WO1994006865A1

WO1994006865A1 - Polyester resin composition

Info

Publication number: WO1994006865A1
Application number: PCT/US1993/008737
Authority: WO
Inventors: Atsushi Mukohyama
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1992-09-22
Filing date: 1993-09-21
Publication date: 1994-03-31
Also published as: JPH06263968A

Abstract

Incorporation of a polyolefin into a polybutylene terephthalate composition yields a composition having good melt stability, said composition being particularly useful in making dimensionally stable molded articles.

Description

TITLE

POLYESTER RESIN COMPOSIΗON FIELD OF THE INVENTION

The present invention relates to a polyester resin composition that is excellent in impact resistance, melt stability, heat resistance, and mechanical properties, and which has a low specific weight. The composition is comprised of polybutylene terephthalate (PBT) and a polyolefin. _

BACKGROUND OF THE INVENTION Polyester resin compositions mainly comprised of PBT are known to exhibit good mechanical properties, electrical properties, and chemical resistance. However, such polyester resin compositions mainly comprised of PBT have been deficient in that their low melt stability tends to cause degradation when held in the melted state for molding. The expression "having high melt stability" in this application refers to, as described in detail later, a situation where a melt viscosity measured by a "capillograph" after a long residence time in said capillograph is sufficiently high relative to a melt viscosity determined after a short residence time. Having high melt stability means that a resin composition can be molded without significantly adversely affecting the resultant molded articles when variations, such as molding pressure variations, occur during molding operating conditions. Conversely, a low melt viscosity means that when a resin composition is molded, it tends to generate so-called burrs, which not only adversely affect the appearance of the molded article, but also cause variations in the dimensions and weights of the molded articles.

Therefore, there has been a demand for a polyester resin composition mainly comprising PBT which exhibits not only excellent mechanical properties, but also improved impact resistance and melt stability SUMMARY OF THE INVENTION

In the present invention, it was discovered that adding a specific amount of polyolefin to PBT can appreciably improve the melt stability of PBT without significantly adversely affecting the inherent properties of the PBT. More specficially, the present invention relates to a composition comprising PBT and a polyolefin, wherein there are 1-30 parts by weight of polyolefin per 100 parts by weight of PBT. DETAILED DESCRIPTION OF THE INVENTION

Polybutylene terephthalates which are used in this invention are known in the art. They can be homopolymers obtained by polycondensing terephthalic acid and butane diol, but may also be copolymers containing other comonomer components within a range of providing the physical and chemical properties of PBT. That is, copolymer components which may be used in the preparation of PBT copolymers include glycol components, such as ethylene glycol, 1,2-propylene glycol, pentanedoil, hexanedoil, 1,4- cyclohexane dimethanol, and the like, and dicarboxylic acid components, such as isophthalic acid and naphthalene dicarboxylic acid. Specific examples of these PBT copolymers include, but are not limited to, (poly)butylene-CO-ethylene terephthalate, (poly)butylene-CO-l, 4- cyclohexane-terephthalate, (poly)butylene-terephthalate-isophthalate, (poly)butylene-terephthalate-naphthalene dicarboxylate, and the like. The polybutylene terephthalates used in this invention preferably have an inherent viscosity of at least about 0.4 when measured at 30° C in a 0.1% m-cresol solution, but may be used up to an inherent viscosity of about 1.2.

The polyolefins which may be used in this invention include polyethylene, polypropylene, polybutylene, ethylenerpropylene copolymer, and other polyolefins such as glycidyl-methacrylate-modified polyolefins and olefin-vinyl compounds and/or acrylic copolymers or graft polymers. From among these polyolefins, it is preferred to use polypropylene. The polypropylene used preferably has a melt index (ASTM D-1238) of 0.1-50 g/10 in, particularly 0.6-20 g/min. The amount of the polyolefin to be used is selected by taking into consideration the physical properties of the molded articles to be obtained. The amount of the polyolefin is preferably 1-30 parts by weight, more particularly 2-17 parts by weight, per 100 parts by weight of PBT. The use of 2 parts by weight or less polyolefin can present difficulty in obtaining sufficient impact resistance and melt stability from the polyolefin, while a level greater than 20 parts by weight polyolefin can cause a reduction in the heat resistance and the mechanical properties of the resultant molded articles. The addition of more than 30 parts by weight polyolefin may deposit the resin composition in the mold at the time of molding, generating a scorched molded article. The compositions of the present invention can additionally contain inorganic reinforcing materials (such as glass fibers, mica, whiskers, and the like) or flame retardants in amounts of 5-150 parts per 100 parts per weight of the polyolefin and the PBT. Molded articles obtained from compositions containing these inorganic reinforcing materials will show not only excellent melt stability and impact resistance, but also excellent heat resistance, stiffness and mechanical strength as well.

