Note: Descriptions are shown in the official language in which they were submitted.
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OVERBASED PVC STABILIZER
The present invention relates to stabilizer
compositions for polyvinyl chloride resins and to
polyvinyl chloride resin compositions having improved
resistance to degradation caused by heat. Although
capable of a variety of uses, this invention finds
advantageous utility in providing improved long term
stability at moderate temperatures to motor vehicle
components shaped from polyvinyl chloride resin
compositions, especially where the polyvinyl chloride
resin compositions are used in combination with
urethane.
The problem of imparting to polyvinyl
chloride a sufficient heat processing stability at
temperatures at which the polymer becomes sufficiently
fluid or softened to permit shaping is of course of
long standing, and has been satisfactorily resolved by
addition to the polymer of various combinations of
known heat stabilizers. At processing temperatures,
the resin can degrade, liberating hydrogen chloride,
and discolor, become brittle, and stick to the
equipment. These problems are overcome by combining
with the polymer before heat processing or during heat
processing one or more of the well established and
successful conventional heat stabilizers, such as, for
example, organotin stabilizers and/or barium-cadmium
or barium-zinc salt stabilizers.
Although the well established and successful
3p conventional heat stabilizers provide effective
' stabilization to the polymer at elevated heat
A
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processing temperatures during standard processing,
they may not provide effective stabilization to the
polymer at lower more moderate temperatures after such
heat processing. For example, protection against
t
discoloration at moderate temperatures over long
periods is a particular problem with motor vehicle
components shaped from polyvinyl chloride resin
compositions despite such compositions having
contained conventional heat stabilizers during their
heat processing. Depending upon their location in the
vehicle, these components may be exposed to varied
amounts of light, and also different rather high
(above ambient? temperatures in use, and these
differences can degrade motor vehicle components at
differing rates. One result is the volatilization of
one or more components, or of decomposition products
therefrom, which condense as "fog" on interior
surfaces such as the windows and windshield.
Additionally, when polyvinyl chloride resin
compositions are associated with a polyurethane foam
backing, e.g. automobile instrument panels, glove
compartments, door handles, arm and head rests, the
amine from the urethane can contribute to
discoloration of the polyvinyl chloride resin
composition.
A number of stabilizing systems have been
proposed for imparting polyvinyl chloride resin
articles molded with a polyurethane foam backing with
resistance to deterioration from exposure to long term
3p moderate heat and from exposure to an amine from
urethane. For example, the art has recognized the use
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of perchlorate salts in polyvinyl chloride resin
stabilization and in particular in stabilizing polyvinyl
chloride that is used in contact with polyurethane foam or
plastic. This art, however, does not address the problem of
"fog" and does not suggest how to alleviate that problem.
For instance, European Patent Publication No. 0 252 559 A1,
published January 13, 1988, discloses polyvinyl chloride
resin stabilizer compositions comprising a 2,2, 6, 6-
tetramethyl piperidinyl compound and an ammonium or metal
perchlorate. This publication also discloses the use of
such stabilizer compositions for polyvinyl chloride resin
articles molded with polyurethane foam backing.
U.S. Patent No. 4,861,816 discloses polyvinyl
chloride compositions containing a stabilizer mixture of
certain barium/zinc carboxylic acid salts and a metal
perchlorate and/or perchlorate ion type hydrotalcite.
According to the '816 patent the perchlorate and perchlorate
ion type hydrotalcite compound give excellent amine
resistance, particularly to urethane attached polyvinyl
chloride sheets. U.S. Patent No. 5,225,108 also discloses
the use of metal perchlorates in PVC stabilizers, but does
not address how to remedy the formation of "fog".
Other patents disclose PVC stabilizers but do not
address the problems of "fog" formation nor of interaction
with polyurethane components. For instance, U.S. Patent No.
3,396,132 and U.S. Patent No. 5,102,933 disclose magnesium-
zinc benzoate-stearate stabilizers with polyhydric alcohols
and, in the case of U.S. Patent No. 5,102,933, with beta-
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diketones. U.S. Patent No. 4,950,704 also discloses
the use of betadiketones for PVC stabilizers. None of
these patents addresses the problem the tendency of
the stabilized PVC to form "fog". U.S. Patent No.
