JPH073603B2 - Method for producing liquid developer for electrophotography - Google Patents

Description

The present invention relates to a method for producing a liquid developer for electrophotography having excellent image reproducibility, which is used for developing an electrostatic latent image.

"Prior Art" Generally, a liquid developer for electrophotography is provided with a colorant such as carbon black or phthalocyanine blue and the adsorption or coating on the colorant to promote the adjustment and dispersion of the charge of toner particles and the fixing property of the image after development. A coating agent, a dispersant which dissolves or swells in a carrier liquid and imparts dispersion stability to toner particles,
It comprises a charge control agent for controlling the charge amount of toner particles and a carrier liquid having a high electric resistance (10 ⁹ to 10 ¹⁵ Ω · cm).

As a method for producing such a liquid developer, there are generally the following methods. First, a colorant and a resin as a coating material are mixed and melt-kneaded at a temperature not lower than the softening temperature of the coating material using a kneading machine such as a Banbury mixer, an extruder, a kneader, or a three-roll mill to obtain a mixture. Alternatively, the colorant and the coating agent are dispersed and kneaded in the hydrophilic solvent by a disperser such as a ball mill or an attritor, and the kneaded product is dried or added to a non-solvent to obtain a mixture.

The mixture thus obtained is dry pulverized by various pulverizers, and then wet-dispersed with a dispersant by a disperser such as a ball mill, a paint shaker or a sand mill to obtain a toner concentrated liquid. This toner concentrated liquid is added to a carrier liquid containing a charge control agent to obtain a liquid developer for electrophotography.

However, most of the liquid developers obtained in this manner cause tailing on the downstream side of the formed image (downstream side in the direction in which the developer flows), that is, so-called image deletion occurs, or around the characters or line drawings. There was a double image at the same time.

Further, there is a drawback in that the resin coated with the colorant is desorbed with the passage of time, causing aggregation of particles, resulting in an increase in the amount of sedimentation and a change in the amount of charge, which deteriorates the image quality.

The image flow can be reduced to some extent under the developing conditions such as decreasing the flow velocity of the developer, but the developing time is increased and the image density is decreased, which is not always preferable and is solved by the characteristics of the toner particles. Is desired.

Further, desorption of the coating resin from the colorant is an essential problem in the developer prepared in this way, and cannot be solved by an additive such as a charge control agent.

[Problems to be Solved by the Invention] An object of the present invention is to provide a liquid developer for electrophotography which provides excellent image reproducibility without image deletion or double image.

Still another object of the present invention is to provide a liquid developer for electrophotography which is excellent in stability over time.

"Means for Solving the Problems" As a result of earnest research by the present inventors, the electrophotography containing a colorant coated with a polymer resin dispersed in an electrically insulating carrier liquid, and a dispersant. The object of the present invention is achieved by subjecting the liquid developer for dispersion to a dispersion treatment, and then performing a heat treatment at a temperature within a softening range of 20 ° C. lower than the softening start point of the polymer resin.

Next, the present invention will be described in detail.

First, a colorant and a resin as a coating material are mixed and melt-kneaded with a kneading machine such as a Banbury mixer, an extruder, a kneader, or a three-roll mill at a softening temperature of the coating material or higher to obtain a mixture. As another method, the resin is dissolved in the hydrophilic solvent of the coating agent and the colorant is added, and then a ball mill, an attritor,
After dispersing and kneading with a dispersing machine and a kneading machine such as a sand mill, a Banbury mixer, an extruder, a kneader, and a three-roll mill, the kneaded product is dried or added to a non-solvent to cause precipitation to obtain a mixture. Among them, the method of melt-kneading is a preferable method because the adhesion of the colorant and the coating agent is good and the desorption due to the subsequent dispersion process and aging is less than that of other methods.

