NOVEL THERMOPLASTIC POLYESTER COMPOSITIONS CONTAINING CERTAIN LOW MOLECULAR WEIGHT DEPOXIDE RESINS AND HAVING IMPROVED IMPACT BEHAVIOUR

Abstract: Novel thermoplastic polyester compositions having im­ proved impact behavior are produced. These compositions comprise a blend of poly (C₂-C₄ alkylene terephthalate) with certain low molecular weight diepoxide resins, a triphenyl phosphonium halide catalyst, and a multiphase composite polymer. The multiphase polymer has a first elastomeric phase polymerized from a monomer system including butadiene or butadienestyrene and a final rigid thermoplastic phase poly­ merized in the presence of the elastomeric phase.

Description: FIELD OF THE INVENTION This invention relates to the production of thermoplastic polyester compositions. BACKGROUND OF THE INVENTION Poly (C₂-C₄ alkylene terephthalate) such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) are well known resins for a number of uses including molding applications. Such resins are frequently blended with various additives to improve properties such as impact strength, resistance to warping, flame resistance, and thermal stability. U.S. Patents 4,393,153; 4,180,494; 4,096,202; and 4,034,013 describe certain impact modifiers which have been suggested for use with polyalkylene terephthalates. U.S. Patents 4,010,219 and 4,101,601 describe certain epoxy compounds which have been suggested for use in imparting improved tensile and melt strength properties to polybutylene terephthalate molding compounds. U.S. Patent 4,195,134 describes a combination of certain impact modifiers and certain diepoxy compounds for use in polyalkylene terephalate molding compositions for improving the hydrolytic stability of such compositions. The search has continued, however, for polyalkylene terephthalate molding compositions having even further improved impact behavior. The present invention was made as a result of such a search. SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide improved thermoplastic polyester compositions suitable for the production of molded articles as well as a process for producing molded articles from such compositions and molded articles of such compositions. As compared with known prior art compositions, molded articles of the present invention have a combination of desirable properties including improved impact behavior without sacrifice of other desirable properties. In accordance with a broad aspect of the present invention, thermoplastic polyester compositions are provided which comprise a blend of: (a) at least about 20 weight percent of at least one poly (C₂-C₄ alkylene terephthalate); (b) between about 0.1 and about 8 weight % based on poly (C₂-C₄ alkylene terephthalate) of at least one diepoxide resin having a molecular weight between about 350 and about 2100 and consisting essentially of at least one condensation product of bisphenol A or brominated bisphenol A and epihalohydrin and represented by the general formula (I): wherein X is hydrogen or bromine; and n is an average number ranging above zero and less than about 2.3; (c) a catalytic amount of at least one catalyst selected from the group consisting of alkyl triphenyl phosphonium halides and alkenyl triphenyl phosphonium halides; and (d) between about 5 and about 30 weight % based on poly (C₂-C₄ alkylene terephthalate) of at least one butadiene-based multiphase composite polymer having an elastomeric core of polybutadiene or polybutadiene/styrene and a thermoplastic shell of polymethylmethacrylate. In a preferred aspect of the present invention, the thermoplastic polyester composition consists essentially of at least about 60 weight percent (wt. %) polybutylene terephthalate (PBT) having an initial intrinsic viscosity between about 0.4 and about 1.3 deciliters per gram (dl/g) as determined in orthochlorophenol at 25°C; a diepoxide resin of Formula (I) having a molecular weight between about 370 and 400; butyltriphenylphosphonium bromide catalyst; and 5 to 30 percent based on polybutylene terephthalate of a multiphase composite polymer having an elastomeric first phase of butadiene or butadiene-styrene and a thermoplastic final phase of polymethylmethacrylate. Further preferred aspects involve the use of polycarbonate and/or polyarylate resins and/or glass reinforcing fibers and mineral fillers in amounts between about 1 and about 100 weight percent based on polyalkylene terephthalate as well as preferred multiphase polymer and diepoxide resins as described below. A central feature of the present invention is the surprising discovery that only certain low molecular weight diepoxide resins impart improved impact behaviour to catalyzed blends of PBT and butadiene-based multiphase polymer. The desirable