Granular flame retardant agents and process for their preparation

Granular flame retardant agents are disclosed which incorporate halogenated organic flame-retardant compounds, without any binders. The granular agents may further contain desired additives and organic or inorganic flame-retardant synergistic materials. The granular agents are dust-free and are usefully employed in a method for imparting flame-retardant properties to flammable plastic materials. A process for the preparation of the granular flame retardant agents of the invention by cold compaction is also described.

BACKGROUND OF THE INVENTION 
1. The Field of the Invention 
The present invention relates to granular flame retardant agents, to a 
process for preparing the same, to a method for imparting flame-retardant 
properties to plastic materials using said agents, and to flame-retarded 
plastic materials obtained thereby. 
More particularly, the present invention refers to the use of halogenated 
hydrocarbon flame retardant agents, alone or in admixture with organic 
flame-retardant agents and synergists. 
2. The Prior Art 
It is well known in the art to use halogenated hydrocarbons to impart 
flame-retardant (FR) properties to flammable plastics. Examples of 
commercially available FR agents are Decabromodiphenyl oxide, Penta- and 
Octabromodiphenyl oxide, Hexabromocyclododecane and Tetrabromobisphenol A. 
It is also known that it is possible to employ mixtures of two or more of 
such halogenated hydrocarbons, which may be both in solid form or not, 
and/or mixtures which comprise inorganic or synergistic FR agents, such as 
antimony oxide or melamine isocyanurate. Non-solid FR compounds comprise, 
for instance, pentabromodiphenyl oxide. Other various additives are also 
often employed in admixture with the FR composition, such as binders or 
carriers, lubricants, smoke suppressors, anti-dripping agents, such as 
DPFA, and thermal stabilizers. 
The halogenated FR compositions, however, are usually in fine powder form 
which presents several problems. Dispersion of the FR compound within the 
processed plastic is often nonhomogeneous, pollution problems due to dust 
formation are severe and certain additives, e.g., antimony oxide, are 
toxic. Therefore, several approaches have been tried in order to avoid 
direct use of FR compositions in powder form, for instance, by preparing 
master batches of the plastic containing high concentrations of FR 
composition; or colloidal suspensions of the FR compounds are prepared, 
which are then mixed with the monomer, or binders are used in order to 
prepare agglomerates of FR compounds. 
SUMMARY OF THE INVENTION 
It has now been found, and this is an object of the present invention, that 
it is possible to employ relatively large granules sizes (2-4 mm), for 
granules obtained through compaction and grinding, and that the said 
granules can be obtained without the addition of any binding agent. 
It is a further object of the invention to provide a method for imparting 
flame retardancy to polymers, which eliminates the problem of dusting and 
potential health hazards existing in the methods known in the art. 
It has further been found, and this is another object of the invention, 
that FR plastic material obtained through the use of the granular FR 
compositions of the invention do not show any appreciable difference in 
their properties, as compared to the material obtained by using the same 
FR agent in powder form. Furthermore, no difference in processability of 
the two different FR formulations (those processed with compacted agents 
and those processed with powders) is observable, in the normal course of 
polymer processing. 
The FR compositions and process of the invention obviate many disadvantages 
of known processes, and further present several other advantages, as will 
be apparent hereinafter. 
The flame-retardant granular compositions according to the invention are 
characterized in that they contain, in compacted granulated form, one or 
more halogenated hydrocarbon flame retardant compounds, alone or in 
admixture with organic or inorganic flame-retardant or flame-retardant 
synergistic compounds and/or additives. Preferably, the compacted form is 
a cold-compacted form. 
By cold compaction it is meant that no external heat is added during the 
compaction operation for the purpose of aiding or promoting compaction and 
that compaction is substantially carried out by mechanical pressure. 
However, as it will be apparent to a person skilled in the art, it may be 
advantageous in some instances to maintain during processing, or during 
one or more stages thereof, a temperature higher than room temperature, 
e.g., for the purpose of promoting removal of volatile materials contained 
in the solid FR material or mixture. Thus, for example, DECA powder may 
contain some such volatile matters the removal of which can be assisted by 
causing the temperature to raise slightly, up to 40.degree.-60.degree. C. 
The heating of the FR material during processing, if effected for such 
purposes, does not substantially alter or affect the process of compaction 
as herein described, and any process employing such heating for purposes 
unrelated to the compaction process--and with temperatures which do not 
affect the mechanical properties of the material to be granulated--does 
not exceed the scope of the present invention. 
