JP6048214B2 - Liquid developer - Google Patents

Description

  The present invention relates to a liquid developer.

  A liquid developer used in an electrophotographic image forming apparatus is configured by dispersing toner particles in an insulating liquid. The insulating liquid is appropriately selected so that the toner particles can be stably dispersed.

  For example, JP 2007-41162 A (Patent Document 1) discloses a first liquid having a weight average molecular weight of 300 or less and a viscosity of 0.5 to 30 mPa · s, a weight average molecular weight of 300 to 1000 and a viscosity. Insulating liquid containing 2nd liquid whose is 30-1000 mPa * s is disclosed.

  Japanese Patent Laid-Open No. 2006-99127 (Patent Document 2) discloses an insulating property including 0.5 to 4% low-volatile hydrocarbon and 96 to 99.5% highly-volatile hydrocarbon. A liquid is disclosed.

JP 2007-41162 A JP 2006-99127 A

  In an electrophotographic image forming apparatus, there is a step of transferring a toner image from a photosensitive member to an intermediate transfer member or from an intermediate transfer member to a sheet. In the transfer process, it is common to use a method in which charged toner particles are moved by an electric force. When transferring from the photosensitive member to the intermediate transfer member, a power source device is provided on one or the other, and a potential difference (transfer electric field) is generated between the two to move the toner particles. When transferring from the image carrier (photosensitive member or intermediate transfer member) to the paper, a transfer member is provided so as to sandwich the paper so as to face the image carrier, and power is supplied to both or one of the image carrier and the transfer member. An apparatus is provided to generate a potential difference (transfer electric field) between the two to move the toner particles.

  In order to obtain a good image, it is necessary to transfer the image well so that the image is not disturbed in the transfer process. However, in the wet electrophotographic system, since a liquid developer is used, granular density unevenness (hereinafter referred to as “granular unevenness”) may occur in the transfer process.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a liquid capable of suppressing a granular unevenness generated in a transfer process in an image forming apparatus and obtaining a good image. It is to provide a developer.

  In order to solve the above problems, the inventors first examined the cause of the granular unevenness, and in the process of transferring the toner image from the photosensitive member to the intermediate transfer member or from the intermediate transfer member to the paper, There is a possibility that the electric field acts on a wider area than the transfer part and the toner particles in the liquid developer move before passing through the transfer part, so that the toner particles easily gather locally. I found out. Due to such a cause, it is expected that occurrence of granular density unevenness in the transfer process can be suppressed by making it difficult for the toner particles to move in the liquid developer.

  In order to make it difficult for the toner particles to move in the liquid developer, it may be possible to increase the viscosity of the insulating liquid. This makes it impossible to obtain a good image output. The problem of fixability is a phenomenon in which a lot of insulating liquid remains in the toner layer before fixing, and the toner layer is divided by the roller pressure by passing a heat roller for fixing in this state (hereinafter, “ Image flow). When the image flow occurs, the image density decreases or the image is displaced. The present inventors have intensively studied the insulating liquid used in the liquid developer in consideration of the above and completed the present invention.

  That is, the liquid developer of the present invention includes toner particles and an insulating liquid, and the insulating liquid contains 10 to 60% by mass of a first hydrocarbon having 11 to 16 carbon atoms and 17 to 17 carbon atoms. 1st hydrocarbon, 2nd carbonization which contains 40-90 mass% of 20 2nd hydrocarbons, does not contain the 3rd hydrocarbon of carbon number 21 or more, or is 10 mass% or less, and is contained in this insulating liquid The total amount of hydrogen and the third hydrocarbon is 95% by mass or more.

  Here, it is preferable that this insulating liquid contains 10-30 mass% of 1st hydrocarbons, and 70-90 mass% of 2nd hydrocarbons.

  Moreover, it is preferable that this insulating liquid does not contain a 3rd hydrocarbon, or contains 1 mass% or less.

  The toner particles include a resin and a colorant, and the resin is preferably a polyester resin having an acid value of 20 mgKOH / g or more.

  The liquid developer of the present invention has an excellent effect that the occurrence of granular unevenness is suppressed without degrading the image quality.

FIG. 2 is a cross-sectional view schematically showing how a toner image is transferred from an intermediate transfer member to a sheet (FIG. 1A), and an enlarged view of a nip portion in FIG. 1A (FIG. 1B). A toner image after transfer when the toner image is uniformly transferred (FIG. 2A), and a toner image after transfer when the toner image is transferred in a state where granular unevenness occurs (FIG. 2B )) Is a diagram schematically showing. 1 is a schematic diagram illustrating an example of an image forming apparatus.

Hereinafter, the present invention will be described in more detail.
<Liquid developer>
The liquid developer of the present invention contains toner particles and an insulating liquid. Such a liquid developer can contain other arbitrary components as long as these components are contained. Examples of the other components include a charge control agent, a thickener, and a dispersant for dispersing toner particles (hereinafter referred to as “toner dispersant” for convenience). The mixing ratio of the liquid developer can be, for example, 10 to 50% by weight of toner particles and 50 to 90% by weight of insulating liquid. Such a liquid developer is useful as a developer for an electrophotographic image forming apparatus such as a copying machine, a printer, a digital printing machine, and a simple printing machine.

