POLYMER COMPOSITION CONTAINING A POLYMER IN A RIGID PHASE AND RUBBERY POLYMER PARTICLES WITHOUT INHOMOGENITIES

Abstract: The invention relates to a polymer composition containing a semi-crystalline or glass-forming polymer in a rigid phase and, as impact modifier therein, a rubbery polymer. The polymer composition according to the invention is characterized in that it has no morphological inhomogeneities with a diameter larger than 20 micrometer as visible on a Scanning Electron Microscopy (SEM) picture of the surface of fracture of a test bar broken in a fatigue test. As a result, the elongation at break, the fatigue resistance and the total useful service life of an object manufactured from this composition are much higher.

Description: POLYMER COMPOSITION CONTAINING A POLYMER IN A RIGID PHASE AND RUBBERY POLYMER P ARTICLES WITHOUT INHOMOGENITIES The invention relates to a polymer composition containing a semi-crystalline or glass-forming polymer in a rigid phase and, as impact modifier 10 therein, a rubbery polymer. Such a polymer composition is characterized by a very high toughness at service temperature and at low temperatures. Furthermore these materials also have a high elongation at break. These properties make this polymer composition eminently suitable for use in all kinds of applications in which 15 very high demands are to be met, such as telephone housings and the like. A disadvantage of the known polymer compositions is that the fatigue resistance is not of the desired level so that the useful service life of an object manufactured from this composition is limited to an unwanted degree. In addition, further improvement of the elongation at break is desirable. 20 The aim of the invention is to improve the fatigue resistance and the elongation at break. This aim is achieved in that the polymer composition has no morphological inhomogeneities with a diameter larger than 20 micrometer as visible on a Scanning Electron Microscopy (SEM) picture of the surface of fracture 25 of a test bar broken in a fatigue test. A fatigue test is a test in which a dumbbell-shaped test bar with a shape according to ISO R527 is subjected to a cyclic tensile load at a frequency of 1-10 Hz at a stress ratio between minimum and maximum load of 0.1 and a maximum stress of a suitably chosen percentage of the yield stress determined in a static tensile test. A suitable percentage for example is 66% for polycarbonate mixtures and 80% for polybutylene terephthalate mixtures. Morphological inhomogeneity is understood to be a part of the volume part with deviating composition and a dimension that is a multiple of that of the dispersed phase. Where inhomogeneities have a shape other than round, the equivalent diameter is used, which is the diameter of a circle with the same cross-sectional area as of the inhomogeneity on the SEM picture. It has been found that the polymer composition according to the invention has a significantly improved fatigue resistance so that its life is much longer. The elongation at break, too, is considerably improved. The invention applies in particular to morphological inhomogeneities consisting substantially of polymer material built up from building blocks of the surrounding polymer composition but having a composition deviating from that of the surrounding polymer composition. More in particular the invention applies to morphological inhomogeneities that consist substantially of the rubbery polymer of the disperse phase. It has been found that small quantities of relatively large morphological inhomogeneities apparently occur in these rubber-modified polymer compositions. The morphological inhomogeneities are normally almost undetectable for the usual measuring techniques because they occur in a very low concentration, for example less than approximately 100 ppm or even less than 10 ppm. Furthermore these inhomogeneities do not affect the mechanical properties of the polymer composition such as strength, impact strength and modulus. It is therefore surprising to find that morphological inhomogeneities larger than 20 micrometer (as visible on a Scanning Electron Microscopy (SEM) picture of the surface of fracture of a test bar broken in a fatigue test) have a very adverse effect on the fatigue resistance of the polymer composition. This method shows only the largest inhomogeneities, these inhomogeneities causing and being the location of the fracture. This implies that if no particles larger than 20 micrometer occur in a fatigue fracture surface thus obtained the chance is very small. The fatigue resistance is very strongly related to the size of these morphological inhomogeneities. Preferably the polymer composition according to the invention has no morphological inhomogeneities with a diameter larger than 15 micrometer, preferably 10 micrometer and even more preferably 5 micrometer. The invention also relates to a process for the preparation of a polymer composition according to the invention in which the polymer of the rigid phase and the rubbery polymer, which contain no morphological inhomogeneities with a diameter larger than 20 micrometer, are mixed. Preferably the polymer composition according to the invention is prepared using a process in which the morphological inhomogeneities with a diameter larger than 20 micrometer are removed from the polymer of the rigid phase and or the rubbery polymer before, during or after the mixing thereof. Preferably the morphological inhomogeneities are removed by filtration. The invention also relates to a polymer composition obtainable using the said processes and to moulded articles containing a polymer composition according to the invention. Such moulded articles combine very good mechanical properties such as impact strength with a very good fatigue resistance and a very high elongation at break. The polymer composition according to the invention can have very divergent compositions of two or more components. Preferably the polymer in the rigid phase has been chosen from the group of polycarbonates, polyesters, polyamides, or styrene polymers and the rubbery polymer from the group of EPDM (ethylene-propylene-third monomer rubber), EP (ethylene-propylene rubber), SBR (styrene-butadiene rubber), PB (polybutadiene), MBS (methyl methacrylate butadiene styrene) or acrylate rubbers. The advantages of the invention are most evident where the rigid phase is a glass, for example polycarbonate. This polymer being very sensitive to fatigue, the improvement brought about by the measure according to the invention is very great. The rubbery polymer then preferably is polybutadiene.

