Note: Descriptions are shown in the official language in which they were submitted.
2~ 771 03
TONER FOR TWO-COMPONENT MAGNETIC DEVELOPING AGENT
BACRGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner for a
two-component magnetic developing agent having
excellent resistance against being spent. More
specifically, the invention relates to a toner for a
two-component magnetic developing agent without
containing charge control agent that has a property to
migrate onto the carrier surfaces.
2. Description of the Prior Art
A so-called two-component magnetic developing
agent has been widely used for developing static charge
image formed on an electrophotosensitive material.
The two-component magnetic developing agent is
constituted by a mixture of a magnetic carrier
comprising iron powder, ferrite particles, etc. and an
electroscopic toner comprising a colored resin
composition. The magnetic carrier and th-e toner are
mixed together so that the toner particles are
electrically charged to a predetermined polarity. To
effect the developing, the mixture is conveyed in the
form of a magnetic brush up to the photosensitive
material, the surface of the photosensitive material is
rubbed with the magnetic brush, and the charged toner
is adsorbed and held by the charge image on the surface
of the photosensitive material so as to form a visible
image.
Generally, a charge control agent is contained in
the toner particles so that the toner particles will be
frictionally charged to a predetermined polarity. A
negatively charging toner uses a negative charge
control agent such as a metal-cont~; n; n g complex salt
dye or a metal complex of oxycarboxylic acid (e.g.,
21 771 03
Japanese Laid-Open Patent Publication No. 67268/1991),
and a positively charging toner uses a positively
charging control agent such as an oil-soluble dye~for
example, Nigrosine or an amine-type control agent
(e.g., Japanese Laid-Open Patent Publication No.
106249/1981).
A magnetic toner has long been used as a toner for
the two-component magnetic developing agent. For
instance, the above-mentioned Japanese Laid-Open Patent
Publication No. 106249/1981 and Japanese Laid-Open
Patent Publication No. 162563/1984 disclose toners to
which a magnetic power is internally added, i.e.,
disclose toners containing a magnetic powder, and the
above-mentioned Japanese Laid-Open Patent Publication
No. 67268/1991 discloses a toner to which a magnetic
powder is externally added, i.e., discloses a toner to
which is added and mixed a silica powder and a magnetic
powder.
It has been known that the two-component magnetic
developing agent ~xh;hits satisfactory charging
property in its early stage of use upon m; ~; ng the
magnetic carrier and the toner together, but loses its
charging property due to the occurrence of a so-called
spent toner causing its life to be shortened.
The spent toner is a phenomenon in which the toner
component adheres like a film onto the surfaces of the
magnetic carrier. That is, the surfaces of the
magnetic carrier become close to those of the toner,
and the frictional series of the two become close to
each other, so that predetermined charging property is
no longer maintained. When the spent occurs,
therefore, the magnetic carrier must be discarded and
must be replaced by the new magnetic carrier.
SUMMARY OF THE INVENTION
The object of the present invention therefore is
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to provide a heat-fixing toner for a two-component
magnetic developing agent having excellent resistance
against being spent and featuring extended life of
toner and carrier.
Another object of the present invention is to
provide a heat-fixing toner for a two-component
magnetic developing agent without containing charge
control agent (CCA) that has a property to migrate onto
the carrier surfaces, the toner without scattering at
the time of developing and being capable of increasing
apparent developing sensitivity.
A further object of the present invention is to
provide a heat-fixing toner for a two-component
magnetic developing agent, which enables the image to
be efficiently transferred onto the paper from the
surface of the photosensitive material though it does
not contain the charge control agent having migrating
property.
According to the present invention, there is
provided a negatively charging toner for a two-componen
t magnetic developing agent obtained by dispersing
carbon black in a fixing resin medium, wherein:
said fixing resin medium is a copolymerized resin
or a resin composition having a free or neutralized
anionic polar group and has an acid value of from 4 to
30 by measuring said anionic polar group in the form of
a free acid; and
said carbon black has a pH of smaller than 7 and a
ratio (7-pH)/specific surface area (m2/g) of from 0.010
to 0.050, and is blended in an amount of from 4 to 15%
by weight per said resin fixing medium.
According to the present invention, furthermore,
there is provided a two-component magnetic developing
agent comprising the above-mentioned toner and a
magnetic carrier coated with a resin or a magnetic
21 77~ Q3
earrier obtained by dispersing a magnetie powder in a
resin.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a graph showing a curve of absorbancy at
wavelengths of from 200 to 700 nm of an extract
obtained by extracting with methanol a toner that
contains a chromium eomplex salt dye (2:1 type) as a
eharge eontrol agent;
Fig. 2 is a graph showing a eurve of absorbancy at
wavelengths of from 200 to 700 nm of an extract
obtained by extracting with methanol a toner that
eontains a metal salieylate eomplex as a eharge eontrol
agent;
Fig. 3 is a graph showing a eurve of absorbancy at
wavelengths of from 200 to 700 nm of an extract
obtained by extracting with methanol a carrier, which
is poorly charged due to the occurence of spent toner,
in a two-component magnetic developing agent containing
the toner used in the measurement of Fig. l;
Fig. 4 is a graph plotting relationships between
the m;x;ng time and the spent amount of when there are
used a mixture of a toner containing a positive charge
control agent and a magnetic carrier, and a mixture of
a toner without containing charge control agent and the
magnetic carrier;
Fig. 5 is a graph plotting relationships between
the m; X; ng time and the àmount of charge of when there
are used a mixture of a toner containing a negative
eharge control agent and-a magnetie earrier, and a
mixture of a toner without containing eharge control
agent and the magnetie earrier;
Fig. 6 is a graph illustrating relationships
between the spent amount of the earrier on which the
spent toner is adhered and the amount of the charge
eontrol agent in the spent toner;
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Fig. 7 is a graph illustrating relationships
between the m; X; ng time and the spent amount of when
each of the components in the toner and the magnetic
carrier are mixed together;
Fig. 8 is a diagram illustrating the mechanism of
poor charging due to the occurrence of spent toner in
the conventional two-component magnetic developing
agent;
Fig. 9 is a graph showing a curve of absorbancy at
wavelengths of from 200 to 700 nm of an extract
obtained by extracting with methanol a negatively
charging toner of the present invention;
Fig. 10 is a diagram of an apparatus for measuring
the resistivity of a carrier;
Fig. 11 is a diagram of a curve representing the
distribution of GPC molecular weights of a low
molecular polymer synthesized for the preparation of a
fixing resin medium according to Example l; and
Fig. 12 is a diagram of a curve representing the
distribution of GPC molecular weights of a fixing resin
medium used for the toner of the present invention
prepared according to Example 1.
DET~TTT~n DESCRIPTION OF THE INVENTION
The present inventors have forwarded the study in
an effort to prevent the occurrence of spent toner and
have found an interesting fact.
Fig. 1 is a graph showing a curve of absorbancy at
wavelengths of from 200 to 700 nm of an extract
obtained by extracting with methanol a toner that
contains a chromium complex salt dye (2:1 type) as a
charge control agent among toners for the conventional
two-component magnetic developing agent used for
developing positively charged image, the peaks lying
over a region of wavelengths of from 400 to 700 nm.
Fig. 2 is a graph showing a curve of absorbancy at
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wavelengths of from 200 to 700 nm of an extract
obtained by extracting with methanol a toner that
contains a metal salicylate complex as a charge control
agent, the peaks lying over a region of wavelengths of
from 280 to 350 nm.
From these results, the two extracts exhibit
characteristic absorption peaks due to the charge
control agents. This means that the charge control
agent is contained at a considerably high concentration
in the surfaces of the toner particles.
Fig. 3 is a graph showing a curve of absorbancy at
wavelengths of from 200 to 700 nm of an extract
obtained by extracting with methanol a carrier which is
poorly charged due to the occurrence of spent toner.
The carrier is contained in a two-component magnetic
developing agent containing the toner used in the
measurement of Fig. 1. In the curve, the peaks lying
over a region of wavelengths of from 400 to 700 nm.
The result of the measurement reveal an
astonishing fact that the charge control agent is
adhered and deposited at a high concentration even on
the carrier surfaces, and poor charging due to the
spent toner is not caused by a simple filming of the
toner resin on the carrier surfaces that was so far
considered but is caused by the migration of the charge
control agent onto the carrier surfaces.
This fact becomes even more obvious with reference
to Figs. 4 and 5. Figs. 4 and 5 are graphs plotting
relationships between the m; X; ng time and the spent
amount, and relationships between the m;X;ng time and
the amount of charge of when there are used a mixture
of a toner containing a positive or negative charge
control agent and a magnetic carrier, and a mixture of
a toner without containing charge control agent and the
magnetic carrier. From these results, the fact becomes
` - 2177103
obvious in that when the charge control agent is
contained, the spent amount increases with an increase
in the mi X; ng time, and the amount of charge decreases
to a large extent.
Fig. 6 is a graph illustrating relationships
between the spent amount of the carrier to which the
spent toner is adhered and the charge control agent in
the spent toner, wherein a dotted line is drawn by
plotting estimated values calculated from the toner
recipe. These results reveal the fact that the charge
control agent selectively migrates and adheres onto the
carrier surfaces in an early stage of occurrence of the
spent toner. In Fig. 6, the amount of the charge
control agent approaches the values estimated from the
toner composition with an increase in the spent amount
due to the fact that the mixture system is a closed
system where no toner is replenished. When the toner
is exchanged in the copying machine, it is estimated
that the difference further increases depending upon
whether the charge control agent is used or not used.
Fig. 7 illustrates relationships between the
m; x; ng time and the spent amount of when each of the
components in the toner and the magnetic carrier are
mixed together. These results tell the fact that among
the components of the toner, the charge control agent
migrates overwhelmingly onto the carrier surfaces,
giving rise to the occurrence of spent toner.
From the foregoing results, the conventional two-
component magnetic developing agent becomes poorly
charged due to the occurrence of spent toner as
explained in Fig. 8. That is, in an early stage of use
of the mixture, the carrier has been positively charged
and the toner has been negatively charged. As the
charge control agent selectively migrates onto the
carrier surface to form spent toner, however, the spent
2 1 77 ~ 03
layer is negatively charged and whereby a toner of a
reverse polarity (positively charged) is formed.
