Note: Descriptions are shown in the official language in which they were submitted.
8 CH 2~33
~9~3~
The present invention relates to plasticized
thermoplastic polyphenylene ether compositions which contain,
as a surprisingly effective drip-retardant additive, a
microfibrillar poly(tetrafluoroethylene)resin. The
compositions of this nvention possess improved drip
retardancy even when subjected to stringent test conditions
which more closely simulate real large-scale fire situations
than prior art test methods. The present compositions can
optionally include impact modifiers for the polyphenylene
ether resin, such as A-B-Al block copolymers, e.g.,
polystyrene-polybutadiene-polystyrene.
The polyphenylene ether resins are well known in
the art as a class of thermoplastics which possess a number
of outstanding physical properties. They can be prepared,
in general, by oxidative and non-oxidative methods, such as
are disclosed, for example, in Hay, U.S. 3,306,874 dated
February 28, 1967 and 3,306,875 dated February 28, 1967
and Stamatoff, U.S. 3,257,357 dated June 21, 1966 and
3,257,358 dated June 21, 1966.
It is known that when the polyphenylene ether
resins are combined with styrene resins, such as crystal
grade homopolystyrene or high impact rubber modified
polystyrene, there are obtained compositions having many
properties which are improved over those of either the
polyphenylene ether or polystyrene alone. Moreover, these
respective polymers are combinable in virtually all pro-
portions, e.g., from 1 to 99 parts of polyphenylene ether to
99 to 1 parts of polystyrene. Examples of polyphenylene
ether-polystyrene compositions are disclosed in Cizek,
U.S. 3,383,435 dated May 14, 1968.
In recent years, there~has been increasing concern
; about the performance and safety of thermoplastic materials,
~ , '
-.1 - ~ .
: ~ . . . : . . , : ~
8 C~l 2433
3~
includiny -the a~ore-mentioned polyphenylene compositions
during real-life fire situation. One o~ the potential
hazards presented by the presence of thermoplastics in ~ires
is that they can contribute to f:ire spread by dripping
flaming and/or molten resin.
The term "dripping" has an art-recognized meaning.
More particularly, in a fire situation, a thermoplastic can
become hot enough to exhibit some degree of melt flow. When
this flow is extensive enough to result in the ph~sical sepa-
ration of the molten mass ~rom the main body of the plastic,
"dripping" is said to have taken place~ Because the dripped
material is sometimes flaming and since dripped flaming resin
is a means by which fire can spread to combustible surround-
ings, dripping is undesirable in a thermoplastic material.
Of particular interest herein are plasticized
thermoplastic compositions comprised of a polyphenylene ether
resin, plasticizer(s) present in plasticizing amounts, and
optionally, impact modifiers such as rubber~modified, high-
impact polystyrene resins or A-B-~ block elastomeric
copolymers. These compositions have now been investigated
under test conditions which are even more closely related to
real-life large-scale fire conditions than are more
conventional and more widely used tests such as the Under-
writers Laboratories Bulletin No.94 critical burning test.
The UL-9~ test is generally carried out by
preparing a molded test piece of about 5" x 1/2" x 1/1~",
supporting the sample verticallyr and igniting it. If the
sample does not form flowing droplets sufficient to ignite
a piece of cotton held 12 inches beneath and extinguishes
itself within an average of 5 seconds after each of two
10-second~ignitions, the compo~ition is deemed to be non-
dripping and ~lame-retardant to the point where it satisfies
~' . ~' .
--~2--
- - .
~ 8 CH 2433
the V-O requirements of the Underwriters' Laboratories.
If the test sample extinguishes i-tself within 30 seconds,
after two 10-second ignitions, the composition is deemed
to be flame-retardant and non-dripping in satisfaction of
the V-l requirements.
Because the heat flux generated during the usual
Underwriters Laboratories Bulletin No.9~ test is relatively
small in comparison with heat flow which prevails during
real, large scale fires, the following test has now been
devised which more closely simulates reality than the UL-94
test:
The barrel of a Bunsen burner is screwed
down (clockwise) so that the air ports are
closed. The gas flow is adjusted to produce
a blue/yellow flame of approximately 5-6
inches in height. A 5" x 1/2" x 1/16" test
sample is suspended vertically in the center
of the flame and about 3/8" above the burner
top, until either dripping takes place or 5
minutes of continuous ignition time has
elapsed.
