Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
This invention relates to uniquely alloyed mixed metal
soaps of calcium and zinc having outstanding lubricant qualities,
partic:ularly for polymeric resins and plastics, and which melt
sharply at surprisingly low temperatures.
Several metallic soaps of substantially saturated fatty
acids such as stearic acid, notably calcium strearate and zinc
stearate, have achieved commerical status as lubricants and/or
anti-tack agents (abherents) in the plastics and metal working
fields. However, to date mixed metal soaps have not received
any special acclaim for such functions or exhibited any unexpected
advantages therewith. Instead, the use of combined metal lubri-
cants has evidently provided only expected levels of performance
pretty much in direct proportion to the amounts of the individual
components and their relative contributions when used separately.
It i8 a major objective of this invention to provide
pulverulent metallic soaps, e.g. stearates, with superior lubri-
cant and abherent properties. A related object is to provide
mixed metal soaps of exceptional uniformity, homogeneity and
suitability for lubricant type uses.
A more specific goal of this invention is to provide
mixed metal soaps of calcium and zinc in such intimate associa-
tion that they are completely homogeneous even in their finest
particulate state of subdivision. Another specific object is
to provide such soaps which are easy to handle, free flowing
powders at normal temperatures and yet melt quickly and uniformly
under heat processing operations, such as the milling and thermo-
forming of polymeric resins and similar plastic substances. Still
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other objectives and advantages will be obvious from the detailed
descriptiOn of our invention which follows.
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SUMMARY OF THE INVENTION
~ In accordance with the present invention such highly
desirable lubricant soaps can be obtained by intensively mixing
together a liquid mass containing fatty acid anionic groups and
a metal bearing material the metal content of which consists
essentially of zinc and calcium in an atomic ratio of zinc/cal- : .
cium of between 2/3 and 3/1, the consistency and uniformity of
said metal bearing material being such that it is readily dispersed
by said intensive mixing at a substantially constant Zn/Ca ratio
throughout said liquid mass and maintaining the temperature of
the resultant mixture at a level sufficient to effect simultaneous
reaction of both zinc and calcium with said fatty acid groups
but not substantially above 100C, thereby effecting simultaneous
formation of zinc and calcium soaps which coprecipitate from
the reaction mixture in intimate association as fine solid
particulates of substantially uniform metallic ratio.
The first reactant, namely the liquid mass containing
fatty acid anionic groups can be either of two general types as
follows:
1) Molten fatty acids per se or fatty acids liquified
`~ ~ with the aid of hot, chemically inert miscible di-
: luents or solvents such as paraffinic oils like
kerosene; and
2) Aqueous solutions of water soluble soaps, usually
of alkali metals like sodium and pot~ssium, but
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including ammonium soaps or certain organic amine
soaps, e.g. those formed by triethanol amine.
DETAILED DESCRIPTION OF INVENTION
Said second type of liquid mass, i.e. an aqueous
solution of water soluble soap, is preferred because of the
handling convenience of same as well as the simplicity of pro-
viding a suitably homogeneous, easily dispersible metal bearing
coreactant. Thus, aqueous solutions of water soluble salts of
calcium and zinc can be readily prepared of almost any desirable
metals content and with very uniform and precise control of the
atomic ratio of zinc/calcium therein. On the other hand, when
the fatty acid reactant is supplied as the first type of liquid
mass, i.e. in the free acid form, the coreactant metal bearing
material will generally be derived from either the free metals
or their oxides or hydroxides, Special attention is then required
to provide such materials in a sufficiently fine state of sub-
division to render same readily dispersible in said liquid mass
while simultaneously insuring a correct, uniform ratio of calcium
and zinc throughout said subdivided material.
We have found that the reaction between the free fatty
acid type medium and the appropriate metal bearing coreactant
materials therefor can best be carried out at temperatures
between about 80 and llo& and preferably at temperatures between about 90
and 105&. H~wever, when the reaction is betw~en aqueous soap solution
and an aqueous solution of metal salts, soE~at lower reaction tempera-
tures are generally in order with the range of prim~ry interest being from
about 50C to about loo& and most preferably from about 60 to 90C.
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The coformed calcium and zinc soaps of this invention
having zinc/calcium atomic ratios of between 2/3 and 3/1 are ex-
ceptionally effective as lubricating and processing aids for
plastics or metal working, molding and like operations. This
perforrnance appears to be attributable to the intimate associa-
tion of zinc and calcium soaps therein, somewhat analogous to
the amalgamation of metals in alloys, as shown by the sharp
and surprisinglylow melting points possessed by the present
soaps. Thus, although the melting point of calcium stearate
is about 155C, the melting points of coformed zinc-calcium
stearates prepared in accordance with this invention at zinc/
calcium atomic ratios of between 2/3 and 3/1 are actually signi-
ficantly below even the 122C melting point of zinc stearate
its~elf. The eutectic among these mixed zinc-calcium stearates
appears to occur at a Zn/Ca atomic ratio of about 3/2, exhibiting
a melting point of only 180C as well as peak abherent properties.
