Abstract:
Carbonate polymers (PC) such as randomly branched carbonate polymers, linear carbonate polymers and blends thereof are blended with ABS polymers and acrylonitrile-styrene-acrylate rubber (ASA) polymers as impact modifiers. The ABS polymers have greater than 18% acrylonitrile. The ASA impact modifier is in the PC and the ABS resin interphases so that higher melt elasticity is achieved.

Description:
BACKGROUND OF THE INVENTION 
     This application is a Continuation-in-Part of the copending application Ser. No. 07/320667, filed Mar. 8, 1989, now abandoned. 
    
    
     This invention relates to thermoplastic resin compositions and more particularly relates to improved blow moldable or thermoformable compositions of carbonate polymers and acrylonitrile-styrene-acrylate (ASA) copolymers and to a process of making blow molded articles using the improved compositions. 
     More specifically, this invention relates to blow molding compositions comprising a blend of (1) carbonate polymers with (2) graft copolymers of an alkyl acrylate or a alkyl acrylate-vinyl aromatic hydrocarbon copolymer with a mixture of acrylonitrile and a vinyl aromatic hydrocarbon and (3) core/shell graft copolymers of alkyl acrylate or butadiene or butadiene-vinyl aromatic hydrocarbon or butadiene-vinyl aromatic hydrocarbon-alkyl acrylate with a second optional phase of vinyl aromatic hydrocarbon and a outer shell of polyalkylacrylate and/or polyalkylmethacrylate. 
     Although carbonate polymer/ASA compositions have been found to be thermoplastically moldable under a broad range of injection molding conditions, only select polycarbonate blends are suitable for blow molding. This is due to the unique requirement of thermoplastic resin for blow molding operations. 
     In the conventional blow molding operation, as taught in U.S. Pat. No. 4,652,602 and U.S. Pat. No. 4,474,999, a tube or parison of the heat softened thermoplastic blend may be extruded vertically downward into a mold. The extrudate is then pressed unto the mold surfaces with a pressurized gas flow (usually air or inert gas), shaping the heat softened resin. As appreciated by those skilled in the art, the successful molding of a given thermoplastic resin is dependent upon a number of factors, including the characteristics and physical properties of the heat softened resin. The length and diameter of the tube and the quantity of material forming the tube are limiting factors in determining the size and wall thickness of the object that can be molded by this process. The fluidity of the melt obtained from polycarbonate/ASA blends, or the lack of melt strength as well as the paucity of extrudate swelling, serve to limit blow molding applications to relatively small, thin walled parts. These factors alone are of considerable importance in the successful blow molding of any resin, particularly in regard to the molding of large articles. 
     It is known from Japanese patent 58/59258 that resin compositions with good weld strength can be obtained from blends of linear polycarbonate resins, acrylonitrile-butadiene-styrene resins (ABS), and rubbery graft copolymer resins (MBS). However, this reference does not suggest the advantage of using ASA a more environmentally stable resin or controlling rubber placement and in fact is attempting to modify the ABS phase to improve the weldline by utilizing MBS resins containing 30-50% rubber and styrene in the outer shell. Having styrene in the outer shell helps to derive the MBS resins into the ABS phase where the added rubber helps to improve the poor weldline properties of the ABS. It is also recognized by those knowledgeable of ABS resins that resins having low acrylonitrile levels have higher weldline strengths. 
     It is further known from U.S. Pat. No. 4,677,162 that a moldable blend of both linear or branched polycarbonate resins (PC), acrylonitrile-butadiene-styrene resins (ABS), and rubbery graft copolymers (MBS) is useful to form articles with good impact and low gloss. However, this reference utilizes only ABS resins and does not recognize the advantage of using ASA a more environmentally stable resin. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a thermoplastic blend composition useful for blow molding comprising 
     A) about 20 to about 95% by weight and preferably about 30 to about 85% by weight of a carbonate polymer selected from (i) randomly branched carbonate polymers, (ii) linear carbonate polymers, and (iii) blends of randomly branched carbonate polymers with linear carbonate polymers, 
     B) about 5 to about 75% by weight and preferably about 15 to about 70% by weight of a vinyl cyanide-vinyl aromatic hydrocarbon-acrylate rubber copolymer, and 
     C) about 0.5 to about 20% by weight and preferably about 2 to about 15% by weight of a core-shell graft copolymer of a butadiene polymer or a graft copolymer of butadiene or alkyl acrylate polymer having an outer shell of a polymerized alkyl (meth)acrylate. 
     A further aspect of the present invention is a process of preparing blow molded articles using the above composition. 
     The articles produced and/or molded by using the compositions of the invention are useful as automotive components, bottles, tool housings and the like. 
    