According to the present invention, there is used
no charge control agent having property to migrate onto
the toner particles, and, hence, no charge control
agent migrates onto the surfaces of the magnetic
carrier. As represented by a curve of absorbancy of
Fig. 9, therefore, in the extract of the negatively
charging toner of the present invention extracted with
methanol, the absorbancy is substantially zero over
wavelengths of from 400 to 700 nm. The toner of the
present invention is not, as a matter of course,
blended with a positive charge control agent such as
metal salicylate complex, and its extract with methanol
exhibits no peak of absorbancy over the wavelengths of
from 280 to 350 nm.
In this specification, the absorbancy which is
substantially zero stands for that no absorption peak
is quite detected in the above-mentioned wavelength
region from an extract obtained by extracting 0.1 g of
toner with 50 ml of methanol or the absorbancy at the
peak is not larger than 0.05 if it is detected.
Here, as shown in Fig. 5, the toner without
containing charge control agent is electrically charged
in an amount which is inevitably smaller than that of
the toner containing the charge control agent. To
overcome this inconvenience according to the present
invention, use is made of a copolymerized resin
composition having anionic polar group as a fixing
resin medium, and use is further made of carbon black
having a pH on the acidic side as a coloring agent.
Use of such a fixing resin medium and carbon black
enables the toner to be electrically charged in an
amount large enough for effecting the developing.
That is, the anionic polar group possessed by the
21 771 03
.
fixing resin medium gives a negatively charging
property to the toner a~d exists in the molecular
skeleton of the resin. Therefore, the anionic polar
group does not migrate onto the carrier surfaces and
does not become a cause of spent toner unlike the
charge control agent.
As described above, the fixing resin medium used
in the present invention has an acid value in
connection with the possession of an anionic polar
group. Here, however, the acid value must lie within a
range of from 4 to 30. When the acid value is larger
than 30, the amount of anionic groups increases whereby
the toner ~xh;hits increased hygroscopic property
making it difficult to frictionally charge the toner
maint~;n;ng stability. -When the acid value becomes
smaller than 4, on the other hand, the amount of
anionic groups is so small that it becomes difficult to
maintain the electric charge of the toner in an amount
large enough for the developing. The anionic polar
group may exist in a free form (in the form of a free
acid) or may exist in the form of a metal salt such as
sodium salt or the like salt, i.e., may exist in a
neutralized form. The acid value is measured in the
form of a free acid. That is, in the present
invention, if the anionic polar groups at least partly
exist in the neutralized form, the acid value stands
for a value that is fou~d by hydrolyzing the groups to
form free acids.
In the present invention, furthermore, carbon
black which is a coloring agent must have a pH which
lies on the acidic side (i.e., smaller than 7) and a
ratio (7-pH)/specific surface area (m2/g) that lies
within a range of from 0.010 to 0.050.
In general, the carbon black has a pH of about 8
which is on the neutral to alkaline side. In order to
2177103
control the electrically conducting property,
furthermore, there has been used the carbon black which
is treated with an acid so that it has a pH of smaller
than 7. The present invention selectively uses the
carbon black having a pH of smaller than 7 which,
however, does not mean that the invention uses the
carbon black of which the electrically conducting
property is controlled.
The present inventors have confirmed through their
study that the carbon black is negatively charged when
the carbon black and the magnetic carrier are mixed
together and are stirred. That is, according to the
present invention which uses the acid-treated carbon
black having a pH of smaller than 7, the fixing resin
medium having the anionic polar group exhibits
reinforced negatively charging property, and the drop
of the charging property is effectively prevented
despite the negative charge control agent is not
blended.
In the present invention, the ratio (7-pH)
/specific surface area is an index representing the
degree of treatment with acid, i.e., representing the
density of acidic functional groups existing on the
surfaces of the carbon black. When this value is
smaller than the aforementioned range, the negatively
charging property is not reinforced to a sufficient
degree and the charging property inevitably drops.
When this value is larger than the aforementioned
range, on the other hand, the toner exhibits increased
hygroscopic property and it becomes difficult to stably
maintain the amount of charge by friction.
The pH of carbon black is measured in the
following way. Five grams of a sample is put into 100
ml of ion-exchanged water and is boiled for 5 minutes.
After left to cool, water is replenished by an amount
2177103
that has vaporized and is filtered using a paper.
Then, the filtrate is measured by using a commercially
available glass-electrode pH measuring instrument.
(Resin Medium)
The fixing resin medium used in the present
invention is a copolymerized resin having an anionic
polar group. The anionic polar group may be any polar
group such as of carboxylic acid, sulfonic acid or
phosphonic acid. Among them, however, the anionic
polar group of carboxylic acid is particularly
preferred. The copolymerized resin having such an
anionic polar group is obtained by incorporating a
monomer having a polar group into a resin relying upon
random copolymerization, block-copolymerization or
graft-copolymerization. Preferred examples of the
monomer are as described below. In the following
description, a lower alkyl group stands for the one
having not more than 5 carbon atoms, and a higher alkyl
group stands for the one having not less than 12 carbon
atoms.
Examples of those of the carboxylic acid type
include ethylenically unsaturated carboxylic acid, such
as acrylic acid, methacrylic acid, crotonic acid,
maleic acid, maleic anhydride, fumaric acid, lower
alkyl half ester of maleic acid, lower alkyl half ester
of fumaric acid and the like.
Examples of those of the sulfonic acid type
include styrenesulfonic acid, 2-acrylamide-2-methylprop
anesulfonic acid and the like.
Examples those of the phosphonic acid type include
2-acid phosphoxypropyl methacrylate, 2-acid
phosphoxyethyl methacrylate, 3-chloro-2-acid
phosphoxypropyl methacrylate and the like.
These anionic polar group-contA; n; ng monomer units
may be incorporated in the form of free acids or in the
2177103
form neutralized with an alkali metal such as sodium or
potassium, an alkaline earth metal such as calcium or
magnesium, or zinc.
Another monomer which is a chief component of the
copolymerized resin composition exhibits fixing
property and charging property required for the toner
when it is polymerized, and may be one or two or more
kinds of monomers having an ethylenically unsaturated
bond.
Preferred examples of the monomer include acrylic
ester type monomer, aromatic monovinyl monomer, vinyl
ester type monomer, vinyl ether type monomer, diolefin
type monomer and monoolefin type monomer. Described
below are concrete examples.
The acrylic ester type monomer is represented by,
for example, the following general formula (1),
CH2 = C(Rl) - COOR2 (1)
wherein R1 is a hydrogen atom or a lower alkyl
group, and R2 is a hydrocarbon group having up to
11 carbon atoms, a hydroxyalkyl group or a higher
alkyl group.
Preferred examples include methyl acrylate, ethyl
acrylate, butyl acrylate, 2-ethylhexyl acrylate,
cyclohexyl acrylate, phenyl acrylate, methyl
methacrylate, hexyl methacrylate, 2-ethylhexyl
methacrylate, ~-hydroxyethyl acrylate, ~-hydroxypropyl
acrylate, ~-hydroxybutyl acrylate, ~-hydroxyethyl
methacrylate, lauryl acrylate, tridecyl acrylate,
stearyl acrylate, docosyl acrylate, dicyclohexylmethyl
acrylate, dicyclohexylpropyl acrylate, cyclododecyl
acrylate, cycloundecanemethyl acrylate, lauryl
methacrylate, tridecyl methacrylate, stearyl
methacrylate, docosyl methacrylate, dicyclohexylmethyl
methacrylate, dicyclohexylpropyl methacrylate,
cyclododecyl methacrylatè, cycloundecanemethyl
- 2177103
methaerylate, etc.
The aromatic monovinyl monomer is represented by
the following general formula (2),
CH2 = C(R3j - ~ - R4 (2)
wherein R3 is a hydrogen atom, a lower alkyl
group, a halogen atom or a higher alkyl group, R4
is a hydrogen atom, a lower alkyl group, a higher
alkyl group, a halogen atom, an alkoxy group, an
amino group or a nitro group, ~ is a phenylene
group whieh may have, as a substituent, a lower
- alkyl group, a higher alkyl group, a halogen atom,
an alkoxy group, an amino group or a nitro group.
Preferred examples include styrene, a-
methylstyrene, vinyltoluene, a -chlorostyrene, o-, m-
or p-chlorostyrene, p-ethylstyrene, m- or p-
laurylstyrene, m- or p-stearylstyrene, a -methyl-3-
stearylstyrene, m- or p-stearoxystyrene, 4-vinylstearyl
benzoate and 4-stearoylaminostyrene.
The other monomer is represented by the following
general formula (3), (4), (5) or (6),
CH2 = CH - OOCR5 (3)
wherein R5 is a hydrogen atom, a lower alkyl group
or a higher alkyl group,
like sueh vinyl esters as vinyl formate, vinyl acetate,
vinyl propionate, vinyl laurate, vinyl trideeanoate,
vinyl stearate, vinyl doeosanoate, vinyl
triaeontanoate, vinyl pentyleyelohexanoate, vinyl
dicyclohexyl acetate, ete.,
CH2 = CH - O - R6 (4)
wherein R6 is a monovalent hydroearbon group
having up to 11 earbon atoms or a higher alkyl
group,
like sueh vinyl ethers as methyl vinyl ether, ethyl
vinyl ether, vinyl-n-butyl ether, vinylphenyl ether,
vinyleyelohexyl ether, vinyllauryl ether, vinylstearyl
2177103
14
ether, vinyldocosyl ether, vinylcyclododecyl ether,
etc.,
CH2 = C(R7) - C(R8) = CH - R9 (53
wherein R7, R8 and R9 are each a hydrogen atom, a
lower alkyl group, a higher alkyl group or a
halogen atom,
like such diolefins as butadiene, isoprene,
chloroprene, 1,3-hexadecadiene, 1,3-docosadiene, 2-
methyl-1,3-docosadiene, etc.,
CH2 = C(R10) - R11 (6)
wherein R10 and R11 are each a hydrogen atom, a
lower alkyl group or a higher alkyl group,
like such monoolefins as ethylene, propylene,
isobutylene, butene-l, pentene-l, 4-methylpentene-1, 1-
tetradecene, l-eicosene, etc.