Compositions of this invention may also be mixed with other additives known in the art. These other additives include antioxidants, UV stabilizers, heat stabilizers, light stabilizers, lubricants, colorants, mold releases, and the like.

The polyester resin composition of the present invention is prepared by melt mixing by means of commonly-used mixing devices, such as Banbury mixers, extruders, a variety of kneaders, and the like. In regard to the order of mixing the components in preparing the polyester resin composition of this invention, all the components may be mixed in one shot or alternatively, the polyolefin may be fed from a side feeder. A variety of known methods are applicable for molding the mixed composition. For molding a composition of this invention, it is preferred to first completely dry the composition due to the fact that if water is present, the polyester can experience degradation on melt processing due to hydrolysis.

The polyester resin composition of this invention has a high melt stability and will resist forming any burrs even after an extended residence time during molding, so as to give molded articles with a good appearance and little variation in dimensions and weight.

EXAMPLES The present invention is now described in detail by examples and control examples, but the invention is not limited to these examples.

Compositions for Examples 1-5 and Control Example 1 are set forth in Table 1. below. Table 1

^W eight percent based upon total composition weight

In Table 1. "PBT" was a polybutylene terephthalate product of the DuPont Company which had an inherent viscosity of about 0.70. P" was polypropylene K1008, a product of Chisso Company, which had a melt index of 10 g/10 min. The compositions in Table 1 also contained conventional antioxidants and lubricants.

The compositions of Table 1 were prepared by tumbling all ingredients together for about twenty minutes and melt mixing the resultant mixture in a Toshiba Kikai Company twin screw extruder TEM35B using a temperature setting of 265° C. The compositions were subjected to measurements of melt viscosity on a capillograph of the Toyoseiki Company at 250PC at a shear stress of 1216 (sec"¹). The term "Standard Melt Viscosity" refers to melt viscosity measured on pellets of the composition having a water content of not more than 0.02%, at a melt temperature of 250° C and a residence time of three minutes. The term "Melt Viscosity After Residency at High Temp" is the melt viscosity measured after a thirty minute residence time at a melt temperature of 270PC.

The term "Melt Viscosity Retention After Residency, %" means the value obtained from the following equation:

Percent Melt Viscosity After Residence (%) = (A/B) x 100 wherein

A = Melt Viscosity After Residency at High Temp and B = Standard Melt Viscosity Actual moldings may require mold temperatures of about 27 f C with residence times being extended over thirty minutes when problems occur. Therefore, resistance to change of the melt viscosity under such conditions can permit the continuation of the production of stable molded products, thereby substantially improving production efficiency in actual production steps.

Tests on the physical properties of the composition were carried out by drying the composition at 135° C for three hours, followed by fabricating standard physical testing pieces on a molding machine using a temperature setting of 260° C and a mold temperature setting of 8(f C. The physical properties were measured on the dry composition. The test procedures were ASTM-638 for tensile testing and ASTM-790 for flexural tests. The Izod impact test was carried out in accordance with ASTM D- Water content was measured by the Karl-Fisher method.

The measured data given in Table 1 clearly show that the polyester resin compositions of the present invention have excellent mechanical properties and excellent melt stability.

Claims

1. A composition comprised of polybutylene terephthalate and a polyolefin, wherein the amount of the polyolefin is 1-30 parts by weight per 100 parts by weight of the polybutylene terephthalate.

2. The composition of Claim 1 in which the polyolefin is polypropylene.

3. The composition of Claim 1 further containing at least one of inorganic reinforcing materials, flame retardants, antioxidants, UV stabilizers, heat stabiliers, light stabilizers, lubricants, colorants, and mold release agents.