    
     BRIEF DESCRIPTION OF THE FIGURE 
     The figure of this invention is a transmission electron micrograph (TEM) photograph of Example 1 showing that the PC/ASA/MBS blend preferentially has more of the MBS rubber located in the darker gray PC phase and interphase with the lighter gray phase being the alkyl acrylate modified SAN phase. The photograph show the location of the small particles of rubbery impact modifier in both the polycarbonate and the ASA resin interphases and this location of the rubber particles in both phases or interphases results in higher melt elasticity, elastic modulus and higher zero shear viscosity. These are properties which are desirable and/or useful in blow molding of large parts since high R* values (a measure of melt elasticity) are needed for the blow molding of parisons weighing 2 pounds or more. The ability to control the placement of rubber, such that rubber now resides in each phase of a multi-phase polymer blend, is critical to increase the melt elasticity of compositions used for large part blow molding or thermoforming applications. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The carbonate polymers employed in the present invention are advantageously aromatic carbonate polymers such as the trityl diol carbonates described in U.S. Pat. Nos. 3,036,036; 3,036,037; 3,036,038 and 3,036,039; polycarbonates of bis(arhydroxyphenyl)-alkylidenes (often called bisphenol-A type diols) including their aromatically and aliphatically substituted derivatives such as disclosed in U.S. Pat. Nos. 2,999,835; 3,028,365 and 3,334,154; and carbonate polymers derived from other aromatic diols such as described in U.S. Pat. No. 3,169,121. 
     It is understood, of course, that the polycarbonate may be derived from (1) two or more different dihydric phenols or (2) a dihydric phenol and a glycol or a hydroxy or acid terminated polyester or a dibasic acid in the event a carbonate copolymer or interpolymer rather than a homopolymer is desired. Also suitable for the practice of this invention are blends of any one of the above carbonate polymers. Also included in the term &#34;carbonate polymer&#34; are the ester/carbonate copolymers of the types described in U.S. Pat. Nos. 3,169,121; 4,287,787; 4,156,069; 4,260,731; 4,330,662; 4,360,656; 4,374,973; 4,225,556; 4,388,455; 4,355,150; and 4,105,633. Of the aforementioned carbonate polymers, the polycarbonates of bisphenol-A and derivatives, including copolycarbonates of bisphenol-A, are preferred. Methods for preparing carbonate polymers for use in the practice of this invention are well known, for example, several suitable methods are disclosed in the aforementioned patents which are hereby incorporated by reference in their entirety. 
     The branched chain polycarbonates used in this invention are prepared by reacting a dihydric phenol with phosgene in the presence of a trihydric and/or tetrahydric phenol. U.S. Pat. No. 3,544,514 discloses the process details and this patent is incorporated herein by reference. 
     Blow moldable resins and their desired properties are taught in U.S. Pat. Nos. 4,652,602 and 4,474,999 which are incorporated herein by reference. U.S. Pat. No. 4,652,602 is particularly pertinent since it gives a definition of R* which is a measure of blow moldability, particularly for small molded articles. 
     The grafted copolymers of the present invention are generally characterized as having a core-shell structure, typically prepared by means of an emulsion polymerization process, or a core-matrix structure, typically prepared by a mass polymerization process. Blends of PC/ASA/MBS and other rubber modified SAN copolymers such as ABS or AES may be added. The grafted copolymers of the present invention generally comprise about 5% to 95% by weight of an elastomeric rubber core, and about 95% to about 5% by weight of either a rigid grafted-on thermoplastic polymer shell in the case of a core-shell copolymer, or a grafted-on thermoplastic polymer matrix in the case of a core-matrix copolymer. Examples of suitable grafted copolymers of the core-shell type are a methylmethacrylate/butadiene/styrene grafted copolymer (MBS rubber), and a butyl acrylate core-rigid thermoplastic shell copolymer. An example of a suitable grafted copolymer of the core-matrix type is an acrylonitrile/butylacrylate/styrene grafted copolymer (ASA copolymer). 
     The preferred grafted copolymers are generally obtained by polymerizing certain monomers in the presence of an acrylate or diene rubber core. By the term diene rubber is meant homopolymers of conjugated dienes have 4 to 8 carbon atoms such as butadiene, isoprene, piperylene, chloroprene, and copolymers of such dienes with other monomers, such as for example, acrylonitrile, methacrylonitrile, butyl acrylate, methyl methacrylate, styrene, α-methylstyrene, and the like. By the term acrylate is meant homopolymer of alkyl acrylates or methacrylates where the alkyl contains C 1  to C 10  carbon atoms such as butyl acrylate, 2 ethyl hexyl acrylate, hydroxy ethyl acrylate and copolymers with other monomers. The rubber core may be at least partially crosslinked, or may contain thermoplastic polymer inclusions such as for example when mass polymerization is used to prepare the grafted copolymer. The