U.S. patent application number 09/897029 was filed with the patent office on 2001-12-13 for electrostatic image developing toner.
Invention is credited to Emura, Yuji, Hisamatsu, Kazuo, Maekawa, Hiroshi, Mizushima, Katsuhiko, Ogawa, Koichi.
Application Number | 20010051704 09/897029 |
Document ID | / |
Family ID | 26581179 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010051704 |
Kind Code |
A1 |
Maekawa, Hiroshi ; et
al. |
December 13, 2001 |
Electrostatic image developing toner
Abstract
An object of the present invention is to provide an
electrostatic image developing toner having good charge properties,
low-temperature fixing properties, offset resistance and blocking
resistance as well as good resistance against sticking to a heated
roll and wax dispersibility and a novel urethane-modified polyester
resin used for the toner. Provided in the present invention is a
novel urethane-modified polyester resin which has a total acid
value not greater than 10 KOH mg/g and has been obtained by
kneading, in a molten state, a base polyester resin (A) having an
acid value of 5 to 20 KOH mg/g and a hydroxyl value of 40 to 70 KOH
mg/g, a low-molecular-weight polyester resin (B) having an acid
value not greater than 5 KOH mg/g, a hydroxyl value not greater
than 10 KOH mg/g and a weight-average molecular weight of 3,000 to
5,000 and a polyisocyanate compound, by using the components (A)
and (B) at a weight ratio of 3 to 5:7 to 5 and the polyisocyanate
compound in an amount of 0.2 to 1.2 equivalent, in terms of an
isocyanate group per equivalent, of the total hydroxyl groups of
all the resins. This novel urethane-modified polyester resin (C) is
used as a binder resin for the toner. For the preparation of the
toner, the resin is mixed and kneaded with a colorant, magnetic
powders, charge control agent and the like under a molten state,
followed by cooling and pulverization.
Inventors: |
Maekawa, Hiroshi; (Chiba,
JP) ; Hisamatsu, Kazuo; (Kanagawa, JP) ;
Emura, Yuji; (Kanagawa, JP) ; Ogawa, Koichi;
(Saitama, JP) ; Mizushima, Katsuhiko; (Saitama,
JP) |
Correspondence
Address: |
Robert G. Mukai
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
26581179 |
Appl. No.: |
09/897029 |
Filed: |
July 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09897029 |
Jul 3, 2001 |
|
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09460416 |
Dec 14, 1999 |
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6284423 |
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Current U.S.
Class: |
528/80 ; 430/965;
522/173; 522/174; 525/440.01; 525/440.04; 528/83 |
Current CPC
Class: |
G03G 9/08755 20130101;
C08G 18/0895 20130101; C08G 18/4255 20130101; G03G 9/08764
20130101; C08G 18/4202 20130101 |
Class at
Publication: |
528/80 ; 525/440;
528/83; 430/965; 522/173; 522/174 |
International
Class: |
C08G 018/42; C08L
075/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 1998 |
JP |
360991/1998 |
Claims
What is claimed is:
1. An electrostatic image developing toner comprising an
urethane-modified polyester resin (C) which has a total acid value
not greater than 10 KOH mg/g and has been obtained by reacting,
with a polyisocyanate compound, a molten mixture of a base
polyester resin (A) having an acid value of 5 to 20 KOH mg/g and a
hydroxyl value of 40 to 70 KOH mg/g and a low-molecular-weight
polyester resin (B) having an acid value not greater than 5 KOH
mg/g, a hydroxyl value not greater than 10 KOH mg/g and a
weight-average molecular weight of 3,000 to 5,000 by using the
components (A) and (B) at a weight ratio of 3 to 5:7 to 5 and the
polyisocyanate compound in an amount of 0.2 to 1.2 equivalents, in
terms of an isocyanate group, per equivalent of the total hydroxyl
groups of the base polyester resin (A) and the low-molecular-weight
polyester resin (B).
2. An electrostatic image developing toner according to claim 1,
wherein the base polyester resin (A) has a glass transition point
of 10 to 60.degree. C. and has been obtained by polycondensation of
at least three monomers, that is, at least one diol, at least one
dicarboxylic acid and 0.5 to 20 mole %, based on the total amount
of all the starting material monomers, of at least a polyol
component having three or more hydroxyl groups; the low-molecular
weight polyester resin (B) is a linear polyester resin having a
glass transition point of 40 to 70.degree. C. and having been
obtained by polycondensation of at least two monomers, that is, at
least one diol and at least one dicarboxylic acid; and the
polyisocyanate compound is a diisocyanate compound.
3. An electrostatic image developing toner according to claim 2,
wherein the base polyester resin (A) has been obtained by
polycondensation of at least one diol, at least one dicarboxylic
acid, 2 to 20 mole %, based on the total amount of all the starting
material monomers, of at least one long-chain aliphatic
monocarboxylic acid or long-chain aliphatic monoalcohol and 2 to 20
mole %, based on the total amount of all the starting material
monomers, of a polyol component having three or more hydroxyl
groups.
4. An electrostatic image developing toner according to claim 2,
wherein the low-molecular weight polyester resin (B) has been
obtained by polycondensation of at least one diol, at least one
dicarboxylic acid and at least one monocarboxylic acid.
5. An electrostatic image developing toner according to claim 3,
wherein the low-molecular weight polyester resin (B) has been
obtained by polycondensation of at least one diol, at least one
dicarboxylic acid and at least one monocarboxylic acid.
6. An electrostatic image developing toner according to claim 1,
wherein the polyisocyanate compound is employed in an amount of 0.3
to 1.0 equivalent, in terms of an isocyanate group, per equivalent
of the total hydroxyl groups of the base polyester resin (A) and
the low-molecular-weight polyester resin (B).
7. An electrostatic image developing toner according to claim 2,
wherein the polyisocyanate compound is employed in an amount of 0.3
to 1.0 equivalent, in terms of an isocyanate group, per equivalent
of the total hydroxyl groups of the base polyester resin (A) and
the low-molecular-weight polyester resin (B).