4,123,399 discloses combinations of beta diketones and
polyhydric alcohols but it, too, does not suggest how
to reduce the tendency of the stabilized PVC to form
.. fog..
There remains a need for PVC stabilizers
which reduce the tendency of the stabilized PVC
composition to form "fog" upon moderate heating, yet
which retain heat stability and satisfactory
processability in the stabilized PVC composition.
The present invention satisfies the
aforementioned objectives and affords as well the
other advantages described herein.
The present invention is directed to a
composition of matter useful as a thermal stabilizer
for polyvinyl chloride resin and which exhibits a
reduced tendency to volatilize when heated, comprising
(a) a mixture ofsalts of one or more
aromatic acids with two or more of calcium, magnesium,
zinc and barium, which is overbased with one or more
of said metals; in admixture with
2-r, (b) a carbonate orsilicate thermal
stabilizer for polyvinyl chloride.
In preferred embodiments of this aspect of
the invention, the aforesaid mixture also contains
salts of two or more of said metals with an alkanoic
3p or alkenoic acid containing at least about 18 carbon
atoms, such as stearate. Other preferred embodiments
A
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contain non-fogging amounts of polyol, as defined
herein, and/or a perchlorate stabilizer.
The present invention is further directed to
polyvinyl chloride formulations stabilized against
heat-mediated degradation and exhibiting a reduced
tendency to volatilize upon exposure to moderate heat,
comprising a polyvinyl chloride polymer and an
effective amount of any of the foregoing compositions
of matter. The present invention is particularly
useful in the fabrication of shaped motor vehicle
components, especially components comprising PVC and
polyurethane.
The reduced tendency of a polyvinyl chloride
composition to form "fog" in use is also expressed
herein as a reduced tendency of the composition to
volatilize, by which is meant that the composition
emits a reduced amount of, and preferably little or
no, compounds into the ambient atmosphere when the
composition is exposed to moderate heat, typically
temperatures of about 60 to 130C (140 to 270F).
Such compounds emitted by polyvinyl chloride
compositions under such conditions can comprise one or
more components of the polyvinyl chloride composition
itself, products of the degradation of one or more
components of the polyvinyl chloride composition,
compounds formed by the reaction of any such emitted
compounds or degradation products, or mixtures of any
of the foregoing.
One component of the stabilizer composition
of the present invention is an overbased mixture of
. metal salts of one or more aromatic acids. The metal
a
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salts are formed of two, or more, of the group
consisting of calcium, magnesium, zinc, and barium.
Preferably, barium is not present in the stabilizer
composition at all, because of its reputed implication
V
in health and environmental concerns. Also, it is
preferred that the composition contains zinc. The
term "aromatic acids" is used herein to mean benzoic
acid wherein the phenyl ring either is unsubstituted,
or is substituted with one, two or three alkyl groups
each of which can contain 1 to 6 carbon atoms and can
be straight or branched. Examples of such alkyl
substituents include methyl, and tert-butyl. A
preferred example of such a substituted benzoic acid
is any toluic acid, such as meta-toluic acid.
Mixtures of substituted and unsubstituted benzoic acid
salts can also be used.
The mixture of salts may also include one or
more salts of one or more fatty alkanoic and/or
alkenoic aliphatic acids. Preferably, salts of such
aliphatic acids are present, to impart increased
lubricity. The fatty aliphatic acids useful in this
component of the present invention have at least about
18 carbon atoms, up to about 30 carbon atoms. The
preferred fatty aliphatic acid is stearate. Other
useful fatty acids include lauric and behenic acids.
The molar ratio of aromatic carboxylate to fatty
aliphatic carboxylate, if present, can effectively lie
in the range of 0.5: 1 to about 2:1, preferably in the
range of 0.8 to 1.2:1.
3p As indicated, the mixture of salts of
aromatic acids, or salts of aromatic and fatty
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1 aliphatic acid(s), is overbased, by which is meant
that the total amount of all of calcium, magnesium,
zinc and barium present in said salt mixture exceeds
the total amount of aromatic carboxylate and fatty
aliphatic carboxylate present, on an equivalents
basis. The degree of overbasing, that is, the ratio
of-( Ca + Mg + Zn + Ba present) . (aromatic
carboxylates and fatty aliphatic carboxylates present)
(on an equivalents basis) is of course greater than
1:1, and can range up to about 1.8:1 and more
preferably up to about 1.3:1. The ratio of (magnesium
and calcium) to zinc present in this mixture can
typically fall in the range of 0.5:1 to about 2:1, and
preferably in the range of about 1.3:1 to about 1.5:1
on a mole basis.
