Abstract:
A method for improving at least one property of a polyester, the property selected from the group consisting of impact strength, color, or tensile modulus of a polyester comprising reacting the polyester with an epoxy silane wherein the epoxy is attached to a terminal cycloaliphatic ring system, the reaction product having improved at least one of the properties of impact strength, color, and tensile modulus.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Polyesters are well known in polymer chemistry for many decades. Among the properties for which polyesters are known are electrical, HDT, flow rate, solvent resistance, and the like. When used in blends with the materials such as polycarbonates, impact modifiers and the like, it is usually the above-mentioned polyester properties which are sought after.  
         [0002]     We have now found that a polyester&#39;s [polybutylene terephthalate (PBT)] basic properties of impact strength, color, and tensile modulus can be significantly improved when the polyester is contacted with an epoxysilane, wherein the epoxy is attached to a terminal cycloaliphatic ring system. When the epoxy is attached to a normal alkylene group, no significant improvement in these properties is observed.  
       SUMMARY OF THE INVENTION  
       [0003]     In accordance with the invention there is a method for improving at least one of the properties of impact strength, color, and tensile modulus of a polyester comprising reacting the polyester with an epoxy silane wherein the epoxy is attached to a terminal cycloaliphatic ring system, the reaction product having improved at least one of the properties of impact strength, color, and tensile modulus.  
         [0004]     Additionally, there is a composition comprising a polyester reacted with an epoxysilane, the product of said reaction having improved at least one of the properties of impact strength, color, and tensile modulus compared to the initial polyester. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0005]     The singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.  
         [0006]     “Optional” or “optionally” as used herein means that the subsequently described event may or may not occur, and that the description includes instances where the event occurs and the instances where it does not occur.  
         [0007]     Any polyester can be the initial polyester provided it has carboxyl and/or alcohol end groups available for reaction with the epoxy silane. Such polyesters include those comprising structural units of formula 1:  
                         
 
 wherein each R 1  is independently a divalent aliphatic, alicyclic or aromatic hydrocarbon or polyoxyalkylene radical, or mixtures thereof and each A 1  is independently a divalent aliphatic, alicyclic or aromatic radical, or mixtures thereof. Examples of suitable polyesters containing the structure of the above formula are poly(alkylene dicarboxylates), liquid crystalline polyesters, and polyester copolymers. It is also possible to use a branched polyester in which a branching agent, for example, a glycol having three or more hydroxyl groups or a trifunctional or multifunctional carboxylic acid has been incorporated. Furthermore, it is sometimes desirable to have various concentrations of acid and hydroxyl end groups on the polyester, depending on the ultimate end-use of the composition. 
 
         [0008]     The R 1  radical may be, for example, a C 2-10  alkylene radical, a C 6-12  alicyclic radical, a C 6-20  aromatic radical or a polyoxyalkylene radical in which the alkylene groups contain about 2-6 and most often 2 or 4 carbon atoms. The A 1  radical in the above formula is most often p- or m-phenylene, a cycloaliphatic or a mixture thereof. This class of polyesters includes the poly(alkylene terephthalates). Such polyesters are known in the art as illustrated by the following patents, which are incorporated herein by reference.  
         [0009]     U.S. Pat. Nos. 2,465,319 2,720,502 2,727,881 2,822,348 3,047,539 3,671,487 3,953,394 4,128,526  
         [0010]     Examples of aromatic dicarboxylic acids represented by the dicarboxylated residue A 1  are isophthalic or terephthalic acid, 1,2-di(p-carboxyphenyl)ethane, 4,4′-dicarboxydiphenyl ether, 4,4′ bisbenzoic acid and mixtures thereof. Acids containing fused rings can also be present, such as in 1,4-1,5- or 2,6-naphthalenedicarboxylic acids. The preferred dicarboxylic acids are terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, cyclohexane dicarboxylic acid or mixtures thereof.  
         [0011]     The most preferred polyesters are poly(ethylene terephthalate) (“PET”), poly(1,4-butylene terephthalate) (“PBT”), poly(ethylene naphthanoate) (“PEN”), poly(butylene naphthanoate) (“PBN”), (polypropylene terephthalate) (“PPT”), poly(1,4-10 cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate) (“PCCD”), poly(1,4-cyclohexylenedimethylene terephthalate) (“PCT”), poly(cyclohexylenedimethylene-co-ethylene terephthalate) (“PCTG”), and mixtures thereof.  
         [0012]     Also contemplated herein are the above polyesters with minor amounts, e.g., from about 0.5 to about 5 percent by weight, of units derived from aliphatic acid and/or aliphatic polyols to form copolyesters. The aliphatic polyols include glycols, such as poly(ethylene glycol) or poly(butylene glycol). Such polyesters can be made following the teachings of, for example, U.S. Pat. Nos. 2,465,319 and 3,047,539.  
         [0013]     The epoxy silane which is contacted with and reacts with the polyester is generally any kind of epoxy silane wherein the epoxy is at one end of the molecule and attached to a cycloaliphatic group and the silane is at the other end of the molecule. A desired epoxy silane within that general description is of formula 2.  
                         