Claims: CLAIMS 1. Polymer composition containing a semi-crystalline or glass-forming polymer in a rigid phase and, as impact modifier therein, a rubbery polymer, characterized in that the polymer composition has no morphological inhomogeneities with a diameter larger than 20 micrometer as visible on a Scanning Electron Microscopy (SEM) picture of the surface of fracture of a test bar broken in a fatigue test. 2. Polymer composition according to claim 1 , characterized in that the morphological inhomogeneities consist substantially of polymer material built up from building blocks of the surrounding polymer composition but having a composition deviating from the surrounding polymer composition. 3. Polymer composition according to claim 1 or 2, characterized in that morphological inhomogeneities mainly contain the rubbery polymer. 4. Polymer composition according to any one of claims 1 -3, characterized in that the polymer in the rigid phase has been chosen from the group of polycarbonates, polyesters, polyamides, or styrene polymers and the rubbery polymer has been chosen from the group of EPDM, EP, SEBS, SBR, PB, MBS or acrylate rubbers. 5. Polymer composition according to claim 4, characterized in that the rigid polymer is polycarbonate. 6. Polymer composition according to claim 5, characterized in that the rubbery polymer is polybutadiene. 7. Process for the preparation of a polymer composition according to any one of claims 1-6, characterized in that the polymer of the rigid phase and the rubbery polymer, which contain no morphological inhomogeneities with a diameter larger than 20 micrometer, are mixed. 8. Process for the preparation of a polymer composition according to any one of claims 1-6, characterized in that the morphological inhomogeneities with a diameter larger than 20 micrometer are removed from the polymer of the rigid phase and/or the rubbery polymer before, during or after the mixing thereof. 9. Process according to claim 8, characterized in that the morphological inhomogeneities have been removed by filtration. 10. Polymer composition obtainable according to the process according to claim 7, 8 or 9. 11. Moulded articles containing a polymer composition according to any one of claims 1-6 or 10.

Inventors: MARISSEN ROELOF, VAN HARTINGSVELDT EDWIN ADRIAA, MARISSEN, ROELOF, VAN HARTINGSVELDT, EDWIN, ADRIAAN, ANDRE
Applicants: DSM NV, HARTINGSVELDT EDWIN ADRIAAN AN, MARISSEN ROELOF, DSM N.V., MARISSEN, ROELOF, VAN HARTINGSVELDT, EDWIN, ADRIAAN, ANDRE
Application year: 2001
Main classification: C08L67
IPC codes: C08L67, C08L69, C08L77