Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED FLAME RETARDANT ADDITIVE_FOR THERMOPLASTICS
The present invention relates to flame
retardant additives and particularly such additives
for thermoplastics. More particularly, the present
invention relates to silicone based flame retardant additives for thermoplastics including polyolefins.
Background of the Invention
Considerable efforts have been expended in
the past to flame retard thermoplastic resin wlthout
the use of halogen. Typically, it has been necessary
to heavily fill the plastic or thermoplastic material
with additives until the desired dlegree of flame
retardancy is achieved. Heavy filling offers several
disadvantages due to the fact that a large proportion
of additives can normally be expected to detract from
the physical properties of the plastics material.
Further, the additive may bring complications inherent
to the additive itself, such as, for example, foaming,
which must be dealt with in addition to a general
lessening of physical properties.
The present invention provides flame
retardant additives which not only provide improved
flame retardance in the absence of organic halides,
but also do not exhibit poor processability as might
be expected from the prior art.
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U.S. Patent No. 4,387,176, issued June 7,
1983 to Frye, assigned to the instant assiynee,
discloses a flame retardant additive for
thermoplastics which contains a silicone oil, a
sillcone resin, and a Group IIA metal salt. This
flame retardant additive is most effective with the
addition of a halogen.
U.S. Patent No. 4,115,351, issued September
19, 1978 to Joh, discloses synthetic fibers dipped in
solutions containing inorganic phosphorus and
inorganic nitrogen compounds. To render the compounds
more convenient for use in the dip solution, they are
coated with inactivating materials including silicone,
paraffin, and grease.
U.S. Patent No. 3,936,416, issued February
3, 1976 to Brady, discloses the use of ammonium
polyphosphate and dipentaerythritol as a flame
retardant in polypropylene. In addition to
insufficient flame retarding effect, there is a
problem of flame retardant foaming during melt
processing of the polypropylene.
It is an object of the present invention to
produce a non-halogen containing flame retardant
additive for thermoplastic resin.
It is another object to produce a
non-halogen containing flame retardant additive with
improved flame retardant effect.
It is yet another object of the present
invention to produce a phosphorus and nitrogen
containing flame retardant for thermoplastic resins
which does not foam during melt processing.
Description of the Invention
Briefly, there is provided according to the
present invention a flame retarded composition
~5 comprising:
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(A) 100 parts by weight a thermoplastic resin
and
(B) from about 2 to about 30 parts by weight a
flame retardant additive comprising:
(i) 20 to 60% by weigh-t a silicone oil,
(iij 20 to ~o~ by weight a silicone resin,
and
(iii) 5 to 60% by weight a gassing agent
selected from the group consisting of
compounds containing both phosphorus
and nitrogen or a mixture of
phosphorous containing compounds with
nitrogen containing compounds.
Optionally r there may be added a polyhydric alcohol to
promote char formation.
A major lngredient contained in the flame
retardant additive is approximately 40 to 80 percent
by weight of silicone oil. The term "silicone oil" as
used herein is generic for a wide range of
polysiloxane materials which can be advantageously
utilized in the eomposition of the present invention.
For purposes of the present specification it is
intended that t~le expression "silicone oil" be
; construed as including those effective silicone
materials as described by MacLaury and Holub in U.S.
Patent No. 4,273,691, issued June 16, 1981, as well as
other effective silicone materials, several of which
will be deseribed below. Typically, effective
silicone will be those silieone fluids or gums which
are organopolysiloxane polymers eomprised of
ehemieally eombined siloxy units typically selected
from the group consisting of R3Sioo 5, R2Sio,
RlSio0.5, RlR2Sioo 5, RRlSio~
(R~)2SiO, RSiO1.5 and sio2 units and mixtures
thereo~ wherein eaeh R represents independently a
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saturat~d or unsaturated monovalent hydrocarbon
radical, Rl represents a radical such as R or a
radical select~d from the group consisting of a
hydrogen atom, hydroxyl, alkoxy, aryl, vinyl, or allyl
radicals etc. and wherein said organopolysiloxane has
a viscosity of approximately 600 to 300,000,000
centipoise at 25C. A preferred silicone oil is an
essentially linear polydimethylsiloxane having a
viscosity of approxi~lately 90,000 to 150,000 centi-
poise at 25C. Such effective silicone oils are to bedistinguished from the class of materials referred to
as silicone resins. Such silicone oils are readily
available under a wide variety of brand and grade
designations.
