Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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COMPOSITIONS AND PROCESS FOR METAL TREATMENT
This invention relates to compositions
and processes for metal treatment utilizing such
compositions. More particularly, novel titanium
containing compositions are provided which are
useful for the treatment of ferrous metals prior to
applying protective coatings such as zinc phosphate
and chrome.
The art of forming protective layers on
ferrous metals has been the subject of investigation
for many years. It has long been known to apply
coatings to metal, particularly to ferrous metals,
for the purpose of inhibiting corrosion. Paint
materials as protective coatings are common and it is
known that by improving the adhesion of paint to the
metal more durable protection is provided by the
paint.
In efforts to provide improved adhesion of
paint layers on ferrous metals it was discovered that
a thin layer of zinc phosphate directly on the metal
greatly increased the ability of paint to adhere as
well as inhibit corrosion.
The phosphating art greatly improved when
it was discovered that ferrous metal surfaces treated
or contacted with a solution containing a small
amount of titanium together with sodium phosphate
prior to zinc phosphating provided a zinc phosphate
layer on the metal which was more evenly distributed
and in smaller particle size. This discovery was made
by G. W. Jernstedt who was awarded several patents in
the area including U.S. Patents 2,310,239; 2,456,947;
2,462,196 and 2,490,062. It is believed that the
solution of sodium phosphate and titanium "activate"
the metal such that the metal is more readily coated
a~
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with zinc phosphate in the following step. The
titanium containing materials or activating composi-
tions became known as "Jernstedt salts".
Typically, Jernstedt salts are prepared by
first dissolving disodium phosphate in water and adding
titanium as a soluble salt. The aqueous solution is
heated within a limited temperature range of from about
60C. to about 85C. with mixing for about 10 hours.
The solution is then evaporated to dryness at elevated
temperatures and the dry material is used to prepare
aqueous solutions for metal pretreatment. It is known
that the temperature to which the initial titanium of
sodium phosphate solution is heated prior to evaporation
is critical. Such temperature can be varied within
only narrow limits as higher temperatures result in
degraded product and lower temperatures result in
inactive product.
Because of the sensitivity of Jernstedt salts
with respect to the temperature range employed in
their preparation, attempts have been made to eliminate
the need for any heat to form the dry solid activating
compositions. One other reason for attempting to
eliminate the heating step is to conserve energy.
One attempt in reducing the requirement for heat in
the preparation of Jernstedt salts is shown in U.S.
Patent 4,152,176 to Guhde. This patent describes a
method for preparing a Jernstedt salt, which includes
sodium tripolyphosphate as a cleaner for the metal,
by the steps of preparing a mixture of water, sodium
tripolyphosphate, disodium phosphate and a titanium-
containing compound. This aqueous mixture is heated
to a temperature of from 65C. to about 95C. and the
solution is then added to solid disodium phosphate
with mixing to obtain a solid titanium phosphate
composition. The solid composition is then employed
to prepare solutions for treating metal surfaces prior
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to aqueous phosphating in the typical manner. Although
the final mixture with disodium phosphate is considered
to provide a dry activating composition such composi-
tions contain about 15% water. Such mixtures are then
employed to prepare Jernstedt salt solutions in the
usual manner.
Further attempts to improve upon Jernstedt
salts is shown in U.S. Patent 4,539,051 to Hacias.
In the aforementioned patent the Jernstedt salt
contains tetrasodium pyrophosphate in addition to the
small amount of titanium and a sodium phosphate
compound. It is claimed that by including the pyro-
phosphate, comparatively smaller amounts of the dry --
particulate salt are required in aqueous metal treating
solution to activate the metal and thus provide
superior phosphate coating.
The aqueous treatment bath temperature at
which a metal surface is to be effectively treated has
been known to be in the range of from about ~9C. to
about 64C. for one step cleaning and conditioning or
activating. In an effort to reduce the required
temperature of the bath, multi-component baths have
been disclosed wherein the basic Jernstedt salt
solution is employed together with other ingredients
which perform adequate metal conditioning prior to
the phosphating process. One such disclosure is found
in U.S. Patent 4,497,667 to Vashi. According to this
patent the aqueous bath temperature is lowered to
about 38C. while obtaining adequate conditioning.
Surfactants, sequestrants, buffers such as alkali
metal carbonates, silicates and other ingredients
are employed to achieve the desired result.
In all of the known preparations of Jernstedt
salts it is the conventional wisdom to incorporate in
aqueous solution a titanium salt having some solubility
in water together and a sodium phosphate compound
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followed by heating these ingredients together at a
temperature within a narrow range. In most instances
the aqueous solution is evaporated to dryness requiring
close attention to avoid an inferior product.