<Insulating liquid>
The insulating liquid contained in the liquid developer of the present invention is preferably a liquid that is non-volatile at normal temperature and exhibits electrical insulation (for example, a resistance value in the range of 10 ¹¹ to 10 ¹⁶ Ω · cm). . This is because the electrostatic latent image is not normally disturbed if it has a resistance value in this range. Further, as such an insulating liquid, those having no odor and toxicity are preferable.

  The insulating liquid mainly consists of a mixture of hydrocarbons having different carbon numbers. Specifically, 10 to 60 mass% of the first hydrocarbon having 11 to 16 carbon atoms (C11 to C16) and 40 to 90 mass% of the second hydrocarbon having 17 to 20 carbon atoms (C17 to C20). %, And does not include a third hydrocarbon having 21 or more carbon atoms (C21 or more) or 10% by mass or less. The total amount of the first hydrocarbon, the second hydrocarbon, and the third hydrocarbon contained in the insulating liquid is 95% by mass or more.

  First, the cause of the occurrence of grainy irregularities in the process of transferring the toner image from the intermediate transfer member to the paper will be considered with reference to FIG. FIG. 1A is a cross-sectional view schematically showing how a toner image is transferred from an intermediate transfer member to a sheet. The toner image 4 (before transfer) on the intermediate transfer body 2 is affected by the electric field generated by the potential difference between the intermediate transfer body 2 and the transfer roller 1 at the nip portion between the intermediate transfer body 2 and the transfer roller 1. The toner image 5 (after transfer) is formed by being transferred onto the surface. FIG.1 (b) shows the enlarged view of the nip part of Fig.1 (a). Although the toner image moves in the nip portion 9 between the intermediate transfer body 2 and the transfer roller 1, the influence of the transfer electric field extends over a wider range than the nip portion 9, for example, the range 8. Therefore, before reaching the nip portion 9, the toner particles in the toner image 4 are affected by the transfer electric field and move in the liquid developer toward the surface 7. For example, in the range 10, the toner particles are likely to be aggregated in the vicinity of the surface 7 as the toner particles move to the vicinity of the surface 7. The agglomeration of the toner particles generated in this way is transferred as it is in the nip portion 9 to cause granular unevenness. It is considered that the cause of the occurrence of granular unevenness in the transfer process from the photosensitive member to the intermediate transfer member is the same.

  2 shows a toner image after transfer when the toner image is uniformly transferred (FIG. 2A), and a toner image after transfer when the toner image is transferred in a state where granular unevenness has occurred (FIG. 2). 2 (b)). When the grainy unevenness occurs, the white background portion increases and the image density decreases.

  By adjusting the viscosity of the insulating liquid, for example, by setting the viscosity to 3 mPa · s or more, it is possible to suppress granular unevenness. When the second hydrocarbon and the third hydrocarbon having 17 or more carbon atoms are mainly used, the viscosity of the insulating liquid can be adjusted to 3 mPa · s or more, and granular unevenness can be suppressed. However, with only the second hydrocarbon and the third hydrocarbon having 17 or more carbon atoms, the permeation speed of the insulating liquid into the medium such as paper is slow, and contact such as fixing with a heat roller immediately after transfer to the medium. When fixing is performed, the toner layer may be divided and image flow may occur. In particular, the third hydrocarbon has an extremely slow permeation rate and is liable to generate image flow.

  Therefore, in the present invention, the first hydrocarbon is included in the insulating liquid. Since the first hydrocarbon has a low viscosity, it has a high penetration rate into media such as paper, and easily volatilizes. Therefore, the amount of the insulating liquid contained in the toner layer can be reduced, and a fixing process using a heat roller. It is possible to suppress the occurrence of image flow in the image. In addition, the suppression effect of the granular nonuniformity originating in the 2nd hydrocarbon and 3rd hydrocarbon whose carbon number is 17 or more can be maintained by containing 1st hydrocarbon within the range of the said numerical value.

  When the content of the first hydrocarbon (C11 to C16) is less than 10% by mass or when the content of the second hydrocarbon (C17 to C20) exceeds 90% by mass, the image flow becomes remarkable. Further, when the content of the first hydrocarbon (C11 to C16) exceeds 60% by mass, or the content of the second hydrocarbon (C17 to C20) is less than 40% by mass, the granular unevenness becomes remarkable. . Further, when the content of the third hydrocarbon (C21 or more) exceeds 10% by mass, the image flow becomes remarkable. In addition, when the volatilization rate of the hydrocarbon having 16 carbon atoms (C16) and the hydrocarbon having 18 carbon atoms (C18) was confirmed, the hydrocarbon having 16 carbon atoms (C16) is more volatile and permeable. Was significantly higher. Therefore, in the present invention, the upper limit value of the number of carbon atoms of the first hydrocarbon is set to 16, the content of the first hydrocarbon is defined as described above, and an increase in the residual liquid in the medium is suppressed.