Next, after dry-milling the mixture thus obtained,
A toner concentrated liquid is obtained by wet dispersion with a disperser such as a ball mill, attritor, paint shaker, or sand mill. This toner concentrated liquid is added to a carrier liquid containing a charge control agent to obtain a liquid developer for electrophotography.
In the present invention, the use liquid diluted with the toner concentrated liquid or the carrier liquid thus obtained is heat-treated at a temperature within a softening range of 20 ° C. lower than the softening start point of the coating resin forming the toner particles. Is characterized by. At this time, the charge control agent may or may not coexist. Preferably, the charge control agent is made to coexist.

The important point here is to perform heat treatment after the dispersion is completed. Here, the term "dispersion" means pulverization by utilizing the collision of media in the presence of media, and the heat treatment of the present invention is carried out with stirring without media or without stirring. When this heat treatment is carried out during dispersion, the effect of the present invention is not exhibited, and conversely the phenomenon of image deletion increases. In addition, when a developing solution is used in the dispersion process in which unexpected heat is generated due to dispersion conditions or mechanical factors, image deletion may occur. If you heat up or generate heat during dispersion,
It is considered that this is because the coating agent resin coating the colorant softens or melts, so that desorption is easily caused by the shearing force applied during the dispersion. The heat treatment conditions such as the heating temperature and the heating time differ depending on the softening temperature of the coating material forming the toner particles. It takes a long time for the effect to be exhibited in heating on the lower temperature side of the heat treatment temperature range allowed by the coating agent, and the effect is exhibited in a shorter time for heating at a higher temperature. However, it is more preferable to heat-treat at a lower temperature for a long time because unnecessary aggregation of toner particles and desorption of the coating agent from the colorant are less likely to occur.

The reason why this effect is expressed has not been elucidated, but the inventors tentatively think as follows. When the particles coated with the coloring agent are subjected to a crushing action or a dispersing action during the dispersion process, the coating agent is partially desorbed from the coloring agent due to impact force or shearing force. If the dispersion is continued, more particles will be desorbed. After the dispersion is completed, the dispersion is a mixture of normally coated particles, particles partially desorbed with the coating agent, and particles desorbed completely. In such a mixture, the adsorption degree of the charge control agent is different, and particles having various charges are present.

Further, the partially desorbed particles are easily desorbed depending on the diameter, and when the amount of charge is changed from that in the initial stage and the image is developed, it appears as a change in the image. When heating is performed at a temperature within the softening range of the coating agent after completion of the dispersion, the coating agent is softened or partially melted to fuse toner particles with each other, resulting in uniform coating and uniform particle size. As a result, the toner particles are evenly charged. As a result, it is presumed that the effects of the present invention will be achieved. If a charge control agent is allowed to coexist during this heat treatment, it is possible to prevent non-uniform aggregation of toner particles due to repulsion between particles due to charge, and it is possible to reduce the heat treatment time dependency. The coexistence is a more preferable form.

The specific heat treatment time is clarified in the examples, but generally, it is sufficient that the temperature is 20 ° C. lower than the softening start point of the coating agent, 6 hours or more, and the softening end time is 1 hour or more. It's different. Therefore, the heat treatment time is from 1 hour to a dozen days, and it may be determined depending on the relationship between the temperature and the manufacturing cost. If the charge control agent coexists, if the optimal treatment time when not coexisting is 12 hours, in many cases the treatment time can be extended to 12 days or more and up to 3 days. The effect is exhibited at any time. It is more effective to treat for as long as possible within the range where aggregation does not occur during heat treatment.

The concentration of toner particles (concentration of coating resin and colorant) at the time of heat treatment is not particularly limited, but it is about 0.1 g to 10 g per 1 when using the used liquid, and about 10 g to 500 g when the toner concentrated liquid is used. Is the concentration of. If the toner particle concentration is within this range, the heat treatment can be effectively performed. Further, no difference has been found in the effect and the required heat treatment time between the case of using the used liquid state and the case of performing the toner concentrated liquid state.

