Note: Descriptions are shown in the official language in which they were submitted.
3~
E420
STABILIZATION OF RED PHOSPHORUS
The present invention relates to the stabilization
o~ red phosphorus against oxidation.
It is known that red phosphorus undergoes a
chemical reaction upon storage in a moist atmosphere to
form phosphine and various acids of phosphorus, mainly
phosphorous acid and phosphoric acid. The formation of
the highly toxic phosphine gives rise to hazardous
working conditions and unpleasant odours and the
formation of the phosphorous and phosphoric acids is
undesirable in end uses of red phosphorus. Aluminum in
the form of its hydroxide has been widely used to
stabilize red phosphorus against such degradation.
However, relatively large amounts of aluminum are
requirec`l to achieve a significant degree of
stabilization.
An additional problem which arises with the prior
art aluminum treatment is that the product is difficult
to process. A layer of alumina is precipitated onto
the red phosphorus partlcles in an a~ueous dispersion
thereof and the treated red phosphorus is filtered and
dried. Efficient filtration of the treated red
phosphorus is difficult to achieve as a result of
gelation of the aluminum hydroxide and large quantities
of water are retained by the aluminum hydroxide.
More recently, as described in U.S. Patent No.
4,4~1,728, it has been found that stabilization of red
phosphorus can be achieved using titanium dioxide or
titanium phosphate in lesser quantities than required
for aluminum hydroxide treatment and further that the
treated red phosphorus is readily and rapidly filtered.
Another advantage of the titania-treated red phosphorus
is that it may be heated at elevated temperatures up to
300~C without the evolution of water, so that the
product is suitable for addition to plastics which are
processed at high temperatures.
It has also been suggested in Canadian Patent No.
1,097,152 to stabilize red phosphorus against oxidatio~
2 ~2~'~3~
by superficially covering each red phosphorus particle
with a thin film of a hardened melamine-formaldehyde
resin.
It further has been suggested in U.SO Patent No.
4,315,897 to stabilize red phosphorus against oxidation
by the simultaneous treatment of red phosphorus
particles by aluminum hydroxide and hardened epoxy
resin.
In accordance with the present invention, it has
now been surprisingly found that a combination of
titanium in the form o~ titanium dioxide or titanium
phosphate and certain organic resins are particularly
effective as a stabilizer for red phosphorus. In this
invention, the stabilization is both the retardation of
oxidation of red phosphorus and the inhibition of
phosphine formation.
In accordance with one aspect of the present
invention, there is provided a homogeneous blend of red
phosphorus having a particle size of at most about 2 mm
and a mixture of titanium in the form of titanium
dioxide or titanium phosphate and a certain organic
resin, the titanium being present in an amount of about
0.05 to about 1.0 wt% and the organic resin being
present in an amount of about 0.1 to about 5.0 wt~
The organic resin which is utilized in the present
invention is an epoxy resin, a melamine-formaldehyde
resin or a urea-formaldehyde resin. When the
combination of TiO2 with epoxy resin is employed in
this invention, the improvement in stability against
oxidation which is attained in comparison with
treatment with resin alone is considerably greater than
that which is attained using the prior art combination
of aluminum hydroxide and epoxy resin.
The present invention also includes a method of
treating phosphorus particles to form such blends.
Accordingly, in another aspect, the present invention
provides a process for producing treated red phosphorus
which comprises forming a slurry of red phosphorus
particles of particle size of at most about 2mm;
3 ~
heating the slurry to a temperature of about 60 to
about 95C; adding to the heated slurry a titanium
compound which enabl~s titanium dioxide or titanium
phosphate precipitates in the slurry; adjusting the pH
of the slurry to a value of about 2 to 4 to effect
precipitation of titanium dioxide or titanium phosphate
on the red phosphorus particles in an amount of about
0.05 to about 1.0 wt.~ as Ti; introducing a
water-soluble or water emulsifiable uncured organic
resin to the slurry and subjecting the slurry to
conditions which effect precipitation of cured organic
resin on the red phosphorus particles in an amount of
about 0.1 to about 5.0 wt.~; separating the red
phosphorus particles so treated from the slurry;
washing the separated red phosphorus particles with
water; and drying the separated washed red phosphorus
partic]es to form a homogeneous blend of red phosphorus
particles, titanium dioxide or titanium phosphate~ and
cured organic resin.
