Abstract: The invention provides a process for preparing expandable styrene polymers which comprises the steps of: (a) adding an aqueous phase comprising a suspension stabilizer and an organic phase comprising styrene and an initiator to a reactor, (b) commencing the addition of a blowing agent at a styrene conversion in the range from 40 to 70% and adding the blowing agent over a period ranging from 30 to 60 minutes, (c) adding a stabilizer to stabilize the bead size distribution of the expandable styrene polymer at a styrene conversion in the range from 65 to 99%.

Abstract: The invention provides a process for preparing expandable styrene polymers which comprises the steps of: (a) adding an aqueous phase comprising a suspension stabilizer and an organic phase comprising styrene and an initiator to a reactor, (b) commencing the addition of a blowing agent at a styrene conversion in the range from 40 to 70% and adding the blowing agent over a period ranging from 30 to 60 minutes, (c) adding a stabilizer to stabilize the bead size distribution of the expandable styrene polymer at a styrene conversion in the range from 65 to 99%.

Abstract: Magnetic recording media consist of a nonmagnetic substrate and at least one magnetizable layer bonded thereon and based on a magnetic material dispersed in at least one polyurethane and one polyurethaneurea (meth)acrylate, the polyurethaneurea (meth)acrylate being obtained by reacting a hydroxyl-containing poly(meth)acrylate with a mixture of di- and polyisocyanates and converting the remaining NCO groups with ammonia or primary or secondary amines into urea groups.

Abstract: In flexible magnetic recording media consisting essentially of a web-like nonmagnetic substrate, the magnetic layer is applied to one main side of the web-like substrate and a backing coating formed on the opposite main side of the substrate from a polymeric binder and nonmagnetic fillers as well as supporting pigments, the backing coating contains a precipitated silica treated on the surface with a phosphate-containing polyurethane.

Abstract: In magnetic recording media consisting of a nonmagnetic substrate and one or more magnetizable layers bonded thereon and based on a polyurethane binder, the binder consists of not less than 50% by weight of an isocyanate-free, branched polyurethane which is soluble in tetrahydrofuran and has sulfonate groups along the polyurethane branches and OH-containing urea groups at the chain ends and a molecular weight of from 4,000 to 30,000.

Abstract: Magnetic recording media consist of a nonmagnetic substrate and one or more magnetizable layers bonded thereon and based on a polyurethane binder, the binder consisting of not less than 50% by weight of a branched polyurethane elastomer having sulfonate groups and possessing urea groups at the chain ends.

Abstract: Magnetic recording media consisting of a nonmagnetic substrate and at least one magnetizable layer which is firmly applied thereon and is based on a magnetic material which essentially consists of ferromagnetic chromium dioxide and is finely dispersed in a polymer binder and further conventional additives are distinguished by a particular stability to the chemical decomposition due to moisture and oxidizable compounds and hence particular stability to the deterioration in the magnetic properties, as a result of the addition of from 0.1 to 8% by weight, based on the amount of chromium dioxide, of a monomeric, polyunsaturated, organic compound to the magnetic layer.

Abstract: Magnetic recording media consist of a nonmagnetic substrate and at least one magnetizable layer which is firmly applied thereon and is based on a polyurethane binder, not less than 50% by weight of the binder consisting of a high molecular weight branched polyurethane elastomer having OH-containing urea groups at the chain ends, and the frictional properties of the binder being improved and its coefficient of friction reduced by incorporation of perfluoro groups.

Abstract: The orientation ratio (R.sub.f) of a magnetic layer is defined as the ratio of the magnetizations in the playing direction and the crosswise direction. Assuming that the magnetic layer has anisotropy with respect to the transmittance of infrared light, owing to the orientation of the magnetic pigments, infrared light from a source (IR) is passed through a polarizer (P). The linearly polarized light strikes the magnetic recording medium (M), which is conveyed over a transparent support (T). The support and polarizer are adjusted with respect to one another so that a detector (D) is exposed to maximum light intensity, which is proportional to the orientation ratio (R.sub.f).

Abstract: Magnetic recording media consist of a nonmagnetic substrate and at least one magnetizable layer which is firmly applied thereon and is based on a polyurethane binder which may be crosslinked with a polyisocyanate, not less than 50% by weight of the binder consisting of a low molecular weight branched polyurethane having OH-containing urea groups at the chain ends, and the frictional properties of the binder being improved and its friction reduced by the incorporation of perfluoro groups.

Abstract: Magnetic recording media consist of a nonmagnetic substrate and at least one magnetizable layer which is firmly applied thereon and is based on a polyurethane binder which may be crosslinked with polyisocyanate, not less than 50% by weight of the binder consisting of a low molecular weight branched polyureaurethane having OH-containing urea groups at the chain ends, and the sliding properties of the said binder being improved and its coefficient of friction reduced by incorporation of siloxane groups.

Abstract: Magnetic recording media consist of a nonmagnetic substrate and one or more magnetizable layers which are firmly applied thereon and are based on a magnetic material which is finely dispersed in a polymer binder and further conventional additives and essentially consists of ferromagnetic chromium dioxide, and the said recording media are particularly stable to the chemical decomposition due to moisture and oxidizable compounds and hence to deterioration in the magnetic properties, owing to the addition of from 0.1 to 8% by weight of an organic compound from the group consisting of the antioxidants, based on the amount of chromium dioxide, to the magnetic layer.