JP4603374B2 - Image forming method - Google Patents

Description

  The present invention relates to an image forming method for forming both a full color image and a black and white monochrome image by an electrophotographic method or an electrostatic recording method.

Conventionally, a laser beam printer, such as an electrostatic copying machine, in a full-color image forming apparatus according to an electrophotographic method or an electrostatic recording method, a black toner, a cyan, a full color image by superimposing the color magenta toner and yellow In particular, in recent years, these image forming apparatuses are required to form high-quality and high-gloss full-color images comparable to silver salt photographs.
In recent years, the demand for full-color images in business documents has increased, but if the text image of a business document formed mainly with black toner has the same high glossiness as a full-color graphic image, There is a problem that it is difficult to read because the interior light is reflected. On the other hand, a black toner for forming a black and white monochrome image (hereinafter referred to as “monochrome image”) such as a character image usually uses a magnetic black toner having a low glossiness. However, in order to obtain a large offset margin at the time of fixing, a low gloss type is widely used. Therefore, an image formed with black toner has a lot of so-called matte image quality in which glare is generally suppressed.

However, in the case where a monochrome image (character image) and a full-color image (graphic image) are mixed, the black portions of the full-color image, when the same were formed with a low gloss toner for matte quality monochrome images, full color image The black portion and the color portion are greatly different in gloss, resulting in a new problem that the entire image is uncomfortable or the color reproduction range is narrowed due to a decrease in brightness difference.

  Various techniques have been proposed in order to solve such problems. Specifically, a technique of applying gloss to a toner image made of low-gloss toner by applying a transparent toner (Patent Document 1), A technology that selectively uses two types of high-gloss non-magnetic black toner and low-gloss magnetic black toner (Patent Document 2), switching the development order according to the image to be formed, and the black toner layer on the final carrier of the toner A technique (Patent Document 3) for changing the stacking order has been proposed.

In addition, when the black portion is expressed with the magnetic black toner alone, the blackness and hiding power of the black portion are insufficient. For example, yellow, magenta and cyan pigments are added to the black toner. (Patent Document 4) and a technique using a magnetic black toner to which a cyan pigment is added (Patent Document 5) have been proposed.
JP 2002-341619 A Japanese Patent Laid-Open No. 9-15925 JP-A-7-120996 JP 2000-112179 A JP-A-4-353867

  However, according to the technique described in Patent Document 1, a large amount of transparent toner and means for forming and transferring a transparent toner image are required. According to the technique described in Patent Document 2, two types of black toner are used. Since an extra developer and developing means are required to properly use the two, it is disadvantageous in terms of cost. In addition, according to the techniques described in Patent Documents 2 and 3, since there are a wide variety of parameters for adjusting the proper use of magnetic toner and non-magnetic toner and the parameters for appropriately adjusting the development order, image formation is executed. There is a problem that the control and mechanism for doing so become complicated.

  Further, in the technique described in Patent Document 4, colored particles containing carbon black and cyan, magenta and yellow pigments are used as the black toner. In the technique described in Patent Document 5, blue powder is used together with magnetic powder. However, when such a toner is used, there is a problem that the gloss of the image cannot be adjusted as appropriate when switching between a monochrome image and a full-color image.

Therefore, an object of the present invention is to improve the blackness and glossiness of the black portion of a full-color image by using a magnetic toner in combination with both a monochrome image and a full-color image in a simple image forming system. An image forming method capable of reducing a gloss difference between a black portion and a color portion in an image, making a monochrome image have a matte tone with reduced gloss, and further improving the blackness and glossiness of the monochrome image as necessary. Is to provide.

