JP2007003944A - Electrophotographic toner set, electrophotographic developer, and image forming method using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic toner set with which an invisible image substantially free of a brightness difference from an image output medium on visual observation and the visible image of high glossiness can be obtained. <P>SOLUTION: The electrophotographic toner set comprises color toner particles including a binder resin, a colorant, and a release agent, and invisible toner particles including a binder resin, a near IR absorptive material, and a release material, in which the weight average molecular weight MwC of the binder resin used for the color toner particles, and the weight average molecular weight MwI of the binder resin used for the invisible toner particles including the near IR absorptive material satisfy the relationship of the following formula: (Number 1) formula (1): 2.0≤MwI≤4.0, formula (2): 8,000≤MwC≤22,000. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic toner, an electrophotographic developer, and an image forming method using the same that can be suitably used when forming an invisible image together with a visible image on the surface of an image output medium such as recording paper. About.

  Conventionally, there is an additional data embedding technique in which additional information is embedded in an image. In recent years, there has been an active movement to use this additional data embedding technology for copyright protection and illegal copy prevention of digital works such as still images, and as one of its methods, it has been used for copying and printing. In order to identify an image forming apparatus, a technique is known in which information is embedded by forming an image that is difficult to visually recognize on the image, or an invisible pattern in that sense. Infrared absorption is used to read the pattern. For example, as in the techniques described in Patent Document 1 and Patent Document 2, electrophotography, electrostatic recording, or inkjet recording, A colored region made of an infrared-absorbing dye and a colored region made of an infrared-reflecting dye are formed on a substrate in parallel or overlapping, and at least one of the colored regions is an image of characters, numbers, symbols, patterns, and the like 2 The image is recorded so that the colored areas of the seeds are substantially indistinguishable or difficult to distinguish with the naked eye.

  Further, in Patent Document 3, an image formed with a normal toner and an image formed with an infrared absorbing material-containing toner are formed in parallel or superimposed, and the two types of image areas are substantially indistinguishable or difficult to distinguish with the naked eye. It is disclosed that an image is recorded so that The concept of reading both of the information is similar, but Patent Document 1 is a technology that makes it impossible to distinguish only the infrared absorbing material by arranging or reflecting the infrared reflecting material of the same color as the infrared absorbing material in parallel or overlapping. The image made with is singly recognized by the naked eye alone. On the other hand, in Patent Document 3, even if an image is formed alone, it is difficult to see with the naked eye, and even if it is combined with C (cyan), M (magenta), Y (yellow), and K (black) images. It is characterized by little change in its hue. For this reason, the invisible image forming method shown in Patent Document 3 is not affected by the place where the invisible image is embedded or the design, so that it is better from an aesthetic point of view than when used for counterfeiting or securities. Technology.

  Further, various invisible infrared absorbing materials have been studied for the additional data embedding technique, and various materials have been disclosed.

  For example, in an inorganic material, as an organic material such as a rare earth metal such as ytterbium (Patent Document 4, Patent Document 5) and an infrared absorbing material containing a copper phosphate crystallized glass (Patent Document 6, Patent Document 7), Examples thereof include an aminium compound (Patent Document 8) and a croconium dye (Patent Document 9). Patent Document 10 has a spectral absorption maximum wavelength at 750 to 1100 nm, and an absorbance at 650 nm at the spectral absorption maximum wavelength. An organic material characterized by containing an infrared absorbing material having an absorbance of 5% or less has been proposed.

JP-A-6-171198 JP-A-6-122266 JP 2001-265181 A JP-A-9-77507 Japanese Patent Laid-Open No. 9-104857 Japanese Patent Laid-Open No. 7-53945 JP 2003-186238 A Japanese Patent Laid-Open No. 7-271081 JP 2001-294785 A JP 2002-146254 A

  Various proposals and conventional techniques described in the publication have the following problems.

  In other words, the techniques described in Patent Document 1 and Patent Document 2 do not define anything about the absorbability in the visible light region of the dye having infrared absorbability and reflectivity, and therefore, the upper layer of the region in which the additional information is embedded In addition, it may be necessary to provide a shielding layer for visually hiding information. That is, there may be a problem that a region or an image in which additional information is embedded is limited. Usually, a shielding layer for visually hiding information from the purpose needs to absorb or reflect all wavelengths in the visible light region, and when absorbing, it is black, and when reflecting, it is a white layer. It becomes. Therefore, there may be a problem that the additional information cannot be embedded anywhere in the region where the visible image is formed. Furthermore, when the additional information is visually concealed with a white shielding layer, it is necessary to embed the additional information between the layer on which the visible image is formed and the surface of the image output medium, and the shielding layer is formed. Later, there may be a problem that additional information cannot be newly added.

    Furthermore, the technique described in Patent Document 1 embeds information consisting of an invisible image in a region where a visible image that looks like a solid image is formed. Accordingly, there is a problem that an invisible image cannot be formed at an arbitrary position on the surface of the image output medium regardless of the position of the visible image formed on the surface of the image output medium.

  On the other hand, in the conventional techniques related to the near-infrared light absorbing material, which is an inorganic material for forming an invisible image described in Patent Document 4, Patent Document 5, Patent Document 6, and Patent Document 7, the light in the visible region is improved. Invisible images can be obtained by reflection, but when the normal image is created on it because the absorption in the infrared region is insufficient and the amount of toner per unit area needs to be increased. The unevenness of the lower invisible toner affects the upper image. As described above, the inorganic infrared absorbing material imposes restrictions on the use as a toner.

  Moreover, the near-infrared light absorbing material of the organic material as shown in Patent Literature 8, Patent Literature 9 and Patent Literature 10 is small in amount because of high infrared absorptivity, and when an inorganic material is used. However, the toner using the material described in the above-mentioned patent document has a large absorption in the visible region, so that the “invisible” target toner is colored.

  Furthermore, color images have a higher gloss than the surface of the image output medium from the viewpoint of the required image quality, but the glossiness of the invisible toner particles and the image output medium can be reduced even if color suppression is attempted by the combined use of a fluorescent brightener. Due to the difference, there is a problem that information that should originally be invisible can be easily read.

  The present invention has been made to solve the above-described problems. When a visible image provided together with an invisible image is visually observed on the surface of the image output medium, the image quality of the visible image is not impaired. Machine reading / decoding process is stable for a long time by light irradiation, and it is provided in an arbitrary area regardless of the area where the invisible image on which information can be recorded at high density and the visible image on the surface of the image output medium are provided. Another object of the present invention is to provide an electrophotographic toner capable of obtaining an invisible image that can be obtained, an electrophotographic developer, and an image forming method using them.

  The present invention has the following features.

  (1) A toner set comprising color toner particles containing a binder resin, a colorant, and a release agent, and invisible toner particles containing a binder resin, a near-infrared light absorbing material, and a release agent, The color toner particles and the invisible toner particles are used to transfer an image to the same image output medium, and then, in the specular gloss measurement according to JIS-Z8741, the 60 ° specular gloss of the color image and the invisible toner image. An electrophotographic toner set comprising a combination of the color toner particles having a degree difference of 20% or more and the invisible toner particles.

  (2) A toner set comprising color toner particles containing a binder resin, a colorant and a release agent, and invisible toner particles containing a binder resin, a near infrared light absorbing material and a release agent, An electrophotographic image in which the weight average molecular weight MwC of the binder resin used for the color toner particles and the weight average molecular weight MwI of the binder resin used for the invisible toner particles containing the near infrared light absorbing material satisfy the relationship of the following formula: Toner set.

(Equation 1)
Formula (1): 2.0 ≦ MwI / MwC ≦ 4.0
Formula (2): 8000 ≦ MwC ≦ 22000

  (3) The toner set for electrophotography according to (1), wherein the near-infrared light absorbing material contains at least one of an aminium salt compound and a naphthalocyanine compound.

  (4) An electrophotographic developer comprising a carrier and an electrophotographic toner, the electrophotographic toner according to any one of (1) to (3) above It is a developer for electrophotography which is a set.

  (5) A toner image formed on an image output medium using the electrophotographic toner set and / or developer according to any one of (1) to (4) above, at a temperature of 140 ° C. to 210 ° C. An image forming method including a step of heat fixing in a region.

  (6) In the image forming method described in (5) above, when an image is formed on an image output medium, the electrophotographic toner set and / or development described in any one of (1) to (4) above The lowermost layer of the toner image formed on the image output medium using an agent is an image of invisible toner particles containing a near infrared light absorbing material.

  According to the present invention, when a visible image provided together with an invisible image is visually observed on the surface of the image output medium, the invisible image is machine-readable by infrared light irradiation without impairing the image quality of the visible image. The decoding process is stable over a long period of time, information can be recorded with high density, and the invisible image can be provided in any area regardless of the area where the visible image is provided on the surface of the image output medium. In particular, an electrophotographic toner capable of obtaining an invisible image capable of recognizing the presence of invisible information and having a counterfeit deterrent effect or the like because there is no difference in gloss from the image output medium when it is visually observed or there is almost no gloss difference. Further, it is possible to provide an electrophotographic developer and an image forming method using them, which is extremely useful in practice.

  Hereinafter, the present invention will be described in detail.

[Electrophotographic toner set]
[Binder resin]
When an image including invisible information is formed on an image output medium, generally a visible image, that is, a color image is mainly used. In particular, full-color images often include illustrations, photographs, etc., and from the viewpoint of high image quality, it is required that the final image quality has a high glossiness. The toner material, particularly the binder resin, is the same as the surface of the image output medium. The material is designed so that the Δ gloss, which is the difference in glossiness, becomes large.

