Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for making
self-extinguishing thermoplastic materials based on synthetic
polymeric substances - such as for example polyamides, poly-
olefins, polycarbonates, polystyrene, copolymers of st~rene
with acrylonitrile and/or butadiene - by addition of red
phosphorus thereto.
Background of the invention
It is known that red phosphorus is an excellent
flame-retardant for many types of polymeric substances.
It is known too that, in order that the flame-
retarding effect of red phosphorus may have - as is desired
- a high efficiency, it is necessary that red phosphorus
should be added by distributing it in the mass of said poly-
meric substances in a homogeneously, finely particulated
form. This cannot be accomplished withou-t technical difficul-
ties according to the usual methods which, besides, having
some draw back connected with the safety and environmental
hygiene in relation to the necessity of handling fine red
phosphorus powders which, as is known, are toxic (formation
of phosphine by reaction with hydrogen-containing substances,
in particular water) and create combustion hazard.
Summar~ of the invention
An object of the present invention is therefore to
provide a process which permits fine and homogeneous disper-
sion, by means of a reliable and safe technique, of red phos-
phorus into synthetic thermoplastic materials.
This and still other objects, which will be better
apparent to a technician skilled in the art from the detail-
ed description given hereinafter, are achieved, according to
the present invention, by a process comprising the following
steps:
a) forming a concentrate comprising 30-70% of a
polymeric substance (mother polymeric substance) and 70-30%
of red phosphorus powder,(e.g~ having particle sizes below
~ '~
100 microns) previously encapsulated in a modified cationized
melamine resin;
b) incorporating said concentrate into a thermo-
plastic material, to be made self-extinguishing, consisting
of at least 50% of a polymeric substance similar to or com-
patible with the mother polymeric substance contained in
the concentrate, the amount of said concentrate being quanti-
tatively proportioned in such a manner that the final self-
extinguishing thermoplastic material contains 1-15% by weight
of said encapsulated red phosphorus powder.
The present invention, in particular, provides a
process for making self-extinguishing thermoplastic materials
based on synthetic polymeric substances by incorporation of
red phosphorus into said materials, which process comprises
the steps of:
(a) preparing an in water diluted melamine preco-
densate by first reacting 21.62 to 25.27% by weight
melamine, 30.85 to 36.04% forrnaldehyde, 25.57 to 29.87% by
weiaht triethanolam~ne and 8.82 to 21.96% by weight
of monohydroxyl alcohol having less than 5
carbon atoms, and then cationizing and diluting
with a mineral ac.id and water until a pH of
7 to 7.6 andaviscosity of d~0 to 50 centipoise are
reached;
(b) dispersing a micronized red phosphorus powder
in the cationized solution oE melamine pre-
condensate obtained in step (a), then heating
under stirring at about 100C. to precipitate .
said precondensate in the form of a partially
cross-]inked resin around the red phosphorus
particles and finally drying and completing
the resin's cross-linking at approx~mately 100C.
in an inert atmosphere;
(c) forming, by mixing and extruding, a concentrate
comprising 30 to 70% by weight o:f a mother poly-
meric substance and 70 to 30~ by weight o
the encapsulated red phosphorus obtained in
step (b), said mother polymeric substance
being a synthetic thermoplastic polymer
selected from the group consisting of poly~
amides, polyolefins, copolymers from acrylo-
nitrile-butadiene-styrene pslystyrenes,
~inylchloride homo- and co-polymers, vinyl-
acetate copolymers, polycarbonates and linear
polyesters; and
(d) incorporating said concentrate into a thermo-
plastic material to be made self-extinguising,
consistiny of at least 50% by weight of any
synthetic thermoplastic polymer defined in
step (c), the amount of-the abovesaid con-
centrate being quantitati~ely proportioned in
such manner, that the final self-extinguishing
thermoplastic material contains 1 to 15% by
weight of said encapsulated red phosphorus
powder.