Another major ingredient of the flame
retardant additive is a class of materials referred to
as silicone resin. Silicone resins are well known
materials coming in a variety of forms. Approximately
2 tv 40 percent by weight of the total additive
formulations will be a silicone resin which is soluble
in the above described silicone oil (i.e. fluid or
gum) and which is effective for imparting improved
flame retardancy to the composit:ions of the present
invention. Among the preferred silicone resins are MQ
silicone resins~ The expression "MQ silicone resin"
refers to the face that such resins are typically
comprised primarily of monofunctional M units of the
formula R3Siooo5 and tetrafunctional Q units of the
averaye formula sio2 having a specified ratio of M to
Q units. A notable effective silicone resin for u~e
in the present invention is polytrimethylsilylsilicate
which can have a ratio of, approximately, 0.3 to 4.0 M
units per Q unit. A particularly effective flame
retardant additive package might preferably contain
from 6 to 30 percent by weight of such MQ resin and
have a ratio of, approximately, 0.6 to 2 M
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units per Q units. An example of a commercially
available MQ resin is General Electric SR5~ 5TM
(60% MQ resin solids in toluene). A preferred method
of utilizing such an MQ resin solution is to mix it
5 with the silicone oil component and thereafter remove
the solvent. The solvent can be removed by well known
methods, e.g. by distillation at moderate
temperatures.
It is contemplated that other silicone oil
soluble forms of solid silicone resins may be
effective for use in the flame retardant compositions
of the present invention. Indeed, MT and TQ silicone
resins (where T represents trifunctional ~SiO1 5
units) may also be effective as well as mixtures and
copolymers of each of the resins mentioned. These
silicone resins are well known materials and are
readily available. A criteria for suitability is that
such effective silicone resinous materials be soluble
or dispersible in the silicone oil base.
Additionally, it is to be noted that
although the additive composition specifies the
silicone oll (essentlally D functlonal) and silicone
resin (M, D, T or Q functional) as discrete
ingredients to be admixed, it is intended that the
~5 present invention encompass reaction products of such
materials which may be equally effective as flame
retardant additives. It is also foreseeable that a
copolymer containing requlsite M, D, T or Q
functionality may be utlllzed ln place of discrete
silicone oil and silicone resln constituents.
The flame retardant additlve formulation
further contains a gassing agents are compounds
containing both phosphorous and nitrogen or a mixture
of phosphorus containiny c~mpounds with nitrogen
containing compounds. The function of the gassing
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agent is primarily to produce gas under heat and
thereby retard the supply of oxygen. Also, the
gassing agent may decrease temperature in addition to
~ a~ extinguishable liquid which is able to cover
ignition sites.
Preferred gassing agents are compounds,
particularly inorganic compounds containing both
phosphorus and nitrogen. Suitable such compounds
include ammonium polyphosphates having the general
formula (NH4)n+2Pn3n+1 wherein is greater than 2;
ammonium phosphates, such as primary ammonium
orthophosphate (NH4)H2P04, secondary ammonium
orthophosphate (NH4)H2P04 tertiary ammonium
orthophosphate (NH4)H3P04, ammonium pyrophosphates
such as primary ammonium pyrophosphate (NH4)H3P207,
secondary ammonium pyrophosphate (NH4)2H2P207,
and others like (NH4)3HP207; ammonium phosphites
such as (NH4)H2Po3l (NH4)HOP3; ammonium
hypophosphates such as (NH4)2H2P2o6~
(NH4)2H2P2o6~ (NH4)3HP206; ammonium
hypophosphites such as (NH4)H2Po2~ (NH4)2~P2;
ammonium metaphosphate like (NH4)P03 and ammonium
dihydrogen phosphite (NH4)H2P03 and so forth.
In addition to these examples, compounds
with other metal elements are also involved, for
example, sodium ammonium phosphate NaNH4HOP4,
magnesium ammonium phosphate (NH4)MgP04, ammonium
phosphomolybdate (NH4)3P04x12MoO3, ammonium
phosphotungstate (NH4)3P04, 12 W03, ammonium
cobalt phosphate (NH4)CoP04, ammonium mangan
phosphate (NH4MnP04, Furthermore halogen
containing compounds such as difluoroammonium
phosphate (NH4)P02F2, hexafluoroammonium
phosphate (NH4)PF6, diaminophospho trichloride
C13P(NH2)2, triphospho nitrilochloride
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(PNC12)3, and other compounds such as phosphoamide
OP(NH2)2, metaphosphimic acld P3N3(OH)6 and
its ammonium salt P3N3O6H3(NH4)3/ ammonium
trithiophosphate (NH4)3POS3. The hydrates o~
the above compounds are also included.
Further examples of gassing agents
containing both nitrogen and phosphorous are nitrogen
containing pentate salts, melamine pyrophosphate,
phosphine oxide, etc. Nitrogen containing pentate
salts are further described in U.S. Patent No.
