Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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077108-M
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ENCAPSULATED PHOSPHITES
Description
This invention relates to polymer additives and, in
particular, to certain organic phosphites which are effective to
impart stability at elevated temperatures to such polymers as
polyolefins, vinyl chloride polymers, ABS and the like.
The normal processing operations to which thermoplastic
polymers are subjected invariably invo ~ s high temperatures and
these promote the deterioration of the polymers. The formulation
of a polymer composition, i.e., one which contains the various
stabilizing additives ordinarily required, usually is accomplished
on a heated two-roll mill, or in a heated Banbury mixer, or
both, and the temperatures at which such mixing steps are carried
out are quite high, well above the temperature at which the
polymer becomes fluid. At these temperatures the polymer will
develop color, become brittle, etc., and such evidence of
deterioration cannot be tolerated in the final product.
There are a number of heat stabilizing additives
available which are effective to protect thermoplastic polymers
from such deterioration. Among these are the organic phosphites.
The dialkyl pentaerythritol diphosphites are especially effective
for this purpose and are wideiy used. They are prepared by -
the reaction of two mols of an alcohol with diphenyl (or
dichloro) pentaerythritol diphosphite. The reaction is
illustrated by the equation:
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077108~ 2 -
OCH2 /CH2
2ROH -~ C6H50P > C ~ POC6H5 --
OCH2 CH20
~OC~ ~CH20~
ROP~ ~ C ~ POR
OCH2 CH20
The product shown above is the spiro isomer, and where diphenyl
pentaerythritol diphosphite is the reactant, as above, this
spiro isomer comprises about half of the combined total of
spiro and caged isomers. The caged isomer has -the structure:
~,OCH
P--OCH2--C--CH20P(OR)2
OCH2
When dichloro pentaerythritol diphosphite is substituted for
the diphenyl compound as the reactant, however, the product which
results is relatively pure spiro isomer. Inasmuch as the spiro
isomer is itself more stable to hydrolysis~ it is a preferred
form.
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Phosphite esters generally, however, are prone to
hydrolysis, and their hydrolysis is accompanied by a corres-
ponding loss of heat stabilizing effectiveness with respect to
the polymer compositions in which they are used for that
purpose. ~oreoever, such hydrolysis ~so frequently is accompanied
by a tendency to blocking, i.e., a tendency for the ordinarily
granular phosphite material to congeal into a single solid block.
Nany attempts have been made to solve this problem.
Additives such as triisopropanolamine have been found to impart
a significant hydrolytic stability to dialkyl pentaerythritol
diphosphites. The above-noted process for preparing relatively
pure spiro isomer diminishes the problem. The phosphite can
be stored in isture-proof containers such as polyethylene
bags until just before use. All of these have been very
helpful, but they have not eliminated the problem, nor the
desirability of a solution to the problem.
The lnvention here is an ecapsulated organic phosphite
composition stable to hydrolysis under ordinary conditions of
storage comprising a dialkyl pentaerythritol diphosphite wherein
the alkyl groups each contain 10-20 carbon atoms, coated with
a petroleum or ester wax. The dialkyl pentaerythritol
diphosphite preferably is one wherein the alkyl groups each are
stearyl groups, and an especially preferred embodiment is the
spiro isomer of distearyl pentaerythritol diphosphite. This
preference is based, of course, on the inherent, excellent
hydrolytic stability of this isomer. Another preferred embodiment
is a mixture of approximately equal proportions of spiro and
caged isomers, a preference based on its ready availability
and generally acceptable hydrolytic stability. It is conveniently
prepared, as noted above, by the reaction of stearyl alcohol
and diphenyl pentaerythritol diphosphite.
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The petroleum and ester waxes contemplated within the
scope of the invention include paraffin waxes, beeswax, shellac
wax, woolwax, ~ermaceti, carnauba wax, palm wax, candelilla
wax, flax wax, sugarcane wax, Japan wax, bayberry wax,
myrtle wax, hydrogenated jojoba oil, ,esterified montanic acid,
peat wax, montan wax, ozocerite and cetyl stearate. Suitable
waxes are characterized by melting points within the range of
from about 35C to about 100C. A preferred wax is a glycerol
ester of montanic acid. It has a melting point slightly
above 70C.
A process by which these encapsulated dialkyl p~nta-
erythritol diphosphites may be prepared comprises preparing a
homogeneous liquid mixture of a wax in a solvent in which the
diphosphite is relatively insoluble, preparing a second mixture
of said liquid mixture and the diphosphite, agitating this
second mixture, and removing the solvent from the second mixture
by evaporation. The terminology "homogeneous liquid mixture"
encompasses both solutions of a wax in a solvent as well as
mixtures which are not true solutions, but which nevertheless
are homogeneous, e.g., fluid colloidal systems (sols) and the
like.
