Carrier for electrophotography

This invention relates to carriers for electrophotography comprising a binder component including a binder resin, a polymeric-magnetic coordination complex, and an inorganic magnetic material dispersed in the binder component at the ratio of 100-900 parts by weight to 100 parts by weight of the binder component, which effect the electrical resistance as well as magnetic properties. Carriers of the invention are suitable, in particular, for a copier furnished with a high rotation developing sleeve.

BACKGROUND OF THE INVENTION 
This invention relates to carriers for electrophotography, more 
particulaly, carriers with high electrical resistance used in a developer 
applied to an electrophotographic copier or a printer. 
A method of copying by an electrophotographic copier or a printer consists 
of six processes. These processes include a uniformly charging process of 
a photosensitive member surface, an electrostatic latent image-forming 
process by irradiation of light corresponding to images of a manuscript, a 
developing process of electrostatic latent images on the photosensitive 
member by toners contained in a developer, a transferring process of 
toners on the photosensitive member to a copying thing, such as a paper, a 
fixing process of toners to the copying thing, and a cleaning process of 
the photosensitive member. 
Known developers used in, for example, electrophotographic copiers include 
a two-component developer mainly containing insulating non-magnetic toners 
and magnetic carriers, and an one-component developer mainly containing 
insulating magnetic toners constituted of magnetic materials. The 
two-component developer is used in the following developing system. 
Charges are generated by friction between toners and carriers such as iron 
particles, magnetic brushes of the carriers are formed on a surface of a 
developing sleeve with built-in magnets to stir and transport the toners 
to a developing region, and then the charged toners are contacted with 
oppositely charged electrostatic latent images formed on a surface of a 
photosensitive member to develop the toners. 
A developing system using a two-component developer brings about a defect 
such as white lines in developed images because of a hard ear of brush on 
account of strong suction force between each carrier particle on a surface 
of a developing sleeve. When the content of toners in a developer 
decreases, other troubles occur such as the disorder of electrosttic 
latent images, the deficit of developed images and the adherence of 
carriers to a part of electrostatic latent images on a photosensitive 
member and the like, because the charges of the electrostatic latent 
images on the photosensitive member tend to run away through the low 
specific resistant carriers of 10.sup.6 .OMEGA..cm or less, or charges are 
injected from the developing sleeve to the carriers. 
In order to overcome the aforementioned problems relating to carriers 
consisting of magnetic materials such as iron particles, binder-type 
carriers have been proposed, in which magnetic particles with small 
particle size are blended with insulating binder resin. 
Further, development at high speed, being desired recently, has brought a 
following new problem. Both a sleeve and magnets built in the sleeve are 
required to rotate at a high-speed in order to prevent irregular 
developments when binder-type carriers are used for the high-speed 
development. The high-speed rotation of magnets causes the increase of 
temperature of a sleeve on account of excessive eddycurrent. 
Therefore, it has been proposed that binder-type carriers filled with a 
high content of magnetic particles are used in a copying machine assembled 
so that only the sleeve can rotate and the magnets built in the sleeve are 
fixed. Such carriers, however, have not enough magnetic properties to 
result in adherence of the carriers to a non-image part on the surface of 
an electrostatic latent image carrier. It is not preferred from the 
viewpoint of the retention of electrical resistance of carriers that the 
content of the magnetic particles in carriers becomes very high. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide carriers having enough magnetic 
properties as well as high electrical resistance. 
This invention relates to binder-type carriers for electrophotography 
comprising a polymeric coordination complex.

DETAILED DESCRIPTION OF THE INVENTION 
Binder-type carriers containing magnetic particles in binder resin at a 
high content have not yet enough electrical resistance and magnetic 
properties. The magnetic particles can not be dispersed uniformly as 
primary particles in the resin on account of the high content of the 
magnetic materials, which results in problems such as high specific grvity 
and fragility. 
This invention overcomes the above mentioned problems and provides carriers 
having sufficient magnetic properties, even at a lower content of 
inorganic magnetic materials, as providing well as high electrical 
resistance. 
The object is achieved by binder-type carriers for electrophotography 
comprising a polymeric-magnetic coordination complex. 
Carriers of the invention are suitable for a copier furnished with a high 
rotation developing sleeve. The carriers do not adhere to a photosensitive 
member and do not develop to a part of images, and can form good images 
without the deficits of images and the carrier fogs. The life of a 
photosensitive member and carriers are extended due to the lack of carrier 
development and the decreased consumption of the carriers. Clear color 
images not only with color tones but also without muddiness are obtained 
because carriers are not transferred to the images. 