  On the other hand, an invisible image adds information to the color image, and it is necessary that the invisible image is not revealed by means other than information detection, that is, not visually confirmed. However, when a material design including the same binder resin is applied to the toner particles that visualize invisibility, the difference in glossiness from the surface of the image output medium is small even if the image itself is not colored. However, the part where the invisible information is recorded can be visually recognized.

  Therefore, in a system for visualizing a color image, particularly a full-color image, it is desirable that the visible image is reproduced with high glossiness, and that the invisible information recording image has a small glossiness difference from the image output medium.

  The present invention has been made in view of the above, and the weight average molecular weight of each of color toner particles and toner particles in which a near infrared material for imparting invisible information is dispersed (hereinafter referred to as invisible toner) is provided. The present inventors have found that the problem can be improved by using different binder resins and having a relationship as shown in the following formula, and have completed the invention.

  In the present invention, a toner set composed of color toner particles for visualization purposes and invisible toner particles is applied to the present invention, and the molecular weight of the binder resin used in the toner satisfies the relationship of the following formula: Yes.

(Equation 2)
Formula (1): 2.0 ≦ MwI /: MwC ≦ 4.0
Formula (2): 8000 ≦ MwC ≦ 22000
In the formula, MwI: the weight average molecular weight of the binder resin used for the invisible toner particles,
MwC: Weight average molecular weight of binder resin used for color toner particles

  When the range of the weight average molecular weight in the above formula (1) is less than 2.0, the Δ gloss of the surface of the invisible toner and the image forming medium (also referred to as an image output medium or a recording medium) is increased, and is as high as the color image. The presence of information that would otherwise be invisible because of its glossiness can be recognized visually. Furthermore, when heat-fixing to an image output medium, the binder resin for both the color image and the invisible image is likely to partially dissolve, and the pigment and the near-infrared light absorbing material are mixed, so that the invisible portion is made. There is a possibility that some or all of the assigned information cannot be read.

  When the value of the above formula (1) is larger than 4.0, the Δ glossiness for the color image is large, and when the color image and the invisible image overlap, the high glossiness of the color image may be hindered. The color toner and the invisible toner are assumed to be heat-fixed by the same system. However, the heat-fixing temperature cannot be set in a high temperature range in which a color image causes an offset from the viewpoint of high image quality. . For this reason, the invisible information recording portion having a high molecular weight cannot obtain a sufficient strength, and there is a possibility that the information is lost or completely defeated from the image output medium. Although it is possible to avoid this concern by preparing a fixing system suitable for each case, the system itself becomes larger and complicated, and the controllability of the aircraft deteriorates, so it is not realistic. .

  When the weight average molecular weight in the above formula (3) is less than 8000, the viscoelasticity of the color toner particles is lowered at the time of heat melting and fixing, and troubles such as offset are likely to occur, and further invisible within the range of the formula (1). Since the weight average molecular weight of the binder resin of the toner particles is defined, there is a concern that the glossiness of the invisible image itself is increased and the visual visibility is increased.

  When the weight average molecular weight in the above formula (3) is larger than 22000, the color toner particles cannot be sufficiently melted at the time of heat-melting and fixing, and as a result, the smoothness of the color image surface cannot be obtained and the image quality is deteriorated. Further, even in an invisible image, in the vicinity of the upper limit of the weight average molecular weight defined by the formula (1), sufficient fixing strength cannot be obtained in a fixing temperature range suitable for color toner particles, and image loss or the like may occur. Yes.

[Near-infrared light absorbing material]
In addition, the invisible toner particles of the present invention contain a near-infrared light-absorbing material in order to record invisible information and enable detection as necessary, in addition to the binder resin in the weight average molecular weight range.

  As the near-infrared light absorbing material, in the inorganic material system, for example, a known glass network forming component that transmits visible wavelengths such as phosphoric acid, silica, boric acid, transition metal ions, inorganic and / or organic compounds Inorganic materials such as glass to which a material such as a pigment is added and crystallized glass obtained by crystallizing the material by heat treatment are exemplified. These inorganic materials can reflect light in the visible region well to obtain an invisible image, but on the other hand, the absorption in the infrared light region is not sufficient and the amount of toner per unit area needs to be increased.

  Examples of organic near infrared light absorbing materials include colored materials such as phthalocyanine compounds and anthraquinone compounds, and colorless materials such as aminium salt compounds and naphthalocyanine compounds. The former colorizes the image by addition, so it is not suitable for invisible information recording, but the latter has a sufficiently large absorption in the infrared light region compared to inorganic materials, and the amount added can be suppressed, resulting in As an advantage, the image quality of the color image is not impaired.

  For the reasons described above, it is preferable to use at least one of an aminium salt compound and a naphthalocyanine compound as the near infrared light absorbing material in the present invention. In a more preferred embodiment, the near-infrared light absorbing material is dispersed and contained in the toner particles.

  When the material is externally fixed to the toner surface or mixed and added to the toner particle group, there is a possibility that the material aggregates in the toner particles and the developer. Alternatively, at the stage of developer adjustment, it is lost due to adhesion to the device, etc., and the near-infrared light absorbing material in the invisible image is insufficient or unevenly distributed, so that information cannot be read accurately and stably. Further, there is a possibility that the liberated near-infrared light absorbing material may contaminate the inside of the apparatus, particularly the photoreceptor, and adversely affect other processes such as development and transfer.

  In particular, when using the organic near-infrared light absorbing material described above, the dispersibility to the binder resin is better than that of the inorganic material, and it is uniformly dispersed in the invisible image formed on the image output medium. Without losing invisibility, it can absorb information in the infrared region to record information at high density and has good dispersibility in the toner, so machine reading / decoding processing of invisible images can take a long time. It became possible to carry out stably.

  As the phthalocyanine compound used in the present invention, compounds exemplified by the following formulas (3) and (4) are suitable.

（式（３）において、Ｍは、金属原子又は金属酸化物を表し、Ｒ_１、Ｒ_５及びＲ_７は、同一もしくは異なっていてもよく、それぞれ、水素原子、直鎖もしくは分岐鎖のアルキル基、シクロヘキシルアルキル基、ヒドロキシアルキル基、アルコキシアルキル基、アシルオキシアルキル基、アシルアミノアルキル基、ハロゲン化アルキル基、シアノアルキル基、アルコキシカルボニルアルキル基、アルケニル基又はアラルキル基を表し、Ｒ_２、Ｒ_３、Ｒ_４及びＲ_５は、同一もしくは異なっていてもよく、それぞれ、水素原子、直鎖もしくは分岐鎖のアルキル基、シクロアルキル基、直鎖もしくは分岐鎖のアルコキシ基、シクロアルキルオキシ基、アルコキシアルキル基、アルコキシアルコキシ基、アラルキル基又はハロゲン原子を表し、また、Ｒ_２とＲ_３又はＲ_４とＲ_５が組み合わさって環状基を形成していてもよく、Ｘは、水素原子、ハロゲン原子、アルコキシ基又は水酸基を表し、ｌは、１〜４の整数であり、ｍは、０〜５の整数であり、そしてｎは、０〜１４の整数であり、但し、２ｌ＋ｍ＋ｎは１６である）

(In the formula (3), M represents a metal atom or a metal oxide, and R ₁ , R ₅ and R ₇ may be the same or different, and each represents a hydrogen atom, a linear or branched alkyl group, Represents a cyclohexylalkyl group, a hydroxyalkyl group, an alkoxyalkyl group, an acyloxyalkyl group, an acylaminoalkyl group, a halogenated alkyl group, a cyanoalkyl group, an alkoxycarbonylalkyl group, an alkenyl group, or an aralkyl group, R ₂ , R ₃ , R ₄ and R ₅ may be the same or different and are each a hydrogen atom, a linear or branched alkyl group, a cycloalkyl group, a linear or branched alkoxy group, a cycloalkyloxy group, an alkoxyalkyl group. Represents an alkoxyalkoxy group, an aralkyl group or a halogen atom; R ₂ and R ₃ or R ₄ and R ₅ may be combined to form a cyclic group, X represents a hydrogen atom, a halogen atom, an alkoxy group or a hydroxyl group, and l represents 1 to 4 An integer from 0 to 5 and n is an integer from 0 to 14, where 2l + m + n is 16)

(In the formula (4), Met represents two hydrogen atoms, a divalent metal atom, a trivalent or tetravalent substituted metal atom, and A ^{1 to} A ⁸ may be the same or different, , Hydrogen atom, halogen atom, substituted or unsubstituted alkyl group, substituted or unsubstituted aryl group, substituted or unsubstituted alkoxy group, substituted or unsubstituted aryloxy group, substituted or unsubstituted alkylthio group or substituted or Represents an unsubstituted arylthio group, provided that in each combination of A ¹ and A ² , A ³ and A ⁴ , A ⁵ and A ⁶ , A ⁷ and A ⁸ , both of them simultaneously become a hydrogen atom or a halogen atom. rather, Y ¹ to Y ¹⁶ may be the same or different, each represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, lay be substituted Unsubstituted aryl group, substituted or unsubstituted alkoxy group, substituted or unsubstituted aryloxy group, substituted or unsubstituted alkylthio group, substituted or unsubstituted arylthio group, substituted or unsubstituted alkylamino group, substituted or Unsubstituted dialkylamino group, substituted or unsubstituted arylamino group, substituted or unsubstituted diarylamino group, substituted or unsubstituted alkylarylamino group, hydroxy group, mercapto group, nitro group, nitrile group, oxycarbonyl group Represents an alkoxycarbonyl group, an aryloxycarbonyl group, an aminocarbonyl group, or a mono- or di-substituted aminocarbonyl group)

  Moreover, as an aminium-type compound, the compound which is illustrated to the following formula | equation (5) and Formula (6) is used suitably.

