Image forming system and image forming method

Abstract

To provide an image forming system and an image forming method that can prevent a reduction in image quality caused by exposure of toner particles constituting white toner.SOLUTION: An image forming system comprises: a chromatic toner image forming unit that includes at least an image carrier and a developing unit having therein chromatic toner; a white toner image forming unit that includes at least an image carrier and a developing unit having therein white toner; and a transfer unit. A volume average particle diameter D50C [μm] of toner particles constituting the chromatic toner, and a volume average particle diameter D50W [μm] of toner particles constituting the white toner satisfy a relation of the following formula (1). The volume average particle diameter D50W, a standard deviation σW of a volume particle diameter distribution of the toner particles constituting the white toner, and the volume average particle diameter D50C satisfy a relation of the following formula (2). Formula (1): 1.1×D50C<D50W [μm]. Formula (2): D50W+1.6×σW<1.5×D50C [μm].SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming system and an image forming method, and more particularly to an image forming system and the like that can suppress deterioration of image quality caused by exposure of toner particles that constitute white toner. [Background technology]

[0002] In electrophotographic image forming apparatuses, images are printed on recording media, such as transparent media or colored paper media such as black paper. In this case, a method is used in which the non-image portion of the recording medium makes use of the color and texture of the media, and in the image portion, a color image with good color development is printed without being affected by the color of the media. As such a method, for example, a method has been disclosed in which a color toner layer is formed on a white toner layer to form an image and obtain a high-quality image.

[0003] For example, in the technology disclosed in Patent Document 1, a first toner image formed using a white toner and a second toner image formed using a color toner are transferred onto a recording medium in this order. At this time, the average particle size of the toner particles constituting the white toner is designed to be smaller than the average particle size of the toner particles constituting the color toner. However, since the average particle size of the toner particles constituting the color toner is larger than the average particle size of the toner particles constituting the white toner, this is disadvantageous in terms of image quality. Hereinafter, "toner particles constituting the white toner" will be simply referred to as "white toner particles", and "toner particles constituting the color toner" will be simply referred to as "color toner particles".

[0004] In the technology disclosed in Patent Document 2, a toner image formed using a white toner and a toner image formed using a color toner are transferred onto an image carrier in an overlapping manner. In this case, the average particle size of the white toner particles is within a range of 1.3 to 2.0 times the average particle size of the color toner particles, which is advantageous in terms of image quality. However, there is room for improvement because the size and distribution of some large-diameter particles of the white toner particles are not taken into consideration.

[0005] In the technology disclosed in Patent Document 3, a high-quality image is obtained by setting the average particle size of the white toner particles, the average particle size of the color toner particles, and the particle size difference between these particles within specific ranges. However, as with the technology disclosed in Patent Document 2, there is room for improvement because it does not pay attention to the size and distribution of some large-diameter particles of the white toner particles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-200361 A [Patent Document 2] JP 2002-236396 A [Patent Document 3] JP 2020-56893 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above problems and circumstances, and the problem to be solved is to provide an image forming system and an image forming method that can suppress degradation of image quality caused by exposure of toner particles that make up white toner. [Means for solving the problem]

[0008] In order to solve the above problems, the present inventors have studied the causes of the above problems and found that the above problems can be solved by making the volume average particle size of the white toner particles more than 1.1 times the volume average particle size of the color toner particles, thereby ensuring superiority in terms of image quality, and by suppressing the proportion of large-diameter particles in the white toner particles to a certain level or less, thereby arriving at the present invention. That is, the above problems according to the present invention are solved by the following means.

[0009] 1. An image forming system including a color toner image forming unit, a white toner image forming unit for forming a base layer, and a transfer unit, the color toner image forming unit includes at least an image carrier and a developing unit having color toner therein; the undercoat layer forming white toner image forming unit includes at least an image carrier and a developing unit having white toner therein; The volume average particle diameter D of the toner particles constituting the color toner 50C [μm] and the volume average particle size D of the toner particles constituting the white toner 50W [μm] satisfies the following formula (1), Equation (1) 1.1×D 50C <D 50W [μm] And the volume average particle size D 50W , the standard deviation σ of the volume particle size distribution of the toner particles constituting the white toner W and volume average particle size D 50C satisfies the following formula (2). Equation (2) D 50W +1.6×σ W <1.5×D 50C [μm] 1. An image forming system comprising:

[0010] 2. Volume average particle diameter D 50W [μm], the standard deviation of the volume particle size distribution σ W [μm] and the volume average particle diameter D 50C [μm] satisfies the following formula (3). Equation (3) D 50W +2.0×σ W <1.5×D 50C [μm] 2. The image forming system according to claim 1,

[0011] 3. The color toner is a polymerized toner, and the white toner is a pulverized toner. 2. The image forming system according to claim 1,

[0012] 4. The white toner contains a charge control agent 2. The image forming system according to claim 1,

[0013] 5. An image reading unit that reads patch images for color adjustment formed on the continuous paper and an image control unit are provided; the image reading unit is disposed opposite the continuous paper being transported along a transport path, the image control unit instructs formation of the patch image for color adjustment at a paper edge in a direction perpendicular to a paper feed direction, and Based on the detection result from the image reading unit, an instruction to change the image forming conditions in the color toner image forming unit, the undercoat layer forming white toner image forming unit, and the transfer unit is given. 2. The image forming system according to claim 1,

[0014] 6. An image forming method comprising a color toner image forming step, a white toner image forming step for forming a base layer, and a transfer step, the color toner image forming step develops at least the electrostatic latent image formed on the image carrier with a developer containing a color toner to form a color toner image; the white toner image forming step for forming the undercoat layer develops at least the electrostatic latent image formed on the image carrier with a developer containing a white toner to form a white toner image; The volume average particle diameter D of the toner particles constituting the color toner 50C [μm] and the volume average particle size D of the toner particles constituting the white toner 50W [μm] satisfies the following formula (1), Equation (1) 1.1×D 50C <D 50W [μm] And the volume average particle size D 50W , the standard deviation σ of the volume particle size distribution of the toner particles constituting the white toner W and volume average particle size D 50C satisfies the following formula (2). Equation (2) D 50W +1.6×σ W <1.5×D 50C [μm] 1. An image forming method comprising: Effect of the Invention

[0015] According to the above-mentioned means of the present invention, it is possible to provide an image forming system and an image forming method capable of suppressing deterioration in image quality caused by exposure of toner particles constituting a white toner. Although the mechanism by which the effects of the present invention are expressed or the mechanism by which the effects of the present invention are acted upon has not been clarified, it is speculated as follows.

[0016] First, in this specification, as a premise for explaining the mechanism of manifestation or action of the effects of the present invention, the definitions of chromatic toner, achromatic toner, and clear toner will be explained.

[0017] Toners can be broadly divided into chromatic toners, achromatic toners, and clear toners. Here, "chromatic toners" refer to toners that have three attributes, namely, hue, brightness, and saturation, such as yellow toners, magenta toners, and cyan toners. "Achromatic toners" refer to toners that have no hue or saturation, but only brightness, such as black toners, white toners, and gray toners. "Clear toners" refer to toners in electrophotographic images in which the layer formed by the clear toner transmits almost all light in the visible light range, or light in a part of the visible light range. The layer formed by the clear toner is then visible through the toner, resulting in a so-called transparent state. The light transmittance is not particularly limited as long as it is a transmittance that allows the light to be seen through. The light transmittance is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more. When almost all light in the visible light range is transmitted through the toner, it is colorless and transparent.

[0018] Next, the definitions of the white toner and color toner according to the present invention will be explained.

[0019] "White toner" refers to a toner that has a color (white) that satisfies the following two conditions when a toner layer is formed by transferring only white toner onto a transfer material. Note that the values ​​for the following two conditions are measured using a spectrophotometer in accordance with JIS Z 8781-4:2013 for the surface of the toner layer, and are expressed as CIE L * a * b* This is a value in the color system.

[0020] Condition 1: Brightness L * is 80 or more. Condition 2:a * and b * are -10≦a * ≦10, -10≦b * Meet the condition <= 10.

[0021] "Color toner" refers to a toner that belongs to a group of toners that includes the above-mentioned chromatic toners and the black and gray toners included in the above-mentioned achromatic toners. Note that the color toner does not include white toner and clear toner. Most commonly, white is used as a recording medium (e.g., recording paper), and this white is used as the reference color. For convenience, chromatic toners, black toners, and gray toners that are recognized as different from this white color are referred to as "color toners."

[0022] The image forming system of the present invention is an electrophotographic image forming apparatus including a color toner image forming unit, a white toner image forming unit, and a transfer unit, the color toner image forming unit including at least an image carrier and a developing unit having color toner therein, the white toner image forming unit including at least an image carrier and a developing unit having white toner therein, and a volume average particle diameter D of toner particles constituting the color toner 50C and the volume average particle size D of the toner particles constituting the white toner 50W and satisfy the relationship of the following formula (1), Formula (1) 1.1×D 50C <D 50W And the volume average particle size D 50W , the standard deviation σ of the volume particle size distribution of the toner particles constituting the white toner W and volume average particle size D 50C satisfies the following formula (2). Formula (2) D 50W +1.6×σ W <1.5×D 50C It is characterized by:

[0023] As described above, there is room for improvement in the conventional method of forming an image of good quality by forming a color toner layer on a white toner layer. Furthermore, the size and distribution of large particles of the white toner particles have not been taken into consideration, and this point is taken into consideration in the present invention.

[0024] Hereinafter, a case where a color toner layer is formed on a white toner layer will be considered, with an example being given in which black toner is used as the color toner.

[0025] When an image is formed by applying a normal amount of black toner to form only a black toner layer on white paper, no part of the white paper is exposed between the black toner layers. Here, consider the case where a white toner layer is formed as a base layer on white paper, and a black toner layer is formed on the base layer.

[0026] Fig. 1 is an enlarged view of an image in which a black toner layer is formed on a white toner layer. The enlarged view of Fig. 1 shows the toner layer on paper before the image is fixed after applying a normal amount of black toner to obtain a desired image density. In the following, the term "white toner layer" refers to the base layer formed using white toner, and the term "black toner layer" refers to the toner layer formed using black toner.

[0027] As can be seen from Figure 1, a part of the white toner layer is exposed between the black toner layers. Therefore, the above-mentioned exposure is an image defect caused by forming a black toner layer on a white toner layer.

[0028] Even if a color toner other than black toner is used instead of black toner, it is considered that the desired image density cannot be obtained with the originally designed amount of color toner adhesion if a part of the white toner layer is exposed as shown in Figure 1. Therefore, when forming an image by forming a color toner layer on a white toner layer, the above-mentioned exposure of the white toner layer results in a decrease in the color gamut that can be expressed as an image, causing a problem of deterioration in image quality.

[0029] As a result of further consideration by the inventors of the present invention regarding the exposure of the white toner layer as described above, it has become apparent that the above problem is caused by the difference in the volume average particle size and the volume particle size distribution between the colored toner particles and the white toner particles.

[0030] Further consideration will be given to the case where a color toner layer is formed on a white toner layer. In this case, it is generally considered that the volume particle size distribution of the white toner particles constituting the white toner layer is different from that of the color toner particles constituting the color toner layer. If some particles among the white toner particles are larger in diameter than the color toner particles, the white toner layer may end up with a larger uneven portion compared to the size of the color toner particles.

[0031] Fig. 2 is a simplified schematic diagram of the toner particles that make up the toner layer in an image in which a black toner layer is formed on a white toner layer. From Fig. 2, it can be seen that some of the large particles in the white toner particles are exposed from the gaps between the colored toner particles, forming uneven parts.

[0032] According to the present invention, the proportion of large particles in the white toner particles, which are a cause of deterioration in image quality, is suppressed to a certain level, and it is presumed that this makes it possible to prevent unevenness larger than that of color toner particles from being formed in the white toner layer.

[0033] First, as described above, it is disadvantageous in terms of image quality if the volume average particle size of the color toner particles is larger than that of the white toner particles, and therefore it is necessary for the volume average particle size of the white toner particles to be larger than that of the color toner particles in order to form a high-quality image.

[0034] In order to avoid any disadvantage in terms of image quality, it is considered necessary for the volume average particle size of the white toner particles to be 1.1 times larger than the volume average particle size of the color toner particles. Therefore, it is considered that a high-quality image can be formed by satisfying the following formula (1).

[0035] Formula (1) 1.1×D 50C <D 50W [μm]

[0036] However, if the volume average particle size of the white toner particles is too large compared to the volume average particle size of the colored toner particles, uneven portions larger than the colored toner particles are formed in the white toner layer, resulting in a problem of noticeable exposure of the white toner particles.

[0037] Specifically, it has been found that the above problem occurs when the volume average particle diameter of the white toner particles is 1.5 times or more the volume average particle diameter of the color toner particles. Here, the volume average particle diameter of the toner particles at which the volume average particle diameter of the white toner particles is 1.5 times the volume average particle diameter of the color toner particles is defined as the boundary particle diameter. This boundary particle diameter is the volume average particle diameter D of the color toner particles. 50C Since it is 1.5 times, 1.5×D 50C It is expressed as [μm].

[0038] The volume average particle diameter of the white toner particles is at least the particle diameter of the boundary (1.5×D 50C It is presumed that the occurrence of the above problems can be avoided by keeping the thickness of the insulating film less than 1 μm.

[0039] Next, attention is paid to the volume particle size distribution of the white toner particles and the colored toner particles, and in order to analyze this, the standard deviation σ WBy using this as an index showing the spread of the particle size distribution of the white toner particles, it is possible to know how much the particle size distribution of the white toner particles spreads toward the large particle side.

[0040] FIG. 3 is an example of a graph showing the relationship between the particle size of white toner particles and their abundance ratio in an image obtained by forming a color toner layer on a white toner layer. W represents the particle size of the white toner particles.

[0041] Volume average particle size D of white toner particles 50W , the standard deviation of the volume particle size distribution of white toner particles σ W The following equation expresses the relationship between

[0042] Expression D W =D 50W +p×σ W

[0043] In the above formula, the larger the real number p, the larger the particle diameter of the white toner particles in FIG. 3 shifts to the larger particle side. W , i.e. D 50W +1.6σ W is the boundary particle size that separates the top 10% of particle size distribution ratio from the remaining 90% in a normal distribution. In Figure 3, the line α in the above formula represents the case where P = 0, the line β represents the case where P = 1, and the line γ represents the case where P = 1.6.

[0044] As mentioned above, the particle size of the boundary of the problematic white toner particles is 1.5 times the particle size of the colored toner particles. W The value of D 50W +1.6×σ W If this is the volume average particle size D of the color toner particles, 50CIt is presumed that the problem of partial exposure of the white toner particles can be avoided by making the distance smaller than 1.5 times that of the white toner particles. In other words, it is presumed that by satisfying the following formula (2), a high-quality image can be formed without decreasing the density of the color toner. Equation (2) D 50W +1.6×σ W <1.5×D 50C

[0045] In this way, the particle size of the white toner particles is 1.5×D 50C The ratio of particles larger than [μm] is reduced, which is called D 50W +1.6×σ W This reduces the particle size to a level where the particle size is 100 nm or less. This makes it possible to suppress the proportion of large white toner particles, which leads to a decrease in the density of color toner, to a certain level or less. This makes it possible to achieve a color toner density that is equivalent to that achieved when an image is formed on white paper using color toners without using white toner.

[0046] From the above, the relationship between the particle diameters of all color toner particles and white toner particles provided in the image forming system is designed to satisfy the following formula (1) and also to satisfy the following formula (2). Equation (1) 1.1×D 50C <D 50W Equation (2) D 50W +1.6×σ W <1.5×D 50C

[0047] It is presumed that this makes it possible to form images with a sufficient color gamut while suppressing density reduction for all full-color images, regardless of whether they are monochrome, secondary color, or tertiary color. [Brief description of the drawings]

[0048] [Figure 1] Enlarged image of a black toner layer formed on a white toner layer [Diagram 2] A simplified schematic diagram of toner particles that make up a toner layer [Diagram 3]An example of a graph showing the relationship between the particle size of white toner particles and their abundance ratio [Figure 4] An example of the configuration of the device constituting the image forming system of the present invention [Diagram 5] FIG. 1 is a block diagram showing a configuration of an image forming apparatus. [Figure 6] 1 is a flowchart showing a process of color adjustment in an image control unit. [Figure 7] Schematic diagram of patch image formation of each color gradation pattern in an area not used by the user [Figure 8] Graph showing the relationship between the particle size index of white toner particles and Bk density [Figure 9] A graph showing the measurement results of the Bk density at each image patch position when real-time color adjustment is performed. [Figure 10] A graph showing the measurement results showing the Bk density value at each image patch position when real-time color adjustment is not performed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] The image forming system of the present invention is an image forming system including a color toner image forming unit, a base layer forming white toner image forming unit, and a transfer unit, wherein the color toner image forming unit includes at least an image carrier and a developing unit having color toner therein, the base layer forming white toner image forming unit includes at least an image carrier and a developing unit having white toner therein, and the volume average particle diameter D of toner particles constituting the color toner is 50C [μm] and the volume average particle size D of the toner particles constituting the white toner 50W [μm] satisfies the following formula (1), Formula (1) 1.1×D 50C <D 50W [μm] And the volume average particle size D 50W , the standard deviation σ of the volume particle size distribution of the toner particles constituting the white toner W and volume average particle size D 50C satisfies the following formula (2). Formula (2) D 50W +1.6×σW <1.5×D 50C [μm] It is characterized by:

[0050] This feature is a technical feature common to or corresponding to each of the following embodiments (aspects).

[0051] In one embodiment of the present invention, the volume average particle diameter D 50W [μm], the standard deviation of the volume particle size distribution σ W [μm] and the volume average particle diameter D 50C It is preferable that [μm] satisfies the relationship of the above formula (3) from the viewpoint of suppressing fluctuations in image density.

[0052] It is preferable that the color toner is a polymerized toner and the white toner is a pulverized toner from the viewpoint of easy particle size control and easy addition of a charge control agent.

[0053] From the viewpoint of exerting the effects of the present invention, it is preferable that the white toner contains a charge control agent.

[0054] From the viewpoint of maintaining stable image density in real-time color adjustment, it is preferable to provide an image reading unit that reads a patch image for color adjustment formed on continuous paper and an image control unit, the image reading unit being positioned opposite the continuous paper being transported along a transport path, the image control unit instructing the formation of the patch image for color adjustment at the end of the paper in a direction perpendicular to the paper feed direction, and giving instructions to change the image formation conditions in the color toner image forming unit, the white toner image forming unit for forming the base layer, and the transfer unit based on the detection results from the image reading unit.