The mixture of salts of aromatic
carboxylates, and the preferred mixture of salts of
aromatic plus alkanoic and/or alkenoic carboxylate,
can be formed by any of various procedures familiar to
those of ordinary skill in this art. One convenient
procedure a.s to mix together the desired aromatic
acid(s), the fatty aliphatic acid if desired, and the
oxides of the desired metals (such as zinc oxide and
magnesium oxide) in any order and then to heat'the
mixture until they are completely reacted.
Alternatively, one can separately form individual
salts, such as magnesium carboxylate (e. g. magnesium
stearate) and zinc benzoate, and/or magnesium benzoate
and zinc carboxylate (e. g. zinc stearate), and then
combine these compounds with additional amounts of one
or more metal compounds to provide the desired
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_g_
overbasing. Such compounds can be one or more of, for
instance, magnesium oxide or magnesium hydroxide.
Magnesium oxide is the preferred source of magnesium
for overbasing the mixture in this manner.
A preferred procedure for preparing the
mixture of salts is, first, to melt the aliphatic acid
component and then gradually stir in zinc oxide, in a
stoichiometric amount, under controlled heating
conditions wherein zinc carboxylate is formed and side
l0 reaction products are minimized. This step is carried
out free from magnesium, calcium and barium, and free
from aromatic acids. Next, the desired one or more
aromatic acids are added, followed by reactive
compounds of the one or more other metals, such as
magnesium oxide. At all times the temperatures are
controlled to maintain fluidity and to minimize
formation of side reaction products. Then the
reaction product is heated under reduced pressure, to
remove as volatiles byproducts which could contribute
to formation of "fog" from the PVC compounds.
The stabilizer compositions of the present
invention also include a carbonate or silicate
component which is a heat stabilizer for the polyvinyl
chloride. Examples of such compounds abound and are
well known in the field_ Preferred examples include
inorganic metal silicates such as mono-or condensed
silicates of sodium, calcium, magnesium, aluminum, and
zinc. Other preferred examples include dimetallic and
polymetallic carbonates and silicates, such as
3p magnesium aluminum carbonate, a particularly preferred
example of which is hydrotalcite (corresponding to the '
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_g_
1 formula Mgl _,~AlX ( OH ) 2 ( C03 ) Xia ~ mH20 wherein
x i s between
0 and 1). Yet other preferred examples include sodium
aluminum silicates, and calcium aluminum silicates,
especially zeolites.
. Another component of the stabilizer
compositions of the present invention, which is
optional but preferred, is a polyol component
comprising one or more polyol compounds containing 2
to 10 hydroxyl groups. The polyols useful in this
invention contain generally 2 to 20 carbon atoms, and
may contain 1 or more hetero atoms such as,
especially, one or more nitrogen atoms. Examples of
suitable polyol compounds include ethylene glycol,
propylene glycol, glycerol, sorbitol, mannitol,
xylitol, pentaerythritol, dipentaerythritol,
tripentaerythritol, and tris (2-hydroxyethyl)
isocyanurate, which latter compound is a preferred
polyol in the practice of this invention.
To achieve the desired combination of
properties using a stabilizer of the present
invention, the one or more polyols comprising the
aforementioned polyol component should be present in
such an amount that the polyols do not cause the
stabilizer to exhibit increased fogging. By this is
meant that the polyol should not volatilize at all, or
it should not volatilize to such an extent that it
negates the effect of the overbasing in reducing the
overall tendency of the stabilizer to cause fogging.
Subject to this consideration, the ratio by weight of
the overbased mixture of salts to the amount of the
' one or more polyols present is generally in the range
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1 of about 1:1 to about 2:1, and more preferably about
1.5:1 to about 2:1. The polyol tris(2-hydroxyethyl)
isocyanurate is particularly preferred because of its
low fogging behavior.
