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Патент USA US3041321

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c
l@
3,041,311
"a,
Patented June 2?», 1962
2
group containing from 1 to 16 carbon atoms, an aryl
3,041,311
and substituted aryl group containing from 6 mild carbon
POLYPROPYLENE S'I‘A3ILIZED WITH A DITHIO
atoms, and a cycloalkyl or substituted cycloalkyl contain
PHOSPHATE METAL SALT
ing at least 5 carbon atoms in the cycloalkyl ring and
Bernard 9. Baum, Plain?eld, N.J., assignor to Union
having not more than 16 carbon atoms in all.
Carbide Corporation, a corporation of New York
Organic groups illustrative of this general group are
No Drawing. Filed Dec. 3, 1958, Ser. No. 777,863
7 Claims. (Ci. 260-4515)
This invention relates to polyole?n compositions hav
ing improved stability at elevated temperatures. More 10
particularly, it relates to improved polypropylene com
methyl, ethyl, isopropyl, tertiary butyl, hexyl, octyl,
hexadecyl, phenyl, tolyl, ethylphenyl, tertiary butyl
phenyl, hexylphenyl, naphthyl, ethylnaphthyl, cyclo
pentyl, cyclohexyl, tertiary butylcyclopentyl, isopropyl
cyclohexyl and the like.
I
positions which are capable of withstanding high tem
illustrative of the metal groups suitably employed are
peratures without undue molecular degradation.
Li, Na, K, Mg, Ca, Ba, Zn, Cd, Hg, Pb, and Sn.
One of the principal reasons for the continuing interest
The stabilizers described above may be prepared by
in polypropylene by those concerned with industrial syn 15 methods well known in the art. Conveniently the cor
thetic polymers is that its relatively high melting point,
responding dithiophosphoric acid may be prepared by
refluxing phosphorus pentasul?de and the primary a1»,
of the order of 170° C. to 180° 0., indicates a potential
use for this polymer in the fabrication of articles of com
merce which remain dimensionally unchanged at tem
cohol compound of the R group concerned, i.e., R-OH
or a mixture of R—OH and -R'—OH if R and R’ are
peratures appreciably higher than can be tolerated by 20 different radicals, in an inert solvent medium such as
articles formed from polyethylene.
benzene. The dithiophosphoric acid may then be con
verted to the desired salt by reaction with a basic salt of
the metal within the aforesaid suitable class. Such salts
-
Unlike polyethylene, however, which has a melting
point of from about 105° C. to 135° C., depending on the
method of polymerization employed, polypropylene is ex
include those of weak organic acids, such as, acetates
trcmely susceptible to thermal degradation ‘at high tem 25 which hydrolyze to form metal hydroxides. Metal hy
peratures and cannot in fact Withstand the ordinary hot
droxides per so may also be used.
'
compounding and processing operations without sustain
The polypropylene compositions containing one or
ing serious impairment of its physical properties. The
more of the‘ dithiophosphate salts described above sustain
term “high temperatures” as used herein is intended to
mean temperatures of the order of 500° F. (260° C.) and
above. Temperatures of this magnitude are necessary
to carry out many of the conventional forming processes
in general a greatly lessened degree of molecular weight
degradation when exposed to high temperatures than
otherwise is the case when polypropylene alone is so
thermally treated. Some of the dithiophosphate salt
additives virtually eliminate thermal degradation alto
e.g., injection molding, with‘ polypropylene because of the
high melting point of this polymer. At these tempera
gether.‘ These stabilizers on the other hand, do not sub
tures the molecular degradation is so severe as to reduce 35 stantially alter the strength or electrical properties of the
polymer.
the physical properties to unacceptable levels.
A well-known general approach in attempting to pre
Small quantities of these stabilizers have been found
vent undue thermal degradation in circumstances such as
to be adequate to effectively stabilize the polypropylene
described above is to admix with the given polymer a
at high temperatures. The preferred amount employed
material which, in a manner not completely understood, 40 is in the range of ‘about v0.01 to about 2.0 parts by weight
exerts a stabilizing in?uence on the polymer. Although
per 100 parts by weight of polypropylene. Particularly
polyethylene is in many ways similar to polypropylene in
preferred amounts are in the range of about 0.05 to
physical and chemical properties, it has been found that
about 0.5 part stabilizer per 100 parts polymer on a weight
basis.
many stabilizers highly e?ective in the case :of poly
ethylene are completely unsuitable as stabilizers for poly 45
Incorporation of the dithiophosphate salts into the poly
propylene. In some instances generally excellent poly
ethylene stabilizers have been found actually to aggravate
the instability of polypropylene at the high temperatures
concerned in the present invention.
