Patent Publication Number: US-4927870-A

Title: Ignition resistant modified thermoplastic composition

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to ignition resistant thermoplastic compositions made with thermoplastics such as styrene-butadiene-acrylonitrile copolymers, polyesters, polycarbonates, etc. and blends thereof containing polytetrafluoroethylene, metal salts of inorganic acids and organo phosphorous compounds which act to reduce the susceptibility of such compositions to ignition and/or burning or at least to minimize the dripping of molten polymer when exposed to fire conditions. 
     Thermoplastic polymers have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance, and excellent electrical properties are required. 
     However, these polymers exhibit a brief but definite burning time when contacted with an open flame. 
     In attempts to increase the combustion resistance of thermoplastic polymers, it has been a common practice to incorporate monomeric phosphites, phosphoric acid esters, thiophosphoric acid esters containing halogenated alkyl radicals and halogenated organic compounds into the carbonate polymer. However, in order to obtain any noticeable improvement in combustion resistance, these additives and/or combinations of the additives have been employed in such large quantities that they often adversely affect some of the desirable physical properties of the carbonate polymer such as heat stability, toughness, and ultra-violet light stability. 
     In U.S. Pat. No. 3,671,487 fire retardant polyester resins comprising glass fibers, fire retardant additives such as halogen-containing compounds or phosphate compounds and fibril forming polytetrafluoroethylene (PTFE) are disclosed and claimed. The present invention represents an improvement over this patent in that the need for glass fibers and halogenated compounds has been obviated. 
     U.S. Pat. No. 4,653,496 discloses the use of a combination of halogenated compound and metal oxides for ignition resistance of the blend of polycarbonate and acrylonitrile-butadiene-styrene copolymer (ABS). However, the metal oxides result in the thermal stability of PC. 
     U.S. Pat. No. 4,692,488 discloses a blend of a polycarbonate, a copolymer of styrene and acrylonitrile, triphenylphosphate, and tetrafluoropolyethylene. Comparison example 2 (line 53, page 8) of this patent indicates that without Na 2  SO 4 , the blend of PC and ABS with triphenylphosphate and polytetrafluoroethylene give only V-1 rating. 
     British patent 1,459,648 discloses the use of triphenylphosphate, a non-combustible fibre material and polytetrafluoroethylene as flame retardant additives for PC, polyesters, and ABS. However, the patent shows that polytetrafluoroethylene resin does not prevent dripping without the addition of fibre. 
     Aromatic carbonate polymers having good flame retardant properties are shown in U.S. Pat. No. 4,626,563. However, the present invention represents an improvement over this patent also in that the need for halogenated compounds has been eliminated. The elimination of halogenated compounds is important since the presence of these compounds adversely effects the ultra-violet light stability of the polymers. 
     SUMMARY OF THE INVENTION 
     The present invention is an ignition resistant non-haloaromatic thermoplastic polymer composition comprising 
     (A) a member of the group consisting of 
     (i) a non-carbonate thermoplastic polymer or copolymer, 
     (ii) a carbonate polymer, and 
     (iii) a blend of (i) and (ii), 
     (B) 0.001 to 20% by weight of a high elastic memory polytetrafluoroethylene having a heat shrinkage equal to or greater than 15%, 
     (C) 0.1 to 30% by weight of an organic phosphate, and 
     (D) 0.001 to 10% by weight of a metal salt of an inorganic acid. 
     The first retardant carbonate polymer compositions of the present invention are suitably employed in most applications in which opaque modified polycarbonates have been previously utilized. Applications of particular interest for the utilization of the said carbonate polymer compositions of this invention are pigmented and/or colored carbonate polymers useful as: automobile parts, e.g., air filters, fan housings, exterior components, housings for electrical motors, appliances, business and office equipment, photographic equipment, and aircraft applications. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The carbonate polymers employed in the present invention are advantageously aromatic carbonate polymers such as the trityl diol carbonates described in U.S. Pat. Nos. 3,036,036; 3,036,037; 3,036,038 and 3,036,039; polycarbonates of bis(4-hydroxyphenyl)-alkylidenes (often called bisphenol-A type diols), including their aromatically and aliphatically substituted derivatives such as disclosed in U.S. Pat. Nos. 2,999,835; 3,038,365, 3,334,154, and 4,299,928; and carbonate polymers derived from other aromatic diols such as described in U.S. Pat. No. 3,169,121. 
     It is understood, of course, that the carbonate polymer may be derived from (1) two or more different dihydric phenols or (2) one or more dihydric phenols and one or more hydroxy- or acid-terminated reactants such as dicarboxylic acids, or alkylene glycols in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired. Also suitable for the practice of this invention are blends of any one of the above carbonate polymers. Also included in the term &#34;carbonate polymer&#34; are the ester/carbonate copolymers of the types described in U.S. Pat. Nos. 3,169,121; 4,287,787; 4,156,069; 4,260,731 and 4,105,633. Of the aforementioned carbonate polymers, the polycarbonates of bisphenol-A and derivatives, including copolycarbonates of bisphenol-A, are preferred. Methods for preparing carbonate polymers for use in the practice of this invention are well known; for example, several suitable methods are disclosed in the aforementioned patents which are hereby incorporated by reference in their entirety. 
     The polyesters that can be employed in the present invention are selected from the group consisting of polymeric glycol terephthalate and isophthalate esters having repeating units of the general formula: ##STR1## wherein n is a whole number of from 2 to 4, and mixtures of such esters. The preferred polyesters, for example, are poly(ethylene terephthalate), poly(1,4-butylene terephthalate), and copolyesters. Also included are the branched copolyesters of poly(1,4-butyl terephthalate) and poly(ethylene terephthalate). The following patents show the preparation of polyesters and are incorporated by reference, British 1,459,648 and U.S. Pat. No. 3,671,487. 
     Suitable polytetrafluoroethylene polymers for use in this invention are those adapted to form a fibril structure to stabilize the polymer under molten conditions. Such polymers are generally disclosed by U.S. Pat. Nos. 3,005,795, 3,671,487 and 4,463,130. The teachings of these patents are incorporated herein by reference. In addition, the polytetrafluoroethylene (PTFE) polymers must have a high elastic memory and/or have a heat shrinkage equal to or greater than 15% when tested under the following conditions. 
     Polycarbonate resin with 0.5% of PTFE was injection molded into bars having the dimensions of 5&#34;×1/2&#34;×1/16&#34; and heated at 160° C. for 1 hour. The shrinkage was measured and compared to the length of the sample before and after heating. A 75 ton Newbury molding machine is used. The molding conditions are: 
     
