JP3057510B2 - Wet developer for electrostatic latent image development - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a wet developer for developing an electrostatic latent image for developing an electrostatic latent image in an electrophotographic process or the like.

[Summary of the Invention]

The present invention improves the stability as a developer by subjecting colorant particles contained in a wet developer to a surface treatment with a silane coupling agent having an oxyethylene unit and an alkyl group, thereby improving resolution and gradation. It is intended to obtain the nature.

[Conventional technology]

In the field of image forming technology, a method of selectively irradiating light onto a uniformly charged photoconductor in accordance with an image signal and developing a formed electrostatic latent image is generally called an electrophotographic process. ing. This electrophotographic process is roughly classified into a dry developing method and a wet developing method.

The dry developing method has an advantage that it is excellent in handling property and preservation property of the developed toner because, in principle, the powder of the coloring agent is simply sprayed and adhered to the electrostatic latent image. However, in order to meet the demand for high-quality images, which has been increasing in recent years, as seen in video printers for printing electronic still photographs, it is necessary to give a step to wet development.

On the other hand, the wet developing method is a method using a liquid developer in which a dye or pigment as a colorant is dispersed in an insulating medium. According to the wet development method, it is possible to obtain resolution and gradation comparable to silver halide photography, and especially when a pigment is used as a colorant, the formed image has excellent weather resistance. , Is being developed in various fields.

Conventionally, as a developer used in a wet development method, a wet developer (hereinafter referred to as a liquid) in which an insulating medium is a liquid substance at normal temperature represented by, for example, a saturated hydrocarbon-based Isopar G (manufactured by Esso Corporation). Is called a toner).

As described in JP-A-2-6966, a wet developer (hereinafter, referred to as a wet developer) in which colorant particles and the like are dispersed in an electrically insulating organic material that is solid at room temperature and liquefies by heating.
It is called a solid toner. ) Has also been proposed. Since this solid toner is solid when stored, it has advantages such as easy handling and little change in composition.

In such a wet developing agent, a resin component such as styrene or dodecyl acrylate has been conventionally used to charge the colorant particles. This resin component is dispersed in the developer to form a complex by interaction with the colorant particles. Since the charge donor is incorporated into the resin component, the colorant particles can be charged via the resin component.

[Problems to be solved by the invention]

By the way, in the technique using the resin component as described above, since it is necessary to add the resin component in an amount of 2 to 5 times the amount of the colorant particles, the composition changes due to repeated development and the resin sticks to the developing device. Etc. is a problem.

In addition, since the adsorption of the resin component to the colorant particles is in an equilibrium state, when the resin component not adsorbed to the colorant particles is large, the resin component adsorbs to the colorant particles during the development of the electrostatic latent image. It is considered that the adsorption of the unreacted resin component to the photoconductor eventually occurs earlier than the fixing of the colorant particles to the photoconductor.
Due to such a decrease in fixability of the colorant particles, a sufficient development density may not be obtained.

Further, in order to reduce the amount of the developer, it is necessary to increase the concentration of the colorant particles in the developer. However, when the concentration of the colorant particles is increased, aggregation of the colorant particles occurs, and the resolution is significantly reduced during development.

Such a phenomenon is particularly remarkable in a solid toner that needs to be heated to dissolve the dispersion medium during development. That is, in the case of the solid toner, the equilibrium state of adsorption of the resin component to the colorant particles is likely to be destroyed by heating, and the aggregation of the colorant particles and the decrease in fixability may occur. For this reason, it is difficult to obtain a high resolution.

Therefore, the present invention has been proposed in view of such conventional circumstances, and has an excellent charge characteristic and dispersion stability, and is capable of developing an electrostatic latent image with excellent resolution and gradation. An object is to provide a wet developer.

[Means for solving the problem]

The present inventors have studied to achieve the above-mentioned object, as a result of applying a silane coupling agent having an oxyethylene unit and an alkyl group to the surface of the colorant particles, without adding a resin component. In both cases, it was found that a developer capable of incorporating a charge donor and exhibiting high dispersion stability was obtained, and the present invention was completed.

That is, the wet developer for developing an electrostatic latent image of the present invention comprises a dispersion medium, colorant particles and a charge donor, and the colorant particles are a silane coupling agent having an oxyethylene unit and an alkyl group. Characterized by having been surface-treated.