In order to achieve the above object, the present invention provides:
(1) In an image forming method for forming at least one of a monochrome image and a full-color image including a black portion on a transfer medium using black toner and color toner ,
A magnetic black toner as the black toner, as the color toners, cyan, and each non-magnetic toner of magenta and yellow used,
When forming the black portion of the full-color image, an underlayer is formed on the transfer medium using at least one of the nonmagnetic cyan toner and the nonmagnetic magenta toner, and then the obtained bottom layer is obtained. on the surface of the formation, the black portion is formed by superimposing the magnetic black toner,
When forming the monochrome image ,
(a) forming the monochrome image on the transfer medium using the magnetic black toner alone, or
(b) forming an underlayer on the transfer medium using at least one of the nonmagnetic cyan toner and the nonmagnetic magenta toner, and then forming the magnetic black toner on the surface of the obtained underlayer Forming the monochrome image by superimposing
(2) Black portions in the full-color image or Oite monochrome picture image of the (b),, transfer of non-magnetic toner for forming the underlayer, 0 to the transfer amount of the magnetic black toner. The image forming method according to claim 1, wherein the image forming method is 5 to 1.0 times.
(3) As the underlayer, a layer made of a nonmagnetic cyan toner and a layer made of a nonmagnetic magenta toner are formed, and the underlayer made of the nonmagnetic magenta toner is more than the underlayer made of the nonmagnetic cyan toner. The image forming method according to claim 1, wherein the image forming method is formed on the transfer target side.

  Since magnetic black toner contains a large amount of magnetic material, it has a higher specific gravity than non-magnetic toner. The toner having such a high specific gravity and a large particle size has a small ability to cover a finally fixed carrier (for example, a transfer medium such as paper), and therefore, the color of the final carrier. Susceptible to. Moreover, many binder resins used for magnetic toners are difficult to melt. Therefore, an image formed with magnetic black toner usually has a low image density (that is, blackness) and gloss (glossiness).

In the image forming method of the present invention, when forming a black portion of a full-color image, a base layer of a magnetic black toner is formed using cyan or magenta toner having a relatively low brightness among color toners. .
As a result, the coverage of the toner on the transfer target can be improved, and the melting characteristics of the magnetic black toner can be brought close to the good melting characteristics of the nonmagnetic cyan and / or magenta toner. The smoothness of the surface of the melted toner can be improved as compared with the case where the black toner is melted alone.
Further, as a result, the image density (blackness) and gloss of the black portion of the full-color image formed with the magnetic black toner can be increased , and a good full-color image having no sense of incongruity can be obtained.
In addition, by forming the monochrome image using the magnetic black toner alone, it is possible to obtain a monochrome image that is easy to read without glare as a matte tone with reduced gloss. In addition, if necessary, the glossiness and blackness of a monochrome image can be improved by forming a base layer using cyan or magenta toner on top of the magnetic black toner in the same manner as the black portion of a full-color image. You can also.

  In the present invention, when a non-magnetic black toner having a small specific gravity is used as the black toner instead of the magnetic black toner, the non-magnetic cyan and / or magenta toner serving as a base is replaced by the non-magnetic black toner. As a result, the image quality of the non-magnetic black toner having a low gloss becomes dominant, so that the effect of improving the gloss of the black portion in the full-color image cannot be obtained sufficiently. .

According to the image forming method of the present invention, the image density (blackness) of the black portion is improved (L * a *) as compared with the case where the black portion of the full-color image is formed using the magnetic black toner alone. In addition , the gloss difference between the color portion and the black portion can be reduced, and a good full-color image without a sense of incongruity can be obtained.
In addition, by forming the monochrome image using the magnetic black toner alone, it is possible to obtain a monochrome image that is easy to read without glare as a matte tone with reduced gloss. In addition, if necessary, the glossiness and blackness of a monochrome image can be improved by forming a base layer using cyan or magenta toner on top of the magnetic black toner in the same manner as the black portion of a full-color image. You can also.

When a base layer made of non-magnetic cyan toner is formed below the layer made of magnetic black toner, and further, a layer made of non-magnetic magenta toner is formed below that layer, the base layer is made of non-magnetic cyan toner. With a smaller amount of toner than when only the layer is formed, it is possible to reduce the gloss difference and improve the blackness of the black portion (reduction of L ^* a ^* b ^* ).