  The insulating liquid preferably contains 10 to 30% by mass of the first hydrocarbon (C11 to C16) and 70 to 90% by mass of the second hydrocarbon (C17 to C20). According to such a ratio, it becomes easier to suppress granular unevenness. In addition, it is preferable not to contain 3rd hydrocarbon (C21 or more), and when it contains, it contains in 10 mass% or less range as above-mentioned, Preferably it contains in 1 mass% or less. The third hydrocarbon (C21 or more) is a case where it is contained in order to further reduce the volatilization rate compared with the second hydrocarbon (C17 to C20), and thus suppress an increase in the residual liquid to the medium. Shall be contained in the above range.

  The insulating liquid may contain hydrocarbons having 10 or less carbon atoms (C10 or less), but such hydrocarbons are preferably not contained because they are highly volatile.

  The hydrocarbon contained in the insulating liquid may be any of an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatized hydrocarbon, and a mixture thereof, and is preferably a saturated hydrocarbon. However, unsaturated hydrocarbons may be mixed.

  Examples of the first hydrocarbon (C11 to C16) include undecane, dodecane, tridecane, tetradecane, pentadecane, and hexadecane. Examples of the second hydrocarbon (C17 to C20) include heptadecane, octadecane, nonadecane, and icosane. As the third hydrocarbon (C21 or more), heikosan is exemplified.

  Specifically, the insulating liquid is Moresco White (manufactured by Matsumura Oil Research Co., Ltd.), Isopar (manufactured by Exxon Chemical), Shellsol (manufactured by Shell Petrochemical), IP solvent 1620, IP solvent 2028, IP solvent. The above ratio can be obtained by mixing commercially available paraffin oil such as 2835 (all manufactured by Idemitsu Petrochemical Co., Ltd.).

  Examples of the first hydrocarbons (C11 to C16) include Isopar L (made by ExxonMobil Corporation) and IP Solvent 2028 (made by Idemitsu Kosan Co., Ltd.). Examples of the second hydrocarbon (C17 to C20) include Moresco White P-40 (manufactured by Moresco) and IP Solvent 2835 (manufactured by Idemitsu Kosan). As a 3rd hydrocarbon (C21 or more), Moresco white P-70 (made by Moresco), P-120 (made by Moresco) is illustrated. By mixing these to produce an insulating liquid, an insulating liquid having the above ratio can be obtained.

In the image forming system to which the liquid developer of the present invention is applied, the toner adhesion amount is about 0.5 to 4 g / m ² . According to the liquid developer of the present invention, it is possible to suppress granular unevenness and image flow and to form a good image.

<Toner particles>
The toner particles contained in the liquid developer of the present invention contain a resin and a colorant dispersed in the resin. Such toner particles can contain any other component as long as these components are contained. Examples of other components include a wax and a charge control agent.

  The toner particles preferably have a volume average particle diameter of 0.5 μm or more and 5.0 μm or less. When the volume average particle size is less than 0.5 μm, the particles are too small, the mobility in the electric field is deteriorated, and the developability is lowered. When the volume average particle size is larger than 5.0 μm, the uniformity is lowered and the image quality is lowered, which is not preferable.

<Resin>
The resin contained in the toner particles may be any resin as long as it is thermoplastic. For example, vinyl resins such as styrene, acrylic, vinyl acetate, polyester, polyurethane, epoxy, ethylene, petroleum resins, and the like.

  Among these, a polyester resin having sharp melt properties is preferably used. This is because the polyester resin can change characteristics such as thermal characteristics over a wide range and is excellent in translucency, spreadability, and viscoelasticity. Thus, the polyester resin is excellent in translucency, so that it is possible to obtain a beautiful color when obtaining a color image, and since it is excellent in spreadability and viscoelasticity, an image formed on a medium such as paper ( Resin film) is strong and can be strongly bonded to the media. Furthermore, a polyester resin having an acid value is preferably used. Since the polyester resin having an acid value forms a cross-linked structure, it is difficult for the insulating liquid to enter the resin, and the amount of the insulating liquid in the toner layer is suppressed, and the image flow is easily suppressed. The acid value of the polyester resin is preferably 20 mgKOH / g or more, more preferably 30 mgKOH / g or more. This is because a higher acid value has more cross-linked structures and is more dominant over image flow.

  The polyester resin comprises an acid component (polybasic acid) and an alcohol component (polyhydric alcohol). Here, the polyhydric alcohol is not particularly limited. For example, propylene glycol such as ethylene glycol, diethylene glycol, triethylene glycol, and 1,2-propylene glycol, butanediol such as dipropylene glycol and 1,4-butanediol, Alkylene glycols (aliphatic glycols) such as neopentyl glycol and hexanediol such as 1,6-hexanediol and their alkylene oxide adducts, bisphenols such as bisphenol A and hydrogenated bisphenol, and phenols of these alkylene oxide adducts Examples thereof include triglycols, alicyclics such as monocyclic or polycyclic diols, and aromatic diols, glycerol, trimethylolpropane and the like. These can be used alone or in admixture of two or more. In particular, a bisphenol A alkylene oxide 2-3 mol adduct is preferable because it is suitable as a resin for toner particles of a liquid developer in terms of solubility and stability of the product polyester resin and is low in cost. . Examples of the alkylene oxide include ethylene oxide and propylene oxide.

