Note: Descriptions are shown in the official language in which they were submitted.
CA 02018371 2000-07-OS
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a toner which
includes a vinyl polymer binder that has been prepared by
a particular polymerisation method. The vinyl polymer
binder used in the toner of the present invention is
prepared by suspension polymerisation using a particular
dispersing agent and initiator.
Hitherto, there have been a large number of
inventions relating to binder resins for dry toners.
Vinyl polymers used as a binder resin for toners are
produced by suspension polymerization, bulk
polymerizaton, solution polymerization, emulsion
polymerization, etc. Suspension polymerization is
preferred because the manufacturing costs are minimized.
However, it is not avoidable for the binder resin to
contain the residual decomposition by-products of a
dispersing agent and initiator used in the suspension
polymerization. Toners using such a resin as a binder
are undesirable because toners prepared from them have
problems in terms of chargeability, and particularly
stability (life) of the image quality.
SUMMARY OF THE INVENTION
The present inventors have studied these problems
and found that if the toner is prepared using a vinyl
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polymer binder obtained by suspension polymerisation of a
polymerised vinyl monomer with a non-ionic dispersing
agent and an azo initiator, the resultant toner will have
superior stability of image quality.
According to the present invention, there is
provided a toner comprising a polymeric binder obtained
by suspension polymerisation of a mixture of vinyl
monomers including both styrene or a styrene derivative
and a (meth) acrylic acid ester and an acid vinyl monomer
in an amount of 0.5 to 10 wt. ~ based on the total weight
of the vinyl monomers, the suspension polymerisation
being carried out using a non-ionic dispersing agent and
an azo initiator.
Preferably the polymerisable vinyl monomer includes
an acid monomer in an amount of 1 to 10 wt. o.
The present invention further resides in the use of
an acid vinyl monomer in a process for making a polymeric
binder by suspension polymerisation of a mixture of vinyl
monomers in the presence of a nonionic dispersing agent
and an azo initiator, the vinyl monomer mixture including
both styrene or a styrene derivative and a (meth)acrylic
acid ester and including the acid monomer in an amount of
0.5 - 10 wt. ~ based on the total weight of the monomers,
to provide enhanced stability of the image produced using
the polymer in a toner.
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PREFERRED EMBODIMENTS OF THE INVENTION
The polymerizable vinyl monomers, used in the
present invention may be any of those that may be
S polymerized by suspension polymerization. For example,
there are mentioned styrene and styrene derivatives such
as a-methylstyrene and substituted styrenes having methyl
at the o- or m-position of the benzene ring, or methyl,
ethyl, butyl, hexyl, octyl, nonyl, decyl, methoxy,
phenyl or vinyl at the p-position of the benzene
ring, or methyl at 2- and 4-positions thereof;
acrylic acid esters and methacrylic acid esters
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CA 02018371 1999-06-22
1 represented by the formula: CH2 = CR-COOR', where R repre-
Bents hydrogen or methyl, and R' represents methyl, ethyl,
n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-
butyl, n-pentyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl,
isononyl, decyl, dodecyl, tridecyl, stearyl, docosyl,
cyclohexyl, benzyl, phenyl, methoxyethyl, ethoxyethyl,
butoxyethyl, phenoxyethyl, etc.; vinyl esters such as
vinyl acetate, vinyl propionate, etc.; and acrylic acid
derivatives or methacrylic acid derivatives such as
acrylonitrile, methacrylonitrile, etc. These
polymerizable vinyl monomers are used alone or in
admixture of two or more of them.
As an example of a combination of two or more
polymerizable vinyl monomers, there are mentioned
monomer mixtures comprising as main constituents styrene
and/or its derivatives and alkyl (meth)acrylates.
When the acid monomer is,used as one component
of the polymerizable vinyl monomer, the life of the toner
obtained is further improved. The amount of the acid
monomer is 0.5 to 10 wt.$ based on the total weight of the
polymerizable vinyl monomers. When the vinyl polymer is
obtained by copolymerizing 0.5 wt.$ or less of the acid
monomer, toners containing this vinyl polymer as a binder
exhibit no effect of copolymerization of the acid monomer.
On the other hand, when the vinyl polymer is obtained by
copolymerizing 10 wt.~ or more of the acid monomer, toners
containing this vinyl monomer as a binder exert adverse
effects on their other characteristics.