The organic resin which is used to treat red
phosphorus in accordance with this invention is
employed in an uncured form and is either water soluble
or water emulsifiable. One organic resin which is used
in this invention is an epoxy resin. Epoxy resins are
thermosetting resins based on the reactivity of the
epoxide group. One common type of such resins is made
from epichlorohydrin and aromatic and aliphatic
polyols, such as 2,2-bis (4-hydroxyphenyl)-propane
(bisphenol A) and have terminal glycidyl ether
structures, contain many hydroxyl groups and cure
readily with water-soluble, internally-modified
polyamines. Curing or hardening usually is effected in
the aqueous phase at a temperature of about 20 to
about 90C while maintaining a pH value of the aqueous
phase of about 5 to 9. The epoxy resins which may be
used in this invention usually have an epoxy equivalent
weight of about 170 to 500.
A further organic resin which is used in this
invention is a melamine-formaldehyde resin.
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~". ~
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Melamine-formaldehyde resins are amino resins made from
melamine and formaldehyde. The first step in formation
of those resins is the formation of trimethylol
melamine, the molecules of which contain a ring of
three carbon and three nitrogen atoms. This molecule,
or polymer thereof, is reacted with formaldehyde.
Lower molecule weight uncured melamine resins are
water-soluble syrups and are preferred in this
invention. Curing is effected by heat and acidity.
Another organic resin which is used in this
invention is a urea-formaldehyde resin.
Urea-formaldehyde resins are a further class of amino
resins and are formed in a two-stage process involving
the initial formation of methylolureas which are
subsequently thermoset by controlled heating and
pressure in the presence of acid catalysts.
The red phosphorus, which is treated in accordance
with this invention, is in particulate form with a size
of at most 2 mm and preferably about 0.01 to 0.15 mm.
The red phosphorus particles are treated with titanium
dioxide or titanium phosphate and an organic resin.
The quantity of titanium compound used may vary from
about 0.05 to about 1.0 wt%, expressed as Ti, and the
quantity of the organic resin used may vary from about
0.1 to about 5 wt%.
The treatment of the red phosphorus particles with
titanium dioxide or titanium phosphate and organic
resin usually is effected in two steps, with titanium
dioxide or titanium phosphate first being precipitated
on the particles and subsequently the organic resin is
cross-linked to deposit on the red phosphorus
particles. The treatments with titanium dioxide or
titanium phosphate and organic resin may be effected
simultaneously, if desired.
The treatment of the red phosphorus by titanium
dioxide may be effected in the aqueous phas~ to cause
the precipitation of hydrated titanium dioxide on the
red phosphorus. In this procedure, the red phosphorus
particles may be suspended in water and the resulting
slurry heated to about 25 to about 70C, preferably
about 40 to about 50C. The heated slurry is
gradually mixed with the required amount of a
water-soluble titanium salt, for example, titanium
sulphate, to achieve the desired treatment level at a
slightly acid pH. The pH of the slurry then is
adjusted to a value in the range of about 2 to about 4
to effect precipitation of hydrated titanium dioxide on
the red phosphorus particles.
The slurry next is treated with the organic resin
material. The manner and conditions of organic resin
treatment depend on the form and nature of the resin
used to treat the red phosphorus particles. Usually,
the resin is added to the slurry in an uncured form and
lS is cured on the surface of the red phosphorus
particles.
For example, when the organic resin is an epoxy
resin, an aqueous dispersion of uncured epoxy resin is
admixed with the slurry of titanium compound-treated
red phosphorus particles in an amount sufficient to
provide the desired treatment level and thereafter an
aqueous solution of hardener for the epoxy is added to
the slurry. The pH of the slurry is raised to about 4
to about 6 and the slurry stirred for a time to permit
cross-linking to occur at a temperature of about 40 to
about 80C, preferably about 50 to about 65C, usually
for about 0O5 to about 2 hours. Thereafter, the pH of
the slurry is again raised to about 7 to 8 and the
cross-linking completed over about 10 to about 30
minutes.
