Toner for developing electrostatic latent image containing copolymer of vinyl compound and acid monomer

A toner for developing an electrostatic latent image characterized by a vinyl copolymer whose acid value is in the range of about 5 to 100.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a toner used to develop an electrostatic latent 
image such as by electrophotography, electrostatic recording, 
electrostatic printing or similar techniques. 
2. Description of the Prior Art 
In the reproduction of copies from originals, generally an electrostatic 
image is first formed on a photosensitive medium or a dielectric film 
which is then developed by deposition with fine powder called a toner 
which is made of a colorant dispersed in a binder resin. After 
transferring the toner image to the surface of a support such as paper, 
the transferred image is perpetually fixed on the support surface such as 
by application of heat, to give a copy. A solvent treatment or a finish 
coating treatment has been used to fix a toner image, however, it is a 
more common practice to use a heat fixing method in which a toner image is 
heated up to a temperature at which the toner is capable of flowing so as 
to permit the toner to be fusingly attached to the support, thereby giving 
a final copy of the toner image. 
In an attempt to speed up the duplication, a so-called heat roll fixing 
method has come into practice in which a toner image-bearing support is 
passed between a pair of rolls, i.e., a heat roll and a press roll, to fix 
it under heating and pressing conditions. The heat roll fixing method is 
higher in heat efficiency, lower in heat emission and quicker for fixation 
than other heat fixing methods, and is thus very effective. In this 
method, however, the toner image is brought to contact with the rolls, so 
that part of the toner image is apt to attach to the heat roll, causing 
the so-called offset phenomenon. 
In order to inhibit the offset phenomenon, the surfaces of the rolls are 
usually covered with a material with an excellent releasing property such 
as a fluorine-contained resin and treated with an offset-inhibiting liquid 
such as a silicon oil. The application of the offset-inhibiting liquid in 
turn requires a device for consistently feeding a given amount of the 
offset-inhibiting liquid to the roll surface, coupled with the 
disadvantages that leakage of oil takes place and that silicon oil 
emanates an offensive odor on heating. 
In recent years, attempts have accordingly been made to make the heat roll 
fixation feasible without use of any offset-inhibiting liquid. For 
instance, a method is described in Japanese Patent Publication No. 5549/78 
(U.S. Pat. No. 3,666,247). Attempts to realize this feasibility by 
improvement of the toner are described in Japanese patent application 
(OPI) No. 65231/74 (British Pat. No. 1,442,835). 
In Japanese Application (OPI) No. 65231/74, a mixture of a styrene resin 
and a low molecular weight polypropylene is used as a binder resin for the 
toner. On heating for fixation, the low molecular weight polypropylene 
turns into a liquid of low viscosity and is released on the toner surface 
where it covers the toner, and inhibits the offset phenomenon due to the 
releasing property of the polypropylene itself. According to this 
disclosure, it appears that offset-free, heat roll fixing is possible 
without the use of any offset-inhibiting liquid. However, this technique 
has a number of disadvantages. Poor compatibility of the styrene resin 
with the polypropylene results in the composition of toner particles 
becoming non-uniform (i.e., non-homogeneous). Furthermore, differences in 
the triboelectric charging properties of the toner particles leads to a 
reduction in developability, and results in a short lifetime or in a 
tendency for the toners to aggregate. 
Accordingly, there is a need for a toner which is readily fixed and can 
prevent offset without the use of an offset-inhibiting liquid, and which 
exhibits good developability and cleanability and provides a homogeneous 
toner composition having good workability. 
SUMMARY OF THE INVENTION 
Accordingly one object of the present invention is the provision of a toner 
which can be readily fixed and prevents the offset phenomenon without 
using any offset-inhibiting liquid and which is applicable to heat roll 
fixation. 
Another object of the present invention is to provide a toner which has 
good developability and is particularly stable in its triboelectric 
charging property. 
A further object of this invention is to provide a toner which does not 
form a toner film on, for example, a photosensitive medium and shows good 
cleanability. 