In the image forming method of the present invention, the magnetic black toner is used both for forming a black portion in a full-color image and for forming a monochrome image.
In the image forming method of the present invention, when a black portion in a full-color image is formed, a nonmagnetic cyan toner and / or a nonmagnetic magenta toner (hereinafter referred to as a nonmagnetic cyan toner and a nonmagnetic magenta toner) In some cases, the base layer is formed using “non-magnetic color toner” in some cases, and then the magnetic black toner is overlaid on the surface of the obtained base layer.

The amount of the non-magnetic color toner that forms the underlayer is appropriately set in consideration of the glossiness required for the black portion, the melting characteristics of the toner, and the like, and is not particularly limited. The amount of the magnetic black toner is preferably 0.5 to 1.0 times, more preferably 0.7 to 0.9 times. For example, when the amount of magnetic black toner in the black portion is 0.7 mg / cm ² on the transfer target, the total amount of non-magnetic toner forming the underlayer is preferably 0.35 to 0. .70 mg / cm ² , more preferably 0.49 to 0.63 mg / cm ² . When the amount of the non-magnetic color toner is 0.5 to 1.0 times the amount of the magnetic black toner to be superimposed on the same region, the desired glossiness can be achieved while appropriately suppressing the consumed toner amount. Can be obtained.

  As the nonmagnetic color toner for forming the underlayer, a nonmagnetic cyan toner and a nonmagnetic magenta toner may be used alone, but the underlayer includes a nonmagnetic cyan toner layer and a nonmagnetic magenta toner layer. In particular, a layer made of a nonmagnetic magenta toner is formed on a transfer target, and a layer made of a nonmagnetic cyan toner is further formed thereon. preferable.

The content ratio of the amount C of the nonmagnetic cyan toner and the nonmagnetic magenta toner M in the underlayer is not particularly limited. For example, C: M (weight ratio) is preferably 10: 0 to 3: 7. Yes, more preferably 7: 3 to 3: 7.
In the black portion of the full-color image, the amount of the magnetic black toner depends on the amount of magnetic substance added to the magnetic black toner and the particle size of the toner. , and a 0.6 mg / cm ² or more, more preferably 0.7~0.9mg / cm ² or more.

In the image forming method of the present invention, when forming a monochrome image image, on the transfer member may be formed an image of a magnetic black toner alone. Further, for example, when forming a monochromatic image with high gloss or high blackness, the base layer is formed on the transfer target in the same manner as when forming a black portion in a full-color image, Then, magnetic black toner may be superimposed.

Whether an image to be formed is a full color image or a monochrome image is determined by internal processing in a full color image forming apparatus using an electrophotographic method or an electrostatic recording method such as a laser beam printer or an electrostatic copying machine. Can be discriminated.
Specifically, for example, when developing using magnetic black toner in accordance with information from the document reading unit in the full-color image forming apparatus, the development area (herein simply referred to as “black area”). When there is an area that needs to be developed with color toner (cyan, magenta, or yellow) adjacent to or in the vicinity of the black area, it can be determined that the black area is a black portion in the full-color image. . Therefore, in such a case, first, a base layer made of nonmagnetic cyan toner and / or nonmagnetic magenta toner is formed on the transfer object corresponding to the black region, and then the base layer is further formed. In addition, magnetic black toner may be superimposed.

  On the other hand, if there is no area that requires color toner (cyan, magenta, or yellow) development adjacent to or in the vicinity of the black area, the black area is an area corresponding to a monochrome image. Can be determined. Normally, a monochrome image is mainly a text document, and a high gloss image is not required. In such a case, the magnetic layer is not formed on the transfer material corresponding to the black area without forming the underlayer. An image may be formed with black toner alone.