         ______________________________________                                    
Barrel Temperature     250° C.                                     
Mold Temperature       180° C.                                     
Screw Speed            150 rpm                                            
Pressure               1000 psi                                           
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     The results of several tests ae shown in Table 1. 
     
                       TABLE 1                                                     
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Relationship Between the Shrinkage and UL-94 for                          
Different Polytetrafluoroethylenes (PTFE)                                 
                                UL-94 at                                  
Run     PTFE*         Shrinkage 1/16&#34;                                     
______________________________________                                    
1       8              1        Fail                                      
2       DXL-6000       1        Fail                                      
3       6C            25        V-0                                       
4       60            25        V-0                                       
7       64            15        V-0                                       
8       6CN           24        V-0                                       
9       65            22        V-0                                       
10      67            22        V-0                                       
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 *Various grades of Teflon ™ from DuPont                               
 
    
     Table 1 shows that only high elastic memory PTFE is effective as an ignition resistant (IR) additive. The high elastic memory PTFE helps the polycarbonate sample contract upon exposure to a flame source and thus imparts ignition resistance to the polycarbonate. The relationship between the % shrinkage and the UL-94 test is also shown in Table 1. The PTFE that gives a polycarbonate shrinkage greater than 15% is effective as an IR additive. Some examples of PTFE that have high elastic memory such as Teflon™ 6C, 60, 64, CN, 65, and 67 are shown in Table 1. The PTFE that have a low percent of shrinkage such as Teflon™ DXL-6000 and Teflon™8 did not impart ignition resistance to the polycarbonate. 
     Suitable fluorine containing polymers are those adapted to form a fibril structure to stabilize the polymer under molten conditions. Such polymers are known to include polytetrafluoroethylene, as disclosed by U.S. Pat. Nos. 3,005,795, 3,671,487 and 4,463,130. The teachings of these patents are incorporated herein by reference. 
     The acrylic polymers suitable for this invention are well known and have a repeating unit according to the following formula: ##STR2## wherein R 1  is hydrogen, alkyl, or phenyl substituted 
     R 2  is alkyl, or phenyl substituted 
     The polyacetal polymers suitable for this invention have a repeating unit according to the following formula: ##STR3## wherein R is hydrogen or alkyl groups of 1 to 6 carbons 
     The ABS copolymers are well known and many suitable types are commercially available. Either an acrylonitrile-butadiene-styrene or an acrylonitrile-butadiene-alpha-methyl styrene may be used as the ABS component. Nuclear-substituted styrenes, for example p-methylstyrene can also be used. Particular preferred weight ratios in the ABS copolymer are 2-40% of acrylonitrile, 2-35% of butadiene, and 30-80% styrene. 
     The copolymer can be prepared by free radical polymerization, in particular by emulsion, suspension, solution or bulk polymerization. Useful methods for preparing these copolymers may be found in U.S. Pat. Nos. 2,505,349; 2,550,139; 2,698,313; 2,713,566; 2,820,773; and 2,908,661. 
     Useful inorganic acid metal salts for this invention are metal bisulfates or sulfates. Examples of useful metal sulfates are sodium sulfate, potassium sulfate, lithium sulfate, rubidum sulfate, cesium sulfate, and aluminum sulfate. The corresponding metal bisulfates are also useful. 
     The phosphorus compounds which are suitable according to the invention have the formula below. ##STR4## wherein R 1 , R 2  and R 3  are alkyl groups of 1-8 carbons, 
     or alkyl-substituted aryl groups of 7-20 carbons and &#34;n&#34; represents 0 or 1. 
     Phosphorous compounds which are suitable according to the invention are, for example, triphenyl phosphate, tricresylphosphate, diphenyl 2-ethylcresyl phosphate, tri-(iso-propylphenyl)phosphate, diphenyl methyl phosphate and diethyl phenyl phosphate. 
     The carbonate polymer compositions of the present invention are suitably prepared by combining the ingredients in effective amounts using any of a variety of blending procedures conventionally employed for polymer blends. For example, dry pellets of the carbonate polymer, and the other additives can be dry blended and the resulting dry blend extruded into the desired shape. By &#34;effective amount&#34; is meant the relative amount of the respective components that is sufficient to provide the desired polymer characteristic. 
     The amount of the fibril forming polytetrafluorethylene is preferably in the range from about 0.001 to about 20 percent and preferably in the range from about 0.1 to about 5 percent by weight based on total composition weight. 
     In addition, other additives can be included in the modified carbonate polymer composition of the present invention such as fillers (i.e., glass fibers), pigments, dyes, antioxidants, heat stabilizers, ultraviolet light absorbers, mold release agents, impact modifiers and other additives commonly employed in carbonate polymer compositions. 
    