  As the near-infrared light absorbing material in the present invention, the compounds exemplified above are suitable, but any organic material particles selected from aminium salt compounds and naphthalocyanine compounds are not limited. It is not something.

  The toner set according to the present invention further includes a step of heat-fixing the toner image formed on the image output medium in a temperature range of 140 ° C. to 210 ° C., preferably 160 ° C. to 200 ° C. When the fixing temperature range is higher than the above range, the quality of the main color image cannot be maintained. In other words, by generating a temperature-fall offset, the image surface becomes rough or the image itself is lost, and the demand for image quality cannot be satisfied. On the other hand, if the temperature is below the temperature range, the fixing strength of the invisible toner particles is lowered, and the invisible image is disturbed or lost, and the invisible information cannot be read accurately.

  By controlling the heating and fixing temperature within the temperature range of the present invention, it is possible to suppress visual recognition of an image imparting invisible information while maintaining high image quality in a color image that is a main visualized image.

  Further, common materials used for the toner set will be described in detail below.

<Binder resin>
The binder resin that can be used for the toner particles in the toner set of the present invention is not particularly limited, but is mainly composed of an ethylene-based resin such as polyethylene or polypropylene, polystyrene, α-poly (α-methylstyrene), or the like. (Meth) acrylic resin, polyamide resin, polycarbonate resin, polyether resin, polyester resin and copolymer resins thereof mainly composed of styrene resin, polymethyl methacrylate, polyacrylonitrile, etc. From the viewpoint of charging stability and development durability when used as a toner for a toner, styrene resins, (meth) acrylic resins, styrene- (meth) acrylic copolymer resins and polyester resins are preferred.

  Examples of the condensable monomer used in the polyester resin include condensable monomer components described in, for example, Polymer Data Handbook: Basic Edition (edited by the Society of Polymer Science: Bafukan). There are divalent or trivalent or higher carboxylic acids and divalent or trivalent or higher alcohols. Specific examples of the divalent carboxylic acid include succinic acid, glutaric acid, adipic acid, speric acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2 Dibasic acids such as, 7-dicarboxylic acid, cyclohexanedicarboxylic acid, malonic acid, mesaconic acid, etc., and anhydrides and lower alkyl esters thereof, maleic acid, fumaric acid, itaconic acid, citraconic acid, and other aliphatic unsaturations And dicarboxylic acid. Examples of the trivalent or higher carboxylic acid include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, and the like, and anhydrides thereof. And lower alkyl esters. These may be used individually by 1 type and may use 2 or more types together.

  Examples of the divalent alcohol include bisphenol A, hydrogenated bisphenol A, ethylene oxide or (and) propylene oxide adduct of bisphenol A, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, ethylene glycol, diethylene glycol, Examples include propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, and neopentyl glycol. Examples of the trivalent or higher alcohol include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol and the like. These may be used individually by 1 type and may use 2 or more types together. If necessary, monovalent acids such as acetic acid and benzoic acid, and monovalent alcohols such as cyclohexanol and benzyl alcohol can be used for the purpose of adjusting the acid value and the hydroxyl value.

  The polyester resin can be used in any combination of the condensable monomer components described above, such as “polycondensation” (chemical doujin), “polymer experiment (polycondensation and polyaddition)” (Kyoritsu Shuppan) It can be synthesized using a conventionally known method described in “Polyester Resin Handbook” (edited by Nikkan Kogyo Shimbun), and the transesterification method, the direct polycondensation method, etc. can be used alone or in combination. it can.

  Further, as described above, it is preferable to leave carboxyl groups in the molecular skeleton of the resin. However, since it is difficult to introduce carboxyl groups into the molecular side chains in the manufacturing process, both ends of the resin molecules are made carboxyl groups. Thus, a certain effect can be obtained for controlling the content of the copper compound. Accordingly, the acid value of the resin is preferably higher, and specifically in the range of 5 to 50 mgKOH / g. More preferably, it is 10-40 mgKOH / g.

  Moreover, the following are mentioned as a polymerizable monomer which comprises the above-mentioned styrene-type resin and (meth) acrylic-type resin, especially styrene- (meth) acrylic-type copolymer resin.

  Examples of styrene monomers include styrene, α-methyl styrene, vinyl naphthalene, 2-methyl styrene, 3-methyl styrene, 4-methyl styrene, 2-ethyl styrene, 3-ethyl styrene, 4-ethyl styrene, and the like. Examples include alkyl-substituted styrene having an alkyl chain, halogen-substituted styrene such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene, and fluorine-substituted styrene such as 4-fluorostyrene and 2,5-difluorostyrene. Styrene is preferred as the styrene monomer.

  Examples of the (meth) acrylate monomer include n-methyl (meth) acrylate, n-ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, ( N-pentyl (meth) acrylate, n-hexyl (meth) acrylate, n-heptyl (meth) acrylate, n-octyl (meth) acrylate, n-decyl (meth) acrylate, n (meth) acrylate -Dodecyl, n-lauryl (meth) acrylate, n-tetradecyl (meth) acrylate, n-hexadecyl (meth) acrylate, n-octadecyl (meth) acrylate, isopropyl (meth) acrylate, (meth) acryl Isobutyl acid, t-butyl (meth) acrylate, isopentyl (meth) acrylate, amyl (meth) acrylate, (meth) acrylic acid Pentyl, isohexyl (meth) acrylate, isoheptyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, phenyl (meth) acrylate, biphenyl (meth) acrylate, (meth) acryl Diphenylethyl acid, t-butylphenyl (meth) acrylate, terphenyl (meth) acrylate, cyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, (meth ) Diethylaminoethyl acrylate, methoxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylic acid-β-carboxyethyl, (meth) acrylonitrile, (meth) acrylamide and the like. As the (meth) acrylic acid ester monomer, n-butyl acrylate is preferable.

  When the styrene resin, the (meth) acrylic resin and the styrene- (meth) acrylic copolymer resin contain a carboxyl group, it can be obtained by copolymerizing a polymerizable monomer having a carboxyl group. .

  Specific examples of such a carboxyl group-containing polymerizable monomer include acrylic acid, aconitic acid, atropic acid, allylmalonic acid, angelic acid, isocrotonic acid, itaconic acid, 10-undecenoic acid, elaidic acid, erucic acid, olein. Acid, ortho-carboxycinnamic acid, crotonic acid, chloroacrylic acid, chloroisocrotonic acid, chlorocrotonic acid, chlorofumaric acid, chloromaleic acid, cinnamic acid, cyclohexenedicarboxylic acid, citraconic acid, hydroxycinnamic acid, dihydroxysilicic acid Cinnamic acid, tiglic acid, nitrocinnamic acid, vinyl acetic acid, phenyl cinnamic acid, 4-phenyl-3-butenoic acid, ferulic acid, fumaric acid, brassic acid, 2- (2-furyl) acrylic acid, bromocinnamic acid, Bromofumaric acid, bromomaleic acid, benzylidene malonic acid, benzo Acrylic acid, 4-pentenoic acid, maleic acid, mesaconic acid, methacrylic acid, methylcinnamic acid, methoxycinnamic acid, etc., and acrylic acid, methacrylic acid, maleic acid, cinnamic acid due to the ease of polymer formation reaction, etc. , Fumaric acid and the like are preferable, and acrylic acid is more preferable.

  The binder resin used for the toner particles in the toner set of the present invention can use a chain transfer agent during the polymerization. Although there is no restriction | limiting in particular as a chain transfer agent, The compound which has a thiol component can be used. Specifically, alkyl mercaptans such as hexyl mercaptan, heptyl mercaptan, octyl mercaptan, nonyl mercaptan, decyl mercaptan, and dodecyl mercaptan are preferred, and in particular, the molecular weight distribution is narrow, so that the storage stability of the toner at high temperature is improved. preferable.

  Among the binder resins used for the toner particles in the toner set of the present invention, those that can be produced by radical polymerization of a polymerizable monomer can be polymerized using a radical polymerization initiator.

