Ultraviolet light-stable ignition resistant thermoplastic molding compositions

The novel compositions of this invention are ignition resistant thermoplastic compositions comprising in admixture a thermoplastic resin and an ignition resistant additive selected from the group consisting of: at least one unsymmetrical carbonic acid ester of the general formula ##STR1## at least one unsymmetrical ether of the general formula EQU R.sup.2 --O--R.sup.3 ; and a mixture of at least one unsymmetrical carbonic acid ester and at least one unsymmetrical ether; wherein R, R.sup.1, R.sup.2 and R.sup.3 are selected from the group consisting of a halogenated aryl group, a halogenated alkyl group, a halogenated ether group, and mixtures thereof, containing a halogen selected from the group consisting of Br, Cl, I, Fl, and mixtures thereof, wherein R and R.sup.1 are dissimilar and R.sup.2 and R.sup.3 are dissimilar.

BACKGROUND OF THE INVENTION 
This invention relates to new and novel compounds, and in particular to 
ignition resistant polymer compositions containing the new and novel 
compounds. 
Ignition resistance has been found to be a desirable quality for various 
thermoplastic compounds. These thermoplastic compounds are often used in 
business machine and office equipment structures and in electronics and 
telecommunications equipment, for example, in which malfunctioning 
electrical components or other sources of ignition pose a threat of fire. 
Other uses include thermoplastics for home construction and tools of 
various types. Thermoplastic resins exhibit differing ignition 
temperatures, but in general will support combustion after the source of 
ignition is removed, at least for several seconds. This may be a 
sufficient time period to cause substantial damage to the structure itself 
and also to enable the ignition of surrounding materials. 
However, the time of combustion can be significantly reduced when an 
ignition resistant compound is incorporated into the thermoplastic resin. 
A number of ignition resistant compounds have been identified to date. 
Many of these compounds contain halogens and have been used successfully 
with thermoplastics. However, two problems have been encountered with 
these. First, their use tends to adversely affect the physical properties, 
notably impact resistance, of the thermoplastic, and second, their use 
also tends to impart substantially increased ultraviolet and visible light 
instability to the thermoplastic, which is itself in many cases already 
somewhat unstable in this area. This latter problem, which results in 
increasing discoloration with time, harms the commercial desirability of 
the final product. 
Therefore, it would be desirable to have a group of compounds that impart 
both improved impact strength and improved ultraviolet light stability, as 
well as ignition resistance, when incorporated into a thermoplastic 
composition. The present invention is such a group of compounds. 
SUMMARY OF THE INVENTION 
The novel compositions of this invention are ignition resistant 
thermoplastic compositions comprising in admixture a thermoplastic resin 
and an ignition resistant additive selected from the group consisting of: 
at least one unsymmetrical carbonic acid ester of the general formula 
##STR2## 
at least one unsymmetrical ether of the general formula 
EQU R.sup.2 --O--R.sup.3 ; and 
a mixture of at least one unsymmetrical carbonic acid ester and at least 
one unsymmetrical ether; 
wherein R, R.sup.1, R.sup.2 and R.sup.3 are selected from the group 
consisting of a halogenated aryl group, a halogenated alkyl group, a 
halogenated ether group, and mixtures thereof, containing a halogen 
selected from the group consisting of Br, Cl, I, F, and mixtures thereof, 
wherein R and R.sup.1 are dissimilar and R.sup.2 and R.sup.3 are 
dissimilar. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to the present invention, the ester or ether to be used as an 
ignition resistant additive must be unsymmetrical in order to impart 
improved ultraviolet and visible light stability and to maintain the 
polymer's physical properties, as well as to optimize ignition resistance. 
The unsymmetrical carbonic acid esters and ethers comprise hybrid 
compounds that demonstrate the improved characteristics when compared with 
either symmetrical parent compound. Thus, it is important that, in the 
general formulas noted above, R and R.sup.1 are dissimilar and R.sup.2 and 
R.sup.3 are dissimilar. However, R may of course be the same as R.sup.2 or 
R.sup.3, R.sup.1 may be the same as R.sup.2 or R.sup.3, and so forth. 