  Examples of polybasic acids (polycarboxylic acids) include malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, phthalic acid, and modified acids thereof (for example, hexahydrophthalic anhydride). Acid), isophthalic acid, terephthalic acid, trimellitic acid, trimesic acid, pyromellitic acid, and other saturated or unsaturated (or aromatic) polybasic acids and their acid anhydrides, lower alkyl esters, etc. These can be used alone or in admixture of two or more. Among these, isophthalic acid, terephthalic acid, and trimellitic acid are preferable because they are suitable as a resin for toner particles of a liquid developer in terms of solubility and stability of the product polyester resin and are low in cost. . In particular, use of trimellitic acid having a trifunctional or higher functional group is advantageous for obtaining a polyester resin having a high acid value.

  The number average molecular weight of the polyester resin is preferably 500 or more and 10,000 or less, more preferably 1000 or more and 5000 or less. In the case of the molecular weight, moderate meltability and offset resistance can be obtained.

<Colorant>
The colorant contained in the toner particles of the present invention is dispersed in the above resin. The particle size of such a colorant is preferably 0.3 μm or less. When the particle size of the colorant exceeds 0.3 μm, the dispersion of the colorant is deteriorated, the glossiness is lowered, and a desired color may not be realized.

  Further, the addition amount of the colorant in the toner particles is preferably about 5 to 50 parts by mass with respect to the solid content of the toner particles. If the addition amount is less than 5 parts by mass, a sufficient coloring effect may not be obtained. If the addition amount exceeds 50 parts by mass, uniform dispersion of the colorant becomes difficult, resulting in a decrease in glossiness due to aggregation of the colorant. There is a case.

  As such a colorant, conventionally known pigments, dyes, and the like can be used without particular limitation. From the viewpoint of cost, light resistance, colorability, and the like, for example, the following colorants may be used. preferable. In terms of color composition, these colorants are usually classified into black colorants, yellow colorants, magenta colorants, and cyan colorants. Basically, colors other than black (color images) are yellow colorants and magenta colors. Toning is performed by subtractive color mixing of a colorant and a cyan colorant.

  Examples of the black colorant include carbon black such as furnace black, channel black, acetylene black, thermal black, and lamp black, carbon black derived from biomass, and magnetic powder such as magnetite and ferrite.

  Examples of the colorant for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48; 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the colorant for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 180, C.I. I. And CI Pigment Yellow 185.

  Further, as a colorant for green or cyan, C.I. I. Pigment blue 15, C.I. I. Pigment blue 15; 2, C.I. I. Pigment blue 15; 3, C.I. I. Pigment blue 15; 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. Pigment blue 62, C.I. I. Pigment blue 66, C.I. I. And CI Pigment Green 7.

  These colorants can be used alone or in combination of two or more as required.

<Toner dispersant>
The toner dispersant contained in the liquid developer of the present invention has a function of stably dispersing the toner particles in the insulating liquid. Therefore, the toner dispersant usually exists (adsorbs) on the surface of the toner particles. ing. Such a dispersant is preferably soluble in the insulating liquid.

  Such a toner dispersant is not particularly limited as long as it stably disperses toner particles, and for example, a surfactant, a polymer dispersant and the like can be used. When a polyester resin is used as the resin constituting the toner particles, it is preferable to use a basic polymer dispersant as such a toner dispersant.

  Examples of such basic polymer dispersants include nitrogen-containing resins containing amine, amide, imine, and pyrrolidone in the molecule. Specific examples include polyesteramines, modified polyurethanes, polyalkylene polyamines, modified polyurethanes, and polyester polyamines. Other specific examples of the basic polymer dispersant include “Disperbyk-109” (alkylolaminoamide) and “Disperbyk-130” (unsaturated polycarboxylic acid polyaminoamide) manufactured by BYK Chemie. Further, “S13940” (polyesteramine type), “S17000”, “S18000”, “S19000” (fatty acid amine type), “S11200” and the like manufactured by Abyssia are also included. It is particularly preferable to use a polymer dispersant having a pyrrolidone group as the basic group. This is probably because when the above-mentioned polyester resin constituting the toner particles has a high acid value, a basic polymer dispersant is used so that the good dispersibility of the toner particles is extended over a long period of time due to the interaction between the two. It is thought to be stabilized.

  Examples of such basic polymer dispersants include the pyrrolidone group, for example, an aromatic amino group, an aliphatic amino group, a heterocyclic nitrogen-containing group, a heterocyclic oxygen-containing group, and a heterocyclic sulfur-containing group. A polymeric dispersant can be mentioned. Examples of the pyrrolidone group include an N-vinylpyrrolidone group. Examples of the basic polymer dispersant having an N-vinylpyrrolidone group include N-vinyl-2-pyrrolidone, methacrylic acid ester, and acrylic acid. A random copolymer or a graft copolymer with an acid ester or an alkylene compound can be used. Here, when the methacrylic acid ester and the acrylic acid ester are alkyl esters, the alkyl group preferably has about 10 to 20 carbon atoms. Examples of these commercially available products include “Antaron V-216” and “Antaron V-220” (both are trade names, manufactured by GAF / ISP Chemicals). Further, the alkyl group of the alkylene compound preferably has about 10 to 30 carbon atoms.