As the silane coupling agent having an oxyethylene unit and an alkyl group, the following formula (1) Alternatively, the following equation (2) [However, at least one of X, Y, and Z is halogen or alkoxy (methoxy, ethoxy, etc.). R represents an alkyl group. n is an integer of about 0 to 10. m is an integer of about 2 to 20, preferably about 6 or less. ] The compound shown by these is suitable.

When the surface of the colorant particles is treated with the silane coupling agent, the colorant particles react with a hydroxyl group (for example, a hydroxyl group due to adsorbed water) present on the surface of the colorant particle and chemically bond to the surface.

Therefore, the colorant particles preferably have a hydroxyl group on the surface, but may not necessarily have these functional groups because the reactivity of the silane coupling agent is extremely high.

From such a viewpoint, the colorant particles that can be used include conventionally known inorganic pigments, organic pigments, dyes, and mixtures thereof.

For example, examples of the inorganic pigment include a chromium pigment, a cadmium pigment, an iron pigment, a cobalt pigment, ultramarine, navy blue, and the like. Organic pigments and dyes include Hansa Yellow (CI11680) and Benzidine Yellow G (CI2109
0), benzidine orange (CI21110), fast red (CI37085), brilliant carmine 3B (CI160
15-Lake), Phthalocyanine Blue (CI74160), Victoria Blue (CI42595-Lake), Spirit Black (CI50415), Oil Blue (CI74350), Alkaline Blue (CI42770A), Fast Scarlet (CI12315), Rhodamine 6B (CI45160), Rhodamine Lake (CI45160-Lake), Fast Sky Blue (CI74200-Lake), Nigrosine (CI50415), carbon black and the like. These can be used alone or as a mixture of two or more kinds, and those having a desired color may be selected and used.

In the present invention, the silane coupling agent having an oxyethylene unit and an alkyl group is adsorbed on the surface of the colorant particles by the surface treatment, but the interaction of the silane coupling agent with the charge donor is increased by the oxyethylene unit. In addition, the alkyl group prevents the dispersibility from being lowered.

The oxyethylene unit has a repeating unit of —O—CH ₂ —CH ₂ —, and a coordination field is formed by the oxygen atom.

The oxyethylene unit of the silane coupling agent behaves like a crown ether, and the coordination field formed by the polyoxyethylene chain is surrounded by the metal ion of the charge donor.

The repetition number m of the unit unit of the oxyethylene unit is about 2 to 20, preferably about 6 or less. If m is too large, it will be difficult to dissolve in a nonpolar solvent, and if it is too small, the solubility will be improved but the function as a functional group will be reduced.

On the other hand, the alkyl group of the silane coupling agent may be linear or branched. The alkyl group has about 1 to 30 carbon atoms. If the carbon number is too large, it is difficult to dissolve in a nonpolar solvent.

The wet developer of the present invention contains a dispersion medium, a charge donor, a charge enhancer, and the like in addition to the colorant particles described above.

First, any dispersing medium can be used as long as it is an electrically insulating organic substance, and may be a liquid electrically insulating organic substance at room temperature or an electrically insulating organic substance which is solid at room temperature and liquefies by heating.

As the electrically insulating organic substance which is liquid at normal temperature, for example, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes, etc. can be used, and the volatility, safety, toxicity, odor, etc. Among them, isoparaffinic petroleum solvents are particularly preferable among aliphatic hydrocarbons. Isopar G, isopar G
H, Isopar L, Isopar K (all manufactured by Esso),
Schelsol 71 (manufactured by Shell Sekiyu KK) and the like.