8. An electrostatic image developing toner according to claim 3,
wherein the polyisocyanate compound is employed in an amount of 0.3
to 1.0 equivalent, in terms of an isocyanate group, per equivalent
of the total hydroxyl groups of the base polyester resin (A) and
the low-molecular-weight polyester resin (B).
9. An electrostatic image developing toner according to claim 4,
wherein the polyisocyanate compound is employed in an amount of 0.3
to 1.0 equivalent, in terms of an isocyanate group, per equivalent
of the total hydroxyl groups of the base polyester resin (A) and
the low-molecular-weight polyester resin (B).
10. An urethane-modified polyester resin which has a total acid
value not greater than 10 KOH mg/g and has been obtained by
reacting, with a polyisocyanate compound, a molten mixture of a
base polyester resin (A) having an acid value of 5 to 20 KOH mg/g
and a hydroxyl value of 40 to 70 KOH mg/g and a
low-molecular-weight polyester resin (B) having an acid value not
greater than 5 KOH mg/g, a hydroxyl value not greater than 10 KOH
mg/g and a weight-average molecular weight of 3,000 to 5,000 by
using the components (A) and (B) at a weight ratio of 3 to 5:7 to 5
and the polyisocyanate compound in an amount of 0.2 to 1.2
equivalents, in terms of an isocyanate group, per equivalent of the
total hydroxyl groups of the base polyester resin (A) and the
low-molecular-weight polyester resin (B).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electrostatic image
developing toner suitable for use in electrophotography printing,
electrostatic printing or the like; and a novel urethane-modified
polyester resin used for the toner. More specifically, this
invention relates to an electrostatic image developing toner having
good charge properties, blocking resistance and offset resistance
as well as excellent resistance against sticking to a heated roll
and wax dispersibility; and a novel urethane-modified polyester
resin used for it.
[0003] 2. Description of the Related Art
[0004] With the progress of office automation, a demand for copying
machines or laser printers making use of electrophotography has
shown a rapid increase and at the same time, a requirement for
their performances has come to be severer. In order to obtain a
visible image by electrophotography, a generally adopted process is
to electrify a photo conductor such as selenium, amorphous silicon
or organic semiconductor, expose it to light, develop an image by
using a toner-containing developer, transfer the toner image, which
has been formed on the photo conductor, to a printed body such as
paper and then fix the image by using a heated roll or the like. It
is needless to say that the developed image must be vivid, being
free from fogging and having a sufficient image density. In recent
days, however, it has strongly been requested to carry out fixation
at a lower temperature, from the viewpoint of speeding up, energy
saving and improvement of safety and at the same time, to provide a
toner having excellent low-temperature fixing properties. For
improving the fixing properties of a toner, it is generally
necessary to lower the melt viscosity of the toner, thereby
increasing the adhesion area with a base material to be fixed. For
this purpose, the glass transition point (Tg) or molecular weight
of the conventionally used binder resin is lowered. Such a
countermeasure is however accompanied with the drawbacks that
stable maintenance of the particle condition of the toner upon
usage or storage is not easy, because a resin having a low glass
transition point is usually inferior in blocking resistance; and
upon fixation of the toner image by the heated-roll fixing method,
the heated roll is directly brought into contact with the toner
under a molten state and so-called offset phenomenon occurs, in
other words, a portion of the toner transferred onto the heated
roll smears a printed body such as paper or the like to be fed
next. Such a tendency becomes apparent when the molecular weight of
the resin is smaller.
[0005] Recently, a digital system which can output information from
a computer or facsimile has drawn attentions as an
electrophotographic image forming system. Since laser is used as
exposure means in this digital system, a toner having a small
particle size is required so as to permit the output of a more
minute line and therefore a more delicate image compared with an
analog system. When the particle size of a toner is reduced,
however, the wax having poor dispersibility tends to fall off and
be recovered as a dust. In general, the dust which has appeared in
the pulverizing step is recovered and recycled as the raw material.
A large wax content in the dust makes recycling difficult and is
therefore not preferred. Moreover, the wax falls off from the
surface of the toner during stirring with a carrier in a copying
machine, by which the charge amount becomes unstable or filming
occurs on a photo conductor. It is preferred to use the wax after
being dispersed in the toner minutely and uniformly. As the wax,
low-molecular-weight polypropylene or polyethylene is generally
employed, but owing to poor compatibility with polyester or the
like, the wax tends to have a large particle size in the dispersed
form.
[0006] Various toners using, as a binder resin, a polyester resin
instead of a styrene acrylic resin or epoxy resin are proposed in
consideration of charge properties or fixing properties (ex.
Japanese Patent Laid-Open No. 284771/1986, Japanese Patent
Laid-Open No. 291668/1987, Japanese Patent Publication No.
101318/1995, Japanese Patent Publication No. 3663/1996, U.S. Pat.
No. 4,833,057 and the like). The use of a polyester resin is
however accompanied with the problem that its surface tension is
greater than that of a styrene acrylic resin frequently employed as
a binder resin so that winding of paper and the like onto a heated
roll tends to occur. The use of a polyester resin as a binder
resin, on the other hand, is also accompanied with the problem that
although the negative charge properties of the resulting toner
becomes higher in proportion to the concentration of the terminal
carboxyl group, an increase in the concentration of the terminal
carboxyl group causes lowering of moisture resistance and an
electrified amount of the toner decreases, influenced by the water
content at the time of high humidity, leading to a deterioration in
the quality of the developed image.
[0007] Furthermore, since treatment of a copying machine including
that of a toner is requested to be maintenance free, there is an
eager demand for a toner which can provide a developed image stably
for a long period of time.
SUMMARY OF THE INVENTION
[0008] The present invention has been made with a view to providing
an electrostatic image developing toner which is free from the
above-described conventional problems and at the same time, satisfy
the above-described various properties which the toner has so far
been required to have; and a novel urethane-modified polyester
resin (C) used for the toner.
[0009] An object of the present invention is therefore to provide
an electrostatic image developing toner which is excellent in each
of static properties, image density, low-temperature fixing
properties, offset resistance and blocking resistance and in
addition is good in resistance against sticking to a heated roll
and wax dispersibility. In particular, another object of the
present invention is to provide an electrostatic image developing
toner which permits stable formation of a high-density developed
image even at high-temperature and high-humidity or low-temperature
and low-humidity conditions.