SUMMARY OF 1~; INVENTION
The present invention provides novel compo-
sitions and methods for preparing Jernstedt salt
concentrates useful as activating agents in protective
metal coating processes. The novel compositions are
lQ prepared by the steps of
(a) preparing an aqueous solution comprising
a water soluble titanium compound and a
solubilizing amount of an alkali metal base,
(b) combining the solution with a particu-
late alkali metal phosphate salt compound
and
(c) heating the combination of (b) to
remove free water at a temperature in the
range of from about 60C. up to a temperature
which is below the deactivating temperature
of the titanium.
The dry mixture forms a Jernstedt salt
concentrate that is blended with additional alkali
metal phosphate salt by means of dry mixing when
desired to complete the formation of a typical
Jernstedt salt. Alternatively, the concentrate may
be added to the metal pretreating bath and additional
alkali metal phosphate salt also added directly to the
metal pretreating bath. The additional phosphate salt
combined with the concentrate prepared as described
above reduces the titanium concentration to the usual
range for a Jernstedt salt, i.e. from about .005% up
to about 10% by weight of the mixture.
There has been provided in accordance with
this invention a novel methcd of preparing a Jernstedt
salt having the advantages of economy and convenience.
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The titanium compound is prepared in solution in the
absence of any alkali metal phosphate salt. A concentrate
is formed by combining the titanium solution with only
a fraction of the alkali metal phosphate salt needed to
form a typical Jernstedt salt thus lowering the amount
of material brought to dryness at elevated temperature.
A further advantage of the composition and
process of this invention is the economy achieved by
shipping and storing a concentrate thereby allowing
for completion of the Jernstedt salt at or near the
point of need.
An optional ingredient, a halide ion
producing compound, has been found to be highly
advantageous in metal treating baths of this invention.
A small amount of such halide ion producing compound,
preferably sodium chloride, enhances the metal acti-
vating ~uality of the composition of this invention.
Suitable phosphates include the primary, secondary
and tertiary alkali metal salts of orthophosphoric
acid and mixtures thereof. The preferred salt is
disodium phosphate and, as will be shown below,
disodium phosphate, anhydrous.
DETAILED DESCRIPTION OF THE INVENTION
The Jernstedt salt concentrate of this
invention is prepared by dissolving in water an
appropriate amount of titanium salt. Any suitable
titanium salt can be employed which will dissolve
in water sufficiently to provide the desired amount
of titanium in solution. Any amount of titanium
compound found convenient can be employed to prepare
the initial aqueous solution. In general, the
titanium cation concentration in solution is from
about .5% to about 25% by weight as the titanium ion.
Liquid forms of titanium such as titanium
tetrachloride may be employed directly for addition
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to the alkali metal phosphate salt but such form
of titanium is highly inconvenient.
Typically, previously known titanium salts
employed to prepare Jernstedt salts can be employed
herein and include titanium oxalate, titanium halides,
and preferably titanium sulfate. Titanium halides
include the chloride and fluoride salt. In one
preferred embodiment of this invention a titanium
sulfate salt (TiSo4-H2so4-8H2o) is employed. Other
titanium halides include TiBr3-6H2O, TiBr4, TiF4,
TiF3, TiI2, TiI4.
In the process of this invention wherein
a Jernstedt salt concentrate is prepared there is --
desixably combined with the titanium compound in water
solution a trace amount of a halide ion producing
compound preferably a chloride ion producing compound.
It has been found that when incorporated into the
concentrates of this invention the activation achieved
for purposes of further treatment with zinc phosphate
is greatly enhanced. Any number of chloride ion
producing compounds can be employed in the composi-
tions and processes of this invention which do not
unfavorably react with the other components of the
Jernstedt salt concentrate or prevent ultimate
phosphate coating of the metal. The most commonly
available compound which provides the chloride ion is
the alkali metal chlorides and preferably sodium
chloride. Other chloride ion producing compounds
useful in preparing the Jernstedt salt concentrate
compositions of this invention are POCl3, PCl3,
PCl5, HCl, NaOCl, KOCl, HOCl, ZnCl2, CaCl2, MgCl2,
SnCl2, NaClO3, NaClO4, and the like.
The chloride ion concentration, as mentioned
above, is in trace amounts in the compositions of this
invention. Sufficient chloride ion is provided by
amounts as little as in the range of from about .001
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moles to .02 moles of the chloride ion producing
compound in the metal treating bath containing a
Jernstedt salt. This small amount is incorporated
together with the titanium compound in aqueous solution.
