Patent Publication Number: US-5298549-A

Title: Reinforced polypropylene molding composition

Description:
DESCRIPTION 
     The invention relates to a polypropylene molding composition which is reinforced with a clay mineral of specific composition and, in particular, displays a significantly shifted, advantageous profile of properties compared with talc-reinforced polypropylene molding compositions. 
     Reinforced polypropylene molding compositions are widely used in automobiles, both in the interior and, with an appropriate light-stabilizing finish, in the exterior region. 
     The reinforcing substance chiefly employed in polypropylene for these uses is talc, a naturally occurring silicate having the composition Mg 3  [Si 4  O 10  ](OH) 2  with a lamina structure. On the basis of the more or less pronounced aspect ratio, depending on the working up (grinding, air separation or the like) of the mineral, of between usually 30:1 and 10:1, talc reinforcement has the effect of increasing the flexural strength, but decreasing the toughness as the talc content in the polypropylene molding composition increases. For uses in automobiles, the toughness, in particular the low temperature impact strength, can be greatly improved with the aid of thermoplastic elastomers (for example EP(D)M), although a decrease in the flexural strength values must be expected as the impact strength modifier content increases. 
     Reinforced polypropylene molding compositions usually have the following composition: 
     about 40 to 95 parts by weight of propylene homo- or propylene-ethylene copolymer, 
     about 0 to 30 parts by weight of thermoplastic elastomer, 
     about 5 to 60 parts by weight of talc, 
     about 0.1 to 2 parts by weight of antioxidants, 
     about 0.1 to 2 parts by weight of light-stabilizing finish, 
     about 0 to 10 parts by weight of colored pigments and 0 to 0.5 part by weight of organic peroxide to establish the desired melt viscosity. 
     Particular advantages of talc-reinforced polypropylene molding compositions over the ABS copolymers and ABS-polycarbonate blends likewise employed for the abovementioned uses in automobiles are: 
     the outstanding flow properties of the melt, in particular of CR products having narrow molecular weight distributions (CR =Controlled Rheology); 
     the good acoustic insulating capacity (muffled acoustic pattern); 
     the smooth surface; 
     the good heat distortion point under a low load; 
     the very good resistance to chemicals; 
     the good resistance to weathering with an appropriate light-stabilizing finish; 
     the good recyclability; and 
     the relatively low price. 
     On the other hand, disadvantages of talc-reinforced polypropylene molding compositions are: 
     the inadequate rigidity/toughness ratio for some uses; 
     the low value of the low temperature impact strength and notched impact strength of PP molding compositions which have not been impact-modified, especially at temperatures of below -10° C.; 
     the often unsatisfactory quality of the surface, impaired by differences in gloss (so-called displacement lines) and flow markings, especially as the talc particle size increases, as the melt viscosity increases or as the melt flow index decreases, in impact-modified PP molding compositions and with dark color formulations; 
     the lack of scratch resistance especially with dark color formulations and in impact-modified molding compositions, because of the relatively low ball indentation hardness and because of the specific properties of talc, such as, for example, the low Mohs&#39; hardness (=1); 
     the reduced strength and clearly visible arching in the region of weld lines. 
     Talc-reinforced and impact-modified PP molding compositions are described in various publications (cf., for example, DE 27 35 027, EP 069 479, EP 153 415, EP 204 400, EP 426 315). Clay is also mentioned as a possible filler and reinforcing substance in these publications, but is not specified in more detail. 
     It has been found that polypropylene molding compositions having improved properties are obtained by using a specific clay mineral. 
