A TONER FOR DEVELOPING ELECTROSTATIC LATENT IMAGES AND A METHOD OF PREPARING THE TONER

Abstract: A toner contains an aluminium compound of a hydroxy­ carboxylic acid which may be substituted with alkyl and/­ or aralkyl as a dispersible, stable and heavy-metal free charge control agent.

Description: The present invention relates to a novel negatively chargeable dry toner for developing electrostatic latent images for use in electrophotography, electrostatic recording, electrostatic printing, etc. and to a method of preparing the toner. Electrostatic latent images can be developed into visible images with a toner deposited thereon by electrostatic attraction. Powder developers as well as liquid developers are widely used for developing electrostatic latent images. Powder developers can be divided generally into two-component developers and single-component developers. The two-component developer comprises a finely divided toner having a means particle size of 15 µm and prepared by dispersing a coloring agent, charge control agent, fluidizing agent and the like in a natural or synthetic resin, and a carrier of finely divided iron, ferrite or the like admixed with the toner and 100 to 200 µm in particle size. The latter single-component developer comprises only a finely divided toner having a mean particle size of 15 µm and prepared by dispersing a coloring agent, charge control agent, fluidizing agent, magnetic material and the like in a natural or synthetic resin. Electrostatic latent images are developed with the two-component developer by triboelectrically charging the toner with the carrier and depositing the toner on the latent image. Toners heretofore known and serving as single-component developers include those which are triboelectrically chargeable by a brushlike or platelike friction member used in place of the carrier and having the same function as the carrier. Further provided in recent years are toners which are triboelectrically chargeable by a finely divided magnetic material which is maintained in a dispersed state. These developing toners are charged positively or negatively in accordance with the polarity of the electrostatic latent image to be developed. To enable the toner to retain the charge, it is also proposed to utilize the triboelectric chargeability of the resin used as the main component of the toner, but the toner so adapted is low in chargeability and has a great solid surface resistance value. Consequently the toner image obtained is prone to fogging and obscure. To impart the desired chargeability to toners, it is practice to add to the toner a charge imparting dye or pigment, and a charge control agent. Presently used in the art are oil-soluble nigrosine dyes for imparting a positive charge to the toner as disclosed in Examined Japanese Patent Publication SHO 41-2427, etc., and metal-containing complex salt dyes for giving a negative charge as disclosed in Examined Japanese Patent Publications SHO 41-20153, SHO 43-17955 and SHO 45-26478, etc. However, such dyes or pigments serving as charge control agents are complex in structure and low in stability. For example, they are liable to decompose or degrade, failing to exhibit charge control ability when subjected to mechanical friction and impact, to changes in temperature or humidity or to electric impact, or when exposed to light. Furthermore, they have a substantial defect in that being colored substances, they fail to fulfill the requirement that the charge control agent should be colorless or substantially colorless when to be used for a toner of particular color. Recently, various charge control agents have been disclosed which meet this requirement. Among these, the compounds disclosed in Examined Japanese Patent Publications SHO 55-42452, SHO 58-41508, SHO 59-7348 and SHO 59-26944 contain chromium, cobalt or like heavy metal, while those disclosed in Unexamined Japanese Patent Publications SHO 61-69073 and SHO 61-73963 contain zinc. These compounds therefore have the problem to be solved. EP-A-0 181 081 describes in an electrophotographic process comprising developing a charged image on a photosensitive layer with a chargeable toner to form a toner image, transferring the toner image from the photosensitive layer to a receptor sheet, and fixing it to the receptor sheet, a method of preventing offset which comprises using a toner comprising a fixing resin medium and a hydroxycarboxylic acid complex salt and a releasing agent dispersed therein as the chargeable toner and heat-fixing the toner image by contacting it with a hot roller. Even if there is known a toner for developing electrostatic images which comprises at least one binder resin, a colorant and a metal complex compound of an aromatic hydroxycarboxylic acid, a selection of A1-compounds of such acids cannot be devived from this