When the organic resin is a melamine-formaldehyde
resin, an aqueous solution of a heat-curable uncured
melamine-formaldehyde resin is added to the slurry of
titanium compound-treated red phosphorus particles and
the pH of the slurry adjusted to about 2.5 to about 4.
The slurry then is heated to about 80 to about 100C
to effect heat-curing of the resin, in about 0.5 to
about 2 hours.
6 ~2~
When the organic resin is a urea-formaldehyde
resin, an aqueous solution of uncured urea-formaldehyde
resin is added to the slurry of titanium
compound-treated red phosphorus particles. The pH of
the slurry is adjusted to about 2.5 to about 4.0, the
slurry is heated to about 80 to about 100C to effect
curing of the resin, in about 0.5 to about 2 hours.
The treatment of the red phosphorus particles by
titanium phosphate may be effected in the aqueous phase
in analogous manner to the aqueous phase treatment by
titanium dioxide described above except that
orthophosphoric acid or a water-soluble salt of
orthophosphoric acid, for example, sodium dihydrogen
phosphate, and titanium sulphate are added to the
slurry, rather than titanium sulphate alone. Following
precip:itation of the titanium phosphate, the slurry
next is treated with the organic resin, as described
above for titanium dioxide treatment.
Following completion of the resin-precipitation
step, the mixture is filtered, the treated red
phosphorus is washed with water, dried and dehydrated
at a temperature of about 10~ to about 130C in a
vacuum oven.
Red phosphorus which is treated with titanium
dioxide or titanium phosphate and an organic resin in
accordance with the present invention possesses
improved properties having regard to the prior art.
Red phosphorus treated with titanium dioxide and an
epoxy resin has greater stability to degradation to
form oxidation products and phosphine than red
phosphorus treated with titanium dioxide at the same
titanium concentration level and the same stability can
be achieved using lesser quantities of titanium
dioxide. Improved stability results in a decrease in
acid formation and a decrease in the generation of
phosphine upon storage of the treated red phosphorus.
The presence of the titanium dioxide or titanium
phosphate on the red phosphorus appears to contribute
-s~ most to the low formation of acid while the presence of
the organic resin on the xed phosphorus appears to
contribute most to low phosphine production.
Red phosphorus which is treated with titanium
dioxide and a melamine resin, while having a lesser
stability than red phosphorus tr~ated with titanium
dioxide and an epoxy resin, possesses good water
dispersibility, which is advantageous in certain end
uses of the red phosphorus, such as in the match
industry.
Red phosphorus which has been treated in
accordance with this invention requires much less time
to filter and exhibits a much lower water retention
than aluminum hydroxide-treated red phosphorus,
resulting in a significant decrease in the processing
time required, as compared with aluminum hydroxide
treatment.
This invention is illus-trated by the following
Examples. In the Examples, reference is made to the
accompanying drawings, wherein:
Figure 1 is a graphical representation of the
effect of titanium dioxide and an epoxy resin on the
oxidation stability of red phosphorus;
Figure 2 is a graphical representatlon of the
effect of titanium dioxide and an epoxy resin on the
oxidation stability of wet red phosphorus;
Figure 3 is a graphical representation of the
effect of titanium dioxide, titanium phosphate and a
melarnine-formaldehyde resin on the oxidation stability
of red phosphorus; and
Figure ~ is a graphical representation of the
effect of titanium dioxide and urea-formaldehyde resins
on the oxidation stability of red phosphorus.
Example 1
This Example illustrates stabilization of red
phosphorus by a combination of titanium dioxide and
hardened epoxy resin.
Red amorphous phosphorus ~RAP) of particle size
typically 0.15 to 0.01 mm was suspended in water to a
; concentration of 25 g in 100 ml of water and heated to
60C with stirring. Varyin~ quantities of titanium
sulphate were added to samples of the slurry and the pH
of the slurry adjusted to a value of 3 to cause
precipitation of hydrated titanium dioxide thereon.
The quantity of TiO2 deposited is expressed in these
Examples as ppm of Ti herein.
An aqueous dispersion of an unhardened epoxy resin
then was admixed with the suspension of red phosphorus
particles and a solution of epoxy resin hardener added.