Detailed description of the invention
The abovesaid encapsulated red phosphorus powder is
formulated and obtained, according to the present invention,
according to the process described in European Patent
Application No. 81107981.3, Publication No. 0 052 217
published on May 26, 1982 (corresponding to Canadian
Patent No.1162794)inthe name of the same Applicant. Accord-
ing to the afore cited Application, said encapsulated red
phosphorus powder may be prepared by a process substantially
consisting of coating the particles of a red P powder (in an
aqueous dispersion) with a melamine resin, by precipitation
thereof from a cationized pre-condensate (dissolved in the
same dispersion) obtained from melamine (25.27 - 21.62% by
weight), formaldehyde (36.04-30.85% by weight), triethanolamine
4p~
(29.87-25.57% by weight) and a monohydroxyl aliphatic alco-
hol containing a number of carbon atoms lower than 5, prefer-
ably methanol (8.82-21.96~ by weight). Said red phosphorus
powder so encapsulated ~hereinafter referred to also as en-
capsulated r/P) possesses - in accordance with the purposes
of the encapsulation - high characteristics of stability to
the generation of phosphine, even under very severe conditions
of use.
More particularly, the method for preparing said
encapsulated red phosphorus may comprise the following steps:
(a) preparing the melamine condensate: in a first
step, methanol, triethanolamine, formaldehyde (the last
substance in an aqueous solution at approximate 45~ calculated
on dry basis) are reacted for about 2 hours at approx. 85C
in per cent ratios, referred to the dry substance, respectively
of 8.82%, 29.87% and 36.04~, the remaining 25.27~ being the
melamine which is to be added in a s~cond step, at the end of
the aforesaid reaction, in order to cause the memaline con-
densate to form by heating the aforesaid composition at about
20 90C for approx. 6 hours (-the starting p~ value of 9.5 -
9.8 being adjusted to the value of 7.5 - 7.8 -) till a vis-
cosity of 420-470 centipoises at 20C is attained, whereupon,
after having adjusted the pH to a value of 7-7.6, it is
diluted with water, so obtaining a solution at about 38% of
dry substance and with a viscosity of 40-50 centipoises at
20C. pH adjustments are effected by means of a mineral acid
in an aqueous solution, at 18~ thus cationizing the melamine
condensate.
(b~ encapsulating red phosphorus powder:
a hydrodispersion of micronized red phosphorus powder having
a density of 1.38 - 1.58 is additioned with a desired amount
of the aqueous solution at 38% of cationized melamine con-
densate, prepared as per point (a)i the so obtained phosphorus
dispersion in the melamine condensate solution is heated,
8~
- 5 -
under stirring, for about l hour at approx. lOO~C, keeping
substantially unaltered-by means of a condenser- the reaction
mixture volume: under such conditions the melamine condensate
precipitates slowly and uniformly (evolving formaldehyde) in
the form of a resin partially cross-linked, at first in the
liquid-viscous, then in the solid state, around the red
phosphorus particles, so encapsulating them. Cross-linking
is then completed during dehydration by drying of the product,
preferably in a thin layer, at about 100C and in an inert
gas flow or preferably under vacuum, till formaldehyde does
no longer avolve. At the end a red phosphorus powder is
obtained, which is free-Elowing, stabilized to phosphine
forming and easily dispersible in to the polymeric materials
~for example by means of processes based on plastic mass
melting).
In relation to its excellent properties of chemical
stability, said encapsulated r/P powder can be incorporated
without drawbacks in great amounts (even of the order of
50-70% by weight1 into polymeric substances for providing
concentrates intended for the successive addition of said
encapsulated r/P to thermoplastic materials to be made self-
extinguishing. Such a thermoplastic material is a polymeric
substance identical with or similar to or consistent with the
mother polymeric substance contained in said concentrate.