As described above, even if it is determined that the black area is an area corresponding to a monochrome image, if the user desires a monochrome image with high gloss or high blackness, it is optional. Specifically, the magnetic black toner may be controlled to be superimposed after the underlayer is formed in the black region.
The image forming method of the present invention is a method of improving the image density (blackness) of a black portion of an image and improving the gloss of the black portion in a full-color image by combining the non-magnetic color toner with a magnetic black toner. Therefore, in expressing the black portion of the image, the total amount of toner on the transfer medium tends to increase. Therefore, although there is a concern about the occurrence of offset in the fixing unit, the occurrence of offset can be suppressed by arranging magnetic black toner in the portion closest to the heat source in the fixing unit to secure an offset margin. . Specifically, the uppermost layer of the toner layer may be a layer made of magnetic black toner on the transfer target as the final carrier.

In the image forming method of the present invention, as described above, magnetic black toner is used as black toner, and cyan, magenta, and yellow nonmagnetic color toners are used as color toners.
Examples of the magnetic black toner include resin particles containing a binder resin, magnetic powder, and, if necessary, a charge control agent (charge control agent), wax, and the like.

The resin particles may be those obtained by melting, kneading, pulverizing and then classifying each of the above components, and blending each of the above components excluding the binder resin with a monomer component, and by suspension polymerization. It may be granulated.
Examples of the binder resin for forming the magnetic black toner include styrene polymers such as polystyrene, o, m, p-chloropolystyrene and poly-α-methylstyrene; acrylic polymers, methacrylic polymers; low molecular weight polyethylene. Olefin polymers such as low molecular weight polypropylene; ethylene-vinyl acetate copolymers; ionomers, polyester resins, polyamide resins, polyurethane resins, epoxy resins, diallyl phthalate resins, silicone resins, ketone resins, polyvinyls Examples include butyral resin, phenolic resin, rosin-modified phenol resin, xylene resin, rosin-modified maleic acid resin, and rosin ester. Of these, a styrene polymer and a polyester resin are preferable.

  Examples of the styrenic polymer include not only the homopolymers exemplified above, but also copolymers of styrene and other monomers. Examples of other monomers copolymerizable with styrene include, for example, o, m, p-chlorostyrene, vinylnaphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butadiene, isobutylene; vinyl chloride, vinyl bromide. , Vinyl halides such as vinyl fluoride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; carboxylic acids such as maleic acid; methyl acrylate, ethyl acrylate, n-butyl acrylate , Acrylates such as isobutyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate; methyl methacrylate, ethyl methacrylate, butyl methacrylate Methacrylic acid esthetics such as Other acrylic acid derivatives such as acrylonitrile, methacrylonitrile and acrylamide; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropynyl ketone; N-vinyl pyrrole; Examples thereof include N-vinyl compounds such as N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidene. These monomers can be copolymerized with styrene either alone or in combination of two or more. Of the above-mentioned copolymers of styrene and other monomers, a styrene-acrylic polymer is preferable.

  Examples of the polyester-based resin include those obtained by polycondensation of a polyvalent carboxylic acid component and a polyhydric alcohol component. Examples of the polyvalent carboxylic acid component include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, Divalent carboxylic acids such as malonic acid; n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid Alkyl esters or alkenyl esters of divalent carboxylic acids such as isododecyl succinic acid and isododecenyl succinic acid; 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2 , 5,7-Naphthalenetricarboxylic acid, 1,2,4-na Talentricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid , Tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, emporic trimer acid and other trivalent carboxylic acids. These polyvalent carboxylic acids may be anhydrides. Examples of the polyhydric alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butene. Diols such as diol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; bisphenol A, hydrogenated bisphenol A Bisphenols such as polyoxyethylenated bisphenol A and polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, Taerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4- Examples include polyhydric alcohols higher than triol such as butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

The magnetic powder forming the magnetic black toner is not particularly limited, and various magnetic powders used in the toner can be mentioned. Specifically, for example, powders of metals such as iron, manganese, nickel, cobalt, and iron alloys; magnetite (Fe ₃ O ₄ ), γ-Fe ₂ O ₃ , CrO ₂ , nickel ferrite, nickel-zinc ferrite, copper -Zinc ferrite, barium-zinc ferrite, manganese-zinc ferrite, lithium-zinc ferrite, magnesium-manganese ferrite, magnesium-copper-zinc ferrite, various ferrite powders such as barium-nickel-zinc ferrite, and the like. The magnetic powders exemplified above can be used alone or in admixture of two or more. From the viewpoint of further improving the charging characteristics, it is particularly preferable to use magnetite (Fe ₃ O ₄ ) among the above exemplified magnetic powders.