It has been determined that the presence of
the additional overbasing amount of magnesium, or
other metal, beyond the amount necessary to achieve
neutralization of the aromatic carboxylate and of any
fatty alkanoic and/or alkenoic carboxylate present,
provides a significant and unexpected improvement in
that the stabilizer composition exhibits a greatly
reduced tendency to cause "fogging" (that is, a
reduced tendency to volatilize when heated to
moderately elevated temperatures). In addition, the
polyol component contributes improved heat processing
stability without contributing to windshield fogging,
that is, without contributing to volatilization of the
stabilizer component. Hurthermore, these stabilizer
compositions contribute, to polyvinyl chloride resin _
compositions containing these compositions,
satisfactory stability against heat-mediated
degradation and satisfactory processing stability.
The overbased carboxylate composition does not detract
from the stability against heat-mediated degradation
and processing stability of the polyvinyl chloride
formulations containing this stabilizer.
The stabilizer compositions of the present
invention preferably include one or more optional but
preferred constituents. One such constituent is a
beta-diketone component comprising one or more beta-
diketones having the structural formula '
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1 R1-C (O) -CHz-C (O) -Rz wherein Rl is alkyl having about 10
to about 30 carbon atoms, and R2 is phenyl, phenyl
substituted with up to 3 lower (C1-C6) alkyl groups, or
alkyl containing 1 to 30 carbon atoms.
Examples of suitable beta-diketones include
benzoylacetone, lauroylbenzoylmethane,
myristoylbenzoylemethane, palmitoylbenzoylmethane,
stearoylbenzoylmethane, behenoylbenzoylmethane,
dilauroylmethane, dimyristoylmethane,
dipalmitoylmethane, distearoylmethane,
dibehenoylmethane, lauroylmyristoylmethane,
lauroylpalmitoylmethane, lauroylstearoylmethane,
lauroylbehenoylmethane, myristoylpalmitoylmethane, -
myristoylstearoylmethane, myristoylbehenoylmethane,
palmitoylstearoylmethane, palmitoylbehenoylmethane,
stearoylbehenoylmethane, lauroyl toluyl methane,
stearoyl toluyl methane, lauroyl xyloyl methane,
stearoyl xyloyl methane, 1-phenyltriacontane-1, 3-
dione, acetyltetralone, palmitoyltetralone,
stearoyltetralone, palmitoylcyclohexanone,
stearoylcyclohexanone and (paramethoxybenzoyl)-
stearoylmethane. These compounds are utilized in
amounts of between about 0.05 and 5o by weight
relative to the weight of the PVC and, preferably,
between about 0.1 and 1% by weight.
It is also advantageous to include in the
stabilizer compositions of the present invention, and
in polyvinyl chloride products containing the
stabilizer compositions, a perchlorate component
comprising one or more perchlorate compounds.
Examples include metal-perchlorate salts such as
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barium perchlorate, magnesium perchlorate, aluminum
perchlorate, sodium perchlorate, calcium perchlorate, and
the like. Other examples include the sodium perchlorate/
calcium silicate composition disclosed in U.S. Patent No.
5,225,108. Other examples include perchlorate-derivatized
hydrotalcite compounds such as those disclosed in U.S.
Patent No. 4,861,816. The latter compounds are said to
correspond to the formula Mgl_XAlX(OH)2~(C104)z~mH20 wherein m
represents a positive number and x is greater than 0 and is
less than or equal to 0.5.
The perchlorate helps to retard or prevent
discoloration and chemical interaction between polyvinyl
chloride and adjacent polyurethane materials, such as
encountered in shaped automobile parts. Parts can be
"adjacent" yet subject to such undesired interaction if they
are in physical contact with each other or if they are near
each other, not touching, such that an amine byproduct from
the polyurethane volatilizes and comes into contact with the
polyvinyl chloride formulation. The one or more perchlorate
compounds are preferably present in an amount which is about
10 to about 40 wt.% of the stabilizer composition, and more
preferably about 15 to about 35 wt.o of the stabilizer
composition.