 
 wherein m is an integer 1, 2 or 3, n is an integer of 1 through 6 and X, Y, and Z are the same or different, preferably the same and are alkyl of one to twenty carbon atoms, inclusive, cycloalkyl of four to ten carbon atoms, inclusive, alkylene phenyl wherein alkylene is one to ten carbon atoms, inclusive, and phenylene alkyl wherein alkyl is one to six carbon atoms, inclusive. 
 
         [0014]     Desirable epoxy silanes within the range are compounds wherein m is 2, n is 1 or 2, desirably 2, and X, Y, and Z are the same and are alkyl of 1, 2, or 3 carbon atoms inclusive. Epoxy silanes within the range which in particular can be used are those wherein m is 2, n is 2, and X, Y, and Z are the same and are methyl or ethyl.  
         [0015]     The polyester modified with the epoxy silane can be blended with any of the usual additives and property modifier that polyesters are usually mixed for example glass, clay, mica and the like. Polymer blends can be made with reacted polyester or can be made with the unreacted polyester and the polyester then reacted with the epoxy silane during the blending or extrusion process. Examples of polymer which can be blended include aromatic polycarbonates, polysulfones, polyethesulfones, impact modifiers, and the like.  
         [0016]     The epoxy silane is reacted with the polyester by simply bringing the two components together at a temperature and time period. For example, PBT 195, Intrinsic Viscosity (IV) 1.1 from GE together with PBT 315, IV 0.7 from GE are tumble blended with various additives such as potassium diphenylsulfone sulfonate (KSS), a flame retardant, a hindered phenol such as Irganox 1010 from Ciba Geigy, a catalyst such as sodium stearate, a mold release such as pentaerythritol tetrastearate (PETS) and the epoxy silane beta-(3,4-epoxycyclohexyl)ethyl triethoxysilane Coatosil 1770 from GE and then extruded in a 27 mm twin screw with a vacuum vented mixing screw at a barrel and die head temperature between 240 and 265 degrees Celsius and 450 ppm screw speed. The extrudate is cooled through a water bath prior to palletizing.  
         [0017]     The quantities of epoxy silane employed as a percentage of polyester present in the composition is generally at least about 0.1 wt % and a minimum of about 0.4 wt % can also be employed. Generally, further increases in desirable properties are not observable beyond a maximum of about 5.0 wt %, but further quantities can be used if desired.  
         [0018]     Various processes can be used to bring about a desired final product. Injection molding, blow molding, compression molding, resin transfer molding, and the like are processes which can be employed.  
         [0019]     As noted previously various properties can be improved such as impact strength, color, and tensile modulus through the use of the epoxy silane. Virtually any part for an application can benefit from one or a combination of at least two of these properties. For instance, in one embodiment, with respect to the impact strength, a reaction product has an improved impact strength that is at least 10%, as compared to a reaction product that does not contain the epoxy silane, measured with Notched IZOD or DYNATUP impact testing techniques. In another embodiment, the improved impact strength can range from 10 to 30%, or more, as compared to a reaction product that does not contain the epoxy silane, measured with Notched IZOD or DYNATUP impact testing techniques. With respect to improved color properties imparted by the epoxy silane to an opaque reaction product, an opaque reaction product of the invention can have a reduced Yellowness Index by Reflectance (YIR) of at least two units, as compared to a reaction product that does not contain the epoxy silane. In another embodiment, an opaque reaction product of the invention can have a reduced Yellowness Index by Reflectance (YIR) from two to eleven units, or more, as compared to a reaction product that does not contain the epoxy silane. With respect to improved color properties imparted by the epoxy silane to a transparent reaction product, a transparent reaction product of the invention can have a reduced Yellowness Index (YI) of at least one unit, as compared to a reaction product that does not contain the epoxy silane. In another embodiment, a transparent reaction product of the invention can have a reduced Yellowness Index (YI) from one to eleven units, or more, as compared to a reaction product that does not contain the epoxy silane. With respect to tensile modulus, a reaction product has an improved tensile modulus that is at least 5%, as compared to a reaction product that does not contain the epoxy silane, measured with tensile testing techniques. In another embodiment, the improved tensile strength can range from 5 to 10%, or more, as compared to a reaction product that does not contain the epoxy silane, measured with tensile testing techniques.  
         [0020]     Below are examples of the invention. These examples relative to their control comparisons show significant improvement in the above-identified areas. Additionally tensile elongation at break in the non-glass filled PBT and tensile elongation at yield in the glass filled PBT shows improvements. These improvements are indeed selective as noted by other tests providing virtually no improvement or potentially some small declines in tested values.  
         [0021]     Tensile properties were tested according to ASTM D648 using Type 1 tensile bars at room temperatures with a crosshead speed of 2 in/min.  
         [0022]     Izod testing was done on 3×½×⅛ inch bars according to ASTM D256.  
         [0023]     Yellowness Index (YI) was tested according to ASTM E313-00.  
         [0024]     Yellowness Index by Reflectance (YIR)— This is computed from the spectrophotometric reflectance data of an opaque specimen, which indicates the degree of departure of an object from colorless or from a preferred white, towards yellow. A spectrophotometric method is employed. Acceptable test samples are free from dust, grease, scratches, and visible molding defects. Samples are molded and must have plane-parallel surfaces. Spectrophotometer is a Minolta CM-3600 Spectrophotometer with SpectaMatch software configured for simultaneous capture of YI, % T, and % Haze using Illuminant C—North Sky Daylight and 2° Standard Observer settings. All test specimens are to be conditioned at 23±2° C. relative humidity for not less that 40 hours prior to testing. YIR tests are to be performed in a reflectance mode. A white calibration tile backs the test specimen during testing. YIR is reported to 0.1.  
         [0025]     Results  
                                                                           TABLE 1                           Color comparison of PBT resin with and without epoxysilane                Component   Unit   C1   E1   C2   E2                            PBT 315   %   99.94   98.44   0.0   0.0           PBT 195   %   0.0   0.0   99.94   98.44           CoatoSil 1770   %   0.0   1.5   0.0   1.5           NaSt   %   0.01   0.01   0.01   0.01           Irg 1010   %   0.05   0.05   0.05   0.05           YIR       13.3   8.4   17.1   6.1                      
 
