Abstract: A piston ring mounted in the ring groove of an aluminum alloy piston does not cause aluminum adhesion during the long-term use. The piston ring includes a resin film deposited on at least one of an upper face and a lower face. The resin film contains from 0.5 to 20% by volume of carbon black particles and from 3 to 30% by volume of solid lubricant particles with respect to the total volume of the resin film. The carbon black particles preferably contain one or both of graphitized carbon black particles and composite graphite black particles.

Abstract: In mounting a combined oil control ring in a ring groove formed in a piston, the combined oil control ring is mounted in a form that an opening between but ends of an oil ring body is widened. In such an operation, it is likely that a coil expander falls off the oil ring body thus making the mounting operation cumbersome. To overcome such a drawback, a relationship L1<L2 is established. Here L1 means a axial distance between open peripheries of the groove portion and L2 means a maximum axial distance between peripheries of the groove portion.

Abstract: In a combined oil ring having a spacer expander to be installed between a pair of upper and lower side rails, a plurality of axially protruding inner peripheral protruding portions are formed on the inner peripheral side of the spacer expander along its peripheral direction. The inner peripheral protruding portions press the inner peripheral surface of the side rails. On the outer peripheral side of the spacer expander, a plurality of slits are formed, and a plurality of connecting portions are located in the peripheral direction isolated by the slits. On the plurality of connecting portions, axially protruding outer peripheral protruding portions are formed.

Abstract: In a combined oil ring having a spacer expander to be installed between a pair of upper and lower side rails, a plurality of axially protruding inner peripheral protruding portions are formed on the inner peripheral side of the spacer expander along its peripheral direction. The inner peripheral protruding portions press the inner peripheral surface of the side rails. On the outer peripheral side of the spacer expander, a plurality of slits are formed, and a plurality of connecting portions are located in the peripheral direction isolated by the slits. On the plurality of connecting portions, axially protruding outer peripheral protruding portions are formed.

Abstract: A three-piece combined oil-control ring comprises a pair of upper and lower side rails 222 in the axial direction and a spacer expander 224. The spacer expander is located between the side rails 222, and pushes the side rails from their inner peripheral side to generates the tension of the side rails 222. The ears of the spacer expander made of austenitic stainless steel in contact with inner peripheral surfaces of the side rails, are subjected to gas-nitriding at a temperature of 470° C. or higher to form a 10 to 60 ?m thick gas-nitriding surface-layer comprising a phase having peaks at 2?=40° and 2?=46° by Cu—K ? X-ray diffraction. In addition or alternatively, a resin coating film (31) is formed on at least surfaces of the spacer expander (7) faced to the side surfaces of the side rails or on at least surfaces of the side rails (5,6) faced to the spacer expander (7).

Abstract: In mounting a combined oil control ring in a ring groove formed in a piston, the combined oil control ring is mounted in a form that an opening between but ends of an oil ring body is widened. In such an operation, it is likely that a coil expander falls off the oil ring body thus making the mounting operation cumbersome. To overcome such a drawback, a relationship L1<L2 is established. Here L1 means a axial distance between open peripheries of the groove portion and L2 means a maximum axial distance between peripheries of the groove portion.

Abstract: The present invention provides a linear polyolefin wherein one of the terminals of linear polypropylene or linear ethylene-propylene random copolymer is modified with a (meth)acrylic derivative unit or styrene derivative unit to give a substantially monodipersed system. The feature thereof consists in such a linear polyolefin in which the terminal of linear polypropylene or linear ethylene-propylene random copolymer obtained by living polymerization is modified with a (meth)acrylic derivative unit or styrene derivative unit. For the production thereof, there are used methacrylic acid chloride, acrylic acid chloride, ethylene glycol dimethacrylate, etc. as the (meth)acrylic derivative, and divinylbenzene, etc. as the styrene derivative.

Abstract: The object of the present invention is to provide such a polyolefin that only the terminal of polypropylene or ethylene-propylene random copolymer is modified with a (meth)acrylic derivative unit to give a substantially monodipersed system. The feature thereof consists in such a polyolefin that the terminal of polypropylene or ethylene-propylene random copolymer obtained by living polymerization is modified with a (meth)acrylic derivative unit. As the (meth)acrylic derivative, there are used vinyl methacrylate, allyl methacrylate, trimethylsiloxyethyl methacrylate, 2-trimethylsiloxypropyl methacrylate, N, N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, glycidyl methacrylate, acrylic acid chloride and like.

Abstract: This invention relates to a catalytic component for the polymerization of .alpha.-olefins and provides a catalytic component of magnesium support type capable of exhibiting a high stereoregularity while maintaining an improved strength as well as a high catalytic activity. The features thereof consist in a catalyst component for the polymerization of .alpha.-olefins obtained by contacting (A) a solid component comprising, as essential components, magnesium, titanium, a halogen and an electron-donating compound with (D) an olefin in the presence of (B) a trialkylaluminum and (C) a dimethoxy group-containing compound represented by the general formula R.sup.1 R.sup.2 Si(OCH.sub.3).sub.2 where R.sup.1 and R.sup.2 are, same or different, aliphatic hydrocarbon groups with 1 to 10 carbon atoms and having a volume, calculated by the quantum chemistry calculation, of 230 to 500 .ANG..sup.3 and an electron density of oxygen atoms in the methoxy group, calculated similarly, ranging from 0.685 to 0.800 A. U.