Transparent Compositions of Bisphenol-a-Polycarbonate, Polyalkylene Terephthalate and an Aromatic Polyester Carbonate

This invention relates to the thermoplastic molding compositions of a polyalkylene terephthalate, a bisphenol-A polycarbonate and an aromatic polyester carbonate having improved molded transparency characteristics.

Compositions of polyalkylene terephthalate and polycarbonate resins are well known and have been widely employed in the manufacture of thermoplastic molded articles.

U.S. Pat. No. 3,218,372 which is incorporated herein by reference, describes compositions of polyalkylene terephthalates and polycarbonate resins. These compositions are described as having reduced melt viscosity and higher ductility than either the polycarbonate or polyalkylene terephthalate alone.

Blends of polyalkylene terephthalates and bisphenol-A polycarbonate are known to yield transparent molded articles only in the range of up to about 10 to 12 percent by weight of the polyester component. Articles molded from blends of polyalkylene terephthalates and bisphenol-A polycarbonate having weight percentages of the polyalkylene terephthalate component greater than 12 percent appear translucent or opaque.

It has now been found that the incorporation of an amount of an aromatic polyester carbonate, alternatively known as aromatic polyester cocarbonates, into various blends of polyalkylene terephthalates and bisphenol-A polycarbonates allows the production of transparent molded articles with molding compositions having polyester concentrations significantly greater than 10 to 12 percent by weight.

The present invention provides for a novel thermoplastic molding composition which comprises:

(a) a polyalkylene terephthalate;

(b) a bisphenol-A polycarbonate; and

(c) an aromatic polyester carbonate.

Among the preferred polyalkylene terephthalates advantageously employed in the composition which is the subject of this invention are polyethylene terephthalate and poly(1,4-butylene terephthalate).

The poly(1,4-butylene terephthalate) should have an intrinsic viscosity between 0.4 and 1.2 dl/g. as measured at 30.degree. C. in a 60/40 solution of phenol/tetrachloroethane. A more preferred range is between 0.6 and 0.9 dl/g.

The preferred bisphenol-A polycarbonate may be derived from the reaction of bisphenol-A and phosgene. These polycarbonates have from 100-400 recurring units of the formula: ##STR1##

The polycarbonates are described in U.S. Pat. Nos. 3,028,365; 3,334,154 and 3,915,926, all of which are incorporated by reference. The polycarbonate should have an intrinsic viscosity between 0.3 and 1.0, preferably from 0.3 to 0.45 as measured at 20.degree. C. in methylene chloride.

The preparation of the aromatic polyester carbonates which may be employed in the composition of the present invention are described in U.S. Pat. No. 3,169,121, which is incorporated herein by reference. The preferred polyester carbonate is a terpolymer resulting from the condensation of phosgene, terephthaloyl chloride, isophthaloyl chloride with bisphenol-A and a small amount of p-tertbutylphenol.

The polyalkylene terephthalate component of the composition of the present invention may comprise from 10 to 85 percent by weight of the composition, the bisphenol-A polycarbonate may comprise from 15 to 90 percent by weight of the composition and the aromatic polyester carbonate may comprise from 5 to 50 percent of the composition.

The preferred compositions will include from about 15 to about 50 percent by weight of polyalkylene terephthalate, from about 50 to about 90 percent by weight of bisphenol-A polycarbonate and from about 15 to about 25 percent by weight of the aromatic polyester component.

The composition of the present invention may be prepared by any standard procedure and the particular method employed is not considered critical.

The compositions may also include flame retardants such as those described in U.S. Pat. No. 3,915,926 which is incorporated herein by reference.

The following examples are set forth to further illustrate the present invention and are not to be construed as limiting the invention thereto.

A blend of the following components was prepared and pre-dried for four hours at 200.degree. F.

The blend was then extruded on a Werner-Pfleiderer twin screw extruder and the resultant extruded blend molded on a Van Dorn molding unit into sample parts. The resultant molded parts were opaque.

The following blend was prepared in the same manner as that for example I:

After extruding and molding parts in the same manner as in Example I, the parts appeared transparent.

A blend was prepared in the same manner and ratios as in Example II, except that the poly(1,4-butylene terephthalate) component and aromatic polyester carbonate component were first extruded together and then re-extruded with the bisphenol-A polycarbonate component. The resultant extruded and molded parts were again transparent.

Additional blends were prepared in the proportions indicated in Table I, in the same manner as specified in Example I. These blends were extruded and molded into test parts which demonstrated the visual characteristics indicated in Table I, i.e. all of these blends showed improved transparency for both the extrudate and the molded parts over that which would have been expected without the addition of the aromatic polyester carbonate component.

Additional blends were prepared in the proportions indicated in Table II. These blends were prepared as indicated in Example I and were then extruded on a Werner-Pfleiderer twin screw extruder with a 520.degree. F. profile. Molded parts were then prepared in the same manner as those prepared in the previous examples. The visual characteristics of the extrudate and molded parts for each composition were as indicated in Table II.

Additional blends were prepared in the same manner as set forth in Example I, which were subsequently blended and molded parts prepared in accordance with the procedure followed in Example I. The various compositions of these blends as well as the physical properties and visual appearance of the extrudate and molded parts are set forth in Table III.

Additional blends were prepared in the same manner as set forth in Example I, which were subsequently extruded and molded in accordance with the same procedure followed in Example I. The visual appearance and molded part is set forth in Table IV.

Additional blends were prepared using bisphenol-A polycarbonate, polyalkylene terephthalate alone and polyethylene terephthalate together with poly(1,4-butylene terephthalate) and an aromatic polyester carbonate along with various additives. These blends were prepared, extruded and molded in the same manner as previously set forth in Example I. The compositions and physical properties, including the percent light transmission obtained on the molded parts are set forth in Table V.

Additional blends of bisphenol-A polycarbonate, polyethylene terephthalate alone and together with poly(1,4-butylene terephthalate) and an aromatic polyester carbonate, were prepared, extruded and molded in the same manner as set forth in Example I, except for Examples LV-LXI, in which the bisphenol-A was first extruded together with the aromatic polyester component and the resultant extrudate was re-extruded with the polyethylene terephthalate. The actual compositions and visual appearance of the extrudate and molded parts are set forth in Table VI.

Although the above examples show various modifications of the present invention, other variations are possible in light of the above teachings.

It is, therefore, to be understood that changes may be made in the particular embodiment of the invention described which are within the full intended scope of the invention, as defined by the appended claims.