A still further object of this invention is to provide a toner which is 
improved in kneadability and milling ability at the time of toner 
production and also in the deposition of toner on rotor or the like means. 
Another object of the present invention is to provide a toner which is free 
of a contaminating carrier and shows no tendency to aggregate. 
The above objects of the invention are achieved using, as a binder resin 
for the toner, a vinyl copolymer whose acid value is in the range of from 
about 5 to 100, and preferably from 10 to 40.

DETAILED DESCRIPTION OF THE INVENTION 
The vinyl copolymer whose acid value is in the range of 5 to 100 is a 
copolymer obtained by copolymerizing a vinyl monomer and an acid monomer 
copolymerizable with the vinyl monomer. The copolymer can be obtained by 
copolymerizing one or more vinyl monomers with a copolymerizable acid. 
The vinyl monomers useful in the present invention are those having a 
polymerizable vinyl bond of the formula CH.sub.2 .dbd.CH-- in the 
structural formula. Examples of such vinyl monomer include styrenes such 
as styrene, chlorostyrene, .alpha.-methylene and the like; monocarboxylic 
acid esters such as methyl methacrylate, ethyl methacrylate, n-butyl 
methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, dodecyl 
acrylate, 2-chloroethyl acrylate and the like; vinyl halides such as vinyl 
chloride, vinyl bromide, vinyl fluoride and the like; vinyl esters such as 
vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate and the 
like; acrylic or methacrylic derivatives such as acrylonitrile, 
methacrylonitrile, acrylamide and the like; vinyl ethers such as vinyl 
methyl ether, vinyl ethyl ether, vinyl isobutyl ether and the like; vinyl 
naphthalenes; vinylketones such as methyl vinyl ketone, hexyl vinyl 
ketone, methyl isopropenyl ketone and the like; and N-vinyl compounds such 
as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidone and 
the like. These compounds may be used alone or in combination of two or 
more as the vinyl monomers. 
The copolymerizable acids have a polymerizable bond such as a double bond 
and include, for example, acrylic acid, methacrylic acid, 
.alpha.-chloroacrylic acid, .alpha.-bromoacrylic acid, 
.alpha.-acylamidoacrylic acid, .alpha.-benzamidoacrylic acid, 
.alpha.-phenylacetamidoacrylic acid, .alpha.-ethylacrylic acid, crotonic 
acid and the like. 
The acid value is the amount (mg) of potassium hydroxide required to 
neutralize the acid contained in 1 g of resin. 
One or more of the vinyl monomers may be copolymerized with the 
polymerizable acid monomer by solution polymerization, bulk polymerization 
or suspension polymerization. On copolymerization the mixing ratio should 
be suitably adjusted so that the resulting copolymer has an acid value of 
5 to 100. Though the mixing ratio varies depending on the type and number 
of monomer used, it is important that the mixing ratio is so determined 
that the prepared copolymer has an acid value of 5 to 100. 
For instance, when styrene is used as the vinyl monomer and acrylic acid as 
the polymerizable acid, the amount of the acrylic acid is in the range of 
about 1 to 17 mole % of the total amount of the monomers. 
The copolymer preferably has a glass transition temperature of 40.degree. 
to 70.degree. C. Glass transition temperatures lower than 40.degree. C. 
tend to cause the toner particles to aggregate during storage. On the 
other hand, glass transition temperatures higher than 70.degree. C. 
require higher fixing temperatures making it difficult to readily fix the 
toner. 
As for the molecular weight, it is desired that the weight, it is desired 
that the weight average molecular weight Mw of the polymer is in the range 
of about 50,000 to 500,000, preferably about 80,000 to 300,000, the number 
average molecular weight (Mn) is in the range of about 5,000 to 20,000, 
preferably about 10,000 to 20,000, and the ratio Mw/Mn of the weight 
average molecular weight to the number average molecular weight is in the 
range of about 4 to 30, preferably about 8 to 30. In accordance with the 
present invention the Mw/Mn range may be wider than in the case of no 
acid. In other words, in order to obtain a toner which shows good heat 
roll adaptability, the molecular weight distribution should be as wide as 
possible. A wide Mw/Mn range is desirable in a toner in order to provide a 
broad fusing latitude, which results from the low molecular weight region 
contributing to the low-temperature fixing property, and the high 
molecular weight region contributing to offset-inhibiting property. In 
order to broaden the Mw/Mn range, the weight average molecular weight, Mw, 
is generally increased to high value. To this end, a specific means or 
method is frequently required for the polymerization requiring that the 
heating conditions be continuously or intermittently varied. 
