JP2013142893A - Printed material and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed material with high image qualities excellent in reproducibility of dots and thin lines, and an image forming method for obtaining the printed material.SOLUTION: The image forming method comprises forming a visible image by fixing a chromatic toner particle layer comprising a chromatic toner on an image support material with a transparent fixing layer to cover the chromatic toner particle layer. The method comprises steps of: depositing a chromatic toner particle layer formed by using a chromatic toner through an electrophotographic process on an image supporting material; depositing a transparent toner particle layer formed by using a transparent toner through an electrophotographic process on the chromatic toner particle layer; and heat treating the transparent toner particle layer. The transparent toner used has a softening point lower than that of the chromatic toner; and the heat treatment is carried out at a temperature equal to or higher than the softening point of the transparent toner and lower than the softening point of the chromatic toner, thereby the transparent toner constituting the transparent toner particle layer is softened to form a transparent fixed layer.

Description

  The present invention relates to a printed matter in which a visible image is formed with a colored toner on an image support and an image forming method for forming the printed matter.

2. Description of the Related Art Conventionally, in an image forming method using an electrophotographic method, fixing on an image support is achieved by melting colored toner constituting a visible image. Specifically, as shown in FIG. 3, first, a colored toner particle layer 3 that becomes a visible image is formed on the image support 2 (FIG. 3A), and then the colored toner is melted by heating. Then, it is fixed on the image support 2 (FIG. 3B).
However, as shown in FIG. 3, when the colored toner is melted and fixed to the image support 2, the shape of the colored toner particle layer 3 in a powder state (see FIG. 3A) Since the shape of the melted colored toner layer 3X changes in the direction in which the area expands (see FIG. 3B), the visible image obtained by fixing by such softening and melting of the colored toner is half The reproducibility of dots and thin lines is low, for example, the dots in the tone image are thick, and the thin lines in the thin line image of about 4 to 8 lines / mm are crushed.

On the other hand, in an image forming method using an electrophotographic method, many techniques using a transparent toner together with a colored toner for forming a visible image have been proposed for various reasons such as formation of a protective layer and imparting gloss. .
For example, Patent Document 1 discloses a technique for forming a protective layer with a transparent toner on a colored toner layer formed by softening and melting colored toner. For example, Patent Document 2 discloses a technique for imparting gloss by forming a layer of a transparent toner on a colored toner layer formed by softening and melting a colored toner. Further, for example, in Patent Document 3, a transparent toner particle layer and a colored toner particle layer are superposed in this order on an intermediate transfer member and transferred to reduce the colored toner particles remaining on the intermediate transfer member. A technique for improving the transferability of the layer to the image support is disclosed.
However, in any technique, since the colored toner is softened and melted and fixed on the image support in the fixing step, the reproducibility of dots and fine lines cannot be improved.

Japanese Patent Laid-Open No. 10-123853 JP-A-10-207174 JP 2009-25713 A

  The present invention has been made based on the above circumstances, and an object of the present invention is to provide a print with high image quality excellent in reproducibility of dots and fine lines, and an image forming method for obtaining the same. is there.

The image forming method of the present invention is an image forming method for forming a visible image by fixing a colored toner particle layer made of colored toner on an image support by covering the colored toner particle layer with a transparent fixing layer. There,
A step of laminating a colored toner particle layer formed by electrophotography using a colored toner on an image support;
Laminating a transparent toner particle layer formed by electrophotography using a transparent toner on the colored toner particle layer;
Heating the transparent toner particle layer, and
The transparent toner particle layer is formed by using a toner having a softening point lower than that of the colored toner as the transparent toner, and performing the heat treatment at a temperature not lower than the softening point of the transparent toner and lower than the softening point of the colored toner. The transparent toner is softened to form a transparent fixed layer.

In the image forming method of the present invention, it is preferable that the heat treatment is performed at a temperature of 10 ° C. or lower of the softening point of the colored toner.
In the image forming method of the present invention, the difference in softening point between the transparent toner and the colored toner is preferably 20 ° C. or more.
In the image forming method of the present invention, the colored toner is preferably composed of toner particles not containing wax.

The printed matter of the present invention is a printed matter in which a visible image is formed by fixing a colored toner particle layer made of a colored toner on an image support,
The colored toner particle layer is fixed on the image support by a transparent fixing layer formed by softening a transparent toner so as to cover the colored toner particle layer.

  According to the image forming method of the present invention, using a transparent toner having a softening point lower than that of the colored toner constituting the visible image, the heat treatment of the transparent toner particle layer is performed at a temperature equal to or higher than the softening point of the transparent toner. By performing the treatment at a temperature lower than the above, it is possible to obtain a print with high image quality and excellent reproducibility of dots and fine lines.

FIG. 2 is a schematic diagram for explaining the image forming method of the present invention, in which (a) shows a state in which a colored toner particle layer and a transparent toner particle layer are transferred onto an image support, and (b) shows on the image support. It is a figure which shows the state by which the colored toner particle layer was fixed. 1 is a schematic cross-sectional view illustrating an example of a configuration of an image forming apparatus for performing an image forming method of the present invention. It is a schematic diagram for explaining an example of a conventional image forming method, where (a) is a state in which a colored toner particle layer is transferred onto an image support, and (b) is a color toner melted on the image support. It is a figure which shows the state fixed by doing.

  Hereinafter, the image forming method and printed matter of the present invention will be described in detail.

(Image forming method)
FIG. 1 is a schematic diagram for explaining an image forming method of the present invention, in which (a) shows a state in which a colored toner particle layer and a transparent toner particle layer are transferred onto an image support, and (b) shows an image. It is a figure which shows the state by which the colored toner particle layer was fixed on the support body.
In the image forming method of the present invention, a colored toner particle layer 3 made of a colored toner is fixed on an image support 2 by covering the colored toner particle layer 3 with a transparent fixing layer 9, whereby a visible image is formed. This is a method for obtaining the printed product 1.
Specifically, a colored toner particle layer forming step of laminating a colored toner particle layer 3 formed by electrophotography using a colored toner on the image support 2, and a transparent toner on the colored toner particle layer 3 A transparent toner particle layer forming step of laminating a transparent toner particle layer 5 formed by electrophotography using the toner, a heat treatment step of performing a heat treatment of the transparent toner particle layer 5, and a colored toner as the transparent toner The heat treatment is performed at a temperature higher than the softening point of the transparent toner and lower than the softening point of the color toner, thereby softening and melting the transparent toner constituting the transparent toner particle layer 5. A transparent fixing layer 9 is formed.

As described above, the transparent toner having a lower softening point than the colored toner is used, and the heat treatment is performed at a temperature higher than the softening point of the transparent toner and lower than the softening point of the colored toner. A printed product 1 with high image quality can be obtained.
This is because, in the heat treatment, the colored toner particles constituting the colored toner particle layer 3 are not softened, but only the transparent toner constituting the transparent toner particle layer 5 is softened and melted, and the transparent toner particle layer 5 is colored. Since it is positioned above the toner particle layer 3, the colored toner particle layer 3 is fixed to the image support 2 by being covered with the melted toner particles. That is, since the colored toner particle layer 3 is fixed to the image support 2 without deformation of the colored toner particles constituting the colored toner particle layer 3, a printed material 1 having a visible image excellent in reproducibility of dots and fine lines is obtained. It is done.

