Process fro producing resin for a toner

A process for producing a toner resin by a two-step suspension polymerization process, which entails preparing a polymer of high molecular weight having a weight average molecular weight of greater than about 350,000 from at least one monomer having a polymerizable vinyl group using a compound having at least three t-butyl peroxide groups in one molecule, as a polymerization initiator, and then preparing a low molecular weight polymer in the presence of the high molecular weight polymer. A toner having an excellent fixing property and offset resistance can be obtained from the above resin.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention provides a process for producing resin for a toner, 
which resin has an excellent offset resistance and fixing property. 
2. Description of the Background 
Many proposals have been made regarding dry type toner resins. However, in 
view of the need for an increased information processing rate, it has 
become very desirable for copying machines and recording apparatus to have 
increased copying speeds. 
Additionally, in order to conserve energy, there is also presently a need 
for a toner which can be fixed at lower temperatures than at present. 
On the other hand, the melting viscosity of a resin is reduced if the 
fixing property of the toner at a lower temperature is improved. This 
results in easy deposition of the toner to a fixing roll and worsening of 
offset resistance. One method for resolving this problem has been proposed 
wherein a resin having a wide molecular weight distribution is used for 
the toner. For example, there can be mentioned a method of preparing a 
high molecular weight polymer and a low molecular weight polymer 
separately by solution polymerization and, subsequently, mixing the 
polymers in the liquid state and then removing the solvent. Unfortunately, 
it is difficult to produce a high molecular weight polymer with a weight 
average molecular weight of higher than 200,000 using the solution 
polymerization process. Further, since the solvents used for the high 
molecular weight polymer and those for the low molecular weight polymer 
differ greatly, uniform mixing of the two kinds of the polymers is 
difficult even when in solution. In addition, the above technique requires 
the removal of solvent which is troublesome and increases cost. 
Further, even by the suspension polymerization process which is 
advantageous in view of the cost, it is difficult to produce high 
molecular weight polymers with a molecular weight of higher than 200,000. 
Moreover, polymers having a sufficiently wide molecular weight 
distribution are as yet unobtainable. 
Emulsion polymerization has been used to obtain high molecular weight 
polymers, however, since emulsifier remains in the resin formed, the 
moisture resistance and fluidity of the toner are reduced and/or special 
liquid waste processing is necessary because of high biological oxygen 
demand (BOD) in liquid wastes therefrom. 
Thus, a need continues to exist for a process for producing a uniform resin 
for toner having a wide molecular weight distribution which avoids the 
problems associated with the conventional methods used for preparing toner 
resin. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a process 
for producing a uniform toner resin having a wide molecular weight 
distribution. 
It is also an object of the present invention to provide a process for 
producing a uniform toner resin containing a high molecular wight polymer 
of a specific molecular weight and a low molecular weight polymer produced 
by superior polymerization. 
The above object and others are provided by a process for producing a toner 
resin by a two-step suspension polymerization process, which entails 
preparing a polymer of high molecular weight having a weight average 
molecular weight of greater than about 350,000, from at least one monomer 
having a polymerizable vinyl group using a compound having at least three 
t-butyl peroxide groups per molecule as a polymerization initiator, and 
then preparing a low molecular weight polymer in the presence of the high 
molecular weight polymer. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The object of the present invention is achieved by a process for producing 
a toner resin which comprises a two step suspension polymerization 
process, comprising, first, preparing a polymer of high molecular weight 
having a weight average molecular weight of greater than 350,000, using a 
compound having at least three t-butyl peroxide groups in one molecule as 
a polymerization initiator, and then preparing a low molecular weight 
polymer in the presence of the high molecular weight polymer. 