Possible halogens in this invention include bromine, chlorine, iodine, 
fluorine and mixtures thereof. For example, it was found that 
unsymmetrical octabromodiphenyl carbonate, i.e., pentabromophenyl 
2,4,6-tribromophenyl carbonate, was superior in its improvement of 
qualities when compared with either a symmetrical 
bis(2,4,6-tribromophenyl) carbonate or a symmetrical decabromodiphenyl 
carbonate; thus, bromine is the preferred halogen. Increased loading 
levels of the additive increases the ignition resistance of the 
thermoplastic composition. However, acceptable ignition resistance can be 
attained using this compound at a level that does not substantially 
interfere with the polymer's integrity. For this, the additive may 
preferably be added in an amount within the range of about 5 percent to 
about 25 percent by weight of halogen in the overall composition, and more 
preferably within the range of about 10 percent to about 15 percent. The 
same loading levels also apply when other unsymmetrical compounds of the 
present invention are used in ignition resistant compositions. 
Processing temperatures for the thermoplastic resin with the selected 
ignition resistant compound or compounds are those that would be customary 
for ignition resistant thermoplastic compositions in general. In this 
invention, the thermoplastic resin serves as the polymer matrix in which 
the hybrid compound is an additive. Among possible thermoplastic resins 
used here are polystyrenes, homopolymers and copolymers of acrylonitrile, 
styrene, vinyl acetate, vinylidene halides, butadiene and isoprene, and 
alloys and blends including but not limited to polycarbonate/acrylonitrile 
butadiene styrene (ABS), polyphenylene ether/high impact polystyrene, 
polyphenylene oxide/high impact polystyrene, ABS/polyvinyl chloride, 
styrene acrylonitrile (SAN)/ethylene propylene diene rubber (EPDM) 
terpolymer and others. Generally, blends and alloys combining one or more 
of the following are suitable for the present invention: ABS; SAN; 
polycarbonate; polyolefins; polyphenylene oxide; polyphenylene ether; 
polystyrene; and polyvinyl chloride. Of these, polystyrene, ABS and 
SAN/EPDM are preferred resins. Other additives may also be used without 
interfering with the composition's inherent ignition resistance. These 
include heat stabilizers, ultraviolet light stabilizers, impact modifiers, 
pigments, drip suppressants and the like. 
The unsymmetrical ester or ether of the structure noted is incorporated by 
melt-blending it into the thermoplastic resin. This formulation may then 
be molded into the desired configuration. Various molding methods which 
may be used are: injection molding; compression molding; vacuum forming; 
injection blow molding; structural foam including conventional low 
pressure, high pressure and expanding mold using either chemical or 
physical blowing agents; extrusion, including profile, pipe, wire and 
cable, sheet, and coextrusion; coinjection molding; and thermoforming. A 
synergist is often used to increase the ignition resistance of the 
composition without adding more of the ignition resistant compound. 
Antimony trioxide is the most commonly used synergist for this purpose, 
but other possible synergists include zinc borate, other boron compounds, 
tin oxide, zinc oxide, aluminum trioxide, trihydroxide and mixtures of 
these. When used, the level of the synergist is preferably up to about 50 
percent based on the weight percent of halogen in the overall composition, 
more preferably within the range of about 25 percent to about 40 percent, 
and most preferably within the range of about 30 percent to about 35 
percent. 
Where a mixed carbonic acid ester is chosen, it may be a polyhalodiphenyl 
carbonic acid ester, preferably octabromodiphenyl carbonate of the formula 
##STR3## 
where both R and R.sup.1 are halogenated phenyl groups, and unhalogenated 
sites may be either hydrogen or methyl groups. If hydrogen groups are 
located at these sites, the compound is pentabromophenyl 
2,4,6-tribromophenyl carbonate. Various combinations of halogenated alkyl 
and aryl groups are also possible, such as in a hybrid compound having a 
trihaloneopentyl group and a halogenated phenyl group, for example: 
##STR4## 
This compound, 2,4,6-tribromophenyl tribromoneopentyl carbonate, would 
exhibit improved ultraviolet light stability over either the symmetrical 
bis(tribromoneopentyl) carbonate parent or the symmetrical 
bis(2,4,6-tribromophenyl) carbonate parent. 
