Polyester based shock resistant compositions and process for their preparation
This is a continuation of co-pending application Ser. No. 07/563,854, filed on Aug. 7, 1990, now abandoned, which is a continuation of Ser. No. 07/378,481, filed Jul. 11, 1989, now abandoned, which is a continuation of Ser. No. 07/055,078, filed May 28, 1987, now abandoned. 
    
    
     DESCRIPTION OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to shock-resistant compositions based on polyesters, and to a process for their preparation. 
     More particularly, the present invention relates to polyester-based polymeric compositions endowed with a high shock resistance, particularly at low temperatures. 
     2. Background of the Invention 
     In U.S. Pat. No. 3,919,353 compositions based on saturated polyesters have been disclosed and claimed, the shock resistance of which was enhanced by dispersing into them an elastomeric phase constituted by butadiene rubbers, such as, e.g., polybutadiene or butadiene/styrene copolymers, or by polyolefinic rubbers, such as, e.g., saturated or unsaturated ethylene/propylene copolymers, which have been previously cross-linked and modified by a grafting reaction with polar monomers. In the grafted and cross-linked elastomer, the cross-linked phase is present in an amount of at least 30%, and, preferably, at least 50%. 
     The shock resistance of such compositions, at room temperature, is considerably improved as compared to that of polyesters without such an elastomeric phase; however, their low-temperature shock resistance, in particular within the range of from 0° C. to -40° C., is not completely satisfactory for some applications. 
     New shock-resistant, polyester-based compositions have been now discovered, in accordance with the present invention, which maintain high characteristics of shock resistance also at low temperatures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The compositions of the present invention are characterized in that they comprise: 
     (a) from 55 to 98% by weight of one or more saturated polyesters; 
     (b) from 1 to 35% by weight of butadiene and/or acrylic rubber; and 
     (c) from 1 to 10% by weight of an elastomeric copolyester. 
     The compositions of the present invention may be obtained by dispersing and/or blending the above mentioned (a), (b) and (c) components in the molten state, or as solutions in suitable solvents which are subsequently removed by per se conventional techniques. 
     The preferred process consists in operating at such temperatures as to have the (a) and (c) components in the molten state, blending them with each other, and then dispersing into them the (b) component in the form of small-size particles, preferably with an average diameter within the range of from 0.1 to 2 microns, by using well-known equipment for preparation of polymeric blends, such as mixers, extruders, and so forth. 
     During the preparations of these compositions, several additives, such as stabilizers, antioxidants, pigments, dyes, flame-proofing agents, lubricants, organic and inorganic reinforcing agents (carbon fibers or fiberglass, aramidic fibers, talc, asbestos, etc.), nucleating agents, and so on, may be added. 
     The saturated polyesters (a) used in the compositions of the present invention are thermoplastic resins having an intrinsic viscosity of at least 0.4 dl/g (as measured on a 1:1  phenol/tetrachloroethane mixture), obtained from an aromatic or cycloaliphatic dicarboxylic acid, with a diol having the formula: 
     
         HO-R-OH                                                    (I) 
    