     The invention thus relates to a reinforced polypropylene molding composition, consisting essentially of 
     30 to 95 parts by weight 
     of a partly crystalline isotactic propylene homopolymer having an isotactic content of &gt;80%, a degree of crystallinity of &gt;50% and a melt flow index (230/5) of 0.5 to 1000 g/10 minutes, or 
     of a partly crystalline syndiotactic propylene homopolymer having a syndiotactic content of &gt;80%, a syndiotactic sequence length of &gt;10, a degree of crystallinity of &gt;30% and a melt flow index (230/5) of 0.5 to 1000 g/10 minutes, or 
     of a partly crystalline propylene-ethylene, propylene1-olefin or propylene-ethylene-1-olefin-block copolymer or terpolymer with C 4  -C 8  -1-olefins, having an ethylene and/or 1-olefin content of 2 to 30% by weight and a melt flow index (230/5) of 0.5 to 1000 g/10 minutes, or 
     of a partly crystalline random propylene/ethylene/1-olefin, propylene/1-olefin or propylene/ethylene/1-olefin(ter)-copolymer having an ethylene or/and 1-olefin content of 0.5 to 30% by weight and a melt flow index (230/5) of 0.5 to 1000 g/10 minutes, 
     0 to 30 parts by weight, 
     of a thermoplastic ethylene-propylene or/and ethylene5 propylene-diene rubber having an ethylene content of &gt;45 by weight and a Mooney viscosity ML (1+8) at 127° C. of 20 to 70, 
     0 to 10 parts by weight 
     of an unbranched polyethylene having a density of 0.94 to 0.965 g/cm 3  and a degree of crystallinity of 60 to 80%, and 5 to 60 parts by weight 
     of a clay mineral having an SiO 2  content of 55 to 80% by weight and an Al 2  O 3  content of 10 to 30% by weight, a particle size of at least 95%&lt;20 μm and a high fine particle content with at least 60%&lt;2 μm. 
     The polypropylene molding composition according to the invention comprises using a naturally occurring clay mineral of specific composition as the reinforcing substance. This clay mineral has been employed to date mainly only in the ceramics industry. When the relatively coarse-particled clay mineral is worked up, a so-called filter dust is obtained, which is distinguished by a mainly very low particle size. A uniformly finely divided mineral powder having, for example, a top cut (at least 95%) of &lt;20 μm and also 85 to 90%&lt;6 μm is obtained by air separation. This mineral powder furthermore can be calcined. 
     According to complete silicate analysis, a sample of the non-calcined clay filter dust used has the following chemical composition: 
     76% by weight of SiO 2   
     16% by weight of Al 2  O 3   
     4% by weight of K 2  O 
     1.5% by weight of Fe 2  O 3   
     0.5% by weight of MgO 
     0.7% by weight of TiO 2   
     1.3% by weight of trace elements 
     5.0% by weight of loss on ignition. 
     This corresponds to a mineralogical composition of 
     about 45% by weight of muscovite (mica) 
     about 39% by weight of quartz 
     about 14% by weight of kaolinite 
     about 2% by weight of secondary constituents. 
     The chemical and mineralogical composition thus differs considerably from that of the clay mineral kaolin mentioned in known molding compositions, the main component of which is kaolinite Al 2  [Si 2  O 5  ](OH) 4  which has a similar Al 2  O 3  :SiO 2  ratio to alumina: 46% of Al 2  O 3  +54% of SiO 2 . Another feature of the clay mineral used is the relatively high Mohs&#39; hardness of 3-3.5, compared with the value of 1 for talc. 