Where a mixed ether is chosen, the same possiblities apply, in which at 
least one of R.sup.2 and R.sup.3 may be a halogenated alkyl group, a 
halogenated aryl group, or a halogenated ether group. An example of a 
mixed ether that would exhibit improved qualities is 
##STR5## 
This unsymmetrical diether, pentabromophenoxy 2,4,6-tribromophenoxy 
ethane, would show improved light stability over either a 
bis(pentabromophenoxy)ethane or a bis(2,4,6-tribromophenoxy)ethane. 
Other mixed carbonic acid esters and mixed ethers are also included within 
the scope of this invention. It is important to note that where a 
halogenated alkyl group is being used in this invention, it may be either 
a straight-chain or branched alkyl group. Comparisons with the performance 
of a hybrid compound are essentially limited to the performance of the two 
corresonding parent compounds, since obviously a wide variation in 
qualities will be found among the hybrid compounds. Preparation of the 
hybrid and mixed carbonic acid esters is by methods well known in the art. 
For example, the mixed carbonic acid esters can be made by reacting an 
alcohol with phosgene in an about 1:1 mole ratio to produce the 
chloroformate. This chloroformate, which may be first isolated if desired, 
is then reacted with a second alcohol, again in an about 1:1 mole ratio. 
Both reactions are generally catalyzed by a weak base, commonly pyridine. 
Temperature and pressure may be varied to suit the desired outcome. Upon 
completion of the reaction, the ester is recovered by commonly used 
methods such as crystallization. The mixed ethers may also be prepared in 
a variety of well-known processes.

The following example is set forth to more fully and clearly show the 
present invention. It is intended to be, and should be construed as being, 
merely illustrative and not limitative of the invention. Unless otherwise 
indicated, all parts and percentages are by weight. 
EXAMPLE 1 
About 81 g of unsymmetrical octabromodiphenyl carbonate (i.e., 
pentabromophenyl 2,4,6-tribromophenyl carbonate) was melt blended with 
about 567 g of acrylonitrile butadiene styrene and about 27 g of antimony 
trioxide having a particle size of less than 2 .mu.m. The 
octabromodiphenyl carbonate had been prepared earlier by crystallization 
from methylene dibromide in a commonly known process. 
The formulation was prepared on a Farrel Variable Roll Speed, Fixed Roll 
Friction, 6".times.13" 2-Roll Laboratory Mill according to the following 
conditions: 
Variable Roll: 35 rpm, 
Front Roll: 196.degree. C..+-.3.degree. C., 
Back Roll: 168.degree. C..+-.3.degree. C., 
Time/Sample: 19 minutes. 
The formulation was then used to prepare compression molded specimens which 
were used for flammability and ultraviolet light stability testing. 
Standard molding techniques were employed. The Underwriters' Laboratory 
Standard UL-94 Test (1982) was chosen for flammability testing because it 
is used to determine flammability ratings for office equipment and 
business machine parts, among other things. Under this test, a rating of 
V-0 was recorded. 
The burn time of the unsymmetrical octabromodiphenyl carbonate composition 
was then compared with that of the two symmetrical parent compounds, 
bis(2,4,6-tribromophenyl) carbonate and decabromodiphenyl carbonate 
compounded with the same amount of antimony trioxide. 
______________________________________ 
Compound in ABS Composition 
Total Burning Time, Sec. 
______________________________________ 
Unsymmetrical pentabromophenyl 
0 
2,4,6-tribromophenyl carbonate 
Symmetrical bis(2,4,6-tribromo- 
&gt;200 
phenyl) carbonate 
Symmetrical decabromodiphenyl 
.about.226 
carbonate 
______________________________________ 
The specimens were also used for ultraviolet light exposures to determine 
stability. Long term, low intensity exposures were performed on an Atlas 
HP-UV Accelerated UV Exposure Apparatus for about 307 hours at ambient 
temperature and humidity. Measurement was with a Dian Match Scan 
Spectrophotometer. Under this test, the result obtained showed a .DELTA.E 
value of about 7.37 for the octabromodiphenyl carbonate (i.e., 
pentabromophenyl 2,4,6-tribromophenyl carbonate). This .DELTA.E value was 
then compared with that of two other similarly prepared ABS compositions 
made using other commercially available ignition resistant additives. The 
results were as follows: 
______________________________________ 
Ignition Resistant Additive 
.DELTA.E 
______________________________________ 
bis(tribromophenoxy)ethane 
13.48 
octabromodiphenyl oxide 
26.14 
pentabromophenyl 7.37 
2,4,6-tribromophenyl carbonate 
______________________________________ 
The lower the .DELTA.E value, the less the color discoloration with time. 