The ratio of the coating resin to the colorant used is preferably about 0.1 to 20 parts by weight, and more preferably about 0.5 to 5 parts by weight, relative to 1 part by weight of the colorant. The dispersant is used in an amount of about 0.1 to 10 parts by weight, preferably about 0.2 to 5 parts by weight, based on 1 part by weight of the colorant. In the case of a toner concentrate, the charge control agent is used in an amount of about 1 × 10 ^-4 to 1 mol / mol, preferably about 1 × 10 ^-3 to 1 × 10 ^-1 mol / mol. In the case of the used liquid, it is about 1 × 10 ^-6 to 1 × 10 ^-2 mol /, preferably about 1 ×.
It is used in an amount of 10 ⁻⁵ to 1 × 10 ⁻³ mol.

As the carrier liquid used in the present invention, many kinds of known ones can be used, but the electric resistance is 10 ⁹ Ω · cm or more and the dielectric constant is necessary because it is necessary not to damage the electrostatic latent image during the developing operation. Three
It is desirable to select the following non-aqueous solutions.

Further, it is necessary to select one having low solubility in the coating agent. In general, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes and the like can be used, but they are isomeric in terms of volatility, stability, toxicity and odor. Paraffin-based petroleum solvents are preferred.

Examples of the isoparaffin-based petroleum solvent include Isopar G, Isopar H, Isopar L, Isopar K manufactured by Etsuso Co., and Cielsol 71 manufactured by Ciel Oil Company.

As the colorant used in the present invention, known pigments and dyes conventionally used for liquid developers or both of them can be used.

For example, Hansa Yellow (CI11680), Benzidine Yellow G (CI21090), Benzidine Orange (CI211)
10), Fearstreed (CI37085), Brilliant Carmine 3B (CI16015-Lake), Phthalocyanine Blue (CI74160), Phthalocyanine Green (CI7426)
0), Victoria Blue (CI42595-Lake), Spirit Black (CI50415), Oil Blue (CI7435)
0), Alkali Blue (CI42770A), Farst Carlet (CI12315), Rhodamine 6B (CI45160), Farst Sky Blue (CI74200-Lake), Nigrosine (CI50415), Carbon black, etc. Surface-treated pigments such as Nigrosine Carbon black dyed with can be used.

As the coating resin, a thermoplastic resin that is insoluble or swells in the carrier liquid is used. These resins have the effect of adhering to the colorant or forming a coating film around the colorant to promote the dispersion of the colorant, and the effect of improving the fixability. Examples of the resin include rubbers such as butadiene rubber, styrene-butadiene rubber, and cyclized rubber, styrene resins, vinyltoluene resins, acrylic resins, methacrylic resins, and copolymer resins thereof, polyester resins, polycarbonate resins, Examples thereof include polyvinyl acetate resin, and various alkyd resins. Acrylic resin,
Methacrylic resins and their copolymer resins are preferably used. The reason is that these resins can easily change the softening point and the solubility in the carrier liquid by changing the alkyl chain length of the ester group.

The softening temperature of the coating resin is generally measured by the ring and ball method, the Martens heat resistance test method, the Pickert test, the heating strain temperature test method and the like. The present inventors measured the softening temperature by the strain gauge method described below.

A method for measuring the softening temperature by the strain gauge method will be described with reference to the drawings. The commercially available hot plate melting point measuring device 1 shown in FIG. 1 and the strain gauge (U-gauge) of Shinko Communication Co., Ltd.
5 was combined and measured. As a result of the measurement, the obtained chart is shown in FIG. 2. The softening point was determined from the displacement due to the flow of the heated resin due to the softening.

Specifically, first, the powder sample 3 of the coating resin is applied to the copper plate 2
And pinch it with slide glass 4. The copper plate side is placed on the hot plate of the hot plate melting point measuring device 1. Place the needle tip of the strain gauge 5 on the slide glass 4 and apply a load of 100 g. The strain gauge displacement should be measured by a recorder. Next, it is heated at a constant temperature rising rate with a melting point measuring device. The strain gauge displacement due to softening is recorded as shown in FIG. From FIG. 2, T _S and T _E are calculated and T _S is a softening start point,
T _E was taken as the softening end point. The temperature between T _S and T _E is defined as the temperature in the softening range. Therefore, the heat treatment temperature means a temperature between T _S −20 ° C. and T _E.

Table 1 shows the softening start point, softening end point and heat treatment temperature range of some polymer resins measured by the strain gauge method.