The abovesaid concentrate is prepared in a sàfe
and drawback-free way, according to a preferred but not
exclusive embodiment of the present invention, by first
forming a solid mixture - in the desired ratios and by means
of a conventional apparatus - consisting of said previously
encapsulated red phosphorus powder an~ of a mother polymeric
substance>~ in the form of powder, granules and the like (and
optionally also of additives known in the art, such as dye-
stuffs, stabilizers, lubricants and the like), and by succes-
sively bringing the resulting mixture to the plastic state by
8~
-- 6 --
feeding said mixture (under an inert atmosphere) into an
extruder, preferably a two-screw extruder (equipped with an
electric heating, a vent system and a granulating head) known
to those skilled in the art, wherefrom solidified granules
come out, which exhibit a preferably cylindrical shape
(having dimensions of for example 3x3 mm, and consisting
for instance for 50% of encapsulated r/P and for 50% of
mother polymeric substance~>) and are ready for being utilized -
whenever and whereever desired, in an easy, realiable and safe
manner (in particular : absence of harmful gas exhalations,
absence of mold corrosion) - as vehicles for an optimum
incorporation and dispersion of said encapsulated r/P powder
into the thermoplastic material to be made self-extinguish
ing, which substantially consists of a polymeric substance
identical with (or similar to or consistent with) the one
contained in said concentrate granules, and optionally of
coadjuvant substances known in the art, such as reinforcing
agents, fillers, pigments, `lubricants, stabilizers and the
like.
Said incorporation is easily accomplished by means
of usual apparatuses and processes known in the plastic
material processing technology, for example by continuously
co-feeding, in the desired ratios, to a two-screw extruder,
the abovesaid concentrate granules and the thermoplastic
material to be made self-extinguishing (in the form of powder,
granules or the like), optionally concurrently with one or
more of the abovesaid additives, such as e.g. - in particular -
glass fibres, calcium carbonate, talc, titanium dioxide.
When leaving said extruder, the thermoplastic
self-extinguishing material (homogenized in the hot area of
said extruder) is solidified in the desired form (by equipping
said extruder, case by case, with a suitable head and a proper
cooling system, both known in the art~, for example in the
form of granules and the like, or also in the form of semi-
4~
-- 7 --
finished or finished products, for instance pipes and profiled
elements.
Said granules or the like, semifinished and
finished products have incorporated in their mass the above-
mentioned encapsulated powder of r/P in a finely particulated
and uniformly distributed manner, what results in an excellent
flame-retarding action exerted by the red phosphorus.
The process illustrated hereinabove is employed
very advantageously for making self-extinguishing the poly-
amides, in particular the polyamides obtained by polyconden-
sation of diamines with dibasic organic acids (such as for
example the polyamide-6,6 ) and the polyamides obtained by
polymerization of lactams (for example E-caprolactam), the
structures of both abovesaid types of polyamides being charac-
terized by bonds such as -NH-CO-.
The process forming the object of the present
invention is advantageously applied for making self-extinguishing
also many other thermoplastic materials, such as e.g.:
- homopolymers and copolymers of monomers having
an olefinic unsaturation, such as polyethylene, polypropylene,
ethylene/propylene copolymers, polystyrene, styrene/acrylo-
nitrile copolymers and ABS copolymers (acrylonitrile/butadiene/
styrene), vinyl chloride homo- and co-polymers, vinyl acetate
copolymers;
- polycarbonates, in particular polycarbonates
derived from bisphenol A and phosgene;
- polyacrylates, in particular polymethylmetha-
crylate;
- linear polyesters, such as polyethylene
terephthalate and polybutylene-terephthalate.
With a view to better illustrating the process
forming the ob]ect of the present invention, there are given
hereinafter some examples of embodiments thereof, which are
intended for merely illustrating but not limiting the invention.
~
.~
~a~
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In the following examples, the amounts are expressed
by weight. The values of specific gravity (s.g.) and of
softening point (s.p.) are determined according to ASTM-D 792
and ASTM-D 1525, respectively, while the self-extinguishing
property of the thermoplastic materials is checked by verti-
cal flame method ~L-94 utilizing injection press-molded test
pieces having the following dimensions: 152.4x12.7x1.6 mm.
(a) Preparing encasulated red phosphorus:
640 g of an aqueous solution containing 45~ of formaldehyde,
(9.6 moles) 70.5 g (2.2. moles) of methanol, 238.78 g (1.6
moles) of triethanolamine were introduced into a conventional reactor, known
in the art, eouiPped with electrical heating, a reflux condenser with a vacuum
intake and a ~agnetic stirrer, after having s~ted both stirrer and condenser.
