Modified Polyester Compositions

This invention relates to modified thermoplastic polyester compositions which make moldable articles of improved impact strength and thermal resistance. More particularly, the invention pertains to compositions of (a) a block poly(1,4-butylene terephthalate) ester copolymer resin a polyester blend which are modified with (b) an effective amount of a resinous combination comprising an acrylic or methacrylic grafted polymer of a conjugated diene alone or in combination with a vinyl aromatic and an aromatic polycarbonate. Also provided are such compositions further including (c) fibrous glass reinforcement and/or (d) a flame retardant.

High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter alia in Whinfield et al, U.S. Pat. No. 2,465,319 and in Pengilly, U.S. Pat. No. 3,047,539, incorporated herein by reference. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.

With the development of molecular weight control, the use of nucleating agents and two-step molding cycles, poly(ethylene terephthalate) has become an important constituent of injection moldable compositions. Poly(1,4-butylene terephthalate), because of its very rapid crystallization from the melt, is uniquely useful as a component in such compositions. Workpieces molded from such polyester resins, alone or combined with reinforcements, in comparison with other thermoplastics, offer a high degree of surface hardness and abrasion resistance, high gloss, and lower surface friction.

Stable polyblends of poly(1,4-butylene terephthalate) and poly(ethylene terephthalate) can be molded into useful unreinforced and reinforced articles. See Fox and Wambach, U.S. Pat. No. 3,953,394, incorporated herein by reference.

Block copolyesters containing units derived from poly(1,4-butylene terephthalate) and from an aromatic/aliphatic or aliphatic polyesters are also known. See, copending application U.S. Ser. No. 752,325, filed Dec. 20, 1976, incorporated herein by reference. Such block copolyesters are useful per se as molding resins and also in intimate combination with poly(1,4-butylene terephthalate) and/or poly(ethylene terephthalate).

It has been proposed to increase the impact strengths of polyesters by adding various modifiers. For example, Brinkmann et al in U.S. Pat. No. 3,591,659 discloses that a useful family of modifiers comprises polyalkyl acrylates, methacrylates and/or ethacrylates. Baron et al in U.S. Pat. No. 4,044,073 disclose that a useful impact modifier for such polyesters is an aromatic polycarbonate. Schlichting et al in U.S. Pat. No. 4,022,748 disclose that a rubber-elastic graft copolymer having a glass temperature below -20.degree. C. is a useful modifier. Lane, U.S. Pat. No. 4,034,013, and Farnham et al, U.S. Pat. No. 4,096,202 disclose that useful impact modifiers comprise multiple stage polymers having a rubbery first stage and a hard final stage, preferably including units derived from alkyl acrylates, especially butyl acrylates. Baron et al in U.S. Pat. No. 4,034,016 (corres. German Pat. No. 2,650,870) disclose an impact modifier combination comprising a blend of a polyurethane and an aromatic polycarbonate. Copending application Ser. No. 870,679, filed Jan. 19, 1978, discloses an impact modifier combination comprising a segmented block copolyester and an aromatic polycarbonate. Copending application Ser. No. 957,801, filed Nov. 6, 1978, discloses an impact modifier combination comprising a blend of a polyalkylacrylate and an aromatic polycarbonate. Gergen et al, U.S. Pat. No. 4,090,996 disclose an impact modifier combination for poly(1,4-butylene terephthalate) and other polyester resins comprising a selectively hydrogenated monoalkenyl arene-diene block copolymer, and an engineering thermoplastic, e.g., poly(aryl ether), poly(aryl sulfone), polycarbonate, acetal, etc. Nakamura et al, U.S. Pat. No. 3,864,428 disclose poly(butylene terephthalate) alone or combined in blends with other polyesters, impact modified with conjugated diene/vinyl aromatic copolymers grafted with methacrylate monomer and aromatic polycarbonate. Nakamura et al do not disclose block copolyesters of poly(1,4-butylene terephthalate) and aromatic/aliphatic or aliphatic polyesters. All of the foregoing patents and the application are incorporated herein by reference.

Although filled and/or reinforced and/or flame retardant modifications of the foregoing are described in the above-mentioned references, they lack one or more desirable attributes, when molded.

It has now been discovered that block copolyesters of poly(1,4-butylene terephthalate) and combinations thereof with poly(1,4-butylene terephthalate) and/or poly(ethylene terephthalate) will be greatly improved in impact strength as molded as well as after annealing and at -20.degree. F., by intimately admixing therewith an impact improving modifier combination comprising an acrylic or methacrylic monomer grafted polymer of a conjugated diene alone or combined with a vinyl aromatic and an aromatic polycarbonate resin. As will also be shown, the new compositions of this invention can be reinforced with glass, and/or rendered flame-retardant.