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1 The polymerizableacid monomer
used herein
refers to
monomers having in addition to
one or more the
acid substituents
polymerizable vinyl group. For example, it includes
acrylic acid, methacrylic acid, itaconic acid, citraconic
acid, malefic acid, fumaricacid, crotonic acid, monobutyl
itaconate, monomethyl maleate, monobutyl maleate,
monooctyl maleate, monooctyl itaconate, 2-sulfoethyl
methacrylate, 2-sulfoethyl acrylate, 2-acrylamide-2-
methylpropanesulfonic acid, vinylbenzenesulfonic acid,
etc. These acid monomers are used alone or in admixture
of two or more of them.
For obtaining the vinyl polymer used in the
present invention, a suspension polymerization method
is used.
The azo initiator used in this method is not
critical, it being possible to use the well-known ones.
For example, there are mentioned azobisisobutyronitrile,
2,2'-azobis-(2,4-dimethylvaleronitrile), dimethyl-2,2'-
azobisisobutyronitrile, 2,2'-azobis-(2-methylbutyro-
nitrile), 1,1'-azobis-(cyclohexane-1-carbonitrile),
2,2'-azobis-(2-cyclopropylpropionitrile), 2,2'-azobis-
(4-methoxy-2,4-dimethylvaleronitrile), etc. Among these
initiators, it is preferred to use azobisisobutyro-
nitrile, 2,2'-azobis-(2,4-dimethylvaleronitrile),
dimethyl-2,2'-azobisisobutyronitrile or 2,2'-azobis-
(2-methylbutyronitrile) because these initiators have
properties to keep a polymerization activity upon
the monomer and complete the polymerization in a
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1 relatively short time, and because they do not have a
high tendency to leave their decomposition by-products
in the resulting polymer.
These azo initiators are used alone or in
admixture of two or more of them.
The toner of the present invention has a
remarkably improved life as compared with toners contain-
ing as a binder polymers obtained by the conventional
methods, because it uses as a binder a vinyl polymer
obtained by suspension polymerization with a nonionic
dispersing agent.
Suitable examples of nonionic dispersing agents
for use in the present invention include polyvinyl
alcohol, methyl cellulose, ethyl cellulose,
hydroxypropyl cellulose, gelatin, polyethylene oxide,
etc. Of these nonionic dispersing agents, polyvinyl
alcohol having a saponification degree of 70 to 90%
and a polymerization degree of 500 to 3000 is
preferred because resins obtained with it have good
characteristics as a binder for toners.
The nonionic dispersing agent is used in such
an amount that the polymerization operation can be
completed without causing aggregation of the produced
resin particles in the course of the polymerization.
The amount of the agent is usually 0.01 to 5 parts by
weight, preferably 0.05 to 2 parts by weight based on
100 parts by weight of water.
If necessary, a dispersion auxiliary may be
used. It includes for example electrolytes such as
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1 sodium chloride, potassium chloride, sodium sulfate,
potassium sulfate, etc.
The conditions of the suspension polymerization
vary with the particular polymerizable vinyl monomers
and azo initiators used, and the amounts thereof.
However, the polymerization temperature is generally
30° to 130°C, preferably 60° to 100°C, and the
polymerization time is preferably from about 1 to about 10
hours.
After the completion of the suspension
polymerization, the reaction solution is filtered, and
the resulting polymer is thoroughly washed, dehydrated
and dried. A coloring agent and other additives are
added to this polymer to obtain the toner of the
present invention. The toner thus obtained is one
having an extremely superior life.
The present invention is illustrated below
with reference to the following Examples. In the
Examples, parts are by weight. However, these examples
are not to-be construed to limit the present invention.
Example 1
3 Parts of azobisisobutyronitrile, an azo
initiator, was dissolved in a polymerizable vinyl
monomer comprising 83 parts of styrene, 17 parts of
2-ethylhexyl acrylate and 0.3 part of divinylbenzene.
The resulting mixture was mixed with a polymerization
medium obtained by dissolving 0.2 part of partially
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1 saponified polyvinyl alcohol (PVA-224E produced by
KURARAY CO., LTD.) in 220 parts of deionized water.
The mixture was heated to 80°C, and suspension
polymerization was carried out for 90 minutes at this
temperature. The resulting polymer dispersion was
cooled to room temperature and filtered. The solid
matter obtained was thoroughly washed, dehydrated and
dried to obtain a bead-form binder resin.
92 Parts of the above binder resin, 7 parts
of carbon black (#40 produced by Mitsubishi Kasei Corp.)
and 1 part of a charge control agent (BONTRON - S-34*
produced by ORIENT CHEMICAL INDUSTRIES, LTD.) were
kneaded at 150°C for about 5 minutes on a twin-screw
extruder. After cooling, the kneaded product was finely
pulverized on a jet mill. The fine powders obtained
were classified to collect fine powders having a
particle size of 5 to 15 um. The volume mean diameter
of the fine powders was 9.6 um.