     wherein R is a linear branched alkylene radical containing from 2 to 20 carbon atoms, or an arylene or cycloalkylene radical containing from 6 to 20 carbon atoms. 
     Examples of preferred dicarboxylic acids are terephthalic acid, isophthalic acid and cyclohexane-1,4-dicarboxylic acid; examples of preferred diols are ethanediol, propanediol, butanediol, and hexanediol. 
     Some examples of preferred saturated polyesters are poly(ethyleneterephthalate, poly(propyleneterephthalate), poly (butyleneterephthalate), and poly(hexamethylene-cyclo-hexane-1,4-dicarboxylate), and their blends. 
     These polyesters may be produced according to per se known techniques for polycondensation or polytransesterification 
     The saturated polyesters used in the preparation of the compositions of the present invention may possibly contain, however in amounts smaller than 15% by mol in respect of the aromatic or cyclo-aliphatic acids, aliphatic dicarboxylic acids of from 4 to 20 carbon atoms. As examples of aliphatic dicarboxylic acids which may be used, adipic acid and sebacic acid may be mentioned. 
     The (b) component used in the compositions of the present invention may be a butadiene rubber, or an acrylic rubber. 
     By the term &#34;butadiene rubber&#34;, any elastomeric polymer is meant which is obtained either by direct polymerization, or by polymerization and a subsequent grafting reaction of butadiene and/or isoprene with ethylenically unsaturated monomers, such as, e.g., styrene, acrylonitrile, methacrylonitrile, acrylic and methacrylic esters, acrylic and methacrylic acid, maleic acid and anhydride, maleic and fumaric esters, alkylstyrenes, in any combinations with one another. Typical examples of butadiene rubbers are the butadiene/styrene/acrylonitrile or butadiene/styrene/methylmethacrylate terpolymers, as well as the same terpolymers, or polybutadiene, or natural rubber, or butadiene/styrene or butadiene/acrylonitrile copolymers subsequently modified by a grafting reaction with a polar monomer, such as acrylonitrile, styrene, acrylic or methacrylic esters, methacrylic acid, maleic acid and anhydride, and so forth. 
     By the term &#34;acrylic rubbers&#34;, any elastomeric polymer is meant which is obtained, either by direct polymerization or by polymerization and subsequent grafting reaction of alkyl-esters of acrylic or methacrylic acid, containing from 1 to 10 carbon atoms in their alkyl chain, such as, e.g., ethyl acrylate, butyl acrylate, methyl methacrylate and cyclohexyl methacrylate. Together with these monomers, for the synthesis of the above-said acrylic rubbers, other ethylenically unsaturated monomers may also be used, such as, e.g., styrene, alkylstyrenes, acrylonitrile, methacrylonitrile, and/or, in an amount of from 0.1 to 5% by weight, such di- or poly-functional monomers (cross-linking agents) as ethyleneglycol acrylate or methacrylate, glycidyl methacrylate, allyl methacrylate, diallylmaleate, diallylphthalate, hydroxyethyl methacrylate, etc. Typical examples of acrylic rubbers are the polymers obtained from alkylesters of acrylic or methacrylic acid, such as butyl acrylate, ethyl acrylate and methyl methacrylate, possibly containing minor amounts, e.g., from 10 to 30% by weight, of styrene or acrylonitrile, and small amounts, e.g., from 0.5 to 3% by weight, of ethyleneglycol methacrylate or allyl methacrylate. 
     Said (b) rubbers are characterized by a main glass transition temperature (T g ) lower than 0° C., and by a cross-linking degree (gel content) within the range of from 0 to 99% by weight, and preferably from 50 to 99% by weight. 
     The cross-linking may be already present in the rubber before this is blended with the other components, or it may be achieved during said blending, with the possible further addition of monomers of the above-indicated types and in the presence of free-radical initiators, or with the addition of suitable other cross-linking agents, such as, e.g., diisocyanates, diamines, diols, and so on. 
     The (c) component used in the compositions of the present invention is a block-copolyester having a melting point lower than 190° C., obtained by means of the polycondensation or transesterification of an aropmatic dicarboxylic acid with a diol having the above formula (I), and with a polyetherglycol having the formula: 
     
         HO--(R.sub.1 --O).sub.m --H                                (II) 
    