  There is no restriction | limiting in particular as an initiator for radical polymerization used here. Specifically, hydrogen peroxide, acetyl peroxide, cumyl peroxide, tert-butyl peroxide, propionyl peroxide, benzoyl peroxide, chlorobenzoyl peroxide, dichlorobenzoyl peroxide, bromomethylbenzoyl peroxide, lauroyl peroxide Ammonium persulfate, sodium persulfate, potassium persulfate, diisopropyl peroxycarbonate, tetralin hydroperoxide, 1-phenyl-2-methylpropyl-1-hydroperoxide, tert-butyl hydroperoxide pertriphenyl acetate, tert-butyl formate, Peroxides such as tert-butyl peracetate, tert-butyl perbenzoate, tert-butyl perphenylacetate, tert-butyl permethoxyacetate, tert-butyl perN- (3-toluyl) carbamate, 2,2 '-Azobisp Bread, 2,2′-dichloro-2,2′-azobispropane, 1,1′-azo (methylethyl) diacetate, 2,2′-azobis (2-amidinopropane) hydrochloride, 2,2 ′ -Azobis (2-amidinopropane) nitrate, 2,2'-azobisisobutane, 2,2'-azobisisobutyramide, 2,2'-azobisisobutyronitrile, 2,2'-azobis-2- Methyl methylpropionate, 2,2′-dichloro-2,2′-azobisbutane, 2,2′-azobis-2-methylbutyronitrile, dimethyl 2,2′-azobisisobutyrate, 1,1′-azobis (1 -Sodium methylbutyronitrile-3-sulfonate), 2- (4-methylphenylazo) -2-methylmalonodinitrile, 4,4'-azobis-4-cyanovaleric acid, 3,5-dihy Roxymethylphenylazo-2-methylmalonodinitrile, 2- (4-bromophenylazo) -2-allylmalonodinitrile, 2,2′-azobis-2-methylvaleronitrile, 4,4′-azobis-4 -Dimethyl cyanovalerate, 2,2'-azobis-2,4-dimethylvaleronitrile, 1,1'-azobiscyclohexanenitrile, 2,2'-azobis-2-propylbutyronitrile, 1,1'- Azobis-1-chlorophenylethane, 1,1′-azobis-1-cyclohexanecarbonitrile, 1,1′-azobis-1-cycloheptanenitrile, 1,1′-azobis-1-phenylethane, 1,1 ′ -Azobiscumene, 4-nitrophenylazobenzyl cyanoacetate ethyl, phenylazodiphenylmethane, phenylazotriphenylmeth Tan, 4-nitrophenylazotriphenylmethane, 1,1′-azobis-1,2-diphenylethane, poly (bisphenol A-4,4′-azobis-4-cyanopentanoate), poly (tetraethylene glycol) -2,2'-azobisisobutyrate) and the like, 1,4-bis (pentaethylene) -2-tetrazene, 1,4-dimethoxycarbonyl-1,4-diphenyl-2-tetrazene and the like Can be mentioned.

  The glass transition temperature of the copolymer is preferably 50 to 70 ° C.

  The toner particles in the toner set of the present invention may contain a release material for adjusting fixability, a charge control agent for adjusting charge, or the like as an internal additive to be contained and dispersed in the toner. Good.

<Lubricant>
Known release materials can be used, such as paraffin wax and derivatives thereof, montan wax and derivatives thereof, microcrystalline wax and derivatives thereof, Fischer-Tropsch wax and derivatives thereof, polyolefin wax and derivatives thereof, and the like. is there. This derivative includes an oxide, a polymer with a vinyl monomer, and a graft modified product. In addition, alcohols, fatty acids, plant waxes, animal waxes, mineral waxes, ester waxes, acid amides and the like can be mentioned, but the invention is not limited thereto.

<Charge control agent>
Known charge control agents can be used, but azo metal complex compounds, metal complex compounds of salicylic acid, and resin type charge control agents containing polar groups can be used. When the toner is manufactured by a wet manufacturing method, it is preferable to use a material that is difficult to dissolve in water in terms of controlling ionic strength and reducing wastewater contamination. The toner in the present invention may be either a magnetic toner containing a magnetic material or a non-magnetic toner containing no magnetic material.

<Colorant>
In the toner set of the present invention, the color toner particles used for visible image formation may be known ones of desired colors such as black, yellow, magenta, cyan and red, blue, green, Because it is premised on the combined use with an invisible toner containing a near-infrared light absorbing material, color toner particles having an absorption rate in the near-infrared light region (near-infrared light absorption rate) of 5% or less should be used. However, it is preferable from the viewpoint of ensuring reading accuracy of invisible information.

  When the near-infrared light absorption rate of the visible toner is 5% or more, an image forming surface on which an invisible image and a color image (hereinafter referred to as a visualized image) are formed on the image output medium surface is red. When machine reading is performed by external light irradiation, a visible image may be mistaken as an invisible image. In particular, in the case of machine reading without specifying the area where the invisible image is formed on the image forming surface, or when the invisible image is formed between the visible image and the image output medium surface, information on the invisible image is used. It may be difficult to read only the data and decode correctly.

  The near-infrared light absorptance of the visible toner is determined by using the spectral reflectance measuring device as in the case of the invisible toner described above, and the spectral reflectance in the near-infrared region of the visible image formed with the visible toner is expressed as VT. (I) By measuring the spectral reflectance of the image output medium as M (i), it is obtained as shown in the following equation (7).

  Formula (7): Near-infrared light absorption rate of visible toner = VT (i) −M (i)

  Colorants used to obtain the visible toner as described above include aniline blue, calcoyl blue, chrome yellow, ultramarine blue, duPont oil red, quinoline yellow, methylene blue chloride, malachite green oxalate, lamp black, and rose bengal. , C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 12, C.I. I. Pigment blue 15: 1, C.I. I. Pigment Blue 15: 3 can be exemplified as a representative example.

  Moreover, dye can also be used as needed. Examples of the dye include various dyes such as basic, acidic, dispersion, and direct dyes, such as nigrosine, methylene blue, rose bengal, quinoline yellow, and ultramarine blue, and these can be used alone or in a mixed state. .

  In order to improve the reading accuracy of invisible images, the near infrared light absorption rate of the invisible toner that forms the invisible image should be 15% or more higher than the near infrared light absorption rate of the visible toner that forms the visible image. Is preferable, and it is more preferably 30% or more.

  If the difference between the near-infrared light absorption rate of the invisible image and the visible image is less than 15%, the absorption between the near-infrared absorption rate of the invisible image and the near-infrared absorption rate of the visible image In the rate range, it is difficult to recognize and read only the invisible image by performing binarization processing with a certain contrast (threshold) as a boundary in order to identify and read whether or not the image is invisible when machine reading. There is a case. That is, in such a case, the visible image may become an obstacle when reading the invisible image and further correctly decoding information recorded in the invisible image.

  The difference between the near-infrared light absorption rate of such an invisible toner that forms an invisible image and the near-infrared light absorption rate of the visible toner that forms a visible image (hereinafter simply referred to as “near-infrared light absorption”). The “spectrum difference” may be abbreviated as “spectral reflectance”. The spectral reflectance IP (i) of the invisible image (solid image) formed on the surface of the image output medium and the surface of the image output medium are formed using a spectral reflectance measuring machine. By measuring the spectral reflectance VP (i) of the obtained visible image (solid image), it is obtained as shown in the following equation (8).

  Formula (8): Near-infrared light absorptivity difference = IP (i) −VP (i)

<External additive>
Furthermore, in order to further improve the long-term storability, fluidity, developability, and transferability of the invisible toner, an inorganic powder or a resin powder may be used as an additive.

<Manufacture of toner particles>
As a method of adding the internal additive to the inside of the invisible toner particles, a known method can be used, and a hot melt kneading process is particularly preferably used. The kneading at this time can be performed using various heating kneaders. Examples of the heat kneader include a three roll type, a single screw type, a twin screw type, and a Banbury mixer type.

  In addition, the production method of the invisible toner particles is not particularly limited, and a known method can be used. However, when the kneaded product is pulverized, for example, a micronizer, Ulmax, JET-O can be used. -It can be carried out by means of a mizer, KTM (krypton), turbome jet or the like. Furthermore, as a subsequent process, using a hybridization system (manufactured by Nara Machinery Co., Ltd.), a mechano-fusion system (manufactured by Hosokawa Micron Corporation), a kryptron system (manufactured by Kawasaki Heavy Industries, Ltd.), etc. The toner shape can be changed. In addition, spheronization with hot air can also be mentioned. Further, classification processing may be performed to adjust the toner particle size distribution. The volume average particle size of the invisible toner is preferably in the range of 3 μm to 12 μm, and more preferably in the range of 5 μm to 10 μm. When the volume average particle diameter is smaller than 3 μm, the electrostatic adhesion force becomes larger than gravity, and it may be difficult to handle as a powder. On the other hand, if the volume average particle size is larger than 12 μm, it may be difficult to record high-definition invisible information. If each toner described above is obtained, a method of polymerizing the monomer by emulsion polymerization, suspension polymerization or the like, a resin polymerized by solution polymerization, suspension polymerization, bulk polymerization or the like is dissolved in an organic solvent, and then a dispersant is added. It is also possible to use a solution suspension method in which it is dispersed in water, a method of granulating by spray drying or the like.

<Electrophotographic developer>
The electrophotographic developer of the present invention is an electrophotographic developer comprising a carrier and an electrophotographic toner set, and the electrophotographic toner set is the electrophotographic toner set of the present invention. Is preferred. The electrophotographic developer of the present invention can be obtained by mixing the carrier and the electrophotographic toner of the present invention by a known method. The electrophotographic developer of the present invention is preferably a two-component developer obtained by mixing the toner for electrophotography with a non-magnetic toner and a carrier having magnetism.

  The invisible toner concentration (TC: Toner Concentration) in the developer is preferably in the range of 3% by mass to 15% by mass, and more preferably in the range of 5% by mass to 12% by mass. The invisible toner density (TC) is expressed by the following formula (9).