Further, as a solid electrically insulating organic solid toner at room temperature, the melting point is preferably 30 ° C. or more, more preferably 40 ° C., in consideration of a normal use environment and handling properties.
℃ or more. The upper limit of the melting point is not particularly limited, but practically about 100 ° C. or less, more preferably 8
0 ° C or less. The reason for this is that extra energy is consumed for heating even if the melting point is too high, and that the material must not exceed the heat resistance temperature of the material generally used as a base when used while being held on the base. It depends. Materials that meet these requirements include paraffins, waxes, and mixtures thereof. First,
Examples of paraffins include various normal paraffins having 19 to 60 carbon atoms ranging from nonadecane to hexacontan. Examples of the waxes include vegetable waxes such as carnauba wax and cotton wax, animal waxes such as beeswax, ozokerite, and petroleum waxes such as paraffin wax, microcrystalline wax and petrolatum. These materials are dielectrics having a dielectric constant of about 1.9 to 2.3. Further, a crystal having a long acryl group in a side chain, such as a homopolymer or a copolymer of a polyacrylate such as polyethylene, polyacrylamide, poly n-stearyl acrylate, and poly n-stearyl methacrylate (copoly n-stearyl acrylate ethyl methacrylate). Although hydrophilic polymers can be used, the above-mentioned paraffins and waxes are preferable in consideration of the viscosity during heating and the like. A charge donor is usually added to a wet developer.
Usable charge donors include, for example, metal salts of fatty acids such as naphthenic acid, octenoic acid, oleic acid, stearic acid, isostearic acid or lauric acid, metal salts of sulfosuccinates, metal salts of oil-soluble sulfonic acid esters, abieticin Metal salts such as acids, metal salts of aromatic carboxylic acids and metal salts of aromatic sulfonic acids.

Also, in order to improve the charge of the colorant particles,
Metal oxide particles such as O ₂ , Al ₂ O ₃ , TiO ₂ , ZnO ₃ , Ga ₂ O ₃ , In ₂ O, GeO ₂ , SnO ₂ , PbO ₂ , MgO and mixtures thereof are added as charge enhancers. May be.

Regarding the compounding ratio of each of the above-mentioned components, first, the amount of the colorant particles is preferably 0.01 to 100 g, more preferably 0.1 to 10 g, per 1 of the dispersion medium. In order to perform particularly efficient development and suppress the amount of waste toner, the concentration with respect to the dispersion medium [the ratio of the dispersion medium to the colorant (dilution ratio)] is 2 to 10% by weight.
It is preferable that

Note that the concentration range of the coloring agent is a concentration in the developing step to the last, and may be concentrated to a higher concentration during storage, for example.

The charge donor is added in the range of about the same amount or less as the colorant particles, and is generally in the range of 0.001 to 10, preferably 0.01 to 1 g, based on the dispersion medium 1 like the colorant particles. Further, the charge enhancer is added in a weight ratio of not more than twice, preferably not more than the weight of the colorant particles.

[Action]

When the colorant particles are surface-treated with a silane coupling agent having an oxyethylene unit and an alkyl group, as shown in FIG. 1, the silane coupling agent (1) reacts with a hydroxyl group or the like on the surface of the colorant particles (2). And is chemically bonded to the surface of the colorant particles (2).

When the charge donor acts on the colorant particles (2), the oxyethylene unit (1a) present in the silane coupling agent (1) adsorbed on the colorant particles (2)
It behaves like a crown ether, and the metal ion (3) of the charge donor is incorporated into the coordination field formed by the oxyethylene unit (1a).

Further, since the silane coupling agent (1) has an alkyl group (1b) at a terminal, it has high compatibility with a nonpolar solvent. Accordingly, when the silane coupling agent (1) is adsorbed on the colorant particles (2), the aggregation of the colorant particles (2) is suppressed, and a wet developer for electrostatic latent image development having excellent dispersion stability is obtained. .

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on experimental results.

Synthesis of Silane Coupling Agent A Silane coupling agent A having an oxyethylene structure and a long-chain alkyl group was synthesized by the following route.

Synthesis of Silane Coupling Agent B Silane coupling agent B having an oxyethylene structure and having a long-chain alkyl group and an ester bond was synthesized by the following method.

First, N, N'-dicyclohexylcarbodiimide (DCC) was mixed with arachidic acid and tetraethylene glycol at room temperature in chloroform and esterified. By this reaction, a white precipitate CH ₃ (CH ₂ ) ₁₈ COO (CH ₂
—CH ₂ —O) ₄ H was obtained. The reaction at this time is represented by the following equation (5).
Shown in

Next, NaH was added to the product in the above reaction using dehydrated dimethylformamide (DMF) as a solvent, and the mixture was stirred at about 80 ° C. for about 2 hours. Thereafter, 3-chloropropyltrimethoxysilane, which is a silane coupling agent, is added, and the mixture is stirred at about 35 ° C. for about 2 to 3 hours. The resulting precipitate is dissolved in n-hexane or cyclohexane, and purified until neutral. After washing with water, the obtained product was used as a silane coupling agent B. The reaction at this time is represented by the following equation (6),
This is shown in (7).