The above homogeneous liquid mixture of wax and solvent
generally will contain from about 2% to about 30% by weight of
wax, based on the weight of the mixture. More than this usually
is difficult to work with because of the requirement for
homogeneity and less involves the use of an unduly large
amount of solvent. Sometimes it is desirable to dissolve the
wax at slightly elevated temperatures to facilitate homogenization
and then to lower the temperature for the coating step.
The solvent must, as indicated, be one which will :,
permit the development of a homogeneous mixture with the wax,
but will not dissolve the dialkyl pentaerythritol diphosphite.
Suitable solvents include hexane, heptane, octane, acetone,
methanol and the like. Preferably, the solvent is relatively
low boiling, i.e., below 100C, so as to facilitate its convenient
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077108-M - 5 -
removal from the encapsulated phosphite.
The ratio of wax to phosphite should be at least about
1:100, i.e., at least about 1 part of wax to 100 parts (1%)
of phosphite. The use of less than this amount of wax risks the
possibility that the phosphite will be incompletely encapsulated.
More than this can be used virtually without limit, since the
excess wax will serve as a desired lubricant in the polymer
composition in which the encapsulated phosphite is used.
An illustrative encapsulation procedure is shown in the
following example.
Example
A mixture of 12.5 grams of wax (a triglyceride of
montanic acid) and 50 ml. (34.0 grams) of heptane is warmed
slowly, with stirring, to 70C, by which time it has become
clear, then allowed to cool, with continued stirring until it is
slightly turbid, whereupon it is poured onto 25.0 grams of
distearyl pentaerythritol diphosphite (an approximately 50-50
mixture of spiro and caged isomers). The resulting mixture is
agitated until the solid diphosphite is thoroughly wetted and
then evaporated to dryness at a temperature below 40 C and
at reduced pressure. The residue is the desired encapsulated
product.
The effectiveness of the encapsulated phosphites
herein is shown by the data in Table I. That data is obtained
from a ~ynamic Mill Stability Test wherein the test sample ls
processed on a two-roll mill (150 mm. circumference x 400 mm.
wide; 21/21 rpm) at 200C. The time until development of
charring is noted. Each test sample contains the following
ingredients:
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077108-M - 6 -
Ingredients Parts
Polyvinyl chloride 100
Methyl methacrylatel 10
butadiene/styrene graft
copolymer
Poly(alkyl methacrylate) 0.5
Calcium stearate 0.05
Zinc octoate (12%) 0.15
Epoxidized soya oil 3.0
Glycerol triester of 1.0
montanic acid
In addition: test sample A contains 0.4 part of fresh disteàryl
pentaerythritol diphosphite; test sample B contains 0.54 part*
of the encapsulated distearyl phosphorodithioate prepared as in
15 the above Example and which has aged for 28 days in air (30-50%
relative humidi~y) at room temperature; and test sample C
contains 0.4 part of distearyl pentaerythritol diphosphite
which has aged for 28 days in air (30-50% relative humidity)
at room temperature. The term "fresh distearyl pentaerythritol
diphosphite" refers to such phosphite which has been stored
in a moisture-proof container.
TABLE I
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Polymer Composition Results
A Clear, water-white for 6 minutes,
slightly yellow at 10 minutes, chars
at 10.5 minutes.
B Clear, water-white for 6 minutes,
very slightly yellow at 10.5 minutes,
chars at 11.5 minutes.
C Slightly yellow at 3.0 minutes, medium
yellow at 6 minutes, dark yellow at
11.5 minutes.
D Slightly yellow at 6 minutes, chars
at 6.5 minutes. -:
* containing 0.4 part of distearyl pentaerythritol diphosphite.
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It will be seen that the encapsulated phosphite B
performs about as well as a heat stabilizer as does the fresh
phosphite A. The aged (not encapsulated) phosphite C performs
unsatisfactorily and is inferior both to A and B. The com-
position containing no phosphite clearly is the least stable.
Additional evidence of the improved stabilizing propertiesof the encap~ulated phosphites herein is shown in Table II where
A, B, C and D refer to the same polymer compositions as those in
Table I. The test results of Table IC are obtained from an
Oven Stability Test wherein test strips are heated in an oven
at 200C and removed gradually from the oven so that the various
portions of the sample are heated at this temperature for different
periods of time.
TABLE II
Polymer Compositions Results
A Clear, water-white for 15 minutes,
then chars suddenly.
B Clear, water-white for 10 minutes,
~ gradually changes to a medium
yellow throughout a 21-minute
- period, then chars suddenly.
C Gradually becomes dark yellow
throughout a 21-minute period,
then chars suddenly.
D Clear, water-white for 11 minutes,
then chars suddenly.
The results demonstrate, again, the efficacy as a heat stabilizer
of the encapsulated distearyl pentaerythritol diphosphite.
Test sample B, illustrative of the inventlon, clearly is
superior to test sample C which is illustrative of the prior state
of the art. The latter's darker color throughout the test period
renders it much less acceptable than the polymer composition re-
presented by test sample B.
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