4,154,930, issued May 15, 1979 to Halpern.
As stated above, the gassing agent can also
be a mixture of phosphorous containing compounds with
nitrogen containing compounds. Phosphorus containing
compounds include phosphoric acid, phosphorous acid,
metaphosphoric acid, metaphosphorous acid,
hypophosphorous acid, pyrophosphorous acid,
hypophosphoric acid, pyrophosphoric acid and
preferably salts thereo~. The salts include, ~or
example, sodium salt, potassium salt, lithium salt,
beryllium salt, magnesium salt, calcium salt, zinc
salt, cadmium salt, ammonium salt and so on.
The phosphorus containing compounds are
exemplified by potassium dihydrogen phosphate
KH2PO7 dipotassium hydrogen phosphite K2HOP3,
potassium pyrophosphate K4P2O7, magnesium pyrophosphate
Mg2O2O7, potassium metaphosphate (KPO3)n, sodium
potassium hydrogen phosphate NaKHOP4x7H2O disodium
dihydrogen pyrophosphate Na2H2P2O7, sodium
metaphosphate (NaPO3)6 disodium dihydrogen hypophosphate
Na2H2P2O6, trisodium phosphate Na3PO4xl2H2O,
disodium hydrogen phosphite Na2HPO3x5H2O, disodium
phosphomolybdate Na2PO4xl2MoP3, trilithium phosphate
Li3PO4xl/2H2O, magnesium hydrog~n phosphate
MgHPO4x3H2O, disodium hydrogen phosphate Na2HPO4 and
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its hydrates Na2HPO4x2H2O, Na2HPO4x7H2O,
Na2HPO4xl2H2O, sodium dihydrogen phosphate
NaH2PO~xH2O, primary monomagnesium hydrogen phosphate
~gH4(PO4)2x3H2O, trimagnesium phosphate
Mg3(PO4)2x5H2O, secondary calcium phospha-te
CaHPO42H2O, primary calcium hydrogen phosphate
CaH4(PO4)2, calcium phosphite CaHPO3, tertiary zinc
phosphate Zn3(PO4)2x4H2O, secondary zinc phosphite
ZnHPO3, zinc pyrophosphate ~n~P23O7, aluminum
phosphate AiPo4, and so forth.
Nitrogen containing compounds are readily
available and are preferably ammonium compounds.
Suitable ammonium compounds are ammonium chloride,
ammonium carbonate, ammonium hydrogen carbonate,
ammonium nitrate, ammonium sulfate, ammonium hydroyen
sulfate, ammonium phosphates.
Of course, two or more phosphorus containing
compounds may be mixed with two or more nitrogen
containing compounds. Persons skilled in the art can
determine the relative ratios of phosphorus compounds
and nitrogen compounds necessary to achieve the effect
as a gassing agent. Such rat.io will obviously change
depending on the particular compounds employed.
An optional but preferred ingredient of the
flame retardant additive formulation is a polyhydric
alcohol.
The polyhydric alcohols useful for the
purposes of this invention are acyclic and cyclic
compounds havin~ a plurality of hydroxyl groups
attached thereto, and include, for example,
pentaerythritol, dipentaerythritol tripentaerythritol,
pentitols such as adonitol, arabitol and the like,
hexitols such as dulcitoll inositol and the like, and
saccharides such as amylose, xylan and the like, as
well as such derivatives thereof as N-methyl
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glucamine. The function of the polyhydric alcohol
appears to be that of acting as an additional
carbonific or carbon source for the gassing agent
thereby increasing the amount of char formation and
reducing the amount of gassing agent additive required
to effect useful flame retardant behavior. The amount
of polyhydric alcohol employed will thus necessarily
be selected in proportion to the amount of gassing
agent used, and in general the weight ratio of ga~sing
agent to polyhydric alcohol will be from about 9:1 to
about 5:1. Where lesser amounts of polyhydric alcohol
are employed such that the ratio is greater than about
10:1, the improvement in char formation becomes
negligible, while the use of greater amounts of
polyhydric alcohol tends to reduce the flame retardant
effect by way of supplying the unneeded excess
polyhydric alcohol as a fuel to the flame.
Thermoplastic resins in which the flame
retardant additive formulation described herein is
useful include blowable, extrudable, and injection
moldable thermoplastic resins. Specifically, these
resins include polyolefins such as polyethylene,
polypropylene, polystyrene, PVC, polybutadiene, etc.;
polycarbonate; polyamide; polyester, including
poly(ethylene terephthalat~), poly(butylene
terephthalate), poly(cyclohexanedimethanol
terephthalate), etc.; poly(phenylene oxide);
polyimide; polyacrylate; polyether; epoxy; etc. An
aspect of the present invention is particularly
advantageous for thermoplastics having a melt
temperature greater than about 15C.