The particle size of the magnetic powder is not particularly limited, but is an average particle size (50% particle size), preferably 0.05 to 1.0 μm, more preferably 0.1 to 1 μm, and still more preferably 0.00. 15 to 0.5 μm.
The shape of the magnetic powder is not particularly limited, and includes various shapes such as a spherical shape, a needle shape, a scale shape, and an indefinite shape, but a shape having an edge, that is, for example, a hexahedron, an octahedron, a decahedral, a twelve It is preferably a polyhedron shape such as a plane.

The blending amount of the magnetic powder is not particularly limited, but is preferably 50 to 150 parts by weight, and more preferably 60 to 110 parts by weight with respect to 100 parts by weight of the binder resin forming the magnetic black toner. is there.
The charge control agent (charge control agent) is arbitrarily blended in the binder resin for the purpose of controlling frictional charging of the magnetic black toner. Specific examples thereof are not particularly limited, and can be appropriately selected from various charge control agents according to the charge polarity required for the magnetic black toner.

  As the positive charge control agent, for example, an organic compound having a basic nitrogen atom, for example, a basic dye, an aminopyrine, a pyrimidine compound, a polynuclear polyamino compound, an aminosilane compound, or the basic nitrogen atom exemplified above is used. Examples thereof include a filler that has been surface-treated with an organic compound. Examples of the negative charge control agent include oil-soluble dyes such as nigrosine base (CI5045), oil black (CI26150), Bontron S (manufactured by Orient Chemical Co., Ltd.), and spiron black; compounds containing carboxyl groups (For example, alkyl salicylic acid metal chelates); metal complexes (for example, salicylic acid chromium complexes, azo-based chromium complexes); fatty acid metal soaps, resin acid soaps, naphthenic acid metal salts, and the like. Furthermore, in the present invention, a charge control resin can be used as the charge control agent. Examples of the charge control resin include a positive charge control resin obtained by introducing a functional group containing a basic nitrogen atom such as a quaternary ammonium salt into a resin such as styrene-acrylic resin, styrene resin, or acrylic resin; styrene -Negative charge control resin obtained by introducing a functional group such as imidazole, carboxyl group, or sulfo group into a resin such as an acrylic resin, a styrene resin, or an acrylic resin.

The blending amount of the charge control agent is not particularly limited. For example, it is preferably 3 to 25 parts by weight, more preferably 5 to 20 parts by weight with respect to 100 parts by weight of the magnetic powder forming the magnetic black toner. It is.
The wax is arbitrarily blended for the purpose of adjusting the releasability of the magnetic black toner. Specific examples thereof are not particularly limited, and can be appropriately selected from various waxes blended in the toner. For example, polyhydric alcohol ester or higher alcohol ester of fatty acid; natural wax such as carnauba wax, montan wax, rice wax, paraffin wax; polypropylene wax, polyethylene wax, oxidized polyethylene wax, ester wax, alkylene bis fatty acid amide compound, Fischer Synthetic waxes such as Tropsch wax are listed.

Although the compounding quantity of a wax is not specifically limited, For example, Preferably it is 0.5-7 weight part with respect to 100 weight part of binder resin, More preferably, it is 2-5 weight part.
In addition to the above components, the magnetic black toner contains, for example, a surface treatment agent, a release agent, a lubricant, a flow improver, an abrasive, a conductivity imparting agent, an image peeling prevention agent, a colorant, etc. can do. As these compounding agents, known ones can be used.

In the present invention, as the magnetic black toner, a non-magnetic cyan toner and / or a non-magnetic magenta toner may be used in advance for the purpose of improving blackness and gloss in the black portion of the image.
The magnetic black toner can be produced according to a conventional method. Specifically, for example, after a charge control agent is fixed and bonded to the surface of the magnetic powder as necessary, the obtained magnetic powder, a binder resin, and wax as necessary are melt-kneaded. Further, the magnetic black toner can be produced by pulverizing and classifying the melt-kneaded product.