Any monomer having a polymerizable vinyl group may be used in the present 
invention so long as it can provide a vinyl polymer by suspension 
polymerization. For example, there may be used monomers such as styrene, 
.alpha.-methyl styrene, styrene derivatives having, as a substituent, an 
o-methyl group, m-methyl group, p-methyl group, p-ethyl group, 
2,4-dimethyl group, p-butyl group, p-hexyl group, p-octyl group, p-nonyl 
group, p-decyl group, p-methoxy group, p-phenyl group, etc., acrylic acid 
esters or a methacrylic acid ester of the general formula: CH.sub.2 
.dbd.CR--COOR', in which R represents hydrogen or methyl group and R' 
represents a methyl group, ethyl group, n-propyl group, isopropyl group, 
n-butyl group, isobutyl group, sec-butyl group, t-butyl group, n-pentyl 
group, n-hexyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, 
isononyl group, decyl group, dodecyl group, tridecyl group, stearyl group, 
dococyl group, cyclohexyl group, benzyl group, phenyl group, methoxy ethyl 
group, ethoxy ethyl group, butoxy ethyl group, phenoxy ethyl group, etc., 
vinyl esters such as vinyl acetate and vinyl propionate and acrylic acid 
or methacrylic acid derivatives such as acrylonitrile and 
methacrylonitrile. They may be used alone or in combination using two or 
more. As an example of the combination, there can be mentioned monomer 
mixtures containing styrene and/or a derivative thereof, or (meth)-acrylic 
acid alkyl ester as the main ingredients. 
In the present invention, compounds having three or more t-butyl peroxide 
groups in one molecule are used as the polymerization initiator for the 
preparation of the high molecular weight polymer. For example, there can 
be mentioned 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, which is 
commercially available. 
By using the present initiators, it is possible to obtain a high molecular 
weight polymer with a weight average molecular weight of higher than 
350,000. Such a high molecular weight polymer cannot be obtained by 
suspension polymerization using conventional polymerization initiators. 
The amount of the initiator to be added for the high-molecular weight 
polymer is usually from about 
0.01 to about 1% by weight based upon the monomer, which can be selected 
depending on the properties of the resin being prepared. 
There is no particular restriction for the polymerization initiator used in 
the preparation of the low molecular weight polymer and any known 
initiators, such as peroxides or azo compounds, for example, having 
radical polymerization activity can generally be used. For example, there 
may be used di-t-butyl peroxide, t-butyl cumyl peroxide, dicumyl peroxide, 
acetyl peroxide, isobutylyl peroxide, octanonyl peroxide, decanonyl 
peroxide, lauroyl peroxide, 3,3,5-trimethyl hexanoyl peroxide, benzoyl 
peroxide, m-toluoyl peroxide, t-butyl peroxy acetate, t-butylperoxy 
isobutylate, t-butylperoxy pivalate, t-butylperoxy neodecanoate, 
cumylperoxy neodecanoate, t-butylperoxy-2-ethyl hexanoate, 
t-butylperoxy-3,5,5-trimethyl hexanoate, t-butylperoxy laurate, 
t-butylperoxy benzoate, t-butylperoxyisopropyl carbonate and 
azobisisobutylonitrile. They are used alone or as a mixture of two or more 
of them. Among them, use of octanonyl peroxide, decanonyl peroxide, 
lauroyl peroxide, benzoyl peroxide and m-toluoyl peroxide is preferred in 
view of the long lasting polymerization activity for the monomer and for 
completing the polymerization in a relatively short period of time. The 
amount of the initiator to be added for the low molecular weight polymer 
is usually from about 1 to about 15% by weight based upon the total weight 
of the initiator and monomer. 
For the suspension polymerization of the present invention, a conventional 
method may be used in selecting the polymerization conditions. That is, 
water may be used in an amount of about 1 to 10 times, preferably, 2 to 4 
times to that of the monomer, a suspension-dispersion stabilizer may be 
used and, if required, the dispersion aid is charged in a reactor equipped 
with a thermometer. While stirring is being conducted, monomer and 
polymerization initiator are added under normal temperatures or under 
heating. The monomer is heated to a predetermined polymerization 
temperature, and polymerization is initiated. 
