JP5298651B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wet type developing device which is excellent in both of fixing properties and transfer property with respect to the wet type developing device using wet type developers, comprising carrier liquid having a high-boiling point. <P>SOLUTION: The wet type developing device is used for an image forming apparatus which transfers a plurality of developed toner layers onto an image support. The wet type developing device comprises a plurality of wet type developing liquids, made by dispersing toner particles into nonvolatile carrier liquid, wherein a glass transition temperature of the toner particles in the wet type developing liquid used for forming the toner layer of the uppermost layer among the plurality of toner layers is higher than the glass transition temperature of the toner particles, in the wet type developing liquid used for forming the toner layer of the lowermost layer among the plurality of toner layers. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

Copier, regarding the printer, the image forming apparatus using a liquid electrophotographic method such as a digital printing machine.

  In electrophotographic image formation, generally, an electrostatic latent image is formed on an electrostatic latent image carrier such as a photoconductor by image exposure according to a document image or image data. The electrostatic latent image is developed into a visible toner image, and the toner image is transferred and fixed on a recording material to obtain a target image.

  Development methods can be divided into dry development methods and wet development methods. In the dry development method, a toner or a toner added with a carrier having magnetism or the like is used as a developer. The dry toner usually uses a pigment and a binder resin as main components, and a charge control agent, a conductivity control agent, a plasticizer, a release agent and the like are added or added as necessary. On the other hand, in the wet development method, a wet developer in which toner particles containing a pigment and a binder resin as main components, a charge control agent, a dispersion stabilizer and the like are dispersed in an electrically insulating dispersion medium (carrier liquid). ing. The toner particles used in the wet developer can be made fine because there is no fear of escaping into the atmosphere, and those having an average particle size of submicron are also practical. Therefore, there are advantages such that an image having a high resolution can be obtained and gradation is excellent.

The wet developer can be used for color image formation by taking advantage of the characteristic that high resolution is obtained by its small particle size. For example, Patent Documents 1 and 2 describe the application of wet developers to color image formation. For example, Patent Document 2 discloses a wet electrophotographic apparatus that includes a latent image forming unit, a developing unit, and a transfer unit, and the developing unit includes four developing units. It is described that a toner image is developed, and the toner image is fixed and transferred onto a sheet by a transfer device.
JP-T-2005-516257 JP 2000-25271 A

  A wet developing apparatus used in a full color process contains a plurality of wet developers (wet developers of each color) in which toner particles are dispersed in a non-volatile carrier liquid, and an image carrier using the plurality of wet developers. A plurality of toner layers corresponding to the plurality of wet developing solutions are stacked on the latent image to develop the latent image on the image carrier. Conventionally, toner particles having the same average particle diameter and Tg have been used for each color wet developer. Therefore, there is no positive movement of the excess carrier liquid in the fixing nip, and the uppermost toner first contacting the fixing roller is melted first. Therefore, excess carrier liquid generated when all the toner is melted is discharged from the toner layer to the paper side or remains in the toner layer. As a result, the toner layer strength is reduced, or a carrier liquid (excess carrier liquid) exceeding the liquid absorption capacity of the paper is discharged between the toner and the paper, resulting in the formation of a release layer between the toner layer and the paper. And caused problems such as no adhesion to paper. Therefore, improvement of the fixing property is a problem.

SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus including a wet developing apparatus using a wet developer using a high-boiling carrier liquid and having improved fixability.

To solve the above problem, an image forming apparatus of the present invention is an image forming equipment for transferring a plurality of toner layers developed on the image supporting member, the toner particles are dispersed in non-volatile carrier liquid comprising a plurality of wet development apparatus for developing using a wet developer was, the plurality of toner layers of the glass transition temperature of the toner particles of the wet developer used to form the uppermost layer of the toner layer (hereinafter, referred to as Tg .) Is higher than the glass transition temperature of the toner particles in the wet developer used to form the lowermost toner layer of the plurality of toner layers, and further has a plurality of fixing nips and has a first stage fixing. At least the lowermost toner layer is fixed at the nip, and the uppermost toner layer is fixed at the second and subsequent fixing nips.