The size-distribution of the said granules is preferably comprised between 
about 2 and about 4 mm. The additives which can be admixed with the FR 
compound(s) comprise, e.g., lubricants, thermal stabilizers, non-polymeric 
binders, smoke suppressors and carriers. Suitable smoke suppressors 
employed in the art are, e.g., ammonium molybdate, zinc borate and bismuth 
salts. 
According to a preferred embodiment of the invention the halogenated 
hydrocarbon is selected from among pentabromodiphenyl ether, 
octabromodiphenyl ether, decabromodiphenyl ether, tetrabromobisphenol A 
and its derivatives, tetrabromobisphenol A bis(allylether), 
dibromopentyglycol, tribromopentylalcohol, hexabromocyclododecane, 
tribromophenyl allylether, tetrabromodipentaerythritol, 
bis(tribromophenoxy)ethane, ethylene bis(dibromonorbornane)dicarboximide, 
tetrabromobisphenol S bis(2,3-dibromopropyl)ether, 
poly(pentabromobenzylacrilate), and 
Dodecachloropentacyclooctadeca-7,15-diene, and the inorganic 
flame-retardant/synergistic compound is selected from among antimony 
oxide, magnesium oxide, magnesium hydroxide, ferric oxide, ammonium salts 
and cyanurate derivatives. The compacted material prepared according to 
the invention has a diametral crushing strength of at least 0.3 kg/sq.cm.. 
As it will be apparent to a person skilled in the art, the diametral 
crushing strength is an important parameter in order that a granular 
material be strong enough so that the granules do not disintegrate during 
normal handling. As the person skilled in the art will readily appreciate, 
too high values of the crushing strength may cause difficulties in 
processing, e.g., due to difficult disintegration of the granules. In such 
case, it will be required to adjust this value to the operating parameters 
employed in the process, as it will be apparent to the man of the art. The 
granules so obtained comprise bromo- or chloro-containing hydrocarbons or 
mixtures thereof, alone or in admixture with FR synergistic compounds such 
as metal oxides and sulfides, and organic salts of antimony, boron, 
arsenic and zinc borate. 
The process for preparing a composition according to the invention is 
characterized by the steps of: 
(a) feeding the flame-retardant material or mixture to a compacting 
apparatus; 
(b) carrying out the compaction of the flame-retardant material or mixture 
in the compacting apparatus; 
(c) feeding the resulting compacted material to a granulator; 
(d) granulating the compacted material in the granulator; 
(e) withdrawing the fraction of the throughput from the granulator, which 
has the desired size-distribution; and 
(f) optionally recycling the fraction of the granulated material having 
undesired sizes to the compacting apparatus; 
According to a preferred embodiment of the invention, the compacting 
apparatus is a roll compactor. According to another preferred embodiment 
of the invention the granulator is a screen granulator. 
Granulated flame retardant compositions, whenever prepared by the process 
of the invention, also form part of the present invention. 
The process for producing flame-retarded articles according to the 
invention is characterized in that the material to which it is desired to 
impart flame-retardant properties is mixed during processing thereof with 
a granular composition according to the invention. Flame-retarded 
articles, whenever produced by the said process, also form part of the 
present invention. 
A good distribution of a powder in the polymer is very difficult to obtain. 
Thus, the advantage of using granular material which, apart from the 
aforesaid advantages, is also more easily dispersed in the polymer, is an 
important feature of the invention. Since plastic processing apparatuses 
usually comprises nozzles, the problem of clogging thereof must be 
overcome. For this purpose, the art has employed very small powder sizes, 
or colloidal suspensions of FR material, in order to avoid such clogging 
and size problems. The granules of the invention, however, can be employed 
with large sizes such as 2-4 mm, since the FR material dispersed in the 
polymer melts together with the polymer itself or disintegrates therein, 
and is therefore finely distributed therein. When granules contain 
material which does not melt at the polymer processing temperature, such 
as antimony oxide or DECA, care must be taken to obtain a fine 
distribution of such materials within the FR granules, so that when the 
granules melt or disintegrate they will be liberated in fine powder form 
and homogeneously dispersed in the polymer. It should be noted that when 
pulverized material is employed homogeneous dispersion thereof in the 
polymer is hindered also by the formation of agglomerates of the FR 
material, which is avoided when operating according to the invention. 