Each product in each of the above reactions was confirmed by nuclear magnetic resonance (NMR) measurement.

Example 1 An azo yellow pigment was used as a colorant particle. About 0.5 g of this yellow pigment was mixed with several μ to several hundred μ of the silane coupling agent A synthesized as described above, and the mixture was kneaded. Processing was performed. At this time, about 0.5 g of isoparaffin-based solvent (Isopar H) was used as a solvent. Then, the surface-treated yellow pigment is
The processed powder was prepared by finer processing by the Mahler method.

The reaction between the yellow pigment and the silane coupling agent A is as follows.

Approximately 0.5 g of yellow pigment surface-treated as described above
Dispersed in ml of Isopar H.
Several tens of n was added and stirred for several hours to prepare a developer.

Example 2 Approximately 0.5 g of a yellow pigment surface-treated in the same manner as in Example 1 was dispersed in 50 ml of paraffin liquefied by heating (melting point: about 40 to 100 ° C.). 10 n was added, and the mixture was stirred for several hours while maintaining the temperature at 50 to 70 ° C. to prepare a developer.

Example 3 A developer was prepared in the same manner as in Example 1 except that 0.03 to 0.75 g of silane coupling agent B was added instead of silane coupling agent A used in Example 1 above.

The reaction between the yellow pigment and the silane coupling agent B is as follows.

Example 4 A developer was prepared in the same manner as in Example 2 except that 0.03 to 0.75 g of a silane coupling agent B was added instead of the silane coupling agent A used in Example 2 above.

As described above, development was performed for the purpose of evaluating the development characteristics of the developers prepared in the respective examples.

As a result, in Examples 1 to 4, even when a yellow pigment having the lowest dispersibility and being generally difficult to develop was used, a high resolution of 50 lines / mm or more was obtained, and The toner exhibited good fixability, dispersibility, gradation, and transparency.

Also, from the results of Examples 2 and 4, even if the solid toner needs to be heated during development, if the colorant particles are surface-treated with the silane coupling agent according to the present example,
It was found that excellent development characteristics were obtained. This is because there is no adsorption equilibrium that occurs in the system such as the resin component and the colorant particles, so that even if the dispersion medium is heated to liquefy, there is no risk of aggregation of the colorant particles and high charge characteristics are maintained. It is thought that it is possible.

[Effects of the Invention] As is clear from the above description, in the present invention, the surface treatment with a silane coupling agent having an oxyethylene unit and an alkyl group is performed, and the colorant particles are chemically treated with the silane coupling agent. The charge donor is taken into the oxyethylene unit, and a strong charge structure can be secured. In this charging structure, since there is no adsorption equilibrium that occurs in a system such as a resin component and colorant particles, high charge characteristics can be maintained even at a high temperature. Therefore, even if the dispersion medium is heated to liquefy, the charge donor does not separate from the colorant particles, and the wet development is excellent in resolution, gradation and fixability even at a high temperature of about 50 to 70 ° C. And is useful when applied to a solidified wet toner type developer.

Further, since good dispersion stability is obtained by the alkyl group of the silane coupling agent, there is no possibility that aggregation of the colorant particles occurs even if the concentration of the colorant particles is increased.

Furthermore, in the present invention, since there is no need to use a resin component to charge the colored particles as in the related art, there is no occurrence of a change in composition due to repeated development or sticking of the resin to the developing device.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the state of metal ion uptake by an oxyethylene unit of a silane coupling agent adsorbed on the surface of colorant particles. (1) silane coupling agent (1a) oxyethylene unit (1b) alkyl group (2) colorant particles (3) metal ion

Claims (1)

(57) [Claims] 1. A colorant comprising a dispersion medium, colorant particles and a charge donor, wherein the colorant particles are surface-treated with a silane coupling agent having an oxyethylene unit and an alkyl group. Wet developer for developing electrostatic latent images.