     The polypropylene molding composition according to the invention comprises at least one of the following polymers: 
     1a) a partly crystalline isotactic propylene homopolymer having an isotactic content of &gt;80%, a degree of crystallization of &gt;50% and a melt flow index (230/5) in the range from 0.5 to 1000 g/10 minutes, or 
     1b) a partly crystalline syndiotactic propylene homopolymer having a syndiotactic content of &gt;80%, a syndiotactic sequence length of &gt;10, a degree of crystallization of &gt;30% and a melt flow index (230/5) in the range from 0.5 to 1000 g/10 minutes, or 
     1c) a partly crystalline propylene-ethylene, propylene-1-olefin or propylene-ethylene-α-olefin block copolymer or terpolymer with 1-olefins C n  H 2n  (n=4-8), having an ethylene or/and 1-olefin content of 2-30% by weight and a melt flow index (230/5) in the range from 0.5 to 1000 g/10 minutes, or 
     1d) a partly crystalline random propylene-ethylene, propylene-1-olefin or propylene-ethylene-1-olefin copolymer or terpolymer having an ethylene and/or 1-olefin content of 0.5 to 30% by weight and a melt flow index (230/5) in the range from 0.5 to 1000 g/10 minutes; 
     2) a thermoplastic ethylene-propylene (EPM) or/and ethylene-propylene-diene (EPDM) rubber having an ethylene content of &gt;45% by weight without a diene, up to very high diene contents, and having a Mooney viscosity ML (1+8) at 127° C. in the range from 20 to 70; 
     3) if appropriate an unbranched HD polyethylene having a density of 0.94 to 0.965 g/cm 3  and a degree of crystallization of 60-80%. 
     The molding composition according to the invention furthermore comprises 
     4) a clay mineral having an SiO 2  content of 65±10% by weight, preferably 63 to 66% by weight, and an Al 2  O 3  content of 20±10% by weight, preferably 19 to 22% by weight, and a particle size/top cut of &lt;20 μm, as a filler and reinforcing substance. 
     The polypropylene molding composition according to the invention can additionally also contain the following constituents; 
     5) oxidation stabilizers, such as, for example, sterically hindered phenols, thioethers, phosphites and phosphonites; 
     6) a light-stabilizing finish for internal and/or external uses with UV absorbers and/or HALS (=hindered amine light stabilizers); 
     7) processing auxiliaries, such as lubricants/acid scavengers and antistatics; 
     8) antistatics; 
     9) colored pigments. 
     The melt viscosity and the processing properties of the molding compositions can be adjusted by chemical degradation by means of organic peroxides. Suitable peroxides are 2,5-dimethyl-2,5-bis(tert-butoxy)-hexane, di-t-butyl peroxide and others. 
     The polypropylene molding composition according to the invention comprises the above components 1) to 9) in the following amounts: 
     1) 30 to 95, preferably 50 to 90 parts by weight, 
     2) 0 to 30, preferably 5 to 20 parts by weight, 
     3) 0 to 10, preferably 1 to 3 parts by weight, 
     4) 5 to 60, preferably 10 to 40 parts by weight, 
     5) 0.1 to 2, preferably 0.1 to 1.0 part by weight, 
     6) 0.1 to 3, preferably 0.2 to 0.5 part by weight, 
     7) 0.1 to 3, preferably 0.1 to 1.5 parts by weight, and 
     8) 0 to 10, preferably 0.2 to 2 parts by weight. 
     The individual components are compounded with the aid of customary single- or twin-screw compounders, in particular with twin-screw extruders. The material temperatures in the extruder are as a rule in the range from 180° to 270° C. 
     The resulting strands are cut to pellets having an average length of 2 to 5 mm with the aid of a granulator. 
     Processing of the granules to injection-molded components, for example to test specimens corresponding to ISO and DIN standards for testing the mechanical, thermal and electrical properties of the polypropylene molding composition, is carried out with the aid of customary screw-plunger injection molding machines. The material temperatures in the injection molding machine are usually in the range from 180° to 300° C. and the flow front speeds are between 50 and 500 mm/sec. 
     The properties of the polypropylene molding composition is determined on the test specimens in accordance with the following ISO and DIN standards: 
     tensile tests corresponding to DIN 53 455, 
     modulus of elasticity in tension corresponding to DIN 53 457, 
     bending tests corresponding to DIN 53 452, 
     bending modulus corresponding to ISO R 178, 
     Charpy impact strength corresponding to ISO R 179/1eU, 
     Charpy notched impact strength corresponding to ISO R 179/1eA, 
     ball indentation hardness corresponding to DIN 53 456, 
     heat distortion temperature A corresponding to ISO R 75, 
     melt flow index corresponding to DIN 53 735 and the like. 