In the copolymerized resin having anionic polar
groups used as a fixing resin medium of the present
invention, the anionic polar groups exist in such an
amount that the acid value is from 4 to 30 and,
particularly, from 5 to 15. When the anionic polar
groups of the copolymerized resin are partly or wholly
neutralized, the anionic polar groups inclusive of the
neutralized polar groups are contained in an amount
that corresponds to the above-mentioned acid value. As
described earlier, when the acid value of the
copolymerized resin is smaller than the above-mentioned
range, charging property`of the toner becomes
unsatisfactory. When the acid value of the
copolymerized resin is greater than the above-mentioned
range, on the other hand, the toner becomes susceptible
to humidity, and charging property of the toner becomes
insufficient, too.
A preferred copolymerized resin contains a monomer
having anionic polar groups and one or two or more
kinds of acrylic monomers of the formula (1) and,
21 771 03
further, contains monomers of the formulas (2) to (6)
and, particularly, the $tyrene monomer of the formula
(2).
In the present invention, the copolymerized resin
containing anionic polar group can be used as a fixing
resin medium in a single kind as described above and
can be further used as a composition containing two or
more kinds of anionic polar group-containing
copolymerized resins or as a composition containing an
anionic polar group-cont~;n;ng copolymerized resin and
a copolymerized resin without having anionic polar
group. Even in this case, the content of the anionic
polar groups in the whole resin composition should be
such that the acid value lies within the range
specified above for the copolymerized resin.
In the present invention, it is preferred that the
fixing resin medium has a weight average molecular
weight over a range of from 70,000 to 200,000 to
maintain a property of being pulverized and a
granulating property. In particular, it is desired
that the fixing resin medium contains low molecular
components having peak molecular weights over a range
of from 4,000 to 30,000 and high molecular components
having a molecular weight distribution in a high
molecular weight region. The low molecular components
help increase toner transfer efficiency and heat-fixing
property, and high molecular components help improve
resistance against the offset.
When the developing is carried out for extended
periods of time using the toner obtained by using the
above-mentioned fixing resin medium containing low
molecular components and high molecular components, the
low molecular components in the resin medium tend to
selectively adhere onto the carrier surfaces to form a
spent toner. That is, even when the charge control
2177103
16
agent is not used, it was found through experiment that
the occurrence of spent toner is not perfectly
prevented; i.e., the spent toner is formed by the low
molecular components as the developing is executed for
extended periods of time though the amount of the spent
toner is small. When the anionic polar groups exist in
the low molecular components adhered onto the carrier
surfaces, however, the carrier itself tends to be
negatively charged giving rise to the formation of a
toner charged to an opposite polarity. When the
developing is repeated for extended periods of time,
therefore, the scattering of toner and fogging become
no longer negligible due to the toner charged to the
opposite polarity.
In order to effectively prevent the occurrence of
the toner charged to an opposite polarity due to the
spent toner of low molecular components according to
the present invention, it is desired that the acid
value of the low molecular components in the fixing
resin medium is set to bè lower than the acid value of
the whole resin medium, i.e., set to lie within a range
of from 3 to 15. When the acid value of the low
molecular components is larger than the above-mentioned
range, the amount of the anionic polar groups in the
spent toner becomes so large that it becomes difficult
to effectively prevent the occurrence of the toner
charged to the opposite polarity. When the acid value
is smaller than the above-mentioned range, on the other
hand, difference in the acid value from that of the
high molecular components becomes so large that
compatibility decreases between the high molecular
components and the low molecular components, giving
rise to the occurrence of such inconvenience as
nonuniformity in the charge.
From the standpoint of compatibility between the
- 21 771 03
high molecular components and the low molecular
components and the transfer efficiency, furthermore, it
is desired that the acid value of the low molecular
components is within a range of from 10 to 95% with
respect to the acid value of the whole fixing resin
medium. It is further desired that the low molecular
components are contained in an amount of from 40 to 75%
by weight per the fixing resin medium.
The fixing resin medium can be easily produced by
using monomer components mentioned earlier and by
radical polymerizing with a widely known polymerization
initiator. In this case, the fixing resin medium
containing low molecular components and high molecular
components is obtained by preparing, in advance, the
low molecular components having a predetermined low
acid value and blending them with high molecular
components having a high acid value that are separately
prepared, or by preparing the high molecular components
by effecting the radical polymerization in the presence
of the low molecular components. From the standpoint
of compatibility between the high molecular components
and the low molecular components, in general, it is
desired that the high molecular components are prepared
in the presence of low molecular components.
A preparation method will now be described.
Monomers for low molecular components and the
polymerization initiator are mixed together and stirred
in an organic solvent such as toluene or xylene capable
of dissolving both the monomer components and the resin
that is to be formed. The mixture solution is
introduced into a reaction oven and is polymerized with
sufficient stirring. After the polymerization, the
solution is deaerated and is dried to obtain a polymer
that serves as a low molecular component. Here, the
time and temperature of polymerization are usually from
2177lO3
18
60 to 250C and from about 3 to about 10 hours, though
they may vary depending upon the kind and amount of the
polymerization initiator.
Next, monomers for high molecular components, the
polymer for low molecular component obtained above and
the polymerization initiator are mixed together and
stirred in a solvent capable of dissolving both the
monomer components and the resin. The mixture solution
is introduced into an oven and is polymerized with
sufficient stirring. After the polymerization~ the
solution is deaerated and is dried to obtain a desired
fixing resin medium contàining low molecular components
and high molecular components. In this case, the
temperature and time of polymerization are set
depending upon the kind and amount of the
polymerization initiator so that there is obtained a
polymer having a molecular weight in a desired range.
Usually, however, the temperature and time of
polymerization is from 60 to 200C and from about 5 to
about 24 hours.
The acid value can be easily adjusted by adjusting
the amount of feeding the anionic polar group-
containing monomers.
In order to improve resistance against the offset,
furthermore, a parting agent such as wax is usually
blended in the toner. However, the wax that is blended
as a parting agent has an SP value (solubility
parameter) greatly different from that of the fixing
resin medium and cannot be uniformly dispersed in the
medium causing the amount of wax to vary depending upon
the individual toner particles or causing the wax to be
distributed in deviated amounts on the surfaces of the
toner particles. That is, when the developing is
effected using such a toner, the wax tends to adhere as
spent on the surfaces of the carrier particles. When
- 2177!03
19
the developing agent of a mixture of the toner
particles and the carrier particles is used for
extended periods of time, therefore, charging property
of the carrier particles drops due to the spent
arousing a problem from the standpoint of durability.
When the toner is blended with such a parting agent
according to the present invention, it is desired that
the fixing resin medium contains a polymer component
that has a higher alkyl group with not less than 12
carbon atoms on a side chain thereof. Use of the
polymer component having such a higher alkyl group
makes it possible to effectively solve the above-
mentioned problem that stems from nonuniform dispersion
of the parting agent. Though the reason has not yet
been clarified, the present inventors consider it as
described below.
A polymer having a higher alkyl group on a side
chain thereof has an SP value close to that of the wax,
and is, hence, compatible with the wax. It is
therefore considered that the fixing resin medium
containing such a polymer permits the parting agent to
be uniformly dispersed therein.
The polymer having a higher alkyl group may be the
aforementioned polymer having an anionic polar group
and having a higher alk~l group on a side chain
thereof. Or, the polymer having an anionic polar group
may be used as a separate polymer. Generally, the
former polymer is preferably used. The fixing resin
medium is prepared by using, for example, a monomer for
introducing anionic groups, a monomer for introducing
higher alkyl groups and, as required, other monomers,
and polymerizing these monomers based upon the block-
polymerization, random polymerization or graft-
polymerization. The monomer for introducing higher
alkyl groups will be the`one having a higher alkyl
`- 21 771 03
group selected from the aforementioned monomers of the
formulas (1) to (6).
Preferred examples of the fixing resin medium
include the following copolymers, i.e., (meth)acrylic
acid-stearyl (meth)acrylate copolymer, styrene-stearyl
(meth)acrylate-(meth)acrylic acid copolymer,
(meth)acrylic acid ester-stearyl (meth)acrylate-
(meth)acrylic acid copolymer, styrene-(meth)acrylic
acid ester-stearyl (meth)acrylate-(meth)acrylic acid
copolymer, styrene-stearyl (meth)acrylate-maleic acid
copolymer, maleic acid-stearyl(meth)acrylate copolymer,
styrene-tridecyl (meth)acrylate-(meth)acrylic acid
copolymer, styrene-lauryl (meth)acrylate-(meth)acrylic
acid copolymer.
Even in these fixing resin media composed of the
above-mentioned copolymers, the acid values should lie
within the aforementioned range. It is desired that
the higher alkyl group on the side chain of the polymer
exists in an amount of from 0.1 to 20 parts by weight
and, particularly, from 0.5 to 10 parts by weight per
100 parts by weight of the fixing resin medium on the
basis of the monomer having the higher alkyl group.
When the amount of the higher alkyl group is smaller
than the above-mentioned range, compatibility drops
between the parting agent and the fixing resin medium,
and durability is not improved to a satisfactory
degree. When the amount of the higher alkyl group is
larger than the above-mentioned range, on the other
hand, the fixing resin medium ~xh;hits decreased Tg and
the toner loses preservation stability.
(Carbon Black)
In the present invention, any carbon black can be
dispersed in the fixing resin medium provided it has a
pH of smaller than 7 and, preferably, from 2 to 5 and
has a ratio (7-pH)/specific area (m2/g) of from 0.010
2t77~03
21
to 0.050 and, particularly, from 0.015 to 0.040.
Generally, however, it is desired to use furnace black
treated with acid so as to have a pH value satisfying
the above-mentioned conditions.