A copying test was carried out on a commercial-
ly available copying machine ("Ricopy"* FT 4510 produced
by RICOH CO., LTD.) using the above fine powders as a
toner. As a result, fog-free high-resolution clear
images were obtained at the initial stage of copying
and after 10,000 copying operations. After 20,000
copying operations, however, the images showed a faint
touch of fog and a somewhat lowered resolution degree,
which were however of such a degree as to be out of the
question in practical use.
* Trademark
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CA 02018371 2000-07-04
1 Example 2
A toner was obtained in the same manner as
in Example 1 except that 82 parts of styrene, 17 parts
of 2-ethylhexyl acrylate, 1 part of methacrylic acid
and 0.3 part of divinylbenzene were used as the
polymerizable vinyl monomer. The performances of the
toner were evaluated, and it was found that fog-free
high-resolution clear images were obtained even after
20,000 copying operations.
Example 3
A toner was obtained in the same manner as in
Example 1 except that 82.5 parts of styrene, 17 parts
of 2-ethylhexyl acrylate, 0.5 part of methacrylic acid
and 0.3 part of divinylbenzene were used as the
polymerizable vinyl monomer. The performances of the
toner were evaluated, and it was found that fog-free
high-resolution clear images were obtained at the
initial stage of copying and after 10,000 copying
operations,' but after 20,000 copying operations, the
images showed a faint touch of fog, which was however
of such a degree as to be out of the question in
practical use.
Example 4
A toner was obtained in the same manner as in
Example 1 except that 73 parts of styrene, 17 parts of
2-ethylhexyl acrylate, 10 parts of methacrylic acid and
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~Q~~~~~
1 0.3 part of divinyl.benzene were used as the polymerizable
vinyl monomer. The performances of this toner were
evaluated, and it was found that fog-free high-resolution
clear images were obtained even after 20,000 copying
operations, but the fixability and grindability were
somewhat lowered.
Comparative Example 1
A toner was obtained in the same manner as
in Example 1 except that 3 parts of benzoyl peroxide,
which is not an azo initiator, was used as the poly-
merization initiator, and that the polymerization
temperature was 85°C. The performances of this toner
were evaluated, and it was found that the images at
the initial stage of copying were fog-free high-resolution
clear ones, but that after 5,000 copying operations,
only images having a touch of fog and a lowered resolution
degree were obtained.
Comparative Example 2
A toner was obtained in the same manner as in
Example 2 except that 3 parts of benzoyl peroxide was
used as the initiator and the polymerization temperature
was 85°C. The performances of this toner were evaluated,
and it was found that the images at the initial stage
of copying were fog-free high-resolution clear ones,
but that after 10,000 copying operations, only images
having a touch of fog and a lowered resolution degree
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~t~lt~3'~~.
1 were obtained.
Comparative Example 3
A toner was obtained in the same manner as
in Example 1 except that 0.2 part of an anion-modified
polyvinyl alcohol (KL-318 produced by KURARAY CO., LTD.),
which is not a nonionic dispersing agent, was used
as the dispersing agent. The performances of this
toner were evaluated, and it was found that the images
at the initial stage of copying were fog-free high-
resolution clear ones, but that after 5,000 copying
operations, only images having a touch of fog and a
lowered resolution degree were obtained.
Comparative Example 4
A toner was obtained in the same manner as
in Example 2 except that 0.2 part of an anion-modified
polyvinyl alcohol (KL-318 produced by KURARAY CO., LTD.)
was used as the dispersing agent. The performances of
this 'toner were evaluated, and it was found that the
images at the initial stage of copying were fog-free
high-resolution clear ones, but that after 10,000
copying operations, only images having a touch of fog
and a lowered resolution degree were obtained.
Comparative Example 5
A toner was obtained in 'the same manner as in
2S Example 1 except that 0.2 part of a cation-modified
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1 polyvinyl alcohol (C-318 produced by KURARAY CO., LTD.)
was used as the dispersing agent. The performances of
this toner were evaluated, and it was found that the
images at the initial stage of copying were fog-free
high-resolution clear ones, but that after 5,000 copying
operations, only images having a touch of fog and a
lowered resolution degree were obtained.
Comparative Example E
A toner was obtained in the same manner as
ZO in Example 2 except that 0.2 part of a cation-modified
polyvinyl alcohol (C-318 produced by KURARAY CO., LTD.)
was used as the dispersing agent. The performances of
this toner were evaluated, and it was found that the
images at the initial stage of copying were fog-free
high--resolution clear ones, but that after 10,000 copying
operations, only images having a touch of fog and a
lowered resolution degree were obtained.
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