When the copolymer contains an acid as in the present invention, by 
suitable selection of the amount of the acid it is not necessarily 
required that the molecular weight distribution is widened or the weight 
average molecular weight is increased, which results in higher effects as 
compared to the conventional methods. As desired, there may be used a 
copolymer of wider molecular weight distribution or larger weight average 
molecular weight. 
One of the prominent features of the present invention resides in the use 
of a vinyl polymer as a binder resin for the toner. The use of the vinyl 
polymer is advantageous in offset-inhibiting ability in comparison to 
condensate resins such as polyester or an epoxy resin. Another feature of 
the present invention resides in that the acid value is in the range of 
about 5 to 100, i.e., in the specific content of acid in the binder resin. 
Preferably, the acid value is from 10 to 40. The acid value so specified 
produces a more pronounced offset-inhibiting effect without increasing the 
molecular weight of the vinyl copolymer. The introduction of the acid into 
the copolymer imparts good negative charging property to the copolymer. 
A further feature of this invention resides in the use of a copolymer as 
the binder resin. That is, toner for heat roll fixing described in 
Japanese Application (OPI) No. 65231/74 which serves to prevent occurrence 
of the offset phenomenon without use of any offset-inhibiting liquid makes 
use of a mixture of resins, as opposed to a copolymer, and presents a 
problem of compatability. Further, when the mixture is milled to provide 
toner particles, the individual toner particles obtained are inhomogeneous 
(i.e., aggregate into various sized clusters) which deterimentally affects 
triboelectric charging property, i.e., the triboelectric charging property 
of the resulting toner particles differ from each other, and the fixing 
property therefore varies. On the other hand, the claimed invention is 
free from such problem. In this connection, however, since, according to 
the present invention, the copolymer is used as the binder resin and the 
toner particles of a size on the order of a micron which are much greater 
than molecules in the order of an angstrom have a uniform composition 
leading to stable production and development. 
The copolymer according to the invention may be used alone as a binder 
resin of the toner. Alternatively, it may be used with other resins. In 
the latter case, care must be paid to a combination of resins and a mixing 
ratio to avoid the problem of poor compatability inhomogenity previously 
described. When using in combination with other resin, the vinyl copolymer 
according to the invention should make up a major proportion of the binder 
resin and preferably makes up more than about 80% by weight of the total 
binder resin. 
The vinyl copolymer resin having an acid value of 5 to 100 is mixed with a 
colorant and then finely powder to give a toner. 
Any suitable dye or pigment may be used as the colorant in an amount 
sufficient to color the binder resin therewith. The amount is generally in 
a range up to about 25 wt %, preferably about 1 to 20% by weight, of the 
toner. 
Useful colorant include, for example, carbon black, Nigrosine dyes, Aniline 
Blue, Alkoyl Blue, Chrome Yellow, Ultramarine Blue, Du Pont Oil Red, 
Quinoline Yellow, Methylene Blue, Phthalocyanine Blue, Malachite Green, 
Lamp Black, Rose Bengale and the like. The vinyl copolymer having an acid 
value of 5 to 100 is admixed with a colorant such as a dye or pigment and 
finely milled to give a toner for developing electrostatic latent image. 
Any known method can be used to uniformly disperse the colorant in the 
binder resin to obtain toner particles. For example, the binder resin and 
colorant may be melted and kneaded, then hardened by cooling, and finely 
milled such as by a jet milling machine to give particles of a size 
usually employed as a toner. Typically, the particles have an average size 
below about 30.mu., preferably about 10 to 20.mu.. The binder resin and 
colorant dissolved in solvent may be spray-dried to give a fine powder of 
a toner. The toner is then mixed with a carrier to form a developer. The 
toner may be admixed with a magnetic powder to give a developer without 
the use of any carrier. 