[0055] 6. The image forming method of the present invention is an image forming method having a color toner image forming step, a white toner image forming step for forming a base layer, and a transfer step, in which the color toner image forming step develops at least an electrostatic latent image formed on an image carrier with a developer containing a color toner to form a color toner image, the white toner image forming step develops at least an electrostatic latent image formed on an image carrier with a developer containing a white toner to form a white toner image, and the volume average particle diameter D of toner particles constituting the color toner is 50C [μm] and the volume average particle size D of the toner particles constituting the white toner 50W [μm] satisfies the relationship of the above formula (1), and the volume average particle size D 50W , the standard deviation σ of the volume particle size distribution of the toner particles constituting the white toner W and volume average particle size D 50C The image forming system of the present invention is characterized in that the relationship of the above formula (2) is satisfied, and can be suitably used in the image forming system of the present invention.

[0056] The present invention, its components, and embodiments for carrying out the present invention will be described in detail below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after the symbol "to" are included as the lower limit and upper limit.

[0057] 1. Image forming system The image forming system of the present invention is an image forming system including a color toner image forming unit, a base layer forming white toner image forming unit, and a transfer unit, wherein the color toner image forming unit includes at least an image carrier and a developing unit having color toner therein, the base layer forming white toner image forming unit includes at least an image carrier and a developing unit having white toner therein, and the volume average particle diameter D of toner particles constituting the color toner is 50C [μm] and the volume average particle size D of the toner particles constituting the white toner 50W [μm] satisfies the following formula (1), Equation (1) 1.1×D 50C <D 50W [μm] And the volume average particle size D 50W, the standard deviation σ of the volume particle size distribution of the toner particles constituting the white toner W and volume average particle size D 50C satisfies the following formula (2). Formula (2) D 50W +1.6×σ W <1.5×D 50C [μm] It is characterized by:

[0058] As mentioned above, in order to avoid any disadvantage in terms of image quality, the volume average particle size of the white toner particles needs to be larger than 1.1 times the volume average particle size of the color toner particles. Therefore, by satisfying the above formula (1), a high-quality image can be formed.

[0059] The degradation of image quality is caused by some of the large particles in the white toner particles being exposed through the gaps between the color toner particles, and this can be avoided by keeping the proportion of the large particles in the white toner particles below a certain level.

[0060] As mentioned above, the particle size of the boundary of the white toner particle where the problem occurs is 1.5 times the particle size of the colored toner particle. 50W +1.6σ W By reducing the D, the proportion of large white toner particles that would otherwise cause a decrease in the density of color toners can be kept below a certain level. 50W +1.6σ W is the boundary particle size that separates the top 10% of particle sizes from the remaining 90% in a normal distribution. In this specification, "toner for developing electrostatic images" is also simply referred to as "toner."

[0061] (1.1) Volume average particle size of colored toner particles and white toner particles The volume average particle size D of the color toner particles according to the present invention 50C [μm] and the volume average particle size D of white toner particles 50W The volume average particle diameter D [μm] satisfies the relationship of the above formula (1). 50W , the standard deviation of the volume particle size distribution of white toner particles σ W and volume average particle size D50C is characterized in that the relationship of formula (2) is satisfied.

[0062] In one embodiment of the present invention, the volume average particle diameter D 50W [μm], the standard deviation of the volume particle size distribution σ W [μm] and the volume average particle diameter D 50C It is preferable that [μm] satisfies the relationship of the following formula (3) from the viewpoint of suppressing fluctuations in image density. Formula (3) D 50W +2.0×σ W <1.5×D 50C [μm]

[0063] In the present invention, the volume average particle diameter of the white toner particles described later is set to be more than 1.1 times the volume average particle diameter of the color toner particles, thereby ensuring superiority in terms of image quality. By suppressing the presence ratio of some large-diameter particles in the white toner particles to a certain level or less, the exposure of the white toner particles is suppressed, and a high-quality image is formed.

[0064] As mentioned above, the white toner and color toner according to the present invention will be defined below.

[0065] "White toner" refers to a toner that has a color (white) that satisfies the following two conditions when a toner layer is formed by transferring only white toner onto a transfer material. Note that the values ​​for the following two conditions are measured using a spectrophotometer in accordance with JIS Z 8781-4:2013 for the surface of the toner layer, and are expressed as CIE L * a * b * This is a value in the color system.

[0066] Condition 1: Brightness L * is 80 or more. Condition 2:a * and b * are -10≦a * ≦10, -10≦b * Meet the condition <= 10.

[0067] The term "color toner" refers to a toner that belongs to a group of toners that includes chromatic toners, and black toner and gray toner that are included in achromatic toners, and does not include white toner and clear toner.

[0068] When an image is formed by forming only color toner layers on white paper by applying a normal amount of color toner, no part of the white paper is exposed between the color toner layers. Here, when a white toner layer is formed as a base layer on white paper and a color toner layer is formed on the base layer, the exposure of the white toner layer is observed as shown in Figure 1 above.

[0069] Therefore, when forming an image by forming a color toner layer on a white toner layer, the above-mentioned exposure of the white toner layer results in a decrease in the color gamut that can be expressed as an image, leading to a decrease in image quality.

[0070] As described above, the exposure of the white toner layer is performed by adjusting the volume average particle diameter D 50W This is caused by differences in particle size distribution [μm] and volumetric particle size distribution.

[0071] Furthermore, if the white toner particles include particles having a larger particle diameter than the color toner particles, larger uneven portions are formed in the white toner layer compared to the size of the color toner particles.

[0072] From the above explanation of Figure 2, it can be seen that some of the large particles in the white toner particles are exposed from the gaps between the color toner particles, forming the uneven parts. The ratio of the large particles in the white toner particles is kept below a certain level. This prevents uneven parts larger than the color toner particles from being formed in the white toner layer.

[0073] First, as described above, it is disadvantageous in terms of image quality if the volume average particle size of the color toner particles is larger than that of the white toner particles, and therefore it is necessary for the volume average particle size of the white toner particles to be larger than that of the color toner particles in order to form a high-quality image.

[0074] In order to avoid any disadvantage in terms of image quality, the volume average particle size of the white toner particles must be greater than 1.1 times the volume average particle size of the color toner particles. Therefore, it is believed that a high-quality image can be formed by satisfying the following formula (1).

[0075] Formula (1) 1.1×D 50C <D 50W [μm]

[0076] However, when the volume average particle size of the white toner particles is 1.5 times or more the volume average particle size of the color toner particles, a problem of exposure of the white toner particles occurs.

[0077] Therefore, the volume average particle diameter of the white toner particles is at least the above particle diameter (1.5×D 50C [μm]), occurrence of the above problems can be avoided.

[0078] The relationship between the particle size of the white toner particles and the proportion of the white toner particles in an image obtained by forming a color toner layer on a white toner layer is as explained above with reference to FIG.

[0079] Volume average particle size of white toner particles D 50W , the standard deviation of the volume particle size distribution of white toner particles σ W The relationship between these two is expressed by the following equation using a real number p.

[0080] Expression D W =D 50W +p×σ W

[0081] In the above formula, the larger the real number p, the larger the particle diameter of the white toner particles in FIG. 3 shifts to the larger particle side. W , i.e. D 50W +1.6σ Wis the boundary particle size that separates the top 10% of particle size distribution ratio from the remaining 90% in a normal distribution. In Figure 3, the line α in the above formula represents the case where P = 0, the line β represents the case where P = 1, and the line γ represents the case where P = 1.6.

[0082] And D W The value of D 50W +1.6×σ W If this is the particle size D of the color toner particles, C In other words, by satisfying the following formula (2), it is possible to suppress a decrease in the density of the color toner. Equation (2) D 50W +1.6×σ W <1.5×D 50C

[0083] In one embodiment of the present invention, the volume average particle diameter D 50W [μm], the standard deviation of the volume particle size distribution σ W [μm] and the volume average particle diameter D 50C It is preferable that [μm] satisfies the relationship of the following formula (3) from the viewpoint of suppressing fluctuations in image density. Formula (3) D 50W +2.0×σ W <1.5×D 50C [μm]

[0084] (1.2) Image forming section The image forming system of the present invention includes an image forming section and a transfer section. The image forming section is composed of a color toner image forming section and a white toner image forming section for forming a base layer.

[0085] The image forming unit 70 includes an intermediate transfer belt 72, a color toner image forming unit 70 TC and a white toner image forming unit 70 for forming a base layer TW And, it is equipped with.

[0086] FIG. 4 shows an example of the configuration of an apparatus constituting the image forming system of the present invention.

[0087] The image forming section 70 includes writing sections (not shown) corresponding to the respective basic colors, photoconductors 71Y, 71M, 71C, 71K and 71W, an intermediate transfer belt 72, a transfer roller 73, an opposing roller 74, and the like.

[0088] A latent image is formed on the photoconductors 71Y, 71M, 71C, 71K, and 71W by exposing the writing section according to image data, and a toner image of each color is formed by developing the latent image with a developing device. The toner image is then primarily transferred onto the intermediate transfer belt 72.

[0089] In this specification, the "image carrier" in the image forming unit 70 refers to the above-mentioned "photoconductors 71Y, 71M, 71C, 71K, and 71W." Therefore, for example, the "image carrier 71Y" is synonymous with the "photoconductor 71Y."

[0090] (1.2.1) Color toner image forming section Color toner image forming unit 70 TC The image forming unit 70 includes image carriers 71Y, 71M, 71C, and 71K, and a developing unit (not shown) having color toner therein. After undergoing the charging and exposure processes, the color toner image forming unit 70 TC The color toner supplied from the developing unit is primarily transferred onto the intermediate transfer belt 72 as a toner image.

[0091] (1.2.2) White toner image forming section for forming base layer White toner image forming unit 70 TW The image carrier 71W includes a developing unit (not shown) having white toner therein. After undergoing the charging and exposure processes, the white toner image forming unit 70 TW The white toner supplied from the developing unit is primarily transferred onto the intermediate transfer belt 72 as a toner image.

[0092] (1.3) Transfer section The "transfer section" according to the present invention refers to the peripheral area of ​​the nip portion N where the toner image is secondarily transferred, and includes the transfer roller 73. In addition, this does not include the area where the color toner image and the white toner image are primarily transferred onto the intermediate transfer belt 72.

[0093] The intermediate transfer belt 72 is stretched around a plurality of rollers, including an opposing roller 74. The transfer roller 73 is biased with a predetermined pressure toward the opposing roller 74, with the intermediate transfer belt 72 sandwiched therebetween. As a result, a nip portion N1 is formed between the intermediate transfer belt 72, which covers the opposing roller 74, and the transfer roller 73.

[0094] The color toner image and the white toner image that have been primarily transferred onto the intermediate transfer belt 72 are then secondarily transferred to the recording medium P by the transfer roller 73 at the nip portion N1. At this time, the white toner layer is formed as a base layer, and the color toner layer is formed on the white toner layer.

[0095] (1.4) Other parts (Fixing part) The fixing unit 80 fixes the toner image formed on the surface of the recording medium P by applying heat and pressure at a fixing nip N2. The heating roller 81c has a hollow interior and a plurality of heaters such as halogen lamps.

[0096] An endless fixing belt 81b is stretched between the heating roller 81c and the upper pressure roller 81a. The fixing belt 81b is temperature-controlled (heated) by the heating roller 81c, which is heated by a heater, so that the fixing temperature becomes a predetermined fixing temperature. The fixing temperature is set within a range of 160 to 200°C, for example. The fixing temperature can be varied depending on the type of recording medium P, etc.

[0097] The lower pressure roller 82 is biased with a predetermined pressure toward the upper pressure roller 81a with the fixing belt 81b sandwiched therebetween, whereby the fixing belt 81b covering the upper pressure roller 81a and the lower pressure roller 82 are pressed against each other, forming a fixing nip portion N2 between them.

[0098] The toner image formed on the recording medium P is transported to the fixing nip portion N2 by the transport portion 90. When the toner image passes through the fixing nip portion N2 due to the rotation of the fixing belt 81b and the lower pressure roller 82, the toner image is heated and pressurized, and is fixed to the surface of the recording medium P.

[0099] (Transportation section) The transport unit 90 includes rollers that transport or hold the recording medium P, including a transport roller 91 and a paper discharge roller 92, as well as a motor that drives the rollers. The transport unit 90 may include a movement mechanism for moving the transported recording medium P relative to a colorimeter (not shown) that constitutes the color measurement unit 95.

[0100] The transport path 101 may be configured as a path along which the recording medium P is transported by the rotation of the transport roller 91, the paper discharge roller 92, etc. The transport path 101 may further include a path along which the recording medium P is transported within the paper feeder 120 and the winding device 130.

[0101] (Color measurement department) The colorimeter unit 95 includes a colorimeter, and the colorimeter is provided downstream of the fixing unit 80 along the conveying path 101. The colorimeter is a device that performs spectral analysis of light reflected or transmitted by an object to quantify the color of the object. The colorimeter unit 95 measures the color of an image formed on the recording medium P conveyed along the conveying path 101. Note that the colorimeter unit including the colorimeter in the present invention may be similar to that described in JP 2021-189267 A (paragraph 0046).

[0102] The color measurement unit 95 measures the color of a patch image for color adjustment formed on the recording medium P by the image forming unit 70, for adjusting the color of the image forming unit 70. The patch image for color adjustment is formed in approximately the center of the recording medium P, which can be measured by the color measurement unit 95, and may be a plurality of patch images in which the density is changed stepwise for each basic color.

[0103] Based on the color measurement result of the color adjustment patch image by the colorimeter 95, the image forming process by the image controller 60 and the image forming unit 70 is corrected. Specifically, based on the color measurement result of the color adjustment patch image, a color conversion table used when the image data is color converted by the image controller 60 can be corrected. The color conversion table is, for example, an ICC profile.

[0104] Based on the color measurement results by the color measurement unit 95, for example, the output of the writing unit in the image forming unit 70, the output of the developing bias applied to the developer, etc. may be corrected.

[0105] (others) In this embodiment, an image forming system using an intermediate transfer belt is exemplified, but an image forming system using a direct transfer method in which an image is directly transferred from a photoconductor to a recording medium P without using the intermediate transfer belt 72 may be used. In this image forming system using a direct transfer method, a plurality of photoconductors are arranged in the conveying direction together with a plurality of transfer rollers corresponding to each of the photoconductors. Then, the toner images of each color formed on each photoconductor are transferred onto the recording medium P in sequence, superimposed on top of each other, to form a full-color toner image.

[0106] (1.5) Differences in characteristics between colored toner and white toner due to their manufacturing methods The volume average particle diameters of the color toner particles and the white toner particles have been described above, so the rest of the toner configuration will be described below.

[0107] Generally, toner manufacturing methods are roughly classified into a polymerization method and a pulverization method. Hereinafter, a toner manufactured by a polymerization method is also referred to as a "polymerized toner," and a toner manufactured by a pulverization method is also referred to as a "pulverized toner."

[0108] Here, from the viewpoint of forming a high-quality image, that is, a high-definition and uniform image, the method for producing the color toner is preferably a polymerization method, which is advantageous for reducing the particle size of the toner particles.

[0109] On the other hand, high definition is not required for images formed using the white toner. Therefore, the manufacturing method of the white toner may be either a polymerization method or a pulverization method. Furthermore, the quality of the image formed using the white toner is not affected, and the white toner is generally marketed as a product.

[0110] Images formed using color toners and white toner have the following characteristics: When the recording medium on which an image is formed is the most common type of blank paper, the image is formed using only the four color toners of yellow, magenta, cyan, and black. Therefore, when the recording medium is blank paper and an image is formed on the blank paper, there is no particular need to use white toner. Note that hereinafter, "forming an image" will also be simply referred to as "printing."

[0111] The white toner needs to be used when the recording medium is colored paper such as black paper or craft paper, or transparent film that is frequently used in label printing areas. The usage rate of such recording media such as colored paper or transparent film is not very high as a percentage of the total printing. As a result, it is known that the consumption amount of white toner used during printing is significantly less than that of colored toner. Therefore, when viewed as a total product, the total toner production amount is significantly greater than that of colored toner, resulting in a large difference between the two.

[0112] Considering the above circumstances, it is advantageous to produce white toner by a pulverization method, and there are the following manufacturing reasons for this.

[0113] Because a toner production line using the polymerization method requires a large investment, it is common not to have an independent line for each type of toner (hereinafter also referred to as "toner type"). This makes it necessary to keep investment as low as possible by producing toner with fewer production lines than the number of types of toner used for printing.

[0114] First, a process for producing white toner and color toner on the same production line by polymerization will be considered.

[0115] When white toner and color toner are produced by polymerization, it is important to clean the toner production equipment and remove any adhering matter when switching toner types during printing. This is to prevent cross-contamination between color pigments of different hues that contain resins, etc., and this allows the production of high-quality toner. Therefore, in order to produce high-quality toner, the above-mentioned cleaning of the production equipment and removal of any adhering matter are necessary when switching toner types.

[0116] Color toners, regardless of color, are consumed in large quantities, and since appropriate amounts must be produced for each type of toner and then switched, the frequency of switching operations inevitably increases.

[0117] On the other hand, if white toner, which is consumed in small quantities, is produced on the same production line as color toners, the toner type will be changed frequently, which will increase the overall production cost.

[0118] In order to reduce the manufacturing cost, it is possible to reduce the frequency of manufacturing white toner and produce an amount of white toner to be consumed for a long period of time at one time. However, it is difficult to secure a storage space for the white toner, and the quality of the white toner deteriorates if the toner is stored for a long period of time.

[0119] In addition, because white toner is sensitive to cross-contamination during production due to the characteristics of its color, cleaning work when switching toner types must be performed more thoroughly than with color toners. For these reasons, it can be said that there are high hurdles to manufacturing white toner and color toner on the same production line using the polymerization method.

[0120] Next, we will consider a process in which color toners are produced by polymerization and white toners are produced by pulverization, and both toners are produced on separate production lines. This process has the following advantages over a process in which white toners and color toners are produced on the same production line by polymerization:

[0121] Pulverized toner manufacturing equipment (also called "powder manufacturing equipment") comes in a variety of sizes, from large-scale equipment to small-scale equipment. This makes it possible to select manufacturing equipment suited to the production scale for manufacturing white toner, which is premised on small-lot production. This makes it easy to change the scale of investment to match the scale of production, thereby reducing manufacturing costs. In terms of investment in manufacturing equipment, a manufacturing line can be set up by combining various powder manufacturing equipment already on the market. This allows for flexible response, and a manufacturing line can be set up with less investment.

[0122] For the above reasons, it is preferable to produce the white toner by a pulverization method and the color toner by a polymerization method, since this further reduces the production cost.