[0010] A further object of the present invention is to provide an
electrostatic image developing toner which permits stable formation
of a developed image for a long period of time.
[0011] A still further object of the present invention is to
provide a novel urethane-modified polyester resin used for an
electrostatic image developing toner.
[0012] With a view to attaining the above-described objects, the
present inventors have carried out an extensive investigation. As a
result, it has been found that the above-described objects can be
attained by incorporating, in an electrostatic image developing
toner, an urethane-modified polyester resin (C) which is prepared
by reacting a specific polyester resin, employed as a starting
material, with a polyisocyanate and has a predetermined acid value,
leading to the completion of the present invention.
[0013] The present invention relates to the below-described six
aspects (1) to (6).
[0014] (1) An electrostatic image developing toner comprising an
urethane-modified polyester resin (C) which has a total acid value
not greater than 10 KOH mg/g and has been obtained by reacting,
with a polyisocyanate compound, a molten mixture of a base
polyester resin (A) having an acid value of 5 to 20 KOH mg/g and a
hydroxyl value of 40 to 70 KOH mg/g and a low-molecular-weight
polyester resin (B) having an acid value not greater than 5 KOH
mg/g, a hydroxyl value not greater than 10 KOH mg/g and a
weight-average molecular weight of 3,000 to 5,000 by using (A) and
(B) at a weight ratio of 3 to 5:7 to 5 and the polyisocyanate
compound in an amount of 0.2 to 1.2 equivalents, in terms of an
isocyanate group, per equivalent of the total hydroxyl groups of
the base polyester resin (A) and the low-molecular-weight polyester
resin (B).
[0015] (2) An electrostatic image developing toner as described in
(1), wherein the base polyester resin (A) has a glass transition
point of 10 to 60.degree. C. and has been obtained by
polycondensation of at least three monomers, that is, at least one
diol, at least one dicarboxylic acid and 0.5 to 20 mole %, based on
the total amount of all the starting material monomers, of at least
one polyol component having three or more hydroxyl groups; the
low-molecular weight polyester resin (B) is a linear polyester
resin having a glass transition point of 40 to 70.degree. C. and
having been obtained by polycondensation of at least two monomers,
that is, at least one diol and at least one dicarboxylic acid; and
the polyisocyanate compound is a diisocyanate compound.
[0016] (3) An electrostatic image developing toner as described
above in (2), wherein the base polyester resin (A) has been
obtained by polycondensation of at least one diol, at least one
dicarboxylic acid, 2 to 20 mole %, based on the total amount of all
the starting material monomers, of at least one long-chain
aliphatic monocarboxylic acid or long-chain aliphatic monoalcohol
and 2 to 20 mole %, based on the total amount of all the starting
material monomers, of a polyol component having three or more
hydroxyl groups.
[0017] (4) An electrostatic image developing toner as described
above in (2) or (3), wherein the low-molecular weight polyester
resin (B) has been obtained by polycondensation of at least one
diol, at least one dicarboxylic acid and at least one
monocarboxylic acid.
[0018] (5) An electrostatic image developing toner as described
above in any one of (1) to (4), wherein the polyisocyanate compound
is employed in an amount of 0.3 to 1.0 equivalent, in terms of an
isocyanate group, per equivalent of the total hydroxyl groups of
the base polyester resin (A) and the low-molecular-weight polyester
resin (B).
[0019] (6) A novel urethane-modified polyester resin which has a
total acid value not greater than 10 KOH mg/g and has been obtained
by reacting, with a polyisocyanate compound, a molten mixture of a
base polyester resin (A) having an acid value of 5 to 20 KOH mg/g
and a hydroxyl value of 40 to 70 KOH mg/g and a
low-molecular-weight polyester resin (B) having an acid value not
greater than 5 KOH mg/g, a hydroxyl value not greater than 10 KOH
mg/g and a weight-average molecular weight of 3,000 to 5,000 by
using the components (A) and (B) at a weight ratio of 3 to 5:7 to 5
and the polyisocyanate compound in an amount of 0.2 to 1.2
equivalents, in terms of an isocyanate group, per equivalent of the
total hydroxyl groups of the base polyester resin (A) and the
low-molecular-weight polyester resin (B).
[0020] In the present invention described above, an electrostatic
image developing toner comprising a low-acid-value
urethane-modified polyester resin (C), which has been obtained by
reacting a base polyester resin (A) having a predetermined acid
value and hydroxyl value and a low-molecular weight polyester resin
(B) having a predetermined acid value, hydroxyl value and molecular
weight with a polyisocyanate compound, has excellent charge
properties even if the polyester resin employed has a low acid
value. In addition, the developed image formed using it is good and
has high density even at high temperature and high humidity
conditions owing to excellent moisture resistance brought by the
low acid value of the polyester resin. Moreover, it has good
low-temperature fixing properties, offset resistance and blocking
resistance as well as excellent resistance against sticking to a
heated roll and wax dispersibility. Thus, the electrostatic image
developing toner according to the present invention exhibits
excellent effects for permitting stable development of an image for
a long period of time under any copying circumstance.
DETAILED DESCRIPTION OF THE INVENTION
[0021] As described above, the urethane-modified polyester resin
according to the present invention is obtained using, as starting
materials, a base polyester resin (A) and low-molecular-weight
polyester resin (B) each having a predetermined acid value and
hydroxyl value.
[0022] As the base polyester resin (A), any polyester resin can be
used insofar as it has an acid value of 5 to 20 KOH mg/g and a
hydroxyl value of 40 to 70 KOH mg/g.
[0023] The base polyester resin (A) has a hydroxy value greater
than the low molecular weight polyester resin (B), and in case
these compositions react with a polycondensate compound, mainly a
urethane denaturation reaction occurs, and becomes a polyester
resin component with a heightened molecular weight.