In the image forming method of the present invention, the colored toner particle layer 3 is a layer made of the colored toner formed by developing the electrostatic latent image with at least one kind of colored toner, all of which is so-called undetermined in powder form. It is formed by the contact toner.
Specifically, the colored toner particle layer 3 may be either a layer formed of a single color image formed of colored toner or a layer formed of a multicolor image formed by superimposing colored toners of respective colors.

The transparent toner particle layer 5 is a layer made of the transparent toner formed by developing the electrostatic latent image with the transparent toner, and is all formed of powdered unfixed toner.
The transparent toner particle layer 5 may be formed so as to cover at least all of the colored toner particle layer 3, may be formed in an image-like manner matching the colored toner particle layer 3, and includes an image including the colored toner particle layer 3. Although it may be formed on the entire surface of the support 2, it is preferable that the transparent toner particle layer 5 is formed on the entire surface of the image support 2 including the colored toner particle layer 3. By forming the transparent toner particle layer 5 on the entire surface of the image support 2, for example, gloss can be imparted to the obtained printed matter 1.

FIG. 2 is a schematic cross-sectional view showing an example of the configuration of an image forming apparatus for performing the image forming method of the present invention.
This image forming apparatus is called a tandem color image forming apparatus, and includes a transparent toner particle layer forming portion 20H that forms a transparent toner particle layer 5, and colored toners such as yellow, magenta, cyan, and black, respectively. The colored toner particle layer forming portions 20Y, 20M, 20C, and 20Bk that form the particle layer 3, and the transparent toner particle layer 5 and the colored toner particle layer forming portions 20Y, 20M, 20B, formed in these transparent toner particle layer forming portions 20H, An intermediate transfer unit 10 that transfers the colored toner particle layer 3 formed in 20C and 20Bk onto the image support 2 and a fixing device 26 that heats the transparent toner particle layer 5 are provided.

  The colored toner particle layer forming portion 20Y forms a yellow toner particle layer, the colored toner particle layer forming portion 20M forms a magenta toner particle layer, and the colored toner particle layer forming portion 20C. A cyan toner particle layer is formed, and a black toner particle layer is formed in the colored toner particle layer forming portion 20Bk.

  The transparent toner particle layer forming unit 20H includes a photoconductor 11H that is an electrostatic latent image carrier, a charging unit 23H that applies a uniform potential to the surface of the photoconductor 11H, and a uniformly charged photoconductor 11H. An exposure means 22H for forming an electrostatic latent image of a desired shape, a developing means 21H for conveying the transparent toner onto the photoconductor 11H to visualize the electrostatic latent image, and a photoconductor 11H after the primary transfer. And a cleaning unit 25H for collecting the remaining toner.

  Further, the colored toner particle layer forming portions 20Y, 20M, 20C, and 20Bk are arranged on the surfaces of the photoreceptors 11Y, 11M, 11C, and 11Bk that are electrostatic latent image carriers and the photoreceptors 11Y, 11M, 11C, and 11Bk. Charging means 23Y, 23M, 23C, and 23Bk for giving various potentials, and exposure means 22Y, 22M for forming electrostatic latent images of a desired shape on the uniformly charged photoreceptors 11Y, 11M, 11C, and 11Bk. 22C and 22Bk and developing means 21Y, 21M, 21C, and 21Bk that convey the colored toners of the respective colors onto the photoreceptors 11Y, 11M, 11C, and 11Bk to visualize electrostatic latent images, and the photoreceptor 11Y after the primary transfer. , 11M, 11C, and 11Bk, and cleaning means 25Y, 25M, 25C, and 25Bk for collecting residual toner remaining on the surface.

The intermediate transfer unit 10 includes an intermediate transfer member 16, a primary transfer roller 13H for transferring the transparent toner particle layer 5 formed by the transparent toner particle layer forming unit 20H to the intermediate transfer member 16, and a colored toner particle layer forming unit. The toner particle layers of each color formed by 20Y, 20M, 20C, and 20Bk are transferred onto the intermediate transfer body 16 by primary transfer rollers 13Y, 13M, 13C, and 13Bk for transferring the toner particle layer to the intermediate transfer body 16 and the primary transfer roller 13H. A secondary transfer roller 13A for transferring the colored toner particle layer 3 transferred onto the intermediate transfer body 16 by the transparent toner particle layer 5 and the primary transfer rollers 13Y, 13M, 13C, and 13Bk transferred onto the image support 2; And a cleaning unit 12 that collects residual toner remaining on the transfer body 16.
The intermediate transfer body 16 has an endless belt shape that is stretched by a plurality of support rollers 16a to 16d and is rotatably supported.

  The fixing device 26 is provided in a state in which a pair of heat and pressure rollers 27 and 28 are in pressure contact with each other and a nip portion N is formed in the pressure contact portion.

[Colored toner particle layer forming step and transparent toner particle layer forming step]
In the image forming apparatus as described above, first, in the transparent toner particle layer forming unit 20H and the colored toner particle layer forming units 20Y, 20M, 20C, and 20Bk, charging means is provided on the photoreceptors 11H, 11Y, 11M, 11C, and 11Bk. 23H, 23Y, 23M, 23C, and 23Bk are uniformly charged and exposed by the exposure means 22H, 22Y, 22M, 22C, and 22Bk, so that the electrostatic latent image and the toner particles of each color relating to the transparent toner particle layer 5 are obtained. The electrostatic latent images relating to the layers are respectively formed, and the electrostatic latent images are respectively developed with the transparent toner and the colored toners of the respective colors in the developing units 21H, 21Y, 21M, 21C, and 21Bk, so that the transparent toner particle layer 5 And toner particle layers of the respective colors are formed, and the primary transfer rollers 13H, 13Y, 13M, 13C, The intermediate transfer body 16 transparent toner particle layer 5 and the color toner particles layer on is transferred successively by 3Bk, are superimposed on the intermediate transfer body 16. On the intermediate transfer member 16, the transparent toner particle layer 5, the yellow toner particle layer, the magenta toner particle layer, the cyan toner particle layer, and the black toner particle layer are stacked in this order from the intermediate transfer member 16 side. The colored toner particle layer 3 is superposed in this order, that is, the lowermost layer is the transparent toner particle layer 5.
On the other hand, the image support 2 housed in the paper feed cassette 41 is fed by the paper feed transport means 42 and transported by a plurality of paper feed rollers 44a, 44b, 44c, 44d and registration rollers 46, and is subjected to secondary transfer. The transparent toner particle layer 5 and the colored toner particle layer 3 of each color on the intermediate transfer member 16 are transferred onto the image support 2 in a batch by the roller 13A.