Known suspension-dispersion stabilizers may be used. As specific examples, 
there can be mentioned polyvinyl alcohol, partially saponified vinyl 
alcohol, the sodium salt or potassium salt of a homo- or copolymer of 
acrylic or methacrylic acid, water-soluble resins such as 
carboxymethylcellulose, gelatin or starch, for example. Also, less water 
soluble or non-water soluble inorganic powders such as barium sulfate, 
calcium sulfate, barium carbonate, calcium carbonate, magnesium carbonate 
and calcium phosphate may also be used. These suspension-dispersion 
stabilizers are used in such an amount as required for completing the 
procedures with no coagulation of the resultant resin particles during 
polymerization and they are used, generally, from 0.01 to 5 parts by 
weight, preferably, from 0.05 to 2 parts by weight based on 100 parts by 
weight of water. 
Further, if required, an electrolyte such as sodium chloride, potassium 
chloride, sodium sulfate and potassium sulfate may be used as a dispersion 
aid. 
In the present invention, the low molecular weight polymer is prepared by 
polymerization in the presence of the high molecular weight polymer. 
Usually, polymerization of the low molecular weight polymer is started by 
adding an initiator for the low molecular weight polymer, which is 
dissolved in water or the monomer, when the polymerization degree of the 
monomer for the high molecular weight polymer reaches about 10-15%. At 
this time, additional monomer, water, dispersing agent and chain transfer 
agent, for example, may be added if necessary. When the monomer is added, 
it is added in such an amount that the content of the resultant low 
molecular weight polymer is usually from 50 to 90% by weight in the toner 
resin. The weight average molecular weight of the resultant low molecular 
weight polymer is usually about from 2,000 to 50,000. 
The polymerization is carried out as described above, and after the 
polymerization is completed, the resultant products are heated for a 
certain time, to decompose the residual initiator, and then the products 
are cooled, sufficiently washed, dewatered and then dried. 
As the softening temperature (Ts) and the glass transition point (Tg), for 
the resultant toner resin, it is preferred that Ts be about 
110.degree.-170.degree. C. and Tg be about 40.degree.-80.degree. C. in 
view of the fixing property, offset resistance, storability and fluidity.

The present invention will now be described in further detail with 
reference to examples. It is understood that the present invention is by 
no means restricted by such specific examples as these examples are only 
for the purpose of illustration and are not intended to be limitative. In 
the examples, "parts" mean "parts by weight". 
The evaluation of properties of the resins and toners in the examples were 
conducted using the method described below. 
Softening Point (Ts) 
Sample resin was flown out by one gram using a flow tester, Model CFT-500 A 
manufactured by Shimazu Seisakusho Co., through a nozzle of 1 mm.phi. 
diameter and 10 mm length under a load of 30 kg and at a temperature 
elevation rate of 3.degree. C./min. The temperature when the sample resin 
was flown out by 0.5 g was defined as the softening temperature. 
Glass Transition Temperature (Tg) 
A chromatogram was prepared by a differential thermometer at a temperature 
elevation rate of 10.degree. C./min and the crossing point between the 
base line and the heat absorption curve near Tg in the resultant chart was 
defined as the glass transition temperature of the resin. 
Fixing Property 
A cellophane tape was appended to a fixed toner image and then peeled 
therefrom, and a temperature of a fixing roller when the image density 
(ID) after the separation of the type reached 80% of the ID before 
appending the tape at a level of an initial ID of 0.6 is defined as a 
limit temperature for fixing. At a temperature lower than the limit 
temperature, the ID after the separation of the tape will reduce to lower 
than 80% of the ID before the separation of the tape. 
Offset Resistance 
The extent of contamination of the fixing roller with the toner was 
visually judged and offset resistance was evaluated by the lowest 
temperature at which the contamination of the fixing roller occurs. At a 
temperature higher than the lowest temperature, contamination of the 
fixing roller is observed. 
Storability 
The toner was maintained in a dryer at 50.degree. C. for 50 hours and the 
extent of blocking was visually judged. 
.circleincircle.: not blocked 
.largecircle.: some blocking occurred 
.DELTA.: blocking occurred but the toner usable 
X: remarkable blocking occurred and the toner could not be used 
Moisture Resistance 
The toner was left for 20 hours in two different circumstances for the 
atmospheric temperature and the relative humidity, i.e., 30.degree. C.; 
85% and 10.degree. C.; 15%, respectively, and the charging performance was 
measured and the circumstance dependency was evaluated. 