  The particle size of the magnetic black toner is not particularly limited, but the average particle size (50%) can be used from the viewpoints of uniform charging performance, suppression of deterioration in image quality due to occurrence of fogging, and improvement of resolution. Particle size), preferably 3 to 12 μm, more preferably 5 to 10 μm. In particular, in a small particle size toner for the purpose of improving the image quality of the formed image, the average particle size (50% particle size) of the magnetic toner is preferably about 4 to 8 μm.

The magnetic black toner can be subjected to a spheroidizing process, an external addition process, or the like, if necessary, after the above pulverization process or classification process. What is necessary is just to implement these processes according to a conventional method.
The external additive is not particularly limited. For example, silica (for example, hydrophobic silica), alumina (aluminum oxide), titanium oxide, strontium titanate, cerium oxide, magnesium oxide, chromium oxide, titania, zinc oxide, Inorganic fine particles such as magnetite; Nitride fine particles such as silicon nitride; Carbide fine particles such as silicon carbide; Metal salt fine particles such as calcium sulfate, calcium carbonate and aliphatic metal salts; Acrylic resin, fluororesin, polystyrene resin, Fine particles of organic materials such as polyester resin; fine particles composed of these composites; and those obtained by subjecting these particles to surface treatment. Examples of the surface treatment include treatment with aminosilane, fluorinated silane, silicone resin, alkylsilane, silicone oil, silane coupling agent, titanium coupling agent, and the like.

The particle size of the external additive is not particularly limited, except that it is large enough not to be buried in the colored particles and small enough to be electrostatically attached to the surface of the colored particles, but in general, The thickness is preferably 5 to 30 nm, more preferably 10 to 20 nm.
The blending amount of the external additive is not particularly limited. For example, it is preferably 0.1 to 2.0% by weight, more preferably 0.1 to 1.5% by weight based on the total amount of the colored particles. % By weight.

Nonmagnetic color toners include, for example, colored particles containing a binder resin, a colorant, and, if necessary, a charge control agent, an anti-offset agent, a stabilizer, and the like. And those with externally added fine particles for adjusting the chargeability.
The colored particles may be those obtained by melting, kneading, pulverizing, and classifying each of the above components, blending each of the above components excluding the binder resin and the monomer component, and by suspension polymerization. It may be granulated.

Although it does not specifically limit as binder resin which forms a nonmagnetic toner, For example, the thing similar to binder resin which forms magnetic black toner is mentioned.
The colorant that forms the nonmagnetic toner is not particularly limited, and various pigments can be used. Specifically, for example, purple pigments such as manganese purple, fast violet B, and methyl violet lake; bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, fast Blue pigments such as sky blue and induslen blue BC; green pigments such as chrome green, chromium oxide, pigment green B, malachite green lake, final yellow green G; yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast Yellow, Nickel Titanium Yellow, Naples Yellow, Naphthol Yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow Yellow pigments such as lake, permanent yellow NCG, tartrazine lake; orange pigments such as red lead yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, Indanthrene brilliant orange GK; Bengala, cadmium red, red lead, sulfide Examples thereof include red pigments such as mercury cadmium, permanent red 4R, risor red, pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B.

The colorant can be appropriately selected and used according to the color required for the nonmagnetic toner. The colorants exemplified above may be used alone or in admixture of two or more.
The blending amount of the colorant is not particularly limited. For example, it is preferably 5 to 30 parts by weight, more preferably 10 to 20 parts by weight with respect to 100 parts by weight of the binder resin forming the nonmagnetic toner. is there.

The charge control agent (charge control agent) is arbitrarily blended in the binder resin for the purpose of controlling frictional charging of the nonmagnetic toner. Specific examples thereof are not particularly limited, and examples thereof include the same charge control agents as described above.
The blending amount of the charge control agent is not particularly limited. For example, it is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 100 parts by weight of the binder resin forming the nonmagnetic toner. ~ 8 parts by weight.