On the image support 2, a colored toner particle layer 3 in which a black toner particle layer, a cyan toner particle layer, a magenta toner particle layer, and a yellow toner particle layer are stacked in this order from the image support 2 side, and transparent The toner particle layer 5 is superposed in this order, that is, the uppermost layer is the transparent toner particle layer 5.
Ratio (adhesion amount ratio) between the total toner adhesion amount (A) of each color of the color toner forming the colored toner particle layer 3 and the toner adhesion amount (B) of the transparent toner forming the transparent toner particle layer 5 (B / A) is preferably 2/1 to 1/4.
When the adhesion amount ratio is in the above range, it is considered that the transparent fixed layer 9 obtained by heat treatment covers the upper surface and the side surface of the colored toner particle layer 3.
The specific thickness of the transparent toner particle layer 5 varies depending on the number of colors of the color toner constituting the color toner particle layer 3 and the toner adhesion amount, but is preferably 3 to 30 μm, for example.

Thereafter, the image support 2 having the colored toner particle layer 3 and the transparent toner particle layer 5 is conveyed to the fixing device 26, and the transparent toner particle layer 5 is heated in the fixing device 26, whereby the transparent toner particle layer. The transparent toner constituting 5 is softened to cover the colored toner particle layer 3 and to form a transparent fixing layer 9 fixed to the image support 2, whereby the colored toner particle layer 3 is fixed on the image support 2. As a result, a print 1 on which a visible image is formed is produced.
The printed material 1 on which a visible image is formed on the image support 2 is discharged out of the apparatus by the paper discharge roller 47 and placed on the paper discharge tray 40.

The photosensitive members 11H, 11Y, 11M, 11C, and 11Bk after the transparent toner particle layer 5 or the toner particle layer of each color is transferred to the intermediate transfer member 16 are cleaned by the cleaning means 25H, 25Y, 25M, 25C, and 25Bk. After the toner remaining on 11H, 11Y, 11M, 11C, and 11Bk is removed, the toner is used to form the next transparent toner particle layer 5 or the toner particle layer of each color.
On the other hand, the intermediate transfer body 16 after the transparent toner particle layer 5 and the colored toner particle layer 3 of each color are transferred onto the image support 2 by the secondary transfer roller 13A remains on the intermediate transfer body 16 by the cleaning means 12. After the removed toner is removed, it is subjected to intermediate transfer of the next transparent toner particle layer 5 and each color toner particle layer 3.

[Heat treatment process]
The heat treatment of the transparent toner particle layer 5 in the fixing device 26 needs to be performed at a temperature not lower than the softening point of the transparent toner and lower than the softening point of the colored toner, and differs depending on the respective softening points of the transparent toner and the colored toner. The heating temperature is preferably 10 ° C. or less, more preferably 20 ° C. or less, which is the softening point of the colored toner.
In the present invention, when a plurality of color toners are used as the color toner, the “softening point of the color toner” means the lowest softening point of the color toners of the plurality of colors.
By performing the heat treatment at such a temperature, it is possible to surely soften and melt only the transparent toner constituting the transparent toner particle layer 5 without softening the colored toner particles constituting the colored toner particle layer 3. .
As a specific heating temperature in the heat treatment, it can be set to 100 to 180 ° C., for example.
The heating temperature in the fixing device 26 is the surface temperature of the heating and pressing roller 27 with which the transparent toner particle layer 5 transferred onto the image support 2 comes into contact, and specifically, a nip portion using a non-contact thermometer. The temperature is measured when the surface of the heating member (heating pressure roller 27) at a position of 5 to 50 mm before the N entrance is measured.
When the heating temperature is lower than the softening point of the transparent toner, the transparent toner cannot be softened and the transparent fixing layer 9 cannot be formed. In addition, when the heating temperature is equal to or higher than the softening point of the colored toner, the obtained visible image is inferior in dot and fine line reproducibility due to the colored toner softening.

In this heat treatment, it is preferable that pressurization is performed simultaneously with heating.
The applied pressure is preferably 1 MPa or less.
When the applied pressure is excessive, the arrangement shape of the colored toner particle layer 3 may change, and the reproducibility of dots and fine lines may not be obtained sufficiently.

[Transparent toner]
The transparent toner used in the image forming method of the present invention is composed of toner particles for developing an electrostatic image, and the toner particles constituting the transparent toner contain, for example, at least a binder resin, and further, if desired. A material containing an internal additive such as a charge control agent, magnetic powder, or a release agent (wax) can be used.
Here, the transparent toner refers to a toner whose color is not recognized by the action of light absorption or light scattering. The transparent toner may be substantially colorless and transparent. For example, a toner that does not contain a colorant such as a pigment or a dye, a toner that contains a colorant such as a pigment or a dye that cannot recognize a color, a binder resin or a wax, Examples thereof include a toner whose transparency is slightly lowered depending on the type and amount of the external additive.

[Binder resin]
Examples of the binder resin include various known thermoplastic resins such as vinyl resins such as styrene-acrylic resins, polyester resins, polyamide resins, and polyurethane resins. You may use these individually by 1 type or in combination of 2 or more types. From the viewpoint of controllability of the molecular weight for adjusting the softening point of the binder resin during the production of the transparent toner, it is preferable to use a styrene-acrylic resin.

  The molecular weight of the entire binder resin contained in the transparent toner is preferably a number average molecular weight (Mn) of 3,000 to 6,000, more preferably 3,500 to 5,500, and a weight average molecular weight (Mw). The ratio Mw / Mn of the number average molecular weight (Mn) is 2.0 to 6.0, preferably 2.5 to 5.5.

The molecular weight of the binder resin contained in the transparent toner is measured by gel permeation chromatography (GPC) soluble in tetrahydrofuran (THF), using the measurement sample as a toner. To be done.
That is, using an apparatus “HLC-8220” (manufactured by Tosoh Corporation) and a column “TSKguardcolumn + TSKgelSuperHZM-M3 series” (manufactured by Tosoh Corporation), while maintaining the column temperature at 40 ° C., tetrahydrofuran (THF) was used as a carrier solvent at a flow rate of 0. The sample to be measured (transparent toner) was dissolved in tetrahydrofuran to a concentration of 1 mg / ml under a dissolution condition in which treatment was performed for 5 minutes using an ultrasonic disperser at room temperature, and then the pore size was 0.2 μm. A sample solution is obtained by processing with a membrane filter, and 10 μL of this sample solution is injected into the apparatus together with the carrier solvent described above, detected using a refractive index detector (RI detector), and the molecular weight distribution of the measurement sample is simply determined. Using a calibration curve measured using dispersed polystyrene standard particles calculate. As a standard polystyrene sample for calibration curve measurement, molecular weights manufactured by Pressure Chemical Co., Ltd. are 6 × 10 ² , 2.1 × 10 ³ , 4 × 10 ³ , 1.75 × 10 ⁴ , 5.1 × 10 ⁴ , 1 .1 × 10 ⁵ , 3.9 × 10 ⁵ , 8.6 × 10 ⁵ , 2 × 10 ⁶ , 4.48 × 10 ⁶ , and at least about 10 standard polystyrene samples were measured, and a calibration curve Create A refractive index detector is used as the detector.