  In the present invention, the Tg of the toner particles in the wet developer used to form the uppermost toner layer is the same as that of the toner particles in the wet developer used to form the lowermost toner layer. It is preferably 5 to 20 ° C. higher than Tg.

  Further, the plurality of wet developers are intermediate between the wet developer used to form the lowermost toner layer and the wet developer used to form the uppermost toner layer. And a wet developer used to form the lowermost toner layer, and a wet developer used to form the intermediate toner layer. The Tg of the toner particles is preferably increased in the order of the developer and the wet developer used to form the uppermost toner layer.

  Moreover, it is preferable that Tg of the toner particles contained in the plurality of wet developers is 65 to 85 ° C.

  According to the present invention, the Tg of the toner particles in the wet developer used to form the uppermost toner layer of the plurality of toner layers is used to form the lowermost toner layer in contact with the image carrier. By making it larger than the Tg of the toner particles in the developer, the lowermost toner layer can be melted quickly to form a block layer, so that the excessive carrier liquid can be prevented from moving to the paper side. it can. As a result, the carrier liquid can be effectively removed during fixing, so that sufficient fixing strength can be obtained.

Embodiments of the present invention will be described below.
Figure 1 is a schematic diagram showing an example of the configuration of images forming apparatus of the present invention. Around the drum-shaped intermediate transfer member 105, a wet developing device 100 including developing devices 104, 103, 102, 101 is arranged in order in the rotation direction indicated by the arrow. Each of the developing devices 104, 103, 102, and 101 has a latent image carrier (not shown) made of a photosensitive member and a developing tank (not shown) for storing a wet developer. In each developing device, a wet developer is supplied to the latent image carrier, a toner layer is formed, and the latent image on the latent image carrier is developed. The toner layer of the latent image carrier of each developing device is transferred to the intermediate transfer member 105 in the order of the upstream developing device 104, the developing device 103 on the downstream side, the developing device 102, and the developing device 101 in this order. A toner layer is formed. The four toner layers are transferred to the image support 107 such as paper or film by the secondary transfer roller 106, and the toner is fixed by the heat rollers 108 and 109.

  FIG. 1 shows a configuration in which each developing device includes a photosensitive member and a plurality of toner layers are superimposed on the intermediate transfer member. However, the intermediate transfer member is not used and a plurality of toner layers are directly formed on an image support such as paper. A configuration in which toner layers are superposed or a configuration in which a single photoconductor is used and a plurality of toner layers are superposed on the photoconductor can also be used.

  Although FIG. 1 shows an example having one fixing nip composed of a pair of heat rollers, a plurality of fixing nips may be provided as will be described later.

The wet developer used in the wet developing apparatus used in the image forming apparatus of the present invention contains at least a carrier liquid, toner particles and a dispersant.
(Carrier liquid)
For the carrier liquid, a non-volatile solvent having a high dielectric constant with a dielectric constant of 3 or less can be used. Furthermore, a solvent having no odor and toxicity is preferred. In general, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, polysiloxanes and the like can be mentioned. In particular, a normal paraffin solvent and an isoparaffin solvent are preferable in terms of odor, harmlessness, and cost. Specifically, Moresco White (manufactured by Matsumura Oil Research Co., Ltd.), Isopar (manufactured by Exxon Chemical), Shellsol 71 (manufactured by Shell Petrochemical), IP Solvent 1620, IP Solvent 2028 (all of which are Idemitsu Petrochemical) Etc.). In the present invention, the non-volatile solvent is a solvent having a flash point of 70 ° C. or higher unless otherwise specified.

