Abstract:
A brominated epoxy oligomer of the formula ##STR1## having a molecular weight of least 3,000, useful as a flame retardant additive for polypropylene and ethylene propylene copolymers is described.

Description:
FIELD OF THE INVENTION 
     This invention relates to propylene polymer compositions, particularly based on polypropylene homopolymers or ethylene-propylene copolymers, having good flame retardancy and high thermomechanical stability, as measured by the heat distortion temperature, particularly compositions which contain brominated flame retardant additives. 
     BACKGROUND OF THE INVENTION 
     The expression &#34;polypropylene polymers&#34;, when used hereinafter without further specification, comprises polypropylene and ethylene-propylene copolymers. Polypropylene and ethylene-propylene copolymers have low flame retardancy and in particular fall short of the high standards required in the electronic industry. For this reason, they must be compounded with high amounts of flame retardants (hereinafter also designated as &#34;FR&#39;s&#34;). However, the compositions of propylene polymers and flame retardants known in the art have considerable disadvantages, e.g., brittleness and poor mechanical properties, particularly when high amounts of flame retardants are required to impart the desired properties, and in particular, insufficient thermomechanical stability, as evidenced by a low heat distortion temperature under load (hereinafter HDT). 
     Flame retardancy can in principle be achieved in the art by the addition of brominated organic compounds. One of the most effective of such compounds known in the art is decabromodiphenyloxide (hereinafter Deca), but such an additive, even in combination with a synergist such as antimony trioxide, does not impart to polypropylene or propylene ethylene copolymers a high thermal mechanical stability. 
     It is a purpose of this invention to overcome the defects of previously known flame-retarded propylene polymer compositions. 
     More specifically, it is a purpose of this invention to provide propylons polymer compositions that have high flame retardancy and high heat distortion temperature under load. 
     It is another purpose of the invention to provide additives for propylons polymers that will provide high flame retardancy and a high thermal mechanical stability, and at the same time, involve no problem in compounding them with the base polymer and in working the compounded composition. 
     Other purposes and advantages of the invention will appear as the description proceeds. 
     SUMMARY OF THE INVENTION 
     The polypropylene and ethylene-propylene copolymer compositions, according to the invention, are characterized in that they contain as flame retardant a brominated epoxy oligomer having a molecular weight of at least 3,000. Preferably, the molecular weight should be from 6,000 to 70,000. 
     It should be understood that when a certain molecular weight of such an oligomer is specified hereinafter, it is not intended that it is its invariable and exact molecular weight, but rather that it is its approximate or average molecular weight, or what may be called its &#34;nominal&#34; molecular weight, viz. that indicated in its specifications by the manufacturer. 
     By &#34;brominated epoxy oligomer&#34; is meant herein a compound having the formula ##STR2## 
     wherein N is between 3.9 and 115.37. 
     Such compounds are available on the market and are manufactured, for instance, by Dead Sea Bromine Group as a series of compounds under the collective designation F-2000. Their molecular weights range from 700 upwards. They are suggested as flame retardant additives for a number of plastics, but not for propylene polymers. 
     Preferably, the brominated epoxy oligomer is added in an amount ranging from 6% by weight to 70% by weight, and more preferably between 9 and 60% by weight. All percentages mentioned in this application are by weight, unless otherwise specified. 
     Other flame retardants may be further added, in a weight ratio to the polypropylene or ethylen-propylene copolymer preferably comprised between 0.5 and 55%, preferably from 1 to 25%. Such flame retardants may be chosen from among inorganic or organic flame retardants known in the art. Examples thereof are compounds of antimony, e.g. antimony trioxide or pentoxide, of tin, e.g. tin oxide or maleate, of magnesium, e.g. magnesium hydroxide or hydrotalcite, of aluminum, e.g. aluminum trihydrates, of iron, e.g. ferric oxide, or of bismuth; silicone systems; and organic flame retardants, such as organic compounds containing in their molecule bromine, chlorine, phosphorus, bromine and phosphorus, or melamine compounds, and their combinations. 
     Other additives, known in the art as additives for polymeric compositions, can also be added. Examples of such additives are reinforcing glass or carbon fibers, various fillers, stabilizers, lubricant processing aids, impact modifiers, pigments, compatibilizers, anti-dripping agents, etc. 
     While the invention is directed to compositions based on polypropylene or ethylene-propylene copolymers, such base polymers can be associated, in alloy-like mixtures, with other known polymers, such as polyethylene, polyamides, PBT/PET, fluorlasted homo- and copolymers, etc. 
     It has been found that brominated epoxy oligomers having molecular weight below 3,000 are not effective for the purposes of imparting flame retardancy to propylons polymers. In the first place, they have a poor compatibility with the polymers, as evidenced by the impossibility of processing the mixtures of propylene polymers and such low molecular weight brominated epoxy oligomers without phase separation of the components. Moreover, even when it is possible to overcome the processing difficulties, the resulting compositions have very low viscosity properties and are difficult to handle after molding. 
     Surprisingly, the brominated epoxy oligomers with a molecular weight of at least: 3,000 are much easier to compound with the propylons polymers and to mold by injection. Moreover, the resulting compositions have better flame retardancy on a bromine basis than those containing commonly used FR additives of the prior art. 
     In view of the aforesaid surprising fact, the process of preparing a flame retarded propylene polymer composition which comprises compounding the propylene polymer with a brominated epoxy oligomer having a molecular weight of at least 3,000, and preferably 6,000 to 70,000, is also an aspect of this invention. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The compositions of propylene polymer and brominated epoxy oligomer, described in the following examples and the properties of which are set forth in the following tables, were prepared by compounding a mixture of propylene polymer and brominated epoxy oligomer and pelletizing it in a Brabender twin-screw extruder heated with a temperature profile as follows: 150°-190°-210°-220° C. The granules obtained were injection molded in a press heated at 210°-230°-240°-235° C. to obtain samples for testing. 
     The brominated epoxy oligomers used were the following compounds of the F-2000 series produced by Dead Sea Bromine Group: F-2001, F-2016, F-2300 H and F-2400. Their molecular weights were respectively: 1000, 1600, 20,000 and 40,000. 
    