     wherein R 1  is a linear or branched alkylene radical containing from 2 to 20 carbon atoms, and m is an integer higher than 2, and such that the molecular weight of the polyetherglycol is within the range of from 300 to 10,000, and preferably from 600 to 4,000. 
     Examples of suitable polyetherglycols are polyoxytetramethyleneglycol, polyoxyethyleneglycol, polyoxypropyleneglycol, etc., or mixtures thereof. 
     Said block-copolyesters have a content of rigid segments--by which term is meant segments which are derived from the esterification of the acid with the diol having formula (I)--within the range of from 10 to 75% by weight. Furthermore, the ratio of the number of carbon atoms to the number of oxygen atoms present in the polyetherglycol (II) preferably is equal to, or higher than 2. 
     The lower the content of rigid segments in the compositions of the present invention, the greater is the improvement of the resilience thereof caused by the presence of copolyesters (c). More particularly, a content of rigid segments in the copolyesters, within the range of from 30 to 50% by weight, allows a favorable compromise to be made between stiffness and shock-resistance and shape stability on heating. 
     To the compositions of the present invention other thermoplastic materials may be added, such as, e.g., any per se known type of polycarbonate, in particular that obtained from bisphenol A and phosgene; any known type of thermoplastic polyurethane, and in particular that obtained from methylene-bis(phenylisocyanate), and polyether-glycols and/or polyester-glycols. Furthermore, poly(vinyl chloride), polyamides, polystyrenes, ABS resins, etc., may be added. 
     The amount of said thermoplastic materials may vary over a wide range. In particular, amounts of thermoplastic materials lower than 25%, and preferably within the range of from 1 to 10% by weight, relative to the total composition, are recommended. 
     The compositions of the present invention are mainly characterized by a good low-temperature shock-resistance; more particularly, at temperatures of from 0° C. to -40° C.; they are furthermore endowed with very good resistance to gasolines, to oils, to light, and to thermo-oxidation. Thanks to these peculiar characteristics, the compositions of the present invention are particularly suitable for use in certain fields, such as, e.g., in car and motorcycle field (bumpers, fenders, spoilers, side-body moldings, protective helmets, etc.), and in the sports field (ski-boots, soles for ice skates, etc.), wherein the above-mentioned characteristics have a considerable importance. 
    
    
     EXAMPLES 
     For the purpose of illustrating the present invention still more extensively and in still greater detail, some examples are now supplied, which are in no way to be regarded as being limitative thereof. 
     EXAMPLES 1-4 
     By means of a twin-screen extruder MARIS TM 33, at a temperature of 260° C., and with a screw revolution speed of 150 rpm, blends are prepared which are constituted by: 
     (a) polybutyleneterephthalate having a viscosity of 1.4 dl/g; 
     (b) grafted butadiene/styrene/methylmethacrylate terpolymer with a cross-linking degree (gel content) of 94% by weight, and a glass transition temperature (T g )=-80° C., manufactured by Rohm and Haas under the tradename KM 653 containing from 58-62% by weight polybutadiene, from 12-18% by weight styrene and from 24-26% by weight methylmethacrylate; and 
     (c) copolyesters obtained from terephthalic acid, 1,4-butanediol and polyoxytetramethyleneglycol, with a molecular weight of about 1000, and having different contents of rigid segments, as reported in Table 1 below. 
     During the preparation of said blends, antioxidants, i.e., 0.4% of IRGANOX 1010 and 04% of IRGAFOS 168, are also added. 
     The weight ratios of the blend components are reported in Table 1. 
     Rods from the extruder are pelletized and dried from 2 to 4 hours 80°-140° C. The material is subsequently injection-molded at 260° C. to obtain suitable specimens for property determinations, according to ASTM Standards. 
     Such properties are reported below in Table 1: 
     
                                           TABLE 1                                 
__________________________________________________________________________
                    Example No.                                           
                    1    2    3    4                                      
__________________________________________________________________________
Composition                                                               
__________________________________________________________________________
(a) Polybutyleneterephthalate                                             
                    74.2 74.2 74.2 74.2                                   
(b) Rubber KM 653   25   20   20   20                                     
(c) Copolyester containing:                                               
33% of rigid segments    5                                                
46% of rigid segments         5                                           
66% of rigid segments              5                                      
(d) Antioxidants    0.8  0.8  0.8  0.8                                    
__________________________________________________________________________
Properties Method                                                         
                Unit                                                      
__________________________________________________________________________
Specific   D.720                                                          
                g/cm.sup.3                                                
                    1.21 1.21 1.25 1.25                                   
Gravity at 23° C.                                                  
Yield Strength                                                            
           D.638                                                          
                MPa 35   36   35   35                                     
VICAT      D.1525                                                         
                °C.                                                
                    123  126  130  133                                    
Flexural Modulus                                                          
at 23° C.                                                          
           D.790                                                          
                MPa 1450 1440 1430 1550                                   
at 80° C.                                                          
           D.790                                                          
                MPa 250  250  260  280                                    
IZOD                                                                      
at +23° C.                                                         
           D.256                                                          
                J/m 820  925  910  890                                    
                    PR   PR   PR   PR                                     
at -15° C.                                                         
           D.256                                                          
                J/m 190  650  820  260                                    
                         PR                                               
at -40° C.                                                         
           D.256                                                          
                J/m 100  450  250  150                                    
Distortion                                                                
Temperature (HDT)                                                         
under 4.5 kg                                                              
           D.648                                                          
                °C.                                                
                    80   81   85   97                                     
under 18.2 kg                                                             
           D.648                                                          
                °C.                                                
                    45   47   47   48                                     
__________________________________________________________________________
 PR = Partially cracked.                                                  
 