(Toner particles)
The toner particles include at least a binder resin and a colorant, and may further include additives such as a wax and a charge control agent as necessary. The toner particles are preferably contained in the carrier liquid in an amount of 10 to 50% by weight. The volume average particle diameter of the toner particles is preferably 0.5 to 4 μm. If it is smaller than 0.5 μm, the amount of toner that does not move by the electric field increases, which is not preferable. Moreover, it is because image quality will deteriorate when it becomes larger than 4 micrometers.

  The Tg of the toner particles in the wet developer used to form the uppermost toner layer is larger than the Tg of the toner particles in the wet developer used to form the lowermost toner layer on the image support side. High is preferred. Generally, Tg is related to the melting start temperature of toner particles, and the lower Tg, the more the toner particles can be melted and fixed at a lower temperature. By lowering the Tg of the toner particles in the lowermost toner layer on the image support side, the lowermost toner layer is melted quickly to form a film, thereby forming a block layer for the surplus carrier liquid. Can be suppressed. Excess carrier liquid is discharged from the upper toner layer. As a result, the fixing strength between the toner layer and the image support increases, and the offset can also be reduced.

  The Tg of the toner particles in the wet developer used to form the uppermost toner layer is larger than the Tg of the toner particles in the wet developer used to form the lowermost toner layer on the image support side. It is preferably 5 to 20 ° C higher. If the difference in Tg is within this range, the difference in melting rate between the lowermost layer and the uppermost layer becomes large, so that the excess carrier liquid can be efficiently discharged from the upper layer. If it exceeds 20 ° C., the gloss and offset resistance are lowered, which is not preferable.

  In addition, the plurality of wet developers include a wet developer used to form the lowermost toner layer, a wet developer used to form the uppermost toner layer, and an intermediate toner layer. A wet developer used to form the lowermost toner layer, a wet developer used to form the intermediate toner layer, and an outermost developer. The Tg of the toner particles is preferably increased in the order of the wet developer used for forming the upper toner layer. Accordingly, it is possible to more efficiently discharge the excess carrier liquid from the upper toner layer while suppressing the return to the lower layer. Thereby, the fixing strength can be further increased.

  The Tg of the toner particles is preferably 20 to 85 ° C. More preferably, it is 60-80 degreeC. The “Tg of toner particles” referred to here is Tg in a dry toner state before being made into a wet developer. Use of a toner having a Tg lower than 20 ° C. facilitates melting and tends to cause offset at the time of fixing, and using a toner having a Tg higher than 85 ° C. significantly increases the amount of heat required for fixing and lowers glossiness. Absent.

  When the Tg of the plurality of toner layers is lowered on the lower layer side as described above, a plurality of fixing nips can be provided in accordance with the Tg of each toner layer. For example, in the first fixing nip, fixing is performed at a fixing temperature and nip time at which the uppermost toner layer is not substantially fixed, and the toner layer lower than the uppermost layer, at least the lowermost toner layer is fixed. In the fixing nips after the stage, it is preferable to fix at the fixing temperature and nip time at which the uppermost toner layer is fixed. In the fixing from the first stage fixing to the final stage, the excess carrier liquid is mainly discharged, and in the final stage fixing, the surface smoothness of the fixing toner layer can be improved. As a result, the amount of carrier liquid in the fixing toner toner layer can be reduced and the smoothness of the fixing toner layer can be improved as compared with the case of fixing in one step. Thereby, higher fixability and gloss can be obtained.

(Binder resin)
The binder resin is a thermoplastic resin and is not particularly limited as long as it does not substantially dissolve in the carrier liquid. A polyester resin or a styrene acrylic resin can be used, but a polyester resin is preferable. The polyester resin has sharp melt properties, and it is possible to achieve both storage stability and fixability.

  Specifically, the polyester resin means a resin obtained by polycondensation of a polybasic acid and a polyhydric alcohol. As polybasic acids, isophthalic acid, terephthalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid and its acid anhydride, trimellitic acid, trimesic acid, pyromellitic An acid etc. can be mentioned. Isophthalic acid, terephthalic acid, and trimellitic acid are preferable.

