Note: Descriptions are shown in the official language in which they were submitted.
99:~
Y`he present invention relates to flame-retardant moulding com-
positions of thermoplastic material, the moulding compositions containing
as a flame-retarding agent special grade pulverulent red phosphorus consist-
ing of particles with a si~e of at most about 100 microns.
It has been described that thermoplastic material can be render-
ed flame-retardant by incorporating a certain quantity of pulverulent red
phosphorus therewith. German Patent Specification "Auslegeschrift"
1 769 712, for example, describes a process for making self-extinguishing
thermoplastic moulding compositions, which are based on a copolymer of
acrylonitrile/butadiene/styrene, wherein the aqueous copolymer latex of
styrene and acrylonitrile is admixed with pulverulent red phosphorus, the
resulting material is admixed, with agitation, with an aqueous graft polymer
latex of butadiene/acrylonitrile/styrene, and the graft polymer is precipi-
tated and separated in known manner.
A disadvantage encountered with the process just described resides
in the fact that red phosphorus is liable to undergo a disproportionation
reaction in a moist atmosphere with the resultant evolution of hydrogen
phosphide, which is injurious to the health of the operating personnel.
A further process for making flame-retardant plastics material
has been described in German Patent Specification "Offenlegungsschrift"
2 408 488, wherein attempts are made to avoid the disadvantageous pheno-
~ menon described above with the use of red phosphorus as a flame-retarding
- agent by admixing~ prior to extrusion, the blend of pulverulent plastics
material and red phosphorus with one or more addends which are selected
from melamine, polyacrylonitrile, amidosulfonic acid, ammonium hydrogen
sulfate, and similar materials.
In accordance with the present invention, we have unexpectedly
found that thermoplastic materials which are processed on an extruder and
stored in a moist atmosphere are substantially not liable to evolve hydrogen
phosphide in all those cases in which they are used in admixture with
... .. ..
~l~91~99~L
pulverulent red phosphorus, whose particles are covered superficially with
an aluminum hydroxide layer. In other words, aluminum hydroxide enables
red phosphorus to be stabilized to an unexpected extent.
` The present invention provides more specifically flame-retardant
moulding compositions of thermoplastic material homogeneously blended with
about 1 to 10 weight % of red phosphorus particles with a size of at most
; about 1~0 microns, wherein the individual phosphorus particles are covered
superficially with about 1 to 30 weight % of a protective aluminum hydro-
xide layer, based on the quantity of red phosphorus.
. .
A preferred feature of the present invention provides for the
phosphorus particles to be covered superficially with 1 to 15 weight % of
aluminum hydroxide, based on the quantity of red phosphorus.
The term "thermoplastic materials" as used herein is intended
to mean plastics material, such as a polyurethane, polyamide, polyformal-
; dehyde, polyethylene terephthalate, polybutylene terephthalate, epoxy resin,
styrene/acrylonitrile copolymer, polyvinyl chloride, or polyolefin.
The protective layer of aluminum hydroxide may preferably be
- applied to the phosphorus particles by precipitating the aluminum hydroxide
; from an aqueous aluminum salt solution having pulverulent red phosphorus
suspended therein. The red phosphorus so treated is dried and may then be
incorporated into plastics material, for example by preparing a blend of
pulverulent plastics material and red phosphorus and processing the blend
on an extruder.
As will more clearly result from the following Examples, consider-
ably less hydrogen phosphide is liable to be evolved by thermoplastic ma- ;
terial which has been treated with red phosphorus of which the individual
particles are superficially coated with aluminum hydroxide. This is highly
desirable and a result of the fact that the individual phosphorus particles
are completely embedded in aluminum hydroxide. No such desirable effect
is produced in all those cases in which a mechanically prepared blend of
pulverulent red phosphorus and crystalline aluminum hydroxide is incor-
porated with a thermoplastic material.
The following Examples illustrate the invention which is, how-
ever, not limited thereto.
EXAMPLE 1 ~Invention)
~i Three phosphorus specimens A), B), and C) treated with Al(OH)3
;~ were made as follows:
A) 100 g of fine pulverulent red phosphorus consisting of particles
with a size of 10 to 100 microns was suspended in about 400 cc of water,
the suspension was admixed with 200 cc of a 20 % sodium hydroxide solution,
and the whole was heated for about 2 hours to 100C with agitation and
while passing 10 l/h of nitrogen therethrough. Next, the phosphorus was
filtered and water-washed until free from alkali.