  Formula (9): TC (wt%) = [mass of invisible toner contained in developer (g) / total mass of developer (g)] × 100

<Image forming method>
(Specific examples of invisible images)
Next, the image configuration of the invisible image formed by the image forming method of the present invention, the visual recognition of the invisible image, the machine reading of the invisible image, and the like will be specifically described. The invisible image is formed using the electrophotographic toner of the present invention, and is not particularly limited as long as it is machine-readable by irradiation with near infrared light, but is not limited to letters, numbers, symbols, patterns, pictures. Of course, the image may be a two-dimensional pattern such as a known barcode called JAN, standard ITF, Code 128, Code 39, NW-7, or the like.

  When the invisible image is composed of a two-dimensional pattern such as a barcode, the serial number for identifying the image forming apparatus that has formed the image on the image output medium, or the visible image formed on the surface of the image output medium together with the invisible image. It can be used as a copyright certification number for images. Moreover, when the visible image formed with an invisible image takes the form of a confidential document, securities, a license, a personal ID card, etc., it can also be used effectively to detect the identification of these counterfeits.

  In addition to the above barcode examples, in the present invention, the two-dimensional pattern is not particularly limited as long as it is a known recording method conventionally used as a visible and recognizable image. For example, as a method of forming a two-dimensional pattern in which minute area cells are geometrically arranged, a two-dimensional barcode called a QR code can be cited. In addition, as a method of forming a two-dimensional pattern in which minute line bitmaps are geometrically arranged, a code forming method using a plurality of patterns with different rotation angles, which is a technique described in Japanese Patent Laid-Open No. Hei 4-233683 Is mentioned.

  By forming such an invisible image consisting of a two-dimensional pattern on the surface of the image output medium, it is possible to embed large-capacity information, for example, music information, electronic files of text application software, etc. in an image that cannot be visually understood. This makes it possible to provide a technique for creating a harder confidential document or a digital / analog information sharing document.

  FIG. 1 shows a normal image (when viewed with eyes) of an invisible image forming portion formed of a two-dimensional pattern formed by the image forming method of the present invention, an enlarged view when recognized by infrared light irradiation, and It is a schematic diagram which shows an example at the time of seeing this enlarged view as a bit information image after carrying out decoding conversion to digital information by machine reading. The figure shown on the left side of FIG. 1 shows a case where the surface of the image output medium 12 is viewed with eyes, and an invisible image 11 is formed on the surface of the image output medium 12. In the figure, the invisible image 11 is not actually visible but is shown in halftone for convenience.

  1 is an enlarged portion 13 in which a microscopic region of the invisible image 11 is enlarged when the invisible image 11 is recognized by machine reading by infrared light irradiation. The two-dimensional pattern shown in the enlarged portion 13 shows an example in the case of being formed by a plurality of minute line bitmaps having different rotation angles. Specifically, two kinds of minute patterns having mutually different inclinations are shown. Line units 14 are arranged, one of which represents bit information “0” and the other “1”. A two-dimensional pattern composed of a plurality of minute line bitmaps having different rotation angles is preferably used because noise applied to a visible image is extremely low and a large amount of information can be digitized and embedded with high density. The fine line unit 14 is preferably 3 to 10 dots, more preferably 4 to 7 dots, and one unit is formed. If one unit is smaller than 3 dots, machine reading errors increase, and if it exceeds 10 dots, noise appears in the visible image, which is not preferable.

  The figure shown on the right side of FIG. 1 shows an enlarged portion 13 in which minute line units 14 are arranged as a bit information image 15 after being decoded and converted into digital information by machine reading. In this way, the invisible image is read as a two-dimensional pattern as shown in the enlarged portion 13 by a reading device such as a CCD, and this is decoded and converted into the bit information image 15 as digital information, and further recorded at the time of encoding. It is decoded into audio information, texts, image files, application software electronic files, etc. in a format-compatible manner.

  On the other hand, as technology that has been used for anti-counterfeiting technology, a method that uses cherry paper (a special paper on which characters such as “prohibited copying” appear when optically scanned by a copying machine) is used as an image output medium, or a comparison There is a method of superimposing and recording watermark characters in a pale color, but all of them impair the quality of a visible image composed of a document, a pattern, a picture, etc. formed on the surface of the image output medium. However, when the invisible image formed on the image output medium surface by the image forming method of the present invention is glossy, the invisible image is not visible when viewed from a specific angle with respect to the image output medium surface. When it can be recognized macroscopically and viewed from a different angle, the invisible image can be made unrecognizable, so that the quality of the visible image formed together with the invisible image is not impaired.

  Such an example will be described below.

  FIG. 2 shows a case where a recorded matter in which a visible image is formed together with an invisible image on the surface of the image output medium by the image forming method of the present invention is actually viewed from a substantially vertical direction (front side) of the paper surface of the recorded matter. FIG. 3 is an example schematically showing an image that can be recognized, and FIG. 3 shows the recorded product shown in FIG. 2 from the position (diagonal) shifted from the vertical direction of the paper surface of the recorded product by the image forming method of the present invention. It is an example which showed typically the image which can be actually recognized when it looks visually.

  2 and 3, on the surface of the recorded material 21, an invisible image 22 made up of a pattern (character) called “Confidential” together with a visible image made up of characters, graphs, etc. is placed between the surface of the image output medium and the visible image. Is formed. However, FIG. 2 shows that the invisible image 22 (not shown in FIG. 2) cannot be recognized because it is viewed from a direction substantially perpendicular (front) to the paper surface of the recorded matter 21. On the other hand, in FIG. 3, since the visual observation is made from a position (oblique) shifted from the vertical direction with respect to the paper surface of the recorded matter 21, the gloss difference between the region formed as an invisible image and the other region is remarkable. Therefore, the pattern (character) “Confidential” of the invisible image 22 can be recognized together with the visible image.

  In the example shown in FIG. 2 and FIG. 3, the invisible image 22 can be macroscopically recognized as characters by visual observation, but is not necessarily limited to characters in order to exert a restraining effect against forgery and copying. Is not to be done. Further, since the microscopic region of the invisible image 22 is configured by a machine-readable pattern such as the minute line unit 14 shown in FIG. 1, forgery is more difficult and accurate real recognition is possible. The recorded material 21 can also be used. The invisible image 22 shown in FIG. 3 is actually recognized by glossiness, but for the convenience of explanation, the recorded matter formed by the image forming method of the present invention is presented and explained directly. Therefore, it is drawn as a black pattern (character) having no gloss.

  On the other hand, the visible image formed together with the invisible image by the image forming method of the present invention may be any image, and the image forming method may be any known image forming method including electrophotography. Although it may be used, it is preferable that the near-infrared light absorption rate of the visible image is 5% or less in order to read the invisible image with high accuracy when machine-reading. Further, the image output medium used in the image forming method of the present invention is not particularly limited as long as it can form an image using the electrophotographic toner of the present invention, but is not directly visible on the surface of the image output medium. When images are formed, those that do not absorb near-infrared wavelengths are preferred, and when the invisible toner is made by adding a white pigment such as titania particles, white or high whiteness is used. Is preferred.

  As described above, the invisible image composed of the two-dimensional pattern formed on the surface of the image output medium by the image forming method of the present invention cannot be seen with a wavelength of 700 nm or more, that is, the near-infrared light region. In this case, reading can be performed by a specific means. As specific reading means, for example, an image sensor having sensitivity to infrared light can be read while irradiating the recording paper with illumination having an infrared light component.

  The invisible image composed of the above two-dimensional pattern is superior in confidentiality and high accuracy by adopting a known recording format such as, for example, a specific recording format and adding an encryption key and reading error correction (parity). / Pattern (encode) high-density information, such as copyright, real recognition code, data link address, digital image information registration, etc., and optically read / combine (decode) in the near-infrared region as necessary be able to.

(Specific Example of Image Forming Method of the Present Invention Using Image Forming Apparatus)
Hereinafter, an image forming method according to an embodiment of the present invention will be described in detail with reference to the drawings using an image forming apparatus. In the following description, as an example of an image forming apparatus, an image forming apparatus that forms an invisible image by an electrophotographic method and an image forming apparatus that forms a visible image together with the invisible image will be described as examples. However, the present invention is not limited to these examples.

  FIG. 4 is a schematic diagram showing a configuration example of an image forming apparatus for forming an invisible image by the image forming method of the present invention. The illustrated image forming apparatus 100 includes image forming means including an image carrier 101, a charger 102, an image writing device 103, a developing device 104, a transfer roll 105, a cleaning blade 106, and the like.

  The image carrier 101 is formed in a drum shape as a whole, and has a photosensitive layer on its outer peripheral surface (drum surface). The image carrier 101 is provided to be rotatable in the direction of arrow A. The charger 102 charges the image carrier 101 uniformly. The image writing device 103 forms an electrostatic latent image by irradiating image light onto the image carrier 101 uniformly charged by the charger 102.

  The developing device 104 stores invisible toner, supplies the invisible toner to the surface of the image carrier 101 on which the electrostatic latent image is formed by the image writing device 103, performs development, and develops a toner image on the surface of the image carrier 101. Form. The transfer roll 105 holds the recording sheet (image output medium) conveyed in the direction of arrow B by a sheet conveying unit (not shown) between the image carrier 101 and the toner image formed on the surface of the image carrier 101. Is transferred to a recording sheet. The cleaning blade 106 is for cleaning (removing) the electrophotographic toner remaining on the surface of the image carrier 101 after the transfer.

