US 3625897 A
Description (OCR text may contain errors)
United States Patent Inventors l-lazime Machida;
Zenjiro Okuno, both of Tokyo, Japan App]. No. 832,416 Filed June 11, 1969 Patented Dec. 7, 1971 Assignee Kabushiki Kaisha Ricoh Tokyo, Japan Priority June 19, 1968 Japan 43/41885 LIQUID DEVELOPING AGENT FOR  References Cited UNlTED STATES PATENTS 3,001 ,888 9/1961 Metcalfe et al. 252/621 FOREIGN PATENTS 692,023 8/1964 Canada 252/62.1 1,002,061 7/1965 Great Britain 252/62.l 1,020,503 5/1966 Great Britain 252/621 Primary E.raminerGeorge F. Lesmes Assistant Examiner-J. P. Brammer A!lorney-Woodhams, Blanchard and Flynn ABSTRACT: A liquid developing agent for electrophotography comprising a mixed solution consisting of an insulating carrier liquid containing an organic substance having carboxyl group and a colored solution prepared by solving or dispersing a dye and an amine in a polar solvent which is not miscible with the aforementioned carrier liquid.
LIQUID DEVELOPING AGENT FOR ELECTROPIIOTOGRAPHY BACKGROUND OF THE INVENTION l Field of the Invention The present invention relates to an improvement of liquid developers for electrophotography.
The term electrophotograph" used in the specification is intended to mean a visible reproduction of a so-called electrostatic latent image such as a latent image formed by extinguishing the charge in the exposed area and preserving the charge in the not exposed area by exposure of the photoconductive substances through the original. The copying material was previously impressed, by corona discharge, with. an electrical charge all over the photoconductive substance.
2. Description of the Prior Art As the developing solution for wet process electrophotography which is used for developing the latent electrostatic image, there is used a solution prepared by dispersing coloring particles such as carbon black .in a carrier liquid of high resistance and low dielectric constant together with a polaritycontrolling agent like a resin, if necessary. The polarity-controlling agent behaves in such a way as to give the coloring particles the polarity necessary for them to stick fast to the electrostatic latent image and to act as a dispersing agent for achieving the colloidal stability of the liquid developer, and said agent also has a property of fixing the copied image after the development has been completed. Organic hydrocarbon solvents are generally used as a carrier liquid of the liquid developer of this type but they have a defect of being inflammable. There are other types of widely known carrier liquids, one of which comprises a halogenated hydrocarbon and the other of which comprises fluorinated hydrocarbons, both being free from inflammability; however, they have their respective defects, the former being not satisfactory because of its toxicity and the latter because of its high price.
In another case where an electrostatic latent image is developed by the direct use of water as a carrier liquid, the development procedure is rather difficult because the electrostatic latent image is marred heavily. For instance, a liquid developer of W/O emulsion type prepared by adding water, equal in quantity to the undermentioned carrier liquid, to a liquid developer obtained by dispersing a polarity-controlling agent and coloring particles in a carrier liquid of high resistance has been widely known. This liquid developer only aims at eliminating inflammability of the liquid developer by emulsifying water therein by the use of an emulsifying agent, which results in the presence of unnecessary minute water beads which make no contribution to the development of the electrostatic latent image, in the liquid developer wherein a solution of high resistance and low dielectric constant is used as a carrier liquid. Liquid developers of this type have no satisfactory emulsion stability and since they are substantially prepared according to a method in which the coloring particles which have absorbed not so much controlling agent are deposited electrostatically on the latent image, the resultant image does not have very good fixedness.
SUMMARY OF THE INVENTION The present invention relates to a liquid developing agent for electrophotography comprising a mixed solution consisting of a carrier liquid containing an organic substance having a carboxyl group and a colored solution prepared by solving or dispersing a dye and an amine in a polar solvent which is not miscible with the aforementioned carrier liquid.
DESCRIPTION OF THE PREFERRED EMBODIMENTS As specific examples of a polar solvent immiscible with a carrier liquid that can be used in this invention there are enumerated water, alcohols, acetone, methyl cellosolve, dimethyl-formamide and dioxane. For the dyes, in addition to dyes which are either soluble or insoluble in the aforementioned polar solvent and are insoluble in the carrier liquid, for
.instance, alkali blue (0]. Acid Blue 119), carbolan crimson (C.l. Acid Red 138), carbolan blue (C.l. Acid Blue 138) and the like, such dyes as aniline black (CI. Pigment Black 1), spirit black (C.I. Solvent Black 5) and the like having an amino group which coordinates with carboxylic acid can be used effectively. As the amine to be used, it should be an amine of such type as to coordinate with carboxylic acid, namely a tertiary amine to be converted to a quaternary salt compound by coordinating with a carboxyl group. The amine is required to be soluble in the aforementioned polar solvent and immiscible with the carrier liquid. Trimethylamine, triethylamine and triethanolamine, for instance, may be mentioned as being suitable.
As for the organic substance having a carboxyl group and which is to be dissolved in the carrier liquid, besides acrylic acid, polymers and copolymers such as acrylates or methacrylates which contain methacrylic acid, and such unsaturated resins as alkyd resin, maleic acid resin and the like, varnish, rosin and such higher fatty acids as stearic acid and oleic acid can be used. Referring to the carrier liquid, in addition to such hydrocarbon halogenide as toluene, carbon tetrachloride, any of the chemicals, such as naphtha, isoparaffin and paraffin, that have hitherto been commonly used as a carrier liquid of liquid developers can be used in practising this invention.