[0123] Furthermore, when the toner is produced by a polymerization method, it is preferable because it is easy to appropriately control the particle size, and when the toner is produced by a pulverization method, it is easy to add a charge control agent internally.

[0124] From the above, it is preferable that the color toner is a polymerized toner and the white toner is a pulverized toner, from the viewpoint of easy particle size control and easy addition of a charge control agent.

[0125] (1.6) Characteristics of each device in the image forming system As described above, the image forming system of the present invention is characterized by having at least an image carrier, a developing unit for color toner, and a transfer unit for white toner. In addition, as an embodiment, the system can be configured with various devices. For example, FIG. 4 shows an example of the device configuration that constitutes the image forming system of the present invention.

[0126] The image forming system 100 includes an image forming apparatus 110, a paper feeder 120, and a winding apparatus 130. The image forming apparatus 110, the paper feeder 120, and the winding apparatus 130 are connected to each other via signal lines so as to be able to communicate with each other.

[0127] Image forming system 100 may be configured, for example, by connecting image forming device 110, paper feeder 120, and winding device 130, each of which is housed in a separate housing, via a transport path. Image forming system 100 has image forming device 110, paper feeder 120, and winding device 130 housed in a single housing. In this way, the system may be configured by being connected via a transport path.

[0128] (1.6.1) Paper Feeder The paper feed device 120 stores and holds a paper feed roll (not shown) which is a roll of the recording medium P, and sends out the recording medium P to the image forming device 110 which is downstream in the conveying direction of the recording medium P.

[0129] (Recording medium) For example, a paper-based roll paper made of plain paper is used as the recording medium P. The roll paper includes film-based roll paper made of resin such as polypropylene or polyethylene terephthalate. Coated paper made of plain paper coated with resin can also be used. As for the type of surface other than the material, other than the roll paper, sheets of paper that are pre-cut to a size such as A3 and fed can also be used as the recording medium P.

[0130] (1.6.2) Winding device The recording medium P on which the image has been formed is transported to a winding device 130 downstream in the transport direction of the recording medium P, and is wound up by a recovery roll (not shown). The recording medium P is transported through a transport path 101. The transport direction is indicated by an arrow in FIG. 4.

[0131] (1.6.3) Image forming device The image forming apparatus 110 forms an image on the recording medium P by transferring and fixing a toner image (image) onto the recording medium P by electrophotography, and discharges the recording medium P to a winding device 130. The image forming apparatus 110 also has a control unit 10, a storage unit 20, a communication unit 30, an operation unit 40, a display unit 50, an image control unit 60, an image forming unit 70, a fixing unit 80, a conveying unit 90, and a color measurement unit 95. These are connected to each other via a bus.

[0132] FIG. 5 is a block diagram showing the configuration of the image forming apparatus.

[0133] [Control Unit] The control unit 10 may be configured with a CPU (Central Processing Unit). The control unit 10 controls each component of the image forming apparatus 110 and performs various calculation processes according to a program. That is, the control unit 10 performs general control and processing related to image formation while coordinating with each component constituting the image forming apparatus 110. Furthermore, the control unit 10 communicates with the paper feeder 120 and the winding device 130, obtains information from the paper feeder 120 and the winding device 130, and controls these devices.

[0134] The control unit 10 forms an image on the recording medium P by controlling the image control unit 60, the image forming unit 70, and the fixing unit 80 based on the print job.

[0135] The control unit 10 forms a patch image for color adjustment or the like on the recording medium P and measures the color by the color measurement unit 95. The control unit 10 corrects the image formation process by the image control unit 60 and the image forming unit 70 based on the color measurement result by the color measurement unit 95 of the patch image for color adjustment or the like. Specifically, the control unit 10 corrects a color conversion table for color converting the image data by the image control unit 60 based on the color measurement result by the color measurement unit 95 of the patch image for color adjustment or the like.

[0136] During non-colorimetry, when the colorimetry unit 95 is not measuring the color of the image formed on the recording medium P, the control unit 10 increases the distance between the recording medium P and the colorimeter compared to during colorimetry. This lengthens the transmission path to the colorimeter for the heat stored in the recording medium P as a result of the recording medium P being heated during the fixing operation by the fixing unit 80, thereby suppressing the temperature rise of the colorimeter.

[0137] [Storage section] The storage unit 20 may be composed of a RAM (Random Access Memory), a ROM (Read Only Memory), and a HDD (Hard Disk Drive). The RAM temporarily stores programs and data as a working area for the control unit 10. The ROM stores various programs and data in advance.

[0138] The HDD stores an operation system, each component of the image forming apparatus 110 controlled by the control unit 10, and the paper feeder 120. The HDD also stores various programs including a program for controlling the winding device 130. The HDD also saves print jobs, image data, and other various data received via the communication unit 30.

[0139] Here, the term "print job" is a general term for a print command to the image forming apparatus 110. This includes print data and print settings.

[0140] "Print data" refers to document data to be printed. This may include various types of data, such as image data, vector data, and text data. Specifically, it may be PDL (Page Description Language) data, PDF (Portable Document Format) data, or TIFF (Tagged Image File Format) data.

[0141] The "print settings" are settings related to image formation on the recording medium P. These may include, for example, the number of pages, page layout, number of copies to be printed, the type, thickness, and basis weight of the recording medium P. They may also include various settings such as the conveying speed of the recording medium P. The print settings can also be set from the operation unit 40.

[0142] [Communications Department] The communication unit 30 is an interface for communicating between the image forming apparatus 110 and an external device. A network interface conforming to standards such as Ethernet (registered trademark), SATA, PCI Express, USB, and IEEE1394 may be used as the communication unit 30. In addition, various local connection interfaces such as wireless communication interfaces such as Bluetooth (registered trademark) and IEEE802.11 may also be used as the communication unit 30.

[0143] [Operation unit] The operation unit 40 comprises a touch panel for performing various settings, a numeric keypad for setting the number of copies, etc., a start key for instructing the start of an operation, a stop key for instructing the stop of an operation, and various fixed keys such as a reset key for initializing various setting conditions.

[0144] [Display] The display unit 50 is composed of a touch panel for displaying various information and inputting various settings, and indicator lamps, etc. Note that functions that overlap between the operation unit 40 and the display unit 50 may be provided by either the operation unit 40 or the display unit 50.

[0145] [Image control section] The image control unit 60 performs layout processing and rasterization processing of the print data included in the print job received by the communication unit 30, and generates image data, which is data of an image in a bitmap format. The image data is a CMYK value or an RGB value for each pixel.

[0146] The image control unit 60 converts the color of the image data using a color conversion table, thereby ensuring color reproducibility in the image of the print data included in the print job formed by the image forming unit 70 and the fixing unit 80. To achieve this, the color conversion table is corrected based on the colorimetric values ​​of an adjustment patch image or the like measured by the colorimetric unit 95, as described below. The color conversion table is, for example, an ICC profile. The image control unit 60, together with the image forming unit 70 and the fixing unit 80, constitutes the image forming unit.

[0147] (1.7) Image forming system for continuous paper printing The image forming system of the present invention is equipped with an image reading unit that reads a patch image for color adjustment formed on continuous paper, and an image control unit, wherein the image reading unit is arranged opposite the continuous paper transported along a transport path, and the image control unit instructs the formation of the patch image for color adjustment at the end of the paper in a direction perpendicular to the paper feed direction, and based on the detection results from the image reading unit, instructs changes to the image formation conditions in the color toner image forming unit, the white toner image forming unit for forming the base layer, and the transfer unit, which is preferable from the standpoint of maintaining stable image density in real-time color adjustment.

[0148] The above real-time color adjustment can be performed, for example, by an image forming apparatus described in JP-A-2021-189267.

[0149] Note that "real-time color adjustment" refers to detecting the state of a patch image for color adjustment over time and adjusting the color fluctuation deviation in real time when continuously printing user-specified images based on the detection results.

[0150] (Image formation on sheet-fed paper and image formation on continuous paper) Let us consider a case where a sheet of paper is used as a recording medium and an image is formed by an image forming apparatus for sheet-fed printing. In this case, when an image is fixed to the recording medium (hereinafter, also simply referred to as "paper"), there is a gap between the sheets of paper on the fixing member. Therefore, when a color adjustment operation is required in image formation during continuous printing, it can be performed by utilizing the gap between the sheets of paper.

[0151] In contrast, let us consider the case where continuous paper is used as the recording medium and an image is formed by an image forming device for continuous paper printing. In this case, there is no space between the sheets of paper. Therefore, when a color adjustment operation is required in image formation during continuous printing, it is not possible to use the space between the sheets of paper. Therefore, when a color adjustment operation is required as described above, it becomes necessary to temporarily stop image formation.

[0152] In this case, for example, if the recording medium is white continuous paper, the pause in image formation causes the continuous paper to overrun due to the inertia of the paper transport. This can result in blank areas on the continuous paper where no image is formed. These blank areas become paper waste (waste paper), which increases the printing costs during image formation.

[0153] In addition, a separate operation for removing the blank portions is required in a post-printing process after printing, which reduces the overall productivity. Therefore, during image printing of one job in continuous printing, image formation is not stopped, and color adjustment operations are performed only before and after the job.

[0154] An image forming system having a function for real-time color adjustment can be suitably used as a system for continuous printing using continuous paper as a recording medium without relying on the above-mentioned color adjustment operation. This enables feedback control of the image formation process based on the detection results of the image reading unit during continuous printing, and significantly improves color stability throughout a print job.

[0155] (Real-time color adjustment) As mentioned above, "real-time color adjustment" refers to detecting the state of patch images for color adjustment over time and adjusting the color fluctuation deviation in real time when continuously printing user-specified images based on the detection results. Note that real-time color adjustment is performed, for example, as follows.

[0156] Before the start of a print job, single-color solid patch images of yellow (Y), magenta (M), cyan (C), and black (K) (hereinafter simply referred to as "YMCK solid patch images") are printed on the edge of the paper. At this time, the image density of each color in the YMCK solid patch images is measured. After the start of the print job, the image density of each color in the YMCK solid patch images is read by an image reading unit and compared with the image density before the start of the print job.

[0157] When there is a color whose image density has changed to a higher level after the start of the print job (during the print job) compared to the image density before the start of the print job, the development conditions for this color are shifted to a level that reduces the developability.

[0158] If there is a color whose image density has changed to a lower value after the start of the print job (during the print job) compared to the image density before the start of the print job, the development conditions for this color are shifted to a value that increases the developability. At this time, halftone patch images of Y, M, C, and K may be printed at one or more gradations on the edge of the paper as necessary, and other process conditions such as exposure conditions may also be adjusted according to the results.

[0159] By performing such adjustments for each color as needed during image formation, color variations during a print job can be suppressed without temporarily stopping image formation to perform color adjustment operations.

[0160] In the image forming system of the present invention, the printing operation in the print job includes an operation of forming an image using white toner. Therefore, it is preferable to print two types of patch images for the end patches and adjust the image creation process conditions for each color by reading the fluctuation in density of these patch images. The first of the two types of patch images is a patch image formed only with white toner. The second is a patch image in which a base layer is formed with white toner and a color toner image (toner of the above-mentioned YMCK colors) is formed on top of the base layer.

[0161] (1.7.1) Image reading unit The image reading unit according to the present invention is disposed opposite the continuous paper conveyed along the conveying path in order to read and detect the state of the patch image for color adjustment formed on the continuous paper (the state of color change over time).The detection result is sent to the image control unit, and based on the detection result, the image forming conditions of the color toner image forming unit, the white toner image forming unit for forming the base layer, and the transfer unit are appropriately changed.

[0162] The above-mentioned "patch image for color adjustment" is a patch image formed separately from the image specified by the user. This is formed at the edge of the continuous paper in the direction perpendicular to the paper feed direction (hereinafter, simply referred to as the "paper edge"), and the result of reading the state of the patch image is sent to the image control unit.

[0163] (1.7.2) Image control section The image control unit according to the present invention instructs the image forming unit and the transfer unit on the image forming conditions. Also, while an image is being formed based on instructions from a user, it instructs the formation of a patch image for color adjustment, separate from the image, on the edge of the paper. Then, based on the detection results sent from the image reading unit according to the present invention described above, it instructs the color toner image forming unit, the white toner image forming unit for forming a base layer, and the transfer unit to change the image forming conditions. In this way, by reading and detecting the state of the patch image and feeding it back, it is possible to appropriately adjust color variations caused by deviations from the optimal values ​​of the image forming conditions in image formation. As a result, it is possible to form a high-quality image.

[0164] (1.7.3) Formation of patch images for color adjustment and adjustment of conditions for forming user-specified images As mentioned above, the "patch image for color adjustment" is a patch image formed separately from the image specified by the user. This needs to be formed in an area that is not used by the user. Therefore, it is formed at the edge (paper edge) in the direction perpendicular to the paper feed direction of the continuous paper.

[0165] 6 is a flow chart showing the process of color adjustment in the image control unit when forming an image specified by a user. As shown in FIG. 6, color adjustment in the image control unit is performed as follows.

[0166] First, imaging parameters for various image forming conditions are determined to form an image specified by the user. At this time, a patch image for color adjustment is formed in advance at the edge of the paper. Continuous printing is started, and the color change state of the patch image over time during continuous printing is detected by the image reading unit described above. Then, from the detection result, a value of color variation due to deviation from the optimal value of the image forming conditions is calculated. Next, the calculated color variation value is fed back to the image control unit described above. At this time, if there is no particular need for feedback, printing continues as is and color adjustment is completed.

[0167] The patch image for color adjustment is formed, for example, as shown in FIG. 7 below. FIG. 7 is a schematic diagram of patch image formation of each color gradation pattern in an area not used by the user (shaded area in FIG. 7). Note that in FIG. 7, the patch image P color are yellow (Y), magenta (M), cyan (C), black (K), red (R), green (G), blue (B) and process black (Pbk). The patch images may be formed only in the 100% gradation area, but if color adjustment is desired including intermediate tones, color adjustment may be performed by forming patch images in multiple stages with different gradation values. Note that D in FIG. 7 is the paper transport direction, and P is the user is the user's printed image.

[0168] The patch images are formed as frequently as necessary during continuous printing, and the state of the patch images for color adjustment (the state of color change over time) is read and detected by an image reading unit disposed after fixing. Then, color adjustment of the image designated by the user is performed based on the detection result.

[0169] (1.8) White toner and colored toner The white toner according to the present invention contains at least a white colorant (hereinafter also referred to as "white colorant") and a binder resin. In addition, it may contain other additives such as a release agent and external additives as necessary. On the other hand, the color toner contains a binder resin and a colorant other than white (hereinafter also referred to as "color colorant"). In addition, it may contain other additives such as a release agent and external additives as necessary.

[0170] (1.8.1) Colorants (Colorant for white toner) Colorants for the white toner according to the present invention include, for example, inorganic pigments or organic pigments.

[0171] Examples of inorganic pigments include titanium white, zinc white, titanium strontium white, heavy calcium carbonate, light calcium carbonate, titanium dioxide, aluminum hydroxide, satin white, talc, calcium sulfate, barium sulfate, zinc oxide, magnesium oxide, magnesium carbonate, amorphous silica, colloidal silica, white carbon, kaolin, calcined kaolin, delaminated kaolin, aluminosilicate, sericite, bentonite, and smexite.

[0172] Examples of organic pigments include polystyrene resin particles and urea formalin resin particles.

[0173] Among the above, titanium oxide having a rutile crystal structure and titanium oxide having an anatase crystal structure are particularly preferred as colorants for white toners because of their high whiteness. By using titanium oxide having a particle size within the range of 10 to 1000 nm as a colorant, a white toner having high pigment dispersibility can be obtained, which is preferable. Among titanium oxides, titanium oxide having a rutile crystal structure is preferred from the viewpoint of hiding power.

[0174] In order to stabilize the electrostatic properties of the toner, the electrical resistivity of the pigment used as the colorant is set to 1×10 8 ~1×10 12 It is preferable to keep it in the range of Ω·cm.

[0175] By treating the pigment surface with, for example, a silane coupling agent, silicone oil, a fatty acid such as stearic acid, an alcohol, an amine such as trimethanolamine, or the like, it is possible to easily achieve both extremely high pigment dispersibility and toner charging stability.

[0176] The content of the colorant is preferably within a range of 20 to 170 parts by mass, more preferably within a range of 40 to 80 parts by mass, and further preferably within a range of 50 to 70 parts by mass, relative to 100 parts by mass of the binder resin in the toner particles.

[0177] (Coloring agent for color toner) As colorants for the color toner according to the present invention, for example, yellow colorants, magenta colorants, cyan colorants, orange colorants, green colorants and black colorants can be used.

[0178] Examples of yellow colorants for yellow toner include dyes such as CI Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, and 162. Examples of pigments include CI Pigment Yellow 14, 17, 74, 93, 94, 138, 155, 180, and 185. Mixtures of these may also be used.

[0179] Examples of magenta colorants for magenta toner include dyes such as CI Solvent Red 1, 49, 52, 58, 63, 111, and 122. Examples of pigments include CI Pigment Red 5, 48:1, 53:1, 57:1, 122, 139, 144, 149, 166, 177, 178, and 222. Mixtures of these may also be used.

[0180] Examples of cyan colorants for cyan toners include dyes such as CI Solvent Blue 25, 36, 60, 70, 93, and 95. Examples of pigments include CI Pigment Blue 1, 7, 15:3, 18:3, 60, 62, 66, and 76. Mixtures of these can also be used.

[0181] Examples of orange colorants for orange toner include dyes such as CI Solvent Orange 63, 68, 71, 72, and 78. Examples of pigments include CI Pigment Orange 16, 36, 43, 51, 55, 59, 61, and 71. Mixtures of these can also be used.

[0182] Examples of green colorants for green toner include dyes such as CI Solvent Green 3, 5, and 28. Examples of pigments include CI Pigment Green 7. Mixtures of these can also be used.

[0183] Examples of black colorants for black toner include carbon black, magnetic materials, iron-titanium composite oxide black, etc. Examples of carbon black that can be used include channel black, furnace black, acetylene black, thermal black, lamp black, etc. Examples of magnetic materials that can be used include ferrite, magnetite, etc.

[0184] (1.8.2) Binder resin The binder resin contained in the white toner and color toner according to the present invention preferably contains a crystalline polyester and an amorphous resin.

[0185] (Crystalline polyester) The crystalline polyester is a known polyester obtained by polycondensation reaction between a divalent or higher carboxylic acid (polyvalent carboxylic acid component) and / or a hydroxycarboxylic acid and a divalent or higher alcohol (polyhydric alcohol component). Among them, the crystalline polyester refers to a polyester that has a clear melting peak, not a stepwise change in endothermic heat, in differential scanning calorimetry (DSC). Specifically, the clear melting peak is a peak that means the following:

[0186] In the DSC curve obtained by differential scanning calorimetry of the above-mentioned crystalline polyester alone, the half-value width of the melting peak in the second heating process is within 15°C.