According to this invention, there are provided thermoplastic compositions which are useful for molding, e.g., injection molding, compression molding, transfer molding, and the like, the compositions comprising:

(a) a polyester comprising:

(i) a block copolyester of poly(1,4-butylene terephthalate) and an aromatic/aliphatic or aliphatic polyester;

(ii) a blend of (i) and a poly(ethylene terephthalate) resin; or

(iii) a blend of (i) and a poly(1,4-butylene terephthalate) resin; and

(b) an impact modifier therefor comprising a combination of:

(i) an acrylic or methacrylic grafted polymer of a conjugated diene alone or combined with a vinyl aromatic; and

(ii) an aromatic polycarbonate resin, said impact modifier (b) being present in an amount of up to 60 parts per 100 parts by weight of (a) and (b) together, the weight ratio of said grafted polymer to said polycarbonate resin being between 1:99 and 99:1.

The block copolyester resin component used in (a) above can be prepared by the transesterification of (a) straight or branched chain poly(1,4-butylene terephthalate) and (b) a copolyester of a linear aliphatic dicarboxylic acid and, optionally, an aromatic dibasic acid such as terephthalic or isophthalic acid with one or more straight or branched chain dihydric aliphatic glycols. For example a poly(1,4-butylene terephthalate) can be mixed with a polyester of adipic acid with ethylene glycol, and the mixture heated at 235.degree. C. to melt the ingredients, then heated further under a vacuum until the formation of the block copolyester is complete. As the second component, there can be substituted poly(neopentyl adipate), poly(1,6-hexylene azelate-coisophthalate), poly(1,6-hexylene adipate-co-isophthalate) and the like. The procedures and products are described in the above-mentioned copending application Ser. No. 752,325, filed Dec. 20, 1976. A suitable copolyester is defined under (a)(i) above is available commercially from General Electric Company, Pittsfield, Mass., under the trade designation VALOX 330.

The polyester resin components used as part of (a)(ii) and (a)(iii) of the compositions of this invention are available commercially or can be prepared by known techniques such as by th alcoholysis of esters of terephthalic acid with ethylene glycols with the free acids or with halide derivatives, and similar processes. These are described in U.S. Pat. No. 2,465,319, and U.S. Pat. No. 3,047,539, and elsewhere.

Illustratively, the high molecular weight polyesters will have an intrinsic viscosity of at least about 0.4 deciliters/gram and preferably, at least 0.6 deciliters/gram as measured in a 60:40 phenol/tetrachloroethane mixture at 30.degree. C.

Especially useful when high melt strength is important are branched high melt viscosity poly(1,4-butylene terephthalate) resins, which include a small amount of e.g., up to 5 mole percent based on the terephthalate units, of a branching component containing at least three ester forming groups. The branching component can be one which provides branching in the acid unit portion of the polyester, or in the glycol unit portion, or it can be hybrid. Illustrative of such branching components are tri- or tetracarboxylic acids, such as trimesic acid, pyromellitic acid, and lower alkyl esters thereof, and the like, or preferably, polyols, and especially preferably, tetrols, such as pentaerythritol, triols, such as trimethylolpropane; or dihydroxy carboxylic acids and hydroxydicarboxylic acids and derivatives, such as dimethyl hydroxyterephthalate, and the like.

The branched poly(1,4-butylene terephthalate) resins and their preparation are described in Borman, U.S. Pat. No. 3,953,404, incorporated herein by reference.

Impact modifier (b) comprises a combination of (i) an acrylic or methacrylic monomer grafted polymer of a conjugated diene alone or copolymerized with a vinyl aromatic compound and (ii) an aromatic polycarbonate. The graft copolymer resin (b)(i) can be made in known ways and they are available commercially from Borg-Warner Corp., under the trade designation BLENDEX. In general, any of the graft copolymers described in U.S. Pat. No. 3,864,428 can be used, especially those containing units derived from butadiene or isoprene, alone or in combination with a vinyl aromatic compound. Especially preferably, the copolymer component (b)(i) will comprise a copolymer of styrene and butadiene, onto which has been grafted a C.sub.1 -C.sub.6 alkyl methacrylate monomer, particularly methyl methacrylate. The polycarbonate resins (b)(ii) can be made in known ways and they are available commercially from sources, e.g., General Electric Company, Pittsfield, Mass., U.S.A., under the trademark LEXAN. In general, any of the aromatic polycarbonates described in Baron et al, U.S. Pat. No. 4,034,016 can be used, especially those including units derived from bisphenol-A.

The fibrous (filamentous) glass can be untreated, but preferably, it will be treated with silane or titanate coupling agents, etc. The filamentous glass to be employed in such embodiments of the present compositions is well known to those skilled in the art and is widely available from a number of manufacturers. For compositions ultimately to be employed for electrical uses, it is preferred to use fibrous glass filaments comprised of lime-aluminum borosilicate glass that is relatively soda free. This is known as "E" glass. However, other glasses are useful where electrical properties are not so important, e.g., the low soda glass known as "C" glass. The filaments are made by standard processes, e.g., by steam or air blowing, flame blowing and mechanical pulling. The preferred filaments for plastic reinforcement are made by mechanical pulling. The filament diameters range from about 0.00012 to 0.00075 inch, but this is not critical to the present invention.