    
     The following examples are given to further illustrate the invention and should not be construed as limiting its scope. In the following examples, all parts and percentages are by weight unless otherwise indicated. 
     EXAMPLE 1 
     Ignition resistant polyethylene terephthalate (PET) is prepared by adding 0.5 weight % polytetrafluoroethylene (Teflon™6C from Du Pont), 0.3% sodium sulfate (Na 2  SO 4 ) and 5% triphenylphosphate (TPP) to 94.2% PET base resin having an inherent viscosity of 0.59. The weighed sample is dry blended on a Lightnin blender for 1 minute with constant agitation. The resultant blended material is starve fed to a 30 mm twin screw extruder at 230° C. barrel temperature. The extruded pellets are dried in an oven at 100° C. for 3  hours and molded into bars for flammability measurements. 
     CONTROL 1 
     The procedure for example is repeated using no additives (Teflon™6C, Na 2  SO 4 , and TPP). 
     EXAMPLE 2 
     The procedure for Example 1 is repeated using the same ingredients shown above except that 50% PET and 50% polycarbonate (PC) blend is used. 
     CONTROL 2 
     The procedure for Example 1 is repeated using no additives and 50% PET and 50% PC blend. 
     CONTROLS 3-7 
     The procedure of Example 1 is repeated using a 50% PET and 50% PC blend. The various additive compositions are described in Table 3. 
     EXAMPLE 3 
     The procedure for Example 1 is repeated using 56.5 weight % of PC, 37.7 weight % of PET, 5 weight % of TPP, 0.5 weight % of PTFE and 0.3 weight % of Na 2  SO 4 . 
     CONTROL 8 
     The procedure for Example 1 is repeated using 60% PC and 40% PET and no additives. 
     EXAMPLE 4 
     The procedure for Example 1 is repeated using a blend of PC and polymethylmethacrylate. The composition of the blend and additives is described in Table 4. 
     CONTROL 9 
     The procedure for Example 1 is repeated using 75% PC and 25% polymethylmethacrylate, and no additives. 
     EXAMPLE 5 
     The procedure for Example 1 is repeated using PC and polyacetal. The composition of the blend and additives is described in Table 4. 
     CONTROL 10 
     The procedure for Example 1 is repeated using 75% PC, 25% polyacetal and no additives. 
     EXAMPLE 6 
     The procedure for Example 1 is repeated using PC and styrene-butadiene-acrylonitrile copolymer. The composition of the blend and additives is described in Table 4. 
     CONTROL 11 
     The procedure for Example 1 is repeated using 75% PC and 25% styrene-butadiene-acrylonitrile copolymer, and no additives. 
     EXAMPLE 7 
     The procedure for Example 1 is repeated using PC. The composition is described in Table 4. The extrusion and mold temperature is 250° C. 
     CONTROL 12 
     The procedure for Example 7 is repeated using no additives. 
     EXAMPLE 8 
     The procedure for Example 1 is repeated using aromatic polyester carbonate. The extrusion and mold temperature is 310° C. 
     CONTROL 13 
     The procedure for Example 8 is repeated using no additives. 
     