[0187] The melting point of the crystalline polyester is preferably in the range of 65 to 85°C, more preferably in the range of 75 to 85°C. By having the melting point of the crystalline polyester in this range, sufficient low-temperature fixability and excellent image storage stability can be obtained. The melting point of the crystalline polyester can be controlled by the resin composition. Here, the melting point of the crystalline polyester is the peak top temperature of the melting peak in the second heating process in the DSC curve obtained by differential scanning calorimetry of the above-mentioned crystalline polyester alone. In addition, when there are multiple melting peaks in the DSC curve, the peak top temperature of the melting peak with the largest amount of heat absorption is taken as the melting point.

[0188] The melting point (Tm) of the crystalline polyester is the temperature at the top of the endothermic peak. It can be measured by DSC using a Diamond DSC (manufactured by PerkinElmer). Specifically, it is measured as follows.

[0189] The sample is sealed in an aluminum pan KIT No. B0143013 and set in the sample holder of a thermal analysis device Diamond DSC (PerkinElmer). The temperature is then changed in the order of heating, cooling, and heating. The temperature is raised from room temperature (25°C) during the first heating and from 0°C during the second heating to 150°C at a heating rate of 10°C / min. Then, 150°C is held for 5 minutes, and during cooling, the temperature is lowered from 150°C to 0°C at a heating rate of 10°C / min and the temperature of 0°C is held for 5 minutes. The temperature at the top of the endothermic peak in the endothermic curve obtained during the second heating is measured as the melting point.

[0190] The polyvalent carboxylic acid component for forming the crystalline polyester is a compound containing two or more carboxy groups in one molecule.

[0191] Specifically, examples of the dicarboxylic acid include saturated aliphatic dicarboxylic acids such as succinic acid, sebacic acid, and dodecanedioic acid. Examples of the dicarboxylic acid include alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Examples of the dicarboxylic acid include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid. Examples of the dicarboxylic acid include polyvalent carboxylic acids having three or more valences such as trimellitic acid and pyromellitic acid. Examples of the dicarboxylic acid include anhydrides of these carboxylic acid compounds, and alkyl esters having 1 to 3 carbon atoms.

[0192] As the polybasic carboxylic acid component for forming the crystalline polyester, it is preferable to use a saturated aliphatic dicarboxylic acid. These may be used alone or in combination of two or more.

[0193] The polyhydric alcohol component for forming the crystalline polyester is a compound containing two or more hydroxy groups in one molecule.

[0194] Specific examples of the diol include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, neopentyl glycol, and 1,4-butenediol, as well as trihydric or higher polyhydric alcohols such as glycerin, pentaerythritol, trimethylolpropane, and sorbitol.

[0195] As the polyhydric alcohol component for forming the crystalline polyester, it is preferable to use an aliphatic diol. These may be used alone or in combination of two or more.

[0196] The method for producing the crystalline polyester is not particularly limited. The crystalline polyester can be produced by a general polyester polymerization method in which the above-mentioned polyvalent carboxylic acid and polyhydric alcohol are reacted in the presence of a catalyst. For example, it is preferable to produce the crystalline polyester by using a direct polycondensation method or an ester exchange method depending on the type of monomer.

[0197] In addition, a linear aliphatic hydroxycarboxylic acid can be used in combination with the polyvalent carboxylic acid and / or polyhydric alcohol. Examples of linear aliphatic hydroxycarboxylic acids for forming crystalline polyester include 5-hydroxypentanoic acid, 6-hydroxyhexanoic acid, 7-hydroxypentanoic acid, 8-hydroxyoctanoic acid, 9-hydroxynonanoic acid, 10-hydroxydecanoic acid, 12-hydroxydodecanoic acid, 14-hydroxytetradecanoic acid, 16-hydroxyhexadecanoic acid, and 18-hydroxyoctadecanoic acid. In addition, lactone compounds cyclized with these hydroxycarboxylic acids, or alkyl esters with alcohols having 1 to 3 carbon atoms, etc. can be used. These may be used alone or in combination of two or more.

[0198] In addition, when forming the crystalline polyester, the reaction can be easily controlled by using a polyvalent carboxylic acid and a polyhydric alcohol component, which is preferable because it allows a resin having a desired molecular weight to be obtained.

[0199] Examples of catalysts that can be used in the production of crystalline polyesters include titanium catalysts such as titanium tetraethoxide, titanium tetrapropoxide, titanium tetraisopropoxide, and titanium tetrabutoxide, as well as tin catalysts such as dibutyltin dichloride, dibutyltin oxide, and diphenyltin oxide.

[0200] The ratio of the polyvalent carboxylic acid component to the polyhydric alcohol component is preferably such that the equivalent ratio of the hydroxyl group of the polyhydric alcohol component to the carboxyl group of the polyvalent carboxylic acid component is within the range of 1.5 / 1 to 1 / 1.5. It is more preferably within the range of 1.2 / 1 to 1 / 1.2. The equivalent ratio of the hydroxyl group [-(OH)] to the carboxyl group [-(COOH)] of the polyvalent carboxylic acid component is expressed as follows: Equivalence ratio: [-(OH)] / [-(COOH)]

[0201] The acid value of the crystalline polyester is preferably within a range of 5 to 30 mgKOH / g, more preferably within a range of 10 to 25 mgKOH / g, and further preferably within a range of 15 to 25 mgKOH / g.

[0202] The acid value is the mass of potassium hydroxide (KOH) required to neutralize the acid contained in 1 g of a sample, expressed in mg. The acid value of a resin is measured in accordance with JIS K 0070-1992.

[0203] The molecular weight of the crystalline polyester is measured by gel permeation chromatography (GPC). The weight average molecular weight (Mw) calculated from the molecular weight distribution measured by this GPC is preferably within the range of 5,000 to 50,000. The number average molecular weight (Mn) is preferably within the range of 1,500 to 25,000.

[0204] The content of the crystalline polyester in the binder resin is preferably within a range of 5 to 20% by mass, more preferably within a range of 5 to 10% by mass. By making the content of the crystalline polyester in the binder resin 5% by mass or more, sufficient low-temperature fixability can be reliably obtained. Furthermore, by making the content of the crystalline polyester in the binder resin 20% by mass or less, the crystalline polyester can be reliably introduced into the toner during toner production.

[0205] As the crystalline polyester, a styrene-acrylic modified crystalline polyester in which a styrene-acrylic polymerized segment and a crystalline polyester polymerized segment are bonded may be used.

[0206] Here, "styrene-acrylic modified crystalline polyester" refers to the following resin.

[0207] A resin composed of polyester molecules with a block copolymer structure, in which styrene-acrylic copolymer molecular chains (styrene-acrylic polymerization segments) are chemically bonded to crystalline polyester molecular chains (crystalline polyester polymerization segments).

[0208] The method for forming the crystalline polyester polymer segment is not particularly limited. The specific types of polyvalent carboxylic acid and polyhydric alcohol used in forming the polymer segment and the polycondensation conditions of these monomers are the same as those described above, so the explanation is omitted here.

[0209] On the other hand, the styrene-acrylic polymerized segment constituting the styrene-acrylic modified crystalline polyester is formed by addition polymerization of at least a styrene monomer and a (meth)acrylic acid ester monomer. The styrene monomer and the (meth)acrylic acid ester monomer used are not particularly limited, but may be one or more selected from the following:

[0210] (1) Styrene monomer Styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene and their derivatives, etc.; (2) (Meth)acrylic acid ester monomer Methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate (n-butyl (meth)acrylate), isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-stearyl (meth)acrylate, dodecyl (meth)acrylate, phenyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and derivatives thereof;

[0211] In this specification, the term "(meth)acrylic acid" includes both acrylic acid and methacrylic acid.

[0212] The styrene-acrylic polymer segment may be formed by using the following monomers in addition to the above monomers.

[0213] (3) Vinyl esters Vinyl propionate, vinyl acetate, vinyl benzoate, etc.; (4) Vinyl ethers Vinyl methyl ether, vinyl ethyl ether, etc.; (5) Vinyl ketones Vinyl methyl ketone, vinyl ethyl ketone, vinyl hexyl ketone, etc.; (6) N-vinyl compounds N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidone, etc.; (7) Other monomers Vinyl compounds such as vinylnaphthalene and vinylpyridine; acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile and acrylamide; and the like.

[0214] The method for forming the styrene-acrylic polymerized segment is not particularly limited. Any polymerization initiator such as peroxides, persulfides, persulfates, and azo compounds that are commonly used in the polymerization of the above monomers can be used. The styrene-acrylic polymerized segment can be formed by polymerization using a known polymerization method such as bulk polymerization, solution polymerization, emulsion polymerization, miniemulsion polymerization, and dispersion polymerization.

[0215] The content of the crystalline polyester polymer segment in the styrene-acrylic modified crystalline polyester is not particularly limited, but is preferably within a range of 60 to 99% by mass, more preferably within a range of 70 to 98% by mass, based on 100% by mass of the styrene-acrylic modified polyester.

[0216] The content ratio of the styrene-acrylic polymerized segment in the styrene-acrylic modified crystalline polyester (hereinafter also referred to as "styrene-acrylic modification amount") is not particularly limited. The content ratio is preferably within a range of 1 to 40 mass% relative to 100 mass% of the styrene-acrylic modified crystalline polyester. Also, it is more preferably within a range of 2 to 30 mass%.

[0217] The amount of styrene-acrylic modification is specifically the total mass of the resin material used to synthesize the styrene-acrylic modified crystalline polyester, i.e., the ratio of the total mass of the styrene monomer and the (meth)acrylic acid ester monomer to the total mass of the monomers (1) to (4) below. (1) Monomers for synthesizing unmodified crystalline polyesters that become crystalline polyester polymerization segments (2) Styrene monomer that becomes the styrene-acrylic polymerization segment (3) (Meth)acrylic acid ester monomer (4) Bireactive monomers for binding these

[0218] Here, the "bireactive monomer" is a monomer that bonds a styrene-acrylic polymerized segment and a crystalline polyester polymerized segment, and has both a group selected from a hydroxy group, a carboxy group, an epoxy group, a primary amino group, and a secondary amino group that forms a crystalline polyester polymerized segment, and an ethylenically unsaturated group that forms a styrene-acrylic polymerized segment in the molecule.

[0219] Specific examples of the bireactive monomer include acrylic acid, methacrylic acid, fumaric acid, maleic acid, etc. Furthermore, esters of these hydroxyalkyls (having 1 to 3 carbon atoms) may be used, but from the viewpoint of reactivity, acrylic acid, methacrylic acid, or fumaric acid is preferred. The styrene-acrylic polymerized segment and the crystalline polyester polymerized segment are bonded via this bireactive monomer.

[0220] From the viewpoint of improving low-temperature fixability, the amount of the bireactive monomer used is preferably within a range of 1 to 20% by mass, with the total amount of the monomers constituting the styrene-acrylic polymer segment being taken as 100% by mass.

[0221] The method for producing the styrene-acrylic modified crystalline polyester is not particularly limited as long as it is a method capable of forming a polymer having a structure in which a crystalline polyester polymer segment and a styrene-acrylic polymer segment are chemically bonded. Specific examples of the method for producing the styrene-acrylic modified crystalline polyester include the following methods.

[0222] (A) A method in which a crystalline polyester polymer segment is polymerized in advance, and a bireactive monomer is reacted with the crystalline polyester polymer segment, and then a styrene monomer and a (meth)acrylic acid ester monomer for forming a styrene-acrylic polymer segment are reacted to form the styrene-acrylic polymer segment; (B) A method in which a styrene-acrylic polymerized segment is polymerized in advance, and then the styrene-acrylic polymerized segment is reacted with a bireactive monomer, and then further reacted with a polyvalent carboxylic acid and a polyhydric alcohol for forming a crystalline polyester polymerized segment, thereby forming a crystalline polyester polymerized segment; (C) A method in which the crystalline polyester polymer segment and the styrene-acrylic polymer segment are polymerized in advance, and then reacted with a bireactive monomer to bond the two.

[0223] Among the above formation methods (A) to (C), the method (A) is preferred from the viewpoint of simplifying the production process.

[0224] (amorphous resin) In the present invention, the amorphous resin may be an amorphous polyester or an amorphous vinyl resin.

[0225] The term "amorphous resin" refers to a resin that does not show a clear endothermic peak in differential scanning calorimetry (DSC). In other words, it usually does not have a melting point (a clear endothermic peak in a DSC curve measured using a differential scanning calorimetry (DSC) measuring device) and has a relatively high glass transition point (Tg). More specifically, the Tg of the amorphous resin measured by a differential scanning calorimetry device is preferably within a range of 35 to 70°C, more preferably within a range of 50 to 65°C. By having the Tg of the amorphous resin be 35°C or higher, it is possible to impart sufficient thermal strength to the toner, and sufficient heat-resistant storage stability can be obtained. In addition, by having the Tg of the amorphous resin be 70°C or lower, sufficient low-temperature fixability can be reliably obtained.

[0226] The Tg of the amorphous resin is measured by the method (DSC method) specified in ASTM (American Society for Testing and Materials) D3418-82. That is, 4.5 mg of the measurement sample (amorphous resin) is precisely weighed to two decimal places and sealed in an aluminum pan. Then, it is set in the sample holder of a differential scanning calorimeter "DSC8500" (manufactured by PerkinElmer). An empty aluminum pan is used as a reference, and temperature control is performed in the following order: heating-cooling-heating at a measurement temperature of -10 to 120°C, a heating rate of 10°C / min, and a cooling rate of 10°C / min. Then, analysis is performed based on the data from the second heating. The value of the intersection between the extension line of the baseline before the rise of the first endothermic peak and the tangent line showing the maximum slope from the rising part of the first endothermic peak to the peak apex is taken as the glass transition point.

[0227] The molecular weight of the amorphous resin measured by gel permeation chromatography (GPC) is preferably in the range of 1500 to 25000 in number average molecular weight (Mn). Also, it is preferable that the weight average molecular weight (Mw) is in the range of 10000 to 80000. By having the molecular weight of the amorphous resin in the above range, sufficient low-temperature fixability and excellent heat-resistant storage stability can be reliably achieved. The molecular weight measurement of the amorphous resin by GPC is performed in the same manner as above, except that the amorphous resin is used as the measurement sample.

[0228] [Amorphous polyester] The amorphous polyester is a polyester other than the crystalline polyester.

[0229] The acid value of the amorphous polyester is preferably within the range of 5 to 45 mgKOH / g, more preferably within the range of 5 to 30 mgKOH / g. If the acid value is 45 mgKOH / g or less, it is preferable in that the hygroscopicity is not increased and the chargeability can be prevented from decreasing even under high humidity. If the acid value is 5 mgKOH / g or more, it is preferable in that the dispersion stability of the resin particles can be maintained and the toner can be easily produced. The acid value can be determined in the same manner as described in the explanation of the crystalline polyester.

[0230] The amorphous polyester may be a single type of amorphous polyester, or a mixture of two or more types of amorphous polyesters.

[0231] The amorphous polyester may be a known polyester. The amorphous polyester is synthesized from a polyvalent carboxylic acid component and a polyhydric alcohol component. The amorphous polyester may be a commercially available product or a synthesized product.

[0232] Examples of the polyhydric alcohol component that can be used include diols such as ethylene glycol, propylene glycol, 1,4-butanediol, 2,3-butanediol, diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, bisphenol A, hydrogenated bisphenol A, BPA-PO (an n-mol propylene oxide adduct of bisphenol A), and BPA-EO (an n-mol ethylene oxide adduct of bisphenol A).

[0233] Furthermore, trihydric or higher alcohols such as glycerin, sorbitol, 1,4-sorbitan, and trimethylolpropane can also be used.

[0234] Among these, bisphenol A, hydrogenated bisphenol A, BPA-PO, or BPA-EO is preferable. BPA-PO or BPA-EO is more preferable. Furthermore, a propylene oxide 2-mol adduct of bisphenol A or an ethylene oxide 2-mol adduct of bisphenol A is even more preferable. These may be used alone or in combination of two or more.

[0235] Examples of the polycarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid. Examples of the polycarboxylic acid component include aliphatic saturated dicarboxylic acids such as succinic acid, alkenylsuccinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, and 1,18-octadecanedicarboxylic acid. Examples of the polycarboxylic acid component include aliphatic unsaturated dicarboxylic acids such as maleic acid, maleic acid, fumaric acid, itaconic acid, itaconic anhydride, citraconic acid, citraconic acid, and mesaconic acid. Examples of the polycarboxylic acid component include alicyclic polycarboxylic acids such as cyclohexanedicarboxylic acid. Examples of the salts, lower alkyl esters, and acid anhydrides of these compounds include the above compounds.

[0236] Among these, aromatic dicarboxylic acids, their salts, lower alkyl esters, or acid anhydrides are preferred. Terephthalic acid, phthalic acid, their salts, lower alkyl esters, or acid anhydrides are more preferred. These polyvalent carboxylic acid components may be used alone or in combination of two or more.

[0237] By including a trivalent or higher carboxylic acid as the polyvalent carboxylic acid component, the polymer chain can have a crosslinked structure. The crosslinked structure can further provide an effect of fixing the crystalline polyester once it has been mixed with the amorphous polyester, making it difficult for the crystalline polyester to separate.

[0238] Examples of trivalent or higher carboxylic acids include trimellitic acids such as 1,2,4-benzenetricarboxylic acid and 1,2,5-benzenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, hemimellitic acid, trimesic acid, mellophanic acid, prenic acid, pyromellitic acid, mellitic acid, 1,2,3,4-butanetetracarboxylic acid, their salts, lower alkyl esters and acid anhydrides, etc. Among these, trimellitic acid, its salts, lower alkyl esters and acid anhydrides are particularly preferred.

[0239] When a dicarboxylic acid and a tri- or higher carboxylic acid are contained as the polyvalent carboxylic acid component, the preferred amount of the tri- or higher carboxylic acid to be added is as follows.

[0240] The content is preferably within a range of 1 to 30 mol %, more preferably within a range of 5 to 20 mol %, and more preferably within a range of 10 to 15 mol %, based on the total number of moles of the polyvalent carboxylic acid component.

[0241] The polyvalent carboxylic acid component may contain, in addition to the above-mentioned compounds, a dicarboxylic acid component having a sulfonic acid group.