The developer is brought into contact with an electrostatic latent 
image-bearing photosensitive medium or dielectric film by a cascade 
developing method or a magnetic brush developing method to yield a visual 
toner image. The thus obtained toner image is transferred to a support 
such as paper. The toner image-bearing support is passed between a pair of 
heat rollers, i.e., a heat roll and a press roll. The roll which contacts 
with the toner image is covered on its surface with a fluorine-contained 
resin such as Teflon (a product of E. I. Du Pont de Nemours & Co., Ltd.) 
or a silicon rubber, or has a metal surface, to which no offset-inhibiting 
liquid is fed. After passage of the support between the rolls, the toner 
image is everlasting fixed on the support. When the toner according to 
this invention is used, no deposition of the toner on the roll or the 
support takes place even though no offset inhibiting liquid is used. 
A magnetic powder can also be incorporated with the binder and colorant. 
This is done when it is desired to carry out the development without using 
a carrier. Examples of magnetic powders which can be used are powders of 
metals, e.g., iron, manganese, nickel, cobalt, chromium, etc.; alloys, 
e.g., ferrite, magnetite, etc.; and other strongly magnetic materials. A 
suitable amount of the magnetic powder is about 10 to 70% by weight of the 
weight of the toner. 
When the vinyl copolymer having an acid value of 5 to 100 is used as the 
toner binder resin, the toner shows a pronounced characteristic effect of 
development of electrostatic latent image. This is more pronounced when 
the toner is applied to a heat roll fixing method using no 
offset-inhibiting liquid. Needless to say, use of the vinyl copolymer is 
favorable in view of excellent developability, cleanability and 
producibility of the toner. 
The reason the vinyl copolymer having an acid value of 5 to 100 shows such 
favorable characteristics when applied as a toner is considered as 
follows. Since an acid is contained in a specified amount, an 
intermolecular coagulating force by the action of, for example, hydrogen 
bonds is produced. This is supported, as shown in Example 1 appearing 
herein, by a fact that three types of polymers which have the same 
component ratios but are different in the amount of acid alone and for 
which the differences in the theoretical glass temperature T.sub.g is 
about 2.degree. to 3.degree. C. exhibit a drastically increased measured 
glass transition temperature T.sub.g with an increase of amount of the 
acid. 
Taking into account the fact that the glass transition temperature usually 
increases with an increase in the degree of crosslinking or the molecular 
weight, it is believed that the introduction of the acid into the polymer 
shows similar effects as in the case of increasing the molecular weight of 
the polymer but the actual molecular weight is not so that good fixability 
can not be achieved. 
The present invention will be particularly illustrated by way of the 
following examples. 
EXAMPLE 1 
Resin Preparation 
I-a (Vinyl Copolymer for Comparison) 
300 ml of toluene was added to 1 l four neck distillation flask to which 
was further added 3 g of azobisisobutyronitrile. An initial reaction 
mixture composed of 120 g of styrene, 60 g of methyl methacrylate and 120 
g of iso-butyl methacrylate was dripped from one port of the four neck 
distillation flask at a constant dropping rate, followed by polymerizing 
while agitating at the refluxing temperature (111.degree. C.) of toluene. 
It took about 6 hours from commencement of the dripping till completion of 
the polymerization. After completion of the polymerization, the solvent 
was removed and vacuum dried to obtain a copolymer. The thus obtained 
copolymer had a glass transition temperature (T.sub.g) of 40.degree. C., a 
weight average molecular weight (Mw) of 83,000 and a number average 
molecular weight (Mn) of 10,000. 
I-b (Vinyl Copolymer for Comparison) 
This copolymer was prepared in the same manner as in the above procedure 
I-a except that the initial reaction mixture was dripped at the same rate 
as in procedure I-a up to 3 hours after commencement of the dripping and 
then at a rate twice as high as the first speed. It took 4.5 hours till 
the polymerization was completed. The resulting copolymer had T.sub.g of 
40.degree. C., Mw of 300,000, and Mn of 11,000. 