[0024] The base polyester resin (A) is preferably prepared by
polycondensation of at least three monomers, that is, at least one
diol, at least one dicarboxylic acid and 0.5 to 20 mole %, based on
the total amount of all the starting material monomers, of at least
one polyol having three or more hydroxyl groups, with the
polycondensation in the presence of 2 to 20 mole %, based on the
total amount of all the starting material monomers, of at least one
long-chain aliphatic monocarboxylic acid or long-chain aliphatic
monoalcohol being more preferred.
[0025] As the diol to be used for the preparation of the base
polyester resin (A), any diol employed conventionally for the
preparation of polyester resins can be employed. Preferred examples
include ethylene glycol, 1,2-propylene glycol, 1,3-propylene
glycol, 1,3-butylene glycol, 1,4-butylene glycol, 2,3-butanediol,
diethylene glycol, triethylene glycol, dipropylene glycol,
1,5-pentanediol, 1,6-hexanediol, neopentyl glycol,
2-ethyl-1,3-hexanediol, hydrogenated bisphenol A, an ethylene oxide
adduct of bisphenol A and a propylene oxide adduct of bisphenol A.
As the ethylene oxide adduct of bisphenol A or propylene oxide
adduct of bisphenol A, those represented by the following formula
are preferred. 1
[0026] wherein R represents an ethylene or propylene group, x and y
each independently stands for an integer of 1 or greater, and x+y
stands for 2 to 10 on average.
[0027] As the dicarboxylic acid, any dicarboxylic acid
conventionally used for the preparation of a polyester resin can be
employed. Preferred examples include alkyldicarboxylic acids such
as malonic acid, succinic acid, glutaric acid, adipic acid, azelaic
acid and sebacic acid, unsaturated dicarboxylic acids such as
maleic acid, fumaric acid, citraconic acid and itaconic acid, and
aromatic dicarboxylic acids such as phthalic acid, terephthalic
acid, isophthalic acid and phthalic anhydride, and anhydrides and
lower alkyl esters thereof.
[0028] Examples of the polyol component having three or more
hydroxyl groups include glycerin, 2-methylpropane triol,
trimethylolpropane, trimethylolethane, sorbitol and sorbitan. In
general, when the polyol component having three or more hydroxyl
groups is added in an amount less than 0.5 mole % based on the
total amount of all the starting material monomers, molecular
weight heightening cannot be attained easily, leading to a tendency
to insufficient offset resistance. When it exceeds 20 mole %, on
the other hand, gelation tends to occur, which makes it difficult
to conduct polycondensation. Amounts within a range of 0.5 to 20
mole % are therefore preferred, with a range of 2 to 20 mole %
being more preferred.
[0029] Examples of the long-chain aliphatic monocarboxylic acid
include aliphatic monocarboxylic acids having 8 to 22 carbon atoms,
such as octanoic acid, decanoic acid, dodecanoic acid, myristic
acid, palmitic acid and stearic acid. They may be branched or have
an unsaturated group.
[0030] Exemplary long-chain aliphatic monoalcohols include
aliphatic monoalcohols having 8 to 22 carbon atoms, such as
octanol, decanol, dodecanol, myristyl alcohol, palmityl alcohol and
stearyl alcohol.
[0031] The long-chain aliphatic monocarboxylic acid or long-chain
aliphatic monoalcohol is preferably added in an amount of 2 to 20
mole %, based on the total amount of all the starting material
monomers. When the amount is less than 2 mole %, effects for
improving resistance against sticking to a heated roll and wax
dispersibility are insufficient. When the amount exceeds 20 mole %,
on the other hand, the monofunctional compound disturbs
polymerization, leading to difficulty in molecular weight
heightening. Amounts outside the above-range are therefore not
preferred. The long-chain aliphatic compounds serve to lower the
glass transition point of the resulting resin so that it is
possible to use an aromatic monocarboxylic acid such as benzoic
acid or naphthalenecarboxylic acid for the adjustment of the glass
transition point.
[0032] If necessary, polycarboxylic acids having three or more
carboxylic acids can be used and they are not excluded from the
starting materials of the base polyester resin (A).
[0033] As the low-molecular-weight polyester resin (B), any resin
can be used irrespective of its preparation process or starting
materials employed for its synthesis insofar as it has an acid
value not greater than 5 KOH mg/g, a hydroxyl value not greater
than 10 KOH mg/g and a weight-average molecular weight ranging from
3,000 to 5,000. When the low-molecular-weight polyester resin (B)
has a weight-average molecular weight less than 3,000, the
resulting toner has undesired offset resistance. From the viewpoint
of fixing property, the weight-average molecular weight is
preferred to be not greater than 5,000. Preferred examples of the
low-molecular-weight polyester resin (B) include linear polyester
resins prepared using at least one diol and at least one
dicarboxylic acid and optionally at least one monocarboxylic
acid.
[0034] Preferred examples of the diol and dicarboxylic acid used
for the preparation of the low-molecular-weight polyester resin (B)
are similar to those exemplified as the starting materials for the
preparation of the above-described base polyester resin (A).
[0035] Illustrative of the monocarboxylic acid include aliphatic
monocarboxylic acids having 8 to 22 carbon atoms, such as octanoic
acid, decanoic acid, dodecanoic acid, myristic acid, palmitic acid
and stearic acid; and aromatic monocarboxylic acids such as benzoic
acid. Among them, benzoic acid is particularly preferred.
[0036] The polycondensation for obtaining each of the base
polyester resin (A) and low-molecular-weight polyester resin (B)
can be carried out in a known manner such as polycondensation at
high temperature in a solventless manner or solution
polycondensation, each in an inert gas such as nitrogen gas. Upon
polycondensation, the using ratio of an alcohol (monoalcohol, diol,
triol or the like) to a carboxylic acid (dicarboxylic acid,
monocarboxylic acid or the like) ordinarily ranges from 0.7 to 1.4
as a ratio of the hydroxyl group of the former to the carboxyl
group of the latter.