The procedure to make the liquid developing agent according to the present invention consists of preparing a colored solution obtained by solving or dispersing the aforementioned dyes and amine in a polar solvent and a solution obtained by solving an organic substance which has a carboxyl group in a carrier liquid. Both of the solutions are mixed and stirred fully with a mixer like a homogenizer until a developer of a perfectly homogenized emulsion or suspension is obtained. When dyes having an amino group which coordinate with the carboxylic acid are used in making the developer, the quantity of amine to be added can be decreased to such a degree as to make the amine existing in the colored solution in sufficient quantity to enable it coordinate with the carboxyl group of the organic substance dissolved in the carrier liquid. The emulsification can be promoted by making the colored solution a fatty acid ammonium salt with by the addition of fatty acid beforehand or by using a proper surface active agent if the emulsification or suspension is found to be imperfect.
As mentioned in the foregoing, the developing agent according to the present invention is an emulsion or suspension of a colored polar solution which contains an amine and a solution of a high resistance and low dielectric constant which contains carboxyl group. It is important to determine the ratio of the ingredients of the developing agent in such a way as to present a distinct polarity when the electrostatic latent image is developed. To achieve this purpose it is necessary to mix more than one part by weight of the carrier liquid with one part by weight of the colored solution. A developing agent wherein water is specifically used as a polar solvent to solve the dye is perfectly free from inflammability. Furthermore, the developing agent prepared according to the present invention possesses many excellent merits such as greatly improved dispersibility and stability when compared with those conventional developing agents which are prepared by simply dispersing the polar solvent, in which dyes are solved, in the carrier liquid, since the carboxyl-containing organic substance in the carrier liquid coordinates with the amine contained in the colored solution in which dyes are solved to display an excellent surface activity, and the fixing property of the image is improved very much due to the highly polymerized substance abundantly contained in the developing agent.
EXAMPLE 1 A paste was prepared by mixing a solution, which had been obtained by solving 1 g. of water-soluble carbolan crimson (anthraquinone acid dye manufactured by l.C.1.) in g. of 1 percent trimethylamine-naphthenic acid aqueous solution, 3 percent (by weight) acrylate copolymer and l00 g. of
toluene in the homogenizer for minutes. Ten parts of this paste was dispersed in 50 parts of lsopar H (petroleum hydrocarbon manufactured by Esso Standard Oil Company) to obtain the developing agent. The developing performance of the developing agent thus prepared was not interfered so far as the content of dispersed A paste did not exceed 30 parts.
EXAMPLE 2 B solution was prepared by mixing a solution obtained by solving 125 g. of water soluble carbolan green (anthraquinone acid dye manufactured by l.C.l.) in 150 g. of 1 percent triethanolamine-oleic acid aqueous solution, 3 percent copolymer of styrene methacrylic acid butyl acrylate (mole ratio 50:30:20) and toluene in the homogenizer for minutes. Ten parts of this B solution was dispersed in 50 parts of naphtha No. 6 to obtain the developing agent. The developing property. of the developer thus obtained was not destroyed when the quantity of B solution dispersed in the developer was not in excess of 30 parts.
EXAMPLE 3 One g. of spirit black was mixed with 100 g. of 1 percent triethyl-amine-stearic acid aqueous solution with the homogenizer. This mixture 5 percent copolymer of ethyl acrylate-vinyl benzoic acid-lauryl methacrylate and 50 g. of toluene were mixed with the homogenizer to obtain C solution. Ten parts of this C solution was dispersed in 50 parts of lsopar H to prepare the developing agent. N0 damage of the developing property was observed so far as the quantity of the dispersed C solution remained within the region of 30 parts.
EXAMPLE 4 One g. of aniline black was solved in 100 g. of 1 percent trimethylamine-naphthenic acid. Twenty parts of this solution was dispersed in 50 parts of naphtha No. 6 'to obtain the developing agent.
When the respective developing agents prepared according to the aforementioned examples 1-4 were used to develop the electrostatic latent image of electrophotographic photoconductive paper, each of them produced a clear image and all of the developing agents were found to be stable enough not to show any sign of deteriorated dispersion.
What we claim is:
1. In a liquid developer for electrophotography comprising a carrier liquid selected from the group consisting of toluene, carbon tetrachloride, naphtha and isoparaffic and paraffinic hydrocarbons, said carrier liquid having emulsified or suspended therein a colored solution or dispersion of a dye and a polar solvent, saiddye being selected from the group consisting of alkali blue (C.l. Acid Blue 119), carbolan crimson (C.I. Acid Red 138), carbolan blue (C.l. Acid Blue 138), aniline black (CI. Pigment Black 1), and spirit black (C.l. Solvent Black 5 said polar solvent being selected from the group consisting of water, acetone, methyl cellosolve, dimethylformamide and dioxane, the improvement in which said colored solution or dispersion contains dissolved therein a tertiary amine selected from the group consisting of trimethylamine, triethylamine and triethanolamine, and said carrier liquid contains dissolved therein a carboxyl-containing organic material selected from the group consisting of acrylic acid, acrylate copolymer containing methacrylic acid, methacrylate copolymer containing methacrylic acid, alkyd resin, maleic acid resin, varnish, rosin, stearic acid, oleic acid, styrenem ethacrylic acid-butyl acrylate copolymer and ethyl acrylatevinyl benzoic acid-lauryl methacrylate copolymer, the weight of said carrier liquid present in said developer liquid being greater than the weight of the colored solution or dispersion present'in said carrier liquid.
2. A liquid developer according to claim 1 wherein said colored solution is emulsified in said carrier liquid.
37 A liquid developer according to claim 1 wherein said colored dispersion is suspended in said carrier liquid.
4. A liquid developer according to claim 1 wherein said polar solvent is water.
5. A liquid developer according to claim 2 wherein said dye is dissolved in the polar solvent.
6. A liquid developer according to claim 3 wherein said dye is dispersed in the polar solvent.