Therefore, the chloride ion producing compound is
desirably water soluble at least to some extent.
Water solubility is not critical since such a small
amount of material is required in solution. Expressed
as weight percent of the solution the chloride
producing compound is desirably present in an amount
of from about .5% to about 6% and preferably in the
range of from about .5% to about 2.5% although amounts
up to about 4% have been found to be advantageous. --
To reduce the amount of time required to
dissolve the titanium compound in aqueous solution, ithas been found desirable to add a small amount of an
alkali metal base, preferably sodium carbonate
to the aqueous mixture containing the titanium
compound. It has been found that with the addition of
very small amounts of alkali metal base such as the
oxide, hydroxide or preferably carbonate enables
the titanium compound to dissolve at a much faster
rate. The amount of alkali metal base is not critical
but a minimum amount to alter the solubility character-
istics of the titanium compound is in the range offrom about 1% to about 8% by weight of the aqueous
mixture. Preferably the alkali metal base concentra-
tion is from about 2% to 6% by weight of the solution.
Larger amounts of the alkali metal base may be
employed but the effect on solution rate is not
appreciable. Alkali metal bases such as sodium
potassium and lithium can be employed.
Typically, the titanium compound is brought
into solution in warm deionized water together with the
chloride producing compound and alkali metal carbonate.
Slight heating may be required to further aid the rate
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of solution of the titanium compound. Such heating is
not critical to the operability of the final Jernstedt
salt with respect to its ability to activate metal
surfaces and is in clear contrast to the requirement
of heating followed by evaporation to dryness required
formerly in the preparation of Jernstedt salts.
Typically, adequate rates of solution are obtained by
heating the aqueous mixture to a temperature in the
range of from about 40C. to 70C. and preferably in
the range of from about 45C. to about 55C.
The solution containing the essential
ingredients which are the titanium compound, the
optional chloride ion producing compound and alkali -
metal carbonate is then added preferably slowly to an
alkali metal phosphate salt, preferably disodium
phosphate dihydrate which is in the form of particulate
material. The solution is thoroughly mixed with the
salt to form a paste like or gelled composition.
After thorough mixing to achieve uniform distribution
of the titanium compound the mixture is dried slowly
at a temperature in the range of from about 60C. to
about 90C. and preferably in the range of from about
75C. to about 80C. Drying the mixture at elevated
temperatures is known to deactivate the titanium ions
for the purpose of pretreatment in the phosphating
process for metal surfaces. Such deactivating
temperatures are regarded to be in excess of about
95C. Drying will, of course, depend upon the
apparatus employed, the uniformity of the application
of heat and other mechanical factors. The dried
product may contain small amounts of water of hydration.
However, free water is substantially removed by the
heating step.
The titanium solution is usually combined
with the alkali metal phosphate salt in a ratio such
as to provide about one-fourth of the total amount
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of alkali metal phosphate salt normally employed to
prepare the Jernstedt salt. Lesser amounts of alkali
metal phosphate salt may be employed and the above-
mentioned amount is preferred because the resulting
paste or gel-like product is easily mixed to assure
uniformity of the resulting Jernstedt salt concentrate.
By employing only a fraction of the total amount of
phosphate salt it can be easily seen that the drying
step is more efficient because of the smaller amount
of material requiring drying. Further, the amount of
liguid required to dissolve the titanium compound
compared to the amount of sodium phosphate compound is
very small thereby providing much less liquid which --
requires removal to obtain the dry, particulate
Jernstedt salt concentrate of this invention.
Typically, the ratio of water carrying the dissolved
titanium compound into contact with the alkali metal
phosphate salt is in the range of from about 1:3 to
about 1:7, by weight. The phosphate salt is therefore
only moistened to a small degree and the drying
operation accordingly reduced.
In an alternative embodiment of this
invention the titanium solution (a) above can be mixed
with the total requirement of alkali metal phosphate
salt thereby making a directly useful Jernstedt salt
after drying as described in step (c) above. In this
instance the usual concentration of titanium ion well
known in the art is provided by combining sufficient
alkali metal phosphate salt, i.e., a concentration
usually in the range of from .1% to about 1% by weight.
