Abstract:
A polycarbonate blend composition comprising 95-5 wt % of a polycarbonate resin, 5-95% of an ABS resin and 0-01-5 parts per hundred of a heat stabilizer (relative to the combined resin weight). The heat stabilizers are selected from benzothiazoles of formula: ##STR1## wherein R is selected from hydrogen, alkyl, aryl and benzothiazolyl; benzimidazole compounds of formula: ##STR2## wherein R is selected from hydrogen, alkyl, aryl and benzimidazolyl; hydrazine compound of formula: ##STR3## wherein R is alkyl, and cation exchange materials selected from metal salts of silicaluminate zeolites, metal salts of triphosphates and cation exchange resins. These poly blend composition display improved impact resistance.

Description:
DESCRIPTION OF THE INVENTION 
     The present invention relates to a polycarbonate/ABS blend compositions having improved impact resistance. The present compositions comprise a combination of polycarbonate, ABS resin and heat stabilizer. 
     In recent years, heat stability and impact resistance were required in molding thermoplastic resins which have certain special uses. Under these circumstances, general purpose grade plastics and ABS resins are unable to satisfy these performance requirements. Instead, expensive heat stable engineering plastics such as polycarbonate (PC), polysulfone (PSF) and polyphenylene oxide (PPO) were developed to solve these problems. These high performance resins are not only expensive, but also are difficult to process. In order to improve processing and heat resistance, the simplest way is to use polymer blending techniques, for example, PC/ABS polyblends exhibit very balanced mechanical properties and processability. These polyblending techniques have been described, for example, in Japan Patent Application 38-15225, 39-71, and 42-11496. 
     However, there are unstable quality conditions during blending of PC/ABS resins. The causes of this unstability were believed to be associated with residual impurities present in common preparation procedures for forming ABS. These impurities include emulsifiers, migrating agent, and suspension stabilizer. These trace impurities influnce PC in such a way that, during the melt blending of PC and ABS under elevated temperature, PC resin might be degraded due to heat decomposition. The heat degradation can lead to lower physical properties and darken color. Furthermore, the degree of degradation in blending of PC/ABS is more severe than that in molding of PC alone. In order to overcome these drawbacks, Japan Patent 56-131657 described use of organic and inorganic acids as heat stabilizers of PC/ABS polyblends, while U.S. Pat. No. 4,472,554 disclosed high molecular acids as heat stabilizer of PC/ABS polyblend. 
     Thus, the instant invention provides four types of compounds as heat stabilizers of PC/ABS polyblends: 
     (1) benzothiazole compounds; 
     (2) benzimidazole compounds; 
     (3) hydrazine compounds; 
     (4) cation exchange materials. 
     suitable polycarbonates for use in the present invention include those selected from aromatic polycarbonate, aliphatic polycarbonate, aliphatic-aromatic polycarbonate or halogen-substituted bisphenol-A polycarbonates. 
     Suitable ABS resins for use in the present invention include those selected from resins prepared by emulsion, suspension or solution polymerizations of cyanovinyl compounds, for example, acrylonitrile, conjugated dienes compounds, for example, butadiene, and aromatic-vinyl compounds, for example, styrene; or the polyblend prepared by melt blending of the above prepared resins with cyanovinyl-aromatic vinyl copolymer, for example, ABS/acrylonitrile-styrene copolymer blend. 
     The benzothiazole compounds suitable for use in the instant invention are compounds of general formula (I) ##STR4## where R is selected from hydrogen, alkyl, aryl or benzothiazolyl. 
     The benzimidazole compounds suitable for use as heat stabilizer in the instant invention include compounds of general formula (II) ##STR5## where R is selected from hydrogen, alkyl, aryl or benzimidazolyl. 
     Suitable hydrazine compounds for use as heat stabilizer in the instant invention include compounds of general formula (III) ##STR6## where R 1  and R 2  are independently selected from alkyl, aryl or alkyl- or aryl-substituted aryl. 
     The cation exchange material suitable for use as heat stabilizer in the instant invention comprise various cation salts of silicaluminates, where cations may be sodium, potassium, lithium, calcium, strotium or barium; zeolites having various mole number of crystalline water; metal salts of tripolyphosphate, where the metal ions may be sodium, potassium, calcium, strontium, or barium; or other cation exchange resins. 
     The amount of the above described heat stabilizer in the instant invention is in the range in the 0.01 to 5 phr (part per hundred part) based on the total weight of the PC/ABs polyblend. 
     The improvement of impact resistance of the polycarbonate polyblend through incorporation of the heat stabilizers of the present invention can be illustrated by the following examples, which are not meant to limit the instant invention. Data and figures in the tables are based on weight units unless stated otherwise. 
    
