about 50 weight
percent caustic in the final composition and dispersing and suspending in
the composition a cleaning effective amount of an inorganic particulate
material, said inorganic material being both nonreactive and insoluble in
said caustic of the composition.
The method of use of the composition of the invention is defined as a
method of cleaning a metal surface which includes treating the surface for
a sufficient period of time with a free-flowing, liquid, highly alkaline,
stable cleaner composition having a high total solids content within the
range of about 40 weight percent to about 80 weight percent, said total
solids include from about 20 to about 50 weight percent caustic based on
total composition and a cleaning effective amount of an inorganic
particulate material dispersed and suspended in the caustic, said
inorganic material being both nonreactive and insoluble in said caustic of
the composition.
DETAILED DESCRIPTION OF THE INVENTION
This invention eliminates the previous instability, thickening and maximum
solids limitations of conventional liquid compositions. Because powdered
solid inorganic cleaner additives are only very slightly soluble or
reactive, if at all, at lower temperatures with highly concentrated
caustic solution (above 20%), these inorganic additives can be suspended
and dispersed in caustic solutions containing sodium and/or potassium
hydroxide using the teachings of this invention, without reacting to any
appreciable extent, which reaction would cause the mixture to
significantly thicken or solidify over time. Also, the smaller the size of
insoluble particles in a liquid medium, the easier they are to disperse
and suspend to form a stable colloidal-type suspension. Thus, if the
particle size of the solid additives is reduced below a certain point,
they can be dispersed and suspended in a highly caustic liquid medium with
the aid of surfactants, protective colloids and other methods. The certain
point for the particle size depends on many variables, including the
density of the solid additives chosen, but can be determined through
empirical formulation evaluation using standard sieves of known mesh to
quantify the particle size range distribution of the additives prior to
blending. Once a stable formula has been achieved, the data collected
using the sieves can be used as a guideline for precise production
specifications for a given formulation system.
To prepare high solids liquid alkaline cleaners of this invention, the
procedure described below is utilized.
The caustic liquid, either potassium or sodium hydroxide is charged into
the main blending vessel. Usually 50% sodium hydroxide or 45% potassium
hydroxide is used as a base because they are readily available
commercially and have acceptable freezing points. 70% sodium hydroxide or
higher than 50% concentrations could be used as well, but the freezing
point of liquid sodium hydroxide increases rapidly from 50-70%, which
would require heated storage of the end product. Heated storage for such
high solids formulae would be very difficult due to the accelerated
evaporation of water.
To either liquid caustic base, the solid form of the other caustic base can
be added directly into the main mixing vessel and dissolved. This can be
done to the saturation point for either solid form. For example, using 50%
NaOH as the base liquid, a 70%-50% NaOH/30% solid KOH mixture can be
prepared that is stable and acts similarly to 50% NaOH with respect to
freezing point. A similar blend can be prepared using 45% KOH as the base
fluid and adding solid NaOH. This method of combining the two types of
caustic aids to maximize the total solids content and alkalinity of the
cleaner. The amount added depends on the physicall properties desired in
the end product such as viscosity, alkalinity, specific gravity and pour
point.
Next, the other caustic soluble additives are added and dissolved. The
powdered, caustic insoluble, inorganic additives are added next with
stirring in their desired quantities to form a slurry. Depending upon the
additives used, the maximum amount added represents approximately 45% by
weight. The smaller the particle size of the additives, the better the
slurry stability and homogeneity. A ball or stone mill, or other means of
mechanically grinding these solid additives can be used to improve the
blend, but is not required. The invention requires that enough solid
additives are charged to reach minimum viscosity that will support the
final product as a stable suspension. Using a Brookfield Viscometer, this
viscosity range is on the order of 200-500 cps with a No. 4 spindle at 100
rpm and 100.degree. F.
Generally, any solid additive can be used as long as it will not react
appreciably with the caustic fluid base over the storage time of the
product. Examples of formula variations are included to demonstrate some
of the ranges of this invention.
After preparing the slurry, a premix is then prepared in a second vessel
which contains the organic and inorganic additives required to stabilize
the slurry suspension. The composition and amount of premix required to
stabilize the final product is highly variable, depending upon such
factors as the particle size range and desnity of the solid slurry
additives, the viscosity of the slurry and the desired viscosity of final
product, and the water content of the product and its specific gravity.