Another comparative reading, this time of the values for the symmetrical 
parent compounds, showed a .DELTA.E for the bis(2,4,6-tribromophenyl) 
carbonate of 32.00, and for the decabromodiphenyl carbonate of 17.45. 
Thus, the unsymmetrical compound showed a significant improvement in 
ultraviolet and visible light stability over its symmetrical parent 
compounds. 
Finally, impact strength testing was performed on injection molded 
specimens of the same formulation. These specimens were conditioned 
according to ASTM D 618 (i.e., 23.degree. C. and 50 percent relative 
humidity) and testing was performed under the same conditions. The Notched 
Izod Impact Test results were obtained in adherence to ASTM D 256, Method 
A, and the readings on this test for unsymmetrical octabromodiphenyl 
carbonate showed a Notched Izod Impact Strength of 2.28 ft-lb/in, which 
compares very favorably with the impact strength of ABS with the 
symmetrical bis(2,4,6-tribromophenyl) carbonate (0.86 ft-lb/in) or with 
the symmetrical decabromodiphenyl carbonate (0.83 ft-lb/in). 
EXAMPLE 2 
ABS was also compounded with the unsymmetrical hybrid compound, 
tribromoneopentyl 2,4,6-tribromophenyl carbonate, and its symmetrical 
parent compounds, bis(tribromoneopentyl) carbonate and 
bis(2,4,6-tribromophenyl) carbonate. Preparation methods and amounts, 
including amount of the synergist antimony trioxide, were identical with 
those described in Example 1. Unlike the brominated diphenyls, a 
comparison between .DELTA.E and the UL-94 ratings approaches a linear 
relationship according to the kind of bromine: the more aromatic the 
compound, the greater the .DELTA.E and the less the ignition resistance. 
______________________________________ 
Compound in ABS Composition 
.DELTA.E 
UL-94 Izod (ft-lb/in) 
______________________________________ 
Bis(tribromoneopentyl) 
15.29 V-2 1.46 
carbonate 
Tribromoneopentyl 2,4,6- 
16.86 V-2 1.76 
tribromophenyl carbonate 
Bis(2,4,6-tribromophenyl) 
32 HB 0.86 
carbonate 
______________________________________ 
The bis(2,4,6-tribromoneopentyl) carbonate and the tribromoneopentyl 
tribromophenyl carbonate received comparable V-2 ratings, but this was due 
to dripping. The burn times were overall longer for the hybrid compound, 
although not substantially so (13.5 seconds cf. 26 seconds). 
It is hypothesized that the lower thermal properties of this group in 
general as compared with the carbonates of Example 1, along with the 
variable introduced by comparing two types of bromine (aromatic cf. 
aliphatic), may account for the less significant differences as to 
ultraviolet color stability and ignition resistance between the 
unsymmetrical hybrid compound and its symmetrical parent compounds. 
However, again an improvement in impact strength, as measured by the 
Notched Izod results, is seen in compositions employing the unsymmetrical 
compound as compared with those employing the symmetrical parent 
compounds. It may be that there is less crystallization of the 
unsymmetrical compounds when formulated into the resin, and the improved 
dispersion contributes to the higher impact strength. 
EXAMPLE 3 
About 120 g of pentabromophenoxy 2,4,6-tribromophenoxy ethane is 
melt-blended according to the procedures in Example 1 with about 54 g of 
zinc borate and about 445 g of a styrene acrylonitrile (SAN)/ethylene 
propylene diene rubber (EPDM) terpolymer blend. This provides a 
composition having ignition resistance and improved ultraviolet light 
stability when compared with an SAN/EPDM composition containing either 
bis(pentabromophenoxy)ethane or bis(2,4,6-tribromophenoxy)ethane.