.largecircle.: little circumstance dependency 
.DELTA.: some circumstance dependency 
X: remarkable circumstance dependency 
EXAMPLE 1 
A monomer mixture comprising 80 parts of styrene and 20 parts of n-butyl 
acrylate containing, dissolved therein, 0.1 parts of 
2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane ("Parkadox 12", 
manufactured by Kayaku Nuley Co.) as the polymerization initiator was 
added to a mixture comprising 300 parts of water and 0.2 parts of 
partially saponified Poval (Gosenol GH-20, manufactured by Nihon Gosei 
Kagaku Kogyo Co.). After elevating the temperature up to 95.degree. C. 
under stirring, polymerization was carried out for 4 hours. The degree of 
polymerization was about 34%. Then, 3.5 parts of benzoyl peroxide 
(hereinafter referred to as BPO) was added to the polymer dispersion and 
heated at 95.degree. C. for 3 hours to complete the polymerization. The 
polymerizing degree was 99.9%. 
The resultant polymer dispersion was cooled to room temperature, 
sufficiently washed, dewatered and dried to obtain a resin (R1). The resin 
(R1) had a Ts of 134.degree. C. and Tg of 63.5.degree. C. The resin 
exhibited two peaks as a result of molecular weight distribution analysis 
by GPC, the weight average molecular weight for the respective peaks being 
475,000 and 19,900, the ratio in the content of the high molecular weight 
polymer to the low molecular weight polymer being 35/65. 
Then, 94 parts of the resin (R1), 5 parts of carbon black (#40, 
manufactured by Mitsubishi Kasei Co.), and one part of a charge controller 
(Bontron S-34, manufactured by Orient Kagaku Kogyo Co.) were kneaded at 
150.degree. C. for about 5 min by using a twin-screw extruder, cooled and 
then finely pulverized by using a jet mill, to collect particles of 5-15 
.mu.m size as the toner. 
The fixing property and the offset resistance of the toner were evaluated 
by using a fixing tester manufactured by modifying the fixing station of a 
copying machine, at a processing rate of 130 mm/sec and under a pressure 
of 40 kg. The results obtained are shown in Table 1. 
EXAMPLE 2 
Resin (R2) was prepared using the same procedure as in Example 1, except 
that the amount of BPO added was changed to 5 parts and the toner 
performance was evaluated. The results obtained are shown in Table 1. 
EXAMPLE 3 
Resin (R3) was prepared using the same procedure as in Example 1, except 
that the amount of Parcadox 12 added was changed to 0.2 parts and the 
toner performance was evaluated. The results obtained are shown in Table 
1. 
EXAMPLE 4 
Resin (R4) was prepared using the same procedure as in Example 1, except 
that the polymerization time for obtaining the high molecular weight 
polymer in the first step was changed from 4 hours to 6 hours and the 
toner performance was evaluated. The results obtained are shown in Table 
1. 
COMATIVE EXAMPLE 1 
Resin (R5) was prepared using the same procedure as in Example 1, except 
that BPO is used instead of Parkadox 12 and the polymerization temperature 
in the first step was changed from 95.degree. C. to 70.degree. C., and the 
toner performance was evaluated. The results obtained are shown in Table 
1. 
COMATIVE EXAMPLE 2 
Resin (R6) was prepared using the same procedure as in Example 1, except 
that 0.2 parts of BPO were used instead of 0.1 parts of Parkadox 12 and 
the polymerization temperature in the first step was changed from 
95.degree. C. to 80.degree. C., and the toner performance was evaluated. 
The results obtained are shown in Table 1. 
COMATIVE EXAMPLE 3 
Resin (R7) was prepared using the same procedure as in Comparative Example 
1, except that the polymerization temperature in the first step was 
changed from 70.degree. C. to 80.degree. C. and the polymerization time 
was changed from 4 hours to 7 hours, and the toner performance was 
evaluated. The results obtained are shown in Table 1. 
