Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-12-10
2001-06-26
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400, C430S137170
Reexamination Certificate
active
06251556
ABSTRACT:
1. Technical Field
The present invention relates to a toner used for developing an electrostatic image in electrophotography, electrostatic recording and electrostatic printing.
2. Background Art
A toner for developing an electrostatic image is usually produced by blending a colorant with a binder resin produced by various polymerization methods such as solution polymerization, bulk polymerization, suspension polymerization and emulsion polymerization and further blending suitably with an electrostatic charge-controlling agent, magnetic powder and the like, kneading them under heating and then pulverizing and classifying.
Polymers having a relatively small molecular weight are excellent as a binder resin in characteristics such as a heat-melting property, an adhesive property to various materials, a penetrability and the like and fulfill a large role for fixing a developed toner image on a transfer material such as paper, and therefore a lot of low molecular weight polymers are used as a binder resin alone or in combination with high molecular weight polymers.
When a low molecular weight polymer used as a binder resin is produced by emulsion polymerization, the emulsion polymerization has so far been carried out usually in the presence of a chain transfer agent in order to control the molecular weight of the resulting polymer to a low level. In general, aliphatic mercaptans and halogenated hydrocarbon base chain transfer agents are industrially used as the chain transfer agent.
However, a polymer dispersion obtained in the presence of mercaptans has an undesired specific odor even if the residual mercaptan content is small. Further, when halogenated organic compounds (for example, carbon tetrachloride, bromoform, bromotrichloromethane and the like) are used as chain transfer agents, the chain transfer agents have a relatively high residual content in the polymer dispersions.
Accordingly, when the polymer dispersions thus produced are used as a binder resin for a toner, the problems of unpleasant odor produced in heating and fixing and air pollution are brought about. Further, involved are the problems that since a chain transfer agent is bonded to the end of a polymer molecule, different characteristics from electrostatic characteristics which are intrinsic to the resin are revealed and that a change in the electrostatic characteristics with the passage of time due to the surrounding environment is caused.
The present inventors have found this time that when a radical-polymerizable unsaturated monomer is emulsion-polymerized under a higher polymerization temperature condition than a polymerization temperature usually used for emulsion polymerization, a polymer having a low molecular weight can readily be produced in the absence of a chain transfer agent or in the presence of, if present, a very small amount thereof and that a toner which causes no such problems as described above can be obtained by using the polymer produced in the manner described above as a binder resin.
In addition thereto, they have found that the emulsion polymer of a low molecular weight thus obtained can easily be turned into a toner by a coagulation method and this can provide a toner which has a small particle diameter and a narrow particle size distribution and which is excellent in a homogeneous dispersibility of a colorant without requiring pulverizing and classifying steps, and they have come to complete the present invention.
DISCLOSURE OF THE INVENTION
Thus, the present invention provides a toner for developing an electrostatic image comprising a binder resin and a colorant, wherein the above binder resin comprises a low molecular weight polymer which is obtained by emulsion-polymerizing a radical-poly-merizable unsaturated monomer in the presence or absence of a chain transfer agent and in which a weight average molecular weight is 2,000 to 100,000 and falls in a range shown by the following equation (1):
3≦log Mw<1.5−1.18×log(
S+
0.001) (1)
wherein Mw represents the weight average molecular weight of the polymer, and S represents an equivalent number of a polyatomic radical part of the chain transfer agent bonded to the end of the polymer chain per 100 g of the polymer.
The toner and the production process thereof according to the present invention shall be explained below in further details.
BEST MODE FOR CARRYING OUT THE INVENTION
The low molecular weight polymer (hereinafter referred to as the low molecular weight polymer of the present invention) used as a binder resin in the present invention is produced by emulsion polymerization in the absence of a chain transfer agent or the presence of a small amount, if used, of the chain transfer agent, and it is characterized by having a low molecular weight and a small content of chain transfer agent fragments introduced into the polymer by emulsion polymerization as compared with those of polymers produced by conventional emulsion polymerization methods.
That is, the low molecular weight polymer of the present invention has a weight average molecular weight and a content of a polyatomic radical part of the chain transfer agent falling in a range in which a relation shown by the following inequality is set up between the weight average molecular weight (Mw) and an equivalent number (S; when the chain transfer agent is not used in emulsion polymerization, S=0) per 100 g of the polymer, of a polyatomic radical part (hereinafter referred to as a chain transfer agent fragment) of the remaining chain transfer agent bonded to the end of the polymer chain as a result of emulsion polymerization:
3≦log Mw>1.50−1.18×log(
S+
0.001) (1)
preferably
3.18≦log Mw>1.24−1.18×log(
S+
0.001) (1-1)
and more preferably
3.3≦log Mw>1.06−1.18×log(
S
+0.001) (1-2)
The chain transfer agent is split at a part where it is most easily cleaved in a chain transfer reaction and is turned into a monoatomic radical and a polyatomic radical which is composed of plural atoms, or two polyatomic radicals, wherein one of them is bonded to a polymer radical to terminate a chain propagation reaction, and the other becomes a starting point for a new chain propagation reaction to be bonded to a newly formed polymer. “S” used in the inequality described above is an equivalent number per 100 g of the polymer, of ┌a polyatomic radical┘ bonded to the polymer as a result of such reaction. In general, it falls preferably in a range of 0 to 0.05, particularly 0 to 0.015 and above all, 0 to 0.005.
For example, trichloromethane (CHCl
3
) is cleaved at a part of C—H in emulsion polymerization into a monoatomic radical (H.) and a polyatomic radical (CCl
3
.). When emulsion polymerization is carried out using as a chain transfer agent, mercaptans (RCH
2
SH) or dimercaptans (RCH
2
S—SCH
2
R′), bromotrichloromethane (CCl
3
Br) or carbon tetrachloride (CCl
4
), or dichlorodibromomethane (CCl
2
Br
2
), polyatomic radical parts (chain transfer agent fragments) introduced into the chain terminals of the resulting polymer are ┌RCH
2
S.┘, ┌CCl
3
.┘ and ┌CCl
2
Br.┘ respectively.
The amount of the chain transfer agent fragments bonded to the chain terminals of the low molecular weight polymer of the present invention can be determined in the following manner.
First, a polymer dispersion is left standing at −20° C. through one night to be frozen and then molten at a room temperature. Further, the polymer is separated by means of an ultra-centrifugal separator. The separated polymer is dissolved or swollen in a good solvent such as toluene and then precipitated again in a poor solvent such as methanol or water and washed. In this case, it is to be confirmed that the polymer is not contained in the poor solvent.
The number of chain transfer agent fragments in the resulting polymer is determined by elemental analysis such as ion chromatography according to a combustion method or ICP (high frequency plasma emission a
Masuda Hiroshi
Ogawa Manabu
Serizawa Hiroshi
Yoshida Eiichi
Chapman Mark
Fuji Xerox Co Ltd
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