The treatment with acid can be carried out by
using an inorganic acid such as hydrochloric acid,
sulfuric acid, nitric acid, or phosphoric acid or by
using an organic acid such as acetic acid, citric acid,
propionic acid, benzoic acid, salicylic acid or
toluenesulfonic acid. Due to this treatment, an acidic
group such as carboxylic group is introduced into the
surfaces of the carbon black to reinforce the
negatively charging property of the toner. As will be
obvious from the pH conditions mentioned above, the
acid is used in a very ~m~l 1 amount in the treatment
and does not adversely affect electric properties of
the toner.
It is desired that the carbon black has a specific
surface area of usually not smaller than 50 m2/g and,
particularly, from 100 to 300 m2/g from the standpoint
of dispersion property in the resin.
The carbon black is blended in an amount of from 4
to 15% by weight and, particularly, from 6 to 12% by
weight per the fixing resin medium. When the blending
amount is smaller than the above-mentioned range,
negatively charging property of the toner is not
satisfactory causing fogging to occur. When the carbon
black is used in an amount larger than the above range,
on the other hand, the toner e~h; hits decreased fixing
property.
(Other Blending Agents)
The toner for a two-component magnetic developing
agent of the present invention may be blended with
various additives in addition to the above-mentioned
carbon black like the conventional toners but without
_ ~177103
being blended with the charge control agent. Such
additives may include parting agent, body, fixing
improving agent, magnetic powder, etc.
Parting Agent;
According to the present invention which uses, as
a fixing resin medium, a resin composition containing
the above-mentioned low molecular components and high
molecular components, it is allowed to increase
resistance against the offset during the heat-fixing.
By being blended with a parting agent, furthermore,
resistance against the offset can be further improved.
Such a parting agent may be natural or synthetic
waxes. In general, it is desired to use a polyolefin
wax such as polypropylene wax, polyethylene wax,
propylene-ethylene random copolymer wax and,
particularly, polypropylene wax. Among them, it is
desired to use the one having an average molecular
weight of from 2,000 to 16,000 and, particularly, from
3,000 to 6,000.
Such a parting agent is used in an amount of from
0.01 to 10 parts by weight and, particularly, from 0.1
to 6 parts by weight per 100 parts by weight of the
fixing resin medium. When the amount is smaller than
the above-mentioned range, resistance against the
offset is not satisfactory. When the amount is larger
than the above-mentioned range, on the other hand,
charging property of the toner decreases and the toner
scatters and develops fogging due to poor electric
charge.
To improve resistance against the offset by using
the parting agent, it is desired to use a fixing resin
medium containing a polymer that has a higher alkyl
group on a side chain thereof as mentioned earlier.
The above-mentioned wax can be blended in the
toner by being graft-fixed to a suitable polymer such
21 77103
as the polymer eonstituting the fixing resin medium.
The wax that is blended by the graft-fixing is very
advantageous from the standpoint of uniformly
dispersing the wax in the fixing resin medium.
The wax can be easily graft-fixed relying upon the
radical polymerization in the presence of wax at the
time of synthesizing the copolymerized resin having
anionie polar group based on the radieal
polymerization. That is, the wax is graft-fixed to
part of the eopolymer having anionie polar group; i.e.,
the wax is graft-fixed simultaneously with the
preparation of the eopolymerized resin for fixing.
Moreover, a resin or a eopolymerized resin containing a
polymer to whieh the wax is graft-fixed is obtained by
subjeeting a monomer without anionie polar group, for
example, by subjeeting at least one of the monomers
(preferably, having a higher alkyl group) of the
formulas (2) to (6), to the radieal polymerization in
the presenee of wax. This resin or eopolymerized resin
may be blended with a eopolymerized resin eontaining an
anionie polar group.
Extender Pigment;
The extender pigment is blended to adjust physieal
properties sueh as bulk density, ete., and its examples
include barite powder, barium earbonate, clay, silica,
white carbon, tale, and alumina white. Sueh a pigment
is used in an amount of from 2 to 20 parts by weight
and, partieularly, from 5 to 15 parts by weight per 100
parts by weight of the fixing resin medium.
Magnetie Powder;
Aeeording to the present invention, the fixing
resin medium may be blended with a magnetie powder in
addition to the above-mentioned blending agents. By
being blended with sueh a magnetie powder, the toner
partieles in the magnetie brush during the developing
`- 21 771 03
24
is held on the carrier by the coulomb force as well as
the magnetic attractive force. Accordingly, the toner
is more reliably prevented from scattering, which is
very desirable from the standpoint of preventing the
copying machine from being cont~m;nated with toner and
preventing the copy from developing fogging. Such
advantages are desired as the copying speed increases.
By being blended with the magnetic powder, furthermore,
the amount of charge can be decreased per a toner
particle. Therefore, developing sensitivity can be
- increased and image of a high density can be obtained.
Examples of the magnetic powder include those
magnetic powders that have heretofore been used for the
magnetic toners such as tri-iron tetroxide (Fe3O4),
iron sesquioxide ( r -Fe2O3), zinc iron oxide (ZnFe2O4),
yttrium iron oxide (Y3Fe5O12), cadmium iron oxide
(CdFe2O4), gadolinium iron oxide (Gd3FesO12), copper
iron oxide (CuFe2O4), lead iron oxide (PbFe12O19),
nickel iron oxide (NiFe2O4), neodymium iron oxide
(NdFeO3), barium iron oxide (BaFe12O19), magnesium iron
oxide (MgFe2O4), manganese iron oxide (MnFe2O4),
lanthanum iron oxide (LaFeO3), iron powder (Fe), cobalt
powder (Co), nickel powder (Ni), etc. Particularly
preferred magnetic powder is that of a fine particulate
tri-iron tetroxide (magnetite).
The preferred magnetite is of a regular octahedral
shape having particle sizes of from 0.05 to 1.0 ~m.
The magnetite particles may be treated for their
surfaces with a silane coupling agent or a titanium
coupling agent.
The magnetic powder may be blended in an amount as
small as from 0.1 to 5 parts by weight and,
particularly, from 0.5 to 3.0 parts by weight per 100
parts by weight of the resin medium. In the magnetic
toner used for the conventional one-component magnetic
2177103
developing agent, the magnetic powder is used in an
amount larger than 10 parts by weight per 100 parts by
weight of the resin medium. In the present invention,
however, the magnetic powder is used in an amount
considerably smaller than the above-mentioned amount.
The internal addition of the magnetic powder even in
such a small amount makes it possible to form an image
of a high density yet preventing the toner from
scattering.
Fixing Improvent Agent;
In the present invention, it is desired to blend a
polyethylene having a number average molecular weight
of from 1000 to 7000 as a fixing improving agent. That
is, the anionic polar group contained in the fixing
resin medium gives negatively charging property to the
toner but tends to increase the heat-melting
temperature of the resin medium due to association
among the polar groups. Such a rise in the heat-
melting temperature is not desirable from the
standpoint of fixing. According to the present
invention, the polyethylene having the above-mentioned
number average molecular weight that is blended makes
it possible to prevent a drop in the fixing property
caused by the presence of anionic polar groups but
rather helps increase the fixing property. Though the
reason is not yet obvious why the polyethylene that is
blended helps improve the fixing property, the present
inventors consider it in the following way.
That is, the polyethylene having a number average
molecular weight over the above-mentioned range has a
softening point lower than that of the fixing resin
medium, and loses the viscosity abruptly near its
softening point and melts. When the toner is heat-
fixed, therefore, the polyethylene melts, first, and
infiltrates into the paper. As a result, the fixing
2177103
resin medium loses wettability for the paper and
exhibits improved permeability. The fixing resin
medium that is melted does not diffuse but infiltrates
into the paper enabling the fixing property to be
improved.
It is desired that the polyethylene is used in an
amount of from 0.5 to 5 parts by weight per 100 parts
by weight of the fixing resin medium from the
standpoint of improving fixing property of the toner
without impairing other properties.
(Toner)
The toner of the present invention can be prepared
by a widely known method such as pulverization-
classification method, mèlt-granulation method, spray-
granulation method or polymerization method.Generally, however, the toner is prepared by the
pulverization-classification method. That is, the
above-mentioned fixing resin medium and various
blending agents are pre-mixed together in a mixer such
as Henschel's mixer and are kneaded using a kneader
such as biaxial extruder. The kneaded composition is
cooled, pulverized and is classified to obtain a toner.
It is desired that the particle diameter of the
toner is generally from 5 to 15 ym and, particularly,
from 7 to 12 ym in terms of a volume-based average
particle diameter (median diameter using the Coulter
counter).
As required, a fluidity improving agent such as
silica obtained by the hydrophobic vapor-phase method
is externally adhered onto the surfaces of the toner
particles to improve fluidity of the toner. The
fluidity improving agent is a very fine powder having a
primary particle size of usually as small as from 0.005
to 0.050 ~m, and is externally added in an amount of
from 0.1 to 2.0% by weight with respect to the whole
: 2177103
weight of the toner (total amount of the toner
particles and the externally added agents).
According to the preferred embodiment of the
present invention, furthermore, spacer particles having
a diameter of from 0.05 to 1.0 ~m and, particularly,
from 0.07 to 0~5 ~m larger than the particle diameter
of the fluidity improving agent are externally added to
the toner particles together with the fluidity
improving agent. With such spacer particles being
externally added, bonding is weakened between the toner
image and the latent image on the surface of the
photosensitive member, enabling the toner image to be
easily peeled and the transfer efficiency to be
improved in the step of transferring the toner image.
As the spacer particles, use is made of organic or
inorganic inert particles of a definite shape having
the aforesaid particle diameter. When the particle
diameter is larger than the above-mentioned range, the
bonding force becomes weak between the toner image and
the latent image on the surface of the photosensitive
material, and it becomes difficult to form a favorable
image. When the particle diameter is smaller than the
above-mentioned range, on the other hand, a
sufficiently large gap is not formed between the toner
image and the latent image (photosensitive material),
whereby the bonding force is not weakened between the
two and the transfer efficiency is not improved to a
satisfactory degree.