<Resin manufacturing method>
The polyester resin used as the resin constituting the toner particles can be produced by a conventionally known polycondensation method. That is, although it depends on the type of raw material monomer to be used, it can generally be carried out in a temperature range of 150 to 300 ° C. Moreover, arbitrary conditions, such as using inert gas as atmospheric gas, selecting various solvents arbitrarily, or making the reaction container internal pressure normal pressure or pressure reduction, can be employ | adopted.

  In order to accelerate the reaction, an esterification catalyst may be used. Examples of esterification catalysts include metal organic compounds such as tetrabutyl zirconate, zirconium naphthenate, tetrabutyl titanate, tetraoctyl titanate, 3/1 stannous oxalate / sodium acetate, etc. That which does not color the polyester which is is preferable.

  In addition, the molecular weight of the polyester resin that is a reaction product can be adjusted by adjusting the reaction time. This is because the polycondensation reaction to obtain a polyester resin is a sequential reaction in which a low molecular weight substance increases its molecular weight with the passage of time. Since the relationship between the reaction time and the molecular weight varies depending on the type of raw material monomer, various polymerization conditions, lot scale, etc., it is possible to adjust the reaction time to obtain a desired molecular weight in consideration of these various conditions. preferable.

<Method for producing liquid developer>
The liquid developer can be prepared based on a conventionally known method such as a granulation method or a pulverization method. In the pulverization method, a resin and a colorant are previously melt-kneaded and pulverized. There are methods for pulverization in a dry state or a wet state in oil. Examples of the granulation method include suspension polymerization method, emulsion polymerization method, fine particle aggregation method, method of adding a poor solvent to a resin solution and depositing, and spray drying method.

  Next, the grinding method will be described. The liquid developer can be prepared based on a conventionally known technique. For example, using a kneader such as a pressure kneader, a roll mill, or a three-roller, the resin and the colorant are melt-kneaded at a predetermined blending ratio, and the colorant is uniformly dispersed in the resin, whereby the colorant-resin Obtain a dispersion.

  Subsequently, the colorant-resin dispersion obtained above is cooled, and after cooling, this is coarsely pulverized. Subsequently, the coarsely pulverized colorant-resin dispersion (sometimes referred to as “coarse pulverized toner”) is further pulverized to a desired particle size to obtain toner particles. Examples of the pulverization method that can be used above include a dry pulverization method and a wet pulverization method. However, the pulverization method is not particularly limited as long as it can pulverize to a desired particle size with energy saving.

  For example, a coarsely pulverized toner is obtained by a cutter mill, and then toner particles are obtained by further pulverizing the coarsely pulverized toner to a desired particle size using a jet mill as a dry pulverization method. A liquid developer can be prepared by mixing the toner particles with an insulating liquid and a dispersant.

  On the other hand, when the wet pulverization method is employed, for example, the coarsely pulverized toner obtained by the above method, an insulating liquid, and a dispersant are mixed, and the mixture is pulverized using a sand mill to obtain toner particles as desired particles. The diameter of the liquid developer can be prepared.

<Image forming apparatus>
FIG. 3 is a schematic diagram showing an example of an image forming apparatus that can use the liquid developer according to the present invention as a developer. The image forming apparatus 20 shown in FIG. 3 is a single-color image forming apparatus that performs primary transfer from a photosensitive member to an intermediate transfer member and then secondary transfer to a medium. The liquid developer according to the present invention can also be used in a multicolor image forming apparatus that forms a color image by superimposing these developers.

  In the image forming apparatus 20 shown in FIG. 3, a developer 21 is placed in the developing tank 22. The developer 21 is picked up by an anilox roller 23 that rotates in the f direction and is sent to a leveling roller 25 that rotates in the e direction. Excess liquid developer on the surface of the anilox roller 23 is scraped off by the anilox regulating blade 24 before reaching the leveling roller 25, and the leveling roller 25 is adjusted so that the developer has a uniform layer thickness. The developer is transferred from the leveling roller 25 to the developer carrier 26 that rotates in the direction b.

  The photoreceptor 29 rotates in the a direction, is charged by the charging unit 30, and a latent image is formed by the exposure unit 31. Corresponding to the image formed with the latent image, the developer is charged on the toner by the developing charger 28 and then developed on the photoconductor 29. The liquid developer on the developer carrier 26 that has not been transferred to the photoconductor 29 is scraped off and collected by the downstream cleaning blade 27. The developer developed on the photosensitive member 29 is primary transferred electrostatically to the intermediate transfer member 33 by the primary transfer unit 37. The developer that cannot be transferred and remains on the photoreceptor 29 is scraped off by the cleaning blade 32. The developer carried on the intermediate transfer member 33 is electrostatically transferred to the medium 40 by the secondary transfer unit 38 where the intermediate transfer member 33 and the secondary transfer roller 35 face each other. The developer transferred to the medium 40 is heated and fixed at the opposed portions of the pair of fixing rollers 36a and 36b, thereby completing a printed image. The developer that cannot be completely transferred and remains on the intermediate transfer member 33 is scraped off by the cleaning blade 34. The photoconductor 29 repeats the charging, exposure, and development steps to perform a printing operation.