The function of the premix is to first coat the individual solid particles
of the slurry. Then, since the premix ingredients are insoluble in the
liquid caustic base, these organic and inorganic additives begin to
precipitate or congeal at different rates around the solid particles to
act as a protective colloid. The protective colloid is believed to
function by reducing the density of the individual solid particles by
coating them with the less dense congealed premix ingredients such as
inorganic surfactants or inorganic phosphates or carbonates; and/or
causing a thickening of the product by the formation of aggregate colonies
of solid particles covered with the premix contents which reduces settling
to insignificant levels while maintaining a free-flowing liquid product.
The composition of the premix is highly variable. Products have been
successfully prepared using exclusively inorganic or organic additives.
Normally, however, a combination of these two general classes is used to
provide the best cleaning performance characteristics for the product.
Once the premix has been added to the main vessel with stirring, it is
normally allowed to mix and react for a minimum of 20 minutes. As with the
preparation of the premix and the slurry, no heating is required for the
process. Although a certain amount of heat is generated by exotherms and
mixing during the procedure, the maximum temperature experienced for the
final blend has been 130.degree. F. and no problems have been noticed at
or below this temperature. Lower temperature is actually desirable to
reduce the potential for reaction between the liquid caustic base and the
other ingredients and to reduce the build up of scale in the mixing tank
from dehydration. Also, a higher temperature can slow the complete
precipitation and congealing of the premix, which potentially can result
in the complete gelling of the final product in the shipping container
when it finally cools.
The final blend can then be homogenized mechanically using standard colloid
mills or other units which shear and grind the liquid to increase its
stability. However, depending on the formulation of the product and the
particle size range of the solid additives, this step is not necessary for
the manufacture of a stable product. Homogenization, particularly where
the unit employed has the capability to grind the solid particles to
further reduce their size, as well as shear the liquid, can significantly
reduce the amount of premix required to obtain a stable liquid cleaner. In
fact, using a very efficient grinder, a stable product can be produced if
the particle size range of the solid additives is reduced to a point where
they act as colloidal particles themselves (see Example 4). The required
particle size of the solid matter to yield a stable liquid depends on the
viscosity, specific gravity and solids content of the liquid caustic base,
but the maximum size is on the order of five microns or less. Therefore,
under the proper conditions, this invention includes preparation of high
solids liquid alkaline cleaners without the use of a premix.
Once homogenzied, if desired, the product is complete. The closer the final
product is to ambient temperature when packaged, for reasons discussed
earlier, the better and more consistent its shelf life. This type of
product is a stable, viscous, free-flowing liquid with a high active
ingredient content. It can be employed in any application that requires a
highly alkaline cleaner. Therefore, it would find utiity in industries as
diverse as metalworking, laundry, textiles or maintenance.
The stability and other characteristics of these formuations can vary
considerably, as expected, depending upon their chemical composition and
physical attributes. The minimum stability required to allow a product to
be commercial is dependent upon the storage conditions and time period to
which the product would be subjected. In certain applications where
alkaline cleaner consumption is high, the material is appropriately
purchased in bulk quantities and stored in large tanks equipped with
agitators. Under these circumstances, a liquid cleaner formulation that
exhibits less than 10% top layer separation without the formation of heavy
bottom sedimentation after seven days of static storage is considered to
meet the minimum stability requirements for a commercially viable product.
Of course, during this period the product must not ungergo any significant
changes in the chemical or physical characteristics. With the exception of
the Example 4 non-premix, non-homogenized processed product, all of the
products of the other examples met or exceeded this definition of
stability.
In the Examples that follow, unless otherwise stated, the procedures
specified above were utilized in blending and preparing the product of
each Example.
EXAMPLES
EXAMPLE I
This Example uses only sodium hydroxide as the liquid caustic base,
anhydrous sodium metasilicate fines as the solid slurry additive, and
sodium hexametaphosphate and sodium carbonate (inorganics) in the premix.
The small amount of 50% NaOH is added to the premix to neutralize the
phosphate before adding the carbonate.