[0037] The urethane-modified polyester resin (C) of the present
invention having a total acid value not greater than 10 KOH mg/g is
prepared by reacting the base polyester resin (A) and the
low-molecular-weight polyester resin (B) with a polyisocyanate
compound. When the low-molecular-weight polyester resin (B) is used
in an excessively large amount, the resulting urethane-modified
polyester resin (C), serving as a binder resin for the
electrostatic image developing toner deteriorates the offset
resistance of toner. Excessively large amounts of the base
polyester resin (A), on the other hand, tend to deteriorate the
low-temperature fixing properties of the toner. The mixing ratio of
the base polyester resin (A): the low-molecular-weight polyester
resin (B) is preferably 3 to 5:7 to 5. The total acid value of the
urethane-modified polyester resin (C) exceeding 10 KOH mg/g is not
preferred, because it lowers the charged amount of the toner
containing the resulting urethane-modified polyester resin (C),
which makes it impossible to form a developed image having a
sufficient density even if the temperature and humidity conditions
are not high.
[0038] Examples of the polyisocyanate compound include
diisocyanates such as hexamethylene diisocyanate, isophorone
diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate,
xylylene diisocyanate and tetramethylene diisocyanate; and
isocyanates represented by the following formulas (1) to (5),
respectively. 2
[0039] wherein R.sub.1 represents an alkyl group, and R.sub.2
represents an alkylene group.
[0040] The polyisocyanate is used in an amount of 0.2 to 1.2
equivalents, preferably 0.3 to 1.0 equivalent, in terms of an
isocyanate group, per equivalent of the hydroxyl groups of all the
polyester resins.
[0041] The base polyester resin (A), low-molecular-weight polyester
resin (B) and polyisocyanate compound are reacted by mixing in a
molten state. Preferred is a process to effect the reaction by
adding the polyisocyanate compound to the kneaded mixture of the
base polyester resin (A) and low-molecular-weight polyester resin
(B), each of which has been molten in advance, and then kneading
the resulting mixture in a molten state. Described specifically,
this kneading in a molten state is carried out by pouring a mixture
of the base polyester resin (A) and low-molecular-weight polyester
resin (B) in a twin-screw extruder at a fixed speed and at the same
time, pouring the polyisocyanate at a fixed speed; or by pouring
the low-molecular-weight polyester resin (B), base polyester resin
(A) and polyisocyanate successively in the traveling direction of
the twin screw extruder and reacting them while carrying out
kneading and delivery, for example, at a temperature of 100 to
200.degree. C. At this time, the low-molecular-weight polyester
resin (B) and base polyester resin (A) which are reaction starting
materials to be charged or poured into the twin-screw extruder may
be poured directly into the extruder from the respective reaction
containers without cooling; or a resin once prepared from these
starting materials is fed to a twin screw kneader after cooled and
pulverized or formed into beads. In the present invention, however,
a process for preparing the urethane-modified polyester resin (C)
is not limited to the above-exemplified processes. It is needless
to say that the reaction can be carried out by a proper process,
for example, a conventionally known process of charging raw
materials in a reaction container, heating them so as to convert it
into the solution form and then mixing.
[0042] The urethane-modified polyester resin (C) used in the
present invention preferably has a gel content of 0.1 to 25 wt. %.
The gel content is determined by mixing 5 g of the resin with 100
ml of ethyl acetate for 4 hours, allowing the resulting mixture to
stand overnight, quietly collecting the supernatant from the
reaction mixture by a dropping pipette and then measuring the
amount of the polymer dissolved in the solvent in terms of a
nonvolatile content.
[0043] The term "acid value" as used herein means the number of mg
of potassium hydroxide necessary for neutralizing 1 g of a resin,
while the term "hydroxyl value" means the number of mg of potassium
hydroxide necessary for neutralizing 1 g of the acid consumed for
the reaction between the hydroxyl group of the resin with phthalic
anhydride.
[0044] In the electrostatic image developing toner according to the
present invention, materials ordinarily employed for the
preparation of a toner, for example, a known binder resin (other
than the urethane-modified polyester resin (C)), charge control
agent, colorant, wax, magnetic material, abrasive and fluidizing
agent can be incorporated as needed.
[0045] As the known binder resin to be used together with the
above-described urethane-modified polyester resin (C), binder resin
conventionally employed for electrostatic image developing toners
can be used insofar as it is known to date. Examples include
homopolymers of styrene or substituted styrene such as polystyrene,
poly-p-chlorostyrene and polyvinyl toluene; styrene copolymers such
as styrene-p-chlorostyrene copolymer, styrene-vinyl toluene
copolymer, styrene-vinyl naphthalene copolymer, styrene-acrylate
copolymer, styrene-methacrylate copolymer,
styrene-methyl-.alpha.-chloromethacrylate copolymer,
styrene-acrylonitrile copolymer, styrene-vinyl methyl ether
copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl
methyl ketone copolymer, styrene-butadiene copolymer,
styrene-isoprene copolymer and styrene-acrylonitrile-indene
copolymer; and resins such as polyvinyl chloride resin, phenol
resin, naturally modified phenol resin, natural-resin-modified
maleic acid resin, acrylic resin, methacrylic resin, polyvinyl
acetate resin, silicone resin, polyester resins other than the
above-described urethane-modified polyester resin (C), polyurethane
resin, polyamide resin, furan resin, epoxy resin, xylene resin,
polyvinyl butyral, terpene resin, coumarone indene resin,
petroleum-base resin and cross-linked styrene base copolymer.
[0046] As the charge control agent, known charge control agents can
be used either singly or in combination. It is added in an amount
permitting the toner to have a desired charge amount. For example,
it is preferably added in an amount of about 0.05 to 10 parts by
weight based on 100 parts by weight of the binder resin. Examples
of the positive charge control agent include Nigrosine dyes,
quaternary ammonium salt compounds, triphenylmethane compounds,
imidazole compounds and polyamine resins. Illustrative of the
negative charge control agent include azo dyes containing a metal
such as Cr, Co, Al and Fe, salicylic acid metal compounds,
alkylsalicylic acid metal compounds and calix arene compounds.
[0047] As the colorant usable for the electrostatic image
developing toner of the present invention, any colorant known to be
used conventionally for the preparation of a toner can be employed.