    
     EXAMPLES 
     The methods used in comparative examples 1-3 and examples 1-24 involve the drying of ABS and PC resins, compounding the resins according to suitable ratio, blending in extruder (blending temperature 220°-250° C., screw speed at 150 rpm), pelletizing and drying. The resulting material is injection molded into test specimens specified by ASTM and subjected to impact resistant test in accordance with ASTM D-256. 
     Data in Table 1 shows the effect of two benzothiazole type heat stabilizers on the impact strength of PC/ABS polyblend composition. As can be seen, heat stabilizers were not used in the three comparative examples while the types and amount of heat stabilizers used in examples 1-6 were listed in the Table together with the compositions of PC/ABS polyblend. Where similar polymer compositions were used, the impact strengths obtained in examples 1-6 were significantly higher than those obtained in corresponding comparative example 1-3. The improvements of impact strength of PC/ABS polyblend can be ascribed to the interaction of benzothiazole compounds with the impurities in ABS, for example migrating agent, so as to inhibit the thermal decomposition of PC during high temperature blending. 
     
                                           TABLE 1__________________________________________________________________________The effect of benzothiazole type heat stabilizer onthe impact strength of PC/ABS polyblend compositions.          Comparative          examples    Examples          1   2   3   1   2   3   4   5   6__________________________________________________________________________ABS            75  50  25  75  75  50  50  25  25PC             25  50  75  25  25  50  50  75  75heat   *G--R, R = hydrogen          --  --  --    0.3                          --    0.5                                  --    0.2                                          --stabi-   G--R, R = G --  --  --  --    0.7                              --    0.5                                      --    1.0lizerImpact Strength, notched,            0.2                0.5                    8.0                        5.0                            4.3                                14.5                                    12.0                                        14.2                                            13.8ft-lb/in__________________________________________________________________________ *G = C.sub.6 H.sub.4 SNCS 
    
     Table 2 shows the effect of benzimidazole type heat stabilizers on the impact strength of PC/ABS polyblend compositions. The polymers used in comparative examples 1 to 3 do not include the said heat stabilizer. The types and amounts of heat stabilizers used in example 7-12 are shown together with polymer composition in each example. The impact strengths obtained were significantly enhanced, wherein, the impact strengths obtained in examples with PC composition 25%, 50% and 75% were increased to 25, 30 and 2 times, respectively. 
     
                                           TABLE 2__________________________________________________________________________The effect of benzimidazole type heat stabilizer onthe impact strengths of PC/ABS polyblend compositions.          Comparative          examples    Examples          1   2   3   7   8   9   10  11  12__________________________________________________________________________ABS            75  50  25  75  75  50  50  25  25PC             25  50  75  25  25  50  50  75  75heat   *D--R, R = hydrogen          --  --  --    0.1                          --    0.5                                  --    1.0                                          --stabi-   D--R, R = D --  --  --  --    0.3                              --    0.5                                      --    0.8lizerImpact Strength, notched,            0.2                0.5                    8.0                        5.5                            5.1                                15.1                                    15.5                                        13.6                                            14.0ft-lb/in__________________________________________________________________________ *D = C.sub.6 H.sub.4 NHNCS 
    
     Table 3 shows the effect of 2 hydrazine type heat stabilizers on the impact strengths of PC/ABS polyblend compositions. Similarly, the impact strength in example 13-18 which include heat stabilizer were significantly improved over comparative examples which did not include heat stabilizers. 
     
                                           TABLE 3__________________________________________________________________________The effect of hydrazine type heat stabilizers onthe impact strength of PC/ABS polyblend compositions.          Comparative          examples Examples          1  2  3  13 14 15 16 17 18__________________________________________________________________________ABS            75 50 25 75 75 50 50 25 25PC             25 50 75 25 25 50 50 75 75heat stabilizer*R.sub.1AR.sub.2,          -- -- -- 0.8                      --  0.5                            --  0.1                                  -- ##STR7##R.sub.1AR.sub.2          -- -- -- -- 0.2                         --  0.5                               --  1.0R = C.sub.10 H.sub.20,R.sub.2 = phenylImpact Strength, notched,          0.2             0.5                8.0                   4.1                      4.6                         14.9                            13.5                               13.1                                  13.4ft-lb/in__________________________________________________________________________ ##STR8## 
    
     Table 4 shows the effect of two types of cation exchange materials as the heat stabilizer on the impact strengths of PC/ABS polyblend compositions. The impact strengths obtained in example 19-24 which included with said heat stabilizers showed improved results as compared to the corresponding comparative examples 1-3. 
     
                                           TABLE 4__________________________________________________________________________The effect of cation exchange materials on the impact strengthsof PC/ABS polyblend compositions.        Comparative        examples   Examples        1   2   3   19  20  21  22  23  24__________________________________________________________________________ABS          75  50  25  75  75  50  50  25  25PC           25  50  75  25  25  50  50  75  75heat    Zeolite (NaX)        --  --  --    0.5                        --    0.5                                --    0.3                                        --stabi-    Tripolyphosphate        --  --  --  --    0.9                            --    0.5                                    --    0.7lizerImpact Strength, notched,          0.2              0.5                  8.0                      5.7                          4.6                              15.0                                  12.8                                      14.1                                          13.0ft-lb/in__________________________________________________________________________ 
    
     The improved results of the use of the heat stabilizers of the present invention on the impact strength of PC/ABS polyblend compositions are clearly demonstrated by the forgoing examples.