  The offset preventing agent is arbitrarily blended in the binder resin for the purpose of suppressing the offset phenomenon of the non-magnetic toner during the image forming process (particularly during the fixing process). Specific examples thereof are not particularly limited, and examples thereof include aliphatic hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Of these, aliphatic hydrocarbons having a weight average molecular weight of about 1000 to 10,000 are preferable. More specifically, low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax, low molecular weight olefin polymers composed of olefin units having 4 or more carbon atoms, silicone oil, carbana wax, etc. may be mentioned, and these may be used alone or Two or more kinds can be mixed and used.

Although the compounding quantity of an offset inhibitor is not specifically limited, For example, Preferably it is 0.1-10 weight part with respect to 100 weight part of binder resin, More preferably, it is 0.5-8 weight part.
Examples of the external additive that is externally added (externally added) to the surface of the non-magnetic toner and carried are the same as those described above.

  The nonmagnetic toner is used as a two-component developer in combination with a magnetic carrier. The magnetic carrier is not particularly limited, and examples thereof include various magnetic particles such as ferrite particles, magnetite particles, and iron powder particles. The magnetic carrier is a so-called coat in which the surface of the above exemplified magnetic particles is coated with a resin such as an acrylic resin, a styrene resin, a silicone resin, or an epoxy resin for the purpose of improving chargeability and moisture resistance. The carrier may be a so-called magnetic powder-dispersed carrier in which the above exemplified magnetic particles are dispersed in the above exemplified resin.

The saturation magnetization value of the magnetic carrier is not particularly limited, but is preferably 35 to 50 emu / g. The volume resistivity of the magnetic carrier is not particularly limited, but is preferably 10 ⁸ to 10 ¹² Ω · cm. The volume average particle size of the magnetic carrier is not particularly limited, but is preferably 35 to 50 μm.

Next, although this invention is demonstrated based on an Example, this invention is not limited by the following Example.
In the following examples and controls, the nonmagnetic color toner includes a nonmagnetic cyan toner and a nonmagnetic magenta toner (both are color toners for an electrostatic copying machine “FS-8008” manufactured by Kyocera Mita Corporation); Average particle size (50% particle size) 9 μm) was used. As the magnetic toner, magnetic toner (average particle size (50% particle size) 8 μm) for the electrostatic copying machine “FS-3800” manufactured by Kyocera Mita Co., Ltd. was used as the magnetic black toner.

For evaluation of image density and gloss, plain paper (color paper (C2) paper manufactured by Fuji Xerox Co., Ltd.) is used as a transfer target, and the above-mentioned “FS-8008” is used as an evaluation machine for executing image formation. Machine (which made both magnetic toner and non-magnetic toner developable) was used.
The formed image was a 100% solid image (uniform solid by bias adjustment), and the amount of toner on the transfer medium was adjusted by the thickness of the toner layer. As shown in Table 1, the amount of toner carried on the transfer target was appropriately set for each example.

The present invention is characterized by adjusting the order of stacking of toners to be carried on the transfer body and the amount of toner to be carried, including the purpose of confirming the state of toner on the transfer body. Samples with different conditions in the unfixed state before fixing were sampled, and separately fixed on the transfer medium using the following fixing jig.
As the fixing jig, for the color toner, a fixing unit for the “FS-8008” is used. The fixing conditions during the image forming process were a transfer speed of 136 mm / second and a fixing roller temperature of 160 ° C.

The image density, color coordinates, and glossiness of the formed image were measured after fixing.
Image density and color coordinates (L ^* a ^* b ^* ) were quantified using a spectrophotometer “Spectroeye” manufactured by Gretag Macbeth. The color coordinates (L ^* a ^* b ^* ) were in accordance with JIS Z 8729 “Color Display Method—L ^* a ^* b ^* Color System and L ^* u ^* v ^* Color System”.