Examples include metal salts of a fatty acid, various carbon blacks
and dyes or pigments such as phthalocyanine, rohdamine,
quinacridone, triallylmethane, anthraquinone, azo and diazo. These
colorants may be used either singly or in combination.
[0048] As the magnetic material usable for the electrostatic image
developing toner of the present invention, any
ferroelectric-element-cont- aining alloy, compound or the like
conventionally used for the preparation of a magnetic toner can be
employed. Exemplary magnetic materials include iron oxide or
compounds of a divalent metal and iron oxide such as magnetite,
maghemite and ferrite; and metals such as iron, cobalt and nickel
and alloys thereof with a metal such as aluminum, cobalt, copper,
lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium,
calcium, manganese, selenium, titanium, tungsten or vanadium; and
mixtures thereof. These magnetic materials are preferred to have an
average particle size of 0.1 to 2 .mu.m, more preferably about 0.1
to 0.5 .mu.m. The content of the magnetic material in the toner is
usually about 20 to 200 parts by wt., preferably 40 to 150 parts by
wt. based on 100 parts by wt. of the binder resin. The saturation
magnetization of the toner is preferably 15 to 35 emu/g (measuring
magnetic field: 1 kilo oersted).
[0049] To the toner of the present invention, known additives
conventionally used for the preparation of a toner such as release
agent, lubricant, fluidity improver, abrasive, conductivity
imparting agent, image peeling preventive or the like can be added
further internally or externally as needed. Examples of the release
agent include waxes such as low-molecular-weight polyethylene,
low-molecular-weight polypropylene, microcrystalline wax, carnauba
wax, sazole wax and paraffin wax. The release agent is generally
added to the toner in an amount of about 0.5 to 5 wt. %. Examples
of the lubricant include polyvinylidene fluoride and zinc stearate.
Those of the fluidity improver include colloidal silica, aluminum
oxide and titanium oxide. Those of the abrasive include cerium
oxide, silicon carbonate, strontium titanate, tungsten carbide and
calcium carbonate. Those of the conductivity imparting agent
include carbon black and tin oxide. Fine powders of a
fluorine-containing polymer such as polyvinylidene fluoride are
preferred from the viewpoints of fluidity, grindability and charge
stability.
[0050] The toner according to the present invention can be prepared
in a conventionally known manner. In general, it is preferred to
prepare the toner by sufficiently mixing toner component materials
as described above in a mixer such as ball mill or Henschel mixer,
kneading the resulting mixture well in a heated kneader such as
heated roll kneader or single-screw or twin-screw extruder, cooling
and solidifying the resulting kneaded mass, roughly pulverizing the
mass by a pulverizer such as hammer mill, finely pulverizing the
resulting coarse particles by a jet mill or the like and then
classifying the resulting particles. The preparation process of the
toner is not limited to the above-described process. It is also
possible to prepare the toner by another process, for example, a
process of dispersing, in a binder resin solution, the other toner
component materials, followed by spray drying; the so-called
microcapsule method; or a polymerization-dependent process in which
monomers, which will form a binder resin, are mixed with
predetermined materials and then the resulting mixture is subjected
to emulsion or suspension polymerization.
[0051] The toner according to the present invention can be used as
a two-component developer after mixed with a carrier or as a
one-component developer or microtoning developer having magnetic
powders incorporated in the toner. When the toner of the present
invention is employed as a two-component developer, any
conventionally-known carrier can be used. Examples include magnetic
powders such as iron powders, ferrite powders and nickel powders
and glass beads, and these powders having a surface treated with a
resin. Examples of the resin for covering the surface of the
carrier include styrene-acrylate copolymers, styrene-methacrylate
copolymers, acrylate copolymers, methacrylate copolymers,
fluorine-containing resins, silicon-containing resins, polyamide
resins, ionomer resins and polyphenylene sulfide resins; and
mixtures thereof. Among them, fluorine-containing resins and
silicone-containing resins are particularly preferred for they do
not form a spent toner so much.
[0052] The toner according to the present invention preferably has
a weight-average particle size of 3 to 15 .mu.m. From the viewpoint
of developing properties, more preferred is a toner containing 12
to 60 toner particles % having a particle size not greater than 5
.mu.m, 1 to 33 toner particles % having a particle size of 8 to
12.7 .mu.m, 2.0 wt. % or less of toner particles having a particle
size not less than 16 .mu.m and has a weight-average particle size
of 4 to 10 .mu.m. The particle size distribution of the toner can
be measured using, for example, a Coulter counter.
EXAMPLES
[0053] The present invention will hereinafter be described more
specifically by examples, which are intended to be purely exemplary
of the invention and the present invention is not limited to or by
the following examples.
[0054] Preparation of a Base Polyester Resin (A)
Preparation Example A1
[0055] In a 5-liter four-necked flask equipped with a reflux
condenser, water separator, nitrogen gas inlet tube, thermometer
and stirrer, 40.6 mole % of "Polyol KB300" (trade name; propylene
oxide adduct of bisphenol A prepared by Mitsui Chemicals Co.;
Ltd.), 10.2 mole % of trimethylolpropane, 4.8 mole % of stearic
acid and 44.4 mole % of isophthalic acid were charged. While
introducing nitrogen into the flask, dehydration condensation was
carried out at 180 to 240.degree. C.
[0056] When the acid value and hydroxyl value of the reaction
product each reached a predetermined value, the reaction mixture
was taken out from the flask, cooled and pulverized, whereby a base
polyester resin A1 was obtained. Its physical properties are shown
in Table 1.
Preparation Examples A2 to A5
[0057] In a similar manner to Preparation Example A1 except that
the kinds and amounts (molar ratios) of the carboxylic
acid-compounds and alcohol compounds used as starting materials
were changed as described in Table 1, base polyester resins A2 to
A5 were prepared. Their physical properties are shown in Table
1.