A polymeric-magnetic coordination complex of the invention is a polymeric 
coordination complex having ferromagnetic properties. 
An illustrative example of such a polymeric-magnetic coordination comples 
is PPH-FeSO.sub.4 (simplified form of polybis(2,6-pyridinediyl methylidene 
nitrilohexamethylene nitrilomethylidene iron sulfate), (referred to as F. 
Lions and K. V. Martin: J. Am. Chem. Soc., 79, 2733(1957) and T. Sugano, 
M. Kinosita, I. Shirotani and K. Ohno: Solid State Comm., 45, 99(1983)), 
which is a polymer-magnetic compound. 
The polymeric-magnetic coordination complex of PPH-FeSO.sub.4 was 
synthesized as follows; 2,6-Dialdehydepyridine and 1,6-hexadiamine of an 
equal mole to 2,6-dialdehydepyridine were dehydrated and condensed at 
60.degree. C. in hot ethanol to obtain a ligand, (C.sub.13 H.sub.17 
N.sub.3)n, (which is a white powder, about 140.degree. C. of T.sub.m, and 
simply called PPH hereinafter), and then, the PPH was reacted with 
FeSO.sub.4.7H.sub.2 O in hot water at 80.degree.-90.degree. C,. under 
nitrogen current to obtain dark red solids. The resultant materials were 
dried in a vacuum desiccator for 72 hours to obtain a desired 
polymeric-magnetic coordination complex. The identification was made by an 
elemental analysis and a far infrared absorption spectrum. 
______________________________________ 
elemental analysis 
C N Fe 
______________________________________ 
calcd. 45.21 12.17 8.09 
found 43.95 12.05 7.98 
______________________________________ 
The elemental analysis was calculated from the empirical formula of 
((Fe(C.sub.13 H.sub.17 N.sub.3).sub.2)SO.sub.4.6H.sub.2 O)).sub.n. As the 
molecular weight of PPH-FeSO.sub.4 is 689.9n, the content of each 
element(%) is calculated from the following formula: 
EQU Calc.(%)=(A).times.(N)/(689.9).times.100 
wherein A represents the atomic weight of an element and N represents the 
number of the element per one molecule of PPH-FeSO.sub.4. 
The material has 42 G of Magnetic flux density(Bm), 3.5 emu/g of 
magnetization amount(o), 7.1 G of remanent magnetism(Hc) under 1000Oe of 
applied magnetic field. 
Examples of the binder resin applicable in carriers of the invention are: 
the acrylic resin containing a polar group such as a carboxyl group, 
hydroxyl group, glycidyl group, amino group and the like; for example, a 
copolymer of a monomer such as methacrylic acid, acrylic acid, maleic 
acid, itaconic acid, etc., a hydroxyl-containing monomer such as 
hydroxyl-polypropylene-monomethacrylate, polyethylene 
glycol-monomethacrylate, etc., an amino group-containing monomer such as 
dimethylaminoethyl methacrylate, etc., or glycidyl methacrylate and the 
like with lower alkyl acrylate and/or styrene; polyester resin, for 
example, a condensate of polyol such as ethylene glycol, triethylene 
glycol, 1,2-propylene glycol, 1,4-butanediol, etc., with dicarboxylic acid 
such as maleic acid, itaconic acid, malonic acid, etc.; and thermoplastics 
such as epoxy resin, etc.; a mixture of the above resin. Each resin may be 
crosslinked three dimensionally inorder to adjust the viscosity. 
The above mentioned binder resins are mixed at the ratio of 0-99% by weight 
on the basis of the total amount of carriers. 
Magnetic carriers of a binder-type of the invention are further mixed with 
inorganic magnetic particles. Any inorganic magnetic particles can be used 
in the invention so far as they have specific volume resistance of more 
than 10.sup.5 .OMEGA..cm. In particular, ferrite is preferred. 
Concrete examples of ferrite, which are shown in U.S. Pat. No. 4,473,483, 
have the general formula; 
##EQU1## 
wherein M is an atom selected from the group consisting of Mn, Ni, Co, Mg, 
Cu, Zn and Cd; x is within the range of between 0.5 and 1.0 and y is 
within the range of between 0.1 and 0.571. 
Ferrite of the invention in addition of the above ferrite includes metals 
containing ferromagnetic metals such as magnetite shown by FeO.Fe.sub.2 
O.sub.3, iron, Nickel and Cobalt, etc., alloys of the metals and compounds 
thereof. 
The inorganic magnetic materials are mixed with a binder component 
including the binder resin and the polymeric-magnetic coordination complex 
at the ratio of 100-900 parts by weight, preferably, 200-800 parts by 
weight to 100 parts by weight of the binder components. 