    
     EXAMPLE 1 
     (Comparative) 
     Mixture of polypropylene with MFI 20 and brominated epoxy oligomers having a molecular weight of 1,000 and 1,600 were compounded and pelletized as hereinbefore described. The brominated epoxy with the molecular weight of 1,000 was impossible to process with the polypropylene and a strong phase separation was observed. The oligomer having the molecular weight 1,600 was difficult but possible to compound and mold, but a melt flow index of 850 was obtained, indicating that the mixture is very difficult to mold, and moreover, is difficult to handle after molding. The results are set forth in Table 1. 
     
                                           TABLE I__________________________________________________________________________Molecular weight ofthe brominated epoxy     1000        1600      Reference (No. FR)__________________________________________________________________________Composition %Polypropylene MFI 20     88.5        46.1      100(230 C.-2.16 Kg)Brominated epoxy     9           42oligomerAntimony trioxide     2.5         11.9Compounding     not possible to mix because                 difficult to                           OK     of phase separation                 compound     Impossible to add more     brominated epoxyInjection molding     --          very difficult to mold                           OKMelt flow index     --          350        20(230 C., 2.16 Kg)__________________________________________________________________________ 
    
     Example 2 
     Compositions of polypropylene, flame retarded by means of various FR additives have been prepared as hereinbefore described, and their properties are set forth in Table 2, The compositions listed in said table that are according to the invention (columns 2,3 and 4) additionally comprise an inorganic FR additive, specifically antimony trioxide. For comparative purposes, a composition comprising Deca as flame retardant, also with antimony trioxide, was prepared (column 5), the amount of FR additive being such as to obtain a flame retardancy rating of UL-94 V-0. The brominated epoxy oligomer of column 2 had a molecular weight of 1,600 and the composition is the same as illustrated in the second column of Table 1 and has the same problems- Columns 3 and 4 illustrate the properties of compositions which have a molecular weight above 3,000, precisely 20,000 and 40,000 respectively. These compositions, as well as the comparative Deca flame retarded composition, contained approximately the same amount (12% or thereabout) of antimony trioxide. The first column of Table 21 sets forth, for reference purposes, the properties of polypropylene MFI 20 free from any FR additives. It is seen that the HDT of that polypropylene is 45° C. which is considered a low value, detrimental for application in the electronic industry. The addition of 24.1% of Deca and 12.2% of antimony trioxide provided the required flame retardancy, but did not substantially improve the thermomechanical properties, since the composition of column 5 has an HDT value of 59° C. Non-halogenated flame retardants, such as magnesium hydroxide, as shown in column 6, can provide the required flame retardancy, but only in very large amounts--about 65% in this case--and this has a negative influence on the properties of the compound. Further, despite the high level of magnesium hydroxide, the HDT value is 61° C., and this is still rather low, 
     The compositions illustrated in columns 8 and 4 were prepared with brominated epoxy oligomers having molecular weight 20,000 (compound F-2300 H) and 40,000 (compound F-2400) respectively and have surprisingly high HDT values of more than 90° C. These values are even higher than those usually obtained with high impact polystyrene or ABS used in the electronic industry. The composition prepared with brominated epoxy oligomers of molecular weight 1,600 (compound F-2016), not only was hard to process, as set forth in Example 1, and only with difficulty yields samples for evaluation, but the HDT value is substantially lower than those obtained with the compositions according to the invention. 
     