[0242] The amorphous polyester is produced by a polycondensation reaction between a polyvalent carboxylic acid component and a polyhydric alcohol component at a polymerization temperature in the range of 180 to 260°C, although there is no particular limitation. It is preferable to reduce the pressure in the reaction system as necessary and to carry out the reaction while removing water and alcohol generated during the condensation. The polymerization time is not particularly limited, but is preferably in the range of 1 to 10 hours, and more preferably in the range of 2 to 6 hours.

[0243] If the polymerizable monomers (polyvalent carboxylic acid component, polyhydric alcohol component) are not soluble or compatible at the reaction temperature, a high boiling point solvent may be added as a dissolution aid to dissolve them. The polycondensation reaction is carried out while distilling off the dissolution aid. If a polymerizable monomer with poor compatibility is present in the copolymerization reaction, it is recommended that the poorly compatible polymerizable monomer and the polymerizable monomer be condensed in advance with the acid or alcohol to be polycondensed, and then polycondensed with the main component.

[0244] Examples of catalysts that can be used in the production of amorphous polyesters include alkali metal compounds containing, for example, sodium, lithium, etc. Also, examples of catalysts include Group 2 metal compounds containing, for example, magnesium, calcium, etc. Also, examples of catalysts include metal compounds containing, for example, zinc, manganese, antimony, titanium, tin, zirconium, germanium, etc. Also, examples of catalysts that can be used include phosphorous compounds, phosphoric acid compounds, and amine compounds. These may be used alone or in combination of two or more.

[0245] Among them, from the viewpoint of making Mw / Mn smaller, metal compounds containing zinc, manganese, antimony, titanium, tin, zirconium, germanium, etc. are preferable. Also, metal compounds of tin (tin-based catalysts) are more preferable. Tin-based catalysts are not particularly limited, but examples thereof include dibutyltin oxide, etc.

[0246] The amount of catalyst added is not particularly limited, but is preferably within the range of 0.00001 to 10 mass% based on the total amount of polycarboxylic acid. When the amount of catalyst added is increased, the reaction can proceed more reliably, and when the amount of catalyst added is decreased, it is more economical.

[0247] The content of the amorphous polyester is preferably 5 to 30% by mass, more preferably 5 to 20% by mass, of the total binder resin. When the content is within this range, the toner obtained has excellent blocking resistance and low-temperature fixability.

[0248] [Amorphous vinyl resin] The amorphous vinyl resin is not particularly limited as long as it is a polymer of a vinyl compound. For example, acrylic ester resin, styrene-(meth)acrylic ester resin, ethylene-vinyl acetate resin, etc. may be mentioned. These may be used alone or in combination of two or more.

[0249] Among the above amorphous vinyl resins, styrene-(meth)acrylic acid ester resins (hereinafter also referred to as "styrene-acrylic resins") are preferred in consideration of the plasticity during thermal fixing. Therefore, the following will explain styrene-acrylic resins as amorphous vinyl resins.

[0250] Styrene-acrylic resin is formed by addition polymerization of at least styrene monomer and (meth)acrylic acid ester monomer. The styrene monomer referred to here includes not only styrene represented by the structural formula CH2=CH-C6H5, but also those having a structure with a known side chain or functional group in the styrene structure. The (meth)acrylic acid ester monomer referred to here includes not only acrylic acid ester and methacrylic acid ester represented by the structural formula CH2=CHCOOR (R is an alkyl group), but also esters having a known side chain or functional group in the structure of acrylic acid ester derivatives and methacrylic acid ester derivatives.

[0251] Specific examples of styrene monomers and (meth)acrylic acid ester monomers capable of forming styrene-acrylic resins are shown below. The monomers used in the present invention are not limited to the following.

[0252] Specific examples of styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, etc. These styrene monomers can be used alone or in combination of two or more.

[0253] Specific examples of the (meth)acrylic acid ester monomer include acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, and phenyl acrylate. Specific examples of the (meth)acrylic acid ester monomer include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate, and dimethylaminoethyl methacrylate.

[0254] These acrylic acid ester monomers or methacrylic acid ester monomers can be used alone or in combination of two or more kinds. That is, any of the following (1), (2) and (3) is possible. (1) Forming a copolymer using a styrene monomer and two or more acrylic acid ester monomers (2) Forming a copolymer using a styrene monomer and two or more methacrylic acid ester monomers. (3) Forming a copolymer by using styrene monomer in combination with acrylate and methacrylate monomers.

[0255] The content of structural units derived from styrene monomers in the styrene-acrylic resin is preferably within a range of 60 to 85% by mass relative to the total amount of the styrene-acrylic resin, and the content of structural units derived from (meth)acrylic acid ester monomers in the styrene-acrylic resin is preferably within a range of 15 to 40% by mass relative to the total amount of the styrene-acrylic resin.

[0256] Furthermore, in addition to the above-mentioned styrene monomer and (meth)acrylic acid ester monomer, the styrene-acrylic resin may be addition polymerized with compounds having a carboxy group, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, cinnamic acid, fumaric acid, maleic acid monoalkyl ester, and itaconic acid monoalkyl ester; and compounds having a hydroxy group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and polyethylene glycol mono(meth)acrylate.

[0257] The content of the structural units derived from the above compounds in the styrene-acrylic resin is preferably within a range of 0.1 to 15 mass % relative to the total amount of the styrene-acrylic resin.

[0258] The content of the amorphous vinyl resin is preferably within a range of 40 to 95% by mass, more preferably 60 to 90% by mass, of the total binder resin. In such a range, the toner obtained has a high degree of freedom in resin design and is easy to control the charge.

[0259] (1.8.3) Other components (Release agent) The white toner and color toner according to the present invention may contain a release agent. As the release agent, various known waxes can be used.

[0260] Examples of waxes include polyolefin waxes such as polyethylene wax and polypropylene wax. Examples of waxes include branched chain hydrocarbon waxes such as microcrystalline wax. Examples of waxes include long chain hydrocarbon waxes such as paraffin wax and sazol wax. Examples of waxes include dialkyl ketone waxes such as distearyl ketone. Examples of waxes include ester waxes such as carnauba wax, montan wax, behenyl behenate, trimethylolpropane tribehenate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, tristearyl trimellitate, and distearyl maleate. Examples of waxes include amide waxes such as ethylenediamine behenylamide and tristearyl trimellitate.

[0261] It is preferable to use a release agent that does not have any interaction, such as being compatible with the resin constituting the binder resin.

[0262] Among these, from the viewpoint of releasability during low-temperature fixing, it is preferable to use a release agent having a low melting point, specifically, a melting point within the range of 60 to 100° C. In addition, it is preferable to use a release agent having a melting point of about (Mp1-10) to (Mp1+20)° C., where Mp1 is the melting point of the crystalline polyester constituting the binder resin.

[0263] The content of the release agent in the toner is preferably within a range of 1 to 20% by mass, more preferably within a range of 5 to 20% by mass. By having the content of the release agent in the toner within the above range, both separation property and fixability can be reliably achieved.

[0264] A method of introducing the release agent into the toner includes a method in which particles consisting of only the release agent are aggregated and fused in an aqueous medium together with amorphous resin particles, crystalline polyester particles, etc. in the aggregation and fusion process of the toner manufacturing method described below. The release agent particles can be obtained as a dispersion liquid in which the release agent is dispersed in an aqueous medium. The dispersion liquid of the release agent particles can be prepared as follows.

[0265] The aqueous medium containing the surfactant is heated to a temperature higher than the melting point of the release agent, and the molten release agent solution is added. This provides mechanical energy such as mechanical stirring or ultrasonic energy to finely disperse the release agent, and then the mixture is cooled.

[0266] In addition, when the amorphous resin is a styrene-acrylic resin, the release agent can be incorporated into the toner by mixing the release agent in advance with the amorphous resin particles (styrene-acrylic resin particles) that are to be subjected to the aggregation and fusion processes.

[0267] Specifically, the release agent is dissolved in a solution of polymerizable monomers for forming styrene-acrylic resin. This solution is added to an aqueous medium containing a surfactant, and finely dispersed by applying mechanical energy such as mechanical stirring or ultrasonic energy in the same manner as above. A polymerization initiator is then added and polymerization is carried out at the desired polymerization temperature, a so-called mini-emulsion polymerization method, by which a dispersion of amorphous resin particles containing the release agent can be prepared.

[0268] (Charge control agent) As the charge control agent, various known compounds can be used. The content of the charge control agent in the toner is preferably within a range of 0.1 to 10% by mass, and more preferably within a range of 1 to 5% by mass.

[0269] (1.8.4) Average circularity of toner From the viewpoints of the stability of charging characteristics and low-temperature fixability, the average circularity of each toner particle constituting the toner according to the present invention is preferably within a range of 0.930 to 1.000, and more preferably within a range of 0.950 to 0.995.

[0270] When the average circularity is within the above range, individual toner particles are less likely to be crushed, contamination of the frictional charge imparting member is suppressed, the chargeability of the toner is stabilized, and the image formed has high quality.

[0271] In the present invention, the average circularity of the toner is measured using "FPIA-3000" (manufactured by Sysmex Corporation).

[0272] Specifically, the measurement is carried out as follows.

[0273] The sample (toner) is mixed with an aqueous solution containing a surfactant, and dispersed by ultrasonic dispersion treatment for 1 minute. After that, using the "FPIA-3000" (manufactured by Sysmex Corporation), images are taken at an appropriate concentration of 3,000 to 10,000 HPF detections in the HPF (high magnification imaging) mode under the measurement conditions. Then, the circularity of each toner particle is calculated according to the following formula (T), and the circularity of each toner particle is added and divided by the total number of toner particles.

[0274] Formula (T): Circularity = (perimeter of a circle with the same projected area as the particle image) / (perimeter of the projected image of the particle)

[0275] (1.8.5) Toner manufacturing method The method for producing the toner (toner particles) according to the present invention is not particularly limited, and examples thereof include a pulverization method and a known polymerization method such as a suspension polymerization method, an emulsion polymerization aggregation method, and a dispersion polymerization method.

[0276] Among them, the white toner according to the present invention can be either polymerized toner particles or pulverized toner particles. Among them, in order to adjust the variation coefficient of the particle size distribution to the range of 20 to 30%, it is preferable to adopt the polymerization method, and it is particularly preferable to adopt the emulsion polymerization aggregation method. The emulsion polymerization aggregation method will be described later.

[0277] The pulverization method involves, for example, blending all the toner components in a predetermined amount, mixing and pulverizing them to thoroughly mix all the components, and then pulverizing the resulting mixture into fine powder. Another well-known method for forming toner powder involves ball milling colorants, resins and solvents, and spray drying the resulting toner formulation mixture. Furthermore, the pulverization method is advantageous in terms of production costs, as mentioned above.

[0278] As mentioned above, it is advantageous to produce white toner by the pulverization method, for the following manufacturing reasons.

[0279] Because a toner production line using the polymerization method requires a large investment, it is common not to have an independent line for each type of toner (hereinafter also referred to as "toner type"). This makes it necessary to keep investment as low as possible by producing toner with fewer production lines than the number of types of toner used for printing.

[0280] First, a process for producing white toner and color toner on the same production line by polymerization will be considered.

[0281] When white toner and color toner are produced by polymerization, it is important to clean the toner production equipment and remove any adhering matter when switching toner types during printing. This is to prevent cross-contamination between color pigments of different hues that contain resins, etc., and this allows the production of high-quality toner. Therefore, in order to produce high-quality toner, the above-mentioned cleaning of the production equipment and removal of any adhering matter are necessary when switching toner types.

[0282] Color toners, regardless of color, are consumed in large quantities, and since appropriate amounts must be produced for each type of toner and then switched, the frequency of switching operations inevitably increases.

[0283] On the other hand, if white toner, which is consumed in small quantities, is produced on the same production line as color toners, the toner type will be changed frequently, which will increase the overall production cost.

[0284] In order to reduce the manufacturing cost, it is possible to reduce the frequency of manufacturing white toner and produce an amount of white toner to be consumed for a long period of time at one time. However, it is difficult to secure a storage space for the white toner, and the quality of the white toner deteriorates if the toner is stored for a long period of time.

[0285] In addition, because white toner is sensitive to cross-contamination during production due to the characteristics of its color, cleaning work when switching toner types must be performed more thoroughly than with color toners. For these reasons, it can be said that there are high hurdles to manufacturing white toner and color toner on the same production line using the polymerization method.

[0286] Next, we will consider a process in which color toners are produced by polymerization and white toners are produced by pulverization, and both toners are produced on separate production lines. This process has the following advantages over a process in which white toners and color toners are produced on the same production line by polymerization:

[0287] Pulverized toner manufacturing equipment (also called "powder manufacturing equipment") comes in a variety of sizes, from large-scale equipment to small-scale equipment. This makes it possible to select manufacturing equipment suited to the production scale for manufacturing white toner, which is premised on small-lot production. This makes it easy to change the scale of investment to match the scale of production, thereby reducing manufacturing costs. In terms of investment in manufacturing equipment, a manufacturing line can be set up by combining various powder manufacturing equipment already on the market. This allows for flexible response, and a manufacturing line can be set up with less investment.

[0288] For the above reasons, it is preferable to produce the white toner by a pulverization method and the color toner by a polymerization method, since this further reduces the production cost.

[0289] Furthermore, when the toner is produced by a polymerization method, it is preferable because it is easy to appropriately control the particle size, and when the toner is produced by a pulverization method, it is easy to add a charge control agent internally.

[0290] From the above, it is preferable that the color toner is a polymerized toner and the white toner is a pulverized toner, from the viewpoint of easy particle size control and easy addition of a charge control agent.

[0291] The toner according to the present invention may have a core-shell structure in which the surface of a core particle made of a core resin is covered with a shell layer made of a shell resin. Alternatively, the toner may have a single layer structure. In the case of a core-shell structure, the shell resin is preferably an amorphous polyester or an amorphous vinyl resin, which is an amorphous resin.

[0292] The shell is not limited to one that completely covers the core particle, and the surface of the core particle may be partially exposed. When the toner has a core-shell structure, it is possible to obtain charging stability and heat-resistant storage stability.

[0293] The core-shell structure can be confirmed by observing the cross-sectional structure of the toner using known means such as a transmission electron microscope (TEM) or a scanning probe microscope (SPM).

[0294] The obtained dried toner particles may be used as a toner as it is, but a known external additive may be added by a dry method in which an external additive is added and mixed.

[0295] As a mixer for the external additives, various known mixers such as a Turbula mixer, a Henschel mixer, a Nauta mixer, and a V-type mixer can be used.

[0296] Regarding the toner manufacturing method according to the present invention, a specific example of a method for manufacturing a yellow toner will be described in detail below. In addition, in the method for manufacturing a toner other than a yellow toner, for example, a magenta toner, a cyan toner, a black toner, and a white toner, the method for manufacturing a yellow toner can be suitably adopted by changing the colorant used.

[0297] The method for producing the toner according to the present invention is not limited to the method described below.

[0298] <Preparation of Water-Based Dispersion of Colorant Particles> Sodium dodecyl sulfate is dissolved in ion-exchanged water with stirring, and a yellow colorant is added and dispersed to prepare an aqueous dispersion of colorant particles in which the yellow colorant particles are dispersed.

[0299] <Preparation of aqueous dispersion of release agent-containing amorphous vinyl polymer> (First Polymerization) Sodium dodecyl sulfate and ion-exchanged water are charged into a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device. The mixture is heated while being stirred under a nitrogen stream, and potassium persulfate dissolved in ion-exchanged water is added.

[0300] For example, a monomer mixture liquid consisting of a styrene-based monomer, a (meth)acrylic acid ester monomer, and a compound having a carboxyl group or a hydroxyl group is dropped in. Polymerization is then carried out by heating and stirring to prepare a dispersion liquid (1) of resin particles.

[0301] In this case, for example, styrene is used as the styrene-based monomer, for example, n-butyl acrylate is used as the (meth)acrylic acid ester monomer, and for example, methacrylic acid is used as the compound having a carboxy group or a hydroxy group.

[0302] (Second Polymerization) A solution of polyoxyethylene (2) sodium dodecyl ether sulfate dissolved in ion-exchanged water is charged into a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device. After heating, the above-mentioned resin particle dispersion (1) and a solution of a monomer and a release agent consisting of a styrene monomer, a (meth)acrylic acid ester monomer, a compound having a carboxyl group or a hydroxyl group, n-octyl-3-mercaptopropionate, and a release agent are added. Then, the mixture is mixed and dispersed to prepare a dispersion containing emulsified particles (oil droplets).

[0303] In this case, for example, styrene is used as the styrene monomer. For example, n-butyl acrylate is used as the (meth)acrylic acid ester monomer. For example, methacrylic acid is used as the compound having a carboxy group or a hydroxy group. For example, behenyl behenate (melting point 73°C) is used as the release agent.

[0304] Next, an initiator solution in which potassium persulfate is dissolved in ion-exchanged water is added to this dispersion, and the system is heated and stirred to carry out polymerization, thereby preparing a dispersion (2) of resin particles.

[0305] (Third Polymerization) Ion-exchanged water is added to the dispersion liquid (2) of resin particles and mixed thoroughly, and then a solution of potassium persulfate dissolved in ion-exchanged water is added.

[0306] For example, a monomer mixture liquid including a styrene-based monomer, a (meth)acrylic acid ester monomer, a compound having a carboxy group or a hydroxy group, and n-octyl-3-mercaptopropionate is dropped.

[0307] In this case, for example, styrene is used as the styrene-based monomer, for example, n-butyl acrylate is used as the (meth)acrylic acid ester monomer, and for example, methacrylic acid is used as the compound having a carboxy group or a hydroxy group.

[0308] After the dropwise addition is completed, polymerization is carried out by heating and stirring, and then the mixture is cooled to prepare an aqueous dispersion of a release agent-containing amorphous vinyl polymer.

[0309] <Preparation of Aqueous Dispersion of Crystalline Polyester> (Synthesis of crystalline polyester) The raw material monomers for the addition polymerization resin segment (here, a styrene-acrylic resin segment) and a radical polymerization initiator are placed in a dropping funnel.

[0310] In this case, for example, styrene, n-butyl acrylate, and acrylic acid are used as raw material monomers, and for example, di-t-butyl peroxide is used as a radical polymerization initiator.

[0311] Furthermore, raw material monomers for a polycondensation resin segment (here, a crystalline polyester segment) are placed in a four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer and a thermocouple, and are heated to dissolve.

[0312] In this case, as the raw material monomer, for example, sebacic acid which is an aliphatic dicarboxylic acid, and 1,12-dodecanediol which is an aliphatic diol are used.

[0313] Next, raw material monomers for the addition polymerization resin segment and a radical polymerization initiator placed in a dropping funnel are dropped under stirring, and after maturation, unreacted addition polymerization monomers are removed under reduced pressure.