The length of the glass filaments and whether or not they are bundled into fibers and the fibers bundled in turn to yarns, ropes or rovings, or woven into mats, and the like, are also not critical to the invention. However, in preparing the molding compositions, it is convenient to use the filamentous glass in the form of chopped strands of from about one-eighth to about 2 inches long. In articles molded from the compositions, on the other hand, even shorter lengths will be encountered because, during compounding, considerable fragmentation will occur. This is desirable, however, because the best properties are exhibited by thermoplastic injection molded articles in which the filament lengths lie between about 0.0005 to 0.250 inch.

The amount of the filler can vary widely depending on the formulation and needs of the particular composition. Preferably, however, the filler will comprise from about 1 to about 60% by weight of filler (c) and (a) and (b), combined. Especially preferably the filler will comprise less than about 40% by weight of the combination.

It has further been found that even relatively minor amounts of the modifier (b) are effective in providing significant improvements in impact strength, and the like. In general, however, the modifier (b) will be present in amounts of at least about 1% by weight, up to 60% by weight or preferably from about 2.5 to about 50% by weight of (a) and (b). The ratio of graft copolymer to aromatic polycarbonate can vary widely, i.e., within the range of 1 to 99 parts of the former to, correspondingly, 99 to 1 parts of the latter, but in general, from 60 to 40 parts of the graft copolymer will be present for each 40 to 60 parts of the aromatic polycarbonate.

The impact modified polyesters alone, or in combination with glass and/or filler can be rendered flame retardant with an effective amount of a conventional flame retardant agent (d). As is well known, flame retardants can be based on elementary red phosphorus, phosphorus compounds, halogen and nitrogen compounds alone or preferably in further combination with synergists, such as antimony compounds. Especially useful are polymeric and oligomeric flame retardant agents comprising tetrabromobisphenol-A carbonate units, see, for example, Wambach, U.S. Pat. No. 3,833,685, which is incorporated herein by reference.

Other ingredients, such as dyes, pigments, drip retardants, and the like can be added for their conventionally employed purposes.

The compositions of this invention can be prepared by a number of procedures. In one way, the modifier and, optionally, reinforcing glass and/or fire retardants is put into an extrusion compounder with resinous components to produce molding pellets. The modifier and other ingredients are dispersed in a matrix of the resin in the process. In another procedure, the modifier and any reinforcing glass and/or flame retardants is mixed with the resins by dry blending, then either fluxed on a mill and comminuted, or then are extruded and chopped. The modifying agent and any other ingredients can also be mixed with the resins and directly molded, e.g., by injection or transfer molding techniques.

It is always important to thoroughly free all of the ingredients; resin, modifier, reinforcement and/or filler, flame retardants and any optional, conventional additives from as much as water as possible.

In addition, compounding should be carried out to ensure that the residence time in the machine is short; the temperature is carefully controlled; the friction heat is utilized; and an intimate blend between the resin and the modifier and any other ingredients is obtained.

Although it is not essential, best results are obtained if the ingredients are pre-compounded, pelletized and then molded. Pre-compounding can be carried out in conventional equipment. For example, after carefully pre-drying the polyester and modifier e.g., for four hours at 250.degree. F., a single screw extruder is fed with a dry blend of the ingredients, the screw employed having a long transition section to ensure proper melting. On the other hand, a twin screw extrusion machine, e.g., a 53 mm Werner Pfleiderer machine can be fed with resin and additives at the feed port and reinforcement down stream. In either case, a generally suitable machine temperature will be about 450.degree. to 560.degree. F.

The pre-compounded composition can be extruded and cut up into molding compounds such as conventional granules, pellets, etc., by standard techniques.

The composition can be molded in any equipment conventionally used for thermoplastic compositions, e.g., a Newbury type injection molding machine with conventional cylinder temperatures, e.g., 450.degree.-535.degree. F., and conventional mold temperatures, e.g., 130.degree.-200.degree. F.

The following examples illustrate the invention. They are set forth as a further description but are not to be construed as limiting the invention thereto. In the data tables, the abbreviation "N.D." means not determined. All parts are by weight.

A dry blend of block poly(1,4-butylene terephthalate) aromatic/aliphatic polyester copolymer resin, optionally, poly(ethylene terephthalate), poly(butadiene-styrene)methyl methacrylate graft copolymer, and aromatic polycarbonate of bisphenol-A and phosgene and mold release/stabilizer is compounded and extruded at 520.degree. F. in an extruder. The extrudate is pelletized and injection molded at 510.degree. F. (mold temperature 150.degree. F.). The formulations and physical properties are shown in Table 1.

The compositions of this invention are seen to exhibit excellent impact strength, independent of thickness.

The general Procedure of Example 1 is used to make compositions of a block copolyester of poly(1,4-butylene terephthalate), a methyl methacrylate grafted copolymer of butadiene and styrene, aromatic polycarbonate and reinforcing fibrous glass. The formulation used and the properties obtained are set forth in Table 2.

The composition has especially excellent impact strength.

Impact modified, fire retarded, unreinforced and reinforced compositions are prepared by the general procedure of Example 1. The formulations and results are set forth in Table 3.

Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore, to be understood that changes may be made in the particular embodiments described above which are within the scope of the invention as defined in the appended claims.