I-c (Vinyl Copolymer according to Invention) 
This copolymer was prepared in the same manner as in procedure I-a except 
that 7.5 g of methacrylic acid was added to the initial reaction mixture. 
The resulting copolymer had T.sub.g of 45.degree. C., Mw of 86,000, Mn of 
10,300 and an acid value of 16 (mgKOH/g). 
I-d (Vinyl Copolymer according to Invention) 
This copolymer was prepared in the same manner as in procedure I-a except 
that 15 g of methacrylic acid was added to the initial reaction mixture. 
The copolymer had T.sub.g of 46.degree. C., Mw of 83,000, Mn of 10,700 and 
an acid value of 31 (mgKOH/g). 
I-e (Vinyl Copolymer according to Invention) 
This copolymer was prepared in the same manner as in procedure I-a except 
that 22.5 g of methacrylic acid was added to the initial reaction mixture. 
The copolymer had T.sub.g of 63.degree. C., Mw of 84,000, Mn of 10,000 and 
an acid value of 45 (mgKOH/g). 
I-f (Vinyl Copolymer according to Invention) 
This copolymer was prepared in the same manner as in procedure I-b except 
that 15 g of methacrylic acid was added to the initial reaction mixture. 
The copolymer had T.sub.g of 46.degree. C., Mw of 310,000, Mn of 11,000 
and an acid value of 31 (mgKOH/g). 
Toner Preparation 
100 parts by weight of each of the resins I-a, I-b, I-c, I-d, I-e, and I-f 
and 11 parts by weight of carbon black were melted and kneaded in a 
Banbury mixer and, after rough powdering, finely powdered in a jet mill to 
obtain toners I-1, I-2, I-3, I-4, I-5 and I-6. These toner particles were 
found to have a size of 10 to 20.mu.. 
It will be noted that the toners I-1 and I-2 are for comparative purposes. 
When the Banbury mixer was opened at the lower part thereof after the 
kneading, the toners I-1 and I-2 did not readily drop out because of 
attachment to the rotor and had to be scraped off, thus being poor in 
workability. In contrast, the toners I-3 to I-6 released very smoothly 
from the rotor when the mixer was opened and dropped out without producing 
any residual deposition, thus being very excellent in workability. 
2 parts by weight of each of the toners was mixed with 100 parts by weight 
of iron powder with a size of 100.mu. to give a developer. Each developer 
was used for duplication in a duplicator of the Xerox.RTM. Model 9200 
which was incorporated with a heat roll fixing device including a pair of 
rolls, i.e., a heat roll and a press roll, each having a covering of 
Teflon (product of E. I. DuPont de Nemours & Co., Inc.) and using no 
offset-inhibiting liquid. The results are shown in Table 1. 
It was found that as compared with the comparative samples I-1 and I-2, the 
toners I-3 to I-6 using the copolymers introduced with acids reached a 
final saturated charging level with a shorter mixing time with a carrier 
and the introduction of the acids contributed to imparting negative 
chargeability. 
As for the heat roll fixability, the toner I-2 which was increased in its 
weight average molecular weight was found to produce no offset phenomenon 
even at 210.degree. C. when visually observed and was thus superior in the 
heat roll fixability to the toner I-1. However, when white paper was 
forced against the heat roll while reproducing copies at 200.degree. C., 
it was soiled considerably, revealing that a slight degree of the offset 
phenomenon as could not be observed visually took place. The feed of oil 
is considered essential if this toner is employed. 
In contrast, the toners I-3 to I-6 were found to produce much reduced 
degree of deposition by the offset phenomenon when evaluated by forcing 
white paper against the heat roll, not to mention that there was no visual 
occurrence of offset phenomenon up to 210.degree. C. More particularly, 
the toner I-3 using the polymer with an acid value of 16 was found to be 
much more reduced in soil of the white paper with the toner than the case 
using the toner I-2. The toners I-4 to I-6 using the polymers with acid 
values exceeding 30 showed no soiling of the white paper and were 
completely free from the offset phenomenon even though no oil was used. 