The mixture so obtained,-having a PH = 9.8, was brought to 85C
and maintained at such temperature for 2 hours. After cooling
to 50C. 201.8 g (1.6 moles) of melamine were added (the
mixture now consisted of 36.04% of formaldehyde, 8.82% of
methanol, 29.87% of triethanolamine and 25.27% of melamine).
The pH was adjusted to a value of 7.6 by addition of 48 ml
of hydrochloric acid at 18~ in an aqueous solution, and the
mixture temperature was raised to 90C and kept such for 6
hours, so obtaining a melamine condensate solution having
a viscosity of 450 centipoises at 20C. ~t the end of this
heating period said condensate solution was stabilized by
~5 addition of 390 1 of water and by adjusting the pH to a value
of 7.5 by adding 80 1 hydrochloric acid at 18~ in an aqueous
solution, finally obtaining a solution o~ cationized melamine
condensate at 38.3~ of dry substance having a viscosity of 40
centipoises at 20C. The above-cited pH adjustments represent
the cationizing steps of the melamine condensate.
27.6 1 oE the above-obtained solution of cationized
melamine condensate were drawn and introdueed into a reactor
(equipped with a mechanical stirrer, a condenser and a heating
jacket) along with 300 g of red phosphorus powder, having a
particle size below 10 microns, in the form of an aqueous
dispersion having a density of 1.38. At the conclusion of
this operation the components were homogenized by stirring,
thus obtaining a red phosphorus powder suspension in a
cationized melamine solution condensate, which was heated at
lOODC for 1 hour. During such heating time the condensate
got insoluble (with formaldehyde evolution)and slowly and
uniformly precipitated, in the form of a partially cross-
linked melamine resin, at first in the liquid-viscous state
then turning into the solid state, onto the particles surfaces
of the red phosphorus powder, which were thus encapsulated
by a very adherent, continuous and compact layer of said
resin; finally, a water dispersion of red phosphorus en-
capsulated by melamine resin, having a slurry-like consistence
was obtained, said dispersion was spread to form a thin layer
of 2-3 mm thickness in a tray and was put into an oven at
90C under vacuum, at a residual pressure of approx. 300 mm Hg,
till formaldehyde evolution was no longer observed. During
such drying, both dehydration of said dispersion and completion
of melamine resin cross-linking occured, and at the en~ a
friable layer, easily convertible into a free-flowing product,
of red phosphorus in pow~er encapsulated with 4~ of melamine
resin was obtained; such powder proved to be stable to phos-
phine forming and was easily dispersible into the polymeric
materials.
Example 1
Into a two-screw extruder with a granulating head,
known in the art, equipped with an electric heating and vent
system, there were continuously, simultaneously fed by means
of two screws in a CO2 atmosphere, polyamide-6,6 (s.p. = 205C)
in 3x3 mm cylindrical granules and encapsulated r/P powder
having a particle size below 40 ~ in the following ratio:
- Polyamide-6,6 40 parts
- encapsulated r/P 60 parts.
~: .
:~2~
-- 10 --
About 500 kg of ~oncentrate were produced in the
aggregate without any drawback either of technical or of
hygienic-environmental nature (substantial absence of phos-
phine in the place of work).
The concentrate so obtained was $or the most part
packa~ed and stored for future uses, and in part utilized
for preparing a self-extinguishing polyamide, what was
accomplished by co-feeding and homogenizing, in a plastic
state, in a two-screw extruder similar to the one mentioned
hereinbefore, 20 kg of concentrate and 80 kg of polyamide-
6,6 Is.p. = 226C).
3x3 mm cylindrical granules of self-extinguishing
polyamide -6,6'' containing about 12% of encapsulated r/P
were obtained.
From said granules there were molded (by means of
an injection press) test pieces of 152.4 mm length, 12.7 mm
width and 1.6 mm thickness, wherein it was possible to observe -
under an optical microscope - that the particles of encapsulated
red phosphorus powder were homogeneously distributed in all
the polyamide mass, in compliance with the objects of the
present invention.
Said test pieces proved to be self extinguishing.