[0314] Thereafter, an esterification catalyst is added, the temperature is raised, and the reaction is carried out under normal pressure, and further under reduced pressure.

[0315] Next, after cooling, the mixture is reacted under reduced pressure to obtain a crystalline polyester which is a hybrid resin.

[0316] (Preparation of Dispersion) The crystalline polyester obtained in the above synthesis example is dissolved in a solvent (e.g., methyl ethyl ketone) while stirring. Next, an aqueous solution of sodium hydroxide is added to this solution. Water is added dropwise to this solution while stirring to prepare an emulsion.

[0317] Next, the solvent is removed from this emulsion by distillation to prepare an aqueous dispersion in which the crystalline polyester is dispersed.

[0318] <Preparation of Aqueous Dispersion of Amorphous Polyester> (Synthesis of amorphous polyester) In a reaction vessel equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, for example, bisphenol A propylene oxide 2 mole adduct, terephthalic acid, fumaric acid, and an esterification catalyst are placed. These are subjected to a condensation polymerization reaction, and further reacted under reduced pressure and cooled. At this time, for example, tin octylate is used as the esterification catalyst.

[0319] Thereafter, for example, a mixture of a compound having a carboxy group or a hydroxy group, a styrene monomer, a (meth)acrylic acid ester monomer, and a polymerization initiator is added dropwise.

[0320] In this case, for example, acrylic acid is used as the compound having a carboxy group or a hydroxy group. For example, styrene is used as the styrene monomer. For example, butyl acrylate is used as the (meth)acrylic acid ester monomer. For example, di-t-butyl peroxide is used as the polymerization initiator.

[0321] After the dropping, the mixture is subjected to an addition polymerization reaction, then the temperature is raised and the mixture is kept under reduced pressure. Then, the compound having a carboxyl group or a hydroxyl group, the styrene monomer, and the (meth)acrylic acid ester monomer are removed. This results in the synthesis of an amorphous polyester in which the vinyl resin segment and the crystalline polyester segment are bonded together.

[0322] (Preparation of Dispersion) The amorphous polyester obtained in the above synthesis example is dissolved in a solvent (e.g., methyl ethyl ketone) while stirring. Next, an aqueous solution of sodium hydroxide is added to this solution. Water is added dropwise to this solution while stirring to prepare an emulsion.

[0323] Next, the solvent is removed from this emulsion by distillation to prepare an aqueous dispersion in which the amorphous polyester is dispersed.

[0324] <Production of Yellow Toner> In a reaction vessel equipped with a stirrer, a temperature sensor, and a cooling tube, an aqueous dispersion of a release agent-containing amorphous vinyl polymer and ion-exchanged water are placed. Then, an aqueous sodium hydroxide solution is added to adjust the pH.

[0325] Thereafter, an aqueous dispersion of colorant particles is added, followed by the addition of an aqueous magnesium chloride solution to prepare a mixed solution. The mixed solution is heated, and an aqueous dispersion of crystalline polyester is added to promote aggregation. When the desired particle size is reached, an aqueous dispersion of amorphous polyester is added, and an aqueous solution of sodium chloride dissolved in ion-exchanged water is added to stop particle growth. The mixture is then heated and stirred to promote fusion of the particles. The mixture is then cooled.

[0326] Then, the solid-liquid separation is performed, followed by washing and drying to obtain yellow toner particles.

[0327] A yellow toner can be produced by adding an external additive to the obtained toner particles.

[0328] (Manufacturing method of yellow developer) A yellow developer can be produced by adding and mixing the external additives described below to the above yellow toner.

[0329] <External additives> External additives are attached to the surfaces of the toner base particles for the purpose of controlling the fluidity and chargeability.

[0330] As the external additive, conventionally known metal oxide particles can be used.

[0331] Examples include silica particles, titanium oxide particles, alumina particles, zirconia particles, zinc oxide particles, chromium oxide particles, cerium oxide particles, antimony oxide particles, tungsten oxide particles, tin oxide particles, tellurium oxide particles, manganese oxide particles, boron oxide particles, etc. These may be used alone or in combination of two or more kinds.

[0332] Regarding the silica particles, silica particles produced by the sol-gel method can be used. The silica particles produced by the sol-gel method are characterized by a narrow particle size distribution, which is preferable in terms of suppressing the variation in adhesion strength.

[0333] The number-average primary particle size of the silica particles formed by the sol-gel method is preferably within the range of 70 to 150 nm. Silica particles with a number-average primary particle size within this range have a larger particle size than other external additives, and therefore act as a spacer. They also have the effect of preventing other external additives with smaller particle sizes from being embedded in the toner base particles when they are stirred and mixed in the developing machine. They also have the effect of preventing the toner base particles from fusing together.

[0334] Furthermore, organic particles of homopolymers such as styrene and methyl methacrylate, or copolymers thereof may be used as an external additive.

[0335] The metal oxide particles used as the external additive are preferably those that have been subjected to a hydrophobic surface treatment using a known surface treatment agent such as a coupling agent, etc. As the above surface treatment agent, dimethyldimethoxysilane, hexamethyldisilazane (HMDS), methyltrimethoxysilane, isobutyltrimethoxysilane, decyltrimethoxysilane, etc. are preferred.

[0336] Silicone oil can also be used as the surface treatment agent. Specific examples of silicone oil include organosiloxane oligomers, octamethylcyclotetrasiloxane, or cyclic compounds such as decamethylcyclopentasiloxane, tetramethylcyclotetrasiloxane, and tetravinyltetramethylcyclotetrasiloxane. Linear or branched organosiloxane can also be used. Silicone oils with high reactivity and at least terminal modification, in which modified groups are introduced into the side chain, one terminal, both terminals, one terminal of the side chain, both terminals of the side chain, etc., can also be used. Examples of the modified group include, but are not limited to, an alkoxy group, a carboxy group, a carbinol group, a higher fatty acid modified group, a phenol group, an epoxy group, a methacryl group, and an amino group. Silicone oils with several modified groups, such as amino / alkoxy modified groups, can also be used.

[0337] Also, dimethyl silicone oil, the modified silicone oil, and other surface treatment agents may be used for mixed treatment or combined treatment. Examples of the combined treatment agents include silane coupling agents, titanate coupling agents, aluminate coupling agents, and various silicone oils. Also, examples of fatty acids, fatty acid metal salts, esters thereof, rosin acid, etc. may be used.

[0338] In order to further improve the cleaning property and transferability, a lubricant can be used as an external additive. For example, the following salts of stearic acid such as zinc, aluminum, copper, magnesium, calcium, etc. can be mentioned. In addition, salts of oleic acid such as zinc, manganese, iron, copper, magnesium, etc. can be mentioned. In addition, salts of palmitic acid such as zinc, copper, magnesium, calcium, etc. can be mentioned. In addition, salts of linoleic acid such as zinc, calcium, etc. can be mentioned. In addition, metal salts of higher fatty acids such as salts of ricinoleic acid such as zinc, calcium, etc. can be mentioned.

[0339] The total amount of these external additives added is preferably within a range of 0.1 to 10% by mass, and more preferably within a range of 1 to 5% by mass, based on 100 parts by mass of the toner base particles.

[0340] 2. Image forming method The image forming method of the present invention is an image forming method having a color toner image forming step, a base layer forming white toner image forming step, and a transfer step, in which the color toner image forming step develops at least an electrostatic latent image formed on an image carrier with a developer containing a color toner to form a color toner image, the base layer forming white toner image forming step develops at least an electrostatic latent image formed on an image carrier with a developer containing a white toner to form a white toner image, and the volume average particle diameter D of toner particles constituting the color toner is 50C [μm] and the volume average particle size D of the toner particles constituting the white toner 50W [μm] satisfies the following formula (1), Formula (1) 1.1×D 50C <D 50W [μm] And the volume average particle size D 50W , the standard deviation σ of the volume particle size distribution of the toner particles constituting the white toner W and volume average particle size D 50C satisfies the following formula (2). Formula (2) D 50W +1.6×σ W <1.5×D 50C [μm] The present invention can be suitably used in the image forming system of the present invention.

[0341] The electrophotographic image forming method of the present invention involves superposing an image layer containing white toner particles formed by a white toner and an image layer containing color toner particles formed by a color toner on a recording medium, and then undergoing a process of fixing the image layer of the white toner and the image layer of the color toner (hereinafter also referred to as a toner image). Specifically, the method includes, for example, the following steps (1) to (6). (1) Charging the surface of the image carrier (2) An exposure step in which an electrostatic latent image is formed on an image carrier by exposure to light (3) A developing step in which the electrostatic latent image formed on the image carrier is developed with a developer containing color toner to form a color toner image. (4) A developing step in which the electrostatic latent image formed on the image carrier is developed with a developer containing a white toner to form a white toner image. (5) A transfer process in which the toner image formed on the image carrier is transferred to a recording medium. (6) A fixing process in which the toner image transferred onto the recording medium is thermally fixed. In the above-mentioned transfer step (5), a toner image laminate is formed on the recording medium, in which an image layer of white toner and an image layer of color toner are superimposed. The toner image laminate is preferably formed simultaneously in a so-called one-pass manner. In other words, it is preferable that the image layer of white toner and the image layer of color toner are primarily transferred simultaneously onto the intermediate belt as a laminate.

[0342] In the fixing step (6) above, the white toner image layer and the color toner image layers constituting the toner image laminate formed on the recording medium are fixed at the same time. EXAMPLES

[0343] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the examples, the terms "parts" and "%" are used, but they represent "parts by mass" or "% by mass" unless otherwise specified.

[0344] A. Toner (Various solutions used in the production of toner) When preparing the color toner and the white toner, a solution containing the compounds and ion-exchanged water shown in the following Table I was used. Note that as the color toner, a black toner was used.

[0345] [Table 1]

[0346] (A.1) Toner types As for the color toner, only one type, black toner Bk1, was produced by polymerization.

[0347] A total of thirteen types of white toners, W1 to W13, were produced, and eight types of white toners, W1 to W6, W12 and W13, were produced by the pulverization method.

[0348] Among them, five types of white toners W7 to W11 were produced by polymerization.

[0349] Hereinafter, the above-mentioned "black toner Bk1" will also be referred to simply as "toner Bk1", and the above-mentioned "white toners W1 to W13" will also be referred to simply as "toners W1 to W13".

[0350] (A.2) Preparation of black toner (toner Bk1) by polymerization method (A.2.1) Preparation of black colorant particle dispersion (1) (Preparation of Dispersion (1)) 0.90 kg of n-dodecyl sodium sulfate and 10.0 L of pure water were added and dissolved by stirring. 0.60 kg of carbon black "Regal (registered trademark) 330" (manufactured by Cabot Corporation) was gradually added to this solution and thoroughly stirred for 1 hour. After that, the mixture was continuously dispersed for 20 hours using a sand grinder (medium type disperser) to prepare dispersion (1).

[0351] (Preparation of Latex 1-A) A 100 L glass-lined (GL) reactor equipped with a temperature sensor, cooling tube, and nitrogen introduction device was prepared. 3.41 kg of wax emulsion [1], the entire amount of anionic surfactant solution [1], and the entire amount of nonionic surfactant solution [2] were added to the reactor, stirring was started, and 44.0 L of ion-exchanged water was added. The "wax emulsion" is a polypropylene emulsion with a number-average molecular weight of 3000, a number-average primary particle size of 120 nm, and a solids concentration of 29.9% by mass.

[0352] Next, heating was started, and when the liquid temperature reached 75° C., the entire amount of the polymerization initiator [1] was added dropwise. Thereafter, a premixed solution of 12.1 kg of styrene, 2.88 kg of n-butyl acrylate, 1.04 kg of methacrylic acid, and 548 g of t-dodecyl mercaptan was added dropwise while controlling the liquid temperature at 75±1° C. After completion of the addition, the liquid temperature was raised to 80±1° C., and the mixture was heated and stirred for 6 hours to complete the polymerization.

[0353] Then, the liquid temperature was cooled to 40°C or less, stirring was stopped, and the mixture was filtered through a Pall filter to obtain Latex 1-A. The resin particles in Latex 1-A had a glass transition point of 57°C, a softening point of 121°C, a weight average molecular weight of 12,700, and a weight average particle size of 120 nm.

[0354] (Preparation of Latex 1-B) A 100L glass-lined (GL) reactor equipped with a temperature sensor, cooling tube, nitrogen inlet, and comb baffle was prepared. 3.41kg of wax emulsion [1], the entire amount of anionic surfactant solution [1], and the entire amount of nonionic surfactant solution [2] were added to the reactor, stirring was started, and 44.0L of ion-exchanged water was added. Heating was started, and when the liquid temperature reached 70°C, polymerization initiator [2] was added.

[0355] Next, a premixed solution of 11.0 kg of styrene, 4.00 kg of n-butyl acrylate, 1.04 kg of methacrylic acid, and 9.02 g of t-dodecyl mercaptan was added dropwise. After the dropwise addition was completed, the liquid temperature was controlled at 72°C±2°C and heated and stirred for 6 hours, and then the liquid temperature was raised to 80°C±2°C and heated and stirred for 12 hours to complete the polymerization.

[0356] Then, the liquid temperature was cooled to 40°C or less, stirring was stopped, and the mixture was filtered through a Pall filter to obtain Latex 1-B. The resin particles in Latex 1-B had a glass transition point of 58°C, a softening point of 132°C, a weight average molecular weight of 245,000, and a weight average particle size of 110 nm.

[0357] (Preparation and Stirring of Fused Particle Dispersion (1)) A 100 L SUS reactor equipped with a temperature sensor, a cooling tube, a nitrogen inlet, and a particle size and shape monitoring device was prepared. 20.0 kg of latex 1-A, 5.2 kg of latex 1-B, 0.4 kg of dispersion (1), and 20.0 kg of ion-exchanged water were added to the reactor and stirred.

[0358] After leaving it for 10 minutes, the temperature was raised to 85°C in 60 minutes, and the particle size was increased while salting out / fusing by heating and stirring at 85±2°C, and when the average particle size of the fused particles reached 6μm, "sodium chloride solution G" was added to stop the particle size growth. This liquid was named fused particle dispersion liquid (1).

[0359] Next, 5.0 kg of the above fused particle dispersion (1) was placed in a 5 L reaction vessel equipped with a temperature sensor and a cooling tube. At this time, the mixture was heated and stirred at a liquid temperature of 92±2°C while observing the change in shape of the fused particles in the fused particle dispersion (1). Heating and stirring were continued until the average shape coefficient was 0.98 or more, and dispersion (2) was prepared. The average particle size of the particles in dispersion (2) was 6.3 μm, and the CV value was around 25%.

[0360] Next, the dispersion liquid (2) was washed with ion-exchanged water and filtered three times to make the dispersion liquid (2) into a wet cake. The wet cake-like dispersion liquid (2) was then pre-dried using a flash jet dryer at an intake air temperature of 50°C. It was then further dried at a temperature of 55°C using a fluidized bed dryer to produce black colorant particles [1]. The CV value was around 25%.

[0361] Toner Bk1 was prepared by externally adding and mixing 1.5 parts by weight of hydrophobic silica fine particles R805 to the obtained black colorant particles [1] using a Henschel mixer.

[0362] (A.3) Preparation of white toners (toners W1 to W6, W12 and W13) by pulverization method (A.3.1) Preparation of toner W1 (Preparation of binder) The binder used was a polyester resin prepared as follows.

[0363] Polyoxypropylene (2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxyethylene (2.0)-2,2-bis(4-hydroxyphenyl)propane, and terephthalic acid were mixed in a molar ratio of 3:7:9. This and the polymerization initiator [3] were placed in a four-necked glass flask. The four-necked flask was equipped with a hygrometer, a stainless steel stirring rod, a downflow condenser, and a nitrogen inlet tube.

[0364] Next, the four-neck flask was placed in a mantle heater, and the mixture was heated and stirred while introducing nitrogen into the flask from the nitrogen inlet tube to cause a reaction. The reaction state was tracked while measuring the acid value during the reaction, and the reaction was terminated when a predetermined acid value was reached, and the reaction was cooled to produce a polyester resin. The polyester resin had a number average molecular weight (Mn) of 3300 and a weight average molecular weight (Mw) / number average molecular weight (Mn) of 4.2. The glass transition temperature (Tg) was 68.5°C, the softening point (Tm) was 110.3°C, the acid value was 3.3 KOHmg / g, and the hydroxyl value was 28.1 KOHmg / g.

[0365] [Various measurements] The glass transition temperature (Tg) was measured using a differential scanning calorimeter (Seiko Denshi Co., Ltd.: DSC-200). Alumina was used as a reference, and 10 mg of the sample was measured at a heating rate of 10°C / min between 20 and 120°C. The shoulder value of the main endothermic peak was taken as the glass transition point.

[0366] The softening point (Tm) was measured using a flow tester (Shimadzu Corporation: CFT-500). A die with a hole diameter of 1 mm and length of 1 mm was used. The pressure was 20 kg / cm. 2 , heating rate 6℃ / min, 1cm 2 The softening point of the sample was determined as the temperature corresponding to half the height from the start point of the melt to the end point of the melt.

[0367] To calculate the acid value, 10 mg of the sample was dissolved in 50 mL of toluene, and a mixed indicator of 0.1% bromthymol blue and phenol red was used. The acid value was then calculated from the consumption of the previously evaluated N / 10 potassium hydroxide / alcohol solution. The hydroxyl value was also expressed as the mass [mg] of potassium hydroxide required to neutralize the acetic acid liberated by treating a weighed sample with acetic anhydride and hydrolyzing the resulting acetyl compound.

[0368] (Resin Crushing) The synthesized polyester resin was coarsely pulverized to a particle size of 1 mm or less. Next, this polyester resin and titanium dioxide were charged in a pressure kneader in a mass ratio of 7:3 and kneaded at 120°C for 1 hour. After that, this was cooled and coarsely pulverized with a hammer mill to obtain a pigment master batch with a white colorant content of 30 mass%.

[0369] Next, the ratio of titanium dioxide was adjusted to 7 parts by mass per 100 parts by mass of the polyester resin. The polyester resin and the pigment master batch were placed in a Henschel mixer and thoroughly mixed at a peripheral speed of 40 m / sec for 180 seconds.

[0370] Next, this mixture was melted and kneaded using a twin-screw extrusion kneader (PCM-30, manufactured by Ikegai Iron Works), and the kneaded product was rolled to a thickness of 2 mm using a press roller. After cooling using a cooling belt, it was coarsely pulverized using a feather mill. It was then pulverized using a mechanical pulverizer (KTM, manufactured by Kawasaki Heavy Industries, Ltd.) and further pulverized using a jet pulverizer (IDS, manufactured by Nippon Pneumatic Mfg. Co., Ltd.). It was then classified using a rotor-type classifier (T-Plex type classifier 100ATP, manufactured by Hosokawa Micron Corporation) to produce white toner 1. The shape factor was around 0.980, the average particle size was 14.3 μm, and the CV value was 30%.