aforementioned certain monomers are grafted onto the rubber core to form either the shell or matrix. At least one of these monomers is selected from the group including styrene and its derivatives, such as for example α-methylstyrene, acrylic acids, methacrylic acids, acrylonitrile, methacrylonitrile, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, methyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, glycidyl methacrylate, maleic anhydride and the like. Preferred grafted copolymers are MBS rubbers, butyl acrylate core-rigid shell copolymers, ASA copolymers, and butadiene/styrene/acrylonitrile core-shell type copolymers. Also included within the scope of this invention are other blends of PC/ASA/ core shell rubber with other rubber modified SAN polymers such as ABS or AES. 
     An MBS rubber contains a substrate latex, or core, which is made by polymerizing a conjugated diene, or by copolymerizing a conjugated diene with a mono-olefin or polar vinyl compound, such as styrene, acrylonitrile or methyl methacrylate. The substrate latex is typically made up of about 45-75% conjugated diene and about 25-55% of the mono-olefin or polar vinyl compound. A mixture of monomers is graft polymerized to the substrate latex. A variety of monomers may be used for this grafting purpose, of which the following are exemplary: vinyl compounds such as vinyl toluene, alphamethyl styrene, halogenated styrene, naphthalene, acrylonitrile, methacrylonitrile or alpha-halogenated acrylonitrile, or a C 1  -C 8  alkyl acrylate such as methacrylate, ethylacrylate or hexyl acrylate, a C 1  -C 8  alkyl methacrylate such as methyl methacrylate, ethyl methacrylate or hexyl methacrylate, an acrylic or methacrylic acid, or a mixture of two or more of the foregoing. The extent of grafting is sensitive to the substrate latex particle size, and particle size may be influenced by controlled coagulation techniques among other methods. When the graft level is allowed to reach an excessively high level, the rubbery effect of the relative substrate latex content is reduced. 
     The grafting monomers may be added to the reaction mixture simultaneously or in sequence, and, when added in sequence, layers, shells or wart-like appendages can be built up around the substrate latex, or core. The monomers can be added in various ratios to each other although, when just two are used, they are frequently utilized in equal amounts. A typical weight ratio for an MBS rubber is about 60-80 parts by weight substrate latex, about 10-20 parts by weight first monomer and about 10-20 parts by weight second monomer. A preferred formulation of an MBS rubber is one having a core built up from about 71 parts of butadiene, about 3 parts of styrene, about 4 parts of methyl methacrylate and about 1 part of divinyl benzene; a second phase of about 11 parts of styrene: and a shell phase of about 11 parts of methyl methacrylate and about 0.1 part of 1,3-butylene glycol dimethacrylate, where the parts are by weight of the total composition. A product having substantially such content is available commercially from Rohm and Haas Company as Paraloid™ EXL 3607 core-shell polymer. The MBS rubber and methods for making same, as described above, are discussed in greater detail in U.S. Pat. No. 3,243,481, U.S. Pat. No. 3,287,443, U.S. Pat. No. 3,509,237, U.S. Pat. No. 3,657,391, U.S. Pat. No. 3,660,535, U.S. Pat. No. 4,180,494, U.S. Pat. No. 4,221,833, U.S. Pat. No. 4,239,863 and U.S. Pat. No. 4,617,345 each of which is hereby incorporated by reference herein. 
     Acrylonitrile-styrene-acrylate rubber copolymers are commercially available and well known from U.S. Pat. No. 3,944,631 which is incorporated by reference herein. 
     The following examples and controls are presented to further illustrate the invention. 
     CONTROL 
     One thousand three hundred parts by weight of a linear polycarbonate (Calibre™ 300-10, Dow Chemical Company) was mixed with 700 parts by weight acrylonitrile-styrene-acrylate rubber copolymer (ASA from the Dow Chemical Company), 2 parts by weight epoxy soybean oil (Plas Chek™ 775 from the Ferro Company), and 4 parts by weight Irganox™ 1076 antioxidant (from Ciba Geigy) 
     The mixture was uniformly blended together in a laboratory tumbler. The blend is introduced into a 30 mm Werner-Pfleiderer melt extruder, with heating set points of 270° C. The extrudate is pelletized and dried. The pellets are fed to a 70 ton Arburg injection molding machine to mold test bars of 12.6 cm×2.25 cm with a thickness of 3.175 mm. The moldings are subjected to tests to determine their blow moldability (R* value), and 10 mil notched Izod. 
     The composition of each blend is given in Table 1 below. Each example of the composition was made by following the procedure for the control. The test results are given in Table 2 below. 
     These compositions may be useful for injection molding, blow molding or thermoforming applications and are not intended to be limited to only blow molding applications. 
     These compositions may also contain other ingredients such as UV and antioxidant stabilizers, fillers such as talc, reinforcement agents and such as MICA or glass fibers, ignition resistant additives, pigments, antistat agents, mold release additives, etc. 
     
