Patent Publication Number: US-4320212-A

Title: Ternary polycarbonate compositions containing polyacrylate and thermoplastic polyester

Description:
The present invention is directed to high molecular weight, aromatic polycarbonate compositions having improved aged impact strength and improved low temperature impact strength. 
     BACKGROUND OF THE INVENTION 
     It is well known that high molecular weight, aromatic polycarbonate resins have high impact strength below a critical thickness of between about 1/2 and 1/4 inches. Above this average thickness, the impact strength of such polycarbonate resins is low. It is also known that the impact strength of these polycarbonate resins decreases rapidly as temperatures decrease below about -5° C. as well as after aging at elevated temperatures above about 100° C. These characteristics limit the fields of applications of these resins. Thus, unmodified polycarbonates are not practical for use at low or high temperatures when good impact strength is required. Therefore, it is desirable to improve the impact strength of polycarbonate resins at both low and high temperatures as well as improve their aged impact strength and thereby expand the fields of application of such resins. 
     In copending application Ser. No. 957,801 filed Nov. 6, 1978 U.S. Pat. No. 4,257,937, polyester compositions having improved impact are described. These compositions comprise (a) a polybutylene terephthalate which can also include another polyester copolymer, (b) a polyacrylate, and (c) an aromatic polycarbonate. The amount of polyacrylate employed can range from about 5-20 weight percent while the amount of aromatic polycarbonate employed can range from about 10-20 weight percent. Thus, the primary component in these compositions is the polyester so that the polyacrylate and polycarbonate portions are employed as the modifiers. 
     Polycarbonate compositions having improved impact strength at both high and low temperatures as well as improved aged impact strength are disclosed in co-pending applications Ser. Nos. 69,822; 69,823; 69,824; and 69,825 all of which were filed Aug. 27, 1979 as well as in co-pending applications Ser. Nos. 132,331; 132,325; and 132,190 filed of even date with this application. 
     DESCRIPTION OF THE INVENTION 
     It has now been found that additional ternary compositions comprising a high molecular weight, thermoplastic, aromatic polycarbonate, an acrylate copolymer, and a thermoplastic polyester also exhibit improved aged impact strength and that certain formulations thereof exhibit improved impact strength at both low and high temperatures as compared to unmodified polycarbonate resins. 
     The high molecular weight, thermoplastic, aromatic polycarbonates which can be employed in the present invention are those homopolycarbonates and copolycarbonates and mixtures thereof which have average molecular weights of about 8,000 to more than 200,000, preferably about 20,000 to 80,000, and an intrinsic viscosity (I.V.) of about 0.40 to 1.0 deciliters/grams (dl/g) as measured in methylene chloride at 25° C. These polycarbonates are typically derived from dihydric phenols such as, for example, 2,2-bis(4-hydroxyphenyl)propane (also referred to as bisphenol-A; i.e., BPA), bis(4-hydroxyphenyl)methane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 4,4-bis(4-hydroxyphenyl)heptane, 2,2-(3,5,3&#39;,5&#39;-tetrachloro-4,4&#39;-dihydroxyphenyl)propane, 2,2-(3,5,3&#39;,5&#39;-tetrabromo-4,4&#39;-dihydroxydiphenyl)propane, and (3,3&#39;-dichloro-4,4&#39;-dihydroxydiphenyl)methane. Other dihydric phenols which are suitable for use in preparing these polycarbonates are disclosed in U.S. Pat. Nos. 2,999,835; 3,028,365; 3,334,154; and 4,131,575. 
     The aromatic polycarbonates of the invention can be manufactured by known processes such as, for example, the interfacial polymerization technique wherein a dihydric phenol is reacted with a carbonate precursor, such as phosgene, in the presence of a suitable organic medium, such as methylene chloride. These processes are disclosed in the above identified U.S. patents as well as in U.S. Pat. Nos. 4,018,750 and 4,123,436. Transesterification processes can also be employed to prepare these resins such as are disclosed in U.S. Pat. No. 3,153,008, as well as other processes known to those skilled in the art. 
     In addition, the aromatic polycarbonates of the invention can include the polymeric derivates of a dihydric phenol, a dicarboxylic acid, and carbonic acid, such as are disclosed in U.S. Pat. No. 3,169,131. 
     It is also possible to employ two or more different dihydric phenols or a copolymer of a dihydric phenol with a glycol or with hydroxy or acid terminated polyester, or with a dibasic acid in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired for use in preparing the aromatic polycarbonate to be employed in the invention. In addition, blends of any of the above materials can be used to provide the aromatic polycarbonate. 
     Further, branched polycarbonates, such as are disclosed in U.S. Pat. No. 4,001,184 can also be employed as can blends of a linear polycarbonate and a branched polycarbonate to provide the aromatic polycarbonate of the invention. 
     The &#34;acrylate&#34; copolymer employed in the invention is a copolymer of a C 1  -C 5  methacrylate and a C 1  -C 5  acrylate, wherein the &#34;C 1  -C 5  &#34; represents both saturated and unsaturated, straight or branched chained aliphatic hydrocarbon radicals having from 1 to 5 carbon atoms and which can be employed in amounts of about 2-4.25 parts by weight per hundred parts of aromatic polycarbonate. 
     Preferred acrylates for use in the acrylate copolymer are methyl acrylate, ethyl acrylate, isobutyl acrylate, 1,4-butanediol diacrylate, n-butyl acrylate, and 1,3-butylene diacrylate. Preferred methacrylates for use in this copolymer include methyl methacrylate, isobutyl methacrylate, 1,3-butylene dimethacrylate, butyl methacrylate and ethyl methacrylate. 
     Based on the total weight of the copolymer, the acrylate portion thereof can range from about 50-85 weight percent and the methacrylate portion thereof can range from about 15-50 weight percent. 
     The preferred acrylate copolymer for use in this invention is a copolymer of n-butyl acrylate and methyl methacrylate wherein the weight ratio of n-butyl acrylate: methyl methacrylate is about 3:2. 
     Suitable acrylate copolymers can be prepared by methods well known to those skilled in the art or can be obtained commercially. For example, Rohm and Haas&#39; Acryloid® KM 330 copolymer, a copolymer of n-butyl acrylate and methyl methacrylate, is suitable for use in the present invention. 
     The thermoplastic polyesters which can be employed in the invention include, for example, aliphatic/aromatic polyesters such as poly (1,4-butylene terephthalate), poly (ethylene terephthalate) and the like, as well as block copolyesters such as cyclohexylenedimethanol copolymers as well as blends and mixtures thereof. Other thermoplastic polyesters suitable for use in the compositions of the invention will become apparent to those skilled in the art while others are commercially available such as those sold under the &#34;VALOX&#34; trademark. For both high and low temperature applications, the preferred thermoplastic polyester is poly(1,4-butylene terephthalate). 
     The amount of thermoplastic polyester which can be employed in the ternary compositions of the invention can range from about 0.5-2.5 parts by weight, preferably 1.0-2.0 parts by weight, per hundred parts of the aromatic polycarbonate. 
     It is also regarded to be among the features of this invention to include in the ternary polycarbonate composition conventional additives for purposes such as reinforcing, coloring or stablizing the composition in conventional amounts. 
     The compositions of the invention are prepared by mechanically blending the high molecular weight aromatic polycarbonate with the thermoplastic polyester and the acrylate copolymer by conventional methods. 
    