The above procedure is hereinafter referred to as
the "flame bath" test, because the test specimen is literally
immersed in flames during the test.0
It is now been surprisingly discovered that the
"dripping" (as measured by both the 1/16" UL-94 and "flame
bath" tests) of plasticized compositions of a polyphenylene
ether resin and a plasticizer can be greatly retarded or
completely prevented by the incorporation of microfibrillar
poly(tetrafluoroethylene), in relatively small amounts. It
has been previously proposed, in Canadian application Serial
No. 242,338, filed December 18, 1975, assigned to the same
assignee as herein, that poly(tetrafluoroethylene) acts as
an effective drip-retarding agent for self-extinguishing
~ . . .
polyphenylene~ether compositions which contain fl~me ~etardin~
agents. However, it has not been previously recognized that
.; ::
~ 3~ ~ CH 2433
a particular kind of poly(tetrafluoroethylene), namely micro-
fibrillar poly(tetrafluoroethylene), is a remarkably effective
drip-retarding agent in plasticized polyphenylene ether com-
positions, even in the absence oE flame retarding additives.
Accordingly, the present invention provides in its
broadest aspects, a drip-retardant plasticized thermoplastic
composition which comprises, in admixture:
(a) a polyphenylene ether resin;
(b) a plasticizer in an amount at least
sufficient to provide a plasticized composition after molding;
and;
(c) a microfibrillar poly(tetrafluoroethylene)
resin in an amount at least sufficient to render said thermo-
plastic composition non-dripping when molten and/or burning.
As employed herein the term "plasticized" is used
to describe compositions having a sufficient amount of a
plasticizer which reduces the temperature required for ex-
trusion by at least 50 to 100F. as compared to the analagous
unplasticized compositions.
The polyphenylene ether resin (a) is preferably of
the type having the structural formula:
Q
_~C ~ O
Q
wherein the oxygen ether atom of one unit is connected to the ~-
benzene nucleus of the next adjoining unit, n is a positive
- 30 integer and is at least 50, and each Q is a monovalent sub-
stituent selected from the group consisting of hydrogen, halo-
gen, hydrocarbon radicals free of a tertiary alpha-carbon
atom, halohydrocarbon radicals having at least two carbon
- 4 -
`:
- ~
~8~3~ ~ CH 2433
atoms between the halogen atom and the ph~nyl nucleus,
hydrocarbonoxy radicals and halohydrocarbonoxy radicals having
at least two carbon atoms between the halogen atom and the
phenyl nucleus.
A more preferred class of polyphenylene ether resins
for the compositions of this invention includes those of the
above formula wherein each Q is alkyl, ~st preferably having
from 1 to 4 carbon atoms. Illustratively, members of this
class include poly(2,6-dimethyl-1,4-phenylene)ether; poly-
(2,6-diethyl-1,4-phenylene)ether; poly(2-methyl-6-ethyl-1, 4-
phenylene)ether; poly(2-methyl-6-propyl-1,4-phenylene)ether;
poly(2,6-dipropyl-1,4-phenylene)ether; poly(2-ethyl-6-propyl-
1,4-phenylene)ether; and the like.
Especially preferred is poly(2,6-dimethyl-1,4-
phenylene)ether, preferably having an intrinsic viscosity
of about 0.45 deciliters per gram (dl./g.) as measured in
chloroform at 30C.
The choice of a plasticizer is not critical and
any of the conventional materials used for this purpose can
be employed. Preferably, component (b) will be selected
from among phthalate and phosphate plasticizing materials,
and especially phosphate plasticizers.
The phosphate plasticizer i5 preferably a compound
of the formula:
O
11
OR - P - oR1
R2
wherein Rl, R2 and R3~are the same or dlfEerent and are alkyl,
cycloalkyl, aryl, alkyl substituted aryl, aryl substltuted -
alkyl, hydroxyalkyl,~hydroxyaryl, hydroxyalkaryl, halogen,
haloaryl, and hydrogen and halogen substituted aryl.