The moist phosphorus filter cake was placed in a stirring vessel,
suspended in 500 cc of water, the resulting suspension was admixed with 33 g
of aluminum sulfate (A12~S04)3 . 18 H20) and heated to 60C. Next, a pH-
value of 7 was established by means of a 5 % sodium hydroxide solution.
After a postreaction period of 1 hour, the phosphorus was filtered, water-
washed and dried at 80C in a stream of nitrogen.
B) Specimen B) was prepared in the same manner as specimen A), but
with the use of 65.5 g of aluminum sulfate (A12(S04)3 . 18 H20).
C) Specimen C) was prepared in the same manner as specimen A), but
with the use of 196.5 g of aluminum sulfate (A12(SO4)3 . 18 H2O).
Preparation of polyethylene test sheets containing specimens
A), B), and C), respectively.
450 g of low pressure polyethylene with a melt index (i5) of
10.8 and a density of 0.951 g/cc was extruded in each particular case with
the use of 50 g of one of the specimens A), B) and C), and the extruded
material was compressed in a steam-heated hydraulic press at 180C and
under a pressure of 50 kg/cm into test sheets 2 mm thick. Next, the
-- 3 --
~ '~. J~
'~
~L~3!969~
test sheets were sewn into test tapes of 100 cm2.
Testing tapes for quantity of hydrogen phosphide evolved.
Three tapes which contained phosphorus specimens A), B) and C),
respectively, were stored for 6 days in separate glass vessels at 50C and
100 % of relative atmospheric moisture. The quantity of hydrogen phosphide
evolved was passed together with 10 l/h of air through a small test tube
~a product of Drager company, Lubeck, type hydrogen phosphide 50/a) and
identified by metering the colored indicating layer.
The results obtained are indicated in the Table hereinafter.
EXAMPLE 2 (Comparative Example)
Preparation of four phosphorus specimens D) - G).
D) 100 g of fine pulverulent red phosphorus consisting of particles
with a size of 10 to 100 microns was suspended in about 400 cc of water,
the suspension was admixed with 200 cc of a 20 % sodium hydroxide solution,
and the whole was heated for about 2 hours to 100C with agitation and
while passing 10 l/h of nitrogen therethrough. Nextl the phosphorus was
filtered and water-washed until free from alkali.
The moist phosphorus filter cake was placed in a stirring vessel,
suspended in 500 cc of water, the resulting suspension was admixed with
10 g of fine particulate, crystalline aluminum hydroxide and heated to
~0C. After a postreaction period of 1 hour, the phosphorus was filtered,
water-washed and dried at 80C in a stream of nitrogen.
E) 100 g of fine pulverulent red phosphorus was placed in a stirr-
ing vessel, suspended in about 500 cc of water, the resulting suspension
was admixed with 10 g of fine particulate, crystalline aluminum hydroxide
and heated to 60 C.
F) 100 g of fine pulverulent red phosphorus was intimately blended
with 10 g of fine particulate, crystalline aluminum hydroxide.
G) 100 g of fine pulverulent red phosphorus was intimately blended
with 20 g of fine particulate, crystalline aluminum hydroxide.
X
;~
6~
The polyethylene test sheets containing specimens D) - G), re-
spectively, were prepared, and the quantity of hydrogen phosphide evolved
: by the test tapes D) - G) was determined, in the manner described in
Example 1. ~he results obtained are indicated in the following Table.
~.
~0~69~9~
~ T A B 1, E
:
Test tape containing Quantity o~ hydrogen phosphide
specimen e~ol~ed
m surf2ce . day
A ~.57
B 1O50
C 2.~
: D 8.24
E 10.49
~ . ..., . __
F 20~22
G 19.46
_
The Table shows ~learly that the test tapes con-
; tain~ng the phosphorus specimens A) - C) of the prese~t
invention are ~ubstantially less liable in moist atmo-
sphere to evolve h~drogen phosphid~ than the test tapes
containin~ the ~omparative phosphorus specimens D~ - G).
b
'.
- ,. . . ~