The stabilizer compositions of the present
invention are preferably used to advantage in combination
with vinyl halide resins, preferably
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1 polyvinyl chloride resins. The term "polyvinyl
chloride" as used herein is inclusive of any polymer
formed at least in part of the recurring group
t (-CHC1-CXZ-)P and having a chlorine content in excess
of 40a. In this formula, each of the X groups can be
either hydrogen or chlorine, and p is the number of
units in each polymer chain. In polyvinyl chloride
- homopolymers, each of the X groups is hydrogen. Thus,
the terms, "PVC" and "polyvinyl chloride" include not
only polyvinyl chloride homopolymers but also
after - chlorinated polyvinyl chlorides, as well as
copolymers of vinyl chloride in a major proportion
with other copolymerizable monomers in moderate
proportion such as copolymers of vinyl chloride and
vinyl acetate, copolymers of vinyl chloride with
malefic or fumaric acids or esters, and copolymers of
vinyl chloride with styrene. The stabilizer
compositions are effective also with mixtures of
polyvinyl chloride in major proportion with a minor
proportion of other synthetic resins such as
chlorinated polyethylene or copolymers of
acrylonitrile, butylene and styrene.
Stabilizer compositions of the present
invention can be used with plasticized polyvinyl
chloride resin compositions of conventional
formulation. Conventional plasticizers well known to
those skilled in the art can be employed such as, for
example, dioctyl phthalate, octyl diphenylphosphate,
and epoxidized soybean oil. Particularly useful
plasticizers are the epoxidized esters having form 20
to 150 carbon atoms.
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1 The stabilizer compositions of the present
invention are used in small amounts effective to
impart resistance to heat-mediated deterioration of
the PVC or other polyvinyl chloride resin. That is,
J
"heat-mediated deterioration" includes deterioration
which is due to exposure to excessive heat, as well as
deterioration which is initiated or accelerated by
exposure to heat. Effective heat stability is
afforded generally by adding about 0.5 to about 5 phr
(parts by weight per hundred parts by weight of the
polyvinyl chloride) of the stabilizer_ Preferred
amounts are generally in the range of about 1 to about
4 phr. The stabilizer can be compounded into the
resin formulation in accordance with conventional
compounding techniques abundantly familiar to one of
ordinary skill in this art, wherein the stabilizer is
finely divided so as to aid its dispersibility into
the resin and is then dispersed therein by physical
mixing means.
The stabilized polyvinyl chloride resin
composition comprising these components can also
contain conventional additional additives such as
antioxidants, lubricants, flame retardants, fillers,
pigments, UV absorbers and the like, in relative
amounts effective to fulfill the desired functions of
each such ingredient. These ingredients can be added,
if desired, prior to, during, or subsequent to the
step in which the heat stabilizer composition of the
present invention is compounded into the polyvinyl
chloride composition.
v
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1 Among the preferred antioxidants are
phenolics, generally used in amounts up to about 0.5
wt.~ of the polyvinyl chloride resin composition, such
as 2,~-di-t-butyl-4-methylphenol, 2-t-butyl-4-
v
methoxyphenol, 3-t-butyl-4-methoxyphenol, n-
propylgallate, n-dodecylgallate, dilauryl
thiodipropionate, and the like.
Each of the starting materials used herein,
whether intended to be reactants or as unreacting
additives, should be provided in a high-purity form,
preferably 97~ or higher purity, and free of existing
volatilized contaminants.
The invention is further described in the
following examples, which are included for purposes of
illustration and not for limitation of the scope of
that which the applicants consider to be the
invention.
25
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1 EXAMPLE 1
A stabilizer composition was made by, first,
stirring together the following components in the
amounts indicated in Table 1-A:
Table 1-A
Component Amount (1b.) Amount(wt.~)
Stearic acid 1143_ 57.6
Benzoic acid 247 12.4
Water 20 1.0
Zinc oxide 165 8.3
Meta-toluic acid 276 13.9
Magnesium oxide 136 6.8
(periclase)
Periclase is the highly preferred form of
magnesium oxide for purposes of this invention.
This mixture was formed in a stirred tank
reactor held at 190-199°C under a vacuum of 150 mm Hg
while sparging with nitrogen, until reaction was
complete.
The reaction product was then stirred
together under moderate heating with hydrotalcite,
zeolite and polyol, in the amounts indicated in Table
1-B:
Table 1-B
Component Amount
wt.~
Reaction product 30.0
Hydrotalcite 25.0
("Alcamizer 2",
Kyowa Chemical
Industry Co.) '
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1 Zeolite A 2S.0
Tris (2-hydroxyethyl) 20.0
isocyanurate
The resulting stabilizer-composition was
tested for its ability to impart heat stabilization,
and for resistance to fogging, and was compared to
another non-overbased heat stabilizer.