[0371] [Various measurements] The average particle size is the volume-based median diameter (d 50) was measured and calculated using a measuring device consisting of a "Multisizer 3" (Beckman Coulter) connected to a computer system equipped with the data processing software "Software V3.51". Specifically, it was calculated as follows.

[0372] 0.02g of toner particles are added to 20mL of surfactant solution (a surfactant solution prepared by diluting, for example, a neutral detergent containing a surfactant component with pure water 10 times in order to disperse the toner particles) and mixed. Then, ultrasonic dispersion is performed for 1 minute to prepare a toner particle dispersion. This toner particle dispersion is poured with a pipette into a beaker containing an "ISOTONII" (manufactured by Beckman Coulter) in the sample stand until the concentration displayed on the measuring device is 8%. Then, the frequency value is calculated with the measuring device with a particle count of 25,000 and an aperture diameter of 100μm. At this time, the particle diameter of the 50% with the largest volume cumulative fraction is taken as the volume-based median diameter (average particle diameter).

[0373] The shape factor refers to the average circularity of the toner, and the average circularity of the toner was measured using "FPIA-3000" (manufactured by Sysmex Corporation). Specifically, the measurement was performed as follows.

[0374] The sample (toner) was mixed with an aqueous solution containing a surfactant, and dispersed by ultrasonic dispersion treatment for 1 minute. After that, images were taken using an "FPIA-3000" (manufactured by Sysmex) under the measurement conditions of HPF (high magnification imaging) mode at an appropriate concentration of 3,000 to 10,000 HPF detections. The circularity of each toner particle was calculated according to the following formula (T), and the circularity of each toner particle was added and divided by the total number of toner particles.

[0375] Formula (T): Circularity = (perimeter of a circle with the same projected area as the particle image) / (perimeter of the projected image of the particle)

[0376] The CV value is a value calculated by the following formula from the above particle size distribution analysis.

[0377] Coefficient of variation (CV value) (%) = (S2 / Dn) x 100 (In the formula, S2 represents the standard deviation in the volume-based particle size distribution, and Dn represents the volume-based average particle size.)

[0378] (A.3.2) Preparation of toners W2 to W6, W12 and W13 Toners W2 to W6, W12 and W13 were produced in the same manner as Toner W1, except that the resin was appropriately pulverized in accordance with the above-mentioned toner production guidelines so that the volume average particle size and the standard deviation of the volume particle size distribution would be the values ​​shown in Tables II, V and VIII described below.

[0379] (A.4) Preparation of white toners (toners W7 to W11) by polymerization method (A.4.1) Preparation of toner W7 Toner W7 was prepared in the same manner as toner Bk1, except that in the preparation of dispersion (1), 1.6 kg of titanium oxide was used instead of carbon black "REGAL (registered trademark) 330" (manufactured by Cabot Corporation) and the above-mentioned toner preparation guidelines were followed.

[0380] (A.4.2) Preparation of toners W8 to W11 Toners W8 to W11 were produced in the same manner as toner Bk1, except that the polymerization conditions (association time, etc.) were appropriately changed and particle size was controlled in accordance with the above-mentioned toner production guidelines so that the volume average particle size and the standard deviation of the volume particle size distribution would be the values ​​shown in Tables II, V, and VIII.

[0381] B. Embodiment 1 (B.1) Comparative Examples 1 to 3 and Examples 1 to 3 (B.1.1) Toner type and toner production policy The following Comparative Examples 1 to 3 and Examples 1 to 3 were carried out using each of the prepared toners. The toners used in Comparative Examples 1 to 3 and Examples 1 to 3 are as shown in Table II below. Table III also shows whether the toners in Table II satisfy the particle size indexes of the formulas (1) to (3).

[0382] [Comparative Example 1] The toners used in the embodiment of Comparative Example 1 were toner Bk1 and toner W1.

[0383] Since toner Bk1 is produced by a polymerization method, which makes it easy to produce a toner composed of small particles, toner Bk1 was produced under classification process conditions that would result in a smaller volume average particle size of toner particles constituting toner Bk1 compared to toner W1 produced by a pulverization method.

[0384] Toner W1 was produced under classification process conditions such that the volume average particle size of toner particles constituting toner Bk1 and toners W2 to W11 described later was relatively large, and the standard deviation of the volume particle size distribution was calculated.

[0385] At this time, the volume average particle diameter D 50C [μm] and the volume average particle size D of white toner particles 50W The relationship with [μm] satisfied the following formula (1).

[0386] Formula (1) 1.1×D 50C <D 50W [μm]

[0387] In addition, the volume average particle diameter D of the white toner particles 50W [μm] and standard deviation of volume particle size distribution σ W and the volume average particle size of the color toner particles D 50C [μm] did not satisfy the relationship of the following formula (2).

[0388] Formula (2) D 50W +1.6×σ W <1.5×D 50C [μm]

[0389] [Comparative Examples 2 and 3] The toners used in Comparative Example 2 were toner Bk1 and toner W2, and the toners used in Comparative Example 3 were toner Bk1 and toner W3.

[0390] In Comparative Example 2, white toner was produced by the same pulverization method as in Comparative Example 1, but the volume average particle size of the white toner particles was made smaller than that of Comparative Example 1 by further increasing the removal of large diameter components of the white toner particles using an air classifier.

[0391] In Comparative Example 3, the removal of large diameter components by the air classifier was strengthened more than in Comparative Example 2, thereby making the volume average particle size of the white toner particles smaller.

[0392] At this time, the volume average particle diameter D 50C [μm] and the volume average particle size D of white toner particles 50W The relationship between the volume average particle diameter D of the white toner particles and the volume average particle diameter D of the white toner particles satisfies the relationship of the above formula (1). 50W [μm] and standard deviation of volume particle size distribution σ W and the volume average particle size of the color toner particles D 50C [μm] did not satisfy the relationship of formula (2) above.

[0393] Although an air classifier is used in the manufacturing method of the toner, the large diameter components of the white toner particles may be repeatedly crushed by other equipment to remove the large diameter components.

[0394] Other examples of the equipment include the Cryptron System (Kawasaki Heavy Industries, Ltd.) and the Super Rotor (Nisshin Engineering, Inc.), as well as Turbo Mill (Freund Turbo Corp.) and fine grinders using an air jet system.

[0395] [Examples 1 to 3] The toners used in Example 1 were toner Bk1 and toner W4, the toners used in Example 2 were toner Bk1 and toner W5, and the toners used in Example 3 were toner Bk1 and toner W6.

[0396] In Example 1, white toner was produced by a pulverization method similar to Comparative Examples 1 to 3, but the removal of large diameter components of the white toner particles by an air classifier was further strengthened compared to Comparative Example 3, thereby reducing the volume average particle size of the white toner particles.

[0397] In Example 2, the removal of large diameter components from the white toner particles by the air classifier was further strengthened compared to Example 1, thereby making the volume average particle size of the white toner particles smaller.

[0398] In Example 3, the removal of large diameter components from the white toner particles by the air classifier was further strengthened compared to Example 2, thereby making the volume average particle size of the white toner particles smaller.

[0399] At this time, the volume average particle size D of the color toner particles in Examples 1 to 3 50C [μm] and the volume average particle size D of white toner particles 50W The relationship between the volume average particle diameter D of the white toner particles and the volume average particle diameter D of the white toner particles satisfies the relationship of the above formula (1). 50W [μm] and standard deviation of volume particle size distribution σ W and the volume average particle size of the color toner particles D 50C [μm] satisfied the relationship of formula (2) above.

[0400] [Table 2]

[0401] [Table 3]

[0402] (B.1.2) Image formation As an evaluation device, a device similar to that described in JP 2021-189267 A, which employs an image forming system as shown in FIG. 4, but does not have a colorimeter for real-time color adjustment, was used. 2 A black solid image was formed on the recording medium (Oji Paper) using a combination of colored toners and white toners as shown in Table IV, and the black toner density (also referred to as "Bk density") was measured.

[0403] The amount of white toner attached on the paper is 8 to 9 g / m 2On top of that, the amount of black toner attached is 8 to 9 g / m 2 An image was formed so that

[0404] (Bk concentration) The Bk density of the above image was measured and evaluated according to the following evaluation criteria, using "A" and "C" as the evaluation criteria, with "A" being acceptable for practical use and "C" being unacceptable for practical use.

[0405] [Evaluation Criteria] A Bk density is 1.81 or higher (pass). C Bk density is less than 1.81 (fail).

[0406] (L * value) Recording medium: Tencolor black 151g / m 2 (manufactured by Hokuetsu Corporation) to form a solid white image on the recording medium using white toner, and * The L * The value was evaluated according to the following evaluation criteria, using "A" and "C" as the evaluation criteria, with "A" being acceptable for practical use and "C" being unacceptable for practical use.

[0407] [Evaluation Criteria] AL * The value is greater than 73 (pass). CL * The value is less than or equal to 73 (fail).

[0408] [Table 4]

[0409] (B.1.3) Observations of the results of Comparative Examples 1 to 3 and Examples 1 to 3 The Bk density measured in Comparative Example 1 was 1.48 as shown in Table IV. This was a significant decrease from the reference density of 1.84. When the formed image was magnified and observed using a VHX-1000 (manufactured by Keyence Corporation), exposure of the white toner layer was observed between the black toner layers.

[0410] In addition, the measured L * The result was 75 as shown in Table IV, which demonstrated high hiding power by the white toner and provided excellent practical properties.

[0411] The Bk concentrations measured in Comparative Examples 2 and 3 were as shown in Table IV. Although the Bk concentration was slightly higher than the Bk concentration of 1.48 in Comparative Example 1, it was still lower than the reference concentration of 1.84, and the decrease in concentration was not completely resolved.

[0412] In addition, the measured L * The result was 75 as shown in Table IV, which was no problem for practical use.

[0413] The Bk densities measured in Examples 1 to 3 were as shown in Table IV. As in Comparative Examples 1 to 3, the Bk density achieved the reference density of 1.84, and the decrease in density was completely eliminated.

[0414] In addition, the measured L * The result was 75 as shown in Table IV, which was no problem for practical use.

[0415] From the above, a decrease in Bk density occurred in Comparative Examples 1 to 3, while the decrease in Bk density was completely eliminated in Examples 1 to 3. Below, the causes of these phenomena will be considered in conjunction with the image formation process.

[0416] During image formation in Comparative Example 1 when measuring the Bk density, the printing machine was stopped and an image sample was obtained in a state where a toner image had been printed on the recording medium but had not yet entered the fixing unit.

[0417] The particle size of the white toner particles exposed between the colored toner particles on the image sample was measured using the distance measurement function of a VHX-1000 (manufactured by Keyence Corporation). This revealed that the white toner particles were exposed in areas where white toner particles with a particle size roughly 1.5 times that of the colored toner particles were present.

[0418] Therefore, the volume average particle diameter D 50C Using a particle size 1.5 times larger than the standard particle size, we created Figure 8 to estimate to what level the white toner particles with particle sizes larger than this size must be reduced to in order to eliminate the effect of exposure of the white toner particles. Figure 8 is a graph showing the relationship between the particle size index of the white toner particles and the Bk density.

[0419] FIG. 8 shows the D 50W +1.6×σ W This is a graph plotting the value of [μm] and the Bk density, with the horizontal axis being D 50W +1.6×σ W The vertical axis represents the Bk concentration.

[0420] As mentioned above, FIG. 3 is an example of a graph showing the relationship between the particle size of white toner particles and their abundance ratio in an image obtained by forming a color toner layer on a white toner layer.

[0421] D in Figure 3 W represents the particle size of the white toner particles, and the volume average particle size D 50W , the standard deviation of the volume particle size distribution of white toner particles σ W The following equation expresses the relationship between

[0422] Expression D W =D 50W +p×σ W

[0423] In the above formula, the larger the real number p, the larger the particle diameter of the white toner particles in FIG. 3 shifts to the larger particle side. W , i.e. D 50W +1.6σ W is the boundary particle size that separates the top 10% of particle size distribution ratio from the remaining 90% in a normal distribution.

[0424] 8, the vertical dashed auxiliary lines indicate 9.15 μm, which is 1.5 times the volume average particle diameter of the color toner (black toner in this case), and the horizontal lines indicate the aforementioned reference density of 1.84.

[0425] As can be seen from Figure 8, the grain size causing the exposure is 1.5 × D 50C [μm] and reduce the ratio of white toner particles larger than 1.5×D 50C [μm]=D 50W +1.6×σ W When the large diameter components of the white toner particles are reduced to a level of 1 μm, the density reduction of the color toners does not occur for the first time.

[0426] That is, D 50W +1.6×σ W [μm] x 1.5 50C By making the size smaller than [μm], it is possible to maintain an appropriate image density even when a color toner layer is formed on a base layer formed with a white toner, and this makes it possible to form an image at a level equivalent to the aforementioned reference density.

[0427] From the above, by using an image forming system in which the particle size relationship between all color toners and white toner in the image forming device is designed in this way, it is possible to suppress density reduction for all full-color images, regardless of whether they are monochrome, secondary color, or tertiary color, and to form images with a sufficient color gamut.

[0428] (B.2) Comparative Examples 4 to 6 and Examples 4 and 5 (B.2.1) Toner type and toner production policy The prepared toners were used in the following Comparative Examples 4 to 6 and Examples 4 and 5. The toners used in Comparative Examples 4 to 6 and Examples 4 and 5 are as shown in Table V below. Table VI also shows whether the toners in Table V satisfy the particle size indexes of the formulas (1) to (3).

[0429] [Comparative Examples 4 to 6] The toners used in Comparative Example 4 were toner Bk1 and toner W7, the toners used in Comparative Example 5 were toner Bk1 and toner W8, and the toners used in Comparative Example 6 were toner Bk1 and toner W9.

[0430] Here, since toners W7 to W9 are produced by a polymerization method, it is easy to produce toners composed of small particles. Therefore, compared to toner W6 of Example 3, which has the smallest volume average particle size of white toner particles produced by a pulverization method, it was possible to produce toner particles constituting toners W7 to W9 with a relatively small volume average particle size. The volume average particle size of the toner particles was controlled by appropriately changing the polymerization conditions (association time) and the like.

[0431] At this time, the volume average particle diameter D 50W [μm] and standard deviation of volume particle size distribution σ W and the volume average particle size of the color toner particles D 50C [μm] satisfied the relationship of formula (2) above, but did not satisfy the relationship of formula (1) above.

[0432] [Examples 4 and 5] The toners used in Example 4 were toner Bk1 and toner W10, and the toners used in Example 5 were toner Bk1 and toner W11.

[0433] Toners W10 and W11 were prepared by appropriately changing the polymerization conditions (association time) etc. so that the volume average particle size of the toner particles constituting the white toner was relatively large compared to Comparative Examples 4-6.

[0434] At this time, the volume average particle diameter D 50C [μm] and the volume average particle size D of white toner particles 50W The relationship between the volume average particle diameter D of the white toner particles and the volume average particle diameter D of the white toner particles satisfies the relationship of the above formula (1). 50W [μm] and standard deviation of volume particle size distribution σ W and the volume average particle size of the color toner particles D 50C [μm] satisfied the relationship of formula (2) above.

[0435] [Table 5]

[0436] [Table 6]

[0437] (B.2.2) Image formation Image formation in Comparative Examples 4 to 6 and Examples 4 and 5 was carried out in the same manner as in Comparative Examples 1 to 3 and Examples 1 to 3, and was evaluated in the same manner. The results are shown in Table VII.

[0438] [Table 7]

[0439] (B.2.3) Observations of the results of Comparative Examples 4 to 6 and Examples 4 and 5 The Bk densities measured in Comparative Examples 4 to 6 were shown in Table VII. In Comparative Examples 4 to 6, the Bk density achieved the reference density of 1.84, and the decrease in density was completely eliminated.

[0440] However, the measured L *As shown in Table VII, the value was 73 or less, and the performance in terms of the hiding power of the white toner was reduced compared to when formula (1) was satisfied. This is thought to be because the volume average particle size of the white toner particles became too small, causing the toner particles to get into the unevenness of the black paper fibers before the image was fixed. This reduced the hiding power of the white toner on the black paper, and the L of the solid white image * The value appears to have decreased.

[0441] The Bk concentration measured in Examples 4 and 5 was as shown in Table VII. In Examples 4 and 5, the Bk concentration achieved the reference concentration of 1.84, and the decrease in concentration was completely eliminated.

[0442] L measured in Examples 4 and 5 * The value was increased compared to Comparative Examples 4 to 6, and the L * The result was a L value of 75. This is thought to be because the volume average particle size of the white toner particles is larger than that of Comparative Examples 4 to 6, so the toner does not penetrate into the unevenness of the black paper fibers. As a result, the black paper hiding power of the white toner is increased and a certain level or more can be secured, so that the L value of the white solid image similar to that of Examples 1 to 3 can be obtained. * It is believed that the value was achieved.

[0443] As can be seen from the series of results in Table VII, it is important to design color toners and white toners to satisfy the relationship of the above-mentioned formulas (1) and (2). It can also be seen that even if an image is formed by forming a color toner layer on top of a white toner layer as an underlayer, it is possible to achieve the color gamut of the color toners and the concealment of the color of the recording paper by the white toner. This makes it possible to provide good image quality.

[0444] C. Second embodiment (settings for continuous printing) (C.1) Examples 6 to 10 (C.1.1) Toner type and toner production policy The following Examples 6 to 10 were carried out using each of the prepared toners. The toners used in Examples 6 to 10 are as shown in Table VIII below. Table IX also shows whether the toners in Table VIII satisfy the particle size indexes of the formulas (1) to (3).

[0445] [Examples 6 to 8] The toners used in Examples 6 to 8 were the same as those used in Examples 1 to 3, both for color toner and white toner. Specifically, the toners used in Example 6 were toner Bk1 and toner W4. The toners used in Example 7 were toner Bk1 and toner W5. The toners used in Comparative Example 9 were toner Bk1 and toner W6.

[0446] At this time, the volume average particle diameter D 50C [μm] and the volume average particle size D of white toner particles 50W The relationship between the volume average particle diameter D of the white toner particles and the volume average particle diameter D of the white toner particles satisfies the relationship of the above formula (1). 50W [μm] and standard deviation of volume particle size distribution σ W and the volume average particle size of the color toner particles D 50C [μm] satisfied the relationship of formula (2) above.