Example 2
Using the same concentrate of Example 1 (polyamide-
6,6 at 60~ of encapsulated r/P) there were prepared 100 kg of
self-extinguishing reinforced polyamide-6,6 by ~neading in
the plastic state, in the same extruder as in said example,
the following components in the amounts indicated by side
thereof:
- Concentrate (Polyamide-6,6 at
60~ of encapsulated r/P 15 parts
- Polyamide-6,6 (s.p. = 226C) 60 par-ts
- Reinforcing)~ glass fibres
(about 600 ~ long) 25 parts
~ .~..,~ , .
L3~8~
There were obtained granules of aself-extinguishing reinforced
polyamide -6,6 containing about 9% of encapsulated r/P, in
the form of 3x3 mm cylindrical granules, from which test
pieces having the same dimensions as those of Example 1 were
obtained, and which, like those of Example 1, contained,
incorporated therein, the particles of encapsulated r/P
powder homogeneously distributed in all their mass and which
proved to be self-extinguishing.
Exmaple 3
The same procedure was followed as in Example 1,
with the exception that the process was carried out with a
polyolefin instead of with polyamide.
High-density polyethylene (s.g. = 0.93) in the
form of 3x3 mm cylindrical granules was employed, forming
first a mother polyethylene concentrate containing 60~
of encapsulated r/P and successively producing - by mixing 86
parts of polyethylene with 14 parts of said concentrate -
self=extinguishing polyethylene granules (3x3 mm cylinders)
at about 8~ of red phosphorus, which, one transformed into
test pieces like in Example 1 and observed under an optical
microscope, revealed a homogeneous distribution in their whole
mass of the particles o encapsulated r/P powder, and pro~ed
to be self-extinguishing.
Example 4
By means of a vertical mixer there were prepared
- under a CO2 atmosphere - 100 kg of a mixture, in a ratio
60:40, of encapsulated r/P and styrene-acrylonitrile copolymer
(SAN) at 25~ of acrylonitrile. Said copolymer (s.p. = 93C)
was of the type obtained by the polymerization-in-suspension
process, and therefore in the form of powder (beads). The
mixture obtained hereinabove was brought to the plastic state
and transformed into 3x3 mm cylindrical granules by means of
the two-screw extruder of Example 1, thus obtaining a con-
centrate at 60~ of encapsulated r/P in SAN ~r/P-SAN concentrate).
;~7'~'
- 12 -
Most of such concentrate was packaged and stored for future
uses, while a part thereof was utilized to prepare acryloni-
trile-butadiene-styrene copolymers (known as ABS) of the
self-extinguishing type, as follows:
- in a conventional horizontal mi~er there ~as
prepared a mixture composed as follows:
- r/P-SAN concentrate 15 parts
- SAN 35 parts
- Styrene-acrylonitrile copolymer
grafted on polybutadiene (at 30%
of polybutadiene~ 50 parts
Said mixture was then homogenized to the plastic
state, in an extruder like the one illustrated hereinabove,
and transformed into 3x3 mm cylindrical granules of self-
extinguishing ABS at about 9~ of r/P. Test pieces of said
ABS, produced and tested as in Example 1, proved that the
encapsulated r/P powder was uniformly and homogeneously
distributed in all their mass. Said test pieces resulted
to be self-extinguishing.
From the foregoing description and examples
there are apparent the advantages of the present invention,
- which may be summarized as follows:
- it is possible to obtain, without technical
and hygienic drawbacks, concentrates with a high red phos-
phorus content in polymeric substances. Said concentrates
can be handled, stored, transported and dosed with a high
degree of easiness and safety;
- it is possible to obtain, by using said con-
centrates as red phosphorus vehicles, self-extinguishing
thermoplastic materials (transformable into shaped articles
by means of hot-molding processes, in particular extrusion
and injection molding) wherein red phosphorus is finely
particulated and very homogeneously distributed, what results
in an optimization of the flame-retarding action of said red
~ .'t
8~3
phosphorus.
The process according to the present invention,
as is described hereinbefore and hereinafter claimed, may
be modified with technically equivalent elements, provided
they fall within the scope of the invention. In particular,
for example, the encapsulated r/P powder can be added to the
mother polymeric substance after [instead of before) the
latter has been brought to the plastic state.
