POLYESTER RESIN COMPOSITION

Abstract: The present invention relates to 95/5 - 80/20 polyethyleneterephthalate/polyolefin compositions having good resistance to moisture absorption, stability in a molten state, heat resistance, and mechanical properties.

Description: TITLE POLYESTER RESIN COMPOSITION BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a polyester resin composition excellent in its resistance to moisture absorption, stability under a molten state, heat resistance, and mechanical properties, etc., and having a low specific gravity. More specifically, the present invention relates to a polyester resin composition containing polyethyleneterephthalate as a main component. Description of the Related Art A polyester resin composition containing polyethyleneterephthalate as a main component is known in the art as a resin composition exhibiting excellent mechanical and electrical properties and having a high resistance to chemicals. However, the conventional polyester resin composition containing polyethyleneterephthalate as a main component can be defective in that the composition may have low stability in a molten state and it may fail to exhibit a sufficient resistance to moisture absorption. The stability under a molten state noted above relates to a melt viscosity of the composition measured by a capirograph. If the stability under a molten state is low, so- called "fins" tend to be formed in the molding step of the resin composition, with the result that the outer appearance of the molded article is impaired. In addition, the resultant molded articles can be non-uniform in size and weight. The resistance to moisture absorption noted above relates to the following two conditions: (1) a mechanical strength of the article molded from the resin composition and (2) a melt viscosity of the pellets used for the molding. Where a composition has a high resistance to moisture absorption, a molded article prepared by using pellets having a high water content, e.g., 0.5%, has a mechanical strength sufficiently high relative to the value of another molded article prepared by using pellets of a low water content, e.g., 0.02% or less. Also, the composition has a high melt viscosity even in the case of using pellets having a high water content. Since it is difficult to mold polyethyleneterephthalate under the condition of moisture absorption, it is important to improve the resistance to moisture absorption in a polyester resin composition containing polyethyleneterephthalate as a main component. An object of the present invention is therefore to provide a polyester resin composition containing polyethyleneterephthalate as a main component, said composition exhibiting excellent mechanical properties, achieving marked improvements in both resistance to moisture absorption and stability under a molten state, and permitting a molding treatment under a low temperature. As a result of extensive research made in an attempt to achieve the above-rioted object, it has been found possible, via the present invention, to markedly improve the resistance to moisture absorption and stability under a molten state without impairing the properties inherent in polyethyleneterephthalate by adding a predetermined amount of polyolefin to polyethyleneterephthalate. SUMMARY OF THE INVENTION According to the present invention, there is provided a polyester resin composition consisting essentially of a polyethyleneterephthalate and a polyolefin, with the ratio of the polyethyleneterephthalate to the polyolefin ranging between 95 : 5 and 80 : 20. The composition according to the present invention exhibits excellent stability under a molten state and resistance to moisture absorption, while maintaining excellent mechanical properties that are inherent in a resin containing polyethyleneterephthalate as a main component. DETAILED DESCRIPTION OF THE INVENTION It is desirable for the polyethyleneterephthalate used in the present invention to have an intrinsic viscosity falling within a range of between about 0.4 and about 1.2. The polyolefin used in the present invention includes, for example, polyethylene, polypropylene and other olefin homopolymers; polyolefins modified with giycidyl methacrylate; and copolymers including graft copolymers between olefin and vinyl compound and/or acrylic compound. Particularly desirable is polypropylene having a melt index of 0.1 to 50 g/10 minutes (ASTM D1238), preferably 0.5 to 20 g/10 minutes. The mixing amount of polyolefin is determined in view of the desired properties of the molded article. It is recommended that the ratio of polyethyleneterephthalate to polyolefin fall within a range of between 95 : 5 and 80 : 20. Also, the amount of the polyolefin should desirably be 1 to 30% by weight, more preferably 2 to 15% by weight, based on the total amount of the resin composition. If used in an amount of less than 2% by weight of the entire composition, the polyolefin fails to sufficiently enable the resultant composition to exhibit a high resistance to moisture absorption and a high stability under a molten state. If the polyolefin mixing amount is larger than 15% by weight of the entire composition, the molded article tends to be deteriorated in heat resistance and in mechanical properties. In the present invention, it is also possible to add 5 to 150 parts of inorganic reinforcing materials or flame retardants, such as glass fiber, mica and whiskers, based on 100 parts by weight of the resin composition. A molded article prepared from the composition containing these inorganic reinforcing materials, etc., is excellent in its stability under a molten state and resistance to moisture absorption. In addition, the molded article exhibits excellent heat resistance, rigidity and mechanical strength. It is also desirable for the polyester resin composition of the present invention to contain a nucleating agent in order to improve the moldability of the composition under low temperatures. A sodium compound and/or a potassium compound can be used as the nucleating agent. It is possible to substitute talc for a part or all of these sodium compounds and potassium compounds. Various other nucleating agents can also be used in the present invention. Further, a polyethyleneterephthalate having a sodium or potassium atom at a terminal end thereof can be substituted for a part or all of the main