                       TABLE 2                                                     
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               UL-94 Test (1/16&#34;)                                         
                 Avg      Number                                          
                 time     of                                              
Sample           (sec)    Drips    Rating                                 
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Cntrl 1 PET base resin                                                    
                 100      5/5*     HB                                     
Cntrl 2 50% PET/50% PC                                                    
                 100      5/5*     HB                                     
Ex. 1  Cntrl 1 +     0.8      0      V-0                                  
       0.5% PTFE                                                          
       0.3% Na.sub.2 SO.sub.4                                             
       5.0% TPP                                                           
______________________________________                                    
 PC = polycarbonate                                                       
 PET = polyethylene terephthalate                                         
 TPP = triphenylphosphate                                                 
 PTFE = Teflon ™ 6C                                                    
 *5 bars out of 5 dripped with flame.                                     
 
    
     
                       TABLE 3                                                     
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Effects of the Additive on Ignition Resistance of                         
PC/PET Blend                                                              
                     UL-94 Test                                           
Sample               (1/16&#34;)                                              
______________________________________                                    
Cntrl 3     Cntrl 2 +    HB                                               
            0.5% PTFE                                                     
Cntrl 4     Cntrl 2 +    HB                                               
            5.0% TPP                                                      
Cntrl 5     Cntrl 2 +    HB                                               
            5.0% TPP +                                                    
            0.5% PTFE                                                     
Cntrl 6     Cntrl 2 +    HB                                               
            0.5% Na.sub.2 SO.sub.4 +                                      
            5.0% TPP                                                      
Cntrl 7     Cntrl 2 +    HB                                               
            0.5 Na.sub.2 SO.sub.4 +                                       
            0.5% PTFE                                                     
Ex. 2       Cntrl 2 +    V-0                                              
            0.5% PTFE +                                                   
            0.3% Na.sub.2 SO.sub.4 +                                      
            5.0% TPP                                                      
______________________________________                                    
 PTFE = Teflon ™ 6C                                                    
 TPP = triphenylphosphate                                                 
 
    
     This table shows that the synergism of the three components, Teflon™6C, Na 2  SO 4 , and TPP renders the blend ignition resistance. 
     
                       TABLE 4                                                     
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             Second                                                       
      PC     Polymer  TPP  PTFE  (%)                                      
Sample                                                                    
      (%)    (%)      (%)  (%)   Na.sub.2 SO.sub.4                        
                                        LOI  UL 94                        
______________________________________                                    
Cntrl 60     40 PET   0    0     0      25   HB                           
Ex. 3 56.5   37.7     5    0.5   0.3    28   V-0                          
             PET                             (1/16&#34;)                      
Cntrl 75     25       0    0     0      24   HB                           
9            PMMA                                                         
Ex. 4 66.7   22.3     10   0.7   0.3    26.8 V-0                          
             PMMA                            (1/16&#34;)                      
Cntrl 75     25 PA    0    0     0      21.5 HB                           
10                                                                        
Ex. 5 66.7   22.3     10   0.7   0.3    26   V-0                          
             PA                              (1/8&#34;)                       
Cntrl 75     25 ABS   0    0     0      24   HB                           
11                                                                        
Ex. 6 66.7   22.3     10   0.7   0.3    26.5 V-0                          
             ABS                             (1/16&#34;)                      
Cntrl 100    0        0    0     0      27   V.sub.2                      
12                                                                        
Ex. 7 98.2   0        1    0.5   0.3    NA   V-0                          
                                             (1/16&#34;)                      
Cntrl 100    0        0    0     0      NA   V.sub.2                      
13    AEC                                                                 
Ex. 8 94.2   0        5    0.5   0.3    NA   V-0                          
      AEC                                    (1/16&#34;)                      
______________________________________                                    
 AEC = aromatic polyester carbonate                                       
 PC = polycarbonate                                                       
 PET = polyethylene terephthalate                                         
 PMMA = polymethylmethacrylate                                            
 PA = polyacetal                                                          
 ABS = acrylonitrilebutadiene-styrene copolymer                           
 TPP = triphenylphosphate                                                 
 PTFE = Teflon ™ 6C                                                    
 LOI = Limiting oxygen index (ASTM D2863-70)                              
 
    
     Table 4 shows that ignition resistant (IR) combination of this invention works for a wide variety of thermoplastics such as polycarbonate, aromatic polyester carbonate, polyesters, polycarbonate-polyester blend, polycarbonate-ABS blend, polycarbonate-polyacetal blend, and polycarbonate-polymethylmethacrylate blend.