Concrete examples of the inert particles having a
definite shape may include silica, alumina, titanium
oxide, magnesium carbonate, acrylic resin powder,
styrene resin powder and magnetic powder. They should
be externally added in an amount of not larger than 10%
by weight, preferably, from 0.1 to 10% by weight and,
most preferably, from 0.1 to S% by weight with respect
2177103
28
to the whole weight of the toner (total amount of the
toner particles and externally added materials). When
they are used in excess amounts, the density of the
image decreases. When a magnetic powder is used as the
spacer particles, it is desired that the total amount
of the magnetic powder inclusive of the magnetic powder
that has been internally added to the toner particles
is not larger than 10% by weight with respect to the
fixing resin medium. When the total amount becomes too
large, the density of the image decreases, too.
- In the present invention, furthermore, it is
desired to use, as the above-mentioned spacer
particles, first spacer particles having a resistivity
of from 10 to 105 Q-cm and, particularly from 103 to
105 Q-cm and second spacer particles having a
resistivity of from 108 to 1013 Q-cm and, particularly,
from 109 to 1012 Q-cm in combination. Use of two kinds
of spacer particles having different resistivities
makes it possible to enhance the transfer efficiency of
the toner image from the photosensitive material onto
the transfer paper as well as to divide the resistance
on the surfaces of the toner particles into two. From
the viewpoint of exchange of electric charge of the
toner, therefore, the function is divided for
generating the electric charge and for leaking the
electric charge. As a result, the toner maintains
desired amount of electric charge efficiently and more
stably, so that image is formed maintaining stable
density.
The resistivity can be easily adjusted by treating
the surfaces to be electrically conducting, i.e.,
doping the surfaces with, for example, tin. That is,
the spacer particles that are usually used have a
relatively large resistivity like the second spacer
particles and are treated to become electrically
2177103
.
conducting and to exhibit a decreased resistivity, and
are used as the first spacer particles. In the present
invention, in particular, titanium oxide or magnesium
oxide of which the surfaces are doped with tin is
favorably used as the first spacer particles, and
titanium oxide or magnesium oxide which is not doped
with tin is favorably used as the second spacer
particles.
The first spacer particles and the second spacer
particles are used at a weight ratio of from 1:7 to 7:1
and, particularly, from 1:4 to 4:1, and in a total
amount as described earlier.
The resistivity of the spacer particles can be
measured by using, for example, a resistivity measuring
device 4 shown in Fig. 10.
That is, 8 g of a sample of spacer particles (203)
is introduced into a vinyl chloride tube (41) having an
inner diameter (Hl) of 1 inch and is sandwiched by
electrodes (421) made of a steel. Teflon plates (43)
having a thickness of 2 mm are arranged on both outer
sides of the electrodes (421), and a pressure Pr of 200
kg/cm2 is applied from one side of the Teflon plates
(43) by using a hydraulic pressing machine, in order to
measure a resistance r (Q) at 500 V using an ultra-
insulation resistance tester (42) (Model SM-5
manufactured by Toa Denpa ~ogyo Co.). Overall length
(H2) (cm) of the resistor is measured, the thickness of
the pressurized sample is calculated relying upon a
difference from the overall length (11.35 cm) of when
no sample is charged, and the resistivity (Q cm) is
calculated from the following formula (7),
R = [(2.54/2)2-~/(H2 - 11.35)] x r (7)
In the present invention, furthermore, it is
desired that the surfaces of the toner particles onto
which the spacer particies will be adhered or the
2177103
surfaces of the spacer particles are treated with a
metal stearate or amide, i.e., it is desired that the
metal stearate is adhered onto the surfaces of either
of these particles. In this case, parting property is
not adversely affected between the toner particles and
the surface of the photosensitive material and,
besides, the resistance of the toner suitably
decreases, which is advantageous for forming image
maintaining a high density. In this case, furthermore,
the melting temperature of the toner decreases giving
another advantage in that infiltration of the toner
into the transfer paper is promoted during the heat-
fixing by using a heat roll, and fixing property of the
transferred toner image is enhanced. Besides, since
the melting temperature of the metal stearate is lower
than the melting temperature of the fixing resin
medium, the surface of the image ~hihits improved
smoothness when the transferred toner image is heat-
fixed, making it possible to obtain image with luster.
Examples of the metal stearate or amide include
zinc stearate, magnesium stearate, aluminum stearate,
calcium stearate, chromium stearate, mercury stearate,
cerium stearate, ferric stearate, sodium stearate, lead
stearate, barium stearate and stearic acid amide, which
may be used in a single kind or in a combination of two
or more kinds. Generally, it is desired to use zinc
stearate or magnesium stearate. Most desirably, zinc
stearate is used in a single kind.
It is desired that these metal stearates are used
in an amount of from 0.001 to 3% by weight, preferably,
from 0.003 to 1% by weight and, most preferably, from
0.005 to 0.2% by weight per the whole weight of the
toner. Moreover, the metal stearates may be adhered on
the surfaces of the toner particles or on the surfaces
of the spacer particles.
- 2177103
(Magnetic Carrier)
Any widely known magnetic carrier can be used in
combination with the above-mentioned toner. Desirably,
there can be used magnetite (M = Fe) or ferrite (M is
other than Fe) represented by the following formula
(7),
MOFe2O3 (7)
wherein M is at least one metal selected from the
group consisting of Cu, Zn, Fe, Ba, Ni, Mg, Mn, Al
and Co.
Particularly, there can be used sintered ferrite
particles and, especially, spherical particles of soft
ferrite such as copper-zinc-magnesium ferrite in which
M includes at least one and, preferably, two or more of
Cu, Zn, Mg, Mn and Ni.
The magnetic carrier particles permit electric
resistance to change little depending upon the
environment or aging, and exhibit stable charging
property. Besides, the magnetic brush has a soft ear
and does develop white streaks such as sweeping traces
of magnetic brush on the formed image.
It is desired that the magnetic carrier has an
average particle diameter of generally from 30 to 200
~m and, particularly, from 50 to 150 ~m, a saturation
magnetization of from 30 to 80 emu/g and, particularly,
from 45 to 70 emu/g, and a volume resistivity of from
105 to 109 Q-cm and, particularly from 106 to 108 Q-cm.
Moreover, the magnetic carrier particles serving
as cores may be coated with a variety of thermoplastic
resins and thermosetting resins. Examples of the
thermoplastic resin include thermoplastic acrylic
resin, thermoplastic styrene-acrylic resin, polyester
resin, polyamide resin and olefin-type copolymer resin,
and examples of the thermosetting resin include
modified or unmodified silicone resin, thermosetting
- 21 771 03
acrylic resin, thermosetting styrene-acrylic resin,
phenol resin, urethane resin, thermosetting polyester
resin, epoxy resin, amino resin, fluorine-containing
resin and melamine resin. Such resin coatings make it
possible to more effectively avoid the occurrence of
spent toner. Generally speaking, it is desired that
the amount of resin coating is from 0.001 to 2.5 parts
by weight and, particularly, from 0.005 to 2.0 parts by
weight per 100 parts by weight of the core particles.
In the present invention, furthermore, it is
desired that a cationic polar group is introduced into
the coating resin. That is, provision of the resin
coating layer having a càtionic polar group helps
increase the positively charging property of the
carrier whereby the negatively charging property of the
toner is further enhanced. Such a cationic polar group
can be represented by a basic nitrogen-containing group
such as primary, secondary or tertiary amino group,
quaternary ammonium group, amide group, imino group,
imide group, hydrazino group, guanidino group or
amidino group. Among them, amino group and quaternary
ammonium group are particularly preferred.
To introduce the cationic polar group, the resin
should be produced by using, for example, a monomer
component having the cationic group. The cationic
polar group can be also introduced by treating the
surfaces of the resin using a silane coupling agent
- having a cationic group. Examples of the silane
coupling agent may include N-~ (aminoethyl) r -
aminopropyltrimethoxysilane, N-~ (aminoethyl) r -
aminopropylmethyldimethoxysilane, r-
aminopropyltriethoxysilane, N-phenyl- r-
aminopropyltrimethoxysilane, etc.
It is further possible to introduce the cationic
polar group into the resin by synthesizing the coating
2177103
resin relying upon the polymerization using a
polymerization initiator having a cationic polar group
such as amidine-type azobis compound.
It is desired that the cationic polar group is
introduced usually in an amount of from 0.1 to 2000
millimols and, particularly, from 0.5 to 1500 millimols
per 100 g of the resin.
As desired, furthermore, the resin coating layer
may be blended with a variety of known additives such
as silica, alumina, carbon black, fatty acid metal
salt, silane coupling agent, silicone oil, etc., as a
matter of course.
The carrier particles serving as cores can be
coated with a resin by a widely known method. For
instance, the above-mentioned coating resin is
dissolved in a suitable solvent. By using this resin
solution, the resin is coated by immersion method,
spray method, fluidized bed method, moving bed method
or rolling bed method. In coating the thermosetting
resin, furthermore, the resin may be cured by heating
or the like means after the resin is coated by using a
solution of uncured resin or oligomer.
According to the present invention, furthermore,
it is allowable to use a binder-type carrier obtained
by dispersing a magnetic powder in a binder resin.
As such a magnetic powder, there can be preferably
used the aforementioned magnetic powder and,
particularly, the magnetite having a particle diameter
of not larger than 2.0 ~m and, particularly, from 0.05
to 1.0 ~m. The magnetic powder may ~e used in an
amount of from 150 to 900 parts by weight and,
particularly, from 250 to 600 parts by weight per 100
parts by weight of the binder resin.
Examples of the binder resin include thermoplastic
resin, thermosetting resin which is uncured or in the
2177103
34
form of an initial condensate, such as aromatie vinyl
resin like polystyrene, as well as aerylie resin,
polyvinyl aeetal resin, polyester resin, epoxy resin,
phenol resin, petroleum resin and polyolefin resin.
Among them, styrene resin, acrylie resin and styrene-
aerylie eopolymer resin are preferred.