         [0026]     As seen in Table 1, the addition of epoxysilane Coatosil 1770 significantly reduces the YIR of PBT resin in molded parts. Additionally, the YIR is reduced in pellets as well. The examples shown in Table 1 (E1 and E2) both have 1.5% epoxysilane loading, but similar YIR-reduction were observed when the epoxysilane loading were lower or higher.  
                                                                   TABLE 2                           Effect of epoxysilane on mechanical properties of unfilled PBT            Properties   Unit   C1   E1   C2   E2                    Notched   lbf/in   0.8   1.093   0.781   1.033       IZOD       Unnotched   lbf/in   33.5   39.2   39.2   35.4       IZOD       Dynatup   Ft-lbf   43.1   49.3   32.7   39.5       total       energy       Flex   PSI   12200   12900   12900   12100       strength       Flex   PSI   355000   389000   367000   351000       modulus       Tensile   PSI   8380   8290   8350   8270       strength       at yield       Tensile   %   3.30   2.94   3.30   3.02       elongation       at yield       Tensile   PSI   4250   5710   5860   5280       strength       at break       Tensile   %   162   218   71.3   129.2       elongation       at break       Tensile   PSI   409000   444000   404000   430000       Modulus       Vicat   C.   172   183                  
 
         [0027]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
               
               
                 Effect of epoxysilane on mechanical properties of glass-filled PBT 
               
             
          
           
               
                 Component 
                 Unit 
                 C3 
                 E5 
                 E6 
                 C4 
                 E7 
                 E8 
               