[0447] [Examples 9 and 10] In both Examples 9 and 10, toner Bk1 was used as the color toner. Toner W12 in Example 9 was produced by a pulverization method, and the volume average particle size of the white toner particles was reduced by further strengthening the removal of large diameter components of the white toner particles by an air classifier compared to Example 3. Toner W13 in Example 10 was produced by further strengthening the removal of large diameter components of the white toner particles by an air classifier compared to Example 9, thereby reducing the volume average particle size of the white toner particles.

[0448] [Table 8]

[0449] [Table 9]

[0450] (C.1.2) Image formation As the evaluation device, a device equipped with a colorimeter for real-time color adjustment was used, which is similar to the device described in JP 2021-189267 A, which employs the image forming system shown in FIG. 4 described above. Note that this image formation is premised on the use of continuous paper. Therefore, N Mirror 73 / P22 / G7W manufactured by Oji TAC, which is a roll of paper, was used as the white paper for measuring the reference density.

[0451] In addition, for the roll paper, a transparent film, Fujiclear 50ASW made by Lintec, was used instead of black paper, and when measuring the color, the aforementioned Tencolor Black was placed underneath to measure the white density and the black toner density on top of the white paper.

[0452] The color toner and white toner adhesion amounts of the image forming apparatus were adjusted, and printing was performed immediately after adjusting the adhesion amounts of each toner to the specified amount on the paper. About 20,000 black solid images were printed on the Fuji Clear 50ASW using a combination of color toner and white toner as shown in Table IV. Then, from the 20,000 images formed, a series of image samples for the specified image quality evaluation were taken, one for each 1,000 prints, totaling 20 images.

[0453] During the printing operation of 20,000 sheets, images with an image area ratio of 10% for each color were printed except for the image samples for evaluating image quality.

[0454] In addition, the printing operation of 20,000 sheets was carried out in the following stages.

[0455] First, assuming changes in the usage environment during actual use, the first 5,000 sheets were printed in an environment of 23°C and 50% RH, and then the installation environment was changed to 26°C and 60% RH overnight until the following day, and a further 5,000 sheets were printed in this environment.

[0456] After that, the environment was changed to 23°C and 50% RH overnight until the next day, and another 5,000 sheets were printed.

[0457] After that, the temperature was changed to 21°C and the relative humidity was reduced to 40% overnight until the next day, and the final 5,000 sheets were printed.

[0458] As described above, image formation can be used to evaluate performance when general fluctuations such as changes in the mechanical condition due to durability and changes in the installation environment are assumed when frequent adjustments of the amount of adhesion of color toner and white toner are not performed.

[0459] (Minimum Bk density of image sample) The Bk density of all 20 image samples taken was measured. The lowest Bk density among the measured values ​​(hereinafter referred to as the "lowest Bk density") was evaluated according to the following evaluation criteria. The evaluation criteria were "A" and "C", with "A" being acceptable for practical use and "C" being unacceptable for practical use. The results are shown in Table X.

[0460] [Evaluation Criteria] A Bk density is 1.74 or higher (pass). C Bk density is less than 1.74 (fail).

[0461] [Table 10]

[0462] (C.1.3) Discussion of the results of Examples 6 to 10 In the images of Examples 6 to 8 formed using the same color toners and white toners as those used in forming images in Examples 1 to 3 in the above-described embodiment 1, the Bk density immediately after the first adjustment was the reference density of 1.84, similar to Examples 1 to 3. However, a decrease in density occurred in some images during the printing of 20,000 sheets.

[0463] When some of the images in which density reduction occurred were observed in an enlarged scale, exposure of white toner particles between the black toner layers was observed in all of them, and as shown in Table X, the Bk density was below the standard Bk density of 1.84.

[0464] One of the reasons why the Bk density fell below the standard Bk density of 1.84 in Examples 6 to 8 is thought to be a problem caused by the printing operation after adjusting the amount of white toner attached, and this problem is thought to be caused by changes in the state of the electrophotographic process due to changes in the developer characteristics, changes in the temperature inside the machine, changes in the installation environment over time, etc.

[0465] When the state of the electrophotographic process changes as described above, the toner adhesion amount and the toner movement efficiency in the image forming unit change slightly, causing the mechanical state to deviate from the state intended by the designer. One method for preventing a decrease in density even in the face of such fluctuations is to frequently adjust the mechanical state, including adjusting the toner adhesion amount, so that the state is as intended by the designer. However, frequent adjustment of the mechanical state is undesirable because it reduces productivity.

[0466] The above-mentioned fluctuation in mechanical state is considered to be caused by the large particle components in the white toner particles. Therefore, it is necessary to reduce the ratio of large particles even more than the white toners W1 to W3 used in Examples 1 to 3, and to take measures against environmental fluctuations due to printing operations and aging.

[0467] The reason why the Bk density was lower than the standard value in Examples 6 to 8 is thought to be the proportion of large particles in the white toner particles, as described above. Therefore, in Examples 9 and 10, the removal of large particle components in the white toner particles used in the image formation of Examples 6 to 8 was further strengthened by using an air classifier.

[0468] As shown in Table 10, in Examples 9 and 10, the ratio of large particle diameter components is further reduced compared to Examples 6 to 8. Accordingly, in Examples 9 and 10, no decrease in Bk density occurred in any of the series of image samples for image quality evaluation when 20,000 sheets were printed.

[0469] This shows that satisfying not only the relationship between formulas (1) and (2) but also the relationship between formula (3) suppresses exposure of white toner particles even after printing 20,000 sheets. It is also shown that satisfying the relationship between formulas (1) and (2) and also the relationship between formula (3) can further suppress exposure of white toner particles.

[0470] From the above, it can be seen that although frequent adjustments would normally be necessary to suppress a decrease in Bk density, it is possible to realize an image forming apparatus that is stable and does not experience a decrease in density even in the face of fluctuations such as those described above, without assuming such frequent adjustments.

[0471] (C.2) Comparative Examples 7 to 9 and Examples 11 to 13 (Analysis at the Center and Edges) (C.2.1) Toner type and toner production policy The following Comparative Examples 7 to 9 and Examples 11 to 13 were carried out using each of the prepared toners. The toners used in Comparative Examples 7 to 9 and Examples 11 to 13 are as shown in Table XI below. Table XII also shows whether the toners in Table XI satisfy the particle size indexes of the formulas (1) to (3).

[0472] [Comparative Examples 7 to 9 and Examples 11 to 13] Toner Bk1 was used as the color toner used in Comparative Examples 7 to 9 and Examples 11 to 13. The white toner used in Comparative Examples 7 to 9 was the same as that used in Comparative Examples 1 to 3, and the white toner used in Examples 11 to 13 was the same as that used in Examples 1 to 3.

[0473] [Table 11]

[0474] [Table 12]

[0475] (C.2.2) Image formation As the evaluation device, a device equipped with a colorimeter for real-time color adjustment was used, which is similar to the device described in JP 2021-189267 A, which employs the image forming system shown in FIG. 4 described above. Note that this image formation is premised on the use of continuous paper. Therefore, N Mirror 73 / P22 / G7W manufactured by Oji TAC, which is a roll of paper, was used as the white paper for measuring the reference density.

[0476] In addition, instead of black paper, a transparent film made by Lintec, Fuji Clear 50ASW, was used for the roll paper, and the above-mentioned Tencolor Black was placed underneath it to measure the white density and the black toner density on the white background.

[0477] The color toner and white toner adhesion amounts of the image forming device were adjusted, and printing was performed immediately after adjusting the adhesion amount of each toner to a specified amount on the paper. 500 m of continuous paper printing was performed on the above-mentioned Fuji Clear 50ASW using a combination of color toner and white toner as shown in Table XIIIV.

[0478] At that time, a test pattern (image patch) for density measurement was printed at three points near the center in the width direction on the first and last images of the print job. The average density value of the above three points on the first and last images of the print job was then calculated.

[0479] The test pattern (image patch) for density measurement was formed using a solid patch of color toner Bk1.

[0480] (Bk density fluctuation at the center and edges) The image density fluctuation before and after printing 500 m was calculated using the following formula after calculating the average value. Formula: (Average density value of the last image in the print job)-(Average density value of the first image in the print job)

[0481] The measured image density fluctuation value was evaluated according to the following evaluation criteria, using "A" and "C" as the evaluation criteria, with "A" being acceptable for practical use and "C" being unacceptable for practical use.

[0482] [Evaluation Criteria] A Bk density fluctuation is 0.10 or less (pass). C Bk density variation is greater than 0.11 (fail).

[0483] [Table 13]

[0484] (C.2.3) Observations of the results of Comparative Examples 7 to 9 and Examples 11 to 13 In Comparative Example 7, the toner combination used in Comparative Example 1 was used to print 500 m of continuous paper using a continuous paper press capable of real-time color adjustment.

[0485] In addition, the "image density variation before and after printing 500 m" in Table XIII is a value derived by printing a test pattern (image patch) for density measurement at three points near the center in the width direction on the first and last images of a print job, calculating the average density of the three points, and then using the following formula. Formula: (Average density of the last image in the print job) - (Average density of the first image in the start of the print job)

[0486] The test pattern (image patch) for density measurement was formed using a solid patch of color toner Bk1.

[0487] In Comparative Example 7, even though real-time color adjustment was performed, the density increased by 0.11 before and after printing 500 m.

[0488] To consider this result, the Bk density of the edge patches and central image patch of this print job was measured and compared for the first image at the start of the print job and the last image of the print job, and the differences shown in Figure 9 were observed. Figure 9 is a graph of the measurement results showing the Bk density value at the position of each image patch when real-time color adjustment was performed. In Figure 9, the F edge patch is the edge patch on the front side of the machine, and the R edge patch is the edge patch on the back side of the machine. Additionally, the C image patch refers to the central image patch.

[0489] As can be seen from Fig. 9, there is almost no difference in the density of the edge patches between the first image at the start of the print job and the last image at the end of the print job. This shows that by performing real-time color adjustment, there is almost no change in the density of the edge patches between the first image at the start of the print job and the last image at the end of the print job, and color stability is maintained.

[0490] However, the density of the central image patch increases between the first image at the start of the print job and the last image at the end of the print job, and it can be seen that color stability is not ensured in the central area where stability is originally desired.

[0491] To further investigate the cause, the same 500m of continuous paper was printed using the same device, this time without performing real-time color adjustment. The density of the edge patches and central image patch were measured in the same way for the first image and the last image, and the results are shown in Figure 10. Figure 10 is a graph of the measurement results showing the Bk density value at the position of each image patch when real-time color adjustment was not performed.

[0492] As can be seen from Figure 10, when real-time color adjustment was not performed, the density was reduced at both the edge and center positions compared to the first image at the start of the print job, but the density of the edge patches was reduced more significantly than the density of the central image patch.

[0493] In addition, when the image evaluated in Figure 10 was observed under magnification, it was found that the area ratio of the white toner exposed between the black toner increased in both the center and edge patches compared to the first image, but the degree of increase was greater in the edge patch areas.

[0494] From this, it was found that the difference in density reduction between the central and edge patches from the first image to the final image shown in Figure 10 is due to the difference in the change in the exposed area rate of white toner between the central and edge areas.

[0495] From the above, it is believed that the fluctuation in image density before and after printing 500 m in Comparative Example 7 occurred for the following reasons.

[0496] As the print job progresses, the white toner exposure area ratio of the edge patch increases, and the density of the edge patch decreases slightly. When the image reading unit detects this decrease in density of the edge patch, the control unit shifts the black toner development conditions to conditions that increase the density, and adjusts them to maintain the density of the edge patch.

[0497] At this time, the white toner exposure in the center is not as bad as in the edge patches, and the density in the center increases from the start of printing.

[0498] It is believed that as a result of repeating this series of corrections using real-time color adjustments, the density of the end patches is maintained due to the adjustment effect, while the density of the central area is increased.

[0499] The reasons why the increase in the exposed area ratio of white toner in each part from the first image to the final image, and the increase in the exposed area ratio of white toner in the edge patches was greater than that in the central part during the verification in Figure 10, are thought to be as follows.

[0500] First, the reason for the increase in the exposed area ratio of the white toner in each portion is that the temperature inside the machine increases during a print job, which causes the resistance of the primary transfer roller to decrease.

[0501] The primary transfer current is adjusted to an appropriate current at the start of a print job, but the appropriate current decreases with resistance changes during the print job. As a result, in print jobs with long continuous printing distances, the resistance changes due to temperature increases during the print job, causing the appropriate current to decrease, resulting in printing with a slight overcurrent.

[0502] When the current becomes too high, the transfer efficiency decreases slightly. This causes a decrease in the amount of black toner attached to the paper, resulting in a decrease in density. In addition, the white toner layer becomes more exposed, which also reduces density.

[0503] Next, the reason why the increase in the exposed area ratio of the white toner in the edge patches is greater than that in the central portion is considered to be as follows.

[0504] The primary transfer portion is configured such that the image carrier is sandwiched between a transfer belt, which is an intermediate transfer member, and a primary transfer roller made of an elastic material, thereby forming a primary transfer nip.

[0505] Due to bending of the primary transfer roller, the pressing force in the center of the primary transfer nip is reduced, so the nip width is smaller in the center and becomes larger toward the ends.

[0506] At this time, the transfer current is larger at the ends and smaller at the center in proportion to the nip width, so the degree of the overcurrent is greater at the ends, and as a result, the density reduction is greater at the ends than at the center.

[0507] As a result, it is believed that the exposed area ratio of the white toner in the edge patches increases more significantly than in the central portion.

[0508] From the above, it is considered that in the image forming apparatus of this embodiment, which reads the color adjustment image at the edge and performs the adjustment operation, the color of the central image part is corrected based on the erroneous detection of a decrease in density of the edge patch.

[0509] (About the advantages of applying the image forming system of the present invention to a continuous paper printing machine) The results for Comparative Examples 8 and 9 and Examples 11 to 13 were obtained by using the same toners as in Comparative Examples 2 and 3 and Examples 1 to 3 and printing the same 500 m of continuous paper as above on the same continuous paper printing machine as above.

[0510] As can be seen from Table XIII, the image density fluctuation before and after 500 m of printing decreases with the decrease in the large diameter components of the white toner particles, and in Examples 11 to 13 which satisfy formula (2), the density fluctuation before and after 500 m of printing is substantially eliminated.

[0511] In Examples 11 to 13, the relationship between the volume average particle diameters of the color toners and the white toner satisfies formula (2), so that the white toner layer is not exposed. This is thought to be because there is no difference in color fluctuation between the end patches and the center, and erroneous correction does not occur when performing real-time color adjustment, and it becomes possible to perform correct density adjustment including the center.

[0512] From the above, it can be seen that when the relationship between the volume average particle diameters of the colored toners and the white toner satisfies equations (1) and (2), the exposure of white toner at the edges as described above does not occur, and image formation can be performed while correctly adjusting colors in real time even in continuous paper printing machines that cannot stop printing operations midway to perform adjustment operations. [Explanation of symbols]

[0513] 10 Control section 20 Memory section 30 Communications Department 40 Control section 50 Display section 60 Image control section 70 Image forming section 70 TC Color toner image forming unit 70 TW White toner image forming section for forming base layer 71Y, 71M, 71C, 71K, 71W photoconductor 72 Intermediate transfer belt 73 Transfer roller 74 Opposing Roller 80 Fixing unit 81a Upper pressure roller 81b Fixing belt 81c Heated roller 82 Lower pressure roller 90 Conveyor 91 Transport roller 92 Paper ejection roller 95 Color measurement section 100 Image forming system 101 Transport path 110 Image forming device 120 Paper feeder 130 Winding device N1 Nip section N2 Fixing nip D Paper feed direction P Recording medium P color Patch image for color adjustment

Claims

1. An image forming system including a color toner image forming unit, a white toner image forming unit for forming a base layer, and a transfer unit, the color toner image forming unit includes at least an image carrier and a developing unit having color toner therein; the undercoat layer forming white toner image forming unit includes at least an image carrier and a developing unit having white toner therein; The volume average particle diameter D of the toner particles constituting the color toner ５０Ｃ [μm] and the volume average particle size D of the toner particles constituting the white toner ５０Ｗ [μm] satisfies the following formula (1), Formula (1) 1.1×D ５０Ｃ <D ５０Ｗ [μm] And the volume average particle size D ５０Ｗ , the standard deviation σ of the volume particle size distribution of the toner particles constituting the white toner Ｗ and volume average particle size D ５０Ｃ satisfies the relationship of the following formula (2). Formula (2) D ５０Ｗ +1.6×σ Ｗ <1.5×D ５０Ｃ [μm] 1. An image forming system comprising:

2. The volume average particle diameter D ５０Ｗ [μm], the standard deviation of the volume particle size distribution σ Ｗ [μm] and the volume average particle diameter D ５０Ｃ [μm] satisfies the following formula (3). Formula (3) D ５０Ｗ +2.0×σ Ｗ <1.5×D ５０Ｃ [μm] 2. The image forming system according to claim 1,

3. The color toner is a polymerized toner, and the white toner is a pulverized toner.

2. The image forming system according to claim 1,

4. The white toner contains a charge control agent.

2. The image forming system according to claim 1,

5. The image reading unit reads patch images for color adjustment formed on the continuous paper, and the image control unit is provided. the image reading unit is disposed opposite the continuous paper being transported along a transport path, the image control unit instructs formation of the patch image for color adjustment at a paper edge in a direction perpendicular to a paper feed direction, and Based on the detection result from the image reading unit, an instruction to change the image forming conditions in the color toner image forming unit, the undercoat layer forming white toner image forming unit, and the transfer unit is given.

2. The image forming system according to claim 1,

6. An image forming method including a color toner image forming step, a white toner image forming step for forming a base layer, and a transfer step, the color toner image forming step develops at least the electrostatic latent image formed on the image carrier with a developer containing a color toner to form a color toner image; the white toner image forming step for forming the undercoat layer develops at least the electrostatic latent image formed on the image carrier with a developer containing a white toner to form a white toner image; The volume average particle diameter D of the toner particles constituting the color toner ５０Ｃ [μm] and the volume average particle size D of the toner particles constituting the white toner ５０Ｗ [μm] satisfies the following formula (1), Formula (1) 1.1×D ５０Ｃ <D ５０Ｗ [μm] And the volume average particle size D ５０Ｗ , the standard deviation σ of the volume particle size distribution of the toner particles constituting the white toner Ｗ and volume average particle size D ５０Ｃ satisfies the relationship of the following formula (2). Formula (2) D ５０Ｗ +1.6×σ Ｗ <1.5×D ５０Ｃ [μm] 1. An image forming method comprising:

Images