Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Utility Patent
1999-04-20
2001-01-02
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S106100
Utility Patent
active
06168896
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing a binder resin for a toner for developing an electrostatic image in electrophotography, electrostatic recording, electrostatic printing, and the like.
BACKGROUND ART
A dry development system for developing an electrostatic image has recently undergone rapid technological development.
Various image fixing methods for a dry development system are known. In is particular, a contact heat fixing system typically including a system using a fusing roller unit is superior to a non-contact heat fixing system using, e.g., a hot plate fixing unit, in thermal efficiency and particularly feasibility of fixing at a high speed and a low temperature.
According to the fusing roller fixing system, a toner image formed on an electrostatic recording medium (a photoreceptor drum) is once transferred to a transfer sheet, such as paper, and the transfer sheet is passed through fusing rollers for hot pressing thereby to fuse and fix the toner image onto the sheet.
However, if the fusing roller fixing system is applied to a conventional toner, the toner coming into contact in a molten state with the fusing roller is transferred onto the fusing roller and stains the next transfer sheet (called an offset phenomenon).
A toner for electrostatic image development is generally made up of a resinous component, a colorant comprising a pigment, magnetic powder or a dye, and additives, such as a parting agent and a charge control agent. In order to overcome the above-mentioned problem, it has been studied for securely accomplishing fixing at a fixing temperature to incorporate into the binder resin for a toner a low-molecular weight polymer so as to decrease the toner viscosity and also a high-molecular weight polymer so as to increase the modulus of elasticity of the toner and to prevent the offset phenomenon caused by sticking of part of the toner to a contact fusing roller.
Styrene-based resins are often used as such a binder resin for a toner and comprises a low-molecular weight polymer and a high-molecular weight polymer, and various methods of polymerization have been studied.
For example, Japanese Patent Laid-Open No. 48675/90 discloses a method in which a high-molecular weight polymer is produced by suspension polymerization using a polyfunctional initiator, and a low-molecular weight polymer is then produced in the presence of the high-molecular weight polymer. The resulting polymer is dried to provide a solvent-free polymer mixture comprising a high-molecular weight polymer and a low-molecular weight polymer, which is useful as a binder resin for a toner.
In general, it is relatively easy to obtain a high-molecular weight polymer by suspension polymerization using a crosslinking agent, such as divinylbenzene, diethylene glycol dimethacrylate, and trimethylolpropane dimethacrylate. However, the stage of producing a low-molecular weight polymer involves various problems. That is, in order to obtain a low-molecular weight polymer by suspension polymerization, it is necessary to use a large quantity of a chain transfer agent, such as mercaptans or halogen compounds. In using a chain transfer agent, the polymer must be subjected to post-treatment to remove an undesired odor or a residual halogen compound, which increases the cost. Further, there has been another problem that it is difficult to remove unreacted polymerizable monomers.
Japanese Patent Laid-Open No. 75427/94 discloses a technique comprising dissolving a low-molecular weight polymer obtained by solution polymerization in a polymerizable monomer which is to provide a high-molecular weight polymer and causing the system to polymerize by use of a polyfunctional initiator (having at least trifunctionality) to prepare a binder resin for a toner. However, a solution polymerization system for producing a high-molecular weight polymer encounters troubles caused by the Weissenberg effect (a phenomenon that a resin rises, clinging to a stirring rod), which makes the production difficult.
U.S. Pat. No. 5,084,368 teaches dissolving and mixing a low-molecular weight solution polymerization product and a high-molecular weight bulk polymerization product in a solvent, followed by removing the solvent in vacuum to obtain a mixture of resins different in molecular weight. However, dissolving a high-molecular weight bulk polymer in a solvent requires much labor and high cost.
Further, Japanese Patent Laid-Open No. 118583/90 discloses a technique comprising mixing a low-molecular weight polymer, a high-molecular weight polymer, and a colorant and kneading the mixture to prepare a toner for electrostatic image development. However, since polymers having largely different molecular weights and different compositions generally have poor compatibility with each other, it turned out that the resulting toner involves the drawback of each polymer, i.e., an offset phenomenon attributed to a low-molecular weight polymer and insufficient fixing in low temperatures attributed to a high-molecular weight polymer.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a process for efficiently and easily producing a binder resin for a toner for electrostatic image development in which a low-molecular weight polymer and a high-molecular weight polymer are uniformly and compatibly dispersed and which has reduced odor and, when used in a toner, exhibits satisfactory characteristics, such as anti-offset properties, fixing properties, grindability in the production thereof, antiblocking properties (resistance to agglomeration) during storage, and developing properties in image formation.
The present invention provides a process for producing a binder resin for a toner for electrostatic image development comprising the steps of (1) mixing a resin solution and a resin emulsion with stirring and (2) removing water and the solvent simultaneously with or after the step (1) to obtain a solventless mixed resin composition.
The present invention further provides the above-described process for producing a binder resin for a toner for electrostatic image development, wherein
the solvent of the resin solution is preferably a solvent having an SP value of 6 to 12,
the resin solution is preferably a resin solution obtained by solution polymerization,
the resin emulsion is preferably an emulsion of a polymer obtained by emulsion polymerization,
the resin of the resin solution is preferably a styrene-based resin having a weight average molecular weight of not more than 200,000, and the resin of the resin emulsion is preferably a styrene-based resin having a weight average molecular weight of not less than 50,000,
the resin of the resin solution preferably has a GPC peak molecular weight (Mp) of 1,500 to 30,000 and a weight average molecular weight (Mw)
umber average molecular weight (Mn) ratio of less than 4.0, and the resin of the resin emulsion preferably has a GPC peak molecular weight (Mp) of 300,000 to 3,000,000,
the resin of the resin solution and the resin of the resin emulsion are preferably present in proportions of 50 to 80 parts by weight and 20 to 50 parts by weight, respectively, per 100 parts by weight of their total amount, and/or
the process preferably includes a step of (3) kneading after the step of (1) mixing with stirring and (2) removing water and the solvent.
The present invention furthermore provides a process for producing a toner for electrostatic image development comprising the steps of (1) mixing a resin solution and a resin emulsion with stirring, (2) removing water and the solvent simultaneously with or after the step (1) to obtain a solventless mixed resin composition, and (4) incorporating a colorant into the solventless mixed resin composition.
According to the present invention, a binder resin for a toner for electrostatic image development can be produced efficiently and easily by grinding the solventless mixed resin composition thus prepared. The binder resin for a toner obtained in the present invention provides a toner for electrostatic image development in whic
Kajino Kaoru
Matsuoka Sonoo
Serizawa Hiroshi
Terabayashi Takashi
Goodrow John
Nippon Carbide Kogyo Kabushiki Kaisha
Young & Thompson
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