publication. In view of the foregoing drawbacks of conventional charge control agents, the main object of the present invention is to provide a toner for developing electrostatic latent images having incorporated therein a compound which is useful as a charge control agent for giving a negative charge to the toner, satisfactorily dispersible in the resin component of the toner, highly amenable to pulverization, resistant to the ambient conditions, free from heavy metal or the like and therefore usable with high safety and which can be regarded as almost colorless. To fulfill the above object, the present invention provides a toner for developing electrostatic latent images as claimed in claim 1 which is characterized in that the charge control agent is an aluminum complex compound of an aromatic hydroxycarboxylic acid which is either unsubstituted or substituted with alkyl and/or aralkyl, and a method of preparing a toner as claimed in claim 4. The aluminum compound of an aromatic hydroxycarboxylic acid substituted or unsubstituted with alkyl and/or aralkyl for use in the present invention is prepared from an aromatic hydroxycarboxylic acid substituted or unsubstituted with alkyl and/or aralkyl, by treating the acid with an aluminum imparting agent by a known method. The aluminum compound is obtained, for example, by dissolving a hydroxycarboxylic acid in water with addition of a sufficient amount of an alkali, adding an aluminum imparting agent, such as aluminum chloride or aluminum sulfate, to the solution, heating the mixture and adjusting the pH to 3 to 4 for reaction. The resulting precipitate is filtered off, thoroughly washed with water and dried, whereby the desired compound can be obtained. When required, the reaction can be carried out in an organic solvent. When the aromatic hydroxycarboxylic acid and aluminum are 2:1 in mole ratio, the product will presumably be represented by the following formula. wherein Q and Q' are each an aromatic hydroxycarboxylic acid residue which may be substituted with alkyl and/or aralkyl, and X is a counter ion. In this case, the counter ion can be changed depending on the condition for the aftertreatment of the product. For example, when the reaction mixture is adjusted to a pH of up to 3 before filtration, and the product filtered off is washed until the pH increases to about 6 to about 7, the counter ion is hydrogen ion. If the pH is adjusted to neutrality or alkalinity with an alkali, the counter ion becomes an alkali metal ion or the like. Further treatment, for example, with various amine hydrochlorides affords various ammonium salts. Examples of aromatic hydroxycarboxylic acids which may be substituted with alkyl and/or aralkyl for use in this invention are salicyclic acid, alkyl(C₁-C₁₂)salicyclic acids, 3,5-dialkyl(C₁-C₁₂)salicyclic acids, 1-hydroxy-2-naphthoic acid, 2-hydroxy-3-naphthoic acid, 2-hydroxy-1-naphthoic acid, alkyl(C₃-C₁₂)-2-hydroxy-3-naphthoic acids, 6-(α-methylbenzyl)-2-hydroxy-3-naphthoic acid, etc. The aluminum compound is incorporated into the toner in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, per 100 parts by weight of the resin component of the toner. If the amount of the aluminum compound is less than 0.1 part by weight, the advantage of the invention will not be fully available, whereas when it is more than 5 parts by weight, background smudging or fogging is likely to result. To prepare the toner of the present invention, the aluminum compound is admixed with at least one of known resins for use in toners, such as styrene resin, styrene-acrylic resin, styrene-butadiene resin, epoxy resin, polyester resin and paraffin wax. The resin to be used is selected suitably in view of the adhesion, storage stability and flowability of the toner, the amenability of the toner composition to pulverization, etc. The toner of the present invention may have incorporated therein other additives including, for example, lubricants such as PTFE and zinc stearate, flowability imparting agents such as coloidal silica, titanium oxide and aluminium oxide, anticaking agent, electrical conductivity imparting agents such as carbon black and tin oxide, and auxiliary fixing agents such as low-molecular-weight polyethylene. While a wide variety of known dyes and pigments are usable as coloring agents those especially suited for use in toners for color copies are carbon black, nigrosine dyes, Aniline Black, Benzidine Yellow, Hansa Yellow, chrome yellow, Rhodamine 6G Lake, quinacridone, Rose Bengale, phthalocyanine dyes or pigments including Phthalocyanine Blue B and Phthalocyanine Green, ultramarine, anthraquinone dyes, various dyes soluble in organic solvents, etc. Although the toner of the invention is usually admixed with a carrier to provide a two-component developer, the toner is of course usable as a single-component developer. The present invention will be described below in greater detail with reference to specific preparation examples and examples, in which the parts are all by weight. Preparation Example 1 Preparation of aluminum compound of 3,5-ditertiarybutylsalicylic acid (2:1 in acid/Al mole ratio) A 50 g (0.2 mole) quantity of 3,5-ditert.