〔Release agent〕
When the transparent toner is configured to contain a release agent, the wax contained in the transparent toner includes, for example, polyolefin wax such as polyethylene wax and polypropylene wax, and branched chain hydrocarbon such as microcrystalline wax. Long-chain hydrocarbon waxes such as wax, paraffin wax and sazol wax, dialkyl ketone waxes such as distearyl ketone, carnauba wax, montan wax, behenate behenate, trimethylolpropane tribehenate, pentaerythritol tetrabe Henate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, tristearyl trimellitic acid, distearyl maleate What ester waxes, ethylenediamine behenyl amide, an amide-based waxes such as trimellitic acid tristearyl amide.
Among these, since the transparency in the transparent toner particle layer 5 is improved by having no anisotropy when crystallizing from a molten state, it is preferable to use one having a low degree of crystallinity. For example, it is preferable to use paraffin wax, oxidized polyethylene wax, polypropylene wax, oxidized polypropylene wax, carnauba wax, sazol wax, rice wax, candelilla wax, jojoba oil wax, beeswax wax and the like.
It is preferable that content of a mold release agent is 0.1-30 mass parts with respect to 100 mass parts of binder resin, More preferably, it is 1-10 mass parts.

[Colored toner]
The colored toner used in the image forming method of the present invention may be composed of toner particles for developing an electrostatic image having a function of developing an electrostatic image. Examples of the toner particles constituting the colored toner include a binder. Resin particles containing a colorant and, if desired, an internal additive such as a charge control agent and magnetic powder in the resin can be used, and inorganic fine particles such as colored silica particles and ferrite particles are used. You can also.
Here, the colored toner refers to a toner containing a colorant for the purpose of coloring by light absorption or light scattering.

When the colored toner is made of resin particles, the resin particles preferably do not contain wax. By using a colored toner composed of toner particles made of resin particles not containing wax, a visible image having high transparency and excellent color reproducibility can be formed.
Further, as the resin particles, the binder resin constituting the resin particles is preferably made of a thermoplastic resin. The binder resin may be the same as or different from the binder resin of the transparent toner. May be. Further, as the resin particles, the binder resin constituting the resin particles may not have thermoplasticity, or may be a resin in which a resin having no thermoplasticity and a thermoplastic resin are used in combination. . Specific examples of the binder resin having no thermoplasticity include thermosetting resins and cross-linked resins.

[Colorant]
As the colorant contained in the toner particles constituting the colored toner, various organic or inorganic pigments as exemplified below can be used.
Carbon black, magnetic materials, iron / titanium composite oxide black, etc. can be used as the colorant for black toner, and channel black, furnace black, acetylene black, thermal black, lamp black, etc. can be used as carbon black. Can be used. As the magnetic material, ferrite, magnetite or the like can be used.
Examples of yellow colorants for yellow toner include C.I. I. Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, 162, etc., and C.I. I. Pigment Yellow 14, 17, 74, 93, 94, 138, 155, 180, 185, etc. can be used, and mixtures thereof can also be used.
As a magenta colorant for magenta toner, C.I. I. Solvent Red 1, 49, 52, 58, 63, 111, 122, etc. I. Pigment Red 5, 48: 1, 53: 1, 57: 1, 122, 139, 144, 149, 166, 177, 178, 222, etc. can be used. Mixtures of these can also be used.
As a cyan colorant for cyan toner, C.I. I. Solvent Blue 25, C.I. I. Solvent Blue 36, C.I. I. Solvent Blue 60, C.I. I. Solvent Blue 70, C.I. I. Solvent Blue 93, C.I. I. Solvent Blue 95 and other pigments such as C.I. I. Pigment Blue 1, 7, 15, 60, 62, 66, 76, etc. can be used.
The colorant for obtaining the toner of each color can be used alone or in combination of two or more for each color.

  The content of the colorant is preferably 1 to 10% by mass in the toner, and more preferably 2 to 8% by mass. When the content of the colorant is less than 1% by mass in the toner, the obtained toner may be insufficient in coloring power, while the content of the colorant exceeds 10% by mass in the toner. In some cases, the colorant is liberated or adhered to the carrier, which may affect the chargeability.

[Softening point of transparent toner and colored toner]
The transparent toner and the color toner used in the image forming method of the present invention have a softening point lower than that of the color toner. The difference between the softening point of the colored toner and the softening point of the transparent toner is more preferably 20 ° C. or more, and particularly preferably the difference is 30 ° C. or more. If the difference between the softening point of the colored toner and the softening point of the transparent toner is 20 ° C. or more, it is preferable because the softening of the colored toner is surely suppressed in the heat treatment and the reproducibility of dots and fine lines becomes better. . If the difference between the softening point of the colored toner and the softening point of the transparent toner is 30 ° C. or more, the heating temperature in the heat treatment is 10 ° C. or more of the softening point of the transparent toner and 20 ° C. or less of the softening point of the colored toner. It can be set to be preferable.

The softening point of the transparent toner used in the image forming method of the present invention varies depending on the softening point of the color toner used together, but is preferably 80 to 120 ° C, more preferably 90 to 115 ° C. .
Further, the softening point of the colored toner used in the image forming method of the present invention varies depending on the softening point of the transparent toner used together, but is preferably 120 to 160 ° C.
The softening point of the transparent toner can be controlled, for example, by adjusting the molecular weight of the binder resin contained therein.
When the colored toner is made of resin particles, the softening point of the colored toner can be controlled by adjusting the molecular weight of the binder resin contained therein as in the case of the transparent toner.

The softening point of the transparent toner and the colored toner is measured by a flow tester shown below.
Specifically, in an environment of 20 ° C. and 50% RH, first, 1.1 g of transparent toner (colored toner) is placed in a petri dish and left flat for 12 hours or more, and then the molding machine “SSP-10A” (Shimadzu Corporation) pressurizes with a force of 3820 kg / cm ² for 30 seconds to create a cylindrical molded sample with a diameter of 1 cm, and then the molded sample is flown in an environment of 24 ° C. and 50% RH. With a tester “CFT-500D” (manufactured by Shimadzu Corporation), a cylindrical die hole (1 mm diameter ×× 1 kg), under the conditions of a load of 196 N (20 kgf), a starting temperature of 60 ° C., a preheating time of 300 seconds, and a heating rate of 6 ° C./min. than 1 mm), extruded from the time of preheating ends with piston diameter 1 cm, offset method temperature T _offset measured by setting the offset value 5mm at a melt temperature measurement method of temperature ramps are It is the softening point of the light toner (color toner).

[Toner particle size]
The particle diameters of the transparent toner and the colored toner are preferably 3 to 8 μm in terms of volume-based median diameter. When the volume-based median diameter is 3 to 8 μm, high-quality photographic images can be achieved, and the toner consumption can be reduced as compared to the case of using a large particle diameter toner.