               
                   
               
             
          
           
               
                 PBT 315 
                 % 
                 69.94 
                 68.94 
                 67.94 
                 0.0 
                 0.0 
                 0.0 
               
               
                 PBT 195 
                 % 
                 0.0 
                 0.0 
                 0.0 
                 69.94 
                 68.94 
                 67.94 
               
               
                 Chopped Glass Fiber 
                 % 
                 30.0 
                 30.0 
                 30.0 
                 30.0 
                 30.0 
                 30.0 
               
               
                 CoatoSil 1770 
                 % 
                 0.0 
                 1.0 
                 2.0 
                 0.0 
                 1.0 
                 2.0 
               
               
                 NaSt 
                 % 
                 0.01 
                 0.01 
                 0.01 
                 0.01 
                 0.01 
                 0.01 
               
               
                 Irg 1010 
                 % 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
                 0.05 
               
               
                 Notched IZOD 
                 lbf/in 
                 1.58 
                 2.17 
                 1.83 
                 1.37 
                 1.46 
                 1.58 
               
               
                 Unnotched IZOD 
                 lbf/in 
                 16.2 
                 17.2 
                 16.3 
                 11.3 
                 13.7 
                 17.6 
               
               
                 Dynatup total energy 
                 Ft-lbf 
                 6.7 
                 6.6 
                 7.0 
                 4.9 
                 5.9 
                 7.8 
               
               
                 Flex strength 
                 PSI 
                 25900 
                 28600 
                 28700 
                 25700 
                 27400 
                 28400 
               
               
                 Flex modulus 
                 PSI 
                 1160000 
                 1180000 
                 1240000 
                 1200000 
                 1170000 
                 1190000 
               
               
                 Tensile strength at yield 
                 PSI 
                 17400 
                 18600 
                 18700 
                 17400 
                 18900 
                 19600 
               
               
                 Tensile elongation at yield 
                 % 
                 2.62 
                 3.02 
                 3.18 
                 1.76 
                 2.18 
                 2.58 
               
               
                 Tensile Modulus 
                 PSI 
                 1990000 
                 2300000 
                 2480000 
                 2170000 
                 2090000 
                 2140000 
               
               
                 Vicat 
                 C. 
                 215.6 
                 216.7 
                 214.8 
                 210.2 
                 210.3 
                 212.3 
               
               
                   
               
             
          
         
       
     
         [0028]     As shown in Table 3, the addition of epoxysilane Coatosil 1770 improves the modulus and impact property in both glass-filled and un-filled PBT, especially in materials based on PBT 315.  
                                                                   TABLE 4                           Color comparison of PCTG resin with and without epoxysilane                Component   Unit   C5   E9   E10                            PBT 315   %   99.94   97.94   96.94           CoatoSil 1770   %   0.0   2.0   3.0           NaSt   %   0.01   0.01   0.01           Irg 1010   %   0.05   0.05   0.05           YI       3.15   0.53   0.71           % Transmission   %   85.0   86.1   85.6                      
 
         [0029]     As seen in Table 4, the addition of epoxysilane Coatosil 1770 significantly reduces the YI of PCTG resin in molded parts. Additionally, the YI is reduced in pellets as well. The examples shown in Table 4 (E9 and E10) have epoxysilane loading of 2.0% and 3.0%, respectively, but similar YI-reduction were observed when the epoxysilane loading were lower or higher.  
                                                           TABLE 5                           Effect of epoxysilane on mechanical properties of PCTG            Properties   Unit   C5   E9   E10                    Notched IZOD   lbf/in   26.9   7.1   6.9       Impact Strength       Unnotched   lbf/in   27.0   33.6   37.6       IZOD Impact       Strength       Dynatup total   Ft-lbf   45.6   47.7   51.3       energy       Flex strength   PSI   9380   9450   9574       Tensile strength   PSI   6340   6500   6580       at yield       Tensile   %   4.94   4.55   4.30       elongation       at yield       Tensile strength   PSI   5710   4360   4200       at break       Tensile   %   163.28   115.65   124.33       elongation       at break       Tensile Modulus   PSI   238000   250000   255000                  
 
         [0030]     As shown in Table 5, the addition of epoxysilane Coatosil 1770 improves the unnotched IZOD impact strength and Dynatup impact property in PCTG.