     Compared with talc reinforcement, clay mineral reinforcement results in a characteristic shift of the profile of properties of polypropylene molding compositions. In particular, the very different influence of clay mineral reinforcement on the strength/toughness ratio of PP molding compositions which have been impact-modified with EP(D)M and those which have not been impact-modified compared with talc-reinforced PP molding compositions is surprising: 
     in the case of polypropylene molding compositions which have not been impact-modified and have a clay content of, for example, 20% by weight, the impact strengths at temperatures above -10° C., in particular above the glass transition temperature of PP, are up to 40%, depending on the measurement method, more than the values of corresponding talc-reinforced molding compositions. The improvement in the notched impact strengths at temperatures &gt;-10° C. is less pronounced. On the other hand, no improvement in the low temperature impact strength and notched impact strength at temperatures &lt;0° C. is to be found. The strength values (tensile and bending test) of the polypropylene molding compositions reinforced with clay mineral are slightly reduced and the E modulae are reduced by up to 15%. 
     In the case of impact-modified polypropylene molding compositions reinforced with clay mineral, for example having an EP(D)M content of 10% by weight, in contrast, the impact strength at a temperature &gt;10° C. is up to 15% and the notched impact strength up to 30% below the values of the corresponding talc-reinforced polypropylene molding compositions. On the other hand, no differences are to be found in the low temperature impact strength and notched impact strength. The strength of impact-modified polypropylene molding compositions reinforced with clay mineral is slightly above and the ball indentation hardness is considerably (up to 15%) above the values of talc-reinforced polypropylene molding compositions. 
     Generally, an improved scratch resistance and an improved surface quality are to be found in all polypropylene molding compositions reinforced with clay mineral compared with talc-reinforced polypropylene molding compositions. In particular, the slide lines which often occur with impact-modified talc-reinforced molding compositions are still visible only to a very small extent. 
    
    
     The following examples are intended to illustrate the invention. 
     COMPARISON EXAMPLE A 
     The following were mixed in a fluid mixer: 
     78.0 parts by weight of a partly crystalline isotactic propylene homopolymer having an isotactic content of &gt;90%, a degree of crystallization of about 65% and a melt flow index (230/5) of 7-9 g/10 minutes; 
     2.0 parts by weight of a talc having a relatively wide particle size distribution; cut(80%) &lt;20 μm, cut(50%) &lt;10 μm; 
     0.3 part by weight of octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate; 
     0.3 part by weight of di-octadecyl sulfite; 
     0.4 part by weight of calcium stearate and bis-stearoyl/palmitoyl-ethylenediamine in a ratio of 3:1, 
     0.7 part by weight of Acetogen carbon black. 
     Compounding of the powder mixture and subsequent granulation were carried out with the aid of a W&amp;P ZSK 53 twin-screw extruder at a maximum barrel temperature of 230° C. and a maximum material temperature of 250° C. 
     The resulting granules were processed to DIN and ISO test specimens with the aid of a KM 90-210 B screw-piston injection molding machine at a material temperature of not more than 240° C. The abovementioned DIN and ISO tests were carried out. 
     EXAMPLE 1 
     The procedure of comparison example A was repeated, with the exception of the reinforcing substance, which was replaced by 22.0 parts by weight of clay (65.4% of SiO 2 , 20.3% of Al 2  O 3 ) having a low particle size - cut (at at least 95%) &lt;20 μm, cut (85 to 90%) &lt;6 μm. 
     COMPARISON EXAMPLE B 
     The following were mixed in a fluid mixer: 
     70.0 parts by weight of a propylene-ethylene block copolymer having an isotactic content of about 80%, an atactic content of about 5%, an ethylene content of about 7.5% and a melt flow index (230/5) of 20-30 g/10 minutes; 
     20.0 parts by weight of a talc having a relatively low particle size: top cut (99%) &lt;20 μm, cut (86%) &lt;10 μm. 