    
     EXAMPLES 5-7 
     By operating under the same conditions as in Examples 1-4, granules are prepared from blends consisting of: 
     (a) polybutyleneterephthalate having a viscosity of 1.4 dl/g; 
     (b) polybutylacrylate grafted with methylmethacrylate, having a gel content of 91% by weight, and a glass transition temperature (T g ) of -50° C., manufactured by Rohm and Haas under the tradename KM 323 B; and 
     (c) copolyesters obtained from terephthalic acid, 1,4-butanediol and polyoxytetramethyleneglycol, with a molecular weight of about 1000, and having different contents of rigid segments, as reported in Table 2 below. 
     During the preparation of these blends, 0.8% by weight of antioxidants, as already specified in the foregoing examples, were also added. 
     The weight ratios between the blend components and the properties as determined on the specimens obtained from said blends, are reported below in Table 2. 
     
                                           TABLE 2                                 
__________________________________________________________________________
                    Example No.                                           
Composition         5    6     7                                          
__________________________________________________________________________
(a) Polybutyleneterephthalate                                             
                    74.2 74.2  74.2                                       
(b) Rubber KM 323 B 25   20    20                                         
(c) Copolyester containing:                                               
33% of rigid segments    5                                                
46% of rigid segments          5                                          
(d) Antioxidants    0.8  0.8   0.8                                        
Specific   D.720                                                          
                g/cm.sup.3                                                
                    1.22 1.21  1.22                                       
Gravity at 23° C.                                                  
Yield Strength                                                            
           D.638                                                          
                MPa 38   35    37                                         
VICAT      D.1525                                                         
                °C.                                                
                    120  110   120                                        
Flexural Modulus                                                          
at 23° C.                                                          
           D.790                                                          
                MPa 1650 1550  1620                                       
at 80° C.                                                          
           D.790                                                          
                MPa 360  320   340                                        
IZOD                                                                      
at +23° C.                                                         
           D.256                                                          
                J/m 600  820   650                                        
                    PR   PR    PR                                         
at -15° C.                                                         
           D.256                                                          
                J/m 200  650   450                                        
                         PR    PR                                         
at -40° C.                                                         
           D.256                                                          
                J/m 100  160   140                                        
Distortion                                                                
Temperature (HDT)                                                         
under 4.5 kg                                                              
           D.648                                                          
                °C.                                                
                    85   75    84                                         
under 18.2 kg                                                             
           D.648                                                          
                °C.                                                
                    48   45    46                                         
__________________________________________________________________________
 PR = Partially cracked.                                                  
 
    
     EXAMPLES 8-11 
     Examples 1-4 are repeated, with polybutyleneterephthalate being replaced by a mixture of polybutyleneterephthalate/polyethyleneterephthalate in 40:60 weight ratio. 
     The compositions of the blends, and the properties of the specimens obtained from said blends are reported in the following Table 3: 
     