                       TABLE 1______________________________________PC/ASA BlendsLin.         Bran.             Para   ParaPC           PC       ASA      3607   3330(gms/        (gms/    (gms/    (gms/  (gms/wt %)        wt %)    wt %)    wt %)  wt %)______________________________________Control 1   1300/    0        700/   0      0   65                35Example 1   1240/    0        640/   120/   0   62                32     6Control 2   650/     650/     700/   0      0   32.5     32.5     35Example 2   620/     620/     640/   120/   0   31       31       32     6Example 3   620/     620/     640/   0      120/   31       31       32            6Example 4   460/     460/     1000/   80/   0   23       23       50     4______________________________________ Notes: Lin. PC = linear polycarbonate 10 MFR. Bran. PC = branched polycarbonate 3 MFR. Para 3607 = Paraloid ™ 3607 methylmethacrylatestyrene-butadiene core/shell graft copolymer from Rohm and Haas. Para 3330 = Paraloid ™ 3330 butyl acrylate rubbermethylmethacrylate graft copolymer from Rohm and Haas. ASA = acrylonitrilestyrene-acrylate rubber 15% rubber copolymer from the Dow Chemical Company 
    
     All compositions contained 2 grams of epoxidized soybean oil and 4 grams of Irganox™ 1076 a high molecular weight, sterically hindered phenolic antioxidant from Ciba Geigy. 
     
                       TABLE 2______________________________________    ⊥Izod   ∥IzodR*         23° C.               -29° C.                         23° C.                                -29° C.______________________________________Control 1   3.6    443      58      560    101Example 1   4.7    433      96      539    176Control 2   4.6    192      37      512     69Example 2   5.7    411      96      550    208Example 3   5.0    438      69      619    144Example 4   5.6     80      NA      187    NA______________________________________ Notes: (1) Izod ⊥ = Izod values (according to ASTM D256 in joules/meter) perpendicular to the direction of polymer flow taken at the given temperatures. Izod ∥ = Izod values (according to ASTM D256 in joules/meter) parallel to the direction of polymer flow taken at the given temperatures (2) R* = viscosity ratio. 
    
     Control 1 is an example of a PC/ASA composition. Example 1 illustrates that higher R* values and better low temperature izod impact values are obtained over control 1 when MBS rubber is added and preferentially located in the polycarbonate phase and/or interphase. Example 1 uses only linear PC which has fairly low melt elasticity, thus locating a rubber in the PC phase or interphase can increase the melt elasticity required for improved blow molding resins. 
     Another way to increase the melt elasticity of a PC resin is to use a branched polycarbonate. As expected, Control 2 shows a large increase in R* values with the addition of a branched resin, however in doing so impact properties in the perpendicular direction drop substantially. Examples 2, 3 and 4 show once again large improvements in R* and impact values with the addition of a core/shell rubber to blend of a linear and/or branched polycarbonate and ASA resin.