______________________________________
Ingredients: % by Weight
______________________________________
50% NaOH 53.68
Anhydrous Sodium Metasilicate Fines (Na.sub.2 SiO.sub.3)
40.2
Premix: Water 3.35
Sodium Hexametaphosphate 1.67
50% NaOH 0.1
Sodium Carbonate 1.0
TOTAL 100.0
Properties:
Appearance Viscous
Blueish-
White
Stable
Colloidal
Suspension
Pounds/Gallons (70.degree. F.)
14.9
% Solids 70
Pour Point (.degree.F.) approx.
55
Free Alkalinity, Phenolphthalein, % Na.sub.2 O
39.6
Total Alkalinity, Methyl Orange, % Na.sub.2 O
41.5
% P.sub.2 O.sub.5 1.1
% SiO.sub.2 18.7
Brookfield Viscosities (#4 Spindle at 100 rpm, cps)
Without homogenization (97.degree. F.)
516
Using 4" Colloid Mill* 0.001" Gap (110.degree. F.)
3,400
Using 4" Colloid Mill 0.002" Gap (98.degree. F.)
2,767
Using Supermill* - 85% Load ZrSO.sub.4 (113.degree. F.)
3,040
at 2,000 fpm, 8.0 psig.
______________________________________
*The Colloid Mill and Supermill are manufactured by Premier Mill
Corporation. The Colloid Mill was equipped with KCD Fine Grit tooling and
operated in all cases at 5,500 rpm.
EXAMPLE II
This Example uses a combination of potassium and sodium hydroxide as the
liquid caustic base, anhydrous sodium metasilicate fines as the solid
slurry additive, and a combination of inorganic/organic additives in the
premix.
______________________________________
Ingredients: % by Weight
______________________________________
45% KOH 41.53
Beaded, Solid NaOH 15.38
Anhydrous Sodium Metasilicate
33.31
Fines (Na.sub.2 SiO.sub.3)
Premix: Water 5.34
Sodium Hexametaphosphate
1.14
50% NaOH 0.62
Anionic Phosphate Surfactant
0.62
Anionic Organic Surfactant
1.06
Sodium Carbonate 0.62
Foam Control 220.sup.1 0.38
TOTAL 100.0
Properties:
Appearance Viscous Blueish-White
Stable Colloidal
Suspension
Pounds/Gallon (70.degree. F.)
14.83
% Solids 72
Pour Point (.degree.F.) Less than
10
Free Alkalinity, Phenolphthalein, % Na.sub.2 O
37.7
Total Alkalinity, Methyl Orange, % Na.sub.2 O
39.6
% P.sub.2 O.sub.5 0.8
% SiO.sub.2 15.5
Brookfield Viscosities (#4 Spindle at 100 rpm, cps)
Without homogenization (100.degree. F.)
480
Using 4" Colloid Mill, 0.001" Gap (110.degree. F.)
500
Using 4" Colloid Mill, 0.002" Gap (106.degree. F.)
540
Using 4" Colloid Mill, 0.005" Gap (101.degree. F.)
480
Supermill, 85% Load,
1.6-2.0 mm ZrSO.sub.4 (87.degree. F.)
1,620
at 2,000 fpm, 5.0 psig.
______________________________________
.sup.1 Product made by Pennwalt Corporation, Philadelphia, PA
EXAMPLE III
This Example uses a combination of sodium and potassium hydroxide for the
liquid caustic base, a lesser amount of anhydrous sodium metasilicate and
the addition of sodium carbonate as a filler for the solid slurry
additives, with a combination inorganic/organic premix as specified below.