  The volume-based median diameter of each toner is measured and calculated using a measuring device in which a computer system equipped with data processing software “Software V3.51” is connected to “Coulter Multisizer 3” (manufactured by Beckman Coulter). It is what is done. Specifically, 0.02 g of toner is added to 20 mL of a surfactant solution (for example, a surfactant solution in which a neutral detergent containing a surfactant component is diluted 10-fold with pure water for the purpose of dispersing the toner). Then, ultrasonic dispersion was performed for 1 minute to prepare a toner dispersion, and this toner dispersion was placed in a beaker containing “ISOTON II” (manufactured by Beckman Coulter) in a sample stand. Pipette until the indicated concentration is 8%. Here, a reproducible measurement value can be obtained by setting the concentration range. In the measurement apparatus, the measurement particle count is 25000, the aperture diameter is 50 μm, the frequency value is calculated by dividing the measurement range of 1 to 30 μm into 256, and the volume integrated fraction is 50 % Particle diameter is defined as the volume-based median diameter.

[Average circularity of toner]
In addition, the toner as described above preferably has an average circularity of 0.850 to 1.000, more preferably 0.8, from the viewpoint of improving transfer efficiency of individual toner particles constituting the toner. 900 to 0.995.
When the average circularity is in the range of 0.850 to 1.000, the filling density of the toner particles in the transparent toner particle layer 5 and the colored toner particle layer 3 transferred to the image support 2 is increased, and the transparent toner The fixing property of the transparent toner particles constituting the particle layer 5 is improved, and the fixing offset hardly occurs. In addition, the individual toner particles are less likely to be crushed, the contamination of the frictional charge imparting member is reduced, and the toner chargeability is stabilized.
The average circularity of the toner is a value measured using “FPIA-2100” (manufactured by Sysmex). Specifically, the toner is blended with an aqueous solution containing a surfactant, and subjected to ultrasonic dispersion treatment for 1 minute to disperse, and then measurement conditions HPF (high magnification imaging) are performed according to “FPIA-2100” (manufactured by Sysmex). ) Mode, photographing at an appropriate density of 3,000 to 10,000 HPF detections, calculating the circularity according to the following formula (T) for each toner particle, and adding the circularity of each toner particle , A value calculated by dividing by the total number of toner particles. If the number of HPF detections is in the above range, reproducibility can be obtained.
Formula (T): Circularity = (perimeter of a circle having the same projection area as the particle image) / (perimeter of the particle projection image)

[Method for producing transparent toner and colored toner]
Examples of the method for producing the transparent toner as described above include a kneading and pulverizing method, a suspension polymerization method, an emulsion aggregation method, a dissolution suspension method, a polyester elongation method, and a dispersion polymerization method. Even when the colored toner is made of resin particles, the same method can be used as a method for producing the colored toner.
Among these, it is preferable to employ an emulsion aggregation method from the viewpoints of uniformity of particle diameter, shape controllability, and ease of forming a core-shell structure, which are advantageous for high image quality and high stability.
In the emulsion aggregation method, a dispersion of resin fine particles dispersed with a surfactant or a dispersion stabilizer is mixed with a dispersion of toner particle constituents such as colorant fine particles as necessary, and a flocculant is added. In this method, toner particles are produced by agglomerating until a desired toner particle size is obtained, and thereafter or simultaneously with agglomeration, fusion between resin fine particles is performed, and shape control is performed.
Here, the resin fine particles may optionally contain internal additives such as a release agent and a charge control agent, and are formed of a plurality of layers composed of two or more layers made of resins having different compositions. It can also be.
In addition, it is also preferable from the viewpoint of toner structure design to add different kinds of resin fine particles at the time of aggregation to obtain toner particles having a core-shell structure.
The resin fine particles can be produced, for example, by an emulsion polymerization method, a miniemulsion polymerization method, a phase inversion emulsification method, or the like, or can be produced by combining several production methods. When an internal additive is contained in the resin fine particles, it is preferable to use a miniemulsion polymerization method.

(External additive)
The toner particles constituting each toner can be used as toners as they are. However, in order to improve fluidity, chargeability, cleaning properties, etc., the toner particles are provided with a so-called post-treatment agent, a fluidizing agent and a cleaning aid. A toner to which an external additive such as an agent is added may be used as the toner.
As the post-treatment agent, for example, inorganic oxide fine particles composed of silica fine particles, alumina fine particles, titanium oxide fine particles, etc., inorganic stearate compound fine particles such as aluminum stearate fine particles, zinc stearate fine particles, or strontium titanate, titanium Inorganic titanic acid compound fine particles such as zinc acid are listed. These can be used individually by 1 type or in combination of 2 or more types.
These inorganic fine particles are preferably subjected to a gloss treatment with a silane coupling agent, a titanium coupling agent, a higher fatty acid, a silicone oil or the like in order to improve heat-resistant storage stability and environmental stability.
The total amount of these various external additives added is 0.05 to 5 parts by mass, preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the toner. In addition, various external additives may be used in combination.

(Developer)
Each of the toners as described above can be used for image formation as a magnetic or non-magnetic one-component developer, but may be mixed with a carrier and used as a two-component developer. When the toner is used as a one-component developer for image formation, either a non-magnetic one-component developer or a magnetic one-component developer containing about 0.1 to 0.5 μm of magnetic particles in the toner is used. Can be used. In addition, when the toner is used for image formation as a two-component developer, the carrier is a conventionally known material such as a metal such as iron, ferrite, or magnetite, or an alloy of such a metal with a metal such as aluminum or lead. Magnetic particles can be used, and ferrite particles are particularly preferable. As the carrier, a coated carrier in which the surface of magnetic particles is coated with a coating agent such as a resin, a resin-dispersed carrier in which a magnetic fine powder is dispersed in a binder resin, or the like may be used.

(Image support)
As the image support 2, an appropriate one can be used, for example, plain paper from thin paper to thick paper, high-quality paper, coated printing paper such as art paper or coated paper, commercially available Japanese paper or postcards. Examples include paper, polypropylene synthetic paper, polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, polyimide film, and cloth.
The thickness of the image support 2 is preferably 50 to 150 μm, for example.

  According to the image forming method as described above, using the transparent toner having a softening point lower than that of the colored toner constituting the visible image, the heat treatment of the transparent toner particle layer 5 is performed at a temperature equal to or higher than the softening point of the transparent toner. By performing the treatment at a temperature lower than the softening point, it is possible to obtain a printed product 1 having excellent image quality and excellent reproducibility of dots and fine lines.

[Printed matter]
The printed matter 1 obtained by the image forming method as described above is such that a visible image is formed by fixing a colored toner particle layer 3 made of a colored toner on an image support 2. 3 is fixed on the image support 2 by a transparent fixing layer 9 formed by softening the transparent toner so as to cover the colored toner particle layer 3.