COMATIVE EXAMPLE 4 
A nitrogen gas was blown into a mixture containing 80 parts of styrene, 20 
parts of n-butyl acrylate, 200 parts of water, 0.5 parts of sodium alkyl 
diphenyl ether sulfonate as an emulsifier (Perex SS-H, manufactured by Kao 
Co.) and 0.3 parts of potassium persulfate under stirring the mixture and 
nitrogen substitution was conducted sufficiently. Then, the temperature 
was elevated to 70.degree. C. under nitrogen atmosphere and emulsion 
polymerization was carried out for 5 hours. Thereafter, the resultant 
product was cooled to a room temperature to obtain a liquid emulsion (A). 
After adding a monomer mixture comprising 80 parts of styrene and 20 parts 
of n-butyl acrylate and containing, dissolved therein, 5 parts of BPO to 
80 parts of the liquid emulsion (A), and further adding 300 parts of water 
and 0.7 parts of Gosenol GH-20 and mixing and stirring them, the mixture 
was heated to 85.degree. C. After practicing suspension polymerization for 
about three hours, the resultant product was cooled to room temperature, 
sufficiently washed, dewatered and dried to obtain a resin (R8), and the 
toner performance was evaluated. The results obtained are shown in Table 
1. 
TABLE 1 
__________________________________________________________________________ 
Polymerization condition 
in first step Polymerization 
in second step 
Initiator Polymeri- 
Initiator 
Addi- 
zation Addi- Resin 
tion Temper- tion Property 
amount 
Time 
ature amount T.sub.3 
T.sub.4 
Kind (part) 
(hr) 
(.degree.C.) 
Kind 
(part) 
Resin No. 
(.degree.C.) 
(.degree.C.) 
__________________________________________________________________________ 
Example 1 
Parcadox 12 
0.1 4 95 BPO 3.5 R1 134 
63.5 
Example 2 
" " " " " 5 R2 132 
63 
Example 3 
" 0.2 3 " " 3.5 R3 130 
63 
Example 4 
" 0.1 6 " " " R4 141 
63 
Comparative 
BPO " 4 70 " " R5 120 
60 
Example 1 
Comparative 
" 0.2 " 80 " " R6 127 
63 
Example 2 
Comparative 
" 0.1 7 " " " R7 132 
60 
Example 3 
*1 Potassium per- 
0.3 5 70 " " R8 131 
56 
Comparative 
sulfate 
Example 4 
__________________________________________________________________________ 
Resin Property 
Weight 
Weight average 
average 
molecular 
molecular 
Contest of 
weight of high 
weight of low 
high Non-offset Humidi- 
molecular 
molecular 
molecular 
fixing ty 
weight weight weight 
temperature 
Stor- 
proof- 
polymer polymer 
polymer 
(.degree.C.) 
ability 
ness 
__________________________________________________________________________ 
Example 1 475,000 19,900 34.7 higher than 
.circleincircle. 
.largecircle. 
180-240 
Example 2 458,000 13,200 33.0 higher than 
.circleincircle. 
.largecircle. 
170-240 
Example 3 388,000 24,000 34.7 higher than 
.circleincircle. 
.largecircle. 
170-230 
Example 4 732,800 20,300 54.0 higher than 
.circleincircle. 
.largecircle. 
195-240 
Comparative 
326,000 28,000 9.8 175.about.210 
.largecircle. 
.largecircle. 
Example 1 
Comparative 
204,000 24,800 20.3 180.about.220 
.largecircle. 
.largecircle. 
Example 2 
Comparative 
318,400 25,900 25.3 180.about.225 
.largecircle. 
.largecircle. 
Example 3 
*1 1,012,700 
18,500 18.5 higher than 
X X 
Comparative 170-240 
Example 4 
__________________________________________________________________________ 
*1 first step polymerization: emulsion polymerization 
second step polymerization: suspension polymerization 
Having now described the present invention, it will be apparent to one of 
ordinary skill in the art that the above description may be modified in 
many ways while remaining within the spirit and scope of the present 
invention.