effects of improved impact behaviour are not found if, for example, higher molecular weight diepoxide resins are used at the same or similar epoxide concentration. Other objects, aspects and advantages of the present invention will become apparent to one skilled in the art in view of the following: DESCRIPTION OF THE PREFERRED EMBODIMENTS Polyalkylene terephthalates suitable for use in the invention include for instance polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate. Polybutylene terephthalate (PBT) is especially suitable and in a preferred embodiment of the invention comprises at least about 60 weight percent of the thermoplastic polyester composition. The polyalkylene terephthalate used may be a single polyalkylene terephthalate or a blend of suitable polyalkylene terephthalates. As mentioned the composition of the invention includes at least about 20 weight percent poly (C₂-C₄ alkylene terephthalate). An especially preferred poly (C₂-C₄ alkylene terephthalate) is polybutylene terephthalate having an intrinsic viscosity between about 0.4 and about 1.3 dl/g. The diepoxide resin of Formula (I) above is present in compositions of the present invention in amounts between about 0.1 and about 8, preferably about one and about 3.5, and most preferably 1.5 to 2.0 weight percent based on poly (C₂-C₄ alkylene terephthalate). Suitable diepoxy compounds which may be used in the practice of this invention include polycondensates of Formula (I) of epihalohydrin such as epichlorohydrin with diphenylolpropane (so called bisphenol "A"), or brominated bisphenol A such as tetrabromodiphenylolpropane, in any convenient ratio so that the resulting resins will have terminal epoxy groups and average molecular weights between about 350 and about 2,100, preferably between about 360 and about 1,000, and most preferably between 370 and 400. Illustrative examples by standard trade designations include the commercially available epoxy resins Epi-Rez 509, Epi-Rez 510, Epi-Rez 5163, and Epi-Rez 5183. The catalyst employed in the present invention may be selected from the group consisting of alkyl triphenyl phosphonium halide and alkenyl triphenyl phosphonium halide. The alkyl groups may contain from one to ten carbon atoms, the alkenyl groups may contain from two to six carbon atoms, and the halide anion is selected from the group consisting of chloride and bromide. Alkyl triphenyl phosphonium bromides and alkenyl triphenyl phosphonium bromides are preferred catalysts. Allyl triphenyl phosphonium bromide and n-butyl triphenyl phosphonium bromide are particularly preferred. The use of these compounds in catalytic amounts is advantageous in that the polymers produced in the process of the present invention are both less brittle and less intensely colored than those produced using the same reactants and reaction conditions but using other catalysts such as amine catalysts. The catalyst employed in the present invention may be used in catalytic amounts, i.e., generally from about 0.01 to about 0.1, and preferably from about 0.02 to about 0.06% by weight based upon the weight of the polyalkylene terephthalate present. The catalyst and diepoxide may be present in a mole ratio of diepoxide to catalyst of generally from about 10 to 1 to about 100 to 1, and preferably from about 20 to 1 to about 50 to 1. As noted above, the thermoplastic polyester compositions of the present invention contain at least one butadiene-based multiphase composite polymer. The multiphase composite polymer, sometimes referred to as core/shell elastomer, has an elastomeric first phase or core of polybutadiene or polybutadiene/styrene and a thermoplastic final phase or shell of polymethylmethacrylate. It may also have an intermediate phase of styrene. The most preferred multiphase composite polymers are methacrylated butadiene-styrene copolymer compositions marketed by Rohm and Haas under the trade designations KM-653 and KM-680. For further descriptions and examples of various butadiene-based multiphase polymers suitable for use in the present invention, reference may had to the aforementioned U.S. Patents 4,034,013; 4,180,494; and 4,393,153. Compositions and products of the present invention may also contain about one to about 200, preferably about 60 to 120 weight percent based on polyalkylene terephthalate of aromatic polycarbonate or polyarylates such as bisphenol-A-isophthalate-terephthalate-polyester. The effect of incorporating such polycarbonate and polyarylate is to develop impact behavior with lesser amounts of composite polymer. For further descriptions and examples of such polycarbonates and polyarylates, reference may be had to U.S. Patents 4,180,494 and 4,221,694. Compositions and products of the present