The dispersant is a resin that enhances the dispersibility of the toner, and is a resin that enhances the dispersibility of the toner by dissolving or swelling in the carrier liquid. For example, rubbers such as styrene-butadiene, vinyltoluene-butadiene, butadiene-isoprene, etc., acrylic-based monomers having a long-chain alkyl group such as 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, etc. Polymers and copolymers of them with other monomers (styrene, (meth) acrylic acid and its methyl, ethyl, propyl ester, etc.), and further graft copolymers and block copolymers are used. be able to. Among these preferable dispersants, the synthetic rubber-based dispersants are effective, and the random or block copolymer of styrene-butadiene copolymer can be used as an extremely effective dispersant.

As the charge control agent used in the present invention, conventionally known charge control agents can be used. For example, metal salts of fatty acids such as naphthenic acid, octenoic acid, oleic acid, stearic acid and the like, metal salts of sulfosuccinic acid esters, JP-B-45-556, JP-A-52-37435, JP-A-52-37049 and the like are shown. Oil-soluble sulfonic acid metal salt, metal salt of phosphoric acid ester shown in JP-B-45-9594, metal salt of abietic acid or hydrogenated abitinic acid shown in JP-B-48-25666, JP-B-55- Alkylbenzenesulfonic acid Ca salts shown in 2620, aromatic carboxylic acids shown in JP-A-52-107837, JP-A-52-38937, JP-A-57-90643, JP-A-57-139753, etc. Metal salts of sulfonic acids, nonionic surfactants such as polyoxyethylated alkylamines, lecithin, oils and fats such as linseed oil, polyvinylpyrrolidone, organic acid esters of polyhydric alcohols, JP-A-57-21
The phosphoric acid ester-based surfactants shown in 0345, the sulfonic acid resins shown in JP-B-56-24944, and the like can be used. In addition, Japanese Patent Application No. 58-128227 and Japanese Patent Application No. 59-17
The amino acid derivatives described in 2955 can also be used. The amino acid derivative is a compound represented by the following general formula (1) or (2), or a reaction mixture obtained by reacting an amino acid with a titanium compound in an organic solvent and further reacting with water. .

(In the formula, R ₁ and R ₂ are hydrogen atoms, an alkyl group having 1 to 22 carbon atoms, a substituted alkyl group (as a substituent, a dialkylamino group, an alkyloxy group, an alkylthio group), a carbon number of 6
Up to 24 aryl groups, substituted aryl groups (as substituents dialkylamino groups, alkyloxy groups, alkylthio groups, chloro groups, bromo groups, cyano groups, nitro groups, hydroxyl groups), aralkyl groups, 1 to 22 carbon atoms Up to an acyl group, an alkylsulfonyl group, an alkylphosphonyl group, an arylsulfonyl group having 6 to 24 carbon atoms, or an arylsulfonyl group. R ₁ and R ₂ may be the same or different, and R _{1 and} R ₂ may form a ring, but they do not simultaneously become hydrogen atoms. A represents an alkylene group having 1 to 10 carbon atoms or a substituted alkylene group. X represents a hydrogen atom, a monovalent to tetravalent metal, or a quaternary ammonium cation. n represents a positive integer. Among these, preferred are metal salts of naphthenic acid, metal salts of dioctylsulfosuccinic acid, lecithin, and the amino acid derivatives. More preferred are zirconium, naphthenic acid, cobalt,
Manganese salt, dioctyl sulfosuccinate calcium,
Mention may be made of sodium salts and metal salts of the compounds of the general formula (1). As the metal salt of the compound of the general formula (1), titanium, cobalt, zirconium and nickel salts are particularly preferable.

Two or more kinds of compounds may be used in combination as these charge control agents.

The toner particle concentration in the developer is not particularly limited, but is about 0.1 g to 10 g, preferably about 0.3 g to 10 g per one.

The developer of the present invention can be used for well-known organic photoconductors or photoreceptors using inorganic photoconductors. The developer of the present invention can also be used for developing an electrostatic latent image produced by means other than photosensitization, that is, by charging a dielectric with a charging needle.