In the black portion of the full-color image, the L ^* value is 36 or less, preferably 30 or less, more preferably 23 or less, and further preferably 21 or less for color reproduction. The a ^* value and b ^* value are within ± 5.5, preferably within ± 1.5, and more preferably within ± 1.0.
The glossiness (%) was measured and numerically measured using a gloss meter “IG-330” manufactured by Horiba, Ltd. at an incident angle of 60 °.

Further, each example was determined based on the following criteria based on the measurement results of image density and glossiness.
A: Both image density and glossiness were very good.
○: Both image density and glossiness were good.
Δ: Either or both of the image density and the glossiness were slightly low, but they were at a level causing no practical problems.

  The results are shown in Table 1.

As shown in Table 1, when the black portion of the image is formed using magnetic black toner alone, the glossiness is 1.0% when the toner amount is 0.7 mg / cm ² . (Control 1) When the toner amount is 0.4 mg / cm ² , the glossiness is 2.0% (Control 2). On the other hand, when images were formed using nonmagnetic color toners (cyan and magenta), respectively, the gloss rate was 10.0% when the toner amount was 0.7 mg / cm ^2. Thus, the black image density is about 0.7 to 0.8.

When the toner amount of the magnetic black toner is 0.7 mg / cm ² and this is superposed on the underlayer made of non-magnetic cyan and / or magenta toner (Examples 1, 2, 4, 5, 7 and 8) The image density that could not be obtained when the magnetic black toner was used alone could be obtained, and the color coordinates were such that L ^* was 23 or less, and a ^* and b ^* were It was possible to set within ± 1.5. That is, the blackness in the black portion of the image could be increased.

  In addition, since the glossiness of the black portion was maintained at a relatively high value, even when compared with an image formed by using a nonmagnetic cyan toner and a nonmagnetic magenta toner alone, the difference in glossiness was different. I did not feel much. That is, even if the black portion is a black portion in a full-color image, the color portion and the black portion can be expressed without a sense of discomfort in the full-color image. For example, when a full-color image has a black portion formed with the toner of Control 1 or 2, since the difference in gloss between the color portion and the black portion is large, the black portion is included in the image. There is a problem that the user feels uncomfortable.

In addition, when the toner amount of the magnetic black toner is 0.4 mg / cm ² and this is superimposed on the base layer made of nonmagnetic cyan and / or magenta toner (Examples 3 and 6), the magnetic black toner Since the absolute amount of was small, the image density as black was slightly low, but the blackness and glossiness could be improved as apparent from the comparison with Control 2.

  The present invention is not limited to the above description, and various design changes can be made within the scope of the matters described in the claims.

Claims (3)

In an image forming method of forming at least one of a monochrome image and a full-color image including a black portion on a transfer object using black toner and color toner ,
A magnetic black toner as the black toner, as the color toners, cyan, and each non-magnetic toner of magenta and yellow used,
When forming the black portion of the full-color image, an underlayer is formed on the transfer medium using at least one of the nonmagnetic cyan toner and the nonmagnetic magenta toner, and then the obtained bottom layer is obtained. on the surface of the formation, the black portion is formed by superimposing the magnetic black toner,
When forming the monochrome image ,
(a) forming the monochrome image on the transfer medium using the magnetic black toner alone, or
(b) forming an underlayer on the transfer medium using at least one of the nonmagnetic cyan toner and the nonmagnetic magenta toner, and then forming the magnetic black toner on the surface of the obtained underlayer And forming the monochrome image by superimposing them. Black portions in the full-color image or Oite monochrome picture image of the (b),, transfer of non-magnetic toner for forming the undercoat layer, the transfer amount of the magnetic black toner 0.5-1 The image forming method according to claim 1, wherein the image forming ratio is 0.0 times.   As the underlayer, a layer made of a nonmagnetic cyan toner and a layer made of a nonmagnetic magenta toner are formed, and the underlayer made of the nonmagnetic magenta toner is more transferred than the underlayer made of the nonmagnetic cyan toner. The image forming method according to claim 1, wherein the image forming method is formed on a body side.