The binder-type earrier may be blended with a
known assistant sueh as earbon blaek for adjusting
eleetrie resistanee, dispersing agent, dispersion
assistant, low moleeular or high moleeular eharge
eontrol agent. In the same manner as deseribed above,
furthermore, the eationie polar group may be introdueed
to enhanee the positively eharging property of the
earrier in order to enhanee the negatively eharging
property of the toner.
Even in sueh a binder-type earrier, it is desired
that the average partiele diameter lies in the same
range as that of the aforementioned carrier.
(Two-Component Magnetic Developing Agent)
The toner of the present invention is mixed
together with the above-mentioned various magnetie
earriers and is used as a magnetie developing agent.
Generally, it is desired that these earriers and the
toner are mixed together at a ratio of from 98:2 to
90:10 and, partieularly, from 97:3 to 94:6 on the
weight basis.
In the eleetrophotographie eopying method using
the two-eomponent magnetie developing agent, the
eleetrostatie latent image ean be formed by any known
system. For instanee, the photoeondueting layer on the
eondueting substrate is uniformly eharged and is
exposed to light to form an eleetrostatie latent image.
The eleetrostatie image is easily developed by
bringing a magnetic brush of the two-eomponent magnetie
developing agent into contact with the substrate. The
21~7103
toner image formed by developing is transferred onto a
copying paper and is fixed upon contact with a heating
roll.
The invention will now be described by way of the
following Examples.
(Example 1)
A. Preparation of a fixing resin.
3 Parts of methacrylic acid, 17 parts by weight of
butyl acrylate, 80 parts by weight of styrene and a
polymerization initiator were mixed and stirred in a
solvent to prepare a mixture solution thereof. The
mixture solution was introduced into a reaction oven
and was polymerized at 160C for 6 hours with
sufficient stirring using stirrer vanes. Then, the
reaction solution was deaerated and dried to obtain a
low molecular polymer having an acid value of 5.
Fig. 11 shows a curve of GPC molecular weight of
the low molecular polymer, from which it will be
obvious that the low molecular polymer has a peak
molecular weight in a region of from 4,000 to 30,000.
Next, 10 parts by weight of methacrylic acid, 20
parts by weight of butyl acrylate, 70 parts by weight
of styrene, a polymerization initiator and 100 parts by
weight of the low molecular polymer obtained above were
mixed and stirred in a solvent to prepare a mixture
solution thereof. The mixture solution was introduced
into a reaction oven and was polymerized at 90C for 17
hours with sufficient stirring using stirrer vanes.
Then, the reaction solution was deaerated and dried to
obtain a desired resin for fixing having an acid value
of 10.
Fig. 12 shows a curve of GPC molecular weight of
the resin for fixing, from which it will be obvious
that the resin for fixing exhibits nearly the same peak
molecular weight as that of the above-mentioned low
`_ 2177103
36
molecular polymer and further exhibits molecular weight
distribution on the side of high molecular weight. The
resin for fixing possessed a weight average molecular
weight of 100,000.
B. Preparation of a toner.
The following components:
fixing resin for obtained above, 100 parts by
weight,
carbon black (pH: 3.5, (7-pH)/specific surface
area: 0.025, treated with nitric acid), 9 parts
by weight, and
magnetite (magnetic powder), 2 parts by weight,
were melt-kneaded using a biaxial extruder. The
kneaded product was then pulverized using a jet mill
and was classified by a wind classifier to obtain
particles of a diameter of 10 . 0 ~m.
To 100 parts by weight of the particles were
externally added 0.3 parts by weight of fine
hydrophobic silica particles having an average particle
diameter of 0 . 015 ~m as a fluidity improving agent and
0.6 parts by weight of alumina particles having an
average particle diameter of 0 . 3 ~m as spacer
particles. The mixture was then mixed together by the
Henschel's mixer to obtain a toner.
C. Preparation of a developing agent.
The toner obtained above and an uncoated f errite
carrier having an average particle diameter of 100 ~m
were mixed together to obtain a two-component
developing agent having a toner concentration of 3.5%.
(Example 2)
1000 Parts by weight of spherical ferrite
particles having an average particle diameter of 100 ~m
were added to a coating solution obtained by dissolving
3.5 parts by weight of styrene-acrylic resin and 1.5
parts by weight of methylated melamine resin in 200
21 771 03
parts by weight of toluene, and were heated and
stirred. Then, the solvent (toluene) was removed by
drying from the mixture obtained above and was heat-
treated at 200C for one hour to obtain resin-coated
carrier particles.
A two-component developing agent having a toner
concentration of 3.5% by weight was obtained quite in
the same manner as in Example 1 with the exception of
using the above carrier particles as the magnetic
carrier.
(Example 3)
The following components:
amino group-containing styrene-acrylic resin,
100 parts by weight,
magnetite (magnetic powder), 400 parts by
weight, and
carbon black (pH = 9), 5 parts by weight,
were melt-kneaded using a biaxial extruder. The
kneaded product was then pulverized using a jet mill
and was classified by a wind classifier to obtain
carrier particles of a diameter of 80 ~m.
A two-component developing agent having a toner
concentration of 5.0% by weight was obtained in the
same manner as in Example 1 by using magnetic carrier
particles that were obtained by dispersing the magnetic
powder in the resin.
(Comparative Example 1)
A toner and a developing agent were prepared in
the same manner as in Example 1 but using the carbon
black having a pH of 9 and a ratio (7-pH)/specific
surface area of -0.013 (without treated with acid).
(Comparative Example 2)
A toner and a developing agent were prepared in
the same manner as in Example 1 but using the carbon
black having a pH of 3 and a ratio (7-pH)/specific
2177103
38
surface area of -0.122 (treated with nitric acid).
(Evaluation of toner)
Copies were taken by using the developing agents
obtained in the Examples and Comparative Examples and
by using a copying machine manufactured by Mita Kogyo
Co. (modified machine of a trade name of DC-4086).
Measurements were taken concerning the following items
to evaluate the toners. The results were as shown in
Table 1.
(a) Transfer efficiency.
The amount of toner in a toner hopper prior to
starting the copying operation and the amount of toner
in the toner hopper after a predetermined number of
copies were taken, were measured, and the amount of
toner that was consumed was calculated from a
difference therebetween. Furthe Dore, the amount of
toner recovered in a step of cleaning was measured
while the predetermined number of copies were being
taken to find the amount of toner that was recovered.
Based upon these values, the toner transfer efficiency
was calculated in compliance with the following
formula. Here, the document being copied was a
character document having a black area of 8%.
Transfer efficiency (%) = [(A - B)/A] x 100
wherein A represents the amount of toner consumed,
and B represents the amount of toner recovered.
(b) Image density (I.D.).
By using a character document having a black area
of 8~, copies were taken until the transfer efficiency
became smaller than 70%. The density of a solid black
portion in a sampling image was measured every after
5000 copies by using a reflection densitometer (Model
TC-6D, manufactured by Tokyo Denshoku Co.). The
document used for obtaining a sample every after 5000
copies possessed a black area inclusive of solid black
21 771 03
portion of 15%.
(c) Fogging density (F.D.)
By using a character document having a black area
of 8%, copies were taken until the transfer efficiency
became smaller than 70%. The density of a solid black
portion in a sampling image was measured every after
5000 copies by using the same reflection densitometer
as the one mentioned above. A difference was
calculated between this measured value and a value
found by measuring a base paper of before being copied
using the reflection densitometer, and a m~x;mllm value
was regarded to be a fogging density (F.D.). The
document used for obtaining a sample every after 5000
copies possessed a black area inclusive of solid black
portion of 15%.
(d) Resolution.
After 50,000 pieces of copies were taken (or when
the transfer efficiency became smaller than 70% even
before 50,000 pieces of copies were taken) by using a
character document having a black area of 8%, a copy
was taken by using a predetermined chart document
(document on which a predetermined number of parallel
lines have been drawn within a width of 1 mm) and a
copied image was evaluated by eyes.
(e) Amount of electric charge.
By using a character document having a black area
of 8%, copies were taken until the transfer efficiency
became smaller than 70%. Every after 5,000 pieces of
copies were taken, the amount of electric charge of 200
mg of the developing agent was measured by using a
device for measuring the amount of electric charge of
blow-off powder (manufactured by Toshiba Chemical Co.)
and was expressed in terms of an average amount of
electric charge per gram of the toner.
(f) Spent amount.
- 21 771 03
After 50,000 pieees of copies were taken (or when
the transfer effieieney beeame smaller than 70% even
before 50,000 pieees of eopies were taken) by using a
eharaeter doeument having a blaek area of 8%, the
developing agent was sampled. The developing agent was
plaeed on a sieve of 400 mesh and was sucked by a
blower from the lower side to separate it into the
toner and the carrier. 5 Grams of the carrier
r~m~ i n ing on the sieve was introdueed into a beaker,
and toluene was further added thereto in order to
dissolve the toner that adhered onto the earrier
surfaees as spent toner. Then, the toluene solution
was disearded in a state where the carrier was
attraeted by a magnet from the lower side of the
beaker. This was repeated several times until toluene
beeame eolorless and, then, toluene was dried in an
oven to measure the weight. A differenee between the
weight in the beaker and the weight after drying was a
spent amount. The spent amount was expressed in terms
of milligrams of the spent toner adhered per gram of
the carrier.
(g) Seattering of toner.
After 50,000 pieees of eopies were taken (or when
the transfer effieieney beeame smaller than 70% even
before 50,000 pieees of eopies were taken) by using a
eharaeter doeument having a blaek area of 8%,
seattering state of toner in the copying maehine was
observed by eyes and was evaluated on the following
basis.
O: toner is not scattering
X: toner is seattering
(h) Durability.
Every after 10,000 pieces of copies were taken by
using a eharaeter document having a blaek area of 8%,
the amount of toner consumed was measured and the
2~ 771 03
41
amount of toner recovered was measured, and from which
the toner transfer efficiency was calculated. The
number of pieces of copies after which the transfer
efficiency became smaller than 70% for the first time
was relied upon to evaluate the durability.
(i) High-temperature high-humidity properties.