Sufficient magnetization cannot be achieved if the inorganic magnetic 
particles are less than 100 parts by weight, and carriers are fragile and 
the electrical resistance decreases on account of the non-uniform 
dispersion of magnetic particles (secondary particles) in the resin if the 
inorganic magnetic particles are more than 900 parts by weight. 
Carriers of the invention may be mixed with a dispersant, such as carbon 
black, colloidal silica, colloidal titanium, colloidal alumina, which are 
preferably contained at 0.01-3% by weight in carriers. 
Binder-type carriers using the above mentioned materials are prepared by, 
for example, mixing the materials sufficiently with a mixer etc. and then 
grinding them, followed by fusing and kneading them with a extrusion 
kneader. The kneaded materials thus obtained are cooled, ground finely and 
classified to obtain magnetic carriers having prescribed particle sizes. 
According to the present invention, carriers have high electrical 
resistance as well as high magnetic properties. 
EXAMPLE 
This invention is exemplified in detail by examples, compartive examples, 
and productive examples. 
Electrical resistance of carrier particles in the examples and the 
comparative examples were measured as follows. 
A sample of 1 mm in thickness and 50 mm in diameter was put on a round of 
electrode made of metal and then an electrode of 875.4 g in weight and 20 
mm in diameter and a guarded electrode of 38 mm in internal diameter and 
42 mm in external diameter were put on the sample to be supplied with 500 
V of direct voltage. The value of resistance was read after 1 minute to 
calculate the specific volume resistance of the sample. The environment of 
the measurement was 25.+-.1.degree. C. of temperature and 55.+-.5% of 
relative humidity and the measurement was repeated five times to obtain 
the mean value. 
PREATION EXAMPLE 1 OF TONER 
(-) chargeable toners (toner A) 
______________________________________ 
parts by weight 
______________________________________ 
polyester resin (130.degree. C. of 
100 
softening temperature, 60.degree. C. of 
glass transition temperature) 
carbon black (MA #8 produced by 
50 
Mitsubishi Kasei Co.) 
______________________________________ 
The above materials were mixed sufficiently with ball mills and then 
kneaded on three rolls heated at 140.degree. C. The kneaded materials were 
allowed to cool, ground roughly with a feather mill, ground finely with a 
jet mill, and then air-classified to obtain fine particles of 13 .mu.m in 
mean particle size (toner A). 
PREATION EXAMPLE 2 OF TONER 
(+) chargeable toners (toner B) 
Toner B was prepared similarly as Preparation Example 1 of toner except 
that the following compositions were used. 
______________________________________ 
parts by weight 
______________________________________ 
styrene- n-butylmethacrylate 
100 
resin (132.degree. C. of softening 
temperature; 60.degree. C. of glass 
transition temperature) 
Carbon black (MA #8 produced by 
5 
Mitsubishi Kasei Co.) 
nigrosine dye (Bontron N-01 
3 
produced by Orient Chemical Co.) 
EXAMPLE 1 
polyester resin (123.degree. C. of 
75 
softening temperature, 65.degree. C. of 
glass transition temperature) 
inorganic magnetic particles 
400 
(EPT-1000, made by Toda Kogyo Co.) 
carbon black (MA #8 produced by 
2 
Mitsubishi Kasei Co.) 
Polymeric-magnetic Coordination complex part- 
icles PPH-FeSO.sub.4 
______________________________________ 
The above mentioned materials were mixed and ground sufficiently with 
Henschel mixer, and then fused and kneaded with an extrusion kneader (the 
temperature of the cylinder was 160.degree. C. and that of the cylinder 
head was 150.degree. C.). The kneaded materials thus obtained were cooled, 
ground finely and classified to obtain magnetic carriers having 55 .mu.m 
in mean particle size. 
The resultant carriers had the specific volume resistance of 
7.08.times.10.sup.13 .OMEGA..cm. 
The carriers had 1082 G of magnetic flux density(Bm), 45.6 emu/g of 
magnetization amount(.sigma.), 217.6 G of remanent magnetism(Hc) under 
1000 Oe of applied magnetic field. 
(i) A developer was prepared by mixing Toner A with the carriers at the 
ratio of 10 wt.% of Toner A. The charge amount of the toner after mixing 
for 10 minutes was -11.6 .mu.C/g. 
The charge amount of the toner was -19.9 .mu.C/g after the developer was 
kept under the temperature of 30.degree. C. and the high humidity of 85% 
RH for 24 hours. 