Although the embodiments of the present invention have been specifically described above, the embodiments of the present invention are not limited to the above examples, and various modifications can be made.
For example, in the above embodiment, the colored toner particle layer forming step and the transparent toner particle layer forming step are performed in parallel. However, the present invention is not limited to this, and first, the colored toner particle layer 3 is formed to support the image. Alternatively, the transparent toner particle layer 5 may be formed and transferred onto the colored toner particle layer 3 to be laminated.

  Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

<Example of producing colored toner Bk1>
(1) Preparation of resin fine particle dispersion (a) First stage polymerization 4 parts by mass of polyoxyethylene (2) sodium dodecyl ether sulfate is ionized in a reaction vessel equipped with a stirrer, temperature sensor, cooling tube and nitrogen introducing device. A surfactant solution dissolved in 3000 parts by mass of exchange water was charged, and the internal temperature was raised to 80 ° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream.
To this surfactant solution, an initiator solution prepared by dissolving 5 parts by mass of a polymerization initiator (potassium persulfate: KPS) in 200 parts by mass of ion-exchanged water was added, and the liquid temperature was adjusted to 75 ° C.
Styrene 567 parts by weight n-butyl acrylate 165 parts by weight A monomer mixture consisting of 68 parts by weight methacrylic acid is added dropwise over 1 hour, and this system is heated and stirred at 75 ° C. for 2 hours for polymerization. Thus, a resin fine particle dispersion [A1] in which resin fine particles [A1] are dispersed was prepared.

(B) Second-stage polymerization In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device, 2 parts by mass of sodium polyoxyethylene (2) dodecyl ether sulfate was dissolved in 1270 parts by mass of ion-exchanged water. After charging the surfactant solution and heating to 80 ° C., 40 parts by mass of the resin fine particle dispersion [A1] in terms of solid content is added,
Styrene 123 parts by weight n-butyl acrylate 45 parts by weight Methacrylic acid 20 parts by weight n-octyl mercaptan 0.5 parts by weight of monomer mixture is added, and mechanical disperser “CLEAMIX” (M -A dispersion liquid containing emulsified particles was prepared by mixing and dispersing for 1 hour according to Technique).
Next, polymerization is performed by adding an initiator solution in which 5 parts by mass of potassium persulfate (KPS) is dissolved in 100 parts by mass of ion-exchanged water to this dispersion, and heating and stirring the system for 1 hour. Thus, a resin fine particle dispersion [A2] in which the resin fine particles [A2] are dispersed was prepared.

(C) Third-stage polymerization An initiator solution dissolved in 10 parts by mass of potassium persulfate (KPS) in 200 parts by mass of ion-exchanged water is added to the resin fine particle dispersion [A2], and the liquid temperature is set to 80 ° C. West,
Styrene 393 parts by weight n-Butyl acrylate 125 parts by weight Methacrylic acid 51 parts by weight n-Octyl mercaptan 13 parts by weight A monomer mixture consisting of 13 parts by weight was added dropwise over 1 hour, followed by heating at 80 ° C. for 2 hours. After performing polymerization by stirring, the mixture was cooled to 28 ° C. to prepare a resin fine particle dispersion [A3] in which resin fine particles [A3] were dispersed.

(2) Preparation of Colorant Fine Particle Dispersion While stirring a solution obtained by adding 27 parts by mass of sodium n-dodecyl sulfate to 500 parts by mass of ion-exchanged water, 30 parts by mass of carbon black was gradually added as a colorant, A colorant fine particle dispersion [Bk] in which colorant fine particles are dispersed was prepared by carrying out a dispersion treatment using a mechanical disperser “CLEAMIX” (manufactured by M Technique Co., Ltd.).

(3) Formation of toner particles 1250 parts by mass of the resin fine particle dispersion [A3], 2000 parts by mass of ion-exchanged water, and 165 parts by mass of the colorant fine particle dispersion [Bk] are combined with a temperature sensor, a cooling tube, and a nitrogen introducing device. Then, the mixture was stirred in a reaction vessel equipped with a stirrer to prepare a solution for association. After adjusting the internal temperature of this associating solution to 30 ° C., a 5 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 10.0, and then 52.6 parts by mass of magnesium chloride hexahydrate was ionized. An aqueous solution dissolved in 72 parts by mass of exchange water was added over 10 minutes at 30 ° C. with stirring. After standing for 3 minutes, temperature increase was started, and the system was heated to 90 ° C. over 6 minutes (temperature increase rate = 10 ° C./min).
In this state, the average particle size of the associated particles was measured with “Multisizer 3” (manufactured by Beckman Coulter). When the volume-based median diameter reached 6.7 μm, 115 parts by mass of sodium chloride was ionized. The aqueous solution dissolved in 700 parts by mass of exchange water was added to stop the particle growth, and further, the fusion was continued by heating and stirring at a liquid temperature of 90 ° C. ± 2 ° C. for 6 hours. When the circularity of the associated particles was measured by “FPIA-2100” (manufactured by Sysmex Corporation), the average circularity was 0.958.
Next, the mixture is cooled to 30 ° C. under conditions of 6 ° C./min, the associated particles are filtered, washed repeatedly with ion exchange water at 45 ° C., and then dried with hot air at 40 ° C., whereby toner base particles [Bk1] are obtained. Obtained.
1.0 part by mass of hexamethylsilazane-treated silica (average primary particle size 12 nm, hydrophobization degree 68) and n-octylsilane-treated titanium dioxide (average primary particle size) with respect to 100 parts by mass of the toner base particles [Bk1] A black colored toner [Bk1] was produced by adding an external additive consisting of 0.3 parts by mass of 20 nm, hydrophobization degree 63) and performing an external addition treatment with a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.).
The external addition process using a Henschel mixer was performed under the conditions of a peripheral speed of a stirring blade of 35 m / second, a processing temperature of 35 ° C., and a processing time of 15 minutes.
Table 1 shows the softening points of the colored toner [Bk1].

<Preparation Example of Colored Toners Bk2 to Bk4>
In Colored Toner Production Example Bk1, the amount of resin fine particle dispersion [A1] (in solid content), the amount of n-octyl mercaptan used in the second stage polymerization of the resin fine particle dispersion preparation step, and the third stage polymerization Colored toners [Bk2] to [Bk4] were prepared in the same manner except that the amount of each polymerizable monomer used in was changed according to Table 1.
Table 1 shows the softening points of these colored toners [Bk2] to [Bk4].

<Production Example of Transparent Toner C1>
(1) Preparation of resin fine particle dispersion (a) First stage polymerization Resin fine particle dispersion [A1] in the same manner as (1) First stage polymerization step of Preparation Example 1 of resin fine particle dispersion in Colored Toner Production Example ] Was obtained.