~5 -
~ 3~ 8 C~l 2433
Examples include cresyl diphenyl phosphate, 2-
e-thylhexyl diphenyl phosphate, tricresyl phosphate, tri-
isopropylphenyl phosphate, triphenyl phosphate, triethyl
phosphate, dibutyl phenyl phosphate, diethyl phosphate, cresyl
diphenyl phosphate, isooctyl diphenyl phosphate, tributyl
phosphate, 2-ethylhexyl diphenyl phosphate, isodecyl diphenyl
phosphate, isodecyl dicresyl phosphate, didecyl cresyl phos-
phate, tri-_-hexyl phosphate, di~ octyl phenyl phosphate,
di-2-ethyl-hexyl phenyl and -tri-2-ethylhexyl phosphate tri-
(polychlorophenyl) phosphate or mixtures thereof. Especially
preferred is triphenyl phosphate.
Examples of phthalate plasticizers include dibenzyl
phthalate, phenyl cresyl phthalate, diethyl phthalate, dimethyl
phthalate, phenyl benzyl phthalate, butyl benzyl phthalate,
butyl cyclohexyl phthalate, dibutyl phthalate, octyl cresyl
phthalate, diphenyl phthalate, di-_-hexyl phthalate, disohexyl
phthalate, butyl octyl phthalate, butyl decyl phthalate, di-
isooctyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl
phthalate, diisononyl phthalate, diisodecyl phthalate, di-2-
propyl heptyl phthalate, di~_-nonyl phthalate, di-n-decyl
phthalate and ditridecyl phthalate.
The plasticizer (b) is added in amounts which will
be sufficient to provide a plasticized composition within
the meaning of the term described abo~e. In general, the
plasticizer is present in amounts ranging from about 15 to
about 65 parts of plasticizer per 100 parts of total resin.
Preferably, from about 20 to about 45 parts of plasticizer
per 100 parts of total resin are employed.
The drip-retarding additive (c) of the present ~ `
positions must be a microfibrillar poly(tetrafluoroethylene)
resin. By "microfibrillar", it is meant that the resin forms
microfibrils upon being rubbed between the palms of one's
- 6 -
,
~ 3~ 8 CH 2433
hand. Such resins are commercially available or can be
prepared by known methods. An example of a commercially avail-
B able microfibrillar polytetrafluoroethylene resin is TEFLON
Type 6, sold by the DuPont Company.
Amounts of the microfibrillar poly(tetrafluoro-
ethylene) resin will vary, depending on the particular needs
of the composition, it being essential only that a sufficient
amount is added to render the composition non-dripping or
drip-retardant in accordance with the above-mentioned UL-94
test and more severe "flame bath" test. In general, arnounts
are selected which range from about 0.1 to about 5 parts per
100 parts of the composition, preferably from about 0.5 to
about 1 part per 100 parts of the composition, based on
components (a) and ~b) combined.
The present compositions can also include impact
modi~iers, such as polystyrene resins which have been blended
or co-polymerized with materials which are elastomeric at
room temperature, e.g., 20 to 25C.
The preferred styrene resins will be those having
at least 25% by weight of repeating units derived from a
vinyl aromatic compounds of the formula:
R~ CH2
~ .
i~ ~ (Z) P ," "" ~ "
wherein R is hydrogen, (lower) alkyl or halogen; Z is vinyl~
halogen or (lower) alkyl; and p is 0 or an integer of from
1 to the number of replaceable hydrogen atoms on the benzene
nucleus. Herein the term "(lower)alkyl" means alkyl from
1 to 6 carbon atoms.
-- 7 --
': ' ' ' ~ . ' . . : . , -
8CEI-2~33
3~
The general formula above includes, by way of
illustration, homopolymers sucl~ as homopolystyrene and
monochloropolystyrene, the modified polystyrenes, such as
rubber modified high impact polyst:yrene, i.e., polystyrene
which has been blended for grafted with natural or synthetic
elastomers such as polybutadiene, styrene-butadiene, EPDM
rubber, and the like, and styrene containing copolymers such
as the styrene acrylonitrile copo]ymers, styrene butadiene
copolymers, styrene acrylonitrile-~-alkyl styrene copolymers,
styrene-acrylonitrile-butadiene copolymers, poly ~ methyl-
styrene, copolymers of ethylvinylbenzene, divinylbenzene and
styrene maleic anhydride copolymers, and block copolymers
of styrene-butadiene and styrene-butadiene-styrene.