5,000 Pieces of copies were taken in an
environment of a temperature of 35C and a humidity of
85%, and fogging and scattering of toner were measured
to evaluate high-temperature and high-humidity
properties.
21 771 03
42
Table 1
ExamPles Comparative
Examples
1- 2 3 1 2
Fixinq resin
Acid value of resin 10 10 10 10 10
Acid value of low
molecular component 5 5 5 5 5
Carbon black
pH 3.5 3.5 3.5 9 3
(7-pH)/specific)
surface area 0.025 0.025 0.025 -0.013 0.120
Carrier un- resin- binder- un- un-
coated coated type coated coated
ferrite ferrite carrier ferrite ferrite
Evaluated results
ID 1.432 1.418 1.422 1.450 1.432
FD 0.003 0.002 0.002 0.008 0.003
Resolution 5 5 5 4 5
Amount of charge
(~C/g) -18.9 -21.9 -20.5 -14.8 -18.9
Spent amount (mg)0.60 0.46 0.49 0.69 0.60
Toner scattering O O O X O
Durability 60000 100000 90000 20000 60000
pieces pieces pieces pieces pieces
High-temp. high-humidity
characteristics
FD 0.003 0.003 0.003 - 0.009
Toner scattering O O O --- X
2177103
43
(Consideration of the results of evaluation)
As will be understood from the results of Table 1,
the toners of Examples 1 to 3 were very stable in
regard to image density, fogging and resolution, and
did not scatter. Good high-temperature and high-
humidity properties were exhibited, too.
In Comparative Example 1, on the other hand, the
toner scattered to a conspicuous degree at normal
temperature. Under high-temperature and high-humidity
conditions, furthermore, the toner developed fogging
and scattered to a conspicuous degree.
According to the present invention which is not
blended with a negative charge control agent, the toner
maintains the electric charge in an amount large enough
for effecting the developing, no charge control agent
migrates onto the carrier surfaces, and the charging
property is not deteriorated by the spent toner but is
stably maintained for extended periods of time,
enabling the life of the toner and the carrier to be
lengthened.
By setting the acid value of the low molecular
components contained in the fixing resin medium to be
lower than the acid value of the whole resin,
furthermore, the charging property of the toner is more
reliably prevented from being impaired by the spent
toner, and scattering of toner and fogging can be
effectively avoided.
(Example 4)
As a fixing resin, use was made of a copolymerized
resin containing units inherent in styrene, stearyl
methacrylate, acrylic acid and butyl methacrylate at
weight ratios of 74:4:5:16, having an acid value of 10,
peak molecular weight of a low molecular polymer
component of 10,000, and a weight average molecular
weight of 100,000.
2177103
44
The following components:
fixing resin obtained above, 100 parts by
weight,
polypropylene wax (average molecular weight:
4000), 3 parts by weight,
carbon black (pH: 3.5, (7-pH)/specific surface
area (m2/g): 0.025, treated with nitric acid),
10 parts by weight, and
magnetite (magnetic powder), 2 parts by weight,
were melt-kneaded using à biaxial extruder. The
kneaded product was then pulverized using a jet mill
and was classified by a wind classifier to obtain
particles of a diameter of 10.0 ~m.
To 100 parts by weight of the particles were
externally added 0.3 parts by weight of fine
hydrophobic silica particles having an average particle
diameter of 0.015 ~m as a fluidity improving agent and
0.6 parts by weight of alumina particles having an
average particle diametër of 0.3 ~m as spacer
particles, and were mixed together by the Henschel's
mixer to obtain a toner.
The toner obtained above and a ferrite carrier
having an average particle diameter of 100 ~m were
mixed together to obtain a two-component developing
agent having a toner concentration of 3.5% by weight.
(Example 5)
A fixing resin (ContA;n;ng no higher alkyl group)
comprising a styrene-acrylic acid-butyl methacrylate
copolymer was prepared in the same manner as in Example
1 but using styrene, acrylic acid and butyl
methacrylate at weight ratios of 75:20:5. The resin
possessed a peak molecular weight due to a low
molecular polymer component of 10,000 and a weight
average molecular weight of 100,000.
A toner and a developing agent were prepared in
2 1 77 1 03
the same manner as in Example 4 but using the above
resin for fixing.
(Example 6)
1000 Parts by weight of spherieal ferrite
partieles having an average particle diameter of 100 ~m
were added to a coating solution obtained by dissolving
3.5 parts by weight of styrene-aerylie resin and 1.5
parts by weight of methylated melamine resin in 200
parts by weight of toluene, and were heated and
stirred. Then, the solvent (toluene) was removed by
drying from the mixture obtained above and was heat-
treated at 200C for one hour to obtain resin-coated
carrier partieles.
A two-eomponent developing agent having a toner
eoneentration of 3.5% by weight was obtained quite in
the same manner as in Example 4 but using the above
carrier partieles as the magnetic carrier.
(Example 7)
The following components:
amino group-cont~;ning styrene-aerylie resin,
100 parts by weight,
magnetite (magnetie powder), 400 parts by
weight, and
earbon blaek (pH = 9), 5 parts by weight,
were melt-kneaded using a biaxial extruder. The
kneaded produet was then pulverized using a jet mill
and was elassified by a wind elassifier to obtain
earrier partieles of a diameter of 80 ~m.
A two-eomponent developing agent having a toner
eoneentration of 5.0% by weight was obtained in the
same manner as in Example 1 but using binder-type
earrier partieles that were obtained by dispersing the
magnetie powder in the resin.
The developing agents prepared in Examples 4 to 7
above were tested in the same manner as in Examples 1
2177103
.
46
to 3, and were evaluated. The results were as shown in
Table 2.
Table 2
Ex.4 Ex.5 Ex.6 Ex.7
Fixinq resin
Higher alkyl steàryl none stearyl stearyl
group eontaining methà- metha- metha-
unit crylate erylate crylate
Carbon black
pH 3.5 3.5 3.5 3.5
7-pH/speeifie
surfaee area 0.025 0.0250.025 0.025
Carrier uncoated uncoated resin- binder-
ferrite ferrite coated type
ferrite carrier
Evaluated results
ID 1.422 1.418 1.421 1.386
FD 0.003 0.005 0.003 0.002
25 Resolution 5 5 5 5
Amount of charge -18.2 -17.2 -21.8 -23.9
(~C/g)
Spent amount(mg) 0.62 0.87 0.40 0.38
Toner seattering O O O O
Durability 70000 50000 90000 90000
pieces pieces pieces pieces
_ 2177~03
47
.
When the toner is blended with a parting agent
(polypropylene) as will be obvious from Table 2,
durability is not so high (50,000 pieces) in Example 5
which uses the fixing resin medium without higher alkyl
group-containing polymer component. In Examples 4, 6
and 7 using a higher alkyl group-containing fixing
resin medium, however, the durability is improved to a
considerable degree.
(Example 8)
(Preparation of a fixing resin medium)
The following components:
a mixture of styrene, butyl methacrylate and
acrylic acid at a weight ratio of 80:15:5, 100
parts by weight, and
a polypropylene wax (average molecular weight:
4,000), 0.6 parts.by weight,
a polymerization initiator
were mixed, stirred and dissolved in a solvent. The
obtained mixture solution was introduced into a
reaction oven and was polymerized at 150C for 5 hours
with sufficient stirring using a stirrer vane.
Thereafter, the reaction solution was deaerated and
dried to obtain a low molecular polymer containing a
component to which the polypropylene wax is graft-
fixed. .
The following components:
low molecular polymer obtained above, 100 parts
by weight,
a mixture of styrene, butyl methacrylate and
acrylic acid at a weight ratio of 70:25:5, 100
parts by weight,
the same polypropylene wax as the above one, 5.4
parts by weight, and
a polymerization initiator,
were mixed and stirred in a solvent to prepare a
2177103
48
mixture solution. The mixture solution was introducedinto a reaction oven and was polymerized at 80Aé for 15
hours with sufficient stirring using stirrer vanes.
The reaction solution was then deaerated and dried to
obtain a desired fixing resin having an acid value of
10 .
The fixing resin possessed a peak molecular weight
of 10,000, a molecular weight distribution on the side
of high molecular weights, and a weight average
molecular weight of 100,000.
The following components:
fixing resin obtained above, 103 parts by weight
(cont~;ning 3 parts by weight of wax), carbon
black (pH: 3.5, (7-pH)/specific surface area
(m2/g): 0.025, treated with nitric acid), 10
parts by weight, and
magnetite (magnetic powder), 2 parts by weight,
were melt-kneaded using a biaxial extruder. The
kneaded product was then pulverized using a jet mill
and was classified by a wind classifier to obtain
particles of a diameter of 10.0 ~m.
To 100 parts by weight of the particles were
externally added 0.3 parts by weight of fine
hydrophobic silica particles having an average particle
diameter of 0.015 ~m as a fluidity improving agent and
0.6 parts by weight of alumina particles having an
average particle diameter of 0.3 ~m as spacer
particles, and were mixed together by the Henschel's
mixer to obtain a toner.
The toner obtained above and a ferrite carrier
having an average particle diameter of 100 ~m were
mixed together to obtain a two-component developing
agent having a toner concentration of 3.5% by weight.
( ~x~rle 9 )
A resin for fixing was prepared in the same manner
2 1 77 ~ 03
49
as in Example 8 but without using polypropylene wax.
A toner was prepared quite in the same manner as
in Example 8 but using 100 parts by weight of the above
resin for fixing and 3 parts by weight of the
polypropylene wax used in Example 8. Then, a two-
component developing agent was prepared.
(Example 10)
1000 Parts by weight of spherical ferrite
particles having an average particle diameter of 100 ~m
were added to a coating solution obtained by dissolving
3.5 parts by weight of styrene-acrylic resin and 1.5
parts by weight of methylated melamine resin in 200
parts by weight of toluene, and were heated and
stirred. Then, the solvent (toluene) was removed by
drying from the mixture obtained above and was heat-
treated at 200C for one hour to obtain resin-coated
carrier particles.
A two-component developing agent having a toner
concentration of 3.5% by weight was obtained quite in
the same ~nn~r as in Example 8 but using the above
resin-coated carrier particles.
