Kao Corporation

Hiroki Kubo

Yukihiro Nakano

Shoichi Murata

Norihiro Fukuri

Kazutaka Yamashita

Michitaka Sawada

Hideyuki Kobayashi

Shigeki Nagashima

Osamu Yamashita

Takahiro Yoshikawa

The present invention relates to a toner for electrophotography including core-shell particles as a resin binder each including a core portion containing an amorphous resin (A) having a softening point of 105&#xb0; C. or lower which is obtained by polycondensing a carboxylic acid component containing an alkenyl succinic acid with an alcohol component; and a shell portion containing an amorphous resin (B) obtained by polycondensing an alcohol component containing an aliphatic diol having 2 to 6 carbon atoms with a carboxylic acid component containing a trivalent or higher-valent polycarboxylic acid compound in an amount of 20 mol % or less. The toner for electrophotography according to the present invention is excellent in heat resistant storage property, low-temperature fusing property and durability.

Toners for electrophotography

An ink set comprising a black ink and a color ink, wherein the black ink comprises an aqueous dispersion of water-insoluble vinyl polymer particles containing an oil-soluble black dye or carbon black, the vinyl polymer particles have an ionicity opposite to that of the color ink, and the vinyl polymer comprises a water-insoluble vinyl polymer prepared by copolymerizing (a) a salt forming group-containing monomer, (b) a monomer represented by the formula (I):CH&#x2550;C(R)COO(RO)R&#x2003;&#x2003;(I)wherein Ris hydrogen atom or a lower alkyl group, Ris a divalent hydrocarbon group which may have a hetero-atom, Ris a monovalent hydrocarbon group which may have a hetero-atom, and p is a number of 1 to 60, (c) a macromer, and (d) a monomer copolymerizable with these monomers. The ink set can be used as an ink set for inkjet recording, which is excellent in not only fixing abilities and water resistance, but also bleeding resistance and jettability, and can form very clear printouts.

Ink set

A magnetic recording medium comprising a nonmagnetic substrate having provided thereon an intermediate layer consisting essentially of magnetic powder having a Mohs hardness of not less than 3 and an average particle size of not greater than 0.5 .mu.m and/or nonmagnetic powder having a Mohs hardness of not less than 3, carbon black, and a binder and, as a top layer, a magnetic layer consisting essentially of ferromagnetic metal powder and a binder, in which said magnetic layer has an average center-line surface roughness (Ra) of not greater than 7 nm, and said magnetic layer has an average center-line surface roughness (Ra) of 10 to 30 nm after being immersed in a hydrochloric acid aqueous solution for 24 hours.

Magnetic recording medium

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Wakayama, Japan

Hiroki Kubo