JP3457375B2 - Method for producing liquid developer for electrostatic image development - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a liquid developer for developing an electrostatic image, which is applied to visualizing an electrostatic image. [0002] Conventionally, a method for developing an electrostatic image formed on an electrostatic latent image carrier in processes such as electrophotography, electrostatic recording, and electrostatic printing has been known as liquid development. A liquid developing method using a developer and a dry developing method using a powder developer are known.
The liquid developing method uses a large amount of an organic solvent as a developer, and is unsuitable for general office work due to problems such as solvent vapor diffusion.
In recent years, dry development has become the mainstream because of its ease of handling. However, the dry development method has a limit in obtaining a high-definition image because the powder developer (toner) has a rather coarse particle diameter of about 10 μm. on the other hand,
In the liquid developing method, since developer particles (hereinafter referred to as toner) are extremely fine compared to powder toner, high image quality, which is a market trend in recent years, is possible, and its advantages are being reviewed. [0003] A developer used in the liquid developing method (hereinafter referred to as a liquid developer) is a suspension of colored fine powder in an electrically insulating organic solvent (carrier liquid). As a result, fine line reproducibility is better and a high-contrast image can be obtained as compared with the dry development method, and the characteristic is also obtained in full-color development using four color toners of yellow, magenta, cyan and black. And high resolution and high gradation image quality can be obtained. As a method for producing a liquid developer, for example, there is a method described in JP-A-61-180248. This means that a thermoplastic resin having a property of being insoluble in a nonpolar solvent at a temperature of 40 ° C. or less and solvating the nonpolar solvent at a temperature exceeding 50 ° C. is once solvated with the nonpolar solvent and then cooled. This method is a method for producing a liquid developer by forming finer thermoplastic resin fine particles, and wet-grinding the resin fine particle solvent dispersion together with a pigment, a dispersant, and a nonpolar solvent. However, the resin fine particle solvent dispersion has the following problems. 1. It is easy to cause solvent separation and tends to be non-uniform. 2. Poor production efficiency. For example, it takes 10 hours to convert 25 kg of resin into a fine particle dispersion. [0006] The present invention relates to a manufacturing method for efficiently and stably obtaining a liquid developer. The present invention is characterized in that a thermoplastic resin mechanically pulverized by a low-temperature freezing method is used as a binder component of a liquid developer instead of a solvent dispersion of fine resin particles. And a method for producing a liquid developer. Since the low-temperature freeze-pulverized resin is uniform and can be processed in a large amount at low cost by a pulverizer, there is a great merit that the resin fine particle solvent dispersion step can be omitted. Hereinafter, the present invention will be described in detail. The thermoplastic resin is freeze-pulverized at a low temperature in a liquid nitrogen (-196 ° C) atmosphere, and then coarse particles are removed by a classifier. Next, the low-temperature freeze-pulverized resin, the colorant, the nonpolar solvent and the additive are mixed and pulverized to a predetermined particle size by a wet pulverizer. The thermoplastic resin used in the present invention includes ethyl vinyl acetate copolymer, ethylene copolymer, and acrylic copolymer (ethylene ethyl acrylate, ethylene vinyl acetate, polybutyl methacrylate, polyethyl methacrylate). , Polymethyl methacrylate, etc.) are suitable. The thermoplastic resin may be only one kind or a mixture of two or more different kinds of resins compatible with each other. The low-temperature freeze-pulverization system used in the present invention will be described. Generally, it is difficult to pulverize a granular thermoplastic resin at room temperature. However, a resin and a pulverizer such as a turbo mill are cooled to -196 ° C. with liquid nitrogen and pulverized by utilizing the low-temperature brittleness of the resin, whereby the pulverization can be performed to 500 μm or less. After low-temperature freeze-pulverization, if the particles are classified to an appropriate particle size by a classifier to remove coarse particles, the pulverization efficiency in the next step of wet pulverization is improved. As the colorant used in the present invention, commonly used pigments and dyes can be used. For example, Hansa Yellow, Disazo Yellow, Quinoline Yellow, Permanent Yellow, Benzidine Orange, Bengala, Fast Red, Lisor Red Pigments such as, permanent red, watch red calcium salt, watch red manganese salt, pyrazolone red, lake red C, lake red D, brilliant carmine 3B or 6B, navy blue, phthalocyanine blue, victoria blue, nigrosine, carbon black, or Dyes can be used alone or in combination. The non-polar solvent used in the present invention is:
Electrical insulation with a dielectric constant of 3.0 or less (volume resistivity 10 ⁹
Ωcm or more), preferably a branched aliphatic hydrocarbon. The most common nonpolar solvent having such properties is Isopar (trade name) manufactured by Exxon Chemical Co., Ltd. More specifically, Isopar G, Isopar H, Isopar L, and the like are most preferable. However, the present invention is not limited to this. Other solvents, including those that are added in very small amounts in some cases, include, for example, Shell Sol A and AB (trade names) manufactured by Shell Co., Ltd., and Naphtesol L, M, H (trade names) manufactured by Nippon Oil Co., Ltd. No. As the additives used in the present invention, various dispersing aids, charge imparting agents and the like are used. The above raw materials are mixed and pulverized by a wet pulverizer until the particle size becomes 3 μm or less. Examples of the wet pulverizer used in the present invention include a medial wet pulverizer such as an attritor, a sand mill, a dyno mill, a ball mill, an apex mill, a spike mill, a coball mill, and a diamond fine mill, or a homogenizer, a mycolloider, a trigonal, and a slasher. , Colloid mills, Cavitron, Golator and the like. Hereinafter, the present invention will be described with reference to examples.
The particle size was measured using a particle size distribution analyzer (SA-CP3
L, manufactured by Shimadzu Corporation). The image evaluation was performed on a printed matter obtained by a liquid developing copier (Savin 870, manufactured by Sabin Co.) using a developer diluted to a nonvolatile content of 1.5%. In the examples, “parts” means “parts by weight”. Example 1 Nuclel N410 (trade name, Mitsui DuPont Polychemical Co., Ltd. ethylene-methacrylic acid copolymer, softening point 78)
° C) in a liquid nitrogen atmosphere. The particle size of the obtained pulverized product was 250 μ or less. Ethylene-methacrylic acid copolymer frozen and crushed product 15 parts Lionol Yellow FG1310 (trade name, yellow pigment: manufactured by Toyo Ink Mfg. Co., Ltd.) 3 parts Isopar H (manufactured by Exxon) 100 parts Dispersing aid 0.5 part The mixture is wet-ground with a 2L attritor for 10 hours,
A liquid developer having an average particle size of 2 μ was obtained. The obtained liquid developer was diluted with Isopar H to a nonvolatile content of 1.5%, and lecithin was added at a ratio of 1.0 part to 1,000 parts of the diluted solution, and an image test was performed. Co-reflection density (reflection densitometer, Macbeth RD-
918), and a good image free of background stains of 1.0 or more was obtained. Example 2 Evaflex P-1403 (trade name,
Mitsui Polychemicals Co., Ltd. Ethylene vinyl acetate Softening point 7
(0 ° C.) in a liquid nitrogen atmosphere. The particle size of the obtained pulverized product was 450 μm or less. Ethylene-methacrylic acid copolymer frozen pulverized product 15 parts Lionol Blue FG7310 (trade name, blue pigment: manufactured by Toyo Ink Mfg. Co., Ltd.) 3 parts Isopar H (manufactured by Exxon) 100 parts Dispersing aid 0.5 part The mixture is wet-ground with a 2L attritor for 10 hours,
A liquid developer having an average particle size of 2 μ was obtained. The obtained liquid developer was diluted with Isopar H to a nonvolatile content of 1.5%, and lecithin was added at a ratio of 1.0 part to 1,000 parts of the diluted solution, and an image test was performed. Co-reflection density (reflection densitometer, Macbeth RD-
918), and a good image free of background stains of 1.0 or more was obtained. According to the present invention, if a low-temperature freeze-ground resin is used as a binder component, a liquid developer can be efficiently and stably produced.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-289657 (JP, A) JP-A-2-241787 (JP, A) JP-A-4-13728 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G03G 9/12-9/13

Claims (1)

(57) [Claims 1] A binder is made of a thermoplastic resin having a particle size of 500 μm or less mechanically pulverized by a low-temperature freeze-pulverization method and wet-pulverized together with a coloring agent, a nonpolar solvent and additives. A method for producing a liquid developer for developing an electrostatic image, characterized by comprising: