Image forming method

Abstract

To provide an image forming method that has sufficient bonding strength to a recording medium, and can form an image excellent in heat seal resistance.SOLUTION: An image forming method includes: a toner image forming step S01 of forming, on a recording medium, a toner image including a white toner image and a chromatic toner image arranged on the white toner image; and a toner image fixing step S02 of fixing the toner image obtained in the toner image forming step S01 onto the recording medium. The recording medium is a resin film. The toner image is formed of a white toner and a chromatic toner, and the white toner and the chromatic toner include an amorphous polyester resin as a main component. The content ratio Vw (mass%) of vinyl resin in a binder resin component included in the white toner, and the content ratio Vc (mass%) of vinyl resin in a binder resin component included in the chromatic toner satisfy the following formula (1), and the chromatic toner includes ester wax as a mold release agent. Vc>Vw≥0 (1)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming method, and more particularly to an image forming method capable of forming an image that has sufficient adhesive strength to a recording medium and is also excellent in heat seal resistance. [Background technology]

[0002] In recent years, there has been an increasing demand for short-run printing in the field of flexible packaging printing. One method for short-run printing is the electrophotographic image formation method. In the electrophotographic image formation method, there is a risk that the substrate for flexible packaging may be deformed or melted due to heat during fixing. Therefore, in the electrophotographic image formation method, there is a demand for the development of a toner with excellent low-temperature fixing properties that can suppress heating during fixing.

[0003] As a method for printing on films used for applications such as substrates for flexible packaging, a method has been proposed in which an image is formed on the film by electrophotography using a toner containing a crystalline polyester resin in the binder resin (see, for example, Patent Document 1).

[0004] The printing method described in Patent Document 1 uses a polypropylene film or a polyethylene film as the film on which an image is formed. The printing method described in Patent Document 1 uses a toner containing the above-mentioned crystalline polyester resin to form an image at a specific fixing temperature on a film whose printing surface has a specific surface tension. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-54448 Summary of the Invention [Problem to be solved by the invention]

[0006] Printed materials for flexible packaging, one of the packaging applications, undergo a bag-making process after printing to be processed into a package suitable for the product. For this reason, heat sealing, which uses heat and pressure to melt and bond the film, is sometimes used to bond films for flexible packaging. Printing for flexible packaging applications can be divided into two types: "front printing," in which the printed surface is on the outside of the bag when the film is made into a bag, and "reverse printing," in which the printed surface is on the inside of the bag. "Reverse printing," in which the printed surface is on the inside of the bag, requires a lamination process for bag formation. The lamination process involves adhering a laminate film coated with adhesive onto the image after printing. On the other hand, "front printing," in which the printed surface is on the outside of the bag, can be made into bags without the lamination process described above. Therefore, "front printing" has the advantage of improving productivity. Hereinafter, images printed by "front printing" will be referred to as "front-printed images," and images printed by "reverse printing" will be referred to as "reverse-printed images."

[0007] In the heat-sealing process during the bag-making process, a front-printed image comes into direct contact with the heat seal bar, which can result in excessive heat and pressure being applied to the image. On the other hand, in the heat-sealing process, a reverse-printed image has a printed surface on the inner surface of the bag, so the heat seal bar does not come into direct contact with the image during the heat-sealing process, and heat is transmitted to the image through the film. Therefore, front-printed images are subject to a greater load than reverse-printed images, in which heat is transmitted through the film. Even when using the printing method and toner described in Patent Document 1, the heat-sealing resistance of front-printed images is insufficient, and image peeling during the heat-sealing process cannot be sufficiently suppressed. Therefore, there is a need for an image-forming method that is less likely to cause image peeling, even under harsh heat-sealing conditions such as those of front-printed images.

[0008] The present invention has been made in view of the above problems and circumstances. An object of the present invention is to provide an electrophotographic image forming method that can form an image that has sufficient adhesive strength to a resin film serving as a recording medium such as a substrate for flexible packaging, and that also has excellent heat-sealing resistance during bag production. [Means for solving the problem]

[0009] The present inventors have investigated the causes of the above-mentioned problems in order to solve them. In electrophotographic image forming methods, a white toner layer is formed as a base layer at the bottom, and color toner layers are formed on top of the white toner layer. In the process of investigating ways to improve the heat seal resistance of the surface-printed image thus formed, the present inventors focused on the vinyl resin content in the binder resins of the white toner and color toner used to form the toner image. As a result, they found that the heat seal resistance of the surface-printed image is improved when the vinyl resin content of the color toner is higher than that of the white toner, and have arrived at the present invention. That is, the above-mentioned problems of the present invention are solved by the following means.

[0010] 1. A step of forming a toner image on a recording medium, the toner image including a white toner image and a color toner image disposed on the white toner image; and fixing the toner image on the recording medium, the recording medium is a resin film, the toner image is formed from a white toner and a color toner, the white toner and the color toner each containing an amorphous polyester resin as a main component, When the content ratio (mass%) of the vinyl resin in the binder resin component contained in the white toner is Vw and the content ratio (mass%) of the vinyl resin in the binder resin component contained in the color toner is Vc, the Vw and the Vc satisfy the relationship of the following formula (1), and The image forming method according to claim 1, wherein the color toner contains an ester wax as a releasing agent. Vc>Vw≧0 (1)

[0011] 2. The image forming method described in item 1, wherein Vc satisfies the relationship of the following formula (2): 50≧Vc≧20 (2)

[0012] 3. The image forming method according to item 1 or 2, wherein the vinyl resin is a styrene-acrylic resin.

[0013] 4. The image forming method according to item 1 or 2, wherein at least one of the white toner and the color toner further contains a crystalline polyester resin.

[0014] 5. The image forming method according to item 1 or 2, wherein the melting point of the ester wax is 65 to 90°C.

[0015] 6. The difference in storage modulus at 90°C between the white toner and the color toner is 1.0 x 10 4 Pa~1.0×10 5 3. The image forming method according to item 1 or 2, wherein Pa is

[0016] 7. The image forming method described in item 1 or 2, characterized in that the amorphous polyester resin is a polycondensation product of a polycarboxylic acid and a polyhydric alcohol, and the content of structural units derived from bisphenol A derivatives is 10 mol % or less relative to 100 mol % of all structural units derived from alcohols. [Effects of the Invention]

[0017] By the above means of the present invention, it is possible to form an image that has sufficient adhesive strength to the resin film as a recording medium and also has excellent heat-sealing resistance during bag production.

[0018] The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is speculated as follows.

[0019] First, in the image forming method of the present invention, the white toner and the color toner contain an amorphous polyester resin as a main component. In the present invention, the "main component" of the white toner and the color toner refers to the resin with the highest content among the binder resins constituting the respective toners. The amorphous polyester resin has the property of being able to lower the softening point while maintaining a relatively high glass transition temperature. Therefore, the white toner and the color toner each have good thermal melting properties and good low-temperature fixability. Furthermore, such a toner has the property of being easily thermal melting and easily wetting and spreading on the resin film, which is the recording medium, during fixing, thereby increasing the contact area between the toner and the resin film and improving adhesion.

[0020] Furthermore, color toners contain a specific content of vinyl resin in addition to amorphous polyester resin as the main component. Compared to polyester resin, vinyl resin has the property of being highly elastic and resistant to loss of elasticity even at high temperatures. Therefore, by including such a vinyl resin in the binder resin constituting the color toner, excessive plasticization of the binder resin is suppressed even when heat and pressure are applied. In the course of studying ways to improve the heat seal resistance of images printed by surface printing, the present inventors focused on the content of vinyl resin in the binder resin constituting the toner. As a result, they found that the heat seal resistance of surface-printed images is improved by increasing the content of vinyl resin in color toners compared to white toners.

[0021] Specifically, a surface-printed image has a white toner image formed on the bottom layer (hereinafter simply referred to as the "bottom layer") as a base, and a color toner image formed on top of the white toner image. When a heat-sealing process is performed on the surface-printed image, the color toner image on the top layer is directly exposed to the heat of the heat seal bar. Therefore, the color toner image on the top layer is more susceptible to heat transfer from the heat seal bar and plasticization than the white toner image on the bottom layer. If the elasticity of the color toner image and the white toner image at high temperatures differs significantly, the adhesive strength between the layers in the toner image weakens, resulting in image peeling at the interface between the layers. Therefore, by reducing the difference in elasticity between the top and bottom layers at high temperatures, it is believed that heat-induced peeling between the layers can be suppressed and heat-sealing resistance can be improved. Furthermore, we have found that by incorporating a larger amount of vinyl resin into the color toner forming the top layer, which is more susceptible to heat transfer, than into the white toner forming the bottom layer, the difference in elasticity between the top and bottom layers is reduced, thereby improving the heat-sealing resistance of the surface-printed image.