invention may also contain up to about 25 weight percent, more typically up to 10 percent, based on polyalkylene terephthalate of suitable flame retardant additives, such as decabromodiphenyl ether and antimony oxide, and may contain relatively minor amounts of other materials which do not unduly affect the desired characteristics of finished products. Such additional materials may, depending upon the particular compositions employed and products desired include for instance, colorants or lubricants. Where present such additional materials other than polycarbonate, polyarylate, flame retardants, fibers or filler, normally comprise not more than about 10 weight percent of the total molding composition or finished product. Compositions and products of the present invention may also include reinforcing fiber or inert filler of conventional types and amounts. In a preferred embodiment between about one and about 100 weight percent based on polyalkylene terephthalate of glass reinforcing fibers is present. Inert filler material where used is normally present in amounts between about one and about 100 weight percent based on polyalkylene terephthalate and may include such materials as glass spheres, clay, silica, silicates and oxides, In preparing compositions of the present invention the various ingredients may be prepared by conventional methods and blended in any suitable manner such as by dry blending or melt blending, blending in extruders, heated rolls, or other types of mixers. Conventional master batching techniques may also be used. Suitable manufacture and blending techniques are well known in the art and need not be described in detail here. Compositions according to the invention are especially useful in imparting improved impact behavior to PBT of relatively low initial or starting intrinsic viscosity, especially where the viscosity of the PBT is below 1.0 dl/g such as in the range of about 0.5-1.0 dl/g. This makes the present invention especially significant with respect to such PBT of relatively low initial intrinsic viscosity since, as is well known, PBT of higher intrinsic viscosity is generally more expensive to manufacture. Thus by use of the present invention it is frequently possible to employ for a given end use PBT compositions utilizing PBT of significantly lower initial intrinsic viscosity than would normally be considered acceptable in terms of impact behavior. The following examples are intended to illustrate the invention. In the examples all quantities are given in terms of weight percent based on total compositions unless otherwise stated. In order to evaluate impact behavior of the various compositions tested, samples of the compositions in question were injection molded to produce standard ASTM test specimens. Specimens were then tested for notched Izod impact strength in accordance with ASTM procedure D-256 (except not under controlled humidity conditions which should not materially affect the results). Compositions tested as reported herein were prepared from several different PBT compositions as indicated in the examples. The compositions were compounded on a 2.5 inch Egan extruder using the following conditions: temperature 260°C., pressure 500-2000 psi (3447 - 13789 KPa), and screw RPM 75-150. In each case the pelletized extrudate was then molded on a reciprocating screw injection molding machine to provide test specimens. In the examples the term "epoxy" designates diepoxide resins marketed by Celanese Specialty Operations as their epoxy resins Epi-Rez 510, Epirez 522C, etc. and the term "elastomer" designates multiphase composite polymers marketed by Rohm & Haas as their acryloids KM 653 and KM 680. EXAMPLES 1-2 For these examples a number of compositions were prepared utilizing PBT having an intrinsic viscosity of 1.0 dl/g, .035 percent n-butyltriphenylphosphonium bromide, and containing additional components as indicated in Table I below. These samples were tested for notched Izod impact strength as described above. The results of these tests are also shown in Table I. EXAMPLES 3-10 Example 1 was repeated using varying amounts of Acryloid KM 653, and yielded high notched Izod values. As shown in Table II below, high room temperature impact was found with KM 653 down to 12.5%, while at 17.5%, a notched Izod of 5.43 ft-lb/in. [289.85 J/m] was obtained at -20°C. NOTCHED IZOD, FT-LB/IN. [J/m] Example % Elastomer (KM 653) R.T. 0°C. -20°C. -29°C. 3 12.5 16.3 [870.09] 11.8 /4.5 [629.88/240.21] 1.82 [97.15] --- 4 15.0 16.4 [875.43] 11.9 /3.7 [635.22/197.51] 2.16 [115.30] --- 5 17.5 18.4 [982.19] 15.2 [811.38] 5.43 [289.85] 1.57 [83.81] 6 20.0 17.2 [918.14] 16.9 [902.12] 4.90 [261.56] 2.63 [140.39] 7 25.0 17.6 [939.49] 18.3 [976.85] 2.91 [155.34] 