Organic photoconductors include a wide range of well known organic photoconductors. A specific example is "Research Dice Closure" (Re
Search Disclosure) # 10938 (May, 1973, p. 61, pp. 61, paper entitled "Electrophotographic elements, materials and processes").

Practically used products include, for example, poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9.
An electrophotographic photosensitive member comprising an on-type (US Pat. No. 3,484,23
9), poly-N-vinylcarbazole sensitized with a pyrylium salt dye (Japanese Patent Publication No. Sho 48-25658), electrophotographic photoreceptors containing organic pigment as a main component (Japanese Patent Laid-Open No. 49-37543), dyes and resins. There is an electrophotographic photosensitive member (Japanese Unexamined Patent Publication (Kokai) No. 47-10735) containing a eutectic complex consisting of

Examples of the inorganic photoconductor used in the present invention include "Electro-photograph" RM.
Schaffert, Focal Press (London), published (1975)
The various inorganic compounds disclosed on pages 260 to 374 are typical. Specific examples include zinc oxide, zinc sulfide, cadmium sulfide, selenium, selenium-tellurium alloy, selenium-
Examples include silicon alloys, selenium-tellurium-silicon alloys, and the like.

[Examples] Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 Were mixed and melt-kneaded with a three-roll mill at 120 ° C. for 30 minutes. After cooling to room temperature, coarse pulverization and fine pulverization were performed with a hammer mill and a pin mill.

This pulverized product was dispersed with the following composition.

Dispersion was carried out first with an attritor and then with a supermill for 2 hours at a peripheral speed of 10 m / sec. The dispersion liquid thus obtained has a solid content of 13 wt%. The temperature during dispersion was set to 35 ° C.

The following operations were performed on the thus obtained dispersion liquid.

Toner A: Two-fold dilution of the above dispersion with Isopar G.

Toner B: Toner A in the general formula (1) described in the present specification The charge control agent represented by the formula (1) is contained in an amount of 1 × 10 ⁻⁴ mol per 1 g of toner particles.

Toner A and Toner B were heat-treated at 50 ° C. for 3 days. During that time, the stirring operation was not performed at all. Further, Comparative Toner C was prepared without heat treatment. Each toner was diluted with Isopar G so that the solid content was 1 g per one, to prepare developers A, B, and C, respectively. At this time, the same charge control agent as that of the toner B was added to the toners A and C in the same amount.

The charge amount was measured by the device described in JP-A-57-58176.
Also, the particle size is CAPA particle size measuring device manufactured by Horiba Ltd.
Measured at 500. The results obtained are shown in Table 2.

Compared to the comparative developer C, the developer B had a higher charge amount, while the developer A had a lower charge amount. Further, the particle size of the developer A was increased.

Next, 100 parts by weight of poly-N-vinylcarbazole (PVC _z ), 5 parts by weight of vinylidene chloride-acrylonitrile copolymer, 3 parts by weight of styrene-butadiene copolymer, 2,6-di-t-butyl-4- [ A solution of 4- [N, N-dichloroethylamino) styryl] thiapyrylium tetrafluoroborate in 2000 ml of 1,2-dichloroethane was prepared to a thickness of 60 n.
After coating a 100 μm thick polyethylene terephthalate (PET) film (In ₂ O ₃ electroconductive PET film) having a m In ₂ O ₃ vapor-deposited layer, the solvent was removed by drying and drying.
An electrophotographic film was prepared by providing a photoconductive layer having a thickness of 5 μm.

The surface of this film was charged to + 350V and imagewise exposed through a poly original to produce an electrostatic latent image.

When this electrostatic latent image was developed using the above-mentioned developer, Developers A and B gave very good images with almost no double image and image deletion compared to C. 50 each developer
When subjected to forced aging for 7 days at .degree. C., the image deletion and the double image were significantly increased in the developer C, while the image deletion and the double image were slightly increased in the A and B. In addition, there was almost no difference in image quality between A and B, but there was more sedimentation of toner particles in A.