1TABLE 1 Preparation Example A1 A2 A3 A4 A5 (Molar ratios of
starting materials) mol % Polyol KB 300 40.6 15.3 24.1 24.7 40.6
Trimethylolpropane 10.2 4.3 4.3 2.1 10.2 Diethylene glycol 0.0 34.0
25.2 24.7 0.0 Stearic acid 4.8 0.0 0.0 0.0 4.8 Isophthalic acid
44.4 46.4 46.4 48.5 44.4 (Physical properties) Acid value (KOH mg)
13.0 0.3 0.8 9.5 17.2 Hydroxyl value (KOH mg) 55.3 47.7 45.2 53.4
58.7 Tg (.degree. C.) 40.8 26.1 36.3 35.6 32.1 Mw 9100 15100 12900
7300 21000
[0058] Preparation of a Low-molecular-weight Polyester Resin
(B)
Preparation Examples B1 to B5
[0059] In a similar manner to Preparation Example A1 except that
the kinds and amounts (molar, ratios) of the carboxylic acid
compounds and alcohol compounds used as starting materials were
changed as described in Table 2, low-molecular-weight polyester
resins B1 to B5 were prepared. Their physical properties are shown
in Table 2.
2 TABLE 2 B1 B2 B3 B4 B5 (Molar ratios of the starting materials)
Polyol KB 300 44.9 46.1 45.3 47.7 46.3 Benzoic acid 20.5 15.2 8.4
0.0 11.1 lsophthalic acid 0.0 0.0 46.3 0.0 42.6 Terephthalic acid
34.6 38.7 0.0 0.0 0.0 DMT 0.0 0.0 0.0 52.3 0.0 (Physical
properties) Acid value (KOH mg) 4.4 3.6 26.4 2.7 7.5 Hydroxyl value
KOH mg 4.8 5.0 3.8 4.2 3.9 Tg (.degree. C.) 46.0 57.0 56.2 49.0
52.3 MW 4700 5900 4700 4900 4800 DMT: dimethyl terephthalate
[0060] Preparation of an Urethane-modified Polyester Resin (C)
Example 1
[0061] To a twin screw kneader ("KEX-40", trade name; manufactured
by Kurimoto, Ltd.), 60 wt. % of the low-molecular-weight polyester
resin B1 was fed at a flow rate of 6 kg/hr, followed by feeding of
40 wt. % of the base polyester resin A1 at a flow rate of 4 kg/hr.
The resulting mixture was kneaded and delivered under a molten
state. To the resulting resin mixture under kneading and delivery,
tolylene diisocyanate was fed at a flow rate of 320 g/hr (the
NCO/OH equivalent ratio corresponded to 0.82. A NCO/OH equivalent
ratio=(an equivalent of NCO group of tolylene diisocyanate
supplied/hr)/(an equivalent of OH group of the resin
supplied/hr)=((320/176).times.2/(55.3.times.4+4.8.times.6)/56.11)=0.816).
Kneading was continued to effect the reaction and the resulting
kneaded mass was extruded and then cooled, whereby a
urethane-modified polyester resin C1 was obtained. Its physical
properties are shown in Table 3.
Examples 2 to 5
[0062] In a similar manner to Example 1 except that the kind and
mixing ratio of each of the base polyester resin (A) and
low-molecular-weight polyester resin (B) were changed as shown in
Table 3, polyurethane-modified polyester resins C2 to C5 were
obtained. Their physical properties are shown in Table 3.
Comparative Examples 1 to 6
[0063] In a similar manner to Example 1 except that A1 to A5 were
used as the base polyester resin, B1, B2, B3 and B5 were used as
the low-molecular-weight polyester resin (B), combination and
mixing ratio were in accordance with those described in the columns
of C6 to C11, and tolylene diisocyanate was fed at a flow rate as
described in Table 3, urethane-modified polyester resins C6 to C11
were obtained. Their physical properties are shown in Table 3.
3TABLE 3 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Urethane- C1 C2 C3 C4 C5
modified polyester resin (C) Polyester A A1 A1 A1 A1 A4 Polyester B
B1 B1 B1 B4 B1 A/B mixing 4/6 4.5/5.5 3.5/6.5 4/6 4/6 ratio Amount
of A 4 4.5 3.5 4 4 fed (kg/h) Amount of B 6 5.5 6.5 6 6 fed (kg/h)
Amount of TDI 320 330 310 300 300 fed (g/h) Amount of TDI 0.82 0.76
0.88 0.78 0.81 (NCO/OH equivalent ratio) Total acid 8 8 7 7 6 value
Tg (.degree. C.) 56.2 56.7 56.5 56.7 57.2 Comp. Comp. Comp. Comp.
Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Urethane- C6 C7 C8
C9 C10 C11 modified polyester resin (C) Polyester A A3 A3 A2 A1 A4
A5 Polyester B B1 B2 B3 22 B5 B1 A/B mixing 3/7 3/7 3/7 4/6 4/6 5/5
ratio Amount of A 3 3 3 4 4 5 fed (kg/h) Amount of B 7 7 7 6 6 5
fed (kg/h) Amount of TDI 210 210 180 300 300 300 fed (g/h) Amount
of TDI 0.79 0.78 0.68 0.76 0.81 0.62 (NCO/OH equivalent ratio)
Total acid 3 3 19 7 8 11 value Tg (.degree. C.) 53.6 57.1 55.7 59.8
60.2 52.7
[0064] Evaluation of the Urethane-modified Polyester Resin:
Example 6
[0065]
4 Urethane-modified polyester resin C1 57.5 parts by wt. Magnetic
material (magnetite) 38.0 parts by wt. Charge control agent
(metal-containing chromium 1.5 parts by wt. dye; "Spiron Black
TRH", trade name; product of Hodogaya Chemical Co., Ltd.) Wax
(polyolefin wax, "Mitsui Highwax 3.0 parts by wt. NP 105", trade
name; product of Mitsui Chemicals Co., Ltd.)
[0066] The above-described materials were mixed in a Henschel mixer
and then charged and kneaded in a twin-screw heating kneader. The
extrudate was cooled to room temperature, roughly pulverized in a
hammer mill and then finely pulverized in a jet mill pulverizer.