(B) Second-stage polymerization In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device, 2 parts by mass of sodium polyoxyethylene (2) dodecyl ether sulfate was dissolved in 1270 parts by mass of ion-exchanged water. After charging the surfactant solution and heating to 80 ° C., 2 parts by mass of the resin fine particle dispersion [A1] is added in terms of solid content,
Styrene 123 parts by mass n-butyl acrylate 45 parts by mass Methacrylic acid 20 parts by mass n-octyl mercaptan 2 parts by mass “HNP-57” (manufactured by Nippon Seiwa Co., Ltd.) A monomer mixture consisting of 82 parts by mass is added and circulated. A dispersion containing emulsified particles was prepared by mixing and dispersing for 1 hour using a mechanical disperser “CLEAMIX” (manufactured by M Technique Co., Ltd.) having a route.
Next, an initiator solution in which 5 parts by mass of potassium persulfate (KPS) is dissolved in 100 parts by mass of ion-exchanged water is added to this dispersion, and this system is heated and stirred at 80 ° C. for 1 hour. By performing polymerization, a resin fine particle dispersion [A4] in which resin fine particles [A4] are dispersed was prepared.

(C) Third Stage Polymerization In the third stage polymerization step (3) in the third stage polymerization step of Preparation Example 1 of the resin fine particle dispersion in the color toner production example, the resin fine particle dispersion [A4] is used instead of the resin fine particle dispersion [A2]. A resin fine particle dispersion [A5] was obtained in the same manner except that the amount of each polymerizable monomer used was changed in accordance with Table 1.

(2) Formation of toner particles 450 parts by weight of resin fine particle dispersion [A5] (in terms of solid content) and a surfactant solution in which 2 parts by weight of sodium dodecyl sulfate are dissolved in 1100 parts by weight of ion-exchanged water are used as a temperature sensor. Then, the mixture was stirred in a reaction vessel equipped with a condenser, a nitrogen introducing device, and a stirring device. After adjusting the temperature in the reaction vessel to 30 ° C., a 5 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 10.0, and then 60 parts by mass of magnesium chloride hexahydrate was added to 60 parts by mass of ion-exchanged water. The aqueous solution dissolved in the part was added over 10 minutes at 30 ° C. with stirring. After standing for 3 minutes, temperature increase was started and the system was heated to 85 ° C. over 6 minutes.
In this state, the average particle diameter of the associated particles was measured with “Multisizer 3” (manufactured by Beckman Coulter). When the volume-based median diameter reached 6.7 μm, 200 parts by mass of sodium chloride was ionized. The aqueous solution dissolved in 860 parts by mass of the exchange water was added to stop the particle growth, and the fusion was continued by heating and stirring at a liquid temperature of 90 ° C. ± 2 ° C. for 6 hours. When the circularity of the associated particles was measured by “FPIA-2100” (manufactured by Sysmex Corporation), the average circularity was 0.960.
Next, the mixture is cooled to 30 ° C. under conditions of 6 ° C./min, the associated particles are filtered, washed repeatedly with ion-exchanged water at 45 ° C., and then dried with hot air at 40 ° C., whereby transparent toner base particles [C1] Got.
1.0 part by mass of hexamethylsilazane-treated silica (average primary particle size 12 nm, hydrophobization degree 68) and n-octylsilane-treated titanium dioxide (average primary particles) with respect to 100 parts by mass of the transparent toner base particles [C1] A transparent toner [C1] was prepared by adding an external additive consisting of 0.3 parts by mass with a diameter of 20 nm and a hydrophobization degree of 63) and performing an external addition treatment with a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.).
The external addition process using a Henschel mixer was performed under the conditions of a peripheral speed of a stirring blade of 35 m / second, a processing temperature of 35 ° C., and a processing time of 15 minutes.
Table 1 shows the softening points of the transparent toner [C1].

<Production Example of Transparent Toner C2>
(1) Preparation of polyester resin fine particle dispersion 316 parts by mass of bisphenol A propylene oxide 2-mol adduct, 13 parts by mass of terephthalic acid, and polycondensation catalyst to a reactor equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device As described above, 2 parts by mass of titanium tetraisopropoxide was divided into 10 portions and reacted at 200 ° C. for 10 hours while distilling off the water generated in a nitrogen stream. Next, the reaction was carried out under reduced pressure of 13.3 kPa (100 mmHg), and the reaction was stopped when the weight average molecular weight reached 15000, thereby obtaining a polyester resin.
200 parts by mass of the obtained polyester resin was dissolved in 400 parts by mass of ethyl acetate (manufactured by Kanto Chemical Co., Inc.) and mixed with 638 parts by mass of a 0.26% by mass sodium lauryl sulfate solution prepared in advance, while stirring. Ultrasonic dispersion with ultrasonic homogenizer “UT-150T” (manufactured by Nippon Seiki Seisakusho) at 300 μA for V-LEVEL for 30 minutes, and diaphragm vacuum pump “V-700” (manufactured by BUCHI Co., Ltd.) with weighting to 40 ° C. The ethyl acetate was completely removed while stirring for 3 hours under reduced pressure to obtain a polyester resin fine particle dispersion [B1] having a volume-based median diameter of 180 nm.

(2) Preparation of release agent fine particle dispersion 100 parts by mass of microcrystalline wax “HNP-57” (Nippon Seiwa Co., Ltd.), 21 parts by mass of anionic surfactant “Neogen RK” (Daiichi Kogyo Seiyaku Co., Ltd.) And 860 parts by mass of ion-exchanged water are mixed, heated to 110 ° C., dispersed using a homogenizer “Ultra Turrax T50” (manufactured by IKA), and then dispersed using a Manton Gorin high-pressure homogenizer (manufactured by Gorin). By doing so, a release agent fine particle dispersion [F1] was prepared. The average particle size of the release agent fine particles in the obtained release agent fine particle dispersion [F1] was 250 nm.

(3) Formation of transparent toner In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introduction pipe, 450 parts by mass of polyester resin fine particle dispersion [B1] (in terms of solid content) and release agent fine particle dispersion [F1] 41 parts by mass (in terms of solid content), 2 parts by mass of sodium polyoxyethylene-2-dodecyl ether sulfate and 900 parts by mass of ion-exchanged water were prepared, and the liquid temperature was adjusted to 25 ° C. Of sodium hydroxide was added to adjust the pH to 10, and then, as a polyvalent metal ion compound, an aqueous solution in which 70 parts by mass of magnesium chloride was dissolved in 105 parts by mass of ion-exchanged water was stirred at 30 ° C. for 30 minutes. The system was heated to 80 ° C. over 60 minutes, and the particle growth reaction was continued while maintaining 80 ° C.
In this state, the average particle diameter of the associated particles was measured with “Multisizer 3” (manufactured by Beckman Coulter). When the volume-based median diameter reached 6.7 μm, 75 parts by mass of sodium chloride was ionized. By adding an aqueous solution dissolved in 290 parts by mass of exchange water to stop particle growth, and further heating and stirring at a liquid temperature of 88 ° C., the average circularity is 0.960 as measured by “FPIA-2100”. The toner particles were formed while the fusion between the particles proceeded, and then cooled to a liquid temperature of 30 ° C., hydrochloric acid was added to adjust the pH to 2.0, and stirring was stopped.
The produced toner particles are solid-liquid separated with a basket type centrifuge “MARK III model number 60 × 40” (manufactured by Matsumoto Kikai Co., Ltd.) to form a wet cake of toner particles, and this wet cake is separated from the basket type centrifuge. Then, the filtrate is washed with ion exchange water at 45 ° C. until the electric conductivity of the filtrate reaches 5 μS / cm, then transferred to “flash jet dryer” (manufactured by Seishin Enterprise Co., Ltd.), and dried until the water content becomes 1.0 mass% As a result, transparent toner base particles [C2] were obtained.
1.0 part by mass of hexamethylsilazane-treated silica (average primary particle size 12 nm, hydrophobization degree 68) and n-octylsilane-treated titanium dioxide (average primary particles) with respect to 100 parts by mass of the transparent toner base particles [C2] A transparent toner [C2] was prepared by adding an external additive consisting of 0.3 parts by mass with a diameter of 20 nm and a hydrophobization degree of 63) and performing an external addition treatment with a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.).
The external addition process using a Henschel mixer was performed under the conditions of a peripheral speed of a stirring blade of 35 m / second, a processing temperature of 35 ° C., and a processing time of 15 minutes.
The softening point of the transparent toner [C2] was measured and found to be 95 ° C.