2.75 [146.80] At the 15% level of KM 653, increasing the epoxy resin level from 1.25% to 1.75% caused an increase in impact strength at 0°C and -20°C as shown in Table III below. NOTCHED IZOD IMPACT, FT-LB/IN. [J/m] Example % Epoxy Resin (Epi-Rez 510) R.T. Ft-lb/in. 0°C. [J/m] -20°C. 8 1.25 16.3 [870.09] 5.5 /3.3 [293.59/176.15] 1.30 [69.39] 9 1.50 16.4 [875.43] 11.9 /3.7 [635.22/197.51] 1.82 [97.15] 10 1.75 16.3 [870.09] 12.3 /4.5 [656.57/240.21] 2.41 [128.65] The above examples show the unexpected advantage to be had by using the butadiene-based multiphase polymer latex and certain epoxy resins and catalyst additives in accordance with the invention in terms of improving the impact behavior of PBT molding compositions. While the invention has been described above with respect to certain embodiments thereof,

Claims: A thermoplastic polyester composition having improved impact strength comprising a blend of: (a) at least 20 weight percent poly (C₂-C₄ alkylene terephthalate); (b) between 0.1 and 8 weight % based on poly (C₂-C₄ alkylene terephthalate) of a diepoxide resin having a molecular weight between 350 and 2,100 and consisting essentially of at least one condensation product of bisphenol A or brominated bisphenol A and epihalohydrin and represented by the general formula (I): wherein X is bromine or hydrogen and n is an average number above zero and less than 2.3; (c) a catalytic amount of at least one catalyst selected from the group consisting of alkyl triphenyl phosphonium halides and alkenyl triphenyl phosphonium halides; and (d) between 5 and 30 weight % based on poly (C₂-C₄ alkylene terephthalate) of a butadiene-based multiphase composite polymer having an elastomeric core of polybutadiene or polybutadiene/styrene and a thermoplastic shell of polymethylmethacrylate. A composition according to claim 1 wherein the thermoplastic polyester composition includes at least about 60 weight percent polybutylene terephthalate having an intrinsic viscosity between 0.4 and 1.3 dl/g as determined in orthochlorophenol at 25°C. A composition according to claim 1 or 2, wherein the diepoxide resin of the formula (I) has a molecular weight between 360 and 1,000 and wherein the catalyst is allyl triphenyl phosphonium bromide or n-butyl triphenyl phosphonium bromide. A composition according to claim 1, 2 or 3 further containing between 1 and 100 weight percent based on polyalkylene terephthalate of glass reinforcing fibers. A composition according to claim 1, 2 or 3 further containing from one to 200 weight percent based on polyalkylene terephthalate of aromatic polycarbonate. A composition according to claim 1, 2 or 3 further containing from one to 200 weight percent based on polyalkylene terephthalate of polyarylate. A composition according to claim 1, 2 or 3 further containing between one and 100 weight percent based on polyalkylene terephthalate of inert filler. A composition according to claim 1, 2 or 3 further containing up to twenty-five weight percent based on polyalkylene terephthalate of flame retardant additive. A thermoplastic polyester composition having improved impact strength consisting essentially of a blend of: (a) at least 60 weight percent polybutylene terephthalate having an intrinsic viscosity between 0.5-1.0 dl/g as determined in orthochlorophenol at 25°C; (b) between 1.5 and 2.0 weight % based on polybutylene terepthalate of a diepoxide resin having a molecular weight between 370 and 400 and consisting essentially of at least one condensation product of bisphenol A and epichlorohydrin and represented by the general formula (I): wherein n is an average number above zero and less than about 2.3; (c) a catalytic amount of at least one catalyst selected from the group consisting of alkyl triphenyl phosphonium bromide and alkenyl triphenyl phosphonium bromide; and (d) between 5 and 30 weight % based on polybutylene terephthalate of a butadiene-based multi-phase composite polymer having an elastomeric core of polybutadiene or polybutadiene/styrene and a thermoplastic shell of polymethylmethacrylate. A composition according to claim 9 further containing between 5 and 100 weight percent based on polybutylene terephthalate of glass reinforcing fibers. A composition according to claim 9 further containing from one to 200 weight percent based on polybutylene terephthalate of aromatic polycarbonate. A composition according to claim 9 further containing from one to 200 weight percent based on polybutylene terephthalate of polyarylate.

Inventors: COSTANZO, JEROME L., LA NIEVE, H. LESLIE, MCNALLY, DONAL
Applicants: CELANESE CORPORATION
Application year: 1985
Main classification: C08L67
IPC codes: C08K7, C08L7, C08K3, C08L67, C08L63, C08G59, C08L69, C08L21, C08K5, C08L51