    
     EXAMPLES 
     The following examples set forth the best mode currently known to illustrate the invention and should not be construed as limiting the scope of the invention. In the examples, all parts and percentages are by weight unless otherwise specified. 
     EXAMPLE 1 
     Ninety-four (94.0) parts of an aromatic polycarbonate, derived from 2,2-bis(4-hydroxyphenyl)propane and having an intrinsic viscosity (I.V.) in the range of from about 0.46 to about 0.49 dl/g as determined in methylene chloride solution at 25° C., was mixed with four (4) parts of an acrylate copolymer of n-butyl acrylate and methyl methacrylate having a weight ratio of n-butyl-acrylate: methyl methacrylate of about 3:2, and two (2.0) parts of poly (1,4-butylene terephthalate): i.e. PBT. The ingredients were then blended together by mechanically mixing them in a laboratory tumbler and the resulting mixture was fed to an extruder which was operated at about 265° C. The resulting extrudate was comminuted into pellets and the pellets were injection molded at about 290° C.-310° C. into test specimens of about 5&#34; by 1/2&#34; by 1/4&#34; and 5&#34; by 1/2&#34; by 1/8&#34;, the latter dimensions being the specimen thicknesses. Izod impact strengths of these specimens were measured according to the notched Izod test, ASTM D256, and are set forth in Table I. The ductile-brittle (D/B) transition temperatures, (the highest temperature at which a sample begins to exhibit a brittle mode of failure rather than a ductile mode of failure) were obtained according to the procedures of ASTM D256 and are also listed in Table I. The sample labeled CONTROL was obtained from a polycarbonate resin having an I.V. of about 0.46-0.49 dl/g and was prepared without either the acrylate copolymer or the thermoplastic polyester. 
     EXAMPLE 2 
     The procedure of Example 1 was repeated exactly, except that the weight parts of polycarbonate, acrylate copolymer and PBT in the test specimen were, respectively, 95, 4 and 1. The test results obtained are listed in Table I. 
     EXAMPLE 3 
     The procedure of Example 1 was repeated exactly, except that the weight parts of polycarbonate, acrylate copolymer and PBT in the test specimens were, respectively, 96, 3 and 1. The test results obtained are listed in Table I. 
     EXAMPLE 4 
     The procedure of Example 1 was repeated exactly, except that the weight parts of polycarbonate, acrylate copolymer and PBT in the test specimens were, respectively, 95.5, 4 and 1.5. The test results obtained are listed in Table I. 
     
                                           TABLE I                                 
__________________________________________________________________________
        Impact Strength, ft. lb./in.                                      
        1/4&#34; Thick                                                        
              1/8&#34; Thick                                                  
                    1/8&#34;, Heat Aged at 125° C.                     
                                D/B,°C.**                          
Composition of:                                                           
        Not Aged                                                          
             Not Aged                                                     
                    24 hrs.                                               
                          48 hrs.                                         
                                1/8&#34;, Not Aged                            
__________________________________________________________________________
Example 1                                                                 
        13.3.sup.1                                                        
              *     13.3.sup.1                                            
                          11.8.sup.1                                      
                                -18/-23                                   
Example 2                                                                 
        13.1.sup.1                                                        
              15.3.sup.1                                                  
                    13.2.sup.1                                            
                          12.7.sup.1                                      
                                -18/-23                                   
Example 3                                                                 
        11.8.sup.1                                                        
              15.3.sup.1                                                  
                    13.2.sup.1                                            
                          10.7.sup.1                                      
                                -12/-18                                   
Example 4                                                                 
        12.7.sup.1                                                        
              15.3.sup.1                                                  
                    13.2.sup.1                                            
                          12.7.sup.1                                      
                                -18/-23                                   
CONTROL  1.6.sup.2                                                        
              14.8.sup.1                                                  
                     1.3.sup.2                                            
                          *     &gt;-5                                       
__________________________________________________________________________
 .sup.1 Samples failed with 100% ductility.                               
 .sup.2 Samples failed with 0% ductility.                                 
 * Test not made.                                                         
 **Change from ductile mode of failure to brittle mode of failure noted   
 over indicated range.