It i5 preferred that for each 100 parts by
weight of thermoplastic resin, there be added from
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about 2 to about 30 parts by weight flame re-tardant
additive. More preferably there should be added from
about 10 to about 25 parts by weight flame retardant
additive for each 100 parts by weight thermoplastic
resin.
The flame retardant additive, as stated
above, must contain silicone oil, silicone resin,
gassing agent and optionally polyhydric alcohol.
Based on silicone oil, silicone resin, and gassing
agent content, the flame retardant additive should
contain from about 20 to about 60% by weight silicone
oil, from about 10 to about 40% by weight silicone
resin, and from about 20 to about 60% by weight
gassing agent. Preferably, these constituents in the
flame retardant additive should range from abou-t 30 to
about 50% by weight silicone oil, from about 15 to
about 30% by weight silicone resin and from about 30
to about 50% by weight gassing agent.
In the practice of the present invention the
flame retarded compositions can be made by mixing
together the thermoplastic resin with the silicone
oil, the silicone resin, and the gassing agent by
means of any conventional compounding or blending
apparatus, including a roll mill, a BanburyTM
mixer, or an extruder. The order of addition of the
particular constituents does not appear to be
critical; and those skilled in the art will be able -to
optimize mixing operations to fit their particular
need.
A preferred method of providing the flame
retardant thermoplastic compositions of the present
invention is to premix the silicone oil with the M~
resin solution, and thereafter remove the solvent as
by distillation. This wlll insure complete dispersion
of the resin in the oil. This solution is thereafter
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combined with the remaining ingredients by any
suitable means for providing a homogeneous composi-tion
(e.g. twin screw extrusion).
Preferably all the ingredients are
formulated together at as low a temperature as
possible recognizing, of course, that the temperature
must be at least the melt temperature of the
thermop]astic resin. The gassing agent is sensitive
to heat and will foam the thermcplastic if melt
temperature is excessive. Although it is one aspect
of the present invention that foaming is reduced,
lower formulation temperatures are beneficial to
further reduce foaming. Depending on the particular
thermoplastic resin and gassing agent employed, the
temperature of extrusion may vary between about 250F
and about 600F.
The flame retarded thermoplastic resin may
be molded, extruded, compressed or spun, etc. to form
numerous useful products. These products include
coatinys, injection molded items, sheet, webbing,
fibers and other products. End use may be in
conductive wire, appliance housings, hair dryers,
automotive interiors, fans, motors, pump housings,
power tools, electronic housings, etc. Persons5 skilled in the art can easily imagine others.
Examples
In order that those skilled in the art will
be better able to practice the invention, the
following examples are given by way of illustration
and not by way of limitation. All parts are in parts
by weight.
Examples 1-5
Polypropylene, (Hercules Pro~fax 6523TM
resin), was blended above melt temperature with the
materials shown in Table I on a BanburyTM
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compounder. The resultant material was comminuted
into pellets and injection molded at about 380F into
UL94 test bars.
Table I
1 2 3 4 5
Polypropylene 74.3 78.5 70.8 72.8 72.8
Magnesium Stearate4.4 3.6 -- -- --
Silicone oill 6.3 7.1 4.7 5.2 4.8
Silicone Resin2 3.2 3.6 2.4 2.6 2.4
Decabromodiphenyloxide 6.9 -- -- -- --
Talc 5.0 7.2 -- -- --
Ammonium Polyphosphate3 -- -- 19.7 14.6 14.5
Pentaerythritol4 -- -- 4.4 4.9 5.5
UL-94 V-l V-1 V-0 V-1 V-0
1 Silanol stopped polydimethylsiloxane polymer,
nominal viscosity is 90,000 - 150,000 centipoise
2 MQ silicone resin, M/Q ratio approximately 0.8/1
3 (NH4)n+2 Pn3n-~l. where n = 1000 to 3000,
Monsanto Company
4 Pentaerythrltol
Examples 7 and 8
Polypropylene, (Hercule~ Pro~fax 6523
resin), was melt extruded and cooled in a water bath
with materials shown in Table II. The resultant
extrudate was comminuted into pellets and injection at
about 380'F into UL--94 test plaques.
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Table II
6 7
Polypropylene 72.8 72.8
Silicone Oil 4.8 ----
Silicone Resin 2.4 ----
Ammonium Polyphosphate 14.5 14.5
Pentaerythritol 5.5 5.5
Visual Inspection of Exudate slight foam heavy foam,
pitted surface
Ul-94 V-1consumed