  As the polyhydric alcohol, the polyhydric alcohol is not limited to these, but propylene glycol such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, dipropylene glycol, 1,4- Butanediol such as butanediol, neopentyl glycol, alkylene glycol (aliphatic glycol) such as 1,6-hexanediol and alkylene oxide adducts thereof, bisphenols such as bisphenol A and hydrogenated bisphenol, and addition of these alkylene oxides Phenolic glycols of the product, alicyclics such as monocyclic or polycyclic diols, and aromatic diols, triols such as glycerin and trimethylolpropane. These can be used alone or in admixture of two or more.

(Dispersant)
In order to stably disperse the toner particles in the insulating liquid, it is preferable to use a dispersant that is soluble in the insulating liquid. The type of the dispersant is not limited as long as it stably disperses the toner particles, but a polymer dispersant having a basic group is preferable as the one that stably disperses the toner particles. Basic groups include aromatic amino groups, aliphatic amino groups, heterocyclic nitrogen-containing groups, heterocyclic oxygen-containing groups, and heterocyclic sulfur-containing groups. Specifically, a polymer dispersant having at least one basic group selected from the group consisting of an amino group, an imino group, an amide group, and a pyrrolidone group can be used. For example, a polyalkylene polyamine, a salt of a long-chain polyaminoamide and a high molecular weight acid ester, a salt of a polyaminoamide and a polar acid ester, a modified polyurethane, a polyester polyamine, a polyester polyimine, polyvinyl pyrrolidone, or the like can be used. Polyester polyamine, polyester polyimine, and polyvinyl pyrrolidone are preferable.

(Coloring agent)
The colorant is not limited thereto, but the following pigments can be used. A typical colorant for black is carbon black. Examples of colorants other than black include yellow pigments, magenta pigments, and cyan pigments. Color image formation is performed by subtractive color mixing based on these pigment colors. Examples of cyan pigments include C.I. I. Examples thereof include copper phthalocyanine blue cyan pigments such as Pigment Blue 15: 1 and 15: 3. Examples of magenta pigments include C.I. I. Pigment Red 48, 57 (Kermin 6B), 5, 23, 60, 114, 146, 186 and the like azo lake-based magenta pigments, insoluble azo-based magenta pigments, thioindigo-based magenta pigments, C.I. I. And quinacridone-based magenta pigments such as Pigment Red 122 and 209. Examples of yellow pigments include disazo yellow pigments represented by Color Index (CI) Pigment Yellow 12, 13, 14, 17, 55, 81, 83, and the like. The amount of the colorant added to the binder resin is preferably 5 to 30 parts by weight with respect to 100 parts by weight of the resin.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to a following example. In the examples, “parts” means “parts by weight” unless otherwise specified.

(Synthesis of polyester resin)
700 parts (polyhydric alcohol) of propylene oxide adduct of bisphenol A and 300 parts of terephthalic acid (polyvalent base) as monomers in a four-necked flask equipped with a stirrer, partial condenser, nitrogen gas inlet tube and thermometer Acid), nitrogen gas was introduced with stirring, and polycondensation was performed at a temperature of about 180 ° C. The temperature was lowered to about 100 ° C. for a predetermined time, and 0.01 part of hydroquinone was added as a polymerization inhibitor to stop polycondensation. What was obtained by this was made into the polyester resin 1 (PEs1).

  Furthermore, polyester resins 2 to 9 (PEs 2 to 9) were obtained in the same manner as described above except that the resin composition and the reaction time were changed. Table 1 shows the composition and Tg of the obtained polyester resin.

(Manufacture of toner)
100 parts of PEs1 and 10 parts of carbon black Mogal-L (manufactured by Cabot) were sufficiently mixed with a Henschel mixer, and then melt-kneaded using a co-rotating twin-screw extruder having a heating temperature in the roll of 100 ° C. The mixture was cooled and coarsely pulverized to obtain a coarsely pulverized toner.

  Further, coarsely pulverized toner was obtained for each resin and each color using PEs 2 to 8 and a phthalocyanine pigment, magenta pigment or yellow pigment in the same manner as the above coarsely pulverized toner.