[Developer Preparation Examples Bk1 to Bk4, C1, C2]
Each of the colored toners [Bk1] to [Bk4] and the transparent toners [C1] and [C2] is coated with a silicone resin, and a ferrite carrier having a volume-based median diameter of 60 μm is used. Color toner developers [Bk1] to [Bk4] and transparent toner developers [C1] and [C2] were prepared by mixing so that the concentration of the toner was 6% by mass.

<Examples 1-5, Comparative Examples 1 and 2>
According to Table 2, printed products [1] to [7] on which test images were formed using the color toner developers [Bk1] to [Bk4] and the transparent toner developers [C1] and [C2].
Specifically, the test image was formed using a commercially available digital image forming apparatus “bizhub Pro C6500” (manufactured by Konica Minolta Business Technologies) using a modified machine equipped with a transparent toner particle layer forming unit.
As the image support, a commercially available A4 size image support “J paper” (manufactured by Konica Minolta Business Solutions, Inc.) was used.
The toner supply amount in each toner particle layer forming portion was set to 4 g / m ^2, and these were transferred onto the image support so that the colored toner particle layer was positioned in the lower layer and the transparent toner particle layer was positioned in the upper layer.
The test image includes a halftone image portion having an image density of 0.4 and three types of fine line image portions of 8 lines / mm, 6 lines / mm, and 4 lines / mm.
The heat treatment was performed such that the surface temperature (heating temperature) of the heating roller was 120 ° C., and was performed in a normal temperature and normal humidity environment (temperature 20 ° C., relative humidity 50% RH) at a linear velocity of 100 mm / sec.
The obtained prints [1] to [7] were evaluated as follows. The results are shown in Table 2.

(Dot reproducibility)
The independence of dots constituting the halftone image portion in the printed matter was observed with a magnifying glass having a magnification of 10 times, and evaluated according to the following evaluation criteria.
-Evaluation criteria-
Rank A: It was recognized that each dot constituting the halftone image was formed independently (pass).
Rank B: A place where the independence of each dot was insufficient (intersection of dot ends) was slightly recognized (passed).
Rank C: There was a place where the independence of each dot was insufficient (intersection of dot ends), and some overlapping of dots was clearly recognized (pass).
Rank D: Clear overlapping of dots was recognized, and it was determined that the independence of each dot was insufficient (failed).
Rank E: Each dot was completely crushed, and dot reproducibility was not recognized (failed).

(Fine line reproducibility)
The independence of each thin line constituting the three types of thin line image portions of 8 lines / mm, 6 lines / mm, and 4 lines / mm in the printed matter was observed with a magnifying glass at a magnification of 10 times, and evaluated according to the following evaluation criteria. did.
-Evaluation criteria-
Rank A: No overlap of fine lines was observed in any of the fine line image portions of 8 lines / mm, 6 lines / mm, and 4 lines / mm (pass).
Rank B: Although a slight overlap of fine lines was observed in the thin line image portion of 8 lines / mm, no overlap of thin lines was recognized in the thin line image portions of 6 lines / mm and 4 lines / mm (pass).
Rank C: Overlapping of fine lines was observed in the thin line image part of 8 lines / mm, and slight thin line overlap was observed in the thin line image part of 6 lines / mm, but in the thin line image part of 4 lines / mm. No overlap was observed (passed).
Rank D: Overlapping fine lines were observed in the fine line image portions of 8 lines / mm and 6 lines / mm, and slight thin line overlap was also observed in the thin line image portions of 4 lines / mm (fail).
Rank E: Overlapping of fine lines was recognized in all fine line image portions (failed).

DESCRIPTION OF SYMBOLS 1 Printed matter 2 Image support body 3 Color toner particle layer 3X Color toner melt layer 5 Transparent toner particle layer 9 Transparent fixed layer 10 Intermediate transfer part 11H, 11Y, 11M, 11C, 11Bk Photoconductor 12 Cleaning means 13H, 13Y, 13M, 13C, 13Bk Primary transfer roller 13A Secondary transfer roller 16 Intermediate transfer members 16a to 16d Support roller 20H Transparent toner particle layer forming portions 20Y, 20M, 20C, 20Bk Colored toner particle layer forming portions 21H, 21Y, 21M, 21C, 21Bk Development Means 22H, 22Y, 22M, 22C, 22Bk Exposure means 23H, 23Y, 23M, 23C, 23Bk Charging means 25H, 25Y, 25M, 25C, 25Bk Cleaning means 26 Fixing device 27, 28 Heating and pressing roller 40 Paper discharge tray 41 Supply Paper cassette 42 Paper feeding and conveying means 44a 44b, 44c, 44d feed roller 46 registration rollers 47 discharge roller N nip

Claims (5)

An image forming method for forming a visible image by fixing a colored toner particle layer made of a colored toner on an image support by covering the colored toner particle layer with a transparent fixing layer,
A step of laminating a colored toner particle layer formed by electrophotography using a colored toner on an image support;
Laminating a transparent toner particle layer formed by electrophotography using a transparent toner on the colored toner particle layer;
Heating the transparent toner particle layer, and
The transparent toner particle layer is formed by using a toner having a softening point lower than that of the colored toner as the transparent toner, and performing the heat treatment at a temperature not lower than the softening point of the transparent toner and lower than the softening point of the colored toner. An image forming method comprising forming a transparent fixed layer by softening a transparent toner.   The image forming method according to claim 1, wherein the heat treatment is performed at a temperature of 10 ° C. or less of a softening point of the colored toner.   The image forming method according to claim 1, wherein a difference in softening point between the transparent toner and the colored toner is 20 ° C. or more.   4. The image forming method according to claim 1, wherein the colored toner is composed of toner particles not containing wax. A printed matter in which a colored toner particle layer made of colored toner is fixed on an image support to form a visible image,
A printed matter, wherein the colored toner particle layer is fixed on the image support by a transparent fixing layer formed by softening the transparent toner so as to cover the colored toner particle layer.

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