  The medium 40 used at the time of image formation is not particularly limited as long as a toner image can be formed by an electrophotographic image forming method. Specific media 40 include known ones such as plain paper from thin paper to thick paper, high-quality paper, art paper, coated printing paper such as coated paper, commercially available Japanese paper or postcard paper. , OHP plastic film, cloth and the like.

  In the image forming apparatus shown in FIG. 3, granular unevenness may occur in the toner image transfer process from the photoreceptor 29 to the intermediate transfer body 33 and the toner image transfer process from the intermediate transfer body 33 to the medium 40. When the liquid developer of the present invention is used, the occurrence of such granular unevenness can be suppressed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Production Example 1> Synthesis of Polyester Resin A 1600 parts by mass of a propylene oxide adduct of bisphenol A was added to a round bottom flask equipped with a reflux condenser, a water / alcohol separator, a nitrogen gas inlet tube, a thermometer and a stirrer ( Polyhydric alcohol), 890 parts by mass of terephthalic acid (polybasic acid), nitrogen gas was introduced with stirring, and dehydration polycondensation or dealcoholization polycondensation was performed at a temperature of 200 to 240 ° C. When the acid value of the produced polyester resin or the viscosity of the reaction solution reached a predetermined value, the temperature of the reaction system was lowered to 100 ° C. or less to stop polycondensation. A thermoplastic polyester resin (polyester resin A) was thus obtained. About the obtained polyester resin A, when the weight average molecular weight Mw, the number average molecular weight Mn, the glass transition temperature Tg, and the acid value were measured by the following method, Mw = 6000, Mn = 2200, Tg = 55.3 ° C., acid value = 14.0 mgKOH / g.

<Production Example 2> Synthesis of Polyester Resin B 1600 parts by mass of propylene oxide adduct of bisphenol A was added to a round bottom flask equipped with a reflux condenser, water / alcohol separator, nitrogen gas inlet tube, thermometer and stirrer ( Polyhydric alcohol), 550 parts by mass of terephthalic acid (polybasic acid), and 340 parts by mass of trimellitic acid, introducing nitrogen gas with stirring, dehydration polycondensation or dealcoholization at a temperature of 200 to 240 ° C. Polycondensation was performed. When the acid value of the produced polyester resin or the viscosity of the reaction solution reached a predetermined value, the temperature of the reaction system was lowered to 100 ° C. or less to stop polycondensation. A thermoplastic polyester resin (polyester resin B) was thus obtained. About the obtained polyester resin B, when the weight average molecular weight Mw, the number average molecular weight Mn, the glass transition temperature Tg, and the acid value were measured by the following method, the obtained polyester resin B was Mw = 5400, Mn = 2000, Tg. = 58.3 ° C, acid value = 44.0 mgKOH / g.

[Measurement of molecular weight]
The weight average molecular weight Mw and the number average molecular weight Mn of the polyester resins A and B were calculated from the results of gel permeation chromatography, respectively. The gel permeation chromatography is a high-performance liquid chromatograph pump TRI ROTAR-V type (manufactured by JASCO Corporation), an ultraviolet spectroscopic detector UVDEC427-100-V type (manufactured by JASCO Corporation), and a column Shodex GPC A having a length of 50 cm. -803 (manufactured by Showa Denko KK) was used, and from the results of the chromatography, the molecular weight of the test sample was calculated as polystyrene as a standard substance, and was calculated as polystyrene-equivalent Mw and Mn. The test sample used was 0.05 g of resin dissolved in 20 ml of tetrahydrofuran (THF).

[Measurement of Tg]
The glass transition temperatures Tg of the polyester resins A and B were measured using a differential scanning calorimeter DSC-6200 (manufactured by Seiko Instruments Inc.) under the conditions of a sample amount of 20 mg and a heating rate of 10 ° C./min.

[Measurement of acid value]
The acid values of the polyester resins A and B were measured under the conditions defined in JIS K5400.

<Example 1>
100 parts by mass of polyester resin B and 15 parts by mass of copper phthalocyanine blue are sufficiently mixed with a Henschel mixer, then melt-mixed with a twin-screw extruder kneader, cooled, then coarsely pulverized, and an average particle size of 6 μm with a jet pulverizer. Finely ground. The mixture was melt kneaded using a twin-screw extruder having a heating temperature of 100 ° C. in a biaxial roll, and the resulting mixture was cooled and coarsely crushed to obtain coarsely pulverized toner particles. 34 parts by weight of the toner particles, 1 part by weight of a basic polymer dispersant (“Antaron V-216” (manufactured by GAF / ISP Chemicals)), an insulating liquid (“Isopar L” (manufactured by ExxonMobil, 25 ° C.) Viscosity: 1.1 mPa · s, flash point: 64 ° C. 10% by mass, “Moresco White P-40” (manufactured by Moresco, 25 ° C. viscosity: 5.4 mPa · s, flash point: 144 ° C.) 90 mass % Liquid mixture) and 100 parts by mass of zirconia beads were mixed and stirred in a sand mill for 120 hours to obtain a liquid developer of Example 1. The volume average particle diameter of the toner particles contained in the liquid developer thus prepared was 2.27 μm. The volume average particle size was measured by the method described later. The same applies to the following examples and comparative examples.