Another advantage of the invention is that it is possible to obtain FR 
agents having a bulk density much higher than that of the corresponding 
powdered composition. As it will be apparent to a person skilled in the 
art, this fact is advantageous both for shipping and storage purposes, and 
because it requires that smaller volumes of FR agent be processed, as 
compared to powdered agents. Table I below shows values for three 
different composition: decabromodiphenyl ether (DECA) alone, DECA in 
admixture with antimony oxide with a DECA/AO ratio of 3:1, and 
poly(pentabromobenzylacrilate) (PBB-PA). It can be seen that the bulk 
density of DECA and DECA/AO mixtures is considerably increased by 
compaction, while it remains unchanged for PBB-PA. 
TABLE I 
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Bulk Density (g/cm.sup.3) 
MATERIAL Powder Compacted 
______________________________________ 
DECA 1.043 1.583 
DECA/AO (3:1) 1.107 1.694 
PBB-PA 1.249 1.249 
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While the bulk density is not a parameter having an absolute value inasmuch 
as it is somewhat dependent on the method by which the sample has been 
prepared, such variations are not too great and the above data are 
indicative of the change in bulk density due to compaction granulation. 
The ratio between the halo-containing compound and the synergistic compound 
will depend on the stability of the halo compound and the reactivity of 
the particular synergist employed as well as the plastic material 
employed. Generally this ratio can vary in a broad range such as between 
95 parts synergistic compound to 5 parts halo-compound and 5 parts 
synergistic compound to 90 parts halo compound. 
In addition to the main advantage that the compositions and method of the 
present invention are free from dusting, the effective content of flame 
retardant compositions is very high, since the granules of the invention 
are substantially free from carriers and binding materials. 
The above and other characteristics and advantages of the invention will be 
better understood through the following illustrative and non-limitative 
examples. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

EXAMPLE 1 
Compaction and Diametral Crushing Strength 
Experiments were carried out at ambient temperature for testing the 
characteristics of the compaction of different FR/synergist formulations, 
utilizing the diametral compression test (as described in Materials 
Research & Standards, April 1963, pp. 283-284) for the measurement of 
tensile strength. The apparatus consisted of a circular cylindrical 
specimen, which is compressed diametrically between two flat plates. The 
maximal tensile stresses develop normally to the loading direction across 
the loaded diameter, and are proportional to the applied load. Loading 
produces a biaxial stress distribution within the specimen. The maximal 
tensile stress that acts across the loaded diameter is represented by the 
following formula: 
##EQU1## 
wherein: TS is the maximal tensile strength; P is the applied load; D is 
the specimen diameter and t is the thickness of the specimen. 
This method of testing enables to determine substantially only the tensile 
strength, rather than shear or compressive failures. In the 
diametral-compression specimen, the amount of material subjected to stress 
is proportional to both the length and diameter. It has been found that 
antimony oxide alone cannot be compressed to a compacted form, without the 
aid of additives, by using pressures as high as 500-2000 Kg/sq. cm. By 
incorporating an organic flame retardant material, in amounts ranging from 
10% to 90%, it was surprisingly found that strong granules containing 
antimony oxide can be obtained, whose diametral crushing strength is 
higher than 0.3 kg/sq. cm. Table II below summarizes the results for the 
diametral crushing strength (DCS) of granules obtained from mixtures of 
antimony oxide (AO) with two fire-retardant compounds, viz., DECA and 
tetrabromobisphenol A (TBBA). 
TABLE II 
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Specimen Composition Pressure 
Run wt % applied 
DCS 
No. wt % AO.sup.(1) 
wt % DECA.sup.(2) 
TBBA.sup.(3) 
(k/g) kg/cm.sup.2 
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1 90 -- 10 2000 3.8 
2 75 -- 25 2000 2.8 
3 75 25 -- 2000 0.6 
4 50 50 -- 2000 1.2 
5 50 -- 50 2000 8.6 
6 25 37.5 37.5 2000 4.4 
7 25 75 -- 1000 0.9 
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.sup.(1) antimony oxide produced By Anzon (Timonox White Star .TM.) 