-butylsalicyclic acid was added to a solution of 8 g (0.2 mole) of NaOH in 500 ml of water, and the mixture was heated to about 60° C to completely dissolve the acid. An aqueous solution of 17.1 g (0.05 mole) of aluminum sulfate in 200 ml of water was slowly added dropwise to the acid solution. The mixture was thereafter stirred at about 90° C for 30 minutes, then adjusted to a pH of about 3 and cooled to about 40° C. The cooled reaction mixture was filtered, and the resulting product was washed with water until the pH of the washings was adjusted to neutrality. The washed product was dried at 90° C, giving about 35 g of a white powder (Compound Example (1) given below. Preparation Example 2 Preparation of aluminum compound of 3,5-ditert.-butylsalicyclic acid and 2-hydroxy-3-naphthoic acid A 17.1 g (0.05 mole) quantity of aluminum sulfate was dissolved in 800 g of water, 25 g (0.1 mole) of 3,5-ditert.-butylsalicyclic acid was added to the solution, and the mixture was heated to 90 to 95° C with stirring. Next, 31.5 g of diethanolamine was diluted with 200 g of water, and the solution was added dropwise to the mixture over a period of 60 minutes. After stirring the resulting mixture for about 30 minutes, 18.8 g of 2-hydroxy-3-naphthoic acid was added to the mixture, followed by stirring at 90 to 95° C for 2 hours. The reaction mixture was cooled to about 40° C and then filtered. The product was washed with water until the pH of the washings was adjusted to neutrality,and was thereafter dried at 90°C, affording about 43 g of a pale yellow powder (Compound Example (2) given below). Preparation Example 3 Preparation of aluminum compound of 5-tert.-butylsalicyclic acid (2:1 in acid/Al mole ratio) in the form of n-butylamine salt A 38.8 g (0.2 mole) of 5-tert.-butylsalicyclic acid was added to a solution of 8 g (0.2 mole) of NaOH in 500 ml of water, and the mixture was heated to about 60° C to completely dissolve the acid. An aqueous solution of 13.3 g (0.1 mole) of aluminum chloride in 300 ml of water was slowly added dropwise to the acid solution. The mixture was thereafter stirred at about 90° C for 30 minutes and then cooled to about 60° C. Subsequently, the reaction mixture was adjusted to a pH of about 10 with an aqueous NaOH solution. A solution of 7.3 g (0.1 mole) of n-butylamine in 100 ml of 1N aqueous hydrochloric acid solution was added dropwise to the mixture over a period of about 30 minutes. The resulting mixture was filtered, and the product was washed with water until the pH of the washings was adjusted to neutrality, and was thereafter dried at 90° C, affording about 46 g of a white powder (Compound Example (3) given below). Specific examples of aluminum compounds are given below. Example 1 The above ingredients were premixed uniformly by a high-speed mixer. The premix was then kneaded in a molten state by an extruder, cooled and thereafter roughly divided by a vibrating mill. The resulting mixture was pulverized by an air jet mill equipped with a classifier, giving a black toner 10 to 20 µm in particle size. A developer was prepared by admixing 95 parts of a particulate iron carrier (TEFV 200/300, product of Nippon Teppum Co., Ltd.) with 5 parts of the toner. The developer was -32.2 µC/g in the amount of initial blowoff charges. The amounts of blowoff charges at a low-temperature low-humidity condition (5° C, 30%) and high-temperature high-humidity condition (35° C, 90%) were -33.0 µC/gr and -32.3 µC/g , respectively, which indicated high stability. When the developer was used for a commercial selenium drum by the magnetic brush developing process, fog-free sharp black toner images were obtained with high thin-line reproducibility. The developer was used for making 50,000 copies continually, but the toner images thereafter produced were found to be free of degradation in quality. Example 2 The above ingredients were treated in the same manner as in Example 1 to prepare a blue toner, and a developer was obtained similarly using the toner. The developer was -21.5 µC/g in the amount of initial blowoff charges, and -21.3 µC/g and -18.9 µC/g in the amount of blowoff charges in a low-temperature low-humidity condition (5° C, 30%) and a high-temperature high-humidity condition (35° C, 90%), respectively. This indicates high stability. When used in the same manner as in Example 1, the developer produced distinct blue toner images free from any fog. The developer was used for making 50,000 copies continually, but the toner images thereafter