15
25
c
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1 EXAMPLE 2
A test formulation was prepared containing
100 parts by weight of a PVC/ABS/nitrile rubber
compound, 1.8 parts by weight of a sodium perchlorate
stabilizer, and 2.2 parts by weight of either (A) a
conventional PVC heat stabilizer containing barium and
zinc, not overbased, or (B) the stabilizer composition
prepared in Example 1. Portions of the respective
compounds were milled at 350°F for 5 minutes, formed
into sheeting, and then tested.
Heat Stability: Samples were cut from each
sheet and heated in an oven at 350°F, and at 400°F.
To follow the progress of any deterioration of the
samples (as evidenced by, forinstance, discoloration,
embrittlement, or otherwise), samples were withdrawn
from the 350°F oven every 15 minutes and from the
400°F oven every 10 minutes.
The samples that were subjected to heating
at 350°F progressively darkened over time. The
samples containing the stabilizer according to the
present invention made in Example 1 did not darken as
much at any point in time as the samples containing
the non-overbased barium/zinc stabilizer. In the
samples that were heated at 400°F, those which did not
contain the stabilizer of Example 1 darkened more than
those which contained the stabilizer of Example 1, and
the greater degree of darkening was even more
noticeable at each point in time, even after only 10
minutes of heating and thereafter.
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1 Fogcting~ Reduction: Samples were cut from
each of the aforementioned sheets and were conditioned
and then tested by a standardized procedure for
r measuring fogging. The samples were conditioned by
holding them for one hour at a constant relative
humidity of 49.70 and a constant temperature of 70F.
Then, each sample was placed a.n a separate isothermal
container on which a clean, clear glass plate served
as a lid. The samples were held at 100C in the
isothermal container for 3 hours, during which time
the glass plate was maintained at 21C. Light
reflectivity of the glass plate before and after the
test was compared as a measure of the amount of
material which volatilized from the sample and
condensed on the plate. The reflectivity after the
test is expressed as.a "fog number" which is the
percentage of the reflectivity before the test, so
that a higher fog number correlates with less
volatilization from the sample and an accordingly
better performance by the stabilizer in lessening
volatilization.
The samples stabilized with the stabilizer
according to the present invention made in Example 1
had a fog number of 96, whereas the samples stabilized
with the non-overbased stabilizer had a fog number of
94. This constitutes a significant reduction in
volatilization, and is attributable to the presence of
the stabilizer of the present invention.
35
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1 EXAMPLE 3
Polymer formulations containing PVC were
prepared containing 88 parts by weight polymer, 12
parts by weight processing aid ("Chemigum B"), 1.8
parts by weight sodium perchlorate stabilizer, and 2.2
parts by weight of one of the following four heat
stabilizers:
A) A non-overbased barium-zinc stabilizer
B) An overbased mixture of magnesium and
zinc benzoate and stearate, containing no polyol.
C) The same as in B) but also containing
tris(2-hydroxyethyl) isocyanurate.
D) The same as in C) but in which meta-
toluate replaced half of the benzoate.
The formulations were milled, sheeted, and
cut into samples, placed in ovens held at 350°F and at
375°F, and periodically withdrawn, as set forth in
Example 2.
Samples made with stabilizers C) and D)
behaved similiarly to each other. Compared to samples
with stabilizer B) and with stabilizer A), both were
slightly superior at 350°F and both were noticably
superior after even brief heating at 375°F.
Samples of each formulation were also placed
in contact with polyurethane foam and held in an oven
at 250°F for 21 days, during which time samples were
periodically withdrawn from the oven and compared (the
degree of darkening correlated to the degree of
unwanted interaction between PVC and polyurethane).
As in the heat stability tests, formulations made with
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1 stabilizer C) and D) were similar to each other, and
were both slightly superior to formulations with
stabilizer B), which was similar to formulations with
stabilizer A).
Samples of each formulation were tested for
fogging using the test procedure described in Example
2. .The results are set forth in Table 3-A.
TABLE 3-A
'~ Stabilizer in the Formulation Foci No.
A 91
B 93
C 96
D 93
These data indicate that stabilizers in
accordance with the present invention imparted a
significant reduction in the tendency of the
formulation to emit "fog".
25
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