                                           TABLE 3                                 
__________________________________________________________________________
                    Example No.                                           
                    8    9    10   11                                     
__________________________________________________________________________
Composition                                                               
__________________________________________________________________________
(a) 40:60 Polybutylene-                                                   
                    74.2 74.2 74.2 74.2                                   
terephthalate/polyethylene-                                               
terephthalate blend                                                       
(b) Rubber KM 653   25   20   20   20                                     
(c) Copolyester containing:                                               
33% of rigid segments    5                                                
46% of rigid segments         5                                           
66% of rigid segments              5                                      
(d) Antioxidants    0.8  0.8  0.8  0.8                                    
__________________________________________________________________________
Properties Method                                                         
                Unit                                                      
__________________________________________________________________________
Specific   D.720                                                          
                g/cm.sup.3                                                
                    1.23 1.225                                            
                              1.225                                       
                                   1.227                                  
Gravity at 23° C.                                                  
Yield Strength                                                            
           D.638                                                          
                MPa 40   38   37   39                                     
VICAT      D.1525                                                         
                °C.                                                
                    120  125  127  130                                    
Flexural Modulus                                                          
at 23° C.                                                          
           D.790                                                          
                MPa 1550 1480 1570 1590                                   
at 80° C.                                                          
           D.790                                                          
                MPa 300  260  290  290                                    
IZOD                                                                      
at +23° C.                                                         
           D.256                                                          
                J/m 700  900  800  850                                    
at -15° C.                                                         
           D.256                                                          
                J/m 170  750  600  550                                    
at -40° C.                                                         
           D.256                                                          
                J/m 80   600  450  320                                    
Distortion                                                                
Temperature (HDT)                                                         
under 4.5 kg                                                              
           D.648                                                          
                °C.                                                
                    80   77   79   78                                     
under 18.2 kg                                                             
           D.648                                                          
                °C.                                                
                    54   49   50   52                                     
__________________________________________________________________________
 
    
     EXAMPLES 12-15 
     By operating under the same conditions as in Examples 1-4, blends are prepared which consist of: 
     (a) polybutyleneterephthalate having a viscosity of 1.4 dl/g; 
     (b) butadiene rubber of the KM 653 type, manufactured by Rohm and Haas; 
     (c) copolyester obtained from terephthalic acid, 1,4-butanediol, and polyoxytetramethyleneglycol, having a molecular weight of about 1000, and having a content of rigid segments of 33%; and 
     (d) polycarbonate obtained from phosgene and bisphenol A, manufactured by ENICHEM under the tradename SINVET 271, or thermoplastic polyurethane marketed by UPJOHN under the tradename ISOPLAST 201. 
     The compositions of the blends and the properties of the specimens obtained from said blends are reported in the following Table 4. 
     
                                           TABLE 4                                 
__________________________________________________________________________
                    Example No.                                           
                    12   13   14   15                                     
__________________________________________________________________________
 Composition                                                              
__________________________________________________________________________
(a) Polybutyleneterephthalate                                             
                    67.2 67.2 67.2 67.2                                   
(b) Rubber KM 653   25   20   25   20                                     
(c) Copolyester          5         5                                      
(d) Polycarbonate SINVET 271                                              
                    7    7                                                
Polyurethane ISOPLAST 201     7    7                                      
(d) Antioxidants    0.8  0.8  0.8  0.8                                    
__________________________________________________________________________
Properties Method                                                         
                Unit                                                      
__________________________________________________________________________
Specific   D.720                                                          
                g/cm.sup.3                                                
                    1.198                                                 
                         1.208                                            
                              1.200                                       
                                   1.203                                  
Gravity at 23° C.                                                  
Yield Strength                                                            
           D.638                                                          
                MPa 42   34   42   32                                     
VICAT      D.1525                                                         
                °C.                                                
                    120  135  125  132                                    
Flexural Modulus                                                          
at 23° C.                                                          
           D.790                                                          
                MPa 1350 1500 1420 1380                                   
at 80° C.                                                          
           D.790                                                          
                MPa 220  250  240  230                                    
IZOD                                                                      
at +23° C.                                                         
           D.256                                                          
                J/m 980  1050 200  850                                    
                    PR   PR        PR                                     
at -15° C.                                                         
           D.256                                                          
                J/m 900  1030 180  880                                    
                         PR        PR                                     
at -40° C.                                                         
           D.256                                                          
                J/m 300  900  80   350                                    
                         PR        PR                                     
Distortion                                                                
Temperature (HDT)                                                         
under 4.5 kg                                                              
           D.648                                                          
                °C.                                                
                    88   75   78   70                                     
under 18.2 kg                                                             
           D.648                                                          
                °C.                                                
                    49   46   52   50                                     
__________________________________________________________________________
 PR = Partially cracked.                                                  
 
    
     Although the invention has been described in conjunction with specific embodiments, it is evident that many alternatives and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the invention is intended to embrace all of the alternatives and variations that fall within the spirit and scope of the appended claims.