<Example 2>
A liquid developer of Example 2 was obtained in the same manner as Example 1 except that the insulating liquid used was different. In Example 2, an insulating liquid (“IP Solvent 2028” (manufactured by Idemitsu Kosan Co., Ltd., viscosity at 25 ° C .: 2.5 mPa · s, flash point: 86 ° C.) 20% by mass, “Molesco White P-40” 80 (Mass% mixed solution) was used. The volume average particle diameter of the toner particles contained in the obtained liquid developer of Example 2 was 2.14 μm.

<Example 3>
A liquid developer of Example 3 was obtained in the same manner as in Example 1 except that the polyester resin A was used in place of the polyester resin B and the insulating liquid used was different. In Example 3, an insulating liquid (a mixed solution of 20% by mass of “IP Solvent 2028” and 80% by mass of “Molesco White P-40”) was used. The volume average particle diameter of the toner particles contained in the obtained liquid developer of Example 3 was 1.99 μm.

<Example 4>
A liquid developer of Example 4 was obtained in the same manner as Example 1 except that the insulating liquid used was different. In Example 4, an insulating liquid (50% by mass of “IP Solvent 2028”, 50% by mass of “Moresco White P-40”) was used. The volume average particle diameter of the toner particles contained in the obtained liquid developer of Example 4 was 2.02 μm.

<Example 5>
A liquid developer of Example 5 was obtained in the same manner as Example 1 except that the polyester resin A was used in place of the polyester resin B and the insulating liquid used was different. In Example 5, insulating liquid (“Isopar L” 30% by mass, “Moresco White P-40” 61% by mass, “Moresco White P-120” (manufactured by Moresco, viscosity at 25 ° C .: 23 mPa · s) , Flash point: 200 ° C.) 9 mass% mixed solution). The volume average particle size of the toner particles contained in the obtained liquid developer of Example 5 was 1.83 μm.

<Comparative Example 1>
A liquid developer of Comparative Example 1 was obtained in the same manner as in Example 1 except that the polyester resin A was used in place of the polyester resin B and the insulating liquid used was different. In Comparative Example 1, an insulating liquid (mixed solution of 5% by mass of “Isopar L” and 95% by mass of “Molesco White P-40”) was used. The volume average particle diameter of the toner particles contained in the obtained liquid developer of Comparative Example 1 was 1.9 μm.

<Comparative example 2>
A liquid developer of Comparative Example 2 was obtained in the same manner as in Example 1 except that the polyester resin A was used in place of the polyester resin B and the insulating liquid used was different. In Comparative Example 2, an insulating liquid (mixed solution of 63% by mass of “Isopar L” and 37% by mass of “Molesco White P-40”) was used. The volume average particle diameter of the toner particles contained in the obtained liquid developer of Comparative Example 2 was 1.92 μm.

<Comparative Example 3>
A liquid developer of Comparative Example 3 was obtained in the same manner as in Example 1 except that the insulating liquid used was different. In Comparative Example 3, an insulating liquid (mixed solution of “IP Solvent 2028” 10% by mass, “Molesco White P-40” 78% by mass, “Molesco White P-120” 12% by mass) was used. The volume average particle diameter of the toner particles contained in the obtained liquid developer of Comparative Example 3 was 2.11 μm.

<Comparative example 4>
A liquid developer of Comparative Example 4 was obtained in the same manner as in Example 1 except that the polyester resin A was used in place of the polyester resin B and the insulating liquid used was different. In Comparative Example 4, insulating liquid (“IP Solvent 2028” 20% by mass, “Moresco White P-120” (manufactured by Moresco, viscosity at 25 ° C .: 23.3 mPa · s, flash point: 200 ° C.) 80% by mass % Liquid mixture). The volume average particle size of the toner particles contained in the obtained liquid developer of Comparative Example 4 was 2.17 μm.

<Comparative Example 5>
A liquid developer of Comparative Example 5 was obtained in the same manner as in Example 1 except that the polyester resin A was used instead of the polyester resin B and the insulating liquid used was different. In Comparative Example 5, an insulating liquid (mixture of 97% by mass of “IP Solvent 2028” and 3% by mass of “Molesco White P-120”) was used. The volume average particle diameter of the toner particles contained in the obtained liquid developer of Comparative Example 5 was 1.88 μm.

[Measurement of volume average particle diameter]
The volume average particle size of toner particles contained in each liquid developer was measured using a particle size analyzer (“FPIA-3000S”, manufactured by Sysmex). “Isopar L” was used as the flow solvent. 50 mg of each sample was put into 20 g of “Isopar L” added with 30 mg of a dispersant (“S13940”, manufactured by Nippon Lubrizol Co., Ltd.), and the suspension was subjected to an ultrasonic disperser (“Ultrasonic Cleaner Model VS- 150 ”(manufactured by Welbo Clear) was used to measure the volume average particle size (median diameter D50 of the volume-based particle size distribution) of each sample.