(Synthesis of dispersant)
Moresco White P40 (manufactured by Matsumura Oil Research Co., Ltd.) 100 parts, 45 parts lauryl methacrylate, 3 parts N-vinyl-2-pyrrolidone as a basic monomer and 0.2 part azobisisobutyronitrile as a polymerization initiator Was reacted at a reaction temperature of 60 to 70 ° C. for about 12 hours under a nitrogen atmosphere to obtain an N-vinylpyrrolidone / lauryl methacrylate copolymer.

(Manufacture of wet developer 1)
75 parts of Moresco White P40 (manufactured by Matsumura Oil Research Co., Ltd.), 25 parts of coarsely pulverized toner using PEs1 and 0.5 part of the above dispersant were mixed, and wet pulverized with a sand mill. Wet pulverization was stopped when the predetermined toner particle size was reached, and the wet developer of Example 1 was obtained. Similarly, a wet developer was obtained using a coarsely pulverized toner composed of each resin and each pigment and a dispersant.

(Manufacture of wet developer 2)
In the presence of a surfactant, a pigment dispersion was added to an emulsion obtained by copolymerizing styrene, butyl acrylate, and acrylic acid, aggregated with magnesium chloride, and heated to obtain a colored resin emulsion. The emulsion was dried, added to the carrier liquid, and vigorously stirred to obtain a styrene-acrylic wet developer 1 (abbreviated as St1). The colored resin fine particles had a volume average particle size of 2.0 μm and a glass transition point of 72 ° C. Furthermore, it manufactured similarly by changing a composition and reaction conditions, and obtained the styrene-acryl type wet developers 2-4 (it abbreviates as St2-4).

(Evaluation method)
The Tg and average particle diameter of the toner particles used in the examples were measured by the following methods.
(Measurement method of glass transition point)
The Tg of the toner particles was measured using a differential scanning calorimeter (DSC-6200; manufactured by Seiko Instruments Inc.). As a measurement sample, 20 mg of the coarsely pulverized toner of Examples and Comparative Examples was used, and 20 mg of alumina was used as a reference. In a nitrogen gas atmosphere (30-50 ml / min), the temperature was increased from room temperature to 200 ° C. at a rate of temperature increase of 10 ° C./min, and immediately after cooling to 0 ° C. at 30 ° C./min, the temperature increased as 2nd run. Measurements were made at a temperature rate of 10 ° C./min. The shoulder value of the endothermic shift derived from the glass transition of the resin in the range of 30 to 100 ° C. measured at 2nd run (the temperature at the intersection of the extension line of the base line and the tangent line of the endothermic shift; see FIG. 2) was Tg.

(Measurement method of toner particle size)
A small amount of developer was diluted in a carrier solution, and the volume average particle size was measured with a laser diffraction particle size distribution analyzer SALD-2200S (manufactured by Shimadzu Corporation).

Using the experimental apparatus of the image forming apparatus shown in FIG. 1, a live-action test was performed according to the following procedure, and the following items were evaluated.
Example 9:
In the case of forming a four-layer toner layer, an unfixed toner image of the first color (Y) was first formed on a photoconductor in a desired development process and transferred to an intermediate transfer body with a desired voltage. Subsequently, the unfixed toner images on the photosensitive member are superimposed on the intermediate transfer member in the order of magenta (M), cyan (C), and black (Bk) in the downstream, and then transferred onto the medium, and the image is transferred through a fixing step. Output. The system speed was 40 cm / s, and negatively charged OPC was used for the photoreceptor.
Reference Examples 1-5, Examples 1-3 , 4-6 and Comparative Examples 1-6:
When three toner layers were formed, unfixed toner images on the photoreceptor were superposed on the intermediate transfer member in the order of magenta (M), cyan (C), and black (Bk).