The dried mixture containing the titanium
and chloride ion forming compound is broken up into
fine particulate material after the heating step to
assure uniformity and if necessary the dried material
is comminuted to the desired size. The dried material
can then be employed to prepare an effective Jernstedt
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salt by combining it with further alkali metal phosphate
salt. Typically, the Jernstedt salt concentrate of
this invention can be added to water and additional
amounts of the alkali metal phosphate salt added
thereto thus forming the typical Jernstedt salt in
situ. Alternatively, the additional alkali metal
phosphate salt can be dry mixed with the concentrate
prepared as described above to provide the typical
Jernstedt salt having the percentage compositions
normally employed in the metal treating processes
known in the prior art. Although the amounts of
ingredients are within the control of the user it is
typical to employ about one-fourth of the usually --
required alkali metal phosphate salt in preparing the
concentrate and supplying the remainder of the phosphate
salt either in a dry mix or in aqueous solution as
described above.
As mentioned above, the relative amounts of
ingredients used in the preparation of the concentrate
can be adjusted over a wide range but are chosen to
provide an easily measurable amount of ingredients in
preparing the concentrate and the final usable activat-
ing Jernstedt salt or solution employed in the metal
treating process.
As an example of a preferred embodiment
of the invention 15 grams of titanium sulfate
(TioSo4-H2So4-H2O) were dissolved in 20 ml of warm
deionized water at a temperature in the range of from
about 45C. to about 55C. To the deionized water
were previously added .99 grams of sodium carbonate
and .54 grams of sodium chloride. When a clear
solution was obtained (in about 35 minutes) the
solution was added slowly to 87.75 grams of dry
disodium phosphate dihydrate. During the addition of
the liquid to the solid disodium phosphate dihydrate
the mixture was agitated manually by means of a mortar
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and pestal. The mixture was then heated slowly at
a temperature in the range of from 45C. to about
55C. for 15 minutes while mixing continued. There was
produced a gel-like paste which was then dried in an
oven at a temperature in the range of between 70C.
and 80C. for about 2 hours to form a dry particulate
mixture. To form a Jernstedt salt .37 grams of the
above-described dry mixture and 1.43 grams of anhydrous
disodium phosphate were dissolved in 1.8 liters of
deionized water to provide a solution having a pH of
about 8.4. The solution, at room temperature or about
23C., was employed to activate a cleaned ferrous
metal surface by dipping the metal into the solution
for about 30 - 45 seconds. After removal of the metal
from the activating bath the metal was coated with
zinc phosphate in the typical known manner. Good
results were achieved in the zinc phosphate coating
operation.
In another preferred embodiment the Jernstedt
salt concentrate was prepared as described above with
the exception that only 60 grams of disodium phosphate
anhydrous was employed to prepare the gel-like paste
and in the preparation of the pretreatment activating
bath .5 grams of the concentrate was employed with 1.3
grams of anhydrous disodium phosphate in 1.8 liters of
deionized water to provide a solution having a pH
equal to ~.23. Excellent results were achieved by the
use of both concentrate in activating a ferrous metal
surface by dipping the metal into an activating bath
followed by the zinc phosphate treatment in accordance
with prior art procedures.
The titanium-containing phosphate compositions
prepared in accordance with the process of this inven-
tion are useful in cleaning and activating the surfaces
of ferrous, zinc cadmium or aluminum metals and
alloys thereof wherein said metals or alloys form
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the predominant constituent particularly for subsequent
reaction with phosphate coating solutions. In
preparation of aqueous solutions for activating metal
surfaces for subsequent treatment in a zinc phosphate
coating process the dried concentrate of this invention
is dispersed in water to produce an aqueous pretreat-
ment solution having a concentration o titanium ions
ranging from about .0001% up to about 1% by weight.
Because of the small amount of titanium ion in the
treating solution it may be convenient to premix the
concentrate of this invention with the total amount
of alkali metal phosphate salt in the dry state such
that the amount being measured into the treating bath
may be performed less tediously. However, with the
concentrates of this invention it can be seen that
much smaller amounts of the salts may be shipped and
stored by creating the completed Jernstedt salt at
the point of need rather than forming it at a location
remote from the point of need.
While this invention has been described
with reference to the novel Jernstedt salt concentrates
and their utility it is apparent that the Jernstedt
salt solution employed to treat metals may contain
other additives such as adjuvants, cleaning agents and
surfactants. If desired, dry particulate adjuvants,
cleaning agents or surfactants may be incorporated
into the Jernstedt salt concentrates of this invention
such that when added to the treating bath the only
other required ingredient for a complete treating bath
would be the alkali metal phosphate salt.
While it is apparent that the preferred
embodiments of the invention disclosed are well
calculated to fulfill the objectives of the present
invention, it will be appreciated that the invention
is capable of modification, variation and change
without departing from the scope or fair meaning of
the following claims.