Preferred impact modifiers include A-B-Al block
copolymers. In general, these resins comprise a polymerized
center block B which is derived from a conjugated diene, e.g.,
butadiene, isoprene, 1,3-pentadiene, and the like, and poly-
merized terminal blocks A and Al which are derived from vinyl
aromatic compounds, e.g., styrene, ~ -methyl styrene, vinyl
toluene vinyl xylene, vinyl naphthalene, and the like.
Preferably the A-B-~l block copolymer will have terminal
blocks A and Al comprised of polystyrene and a center block
comprised of polybutadiene;
The linear A-B-A block copolymers are made by an
organometallic initiated polymerization process using, for
example, sodium or lithium metal or an organic derivative
thereof. The diene monomers can be polymerized with a mono-
functional or difunctional initiator, as is described in
Kennedy et al, Intersciene Publishers, Vol. 23, Part II
(1969), pages 553-55g. Other methods of preparing these block
copolymers are described in Zelinski, U.S. 3,251,905 dated May
17, 1966 and Holden et al, U.S. 3,231,635 dated January 11, 1966.
- 8 -
.
: , ~ , .
~ 3~ 8C~L-2433
Commercially ava:ilable A-B-A block copolymers
include Kraton X-4119, a polystyrene-polybutadiene-
polystyrene block copolymer containing 20 weight % of mineral
oil, and the Kratons designated as K-1101 (polystyrene
polybutadiene-polystyrene), K-1102 (polystyrene-
polybutadiene-polystyrene), and K-1107 (polystyrene-
polyisoprene-polystyrene), all from Shell Chemical Co.,
Polymers Division.
Hydrogenated A-B-Al block copolymers can also be
used as impact modifiers in the present compositions. These
are prepared by techniques which are well known in the art.
See, for instance, the disclosure in Jones U.S. Patent 3,431,323
dated March 4, 1969. A preferred commercially available copolymer
of this type is Shell Chemical's KG-6521 M resin.
If an impact modifier is employed it should be
employed at about 3 to 15 parts by weight per 100 parts by
weight of components (a) and (b).
A preferred family of compositions will include a
flame retardant amount of a flame retardant agent. Obviously,
the flame retardant agent can comprise plasticizer component
(b) if (b) itself is a flame retardant and is present in flame
retardant amounts.
Other ingredients, such as fillers, reinforcements,
pigments, stabilizers, lubricants, and the like may be added
for their conventional purposes~
The manner in which the present compositions are
prepared is not critical and conventional methods can be
employed. Pre~erably, however, each of the ingredients is
added as part of a blend premix, and the latter is passed
through an extrucler at an extrusion temperature of from abQut
~ 9~
....
.
3~
8 C~ ~433
450 to about 550F., dependent on the needs of the particular
composition. The strands emerging from the extruder may be
cooled, chopped into pellets, and molded or calendered to
any desired shape.
The following examples are illustrative of the
compositions of this invention. They are not intended to
limit the invention in any manner.
Examples 1-11
The following blends were prepared and tested
for flame retardancy. All parts are by weight.
- `10
:
,
- ` 8 CM 2433
a)
o o U~ o ~ o
~' I ~ I o ,~ I o I
~i
P,l I I ~ ~ I I 1 7 I Ci
~ c) N
i o
C~ D ~
~ i i 1 7 1 7
O L~
q O ~
O
CiD~
~ ~ ~) ~
'¢ ~ I I I I I C C
~ ti ~ i
¢
~ 5
1 ~1
o.C
~ Q~ E~ O
O l l O O l l l l l l l
D :~ I I ~i C~i I I I I ~ l i
~ 1~ . ~ ~
~ O
P~ I O O ~ U~
t~ ~i t~ r) t~ l t~it`J t~J ~1 ~1 .
O ~-r~
O ~
E ~ o
ot~t:: o o o o o o ~ ~ o ~ a
:~ 1~r~ ~ cot~ oo t~ to :~ ~o .~:: ~ r C ,~
t~ . ~ A ~ r~
: ~ ~ a. ,, a O ~ ~ ~
~ e
t~l D O ~ tl)-3C
~i ~.:
: : X : '
~-il
:: : : : :
. ~ . . . . .