                                           TABLE II__________________________________________________________________________Composition no.      1    2    3     4     5   6__________________________________________________________________________FR type    Reference           Br Epoxy                Br Epoxy                      Br Epoxy                            DECA                                Magnesium      (No. FR)           MW 1,600                MW 20,000                      MW 40,000 hydroxide                                Non-halog-                                enated FRComposition %Polypropylene MFI 20      100  46.1 48.7  52.4  63.7                                35(230° C., 2.16 Kg.)Flame retardant 42   40    36.3  24.1                                65Antimony trioxide           11.9 11.3  11.3  12.2Bromine content %      0    21   20    18.5  20  0Flame retardancy:(UL94-3.2 mm)Max. Flaming time. sec           1    0     9     3   3Total Flaming time. sec           1    0     17    17  18Dripping        0    0     0     0   0Rate       non-rated           V-0  V-0   V-0   V-0 V-0Impact notched IZOD,      18   15   24    13    20  11J/mHDT, Celsius (1.8 MPa)      53   63   97    96    59  61MFI, g/10 min      20   350  41    27    23  &lt;5(230 C., 2.16 Kg)__________________________________________________________________________ 
    
     Example 3 
     Compositions containing a brominated epoxy oligomer with a molecular weight of 40,000 (compound F-2400) have been prepared as hereinbefore described. Samples produced by injection molding have been tested, and HDT values obtained are set forth in Table. 3. 
     This example illustrates the surprising efficiency of the combination of brominated epoxy oligomers according to the invention and polypropylene to achieve high thermomechanical properties, evidenced by high HDT values. As a reference, column 7 in Table 3 refers to a composition of polypropylene reinforced with 20% of glass fiber and it is seen that the HDT obtained is only 93° C., while the invention permits to achieve an HDT above 100 without the addition of glass fibers. 
     
                       TABLE III______________________________________Compositionno.      1       2      3     4    5    6     7______________________________________FR type  Reference ← Brominated epoxy oligomer → Reference    (No. FR)MW 40,00020% glassfiberComposition %Polypropylene    100     58.6   52.5  46.3 40.2 34    80MFI2 (230 C.,2.16 KG)Flame retardant  31.4   36.3  41.2 46.1 51Antimony         10     11.2  12.5 13.7 15trioxideGlass fiber                                   20Bromine con-    0       16     18.5  21   23.5 26    0tent, %HDT, Celsius    53      83     96    101  104  108   93(1.8 MPa)______________________________________ 
    
     Example 4 
     In the compositions of this example, an ethylene-propylene copolymer, manufactured by BASF under the trade name Novolen 2600 TCX, has been compounded with brominated epoxy oligomers haying a molecular weight of 40,000 (compound F 9.400) and, for reference purposes, with Deca. The results are tabulated in Table 4. It is seen that an HDT increase of more than 20° C. is obtained by using the brominated epoxy oligomer of the invention, while no increase is noticed with Deca. 
     
                       TABLE IV______________________________________Composition no.        1           2         3______________________________________FR type      Reference   Br. Epoxy DECA        (No. FR)    MW 40,000Composition, %PP block copolymer        100         58.6      69.7(Novolen 2600 TCXBASF)Flame retardant          31.4      23Antimony trioxide        10        7.3Bromine content, %        0           18        18HDT, Celsius (1.8        48.8        69.1      48.5MPa)______________________________________ 
    
     Example 5 
     All the compositions described in the following table have been pelletized on a twin screw co-rotating extruder Berstorff with the following temperature profile: 
     60-175-185-194-210-223-225-230 degrees Celsius. 
     The speed of the screws was 350 rpm. 
     The granules obtained were molded by injection in an Allrounder Arburg press with the following conditions: 
     180-200-220-230 degree Celsius. 
     Table V below summarizes properties of molded parts: 
     
                                           TABLE V__________________________________________________________________________Polypropylene flame retarded by Brominated epoxy oligomersInfluence of fillers and other flame retardants on heat distorsiontemperatureType of additive   ←CaCO.sub.3 →                     ←Mg(OH).sub.2 →                            ←TALC→__________________________________________________________________________Composition, %PP Hipol J400     85               46.4                  37.2                     85 43.6                            85 43.6(Mitsui)Brominated epoxy oligomer Mw 30,000              0               29.3                  35  0 31.4                             0 31.4(Dead Sea Bromine Group)CaCO.sub.3 Avgil 600             15               15 15Talc Extra 510                   15 15(Luzenac)Magnesium hydroxide FR-20 grade 640                     15 15(Dead Sea Bromine Group)Antimony trioxide (Amspec)              0               9.3                  12.8                      0 10   0 10Properties:Flame Retardancy UL 94 (3.2 mm)             NR               V-2                  V-2                     NR V-1 NR V-0RateHeat Distorsion Temperature:             59               91 93 51 90  63 991.8 Mpa degree Celsius__________________________________________________________________________ 
    
     The results in Table V illustrate the surprising efficiency of brominated epoxy oligomers with a molecular weight according to the invention to increase dramatically heat distortion temperatures of polypropylene compounds even if they are filled with calcium carbonate, magnesium hydroxide or talc. The table also illustrates the flame retardancy properties of the compounds containing the brominated epoxy oligomers. NR states that the compounds without brominated epoxy oligomers are Not Rated and consequently do not pass the UL 94 standard under these conditions. 
     While, embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried out by persons skilled in the art with many modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the claims.