It is therefore the general object of the present inven
tion to provide a polypropylene composition which is
meric propylene is accomplished by conventional methods
using such apparatus as a roll mill, Banbury mixer, or the
like. Advantageously the polypropylene is mechanically
worked at a temperature only just su?iciently high, i.e.,\
about 170° C. to 180° C. to achieve a ?uxed material
of ‘fornrable consistency before the stabilizer is added.
This procedure permits a minimum of processing to ob
tain an intimate mixture of. the composition constituents.
capable of withstanding elevated temperatures without
undue molecular degradation.
It is a further object to provide a polypropylene com
The excellent stabilizing action at high temperatures of
position which can be formed at suitably high tempera
the dithiophosphate salts of the present invention is all
tures with no signi?cant reduction in appearance, strength
the more surprising since it has been found that they do
properties, or electrical characteristics.
not eiiectively stabilize polypropylene at lower tempera
These and other objects which will be obvious from
tures. By Way of illustration, 100 parts by weight of a
propylene homopolymer having a melt index of 5 (as
the speci?cation are accomplished in accordance with the
present invention by admixing with polypropylene a small 60 determined by ASTM test ‘method D-1238—57T) and a
density of 0.90 was ?uxed and sheeted on a two roll mill at
amount of a dithiophosphate salt having the general
170° C. Potassium diisopropyldithiophosphate in an
formula:
, amount of 0.5 part by weight was then added to the sheet
[ (|)~R,
i _|D
R—O—P—~S-—M
65
on the mill and thoroughly mixed thereinto by successive
ly removing the sheet from the rolls and end-passing it
through the nip of the mill rolls ten times. A portion of
this composition was compression molded into a 30 mil
thick plaque and suspended in a circulating air oven main
wherein M is a metal selected from Groups I-A, III-A,
tained at 150° C. Periodically the plaque was examined
11-13 and -IV~‘B of the Mendeleeft Periodic System of Ele 70 and subjected to a manually applied bending force. The
ments, n is equal to the valence of the metal, and R and
plaque reacted to the induced stress in one of two ways—
R’ are each selected from the group consisting of an alkyl
either showing no discernible ill effect, or crumbling into
3,041,311
‘
>
4
3
small powdery fragments. Embrittlement, as indicated by
crumbling, occurred before. 6 hours had elapsed.
is most surprising in view of the fact that the same com
pounds do not stabilize polypropylene at lower tempera
tures, e.g., ‘150° C. as shown‘by the time to embrittlement
A more detailed illustration of the invention is set forth
in the following examples.
data. Even more surprising is the fact that 4,4’-thiobis
'
5 (6-tert-butyl-m-cresol) does prevent embrittlernent of poly
EXAIYIPLE -1
0116 hlmdfed Part? by welght of a PI'OPYIF'ne homopoly'
propylene at 150° C. but is completely ineffectual (actual
1y injurious) in polypropylene at high temperatures.
n1E1‘ having a melt Index of 5 (35 defem‘lmed by ASTM
The foregoing examples are intended solely for the
test method 13-123 8—57T) find 9- denslty 0f 0-9 Was ?lflied
purposes of illustration and not by way of limitation. It
and Sheetefl 011 NW0 1'0_11 111111 at 170° C- Potasslum d1}S°' 10 is further to be understood that various other additives
Pmpyldithmphosphate 1T1 3-11 amount Dip-5 Part by Welght
which do not impair the stabilizing action of the dithio
was then added to‘the sheet on the null and blended by
phosphate salts may be incorporated into the compositions
succfisslyely Temoylng @he Sheet ffom the T0115 and_end'
l in the conventional manner. Such additives include ?llers,
Passmg 1t through the 111p of the 111111 r0115 about ten tlmespigments, processing aids, lubricants, corrosion inhibitors,
The thermal stability of the composition at a high tempera- 15 and the like_
_
tul'e wa§_detifrmilled by Placing a
gram Sample of the
compoiltlon 111 a Preheat?d Cy1_111d1'1¢_a1 metal C611 f°m_1ed
The propylene polymers which are e?ectively stabilized
at high temperatures in accordance with the present in
by 61051118 05 the bottom (eXIt) Qrl?ce of an extruslon
plastometer of the same design and dimensions as the melt
vention are those which are normally solid at room tem
peratm-e and may be produced according to any of the
index measuring apparatus described in ASTM 33-12387 20 several methods known in the art. Exemplary of such
57T- The temperature Of the preheated cell was 300° Cprocesses are those described in Australian patent ap
A plus welsluns 100 grams was Placed dlrectly on the
plication No. 6365/55 to Phillips Petroleum Company,
resm composltwn and keptmjlhe cell at 309° C- for 15
United States Patent No. 2,692,259 to Edwin F. Peters,
minutes. At the endrof the tune, the melt mdex of the
and United States Patent No. 72,791,576 to Edmund Field.