[Measurement of molecular weight]
The ratio of the first hydrocarbon, the second hydrocarbon, and the third hydrocarbon contained in the insulating liquid of each liquid developer was confirmed by performing the carbon number distribution evaluation by the following method. First, the liquid developer is solid-liquid separated by a centrifugal separation method, and the carbon number distribution of the supernatant liquid is evaluated by a GC-MS (gas chromatograph mass spectrometry) method under the following conditions, and the first carbonization contained in the insulating liquid is performed. The content ratio of hydrogen, second hydrocarbon, and third hydrocarbon was calculated. The measurement results of the content ratio are shown in Table 1.

(1) GC (gas chromatograph) conditions Device: Capillary gas chromatograph “HP-6890” (manufactured by Hewlett Packard)
Injection part temperature: 300 ° C
Injection method: Splitless mode Sample: Stock solution (100%)
Sample injection volume: 0.1 μL
Carrier gas: helium (1 ml / min)
Interface temperature: 300 ° C
(2) MS (mass spectrometry) conditions Device: Time-of-flight mass spectrometer (manufactured by Micromass Ltd.)
Ionization: Electric field ionization method (extraction voltage: 12 kV)
Mass range: m / z 10-300
Ion detection: Multi Channel Plate
[Evaluation of granular unevenness]
The solid pattern (2 g / m ² on the paper) is fixed on the coated paper (“OK Top Coat Plus 128 g paper”, manufactured by Oji Paper Co., Ltd.) using each liquid developer in the image forming apparatus 20 of FIG. I let you. In the image forming apparatus 20 of FIG. 1, the toner particles are charged to a positive polarity by the developing charger 28, the potential of the intermediate transfer member 33 is -400V, the potential of the two transfer roller 35 is -1200V, and the medium 40 is conveyed. The speed was 400 mm / s. The temperature of the fixing rollers 36a and 36b was 160 ° C., and the nip time by the fixing rollers 36a and 36b was 40 msec. The granular unevenness of the image after fixing was visually evaluated as follows. The evaluation results are shown in Table 1.
A: No granular unevenness was observed.
B: Slight granular unevenness was observed.
C: Granular unevenness was observed.

[Evaluation of image flow]
In the image forming apparatus 20 of FIG. 1, a solid pattern (2 g / m ² on the paper) and a line pattern with a width of 100 μm are coated using each liquid developer (“OK top coat plus 128 g paper”, Oji Paper Co., Ltd.). (Made). In the image forming apparatus 20 of FIG. 1, the toner particles are charged to a positive polarity by the developing charger 28, the potential of the intermediate transfer member 33 is -400V, the potential of the two transfer roller 35 is -1200V, and the medium 40 is conveyed. The speed was 400 mm / s. The temperature of the fixing rollers 36a and 36b was 160 ° C., and the nip time by the fixing rollers 36a and 36b was 40 msec. The image flow of the images after passing through the fixing rollers 36a and 36b was visually observed and evaluated as follows. Since the line pattern is a more detailed image than the solid pattern, image flow is likely to occur. The evaluation results are shown in Table 1.
A: No image flow was observed in both the solid pattern and the line pattern.
B: Although no image flow was observed in the solid pattern, slight movement was observed in the line pattern.
C: A decrease in density was observed in the solid pattern, and movement of the line pattern was observed.
D: A significant decrease in the density of the solid pattern was observed, and a movement of the line pattern was observed.

  As is apparent from Table 1, when the liquid developer of the example is used, the image flow that causes a problem is suppressed while suppressing the granular unevenness as compared with the case of using the liquid developer of the comparative example. It was confirmed that

  1 transfer roller, 2 intermediate transfer body, 3 paper, 4 toner image (before transfer), 5 toner image (after transfer), 7 surface of liquid developer, 8 range of influence of transfer electric field, 9 nip portion, 10 toner particles Range where aggregation is likely to occur, 20 Image forming device, 21 Developer, 22 Developer tank, 23 Anilox roller, 24 Anilox regulating blade, 25 Leveling roller, 26 Developer carrier, 27, 32, 34 Cleaning blade, 28 Developer charger , 29 Photoconductor, 30 Charging unit, 31 Exposure unit, 33 Intermediate transfer member, 35 Secondary transfer roller, 36a, 36b Fixing roller, 37 Primary transfer unit, 38 Secondary transfer unit, 40 Media.

Claims (3)

Including toner particles and an insulating liquid;
The insulating liquid contains 10 to 30 % by mass of a first hydrocarbon having 11 to 16 carbon atoms and 70 to 90% by mass of a second hydrocarbon having 17 to 20 carbon atoms, and has 21 or more carbon atoms. No third hydrocarbon or 10% by weight or less,
The liquid developer, wherein the total amount of the first hydrocarbon, the second hydrocarbon, and the third hydrocarbon contained in the insulating liquid is 95% by mass or more. The liquid developer according to claim 1, wherein the insulating liquid does not contain the third hydrocarbon or contains 1% by mass or less. The toner particles comprise a resin and a colorant, wherein the resin is an acid value of 20 mgKOH / g or more polyester resins, liquid developer according to claim 1 or 2.

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