Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-09-04
2003-04-08
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S067000, C525S069000, C525S902000
Reexamination Certificate
active
06545089
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to an impact modified thermoplastic aromatic carbonate polymer composition having improved resistance to transesterification or degradation and improved thermal stability. More specifically the composition of this invention comprises in combination an aromatic polycarbonate resin and an impact modifier that essentially does not catalyze transesterification or degradation of an aromatic carbonate polymer composition.
BACKGROUND OF THE INVENTION
Addition of rubbery impact modifiers is commonly used to improve the toughness of aromatic carbonate polymer compositions. In comparing the effectiveness of various rubbery modifiers large differences in melt stability are often observed. In aromatic carbonate polymer compositions, the polycarbonate portion of the composition is susceptible to degradation by acids-and bases. Sufficient degradation will cause color formation, loss of molecular weight, reduced chemical and mechanical properties and generation of carbon dioxide which causes surface appearance defects, such as splay in molded parts.
The problem of the melt stability of polycarbonates and blends thereof with other polymers are often addressed by the addition of various stabilizers as disclosed in copending application Ser. No. 08/79112 filed Jan. 30, 1997 and assigned to the same assignee and in U.S. Pat. Nos. 4,532,290, 5,252,536, 5,441,997, 5,502,119 and 5,608,027 all of which are incorporated herein by reference. Rubbery modifiers prepared by emulsion polymerization are useful in polymer blends as impact modifiers due to their fixed particle size. However, they may cause particular problems in the stability of polycarbonates due to the presence of significant amounts of additives employed in preparing the rubbery modifiers such as flow aids, polymerization catalysts, antioxidants and especially emulsifiers. Some of the most common impact modifiers employed in the preparation of a carbonate polymer compositions are polymers themselves prepared by: polymerization techniques employing particular emulsifiers that are utilized in emulsion polymerization reactions; suspension agents utilized in suspension polymerization reactions; surfactants utilized in phase transfer catalysis systems; soluble catalysts utilized in polymerization reactions; and for certain process stabilizers employed during the processing of the polymers either in the polymerization or in the molding thereof. For example, it is now known that residues in an impact modifier from these particular polymerization aids, particularly emulsion polymerization aids employed in preparing certain impact modifiers, quite often catalyze transesterification or degradation of polycarbonates. It is also known that impact modifier additives to carbonate polymer compositions are commonly made by emulsion polymerization processes employing alkali metal salts of fatty acid emulsifiers to stabilize the emulsion during polymerization of the impact modifier. It is also known that the alkali metal salts of fatty acids catalyze transesterification or degradation of polycarbonates which in turn causes inconsistent thermal stability in carbonate polymer composition because of residual amounts of the emulsifier employed in preparing the modifier remaining in the impact modifier. This leads to problems in molding shops because of the variability in viscosity due to the catalytic transesterification or degradation of polycarbonates with such impact modifiers.
U.S. Pat. No. 5,608,027 Table 11 describes the superior performance of complex stabilization systems when impact modifiers are used in polycarbonate compositions and demonstrates problems that can occur with reaction between the polycarbonate and the impact modifier, if complex stabilizers are not added to prevent the reaction.
A large number of patents exists describing the use of additives in polycarbonate compositions. A significant fraction of these are directed to the use of impact modifiers. The instant invention discloses the utilization of certain impact modifiers prepared by emulsion polymerization in carbonate polymer compositions, which impact modifiers are essentially free of particular residual emulsifiers that cause degradation of polycarbonates. The instant invention is directed to an impact modified carbonate polymer composition with better thermal stability than compositions with conventional impact modifiers which employ, for example, alkali metal salts of fatty acid as emulsifiers in the preparation thereof.
SUMMARY OF THE INVENTION
It has now been found that the basic cause of many melt instability issues in impact modified carbonate polymer composition and blends thereof with polyesters is the presence of residual amounts of certain emulsifiers such as alkali metal salts of fatty acids employed in preparing impact modifiers. Alkali metal carboxylates are especially troublesome.
Surprisingly, it has now been discovered that degradation of a polycarbonate is not seen when employing certain surfactants selected from sulfate, sulfonate or phosphate based ionic surfactants in preparing impact modifiers, particularly rubbery modifiers, by the emulsion polymerization process even though the same alkali metal ion may be present. Use of a sulfonate, sulfate or phosphate type surfactant allows preparation of a rubbery modifier by an emulsion polymerization process that even though containing residual amounts of the emulsifier in the carbonate polymer composition, does not result in significant polycarbonate degradation.
Sulfate, sulfonate or phosphate surfactants allow flexibility in the preparation of rubbery modifiers by emulsion polymerization techniques. They do not require acidification of the rubber (which could cause acid catalyzed degradation of polycarbonates or its blends) nor do they require extensive washing or other purification steps to reduce residual surfactant levels in the rubbery modifier. Since these surfactants do not as readily degrade polycarbonates, they can be left in the rubbery modifier.
Thus, this invention is directed to an impact modified aromatic carbonate polymer composition having improved stabilization to degradation or transesterification and improved thermal stability. It has been surprisingly discovered, for example, that when methylmethacrylate-butadiene styrene (MBS) impact modifiers are prepared using certain sulfonates, sulfates or phosphates as surfactants, the carbonate polymer compositions impact modified with such MBS impact modifiers have significantly improved melt and thermal stability. It is also preferred that the impact modifier have a pH of about 3-8. The general invention is directed to the improvement of the melt and thermal stability of polycarbonates by going backward in the process of making the impact modifiers that are utilized in the polymer. Specifically for carbonate polymer compositions, the impact modifier should be essentially free of such residual amounts of emulsifiers as alkali metal salts of fatty acids, alkali metal carbonates, and other basic materials, such as amines or ammonium salts. Some examples of such emulsifiers are metal salts of stearic acid such as sodium stearate, lithium stearate and the like, metal salts of oleic acid such as sodium and potassium oleate and the like, amines such as dodecyl dimethyl amine, dodecyl amine and the like, and ammonium salts thereof. On the other hand, when certain surfactants are utilized in preparing impact modifiers of this invention with polycarbonate containing compositions such as MBS impact modifiers, little or no degradation of the polycarbonate is noted. These surfactants are selected from the group of ionic surfactants consisting of alkyl or arylalkyl sulfonates, alkyl or alkylaryl sulfates, and alkyl or alkylaryl phosphates.
Therefore, it is an object of the invention to provide an impact modified polycarbonate composition having improved resistance to degradation.
Another object of this invention is to provide an impact modifier essentially free of basic materials such as alkali metal salts of
DeRudder James L.
Gallucci Robert R.
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