.sup.(2) DECA Produced by Bromine Compounds Limited 
.sup.(3) TBBA Produced by Bromine Compounds Limited 
From the above table it can be seen that it is possible to obtain high 
diametral crushing strengths, and further that the value of the CDS can be 
tailored to the desired requirements by controlling the composition of the 
FR agent produced and the pressure employed. 
The following examples illustrate the preparation of granular FR 
compositions. In all compaction experiments, a CS-25 compactor model 
(Bepex, Germany) was employed, unless otherwise indicated. In all 
experiments the hydraulic pressure was 40 bar, the pressure of the 
accumulator was also 40 bar and the pressure force was 70 kN. In all 
examples compaction is obtained in the absence of a binding agent. 
EXAMPLE 2 
800 g of octabromodiphenyl ether (OCTA) were fed through a screw feeder to 
the CS-25 compactor, using a roll speed of 7 rpm. The compacted material 
leaving the compactor, in the form of briquettes, was fed to a screen 
granulator which broke the briquettes produced by the compactor. The 
screen placed at the bottom of the granulator permitted to obtain the 
separation of the granules having the desired size-distribution, while 
granules having smaller size-distributions were recycled to the compactor. 
57% of the throughput of the granulator was found to have the desired 
size-distribution (2-4 mm), and 43% thereof was recycled to the compactor. 
EXAMPLE 3 
Operating as in Example 2, but using a mixture of 75% OCTA and 25% Antimony 
Oxide, it was chosen to produce granules having a size-distribution of 2-3 
mm. 30% of the material leaving the granulator was found to have the 
desired size-distribution, and the rest was recycled to the compactor. As 
it will be apparent to the man of the art, restriction of the range of 
sizes of the product results in a much higher recycle ratio, as expected. 
EXAMPLE 4 
Example 3 was repeated, but using pure DECA as the material to be 
granulated, and with a roll speed of 5 rpm. The results obtained were as 
in Example 3. 
EXAMPLE 5 
Example 2 was repeated, but using a mixture of 75% DECA and 25% AO. About 
50% of a product, having a required size-distribution of 2-4 mm, was 
recovered from the granulator. 
EXAMPLE 6 
Example 3 was repeated, using PBB-PA as the material to be granulated, and 
with a roller speed of 12.5 rpm. About 30% of the throughput was recovered 
as granulated material having the desired size-distribution of 2-3 mm, and 
the rest was recycled to the compactor. 
EXAMPLE 7 
Example 6 was repeated, using a mixture of 73.1% PBB-PA, 24.4% Sb.sub.2 
O.sub.3 and 2.5% of calcium stearate. The results obtained were comparable 
to those of Example 6. 
EXAMPLE 8 
Example 6 was repeated, but using hexabromocyclododecane (HBCD) as the 
material to be granulated. 25% of the material having the desired 
size-distribution of 2-3 mm was recovered from the granulator, and the 
remaining fractions were recycled to the compactor. 
EXAMPLE 9 
Example 2 was repeated, but using a L 200/50 P compactor (Bepex), with a 
pressure force of 40 kN, and a mixture of 77% HBCD, 19.3% tribromophenyl 
allyl ether and 3.7% lubricants and heat stabilizers. 54% of the 
throughput of the granulator was found to have the desired 
size-distribution (2-4 mm). 
The following examples illustrate the preparation of flame retarded 
polymeric materials, using the compositions according to the invention and 
compositions known in the art. 
EXAMPLE 10 
Three different runs were carried out, to prepare flame retarded high 
impact polystyrene (HIPS), using as the FR agent three different 
compositions: DECA in powder form, DECA is granulated (compacted) form, 
obtained in Example 4, and a mixture of 75% DECA and 25% AO, in compacted 
form (granules), obtained in Example 5. In all cases, care was taken to 
obtain a product having an identical total Br content of 10%. 
The granules (and the DECA powder) were in each case thoroughly mixed with 
the HIPS (Galiren Q 88-5, produced by Israel Petrochemical Enterprises) by 
dry mixing, and then fed into a Buss Kneader RR 46 type extruder (Buss 
Ltd., Switzerland) at a processing temperature of 160.degree.-190.degree. 
C. Specimens were prepared by injection moulding at 
210.degree.-230.degree. C., with an injection moulder machine of the type 
Allrounder-221-75-350 (Arburg). The FR HIPS so obtained was tested in each 
case for its FR and general properties, and the results of these tests are 
summarized in Table III. 