  Next, formation of an invisible image by the image forming apparatus 100 will be described. First, the image carrier 101 is driven to rotate, and the surface of the image carrier 101 is uniformly charged by the charger 102. Then, the charged surface is irradiated with image light from the image writing device 103, and electrostatically charged. A latent image is formed. Thereafter, a toner image is formed on the surface of the image carrier 101 on which the electrostatic latent image is formed by the developing device 104, and then the toner image is transferred to the surface of the recording paper by the transfer roll 105. At this time, the toner remaining on the surface of the image carrier 101 without being transferred to the recording paper is cleaned by the cleaning blade 106. In this way, an invisible image representing additional information or the like to be visually hidden is formed on the surface of the recording paper.

  The image forming apparatus 100 further records a visible image such as letters, numbers, symbols, patterns, pictures, and photographic images on the surface on which the invisible image is formed on the surface of the recording paper using another image forming apparatus. Also good. As a method for recording the visible image, not only general printing methods such as offset printing, letterpress printing, and intaglio printing, but also known image forming techniques such as thermal transfer recording, ink jet method, and electrophotographic method can be arbitrarily selected.

  Here, when the electrophotographic method is used for forming the visible image, a technique excellent in productivity and confidentiality management can be provided by consistently performing invisible / visible image formation. As an image forming flow in this case, for example, a developer composed of only invisible toner, only yellow toner, only magenta toner, and only cyan toner is included in the developer 104 of the image forming apparatus 100. It is possible to use a method generally called a tandem method in which an accommodated image forming apparatus is provided and sequentially recorded on an image output medium.

  Thus, after forming an invisible image on the surface of the recording paper using the image forming apparatus shown in FIG. 4, a visible image is further formed on the surface of the recording paper. It can be formed in a form embedded between.

  In FIG. 4, when the toner image is transferred onto the surface of the recording paper (an example of the image output medium) by the transfer roll 105, the toner image is heated and fixed in a temperature range of 140 ° C. to 210 ° C., preferably 160 ° C. to 200 ° C. It is desirable.

  FIG. 5 is a schematic diagram showing a configuration example of an image forming apparatus for simultaneously forming a visible image together with an invisible image by the image forming method of the present invention. The illustrated image forming apparatus 200 includes an image carrier 201, a charger 202, an image writing device 203, a rotary developing device 204, a primary transfer roll 205, a cleaning blade 206, an intermediate transfer member 207, and a plurality (three in the drawing). Rolls 208, 209, and 210, a secondary transfer roll 211, and the like are provided.

  The image carrier 201 is formed in a drum shape as a whole, and has a photosensitive layer on its outer peripheral surface (drum surface). The image carrier 201 is rotatably provided in the direction of arrow C in FIG. The charger 202 charges the image carrier 201 uniformly. The image writing device 203 forms an electrostatic latent image by irradiating the image carrier 201 uniformly charged by the charger 202 with image light.

  The rotary developing device 204 includes five developing devices 204Y, 204M, 204C, 204K, and 204F that respectively accommodate yellow, magenta, cyan, black, and invisible toners. In this apparatus, since toner is used as a developer for image formation, yellow toner is used for the developing device 204Y, magenta toner is used for the developing device 204M, cyan toner is used for the developing device 204C, and cyan toner is used for the developing device 4K. The black toner and the invisible toner are accommodated in the developing device 204F, respectively. The rotary developing device 204 is driven to rotate so that the five developing devices 204Y, 204M, 204C, 204K, and 204F sequentially approach and face the image carrier 201, and thereby electrostatic latent images corresponding to the respective colors. The toner is transferred to the surface to form a visible toner image and an invisible toner image.

  Here, the developing devices other than the developing device 204F in the rotary developing device 204 may be partially removed according to the required visible image. For example, a rotary developing device including four developing devices such as the developing device 204Y, the developing device 204M, the developing device 204C, and the developing device 204F may be used. Further, a developing device for forming a visible image may be used after being converted to a developing device containing a developer of a desired color such as red, blue, or green.

  The primary transfer roll 205 sandwiches the intermediate transfer member 207 with the image carrier 201 and transfers the toner image (visible toner image or invisible toner image) formed on the surface of the image carrier 201 to an endless belt-like intermediate transfer. Transfer (primary transfer) is performed on the outer peripheral surface of the body 207. The cleaning blade 206 is for cleaning (removing) the toner remaining on the surface of the image carrier 201 after the transfer. The intermediate transfer member 207 has its inner peripheral surface stretched by a plurality of support rolls 208, 209, and 210, and is supported so as to be able to rotate in the direction of arrow D and in the opposite direction. The secondary transfer roll 211 is a toner transferred to the outer peripheral surface of the intermediate transfer member 207 while sandwiching a recording sheet (image output medium) conveyed in the direction of arrow E by a sheet conveying unit (not shown) with the support roll 210. The image is transferred to a recording sheet (secondary transfer).

  The image forming apparatus 200 sequentially forms a toner image on the surface of the image carrier 201 and transfers it on the outer peripheral surface of the intermediate transfer member 207, and operates as follows. That is, first, after the image carrier 201 is rotationally driven and the surface of the image carrier 201 is uniformly charged by the charger 202, the image carrier 201 is irradiated with image light from the image writing device 203 to statically. An electrostatic latent image is formed. The electrostatic latent image is developed by the yellow developing device 204Y, and then the toner image is transferred to the outer peripheral surface of the intermediate transfer member 207 by the primary transfer roll 205. At this time, the yellow toner remaining on the surface of the image carrier 201 without being transferred to the recording paper is cleaned by the cleaning blade 206. Further, the intermediate transfer member 207 on which the yellow toner image is formed on the outer peripheral surface temporarily moves in the direction opposite to the arrow D direction while holding the yellow toner image on the outer peripheral surface, and then moves to the next magenta. A color toner image is provided at a position where the toner image is laminated and transferred onto the yellow toner image.

  Thereafter, with respect to each color of magenta, cyan, and black, similarly to the above, charging by the charger 202, irradiation of image light by the image writing device 203, formation of toner images by the developing devices 204M, 204C, and 204K, outer periphery of the intermediate transfer member 207 The transfer of the toner image to the surface is sequentially repeated.

  When the transfer of the four color toner images to the outer peripheral surface of the intermediate transfer member 207 is completed in this manner, the surface of the image carrier 201 is then uniformly charged by the charger 202 again, and then from the image writing device 203. Irradiation with image light forms an electrostatic latent image. This electrostatic latent image is developed by an invisible developing device 204F, and then the toner image is transferred to the outer peripheral surface of the intermediate transfer member 207 by the primary transfer roll 205. As a result, both the full color image (visible toner image) and the invisible toner image in which the four color toner images are superimposed are formed on the outer peripheral surface of the intermediate transfer member 207. The full color visible toner image and invisible toner image are collectively transferred to the recording paper by the secondary transfer roll 211. Thereby, a recording image in which a full-color visible image and an invisible image are mixed is obtained on the image forming surface of the recording paper. Further, in the image forming method of the present invention using the image forming apparatus 200, in the region where the visible image on the image forming surface overlaps the invisible image, the invisible image includes the visible image forming layer, the recording paper surface, , Formed between.

  In FIG. 5, after the toner image is transferred onto the surface of the recording paper (an example of an image output medium) by the secondary transfer roll 211, it is heated and fixed in a temperature range of 140 ° C. to 210 ° C., preferably 160 ° C. to 200 ° C. It is desirable to make it.

  In the image forming method of the present invention using the image forming apparatus 200 shown in FIG. 5, in addition to the same effects as the image forming method of the present invention using the image forming apparatus 100 shown in FIG. It is possible to simultaneously perform the formation of the visible image and the embedding of the additional information by forming the invisible image.

  Further, by forming an invisible image between the full-color visible image and the recording paper surface, the invisible image is always in contact with the recording paper surface. Thereby, the gloss difference due to the presence / absence of the invisible image described above can be detected visually, and for example, a counterfeit deterrent effect or the like can be imparted to a confidential document or the like.

  Further, by making the resolution of the invisible image different from the resolution of the visible image at the time of image formation, for example, the frequency component corresponding to the resolution of the visible image is cut as data processing after reading the invisible image. By performing the filtering process, it is possible to efficiently separate the signal (data) resulting from the invisible image and the noise signal resulting from the visible image, and to easily read the invisible image. Incidentally, the resolution at the time of image formation can be adjusted by controlling the writing frequency of the electrostatic latent image by the image writing device 203.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the following description, “part” means “part by mass” unless otherwise specified.

<Particle size measurement method>
The particle size measurement in the present invention will be described. When the particles to be measured in the present invention are 2 μm or more, a Coulter counter TA-II type (manufactured by Beckman-Coulter) was used as the measuring apparatus, and ISOTON-II (manufactured by Beckman-Coulter) was used as the electrolyte.

As a measuring method, 0.5 to 50 mg of a measurement sample is added to 2 ml of a 5% aqueous solution of a surfactant, preferably sodium alkylbenzenesulfonate as a dispersant. This was added to 100 to 150 ml of the electrolytic solution.

  The electrolyte solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 minute, and the particle size distribution of particles of 2 to 60 μm is measured using the Coulter counter TA-II type with an aperture diameter of 100 μm. Volume average distribution and number average distribution were determined. The number of particles to be measured was 50,000.