(Example 11)
The following components:
amino group-cont~;n;ng styrene-acrylic resin,
100 parts by weight,
magnetite (magnetic powder), 400 parts by
weight, and
carbon black (pH = 9), 5 parts by weight,
were melt-kneaded using a biaxial extruder. The
kneaded product was then pulverized using a jet mill
and was classified by a wind classifier to obtain
binder-type carrier particles of a diameter of 80 ~m.
A two-component developing agent having a toner
concentration of 5.0% by weight was obtained in the
same manner as in Example 8 but using binder-type
2177103
carrier particles that were obtained by dispersing the
magnetic powder in the resin.
The developing agents prepared in Examples 8 to 11
above were tested in the same manner as in Examples 1
to 3, and were evaluated. The results were as shown in
Table 3.
3S
2177103
Table 3
Ex.8 Ex.9 Ex.10 Ex.ll
Fixinq resin 3% of no wax 3% of 3% of
wax is is graft wax is wax is
graft- graft- graft- graft-
fixed fixed fixed fied
Carbon black
pH 3.5 3.5 3.5 3.5
7-pH/specific
surface area 0.025 0.025 0.025 0.025
Carrier uncoated uncoated resin- binder-
ferrite ferrite coated type
ferrite carrier
Evaluated results
ID 1.425 1.433 1.408 1.352
FD 0.003 0.005 0.002 0.002
Resolution 5 4 5 5
Amount of charge -18.8 -15.9 -22.1 -24.0
(~C/g)
Spent amount(mg) 0.60 0.80 0.42 0.40
Toner scattering O O O O
Durability 70000 50000 90000 90000
pieces pieces pieces pieces
2177103
As will be obvious from Table 3, when the resin
for fixing is simply blended with wax (Example 9), the
durability is deteriorated to some extent. When the
wax is graft-fixed to the resin for fixing as in
Examples 8, 10 and 11, however, the durability is
improved .
Example 12)
The following components:
resin for fixing (styrene-acrylic copolymer
having a carboxyl group, acid value of 8), 100
parts by weight,
carbon black (pH: 3.5, (7-pH)/specific surface
area (m2/g): 0.025, 7 parts by weight,
magnetic powder (magnetite), 2 parts by weight,
and
polyethylene resin (molecular weight: 4000), 2
parts by weight,
were melt-kneaded using`a biaxial extruder. The
kneaded product was then pulverized using a jet mill
and was classified by a wind classifier to obtain toner
particles having an average particle diameter of 10.0
~m.
To 1`00 parts by weight of the particles were
externally added 0.3 parts by weight of fine
hydrophobic silica particles having an average particle
diameter of 0.015 ~m and 0.3 parts by weight of
magnetite having an average particle diameter of 0.3 ~m
as spacer particles, and were mixed together by the
Henschel's mixer for two minutes to obtain a toner of
the present invention.
The toner obtained above and a ferrite carrier
having an average particle diameter of 100 ~m were
mixed together to obtain a two-component developing
agent having a toner concentration of 3.5% by weight.
(Example 13)
2177103
The toner particles were prepared quite in the
same manner as in Example 12 but without being blended
with polyethylene, and a developing agent was prepared.
By using the developing agents of Examples 12 and
13, images were formed in the same manner as in
Examples 1 to 3, and fixing factors of the obtained
images were found in accordance with a method described
below.
A flat bottom of a weight of 400 g was wrapped
with a uniformly stretched cotton cloth to rub a solid
black portion of the image five round trips at a
predetermined speed. The image density (ID) of before
being rubbed and the image density (ID) of after rubbed
were measured, and a peeling factor was regarded to be
a fixing factor.
ID after rubbing
Fixing factor (%) = x 100
ID before rubbing
In Example 13, the fixing factor was slightly
smaller than 80% but in Example 12, the fixing factor
was not smaller than 90%.
(Example 14)
Styrene, butyl methacrylate and acrylic acid were
mixed together at weight ratios of 80:15:5, and were
mixed and dissolved together with a polymerization
initiator in a solvent with stirring. The reaction
system was heated and polymerized. After polymerized,
the reaction solution was deaerated and dried to
prepare a resin for fixing comprising a styrene-butyl
methacrylate-acrylic acid copolymerized resin. The
resin for fixing possessed an acid value of 10.
The weight average molecular weight of the resin
for fixing was 100,000.
The following components:
resin for fixing obtained above, 100 parts by
2177103
54
weight,
carbon blaek (pH: 3.5, (7-pH)/specific surface
area (m2/g): 0.025, treated with nitric acid), 7
parts by weight, and
magnetite (magnetic powder), 2 parts by weight,
were melt-kneaded using a biaxial extruder. The
kneaded product was then pulverized using a jet mill
and was elassified by a wind classifier to obtain
particles of a diameter of 10.0 ~m.
To 100 parts by weight of the particles were
externally added 0.3 parts by weight of fine
hydrophobic silica particles having an average particle
diameter of 0.015 ~m as a fluidity improving agent and
0.5 parts by weight of magnetite particles (2 x 103
Q em) having an average particle diameter of 0.3 ~m as
spacer partieles, and were mixed together by the
Hensehel's mixer to obtain a toner.
The surfaee-treated toner particles and a ferrite
carrier having an average particle diameter of 100 ~m
were mixed together to obtain a two-eomponent
developing agent having a toner eoneentration of 3.5
by weight.
Example 15
A toner and a developing agent were prepared quite
in the same manner as in Example 14 but using, as
spaeer partieles, 0.5 parts by weight of magnetite
partieles (2 x 10 3 Q-cm) having an average partiele
diameter of 0.3 ~m and 0.5 parts by weight of alumina
partieles (1010 Q-em) having an average partiele
diameter of 0.3 ~m.
(Example 16)
A toner and a deve~oping agent were prepared quite
in the same manner as in Example 14 but externally
adding 0.2 parts by weight of zinc stearate.
(Example 17)
2177103
1000 Parts by weight of spherical ferrite
particles having an average particle diameter of 100 ~m
were added to a coating solution obtained by dissolving
3.5 parts by weight of styrene-acrylic resin and 1.5
parts by weight of methylated melamine resin in 200
parts by weight of toluene, and were heated and
stirred. Then, the solvent (toluene) was removed by
drying from the mixture obtained above and was heat-
treated at 200C for one hour to obtain resin-coated
carrier particles.
A two-component developing agent having a toner
concentration of 3.5% by weight was obtained quite in
the same manner as in Example 14 but using the above
carrier particles as a magnetic carrier.
(Example 18)
The following components:
amino group-conta;n;ng styrene-acrylic resin,
100 parts by weight,
magnetite (magnetic powder), 400 parts by
weight, and
carbon black (pH - 9), 5 parts by weight,
were melt-kneaded using a biaxial extruder. The
kneaded product was then pulverized using a jet mill
and was classified by a wind classifier to obtain
binder-type carrier particles of a diameter of 80 ~m.
A two-component magnetic developing agent having a
toner concentration of 5.0% by weight was obtained in
quite the same manner as in Example 14 but using the
binder-type carrier particles that were obtained by
dispersing the magnetic powder in the resin.
(Comparative Example 3)
A toner and a developing agent were prepared quite
in the same manner as in Example 14 but using the
carbon black having pH of 9 and a ratio (7-pH)/specific
surface area (m2/g) of -0.013, which has not been
2177103
.
56
treated with acid.
(Example 19)
A toner and a developing agent were prepared in
quite the same manner as in Example 14 but without
using spacer particles.
The developing agents obtained in Examples 14 to
19 and Comparative Example 3 were tested in the same
way as in Examples 1 to 3, and were further measured
for their transfer efficiencies in accordance with a
method described below. The results were as shown in
Tables 4 and 5.
Transfer efficiency:
The amount of toner in a toner hopper prior to
starting the copying operation and the amount of toner
in the toner hopper after a predetermined number of
copies were taken, were measured, and the amount of
toner that was consumed was calculated from a
difference therebetween. Furthermore, the amount of
toner recovered in a step of cleaning was measured
while the predetermined number of copies were being
taken to find the amount of toner that was recovered.
Based upon these values, the toner transfer efficiency
was calculated in compliance with the following
formula. Here, the document being copied was a
character document having a black area of 8%.
Transfer efficiency (%) = [(A - B)/A] x 100
wherein A represents the amount of toner consumed,
and B represents the amount of toner recovered.
2177103
Table 4
Ex.14 Ex.15 Ex.16
Spacer particles magnetite magnetite treated
and with
alumina stearic
acid
Carbon black
pH 3.5 3.5 3.5
7-pH/specific
surface area 0.025 0.025 0.025
Carrier uncoated uncoated uncoated
ferrite ferrite ferrite
Evaluated results
ID 1.430 1.426 1.465
FD 0.003 0.003 0.003
Resolution 5 5 5
Amount of charge -18.1 -18.3 -17.5
(~C/g)
Spent amount(mg) 0.60 0.57 0.62
Toner scattering O O O
Durability 80000 100000 80000
pieces pieces pieces
Transfer efficiency 82 83 82
(%)
21771Q3
58
Table 5
Ex.17 Ex.18 Co.Ex.3 Ex.19
pacer particles magne- magne- magne- none
tite tite tite
Carbon black
pH 3.5 3.5 9 3.5
7-pH/specific
surface area 0.025 0.025 -0.013 0.025
Carrier resin- binder- uncoated uncoated
coated type ferrite ferrite
ferrite carrier
valuated results
ID 1.425 1.372 1.453 1.423
FD 0.002 0.002 0.009 0.003
Resolution 5 5 4 5
Amount of charge -20-.3 -23.0 -13.8 -18.8
(~C/g)
Spent amount(mg) 0.41 0.43 0.85 0.80
Toner scattering O O X O
Durability 100000 100000 30000 50000
pieces pieces pieces pieces
Transfer efficiency 83 83 73 78
(%)
2177103
As will be obvious from Tables 4 and 5, use of the
spacer particles makes it possible to enhance
durability and transfer efficiency of the toner.