TABLE III 
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Test Test Test 
FORMULATIONS No. 1 No. 2 No. 3 
______________________________________ 
Components % 
HIPS 83 83 83 
Tinuvin P* 0.5 0.5 0.5 
Tinuvin 770* 0.5 0.5 0.5 
AO 4.0 4.0 -- 
DECA (powder) 12.0 -- -- 
DECA (compacted) 
-- 12.0 -- 
DECA (75%) + AO (25%) 
-- 13 16.0 
(compacted) 
Br content 10.0 10.0 10.0 
Properties 
UL-94 rating V-O V-O V-O 
Flaming time, sec 
0 8 4 
LOI % 23.7 22.3 23.6 
HDT .degree.C. (264 psi) 
63.8 65.4 63.4 
Izod notched impact, J/m 
49 63 64 
Elongation at break, % 
25.5 -- 19 
U.V. stability (DE, 24h) 
36.5 -- 37.5 
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*U.V. stabilizers (CibaGeigy AG) 
EXAMPLE 11 
Three different runs were carried out, to prepare flame retarded 
poly(butyleneterephtalate) (PBT), using as the FR agent three different 
compositions: PBB-PA in powder form, PBB-PA in granulated (compacted) 
form, obtained in Example 6 (composition I), and a mixture of 73.1% 
PBB-PA, 24.4% AO and 2.5 calcium stearate, in compacted form (granules), 
obtained in Example 7 (composition II). 
The FR agent was in each case thoroughly mixed with the PBT, and processed 
as in Example 10. The processing temperature was 260.degree.-275.degree. 
C. and the temperature of injection was 240.degree.-250.degree. C. The 
results of these tests are summarized in Table IV below. 
TABLE IV 
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non compacted compacted 
FORMULATIONS compacted (comp. I) (comp. II) 
______________________________________ 
Components % 
PBT GFR 87 87 87 
Arnite TV4-261* 
PBB-PA 8 -- -- 
Calcium Stearate (CS) 
1 1 -- 
A.O. white star** 
4 4 -- 
PBB-PA (compacted) 
-- 8 -- 
PPB-PA + AO + CS 
-- -- 13 
Flammability 
LOI 29.2 29.5 29.4 
UL-94, 1.6 mm VO VO VO 
HDT .degree.C. 
191.7 198.2 198 
Impact Izod, 82.7 69.4 75.0 
Notched (J/m) 
Tensile Properties 
Maximal Strength, MPa 
102.3 99.8 101.0 
Yield strength, MPa 
92.6 82.3 90.0 
Elongation at break, % 
2.6 2.7 2.5 
MODULUS, Mpa 6900 6670 6800 
Shore Hardness 
75.5 75.5 75.2 
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*Glass-fiber reinforced containing 30% glass fibers (Akzo) 
**Timonox White Star (Anzon) 
The data reported in the above tables have been obtained according to the 
following standard tests. 
Melt flow index: flow rates by extrusion plastometer (ASTM D 1238-79), on 
an extrusion plastometer Tinius Olsen Model Ve 4-78. 
Flammability: UL-94 vertical burning test in a flammability hood (according 
to UL); and Limiting oxygen index (LOI) (ASTM D 2863-77) on a FTA 
Flammability Unit Stanton Redcroft. 
Tensile yield strength; Elongation at break at yield and Modulus: (ASTM D 
638-82) on a Zwick 1435 material testing machine. 
Izod notched impact energy: (ASTM D 256-81) on a Pendulum impact tester 
type 5102 Zwick. 
Tensile impact energy: (ASTM D 1822-79) on a Pendulum impact tester type 
5102 Zwick. 
HDT: Deflection temperature under flexural load (18.5 kg/cm.sup.2) (ASTM D 
648-72) on a CEAST 6055. 
U.V. Stability: Accelerated weathering test--irradiation for 250 hrs and 
measuring of the color change by color deviation, on an Accelerated 
Weathering Tester Q-U-V (B-lamps), (The Q-Panel Co.). 
Color deviation: Color measurement and comparison with reference specimen, 
on a Spectro Color Meter SCM-90, (Techno-Instruments Ltd.). 
The above examples and description have been given for the purpose of 
illustration, and are not intended to be limitative. Many variations can 
be effected in the various compositions, methods and processes, without 
exceeding the scope of the invention.