     10.0 parts by weight of a commercially available impact modifier consisting of: 60% by weight of an EPM rubber having an ethylene content of about 48%, 
     30% by weight of an ethylene-propylene block copolymer and 
     10% by weight of HDPE; 
     0.2 part by weight of pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]; 
     0.3 part by weight of calcium stearate and bisstearoyl/palmitoylethylenediamine corresponding to comparison example A; 
     3 part by weight of a light stabilizer (UV absorber); 
     2.0 parts by weight of colored pigment (ultramarine blue and Acetogen carbon black) 
     Compounding and processing to injection-molded components or test specimens were carried out in accordance with comparison example A. 
     COMPARISON EXAMPLE C 
     The procedure of comparison example B was repeated, with the exception that the acid scavenger Ca stearate was replaced by 0.2 part by weight of MgO. 
     EXAMPLE 2 
     The procedure of comparison example C was repeated, with the exception that the reinforcing substance was replaced by 20 parts by weight of clay mineral corresponding to Example 1. 
     COMPARISON EXAMPLE D 
     The following were mixed in a fluid mixer: 
     80.0 parts by weight of a propylene-ethylene block copolymer having an isotactic content of about 80%, an atactic content of about 5%, an ethylene content of about 10% and a melt flow index (230/5) of 20-30 g/10 minutes; 
     20.0 parts by weight of a talc having a relatively low particle size (corresponding to comparison example B); 
     0.5 part by weight of a combination of a commercially available phenolic and a phosphitic oxidation stabilizer; 
     0.3 part by weight of a combination of Ca stearate and a commercially available wax (corresponding to comparison example B); 
     0.3 part by weight of a light stabilizer; 
     0.98 part by weight of colored pigments for generating a specific black color. 
     EXAMPLE 3 
     The procedure of comparison example D was repeated with the exception that the reinforcing substance was replaced by 20 parts by weight of clay mineral corresponding to Example 1. 
     
                       TABLE 1                                                     
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                       Comparison A                                       
                                   Example 1                              
Properties  Unit       Talc        Clay                                   
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Ignition residue                                                          
            %          20.2        21.0                                   
(1h, 625° C.)                                                      
Melt flow index                                                           
MFI 230/5   g/10 minutes                                                  
                       10.0        9.8                                    
MVI 230/5   g/10 minutes                                                  
                       12.6        10.8                                   
Density     g/cm.sup.3 1.058       1.063                                  
Ball indentation                                                          
hardness                                                                  
30 seconds  N/mm.sup.2 80          85                                     
10 seconds  N/mm.sup.2 85          91                                     
Yield stress                                                              
            N/mm.sup.2 34          33.5                                   
Elongation  %          6           6.2                                    
Stress at break                                                           
            N/mm.sup.2 --          --                                     
Elongation at break                                                       
            %          --          --                                     
Stress at 50%                                                             
            N/mm.sup.2 10          17                                     
Modulus of  N/mm.sup.2 2800        2500                                   
elasticity in                                                             
tension (Secant)                                                          
3.5% bending                                                              
            N/mm.sup.2 44          44                                     
stress                                                                    
Maximum bending                                                           
            N/mm.sup.2 50          49                                     
stress                                                                    
Maximum edge fibre                                                        
            %          6.1         6.0                                    
elongation                                                                
Modulus of  N/mm.sup.2 2700        2500                                   
elasticity in                                                             
bending (tangent)                                                         
Impact strength                                                           
+23° mJ/mm.sup.2                                                   
                       46          55                                     
(Charpy) -20°                                                      
            mJ/mm.sup.2                                                   
                       18          18                                     
Notched impact                                                            
strength                                                                  
(Charpy) +23°                                                      
            mJ/mm.sup.2                                                   
                       4           4                                      
-20° mJ/mm.sup.2                                                   
                       2                                                  
Heat distortion                                                           
            70         64                                                 
temperature A °C.                                                  
Heat aging  hours      800         450                                    
resistance (150° C.)                                               
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                       TABLE 2                                                     
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                       Comp.   Comp.                                      