produced were found to be free of degradation in quality. Example 3 The above ingredients were treated in the same manner as in Example 1 to prepare a red toner, and a developer was obtained similarly using the toner. The developer was -17.8 µC/g in the amount of initial blowoff charges, and -19.6 µC/g and -15.2 µC/g in the amount of blowoff charges in a low-temperature low-humidity condition (5° C, 30%) and a high-temperature high-humidity condition (35° C, 90%), respectively. This indicates high stability. When used in the same manner as in Example 1, the developer gave distinct red toner images free from any fog and with high thin-line reproducibility. The developer was used for making 50,000 copies continually, but the toner images thereafter produced were found to be free of degradation in quality. Example 4 The above ingredients were treated in the same manner as in Example 1 to prepare a yellow toner, and a developer was obtained similarly using the toner. The developer was -23.8 µC/g in the amount of initial blowoff charges, and -23.9 µC/g and -21.9 µC/g in the amount of blowoff charges in a low-temperature low-humidity condition (5° C, 30%) and high-temperature high-humidity condition (35° C, 90%), respectively. This indicates high stability. When used in the same manner as in Example 1, the developer gave distinct yellow toner images free from any fog. The developer was used for making 50,000 copies in succession, but the toner images thereafter produced were found to be free of degradation in quality. Example 5 The above ingredients were uniformly premixed by a ball mill to obtain a premix, which was then kneaded in a molten state at 180°C using a twin-screw extruder (PCM-30, product of Ikegai Seisakusho Co., Ltd.), cooled, roughly crushed, pulverized and classified, giving a toner ranging from 5 to 15 µm in particle size. Two parts of the toner was admixed with 98 parts of a particulate iron carrier (TEFV 200/300, product of Nippon Teppun Co., Ltd.) to obtain a developer, which was found to be -20.1 µC/g in the amount of blowoff charges. When the developer was used for a commercial copying machine (Canon NP201, product of Canon Inc.), fog-free distinct toner images were obtained with good thin-line reproducibility and a reflection density of 1.4 at the solid image area. The toner of the present invention is characterized in that the toner comprises an aluminum compound of an aromatic hydroxycarboxylic acid which may be substituted with alkyl and/or aralkyl and which serves as a charge control agent. The toner is triboelectrically chargeable uniformly with good stability and is outstanding in resistance to ambient conditions (resistance to moisture. During use, the toner remains free of degradation that could lead to variations or reduction in the amount of triboelectric charge and therefore has very high stability. Accordingly, the toner is usable without fogging, staining due to spillage and like objections. Whereas conventional toners have the serious problems of agglomeration, blocking and low-temperature flow during storage, the present toner can be stored for a prolonged period of time free of these problems to give sharp toner images which are excellent in abrasion resistance and amenability to fixing and adhesion. Since the charge control agent is less likely to cause color disturbance, the present toner is usable for color electrophotography to produce copy images of excellent color.

Claims: A toner for developing electrostatic latent images comprising at least one resin, a colorant and a charge control agent consisting of a metal complex compound of an aromatic hydroxycarboxylic acid, characterized in that the charge control agent is an aluminium complex compound of the aromatic hydroxycarboxylic acid, either unsubstituted or substituted with alkyl and/or aralkyl. A toner according to claim 1, characterized in that the toner contains 100 parts by weight of a resin and 0.5 to 5 parts by weight of the aluminium compound. A toner according to claim 1 or 2, characterized in that the toner contains a carrier. A method of preparing a toner for developing electrostatic latent images according to claim 1 by mixing a charge control agent with at least one resin and a coloring agent, other additives being optional, characterized by using as the charge control agent an aluminium complex compound of an aromatic hydroxycarboxylic acid, either unsubstituted or substituted with alkyl and/or aralkyl, in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the resin. A method according to claim 4, characterized by admixing the toner with a carrier.

Inventors: ARAKAWA, MOTOOMI C/O ORIENT CHEMICAL INDUSTRIES,, KIRIU, TAKASHI C/O ORIENT CHEMICAL INDUSTRIES, LTD
Applicants: ORIENT CHEMICAL INDUSTRIES, LTD.
Application year: 1988
Main classification: G03G9
IPC codes: G03G9