The epoxy resin used was that sold under the trademark
D.E.R. 324 by Chemroy Chemicals Ltd. This resin is a
blend of D.E.R. 331 epoxy resin and an aliphatic
reactive diluent which is C12 to C14 aliphatic glycidyl
ether. D.E.R. 324 has an epoxy equivalent weight of
197 to 206 and a viscosity at 25C of 600 to 800 cps.
D.E.R. 331 is a product of the reaction of bisphenol A
with epichlorohydrin, has an epoxy equivalent weight of
182 to 190 and a viscosity at ~5C of 11,000 to 14,000
cps. The resin was employed in the form of an emulsion
in water (3 g of resin in 50 ml of water) with the
addition of 1% of surfactant Tween 20 (sorbitol
monostearate). The hardener was that designated
TSX11-548 by Henkel & Co. Hardener TSX11-548 is a
water-reducible fatty amido amine having an amine value
from 385 to 410 and was used in the form of a water
dispersion (3 g of amine in 50 ml of water).
A pH of 5 next was established by the addition of
5 wt~ NaOH and the suspension stirred for 1 hour at
60C. The pH then was increased to 7 by the addition
of 5 wt% NaOH and the mixture stirred for a further 15
minutes to cross-link the resin and form a coating on
the RAP particles. The mixture thereafter was filtered
and the filter residue washed with water and dried at
about 100C for about 16 hours in a vacuum oven.
The samples of treated red phosphorus were tested
for stability and the results compared with those for
untreated red phosphorus, red phosphorus treated only
with resin, red phosphorus treated with aluminum
., ,
9 ~
hydroxide and epoxy resin, and red phosphorus treated
with titanium dioxide alone.
The stability to oxidation of the red phosphorus
was tested by maintaining the samples in the oven at
70C under 100% relative humidity and measuring the
acidity, expressed as H3PO4, by pH titration. The
results obtained are set forth in the graph of Figure
1. The legends correspond to the samples listed in
Table 1 below.
It will be seen from the results of Figure 1 that
red phosphorus treated with 1000 ppm Ti and small
quantities of resin has about the same stability to
o~idation as 3000 ppm Ti, and is more stable than when
treated with resin alone or with aluminum and resin.
At ~000 ppm Ti and 3000 ppm Ti in combination with
resin, the stability was increased further and was
greater than TiO2 alone or a combination of Al(OH)3
with epoxy resin.
The treated samples were also tested for phosphine
evolution and compared with untreated samples. One
gram portions were stirred with water in vials (69 cu
cm) fitted with a septum to provide for instant access
by syringe. After repeated stirring and leaving to
stand at room temperature, the phosphine concentration
was determined by gas chromatography with a flame
photometric detector. The results obtained are
reproduced in the following Table I:
10 ~
TABLE I
Sample Sample Treatment Exposure PH3 Con.
No. (Days) ~ppm)
..... ~_
5 1 0.78~ resin (1) 6 0.20
2 0.64% resin (2) 6 0.16
3 3000 ppm Ti + 0.78~ resin (1) 6 0.25
4 2000 ppm Ti + 0.78~ resin ( ) 6 0.30
3000 ppm Al ~ 0.78% resin (1) 6 0.22
10 6 1000 ppm Ti ~ 0.36% resin ( ) ~ 0.44
7 1000 ppm Ti ~ 0~50% resin (2) 4 0.24
8 2000 ppm Ti + 0.36% resin (2) 4 0.58
9 2000 ppm Ti -~ 0.50~ resin (2) 4 0.28
3000 ppm Ti -~ 0.20% resin ( ) 4 0.65
15 11 3000 ppm Ti 6 0 83
12(3) 2000 ppm Ti + 0.5Q% resin ( ) 9 0 25
13 Untreated RAP 5 5.80
Notes: 1. Resin to hardener ratio of 1:1
2. Resin to hardener ratio of 1:0.6
3. In this experiment, the titanium was
deposited as the phosphate.
As may be seen from the results of Table I,
phosphine evolution was greatly decreased by treatment
of the red amorphous phosphorus with resin alone or in
2~ combination with Ti or Al. Phosphine evolution was
- less for the resin-treated samples than for treatment
with Ti alone.