36341z 8 CH 2 4 3 3
The dripping tes t results and flame retarding
properties for the above compositions are shown in the
f o 1 lo~ing table.
TABL~_
FLA~: TEST RESULTS
lJ16" UL-g4
Ex2m~1eOxy~en Index (SeClSeC 2_ '~lame Bath''
1 __ 1/2,~/3,1/2 Dripping aftër
1/3 drip,l/2 16-18 seconds
of exposure
2 __ 0/0,0/2,1/~, Dripping after
0ll,0/1 55-65 seconds
3 -- 0/0,0/0,0/1, Dripping after
0/0,0/0 21-25 seconds
4 . -- 0/0,0/0,0/0 J Dripping after
0/0,0/0 80-84 seconds
0.386 0/2,1~1,1/1, Dripping after
1/1,0/1 50-55 seconds
6 0.338 0/1,0/2,0/1, No dripping dur-
0/1,0/1 ing ~irst 300
seconds of ig-
nition; during
that time, test
sample shriveled
up and burned to
form a solid
: ~ h gh integrity
,:: :
7 C.355 1/0,0/2,0/0, Same results as
0 /1, 0 / 0 f or Examp le 6
8 _ l/l,l/l,0/1, Dripping ~after
l/l,0/1 55 seconds
9 ~ - 0/1, 0/1, 0/1, Same results as ;
OlO,0/l f~r E.~ample 6
~ Dripping af ter
: : 35 seconds
- Same results as
for Example 6
:
': : : :
~ ~ ~ : ~ 12-
`: : : ` :
:
. ~ ,
. . ~
- ~ :
~ 3~ 8 CH 2433
It was o~ further interest to learn whether or not
compositions containing microfibrillar poly(tetrafluoroethylene)
would also resist dripping in the presence o~ radiant heat
alone, that is, in the molten state and iIl the absence of
char-promoting flame. Just as in the case of a flame-
producing fire, a thermoplastic material which drips in the
presence of radiant heat is also hazardous. The dripping
behavior of thermoplastlcs in the presence oE radiant heat
was evaluated using the following test procedure:
A test specimen measuring 5" x 1/2"
x 1/16" was clamped at its top edge and
held vertically with its 5" x 1/2" surface
parallel to a radiant panel located about
2 1/4" away. A weight of 42.0 grams was
clamped to its bottom edge to prevent
"curling", i.e., physical distortion by
bending or twisting, of the test specimen
under the influence of radiant heat. The
temperature at the surface of the test
specimen was estimated to be 250C.
Under these test conditions, a slight surface
charring took place on the test specimen, but no flaming
of the specimens occurred at any time.
A composition made up of 80 parts of poly(2,6-
dimethyl-1,4-phenylene)ether resin, 20 parts of
triphenylphosphate and 5.0 parts of K1101 styrene-butadiene-
- styrene block copolymer was tested using the above procedure,
and dripping occurred after 55 seconds of exposure to the
heated panel. The same composition was tested again,
except that 0.5 parts of micro fibrillar poly(tetrafluoroethyl-
ene), TEFLON 6 was added. With this composition, dripping
did not occur until 242 seconds of exposure had elapsed.
The test was again repeated using 1.0 parts of TEFLON 6 in
the composition, and dripping did not occur even after 9Q0
seconds o~ exposure.
It is shown ~rom this test that the drip-
~etarding effect of microfibrilla~ poly(tetrafluoroethyle~e)
13 -
. .- .
.: ~: : . ,. ... . ., - . . . :....... , . . . ............. .:
., , ., .. . . , .. ; , . . . . .. . .. . . .
~8634 8 C~l 2~33
is present regardless of whether heavy char formation takes
place. The above tests indicate that the compositions of
the present invention will resist dripping or sagging during
real, large-scale fire conditions, which involve a
combination of large radiant heat flow and flames.
Obviously, other modifications and variations of
the present invention are possible in the light of the above
description. It is, therefore, to be understood that
changes may be made in the particular embodiments disclosed
herein which are within the full intended scope of the
invention as defined in the appended claims.
,