                       B       C     Example 2                            
Properties  Unit       Talc    Talc  CLAY                                 
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Ignition residue                                                          
            %          19.5    20.8  20.6                                 
(1h, 625° C.)                                                      
Melt flow index                                                           
MFI 230/5   g/10 minutes                                                  
                       18.1    21.8  19.6                                 
MVI 230/5   g/10 minutes                                                  
                       20.1    24.6  21.9                                 
Density     g/cm.sup.3 1.023   1.041 1.041                                
Ball indentation                                                          
hardness 30 seconds                                                       
            N/mm.sup.2 47      52    60                                   
Yield stress                                                              
            N/mm.sup.2 22      22.5  24                                   
Elongation  %          5.6     5.5   5.0                                  
Stress at break                                                           
            N/mm.sup.2 9       9     13.5                                 
Elongation at break                                                       
            %          49      46    37                                   
Stress at 50%                                                             
            N/mm.sup.2 15      16    --                                   
Modulus of  N/mm.sup.2 1680    1660  1670                                 
elasticity in                                                             
tension (Secant)                                                          
3.5% bending                                                              
            N/mm.sup.2 26      27    28                                   
stress                                                                    
Maximum bending                                                           
            N/mm.sup.2 26      27.5  29                                   
stress                                                                    
Maximum edge fibre                                                        
            %          3.6     3.9   4.1                                  
elongation                                                                
Modulus of  N/mm.sup.2 1750    1810  1630                                 
elasticity in                                                             
bending (tangent)                                                         
Impact strength                                                           
(Charpy) +23°                                                      
            mJ/mm.sup.2                                                   
                       NB      127   110                                  
-20° mJ/mm.sup.2                                                   
                       75      37    38                                   
Notched impact                                                            
strength                                                                  
(Charpy) +23°                                                      
            mJ/mm.sup.2                                                   
                       15.3    10.3  7.3                                  
-20° mJ/mm.sup.2                                                   
                       4.5     3     3                                    
OIT (200°  C.)                                                     
            min        44      31    37                                   
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 NB = no break                                                            
 
    
     
                       TABLE 3                                                     
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                        Compari-                                          
                        son D     Example 5                               
Properties  Unit        Talc      Clay                                    
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Ignition residue                                                          
            %           20        21.5                                    
(1h, 625° C.)                                                      
Melt flow index                                                           
MFI 230/5   cm.sup.3 /10 minutes                                          
                        40        37                                      
Density     g/cm.sup.3  1.04      1.07                                    
Ball indentation                                                          
hardness 30 seconds                                                       
            N/mm.sup.2  65        65                                      
Yield stress                                                              
            N/mm.sup.2  28        23                                      
Elongation  %           4         4                                       
Tear strength                                                             
            N/mm.sup.2  4         15                                      
Elongation at tear                                                        
            %           35        30                                      
Modulus of  N/mm.sup.2  2200      1900                                    
elasticity in                                                             
tension                                                                   
Modulus of  N/mm.sup.2  2100      1800                                    
elasticity in                                                             
bending                                                                   
Impact strength                                                           
(Charpy) +23°                                                      
            N/mm.sup.2  105       150                                     
-20° N/mm.sup.2  40        55                                      
Notched impact                                                            
strength                                                                  
(Charpy) +23°                                                      
            N/mm.sup.2  6         7.5                                     
-20° N/mm.sup.2  3         3                                       
Heat distortion                                                           
            70          62        52                                      
temperature A °C.                                                  
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