component polyester. The polyethyleneterephthalate subjected to such a terminal treatment is described in U.S. Patent No. 4,425,470 and can be prepared by the method described in said U.S. Patent. In the case of using a polyethyleneterephthalate having a sodium or potassium atom at a terminal end thereof, the nucleating agent need not be added separately in some cases. The composition of the present invention exhibits a satisfactory melt viscosity, even if a plasticizer is not added to the composition. However, it is possible to add a plasticizer for controlling the melt viscosity of the composition. Further, it is possible for the composition of the present invention to contain various additives, such as anti-oxidants and stabilizers. The polyester resin composition of the present invention can be prepared by the melt kneading method using various kneaders used in general, including, for example, a Banbury mixer and extruder. For preparing the resin composition of the present invention, all the components of the composition can be put together in a kneader so as to simultaneously knead all the components. Alternatively, the polyolefin can be supplied through a side feeder. The polyester resin composition of the present invention exhibits a high stability under a molten state. Thus, fins are unlikely to be formed in the molding step, leading to a good outer appearance of the molded article. In addition, the molded articles are made uniform in size and weight. Also, the composition exhibits a high resistance to moisture absorption. Thus, pellets of the composition can be supplied directly from a paper bag housing the pellets into a mold. In other words, the pellets supplied into the mold without drying can be molded satisfactorily so as to provide a molded article having a high mechanical strength and a good outer appearance. EXAMPLES The Examples that follow illustrate the present invention. The technical scope of the present invention is not restricted by these Examples. Specifically, the compositions shown in Table 1 were prepared and various properties thereof were measured. Table 1 also shows the results of tests on the compositions. Table 1 'MV ... Melt Viscosity Table 1 ("Continued) PET shown in Table 1 denotes polyethyleneterephthalate, manufactured by Du Pont de Nemours & Co., Inc., which has an intrinsic viscosity of about 0.67 to 0.58. PP shown in Table 1 denotes "polypropylene K1008", which is a trademark and a product of Chisso K.K., having a melt index of 10 g/10 minutes. The sodium salt shown in Table 1 denotes "Sahline 8920", which is a trademark and a product of Du Pont de Nemours & Co., Inc. Further, a plasticizer and an anti-oxidant were added to each of the compositions shown in Table 1. The resins, nucleating agent, and other additives in amounts (parts by weight) shown in Table 1 were preliminarily mixed for 20 minutes in a tumbler. Then, the resultant mixture was subjected to kneading under a molten state at 290°C by using TEM35B, which is a trademark of a biaxial extruder manufactured by Toshiba Kikai K.K., so as to obtain a resin composition. The melt viscosity of the composition was measured at 280°C under a shearing stress of 1216 sec "1 by using a capirograph manufactured by Toyo Seiki K.K. The melt viscosity under a dried state shown in Table 1 denotes the melt viscosity measured under the condition that the water content of the composition pellets used was 0.02% or less and the residence time of the composition in the capirograph was 3 minutes. The melt viscosity under the residing state denotes the melt viscosity measured under the condition that the water content of the composition pellets used was 0.02% or less and the residence time of the composition in the capirograph was 30 minutes. Further, the melt viscosity under the moisture-absorbed state shown in Table 1 denotes the melt viscosity measured under the condition that the water content of the composition pellets used was 0.05%. The melt viscosity retention rates under the residing state and under the moisture-absorbed state shown in Table 1 were determined as follows: R (%) = (A/B) x 100 M (%) = (C/D) x 100 where: R ... Melt viscosity retention rate under the residing state; A ... Melt viscosity under the residing state; B ... Melt viscosity under the dried state; M ... Melt viscosity retention rate under the moisture-absorbed state; C ... Melt viscosity under the moisture-absorbed state (residence time of 3 minutes); and D ... Melt viscosity under the dried state (residence time of 3 minutes). For measuring the mechanical properties shown in Table 1, the resin composition was dried at 135°C for 3 hours, followed by preparing, at 290°C, a standard property test piece from the dried composition by using a molding machine with the mold temperature set at 90°C. The tensile test and the bending test were conducted in accordance with ASTM-638 and ASTM-790, respectively. The Izod impact test was conducted in accordance with ASTM D-256. The properties under the moisture-absorbed state denote those of the molded article prepared by using a resin composition containing 0.05% of water. The water content was measured by Karl Fischer method. It is apparent from Table 1 that the polyester resin compositions of the present invention exhibit the excellent mechanical properties inherent in the polyethyleneterephthalate, and that the compositions are excellent in their stability under a molten state and in their resistance to moisture absorption.

Claims: CLAIMS 1. A polyester resin composition consisting essentially of a polyethyleneterephthalate and a polyolefin, wherein the ratio of the polyethyleneterephthalate to the polyolefin is between 95 : 5 and 80 : 20. 2. The polyester resin composition according to Claim 1 wherein said polyolefin is polypropylene. 3. The polyester resin composition according to Claim 1 which further comprises 5 to 150 parts of an inorganic reinforcing material or a flame retardant; based on 100 parts by weight of said composition. 4. The polyester resin composition according to Claim 2 which further comprises 5 to 150 parts of an inorganic reinforcing material or a flame retardant, based on 100 parts by weight of said composition.

Inventors: MUKOHYAMA ATSUSHI, MUKOHYAMA, ATSUSHI
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1992
Main classification: C08L67
IPC codes: C08K7, C08L67