Electrostatic developer with core-shell carrier coated with silicone - contg. urethane bond, giving stable negative charging property under wide range of environmental conditions

摘要

Developer compsn. (I) for electrostatic latent images has a core-shell carrier (II) and a toner (III) of binder resin (IV) and dyestuff (V), (II) having a coating of silicone resin (VI) with a urethane bond. (I) contains 100 (wt.) pts. (II) and 2-10 pts. (III). (II) comprises 100 pts. core material and 0.2-1.6 pts. (VI). (III) contains 100 pts. (IV) and 1-15 pts. (V) and may also contain colloidal silica, Al2O3, polymer beads, polyolefin and/or esp. a charge controller (XI), wax and/or hydrophobic silica (XII). USE/ADVANTAGE - (I) is useful for electromagnetic scanning development. (I) has high negative charging capacity, even under conditions of low temp./low humidity and high temp./high humidity, excellent fixing property and transparency. In an example, carriers were prepd. by spray coating 100 pts. spherical ferrite core material with a dispersion of (A) 0.7, (B) 0.9 pt. mixt. of methyldimethylsilicone resin 'SR2400' (RTM) contg. 5% methyltrimethoxysilane as (IX), (A) 0.15, (B) 0 pt. 'TSR 175' (RTM) as (VIII) and (A) 0.05, (B) 0 pt. 'Coronate 2031' (RTM) as (X) in MEK and heated 30 mins. in a fluidised bed reactor at 300 deg.C. A polyester resin (IVA) was prepd. by polycondensation of 175g polyoxypropylene-(p = 2.0, average)-bisphenol A, 162.5g polyoxyethylene-(p = 2.0, average)-bisphenol A, 83g terephthalic acid, 38.4g trimellitic anhydride and 53.6g dodecenylsuccinic acid, using SnO2 as catalyst. A toner (IIIA) was prepd. by melt kneading 100 pts. (IVA) with 8 pts. C black (Mogul L' (RTM), 1.5 pts. 'Bontron S-34' (RTM) as (XI) and 3.0 pts. wax, pulverising, classifying to an average dia. of 8 microns and adding 0.5% 'R 972'(RTM) as (XII). 1000 Pts. carrier (A) or (B) were mixed with 40 pts. (IIIA) and used in an electrophotographic copier. The copy quality initially after 20,000 copies was (A) o/o, (B) 0/+ at 25 deg.C/50% RH; (A) o/o, (B) +/x at 35 deg.C/85% RH; and (A) 0/0, (B) +/x at 10 deg.C/20% RH (scale o = image density 1.4 or more and fogging 0.01 or less; + = one of these not in class 'o'; x = neither in class 'o').