In fact, with soap forming fatty acids of greatest interest,
i.e. those formed from substantially saturated fatty acids
containing from about 12 to 24 carbon atoms, the optimum propor-
tions of Zn/Ca in the coformed soaps of this invention appearsto lie between atomic ratios of about 1/1 and about 2/1.
Futher details of our invention are illustrated by
the specific examples and embodiments which follow.
EXAMPLE 1
Into a jacketed ~tainless steel reactor equipped with
a variable speed stirrer, eight liters of a dilute aqueous
solution of sodium stearate (0.125 molar) is charged and heated
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to about 80C while stirring slowly. The stirrer speed is then
increased and 325 milliliters of a uniform aqueous solutLon
containing 74 grams CaC12 and 127g ZnC12 per liter is added to
the so~ium stearate solution while mixing rapidly and maintaining
the ternperature of the mixture at about 80C during addition of
said solution of metal chlorides and for an additional 30
minutes thereafter. The resulting fine white powdery precipi-
tate is collected in a filter, washed several times with warm
water and dried to constant weight in shallow trays in a forced
air oven operated at a temperature of 75 to 85C. About 300
grams of fluffy white product are obtained having a uniform sharp
melting point of 108C + 1 and possessing the following
analytical properties:
Moisture Content 0.5~ by wt.
Total ash content 11.8% " "
Zinc content 6.5% " "
Calcium content 2.7% " "
Atomic Ratio (Zn/Ca) 1.48
EXAMPLES 2-7
A series of runs was made using the equipment described
in Example 1 and substantially the same reaction conditions ex-
cept that the proportions of CaC12 and ZnC12 in the uniform
aqueous solution added to the sodium stearate solution was varied
from run to run. In each run a fine, fluffy, white powdered
soap was obtained, the melting points of which varied from run
to run as shown in the following table:
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ZnC12 CaCl2 Zn/Ca
Example Conc Conc Atomic Melting Pt.
No. g./l g./l Ratio of Product
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2 66 124 0.43 120C
S 3 87 107 0.67 115C
4 109 89 1.0 113C
153 53 2.3 113C
6 164 44 3.0 116C
7 175 36 4.0 119C
It will be seen from the above results that simultaneously
formed and coprecipitated zinc-calcium stearates in which the
Zn/Ca ratio is between about 2/3 and 3/1 have surprisingly low
melting points, i.e. significantly lower than the melting point
of pure zinc stearate even though the melting point of pure
calcium stearate is far higher.
Obviously, many substitutions and variations are
possible in the above examples within the general guidelines and
operating limits already specified for the present invention.
For example, potassium stearate or any other sufficiently soluble
stearate can be used as the fatty acid group source and other
water soluble salts of zinc and calcium, such as the nitrates,
can be used in forming the uniform aqueous coreactant solution
with substantially the same results provided that the zinc and
calcium are simultaneously reacted to form particulate bimetallic
stearates having uniform atomic metal ratios within the ranges
specified.
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EXAMPLE 8
The coprecipitated bimetallic stearate produced in
Example 1 was teasted as an internal lubricant and anti-stick
additive in heat curable polyester resin in direct comparison
with pure zinc stearate and pure calcium stearate. The testing
was carried out with thermosetting syrups prepared from an
unsaturated polyester resin sold under the Trade Name of "Hatco
Polyester Resin GR 13037" using the following basic formulation
recipe in parts by weight:
Resin syrup - 100 pts.
Para-t-butyl perbenzoate - 0.6 pts.
Metal stearate powder - "X" pts.
The concentration t"X") of each of the metal stearate
additives in the above recipe Was varied from 1 part to 3 parts
by welght and casts of the well-mixed syrups were cured on shiny
aluminum foils for 5 minutes at 163C. The cured films con-
taining the coprecipitated zinc-calcium stearate of Example 1
at concentrations of 2 parts and above released readily from
the foil whereas about 3 parts by weight of the pure metal
stearates was required for successful parting of the cured
sample from the metal support. Furthermore, the parted surfaces
of the resin films containing the coprecipitated stearates were
noticeably smoother and glossier than those containing the
pure metal stearate additives.
Because of the intimate state of association of the
calcium and zinc species in the coformed bimetallic soaps of
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this invention and the resulting ease of melting and fusion
thereof, these products should prove compatible with a wide
variety of resins and serve as versatile processing aids and
viscosity control agents as well as abherent additives in many
environments.
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