Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-02-29
2002-11-26
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S440000, C524S441000, C524S449000, C524S504000, C524S505000, C524S513000, C524S537000
Reexamination Certificate
active
06486251
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a modified polycarbonate-polyester composition containing special-effect colorants and articles molded from such resin compositions.
BACKGROUND OF THE INVENTION
Polyester resins derived from terephthalic acid and reactive derivatives thereof, such as dimethyl terephthalate, and alkanediols have been known for some time and have become important constituents for moldable compositions. Workpieces molded from such polyester resin compositions, alone, or combined with reinforcements, offer a high degree of surface hardness and abrasion resistance, chemical resistance, and high gloss. Polyester resins are blended with other carefully selected resins to improve impact strength, as well as tensile strength, modulus and distortion temperature. For example, polyesters are blended with aromatic polycarbonates as set forth in Kawase et al, U.S. Pat. No. 3,953,539.
Impact modified polycarbonate/polyester resins are excellent materials for applications requiring high impact, chemical resistance, and appealing aesthetic. In order to improve the appearance, special effect additives have been utilized as colorants. U.S. Pat. No. 5,510,398 to Clark et al relates to a highly filled, extruded polyalkylene terephthalate resin, a polycarbonate resin, a filler, a stabilizer, and a non-dispersing pigment to give the extruded thermoplastic material a speckled surface appearance. Column 5, lines 35 to column 6, line 61, describes impact modifiers. U.S. Pat. No. 5,441,997 to Walsh et al describes the use of impact modifiers in conjunction with polycarbonate/polyester compositions having a barium sulfate, strontium sulfate, zirconium oxide, or zinc sulfate filler. U.S. Pat. No. 5,814,712 to Gallucci et al describes a glycidyl ester as an impact modifier, and optionally other impact modifiers, for a polycarbonate/polyester resin. U.S. Pat. No. 4,264,487 to Fromuth et al describes aromatic polycarbonate, acrylate-based core-shell polymer, and aromatic polyester.
The following patents relate to metallic type pigments. WO 99/02594 which describes the use of rectangular aluminum flakes in Nylon compositions. U.S. Pat. No. 5,091,010 and EP 0 426 446 relate to the aesthetics of molded articles containing flakes. These references do not address mechanical performance concerns which are addressed by the present invention.
Among the problems to be solved when utilizing polycarbonate/polyester resins and particles and pigments to produce special color effects are those related to composition coloring and those related to producing a very bright, metallic reflective sparkle appearance in the molded articles while retaining impact strength. The use of special visual effect colorants in combination with unpreferred impact modifiers may to be detrimental to physical properties such as notched Izod impact. Although various impact modifiers are known in the prior art, the prior art is deficient in addressing the problem of enhancing the impact properties of polycarbonate/polyester resins having special effect colorants.
SUMMARY OF THE INVENTION
A polycarbonate/polyester resin formulation which has enhanced impact resistance comprises flakes having a coloration and/or metallic gloss, and a modifier selected to enhance the impact strength of the molded resin.
In a process for preparing the polycarbonate/polyester resin molding formulation, a desirable flake which is robust under compounding and molding conditions, has desirable color and aesthetics, and is compatible with blend components is selected. A compatible impact modifier is selected for enhancing the impact properties of the molded resin
It is desirable that the flakes display a bright, reflective sparkle or reflective metallic gloss appearance rather than appearing dull. It is further desirable that the look and consistency of the finished product can be controlled.
In a preferred embodiment of the present invention, a molding composition and molded articles which, based on the total weight of the composition, consist essentially of (a) from 10 to 90 weight percent of a polyester resin; (c) from 90 to 10 weight percent of an aromatic polycarbonate resin; (d) an effective amount of an modifier selected to enhance the impact strength of a molded resin, preferably a core-shell modifier having a butadiene-based copolymer rubber substrate with a methacrylate containing graft or an ABA triblock modifier with A polymeric units from styrene or derivatives thereof and B polymeric units from butadiene or derivatives thereof, and (e) a sufficient amount of a flakes for imparting a desired special visual effect, where the impact modifier enhances the impact strength of a molded composition as compared to a molding composition absent the modifier with the notched Izod impact strength preferably being at least about 6 ft.lbs./in., and more preferably at least 9 ft.lbs./in., according to ASTM test D256.
The most preferred molding compositions are MBS modified compositions with low temperature and room temperature impact strength.
According to another embodiment an effective amount of a random, block, and graft copolymers of vinyl aromatic compounds and conjugated dienes may be utilized to enhance the impact strength at higher temperatures.
The blend compositions combine appealing aesthetics, chemical resistance, and high impact properties and will be useful in molded article applications where this combination of properties is desirable.
Thermoplastic polymer blends containing flakes, such as metal or mica, typically drop significantly in notched Izod impact properties if they are not properly impact-modified. Not all impact modifiers are effective for retaining impact properties upon addition of metallic or pearlescent pigments. For example, the notched Izod values of EMA-GMA modified polycarbonate/poly(butylene terephthalate) (PC/PBT) blends can drop from 16 ft.lbs./in. to 2 ft.lbs./in. upon addition of as little as 0.8 weight percent metal flakes. According to the preferred embodiments of the present invention, methacrylate-butadiene-styrene (MBS) modified PC/PBT blends retain average notched Izod values above 6 ft.lbs./in., and more typically above 9 ft.lbs./in., at room temperature in the presence of metal flakes. The EMA-GMA glycidic impact modifiers are described in U.S. Pat. No. 5,814,712 to Gallucci et al.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polyester resin component comprises structural units of the following formula:
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.
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 polyester includes the poly(alkylene terephthalates) and the polyarylates. Such polyesters are known as illustrated by the following patents:
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
Examples of aromatic dicarboxylic acids represented by the dicarboxylated residue A1 are isophthalic or terephthalic acid, 1,2-di(p-carboxyphenyl)ethane, 4,4′-dicarboxydiphenyl ether, 4,4′ bisbenzoic acid and mixtu
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