1. Field of the Invention
This invention relates to a resin composition comprising an aromatic copolyester, a polyamide, and a polyalkylene phenylene ester or a polyalkylene phenylene ester ether and a process for preparing the same.
2. Description of the Prior Art
An aromatic copolyester is obtained from a mixture of terephthalic acid and/or the functional derivatives thereof and isophthalic acid and/or the functional derivatives thereof (with the terephthalic acid unit/isophthalic acid unit molar ratio being about 9:1 to about 1:9) and a bisphenol of the following general formula: ##STR1## wherein -X- is selected from the group consisting of -O-, -S-, -SO.sub.2 -, -SO-, -CO-, and alkylene and alkylidene groups containing 1 to 4 carbon atoms, and R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.1 ', R.sub.2 ', R.sub.3 ', and R.sub.4 ' each represents a member selected from the group consisting of a hydrogen atom, a chlorine atom, a bromine atom and alkyl groups containing 1 to 4 carbon atoms, or the functional derivatives thereof.
It is well known that such aromatic copolyesters have many advantageous properties, for example, superior mechanical properties such as tensile strength, bending strength, bending recovery, or impact strength, a high heat distortion temperature, and a high heat decomposition temperature, electrical properties such as inherent resistivity, dielectric breakdown strength, arc resistance or dielectric characteristics, good fire retardancy, good dimensional stability and good solvent resistance. Because of these properties, in general, molded articles, films, fibers and coating materials produced from the aromatic copolyesters by injection molding, extrusion molding, press molding, and other molding techniques are expected to have a wide range of utility.
Despite the above-described advantageous properties and great utilitarian value in industry aromatic copolyesters have the defect of inferior moldability as compared with conventional thermoplastic resins. For example, in the case of injection molding aromatic copolyesters require a higher molding temperature, e.g., about 320.degree. to about 360.degree. C, a higher injection pressure, e.g., about 1,200 to about 1,500 kg/cm.sup.2, and a higher die temperature, e.g. about 120.degree. to about 140.degree. C, and molded articles made therefrom tend to have sink marks, flow marks, strong internal strain or the like.
Generally, sink marks, flow marks or strong internal strains or the like adversely affect the mechanical properties as well as the appearance of the molded articles to such an extent that the inherent superior properties of the resin cannot be obtained satisfactorily. Also, in some molded articles complete products cannot be obtained because sufficient flow length of the resin used cannot be achieved. In this regard it has hitherto been considered very important requirements in evaluation of engineering plastics (i.e., those plastics which have a superior thermal stability and mechanical strength over polyethylene resins, polypropylene resins, etc., such as polycarbonate resins, polyacetal resins, modified aromatic polyether resins and the like and are useful as materials for various machine parts) that they have many superior properties and especially good moldability.
It is known, however, that the improvement of an engineering plastic in terms of moldability by polymer blending tends to involve the thermal stability of the resin. Also, the improvement of chemical resistance tends to lead to a reduction in heat distortion temperature. Therefore, a resin composition which retains good thermal stability inherent in an engineering plastic and further has good moldability and chemical resistance has long been desired.
In an attempt to improve by polymer blending the moldability of an aromatic copolyester comprising the reaction product of terephthalic acid and isophthalic and and/or functional derivatives thereof and a bisphenol and/or a functional derivative thereof, there has been proposed to blend various resins with the aromatic copolyester. For example, processes using ABS resin (Japanese Patent Application (OPI) 25053/1973), polyethylene terephthalate (Japanese Patent Application (OPI) 23844/1974, U.S. Pat. No. 3,946,091), polyethylene hydroxybenzoate (Japanese Patent Application (OPI) 5443/1975, U.S. Patent 3,884,990), polytetrafluoroethylene (Japanese Patent Application (OPI) 5444/1975), polybutylene terephthalate (Japanese Patent Application (OPI) 34342/1975), a copolymer consisting of ethylene glycol, terephthalic acid and p-hydroxybenzoic acid (Japanese Patent Application (OPI) 64351/1975), an aliphatic polyester or aromatic polyester (Japanese Patent Application (OPI) 96652/1975), etc., are known. These conventional processes, however, have serious defects that the heat distortion temperature and mechanical properties of the aromatic copolyester obtained are reduced greatly.
In preparing a resin composition comprising an aromatic copolyester, a polyamide, and a polyalkylene phenylene ester or a polyalkylene phenylene ester ether, a uniform composition is difficult to obtain using conventional processes wherein melt blending using an extruder is merely applied since the melt viscosity of the aromatic copolyester used is much higher than that of the other components and unmelted aromatic copolyester tends to remain in the resin composition. In the case of extruding the resin composition in the form of, for example, a thin film or a thin monofilament, the presence of unmelted aromatic copolyester can be seen in the appearance thereof; when it is present it damages the appearance of the products badly. Therefore, it has hitherto been desired to improve the above-described disadvantage.
With conventional one step processes for preparing a resin composition comprising an aromatic copolyester, the aromatic copolyester tends to remain unmelted forming heterogeneous regions in the composition and, therefore, a very high temperature is required to obtain a uniformly blended composition. Low melting temperature leads to a non-uniform dispersion of aromatic copolyester and unmelted aromatic copolyester is present in the resulting resin composition. Particularly, when the aromatic copolyester content is not more than 70% by weight based on the total weight of the aromatic copolyester, polyamide and polyalkylene phenylene ester or polyalkylene phenylene ester ether in the blend, the influence of such non-uniform blending is so great that it is very difficult to obtain a resin composition having satisfactory properties using conventional processes. When the content of aromatic copolyester is 50% by weight or less the above tendency is greatly increased.