<Method for measuring molecular weight of binder resin>
In the binder resin used in the electrostatic charge developing toner set of the present invention, the molecular measurement was performed under the following conditions. GPC uses “HLC-8120GPC, SC-8020 (manufactured by Tosoh Corporation)” apparatus, and column uses “TSKgel, SuperHM-H (6.0 mm ID × 15 cm, manufactured by Tosoh Corporation)”. THF (tetrahydrofuran) was used as an eluent. As experimental conditions, the sample concentration was 0.5%, and the flow rate was 0.6 ml / min. The experiment was conducted using a sample injection amount of 10 μl, a measurement temperature of 40 ° C., and an IR detector. The calibration curve is “polystylen standard sample TSK standard” manufactured by Tosoh Corporation: “A-500”, “F-1”, “F-10”, “F-80”, “F-380”, “A-2500”. ”,“ F-4 ”,“ F-40 ”,“ F-128 ”, and“ F-700 ”.

<Near-infrared light absorbing material used for production of invisible toner>
The near infrared light absorbing material used for the production of the invisible toner was selected from the following three types.
Near-infrared light absorbing material (1) Naphthalocyanine-based compound described in formula (3) in the text Near-infrared light-absorbing material (2) Aminium-based compound described in formula (5) Near-infrared light absorption Material (3) Glass comprising CuO: 38.1 parts by weight, Al ₂ O ₃ : 5 parts by weight, P ₂ O ₃ : 53.5 parts by weight, K ₂ O: 3.6 parts by weight is crystallized by heat treatment, Copper phosphate crystallized glass mechanically pulverized until the particle size is about several μm

<Adjustment of binder resin for invisible toner particles>
(Binder resin I1)
370 parts of styrene, 30 parts of n-butyl acrylate, 8 parts of acrylic acid, 4 parts of carbon tetrabromide and 24 parts of dodecanethiol are mixed and dissolved in a nonionic surfactant (Nonipol 400: manufactured by Sanyo Chemical Co., Ltd.) And anionic surfactant (Neogen SC: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) in 550 parts of ion-exchanged water was dispersed and emulsified in a flask, and slowly stirred and mixed for 10 minutes. 50 parts of ion-exchanged water in which was dissolved was added. Next, emulsion polymerization was performed at a temperature of 70 ° C. in a nitrogen atmosphere. The weight average molecular weight of the obtained styrene-acrylic resin was 48,000.

(Binder resin I2)
A styrene-acrylic resin having a weight average molecular weight of 36,000 was obtained using the same formulation as the binder resin I1.

(Binder resin I3)
A styrene-acrylic resin having a weight average molecular weight of 62,000 was obtained using the same formulation as the binder resin I1.

(Binder resin I4)
A styrene-acrylic resin having a weight average molecular weight of 28,000 was obtained using the same formulation as the binder resin I1.

(Binder resin I5)
A styrene-acrylic resin having a weight average molecular weight of 68,000 was obtained using the same formulation as the binder resin I1.

(Binder resin I6)
A styrene-acrylic resin having a weight average molecular weight of 24,000 was obtained using the same formulation as the binder resin I1.

(Binder resin I7)
A styrene-acrylic resin having a weight average molecular weight of 72,000 was obtained using the same formulation as the binder resin I1.

<Manufacture of invisible toner particles and developer>
The invisible toner in the examples was obtained by the following method.

(Invisible toner particles 1 and invisible image forming developer 1)
Binder resin (I1) 55 parts Near-infrared light absorbing material (1) 40 parts Release agent (long-chain straight-chain fatty acid long-chain straight-chain saturated alcohol; stearyl bebenate) 5 parts After kneading and pulverizing with a ruder, fine particles and coarse particles were classified by an air classifier, and particles having a volume average particle size (average particle size D50) of 8.6 μm were obtained.

  Next, as an external additive, 1.5 parts by mass of silica particles (volume average particle size of 40 nm) are externally added to 100 parts by mass of the previously obtained particles using a Henschel mixer, so that invisible toner particles ( 1) was obtained.

  100 parts of carrier particles, in which 8 parts of the invisible toner particles and 100 parts of Mn-Mg ferrite particles are coated with 10 parts of a styrene / butyl methacrylate copolymer having a copolymerization ratio of 25/75, are mixed with a V-type blender. Invisible image forming developer (1) was obtained.

(Invisible toner particles 2 and invisible image forming developer 2)
8.3 μm invisible toner particles 2 and invisible image forming developer 2 were obtained in the same manner as invisible toner particles 1 and invisible image forming developer 1 except that binder resin (I2) was used.

(Invisible toner particles 3 and invisible image forming developer 3)
8.7 μm invisible toner particles 3 and invisible image forming developer 3 were obtained in the same manner as invisible toner particles 1 and invisible image forming developer 1 except that binder resin (I3) was used.

(Invisible toner particles 4 and invisible image forming developer 4)
8.2 μm invisible toner particles 4 and invisible image forming developer 4 were obtained in the same manner as invisible toner particles 1 and invisible image forming developer 1 except that binder resin (I4) was used.

(Invisible toner particles 5 and invisible image forming developer 5)
8.9 μm invisible toner particles 5 and invisible image forming developer 5 were obtained in the same manner as invisible toner particles 1 and invisible image forming developer 1 except that binder resin (I5) was used.

(Invisible toner particles 6 and invisible image forming developer 6)
8.1 μm invisible toner particles 6 and invisible image forming developer 6 were obtained in the same manner as invisible toner particles 1 and invisible image forming developer 1 except that binder resin (I6) was used.

(Invisible toner particles 7 and invisible image forming developer 7)
8.9 μm invisible toner particles 7 and invisible image forming developer 7 were obtained in the same manner as invisible toner particles 1 and invisible image forming developer 1 except that binder resin (I7) was used.

(Invisible toner particles 8 and invisible image forming developer 8)
8.6 μm invisible toner particles 8 and invisible image forming developer 8 were obtained in the same manner as invisible toner particles 1 and invisible image forming developer 1 except that the near infrared light absorbing material (2) was used. .

(Invisible toner particles 9 and invisible image forming developer 9)
8.6 μm invisible toner particles 9 and invisible image forming developer 9 were obtained in the same manner as invisible toner particles 1 and invisible image forming developer 1 except that the near infrared light absorbing material (3) was used. .

<Adjustment of binder resin for color toner particles>
(Binder resin C1)
101 parts of isophthalic acid, 180 parts of a 2 mol adduct of bisphenol A propylene oxide and 5.4 parts of dibutyltin oxide were put into a flask, and a dehydration condensation reaction was performed at 230 ° C. in a nitrogen atmosphere. The weight average molecular weight of the obtained polyester resin was 16,000.

(Binder resin C2)
A polyester resin having a weight average molecular weight of 21,000 was obtained using the same formulation as C1.

(Binder resin C3)
A polyester resin having a weight average molecular weight of 12,000 was obtained using the same formulation as C1.

(Binder resin C4)
A polyester resin having a weight average molecular weight of 8,000 was obtained using the same formulation as C1.

(Binder resin C5)
A polyester resin having a weight average molecular weight of 24,000 was obtained using the same formulation as C1.

<Manufacture of color toner particles and developer>
(Magenta toner particles 1 and magenta developer 1)
Binder resin (C1) 65 parts C.I. I. Pigment Red 57: 1 30 parts release agent (long chain linear fatty acid long chain linear saturated alcohol; stearyl bebenate) 5 parts Except for using the above materials (invisible toner particles 1 and invisible image forming developer 1 ) To obtain 8.3 μm magenta toner particles 1 and a magenta developer 1.

(Cyan toner particles 1 and cyan developer 1)
As a pigment, C.I. I. 8.4 μm cyan toner particles 1 and cyan developer 1 were obtained in the same manner as magenta toner particles 1 and magenta developer 1 except that CI Pigment Blue 15: 3 was used.

(Yellow toner particles 1 and yellow developer 1)
As a pigment, C.I. I. 8.3 μm yellow toner particles 1 and yellow developer 1 were obtained in the same manner as magenta toner particles 1 and magenta developer 1 except that Pigment Yellow 12 was used.

(Developer set 1 for color images)
A developer set including the magenta developer 1, the cyan developer 1, and the yellow developer 1 is referred to as a color image developer set 1.

(Developer set 2 for color images)
The color image developer set 2 was prepared in the same manner as the color image developer set 1 except that the binder resin (C2) was used as the binder resin for each toner particle.

  Each toner particle diameter was as follows.

  Magenta toner particles 2: 8.6 μm, cyan toner particles 2: 8.3 μm, yellow toner particles 2: 8.4 μm

(Developer set 3 for color images)
The color image developer set 3 was prepared in the same manner as the color image developer set 1 except that the binder resin (C3) was used as the binder resin used for each toner particle.

  Each toner particle diameter was as follows.

  Magenta toner particles 3: 8.1 μm, cyan toner particles 3: 8.3 μm, yellow toner particles 3: 8.2 μm

(Developer set 4 for color images)
The color image developer set 4 was prepared in the same manner as the color image developer set 1 except that the binder resin (C4) was used as the binder resin used for each toner particle.

  Each toner particle diameter was as follows.

  Magenta toner particles 4: 8.0 μm, cyan toner particles 4: 8.1 μm, yellow toner particles 4: 8.1 μm

(Developer set 5 for color images)
The color image developer set 5 was prepared in the same manner as the color image developer set 1 except that the binder resin (C5) was used as the binder resin used for each toner particle.

  Each toner particle diameter was as follows.