When the developer B and C were electrodeposited on a conductive base and the toner particles were observed with a scanning electron microscope (see FIG. 3), the toner particles became spherical in the heat-treated B as compared to the non-heat-treated C. I knew it had changed to a similar shape. It is considered that the coating resin was partially fused and coalesced by the heat treatment.

The softening temperature range of the coating agent used in this example was measured by a method using a strain gauge, and the softening initiator T _S
It was 63 ° C. and the softening end point T _E was 91 ° C.

Example 2 The concentrated liquid dispersed in the same manner as in Example 1 had a toner particle concentration of 1 g.
It was diluted with Isopar G to be 1/1. At this time, the same charge control agent as in Example 1 was added and not added, and each was heat-treated at 50 ° C. for 7 days. The developer containing no charge control agent was added in the same amount after heating to obtain a developer.

The charge amount and the particle size were measured in the same manner as in Example 1. The results are shown in Table 3.

In the case of heat treatment without adding a charge control agent, the particle size increased and the charge amount decreased. On the other hand, the particles subjected to the heat treatment with the addition of the charge control agent showed almost no change in the particle size and the charge amount increased.

When each developer was developed in the same manner as in Example 1, both developers D and E had image deletion and gave an image without double images. When the sedimentation property was examined, the developer D heat-treated without adding the charge control agent had a larger sedimentation amount than the others, but there was no difference between the developers E and C.

Example 3 In Example 1, the copolymer as a coating agent was stearyl methacrylate / methyl methacrylate (molar ratio 0.5:
Kneading and dispersion were performed in the same manner except that the procedure was changed to 9.5).

Next, heat treatment was carried out at 70 ° C. for 6 hours in the same manner as in Example 1. As a result, the image which had been subjected to the heat treatment gave an excellent image with less double images and image deletion as compared with the image which was not subjected to the heat treatment.

The softening starting point of this coating material was 75 ° C, and the softening ending point was 117 ° C.

Comparative Example 1 In Example 1, the heat treatment was performed after the dispersion was completed, but for comparison, the heat treatment was performed during the dispersion in Example 1.

The heating temperature was 50 ° C. and the dispersion time was 2 hours. After the dispersion was completed, the same charge control agent as in Example 1 was added and diluted with Isopar G to prepare a developer F. The obtained developer had a charge amount of 48 mv / sec and a particle size of 0.27 μm.

Clearly the particle size was reduced and the charge was significantly increased. When the image was developed in the same manner as in Example 1, remarkable image deletion occurred. This result shows that if the heat treatment is carried out during the dispersion, the effect of the present invention is not exhibited, and the heat treatment must be carried out after the completion of the dispersion.

[Brief description of drawings]

FIG. 1 shows a schematic view of a softening point measuring device for coating resin using a strain gauge, and FIG. 2 shows the obtained softening point chart. Further, FIG. 3A shows a scanning electron microscope photograph of toner particles of the developer C of Example 1, and FIG. 3B shows a toner particle of the developer B of Example 1. The scanning electron microscope was observed at a magnification of 5000 times and an inclination angle of 45 degrees. The symbols in FIGS. 1 and 2 indicate the following. 1 ... Heating part of hot plate melting point measuring device 2 ... Copper plate 3 ... Powder sample 4 ... Slide glass 5 ... Strain gauge 6 ... Recorder 7 ... Softening point chart T _S : Softening start temperature T _E : Softening end temperature T _S -20: Temperature lower than softening start temperature by 20 ° C

Claims (3)

[Claims] 1. A dispersion containing a mixture of an electrically insulating carrier liquid, a colorant coated with a polymer resin, and a dispersant, and then subjected to a dispersion treatment at a temperature 20 ° C. lower than the softening start point of the polymer resin to a softening range. A method for producing a liquid developer for electrophotography, which comprises performing heat treatment at a temperature. 2. The method for producing a liquid developer for electrophotography according to claim 1, wherein the heating time of the heat treatment is 1 hour or more. 3. The method for producing a liquid developer for electrophotography according to claim 1, wherein the liquid developer for electrophotography further contains a charge control agent.