Example 2
This Example illustrates stabilization of red
amorphous phosphorus when stored wet.
The procedure of Example 1 was repeated, except
that the red phosphorus was not dried after treatment.
Oxidation stability and phosphine evolution were
determined as described in Example 1. The oxidation
stability determinations were plotted graphically and
appear as Figure 2, while the phosphine evolution
determinations are reproduced below in Table II:
TABLE_~I
Sample Sample Treatment Exposure PH3 Con.
No. (days)(ppm)
1 Untreated RAP 6 20.8
5 2 3000 ppm Ti 6 5.9
3 2000 ppm Ti + 0.6%
epoxy resin 6 1.1
4 2000 ppm Ti ~ 0.9%
epoxy resin 6 2.1
0.9% epoxy resin 6 2.1
1 6 5000 ppm Ti 6 6.1
It will be seen from the results of Figure 2 that
the use of the combination of titanium dioxide and
epoxy resin leads to enhanced oxidation stability. The
results of Table II show significantly decreased
1 phosphine evolution for wet samples treated with the
combination of titanium dioxide and epoxy resin.
Example_3
This Example -illustrates stabilization of red
phosphorus by a combination of titanium dioxide and
melamine resin.
Red amorphous phosphorus of particle size
typically 0.15 to 0.01 mm was suspended in water to a
concentration of 20 g in 100 ml of water and agitated
and admixed with 3.4 ml of a 10% aqueous solution of
Tioso4-H2so4-3H2o- NaOH (l.ON) was then added to
establish a pH of 3. A 10% aqueous solution of a
melamine resin was added to the mixture in an amount
sufficient to provide the desired treatment and the pH
again adjusted to a value of about 3 by the addition of
5% H3PO~. The suspension was heated with agitation to
95C, allowed to react for 1 hour and filtered. The pH
was controlled during this curing period of the resin
at about pH 3. The filter residue was washed with
water and dried at about 100C for about 16 hours in a
vacuum oven.
The melamine resin used was a methylated
melamine-formaldehyde resin sold by Monsanto under the
trademark Scripset 1~1. The resin was purchased in the
12 ~.2~
form of a 75% aqueous solution. The resin was a
polycondensation product of melamine and formaldehyde.
The samples were tested for stability to oxidation
and for phosphine evolution in the manner descri.bed in
Example 1 and the results compared with those for resin
alone and for untreated red phosphorus. The oxidation
stability results for Scripset 101-treated RAP were
plotted graphically and appear as Figure 3 while the
phosphine evolution data for Scripset 101-treated RAP
is reproduced in Table III below:
TABLE III
Sample Sample Treatment Exposure ~H3 Con.
No. (days) (ppm)
1 2000 ppm Ti + 1% resin 6 0.54
15 2 2000 ppm Ti + 0.5% resin 6 0.57
3 3000 ppm Ti + 0.5% resin 6 0.45
4 1% resin 6 0.91
2% resin 6 0.84
6 2000 ppm Ti + 0.5% epoxy 16 0.61
20 7 Untreated RAP 6 2.23
As may be seen from the results of Figure 3, RAP
stabilized with both TiO2 and melamine resin is stable
against oxidation but the resin alone is not very
effective. Phosphine evolution was decreased by
treatment with both TiO2 and melamine resin in
comparison with untreated RAP and treatment with resin
alone.
Example 4
This Example illustrates stabilization of red
phosphorus by a combination of titanium dioxide and
urea-formaldehyde resin.
The treatment procedure of Example 3 was repeated
using two urea-formaldehyde resins, except that the pH
was controlled during the curing of the resin and
adjusted to 209 to 3.0 with the use of phosphoric acid,
as required. The resins used were those sold by
Monsanto under the trademarks Resimene LTX-31-61 and
LTX-31-62. LTX-31-61 is a modified urea-formaldehyde
~,~ resin having a minimum solids content of 98%~ a
13 ~
viscosity at 25C of 1800 cps and a density at 25C of
1.14g/ml. LTX-31-62 is a modified urea-formaldehyde
resin having a solids content of 93 to 97%, a density
at 25C of l.09 g/ml and a viscosity at 25C of 600
cps.