  Magenta toner particles 5: 8.5 μm, cyan toner particles 5: 8.5 μm, yellow toner particles 5: 8.4 μm

<Example 1>
The color image developer set 1 and the invisible image forming developer 1 were combined to obtain a developer set for developing an electrostatic image.

<Example 2>
The developer set 1 for color images and the developer 2 for forming invisible images were combined to obtain a developer set for developing electrostatic images.

<Example 3>
The developer set 1 for color images and the developer 3 for forming invisible images were combined to form a developer set for developing electrostatic images.

<Example 4>
The color image developer set 2 and the invisible image forming developer 3 were combined to form an electrostatic charge image developer set.

<Example 5>
The developer set 3 for color images and the developer 2 for forming invisible images were combined to form a developer set for developing electrostatic images.

<Example 6>
The color image developer set 1 and the invisible image forming developer 8 were combined to obtain an electrostatic charge image developer set.

<Example 7>
The developer set 1 for color images and the developer 9 for forming invisible images were combined to form a developer set for developing electrostatic images.

<Comparative Example 1>
The color image developer set 1 and the invisible image forming developer 4 were combined to form an electrostatic charge image developer set.

<Comparative example 2>
The developer set 1 for color images and the developer 5 for forming invisible images were combined to form a developer set for developing electrostatic images.

<Comparative Example 3>
The developer set 5 for color images and the developer 6 for forming invisible images were combined to form a developer set for developing electrostatic images.

<Comparative example 4>
The color image developer set 5 and the invisible image forming developer 7 were combined to form an electrostatic charge image developer set.

  Using the developer set thus obtained, an image forming test was performed using an image forming apparatus, and various evaluations were performed.

[Image formation by image forming apparatus]
<Image forming apparatus>
For an image formation test using the developer set for developing an electrostatic charge image produced according to each of the examples and comparative examples, a modified DocuCenterColor 400 manufactured by Fuji Xerox Co., Ltd. shown in FIG. 5 was used as an image forming apparatus. In this image forming apparatus, the heat fixing unit is removed, and the toner image formed on the image output medium by development and transfer can be taken out in a form that is not melt-fixed to the image output medium. The yellow developer unit, magenta developer unit, and cyan developer unit are filled with color image developers used in the examples and comparative examples corresponding to the respective colors, and the black developer unit is also invisible. An image forming developer was filled to form an image.

  In Example 8, an invisible image forming developer is filled in a yellow developer, and a yellow developer, a magenta developer, and a cyan developer are respectively added to a magenta developer, a cyan developer, and a black developer. An image was formed in the same manner as described above except that was filled.

  As an image output medium used for the image formation test, A4 size white paper (manufactured by Fuji Xerox, J paper, width: 210 mm, length: 297 mm) was used. In addition, when J paper manufactured by Fuji Xerox Co., Ltd., which is an image output medium, was measured using a 60-degree specular gloss measurement defined in JIS standard “Z8741” described later, Gs (60 °) = 5.3% Met.

<Image formation and creation of fixed image samples>
A recorded product obtained by forming an image on the surface of an image output medium using an image forming apparatus using the developer described above has a visible image and an invisible image formed on the image forming surface. Academic Society Test Chart No. It is the image output using 5-1. On the other hand, the invisible image is composed of a two-dimensional pattern that can be machine-read / decoded formed by two kinds of minute line bitmaps having different rotation angles as shown in FIG.

  Using the external fixing device (Fuji Xerox Co., Ltd., DCC400 fixing device removed from the main body and remodeled so that the roll heating temperature can be controlled arbitrarily), the above image was fixed under Nip 6.5 mm, fixing speed fixing speed 180 mm / In sec, fixing was performed while increasing the fixing temperature from 140 ° C. to 220 ° C. every 10 ° C., and an image sample for evaluation was prepared.

[quality evaluation]
<Invisible information restoration rate>
The evaluation of the invisible information restoration rate is based on a ring-shaped LED light source (manufactured by Kyoto Electric Co., Ltd.) that irradiates light in the near-infrared wavelength region, which is set on the image forming surface of the recorded matter 1 approximately 10 cm directly above the image forming surface. , LEB-3012CE). In this state, a CCD camera (manufactured by KEYENCE, having a light receiving sensitivity in a wavelength region of 800 nm to 900 nm, which is installed at a position approximately 15 cm directly above the image forming surface and which has a filter for cutting a wavelength component of 800 nm or less mounted on the lens unit. CCD TL-C2) reads the image forming surface, binarizes with a certain contrast (threshold) as a boundary, extracts an invisible image, decodes it with software, and copyright information We evaluated whether it was possible to restore correctly. And when this evaluation was implemented 500 times, the frequency | count that information was correctly decompress | restored was shown in Table 1 as an invisible information restoration rate (%). If the invisible information restoration rate (%) is 85% or more, the level is practically acceptable.

<Visibility of invisible information>
For the image samples fixed at each temperature, visibility was evaluated by the following criteria using 20 randomly selected monitors.
○: All 20 people could not visually recognize invisible information.
(Triangle | delta): The number of persons who could visually recognize invisible information was 2 or less in 20 persons.
X: The number of persons who were able to visually recognize invisible information was 2 or more out of 20 and 10 or less.
Xx: The number of persons who could visually recognize invisible information was 10 or more out of 20.

<Image quality of color image>
In the specular gloss as defined in JIS standard “Z8741”, using the 60 ° specular gloss Gs (60 °) measurement method, the color image and the invisible image overlap at a fixing temperature of 170 ° C. The image surface gloss was measured. If the surface glossiness Gs (60 °) ≧ 50%, it was determined that there was no problem in image quality. In addition, the glossiness (Gardner's glossiness meter "micro-tri-gloss glossiness meter" was used for the said glossiness.

  Tables 1 to 3 show the results of the above evaluation on the examples and comparative examples in the present invention.

  The toner for electrophotography of the present invention is particularly useful for uses such as electrophotography and electrostatic recording.

The invisible image forming part formed of the two-dimensional pattern formed by the image forming method of the present invention, a normal image (when viewed visually), an enlarged view when recognized by infrared light irradiation, and the enlarged view It is a schematic diagram which shows an example at the time of grasping | ascertaining as a bit information image after carrying out decoding conversion to digital information by machine reading. By the image forming method of the present invention, an image that can be actually recognized when a recorded matter in which a visible image is formed together with an invisible image on the surface of the image output medium is visually observed from a substantially vertical direction (front side) of the paper surface of the recorded matter. It is an example schematically shown. FIG. 2 is an example schematically showing an image that can be actually recognized when the recorded matter shown in FIG. 2 is visually observed from a position (diagonal) deviated from the vertical direction of the recorded matter by the image forming method of the present invention. is there. 1 is a schematic diagram illustrating a configuration example of an image forming apparatus for forming an invisible image by the image forming method of the present invention. It is the schematic which shows the structural example of the image forming apparatus for forming simultaneously a visible image with an invisible image with the image forming method of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 Invisible image, 12 Image output medium, 13 Enlarged part, 14 Minute line unit, 15 bit information image, 21 Recorded object, 22 Invisible image, 100 Image forming apparatus, 101 Image carrier, 102 Charger, 103 Image writing apparatus, 104 Developing Device, 105 Transfer Roll, 106 Cleaning Blade, 200 Image Forming Device, 201 Image Carrier, 202 Charging Device, 203 Image Writing Device, 204 Rotary Developer, 204Y Yellow Developer, 204M Magenta Developer, 204C Cyan Developer, 204K black developer, 204F invisible developer, 205 primary transfer roll, 206 cleaning blade, 207 intermediate transfer member, 208, 209, 210 support roll, 211 secondary transfer roll.

Claims (6)

A toner set comprising color toner particles including a binder resin, a colorant, and a release agent, and invisible toner particles including a binder resin, a near infrared light absorbing material, and a release agent,
The color toner particles and the invisible toner particles are used to transfer images to the same image output medium, and then in the 60-degree specular gloss measurement in accordance with JIS-Z8741, the color image and the invisible toner image are 60 degrees. An electrophotographic toner set comprising a combination of the color toner particles and the invisible toner particles having a specular gloss difference of 20% or more. A toner set comprising color toner particles including a binder resin, a colorant, and a release agent, and invisible toner particles including a binder resin, a near infrared light absorbing material, and a release agent,
The weight average molecular weight MwC of the binder resin used for the color toner particles and the weight average molecular weight MwI of the binder resin used for the invisible toner particles containing the near infrared light absorbing material satisfy the relationship of the following formula. A toner set for electrophotography.
(Equation 1)
Formula (1): 2.0 <= MwI / MwC <= 4.0
Formula (2): 8000 ≦ MwC ≦ 22000   The toner set for electrophotography according to claim 1, wherein the near-infrared light absorbing material contains at least one of an aminium salt compound and a naphthalocyanine compound.   An electrophotographic developer comprising a carrier and an electrophotographic toner, wherein the electrophotographic toner is the electrophotographic toner set according to any one of claims 1 to 3. An electrophotographic developer characterized by the above.   A toner image formed on an image output medium using the electrophotographic toner set and / or developer according to any one of claims 1 to 4 is heated and fixed in a temperature range of 140 ° C to 210 ° C. An image forming method comprising the step of: The image forming method according to claim 5.
A toner image formed on the image output medium using the electrophotographic toner set and / or developer according to any one of claims 1 to 4 when forming an image on the image output medium. An image forming method, wherein the lowermost layer is an image of invisible toner particles containing a near infrared light absorbing material.

Images