The developer was put to use to develop positively-charged electrostatic 
latent images according to the magnetic brush developing method with the 
developing machine equipped with a (+) chargeable Se-type photosensitive 
member and a heat-fixing roll coated with teflon (registered trade mark). 
The development was continuously repeated 60000 times. 
The image quality was excellent and had no carrier fogs after the copying 
resistant test of 60,000 times as well as at the initial stage of the 
test. No carriers were seen adhered to the photosensitive members. 
(ii) A developer was prepared similarly as (i) using Toner B of Preparation 
Example 2, and evaluated similarly as (i) to obtain the following results; 
The charge amount of the toner after mixed for 10 minutes was +12.4 
.mu.C/g. The charge amount of the toner was +12.1 .mu.C/g after the 
developer was kept under the temperature of 30.degree. C. and the high 
humidity of 85%RH for 24 hours. 
Even after the same copying resistance test as (i), the image quality was 
excellent and had no carrier fogs as well as at the initial stage of the 
test. But, in this case the copying resistance test was carried out by 
developing negatively-charged electrostatic latent images with a (-) 
chargeable laminated organic photosensitive member. 
EXAMPLE 2 
Carriers were prepared similarly as EXAMPLE 1 except that 400 parts by 
weight of the magnetic particles, 90 parts by weight of the 
polymeric-magnetic coordination complex and 10 parts by weight of the 
resin were used. 
The obtaned carriers had the specific volume resistance of 
1.26.times.10.sup.14 .OMEGA..cm. 
The carriers had 1257 G of magnetic flux density(Bm), 61.5 emu/g of 
magnetization amount(.sigma.), 246.2 G of remanent magnetism(Hc) under 
1000 Oe of applied magnetic field. 
The two kinds of developers were prepared similarly as EXAMPLE 1 (i) and 
(ii) using toner A and toner B. The charge amounts of the toners were 
-12.5 .mu.C/g and +13.0 .mu.C/g respectively. After the developers were 
kept under the temperature of 30.degree. C. and the high humidity of 85%RH 
for 24 hours, the charge amounts of the toner were -11.1 .mu.C/g, and 
+12.6 .mu.C/g respectively. 
Each developer was put to the copying resistance test similarly as EXAMPLE 
1. After the copying resistance test, the image quality was respectively 
excellent and had no development and no adherence of carriers as well as 
at the initial stage of the test. The surface of the photosensitive member 
was good. 
COMATIVE EXAMPLE 1 
Carriers were prepared similarly as example 1 except that a 
polymeric-magnetic coordination complex was not used. The obtained 
carriers had the spcific volume resistance of 5.62.times.10.sup.11 
.OMEGA..cm. The carriers had 1032 G of magnetic flux density(Bm), 43.5 
emu/g of magnetization amount(.sigma.), 213 G of remanent magnetism(Hc) 
under 1000 Oe of applied magnetic field. 
The specific volume resistance and the magnetic properties of the carriers 
were much worse than the carriers of Examples 1 and 2 although the same 
parts by weight of the magnetic carriers were used. Accordingly, it is 
understood that the polymeric-magnetic coordination complex affects the 
maintenance (or improvement) of electrical resistance and magnetic 
properties. 
(i) A developer was prepared by mixing Toner A with the carriers at the 
ratio of 10 wt.% of Toner A. The charge amount of the toner after mixing 
for 10 minutes was -12.0 .mu.C/g, the value of which was almost the same 
as those of the Examples (-11.6 .mu.C/g, -12.5 .mu.C/g). Accordingly, it 
is understood that the compounding of the polymeric-magnetic coordination 
into carriers does not impair static properties. 
Copies were made with the same copying machine as Example 1. The image 
quality was not good because of the developments of carriers onto a 
substrate and the fogs of carriers at the edges as predicted from the 
value of electrical resistance. 
(ii) A developer was prepared with toner B similarly as (i). The charge 
amount of the toner after mixing for 10 minutes was +12.7 .mu.C/g, the 
value of which was almost the same as those of the Examples (+12.4 
.mu.C/g, +13.0 .mu.C/g). Copies were made with the same copying machine as 
Example 1. The image quality was not acceptable because of the fogs of 
carriers on both a substrate and at the edges as predicted from the value 
of electrical resistance. 
If the specific volume resistance of the carriers is as low as 10.sup.8 
-10.sup.12 .OMEGA..cm, the specific volume resistance of the developers 
also decreases. In such case, the latter resistance can be made higher by 
increasing the content of the toner in the developer (generally 5 wt.% or 
more), but this manner is not preferred, because it does not give a 
suitable edge-effect and many carriers are inevitably adhered to images by 
injected charges when the content of toner in the developer decreases as 
the developing progresses.