The samples were tested for stability to oxidation
and for phosphine evolution in the manner described in
Example 1 and the results compared with those for resin
alone and for untreated red phosphorus. The oxidation
stability results were plotted graphically and appear
as Figure 4 while the phosphine evolution data is
reproduced in Table IV below:
Table IV_
Sample Sample Treatment Exposure PH Con.
15 No. (days) (ppm)
_ . . . . _
l 0.5% LTX 31-61 12 0.8
2 1.0% LTX 31-61 12 0.9
3 2000 ppm Ti + ~.5% LTX 31-61 12 1.7
4 2000 ppm Ti + 1.0% LTX 31-61 12 2.2
2000 ppm Ti(l) + 1.0~ LTX 31-61 12 2.7
6 2000 ppm Ti + 0.5~ LTX 31-62 5 0.5
7 2000 ppm Ti + 1.0% LTX 31-62 5 0.5
Note: (1) Ti was precipitated as titanium
phosphate.
As may be seen from the graphical results of
Figure 4 the combination of TiO2 or titanium phosphate
with the urea-formaldehyde resins increased stability,
with the LTX 31-62 resin being more effective. Example
This Example contains a compilation of data from
previous Examples with some additional experimental
results for the purposes of comparison and the drawing
of conclusions from the data.
Selected data from previous Examples is repeated
in Table V below:
. .
1~ ~Z~3~
Table V
Sample Treatment Time Acidity Expo- PH3 Example
in (mg sure Con.(sample)
Oven H,PO4/g (days) (ppm)
(hrs) R~P)
- ~ __ _ _ _
3000 ppm Ti 168 4 6 0.9 1(11)
3000 ppm Al as ( )
Al~OH)3 120 88 x _ _ _
0.78 wt% epoxy
resin 168 19.5 6 0.2 1(1)
3000 ppm Ti + 0.78%
epoxy 168 1.5 6 0.25 1~3)
3000 ppm Al + 0.75~
epoxy 168 12.5 6 0.2 1(5)
2000 ppm Ti 144 17.0(x) - - -
2000 ppm Ti + 2000 ( )
ppm Al 144 16.0 x _ _ _
2000 ppm Ti + 0.5%
epoxy 168 2.1 6 0.3 3(~)
2000 ppm Ti + 0.5%
melamine 168 11.7 6 0.6 3(2)
0.5% melamine 168 90.2(X) 5 0.9
0.5% urea-
formaldehyde 122 114.0 12 0.8 4(1)
200~ ppm Ti + 0.5%
U-F 122 39.0 12 1.7 4(3)
2000 ppm Ti + 0.5%
U-F 144 17.0 5 0.5 4(6)
(x) Data obtained from additional experiments
The following conclusions can be drawn from this
data:
(a) TiO2 in combination with epoxy resin improved the
stability of RAP treated thereby by a factor of
about 5 when compared with resin alone, whereas
Al (OH) 3 in combination with the epoxy resin
improved the stability only by a factor of about
2;
(b) TiO2 in com,bination with melamine resin improved
the stability of RAP treated thereby by a factor
of about 8 when compared with RAP treated by resin
alone;
(c) TiO2 in combination with urea-formaldehyde resin
improved the stability of RAP treated thereby by a
factor of about 3 when compared with treatment
with resin alone;
(d) Treatment of RAP with TiO and epoxide resins gave
,,j.. ~,,~ 2
! ~f,~ the best overall result in terms of best stability
15 ~
against oxidation and lowest evolution of
phosphine;
- (e) In general, treatment of RAP with resins,
especially epoxy resin decreases the amount of
phosphine evolved;
(f) While both Ti02 and Al(OH)3 are stabilizers of RAP
against oxidation, the addition of Al(OH)3 to RAP
treated with TiO2 does not improve the stability
of RAP.
In summary of this disclosure, the present
invention provides a novel red amorphous phosphorus
having improved stability against oxidation and
phosphine generation by treatment with titanium dioxide
or titanium phosphate and an organic resin.
Modifications are possible within the scope of this
invention.
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