______________________________________
Ingredients: % by Weight
______________________________________
45% KOH 44.53
Beaded Solid Caustic (NaOH)
16.95
Anhydrous Sodium Metasilicate
10.54
Fines (Na.sub.2 SiO.sub.3)
Light Density Sodium Carbonate
18.13
Premix: Water 5.38
Sodium Hexametaphosphate
1.15
50% NaOH 0.62
Anionic Phosphate Surfactant
0.62
Anionic Surfactant 1.08
Sodium Carbonate 0.62
Foam Control 220 0.38
TOTAL 100.0
Properties:
Appearance Viscous
White Stable
Colloidal
Suspension
Pounds/Gallon
% Solids 70
Pour Point (.degree. F.) Less than
10
Free Alkalinity, Phenolphthalein, % Na.sub.2 O
34.2
Total Alkalinity, Methyl Orange, % Na.sub.2 O
40.5
% P.sub.2 O.sub.5 0.8
% SiO.sub.2 4.9
Brookfield Viscosities (#4 Spindle at 100 rpm, cps)
Without homogenization (96.degree. F.)
240
Using 4" Colloid Mill 0.001" Gap (110.degree. F.)
460
Using 4" Colloid Mill 0.005" Gap (96.degree. F.)
420
Using Supermill, 85% Load,
1.6-2.0 mm ZrSO.sub.4 (78.degree. F.)
at 2,000 fpm at 4.0 psig;
800
at 3.5 psig 880
______________________________________
EXAMPLE IV
This Example contains only 50% sodium hydroxide for the liquid caustic base
and anhydrous sodium metasilicate as the solid slurry additive. No premix
was used to determine if physical means alone, using a homogenizer, could
form a stable product.
______________________________________
Ingredients: % by Weight
______________________________________
50% NaOH 57.l2
Anhydrous Sodium Metasilicate
42.88
Fines (Na.sub.2 SiO.sub.3)
TOTAL 100.0
Properties:
Appearance Blueish-White
Viscous Liquid
Pounds/Gallon
% Solids 71.5
Pour Point (.degree. F.) approx.
55
Free Alkalinity, Phenolphthalein, % Na.sub.2 O
41.9
Total Alkalinity, Methyl Orange, % Na.sub.2 O
43.5
% P.sub.2 O.sub.5 0
% SiO.sub.2 20
Brookfield Viscosities (#4 Spindle at 100 rpm, cps)
Without homogenization (75.degree. F.)
460
Using the 4" Colloid Mill,
420
0.001" Gap (76.degree. F.)
Using the 4" Colloid Mill,
321
0.002" Gap
Using Supermill, 85% Load,
1.6-2.0 mm ZrSO.sub.4 (108.degree. F.)
at 2,000 fpm at 7.0 psig;
3,560
at 8.0 psig (113.degree. F.)
2,761
______________________________________
This Example is the only Example that was not stable enought without
homogenization to be considered a viable commerical product. Without
homogenization, this product experienced gross separation within a matter
of hours. Furthermore, even when homogenized using the Colloid Mill at
either the 0.001" or 0.002" gap settings, the product still experienced
greater than 20% separation within 24 hours. However, when this product
was homogenized using the Supermill, a much more sever grinding mill, the
resulting product experienced less than 5% separation within 24 hours.
However, when this product was homogenized using the Supermill, a much
more severe grinding mill, the resulting product experienced less than 5%
separation over a period of one week. Although not completely stable, this
product could be commercially viable if the storage container was equipped
with a mixing device.
EXAMPLE V
This is an example of a phosphated-silicated formula using three types of
phosphates.
______________________________________
Ingredients: % by Weight
______________________________________
45% KOH 42.09
Beaded Solid NaOH 16.04
Crystalline Trisodium 8.15
Phosphate (Na.sub.3 PO.sub.4 *10H.sub.2 O)
Anhydrous Sodium Tripolyphosphate
5.21
Anhydrous Sodium Metasilicate Fines
20.71
Premix: Water 4.25
Sodium Hexametaphosphate
0.92
50% NaOH 0.49
Anionic Phosphate Surfactant
0.49
Anionic Surfactant 0.86
Sodium Carbonate 0.49
Foam Control 220 0.30
TOTAL 100.0
Properties:
Appearance White Viscous
Colloidal
Suspension
Pounds/Gallon 14.8
% Solids 67.8
Pour Point (.degree. F.)
Not Established
Free Alkalinity, Phenolphthalein, % Na.sub.2 O
33.2
Total Alkalini:y, Methyl Orange, % Na.sub.2 O
35.5
% P.sub.2 O.sub.5 5.1
% SiO.sub.2 9.6
Viscosity Not Established
______________________________________
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