composition was determined to be about 16 (-ASTM 25 What is claimed is;
D—1238~57T)-
1
*
1. A heat stabilized polypropylene composition re
EXAMPLE II
1
sistant to molecular degradation at high temperatures
Additional compositions consisting of polypropylene
‘Vb-"{1} _c°mP1‘1$eS normally _S°11d Polypropylene find a
and a dithiophosphate salt high temperature stabilizer were
Stablhzmg amount Pf a dlthloPhosphate Salt havmg the
prepared according to the same procedures as set forth 30 general {01111111313
in Example I and tested for embrittlement time and molecular degradation at high temperatures. Additionally a.
\
s
-|
R_f0__ill,_s
M
control sample of polypropylene having admixed there-
.
with'4,4'-thio bis-(6-tert~butyl-m-cresol) , which is general~
I J
"R
“
ly regarded as an excellent thermal stabilizer for poly- 35
propylene, was tested. In all instances polypropylene havwherein R and R’ are each selected from the class con
ing an initial melt index of S was used and the quantity of
sisting of an alkyl group containing from- 1 to 16 carbon
modi?er employed was 0.5 part by weight per 100 parts by ' atoms, monovalent aromatic hydrocarbon groups con
weight of polypropylene. The results are shown in Table
taining from 6'to 16 carbon atoms, and monovalent
I. Embrittlement time was determined by compression 40 cycloalkyl hydrocarbon groups containing from 5 to 16
molding the compositions into 30 mil thick plaques and
carbonatoms, and wherein M is a metal selected from
suspending these plaques in a circulating air oven at
Groups I-A, II-A, 11-13. and IV-B of the Mendelee?
150° C. Embrittlement is indicated by a crumbling of the
> Periodic System of Elements and n is equal to the
plaque under a manually applied bending stress.
valence of said metal.
Table I
Time
to Em-
Additive
Structure
- 150° 0.
(hrs)
None_‘..
CH3
Melt
Index of
brittle- Composi
mental; tlon after
0H3
15 min.
at 300° 0.
v<6
>100
24-43
>>10o
' <6
16
<6
14
<6
15
’
s
4,4’-thiobis(Mert-butyl-mcresol) ........ --
/
no
on
t-étiJaHo ' I #4434110 '
potassium diisopropyldithiophosphate-.-_. il3.-iH10—1L‘—-Se-Pv
‘
.O-—i'Ga-'H1
'
'
'
ll
‘
zinc diisopropyldithiophosphate ________ -_ [i——C3H70—P-+S~——-Zn
-
\
-
,
l
,
Q-iGaHLJ
>
i
w
cadmium diisopropyldithiophosphate____ _- [i—~CsH10.—P—S—-_—‘—'—Cd
i
'
V
OTEICSH7_Q
V 2. The composition of claim 1 in which R and R’ are
It is clear from the data of Table I_ that the stabilizing
action at high temperatures of the dithiophosphate salts 75 each alkyl groups containing from 1 to 16 carbon atoms
3,041,3ii
5
6
and M is a metal of Group II-B of the Mendeleeii
6. The heat stabilized polypropylene composition of
Periodic System of Elements.
3. The heat stabilized polypropylene composition of
claim 3 in which the stabilizer is zinc diisopropyl‘dithio
phosphate.
claim 1 in which the dithiophosphate salt stabilizer is
7. The heat stabilized polypropylene composition of
present in ‘an amount of from about 0.01 to about 2.0 5 claim 3 in which the stabilizer is cadmium diisopropyl
parts by weight per 100 parts by weight of said polypro
dithiophosphate.
pylene.
4. The heat stabilized polypropylene composition of
_ claim 2 in which the dithiophosphate salt stabilizer is
present in an amount of from about 0.05 to about 0.50 10
part by weight per 100 parts by weight of said polypro
2,552,570
2,739,122
2,739,123
pylene.
5. The heat stabilized polypropylene composition of
claim 3 in which the stabilizer is potassium diisopropyl
dithiophosphate.
References Cited in the ?le of this patent
UNITED STATES PATENTS
15
McNab et a1. ________ __ May 15, 1951
Kennerly et a1. ______ __ Mar. 20, 1956
Kennerly et a1. ______ .. Mar. 20, 1956
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