The finely-pulverized particles were introduced into a classifier,
whereby a magnetic toner having an average particle size of 12.5
.mu.m and containing 1.0 vol. % or less of particles having a
particle size not greater than 6.4 .mu.m and 1.0 vol. % or less of
particles having a particle size not less than 20.0 .mu.m. To 100
parts by weight of the resulting toner particles, 0.3 part by
weight of hydrophobic silica ("Aerosil R-972", trade name; product
of Nippon Aerosil Co., Ltd.) was added, followed by mixing, whereby
a one-component magnetic developer was obtained.
[0067] The charge properties and image forming properties of the
resulting one-component magnetic developer were evaluated and the
results are shown in Table 4. As can be seen from Table 4, the
developer obtained in this example is good in both of the charged
amount and image density.
[0068] The charge properties and image forming properties were each
evaluated as follows:
[0069] (Charged Amount)
[0070] In a 50-cc polyethylene bottle, 1 g of the one-component
magnetic developer and 19 g of non-coat ferrite carrier were
charged and they were mixed for 30 minutes. The charged amount of
the toner was then measured using a blow-off powder charge amount
measuring device (manufactured by Toshiba Chemical
Corporation).
[0071] (Test on Image Forming Properties)
[0072] Using "NP-6650" manufactured by Cannon Corp. as a copying
machine, 30,000 copies were made at normal temperature and normal
humidity (23.degree. C., 50%) (N/N), while 5,000 copies were made
at high temperature and high humidity (30.degree. C., 85%) (H/H).
The image density of each of the first copy and the 30,000th copy
or 5,000th copy was measured.
Examples 7 to 10
[0073] In a similar manner to Example 6 except for the use of the
urethane-modified polyester resin C2 to C5 instead of the
urethane-modified polyester resin C1, a one-component magnetic
developer was obtained. The resulting developer was evaluated as in
Example 6 and the results are shown in Table 4. As is apparent from
Table 4, each of the developers obtained in Examples 7 to 10 is
excellent in charged amount, image density, durability and
environmental stability.
Comparative Examples 7 to 12
[0074] In a similar manner to Example 6 except for the use of
urethane-modified polyester resins C6 to C11 instead of the
urethane-modified polyester resin C1, one-component magnetic
developers were obtained. The resulting developers were evaluated
as in Example 6 and the results are shown in Table 4. As is
apparent from Table 4, the developers obtained in Comparative
Examples 7 to 12 are inferior to those obtained in Examples 6 to 10
both in charged amount and density of developed image.
5TABLE 4 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Urethane-modified polyester
C1 C2 C3 C4 C5 resin (C) Charged amount (.mu.C/g) 13.5 13.7 13.6
13.4 13.5 Image density (N/N) Initial stage 1.28 1.30 1.31 1.30
1.30 30,000-th copy 1.38 1.39 1.38 1.38 1.39 Image density (H/H)
Initial stage 1.25 1.26 1.24 1.27 1.26 5,000-th copy 1.33 1.30 1.31
1.32 1.31 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 7 Ex. 8 Ex. 9 Ex.
10 Ex. 11 Ex. 12 Urethane- C6 C7 C8 C9 C10 C11 modified polyester
resin (C) Amount of 14.0 14.2 14.0 13.8 14.1 14.2 electricity
charged (.mu.C/g) Image density (N/N) Initial stage 1.32 1.32 1.30
1.30 1.30 1.33 After 30,000 1.25 1.25 1.24 1.37 1.24 1.23 copies
Image density (H/H) Initial stage 1.25 1.25 1.24 1.27 1.25 1.27
After 5,000 1.20 1.20 1.18 1.32 1.20 1.20 copies
[0075]
6TABLE 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Lowest fixing tem- 160<
160< 160< 160< 160< perature (.degree. C.) Offset
appearing tem- >240 >240 >240 >240 >240 perature
(.degree. C.) Blocking resistance A A A A A Wax dispersibility A A
A A B Resistance against A A A A B sticking to heated roll Comp.
Comp. Comp. Comp. Comp. Comp. Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex.
12 Lowest fixing 170< 180< 160< 180< 160< 160<
temperature (.degree. C.) Offset appear- >230 >230 >240
>230 >240 >240 ing temperature (.degree. C.) Blocking A A
A A A A resistance Wax dis- C C C A C B persibility Resistance C C
C C C B against sticking to heated roll
[0076] With regards to the toners obtained in Examples 6 to and
Comparative Examples 7 to 12, lowest fixing temperature, offset
appearing temperature, blocking resistance, wax dispersibility and
resistance against sticking to a heated roll were studied. The
results are shown in Table 5. Evaluation was carried out as
follows:
[0077] (Lowest Fixing Temperature)
[0078] Using "NP-6650" (trade name; manufactured by Cannon Corp.)
as a testing machine, each of the toners was fixed and the lowest
fixing temperature which permitted fixation without causing
low-temperature offset was taken as the lowest fixing
temperature.
[0079] (Offset Appearing Temperature)
[0080] The temperature at which high-temperature offset occurred
was taken as the offset appearing temperature.
[0081] (Blocking Resistance)
[0082] In a wide-mouthed bottle, 50 g of each of the developers was
charged and allowed to stand at 50.degree. C. for 24 hours. Then,
the temperature was caused to rise back to room temperature and
existence of a large caking in the developer was visually
evaluated.
[0083] A: No large caking
[0084] B: There exists a large caking but it can be loosened
easily.
[0085] C: There exists a large mass which cannot be loosened
easily.
[0086] (Wax Dispersibility)
[0087] The toner particles was observed by a transmission electron
microscope. The toner particles which were confirmed to contain
particles having a wax particle size not less than 5 .mu.m were
evaluated as C, those which were confirmed to contain even a small
amount of particles having a wax particle size not less than 5
.mu.m were evaluated as B and those containing particles having
smaller particle size than the above ones were evaluated as A.
[0088] (Resistance Against Sticking to a Heated Roll)
[0089] Sticking of a sheet of paper to a heated roll was observed
at around the lowest fixing temperature and the toner was evaluated
as C when eminent sticking was observed, as B when sticking was
observed but not so eminent and as C when no sticking occurred.
* * * * *