(Fixing strength test)
Solid patterns (10 cm × 10 cm, adhesion amount 2 mg / m ² ) of the liquid developers of Reference Examples, Examples and Comparative Examples were formed on fine paper / coated paper. Subsequently, fixing was performed with a heat roller (180 ° C. × nip time 80 msec). Thereafter, the part without offset is rubbed twice with a pressing load of 9.80 N with an eraser (manufactured by Lion Koki Co., Ltd., sand extinguisher “LION 26111”), and the residual ratio of image density is “X-Rite model 404” manufactured by X-Rite. ”And the following four ranks were evaluated.
A: Image density residual ratio is 90% or more.
○: Image density remaining rate is 80% or more and less than 90%.
Δ: Image density remaining rate is 70% or more and less than 80%.
X: Image density residual ratio is less than 70%.

(Glossiness test)
Solid patterns (10 cm × 10 cm, adhesion amount 2 mg / m ² ) of the liquid developers of Reference Examples, Examples and Comparative Examples were formed on fine paper / coated paper. Subsequently, fixing was performed with a heat roller (180 ° C. × nip time 80 msec). The glossiness was measured using a gloss meter (VG2000, manufactured by Nippon Denshoku Industries Co., Ltd.). The glossiness of the fixed image was measured.
A: The glossiness is 25 or more.
○: Glossiness is 20 or more and less than 25.
X: Glossiness is less than 20.

(Offset resistance evaluation method)
Solid patterns (10 cm × 10 cm, adhesion amount 2 mg / m ² ) of the liquid developers of Reference Examples, Examples and Comparative Examples were formed on fine paper. Subsequently, fixing was performed with a heat roller (180 ° C. × nip time 80 msec). When fixing an unfixed image, white plain high-quality paper is passed through the fixing device immediately after passing the fixed image. The amount of the toner offset on the surface of the heating roller fixed on the high-quality paper was evaluated. The evaluation rank is set as follows.
◎… No toner adhesion ○… A very small amount of toner adheres
Δ: A small amount of toner adheres

(result)
Tables 2 and 3 show the evaluation results. In the examples, the adhesive strength with paper was high, high fixability was obtained, and excellent gloss was obtained. Further, the gloss can be further enhanced by setting the number of fixing steps to two.

Is a schematic diagram showing an example of the configuration of images forming apparatus of the present invention. It is an example of the graph which shows the evaluation method of Tg in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Wet developing device 101 Developing device 102 Developing device 103 Developing device 104 Developing device 105 Intermediate transfer member 106 Second transfer roller 107 Image support member 108 Heat roller 109 Heat roller

Claims (4)

An image forming equipment for transferring a plurality of toner layers developed on the image supporting member,
Includes a wet development apparatus for developing with a plurality of wet developer formed by dispersing toner particles in non-volatile carrier liquid,
The wet developer used for forming the lowermost toner layer of the plurality of toner layers having a glass transition temperature of the toner particles in the wet developer used for forming the uppermost toner layer of the plurality of toner layers. Higher than the glass transition temperature of the toner particles inside,
An image forming apparatus further comprising a plurality of fixing nips, wherein at least the lowermost toner layer is fixed at the first fixing nip, and the uppermost toner layer is fixed at the second and subsequent fixing nips. The glass transition temperature of the toner particles in the wet developer used to form the uppermost toner layer is the glass transition temperature of the toner particles in the wet developer used to form the lowermost toner layer. The image forming apparatus according to claim 1, wherein the image forming apparatus is higher by 5 to 20 ° C. The plurality of wet developers include a wet developer used to form the lowermost toner layer, a wet developer used to form the uppermost toner layer, and an intermediate layer therebetween. And a wet developer used for forming the lowermost toner layer, and a wet developer used for forming the intermediate toner layer. The image forming apparatus according to claim 1, wherein the glass transition temperature of the toner particles increases in the order of the wet developer used to form the uppermost toner layer. 4. The image forming apparatus according to claim 1, wherein Tg of toner particles contained in the plurality of wet developers is 65 to 85 ° C. 5.

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