TABLE 1 
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Triboelectric 
Triboelectric 
Minimum 
Offset 
State of 
Saturation 
Charging 
Fixing 
Initiating 
Offset 
Acid 
Velocity.sup.1 
Quantity.sup.2 
Temp. 
Temp. 
at 
Toner 
Classification 
Value 
(sec) (.mu.c/g) 
(.degree.C.) 
(.degree.C.) 
200.degree. C. 
__________________________________________________________________________ 
I-1 Comparative 
-- 60 5 160 190 Very con- 
Example siderable 
I-2 Comparative 
-- 90 3 160 &gt;210 Consider- 
Example able 
I-3 Example 
16 15 15 160 &gt;210 Very 
slight 
I-4 " 31 30 15 162 &gt;210 Nil 
I-5 " 45 15 20 165 &gt;210 Nil 
I-6 " 31 15 15 170 &gt;210 Nil 
__________________________________________________________________________ 
(1) 2 g of a toner is added to 100 g of a carrier in a glass bottle and its 
charging quantity is measured by the Turbula mixing machine (product of 
Willey A. Barphoen Co., Ltd.) while changing a mixing time of from 15 
seconds to 180 seconds at 15 seconds intervals (whereupon samples are 
freshly prepared whenever changing the mixing time). Then, a mixing time 
to charging quantity ratio is plotted on a section paper to read a mixing 
time at which the charging quantity reaches a saturation. 
(2) Charging quantity 15 seconds after mixing with carrier when measured by 
the above procedure (1). 
EXAMPLE 2 
Resin Preparation 
II-a (Vinyl Copolymer for Comparison) 
This copolymer was prepared in the same manner as in procedure I-a except 
that 120 g of styrene and 180 g of n-butyl methacrylate were used as the 
initial reaction mixture. The copolymer had T.sub.g of 40.degree. C., Mw 
of 150,000 and Mn of 10,000. 
II-b (Vinyl Copolymer according to Invention) 
This copolymer was prepared in the same manner as in procedure II-a except 
that 7.5 g of acrylic acid was added to the initial reaction mixture. The 
copolymer had T.sub.g of 41.degree. C., Mw of 90,000, Mn of 10,000 and an 
acid value of 19 (mgKOH/g). 
II-c (Vinyl Copolymer according to Invention) 
This copolymer was prepared in the same manner as in procedure II-a except 
that 15 g of acrylic acid was added to the initial reaction mixture. The 
copolymer had T.sub.g of 45.degree. C., Mw of 90,000, Mn of 10,000 and an 
acid value of 37 (mgKOH/g). 
Toner Preparation 
Example 1 was repeated using the resins II-a, II-b and II-c to obtain 
toners II-1, II-2 and II-3. 
The toner II-1 is a toner for comparative purpose. Similarly to Example 1, 
the toners of the present invention were found to show good producibility. 
After preparation of developers in the same manner as in Example 1, the 
duplication test was conducted. The results are shown in Table 2. 
TABLE 2 
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Triboelectric 
Triboelectric 
Minimum 
Offset 
State of 
Saturation 
Charging 
Fixing 
Initiating 
Offset 
Acid 
Velocity.sup.1 
Quantity.sup.2 
Temp. 
Temp. 
at 
Toner 
Classification 
Value 
(sec) (.mu.c/g) 
(.degree.C.) 
(.degree.C.) 
200.degree. C. 
__________________________________________________________________________ 
II-1 
Comparative 
-- 90 10 155 &gt;210 Very 
Example consider- 
able 
II-2 
Example 
19 30 25 159 &gt;210 Very 
slight 
II-3 
" 37 30 30 160 &gt;210 Nil 
__________________________________________________________________________ 
.sup.1 & .sup.2 : the same as defined in Table 1 
As will be clear from the results, similar to Example 1, the toners 
according to the present invention can suppress the offset phenomenon even 
when using no offset-inhibiting liquid and satisfy all the characteristics 
required for a toner. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.