[0022] In the image forming method of the present invention, the color toner contains an ester wax as a release agent. The ester wax has a high affinity with the amorphous polyester resin. The wax in the image formed with this color toner has a small and uniform particle size, and is more abundant on the surface side of the image. Therefore, the image formed with this color toner has a reduced adhesive strength with the heat seal bar, and the heat seal resistance is further improved. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a flowchart illustrating an embodiment of an image forming method of the present invention. [Figure 2] FIG. 1 is a diagram schematically illustrating an example of the configuration of an image forming apparatus. [Figure 3] 1 is a diagram schematically illustrating an example of the configuration of an image forming apparatus for carrying out an image forming method using a recording medium stored in a roll form. DETAILED DESCRIPTION OF THE INVENTION

[0024] As shown in Fig. 1, one embodiment of the image forming method of the present invention is an image forming method having a toner image forming step S01 for forming a toner image and a toner image fixing step S02 for fixing the toner image on a recording medium. The toner image forming step S01 is a step for forming a toner image on a recording medium, the toner image including a white toner image and a color toner image disposed on the white toner image. The toner image fixing step S02 is a step for fixing the toner image obtained in the toner image forming step S01 onto the recording medium. Fig. 1 is a flowchart showing one embodiment of the image forming method of the present invention.

[0025] In the toner image forming step S01, a toner image including a white toner image and a color toner image is formed from a white toner and a color toner. More specifically, the white toner image formed as the bottom layer on the recording medium is formed from a white toner. The color toner image is formed from a color toner.

[0026] In the image forming method of this embodiment, the white toner and color toners that form the toner images contain an amorphous polyester resin as a main component. The "main component" of the white toner and color toner refers to the resin with the highest content among the binder resins constituting each toner. If the content (mass%) of the vinyl resin in the binder resin component contained in the white toner is Vw and the content (mass%) of the vinyl resin in the binder resin component contained in the color toner is Vc, then Vw and Vc satisfy the relationship shown in formula (1) below. Furthermore, the color toner contains an ester wax as a release agent. Hereinafter, the "content (mass%) of the vinyl resin in the binder resin component contained in the white toner" may be referred to as the "content (mass%) of the vinyl resin in the white toner (Vw (mass%)"). Similarly, the "content (mass%) of the vinyl resin in the binder resin component contained in the color toner" may be referred to as the "content (mass%) of the vinyl resin in the color toner (Vc (mass%)." Furthermore, the white toner and color toner may be collectively referred to simply as "toner." Vc>Vw≧0 (1)

[0027] According to the image forming method of this embodiment configured as described above, it is possible to form an image that has sufficient adhesive strength to the resin film as a recording medium and also has excellent heat-sealing resistance during bag production. The resin film as a recording medium is preferably used as a flexible packaging material, which is one type of packaging material. Therefore, the image forming method of this embodiment can form an image that is less likely to peel, even when using a front-side printing method in which the image comes into direct contact with a heat seal bar during the heat-sealing process in the bag-making process.

[0028] The toners used in the image forming method of this embodiment contain an amorphous polyester resin as a main component, which makes them easy to heat-melt and fix at low temperatures. Furthermore, they have the property of easily wetting and spreading on the resin film serving as a recording medium during fixing, which increases the contact area between the toner and the resin film and improves adhesion.

[0029] Furthermore, by making the color toner that forms the upper layer, which is more susceptible to heat transfer during heat sealing, contain more vinyl resin than the white toner that forms the lower layer, the difference in elasticity between the upper and lower layers can be reduced.By reducing the difference in elasticity between the upper and lower layers that form the image, the heat sealing resistance of the surface-printed image can be improved.

[0030] Furthermore, color toners contain ester wax as a release agent. Images formed using such color toners have reduced adhesive strength with a heat seal bar and improved heat seal resistance. That is, the wax in images formed using color toners has small and uniform particle sizes, and is more abundant on the surface side of the image. Therefore, such images have reduced adhesive strength with a heat seal bar and improved heat seal resistance.

[0031] 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" indicating a range of values ​​is used to mean that the values ​​before and after the symbol "to" are included as the lower limit and upper limit.

[0032] In the present invention, first, "chromatic toner" refers to a toner, such as yellow toner, magenta toner, or cyan toner, that basically has the three attributes of hue, lightness, and saturation. On the other hand, "achromatic toner" refers to a coupler, such as black toner, white toner, or gray toner, that basically has only lightness, without hue or saturation. Furthermore, "clear toner" refers to a toner in an electrophotographic image in which a layer formed with the clear toner transmits light in almost all or part of the visible light range, making it transparent, allowing the view beyond the layer to be seen through. The light transmittance is not particularly limited as long as it is sufficient to allow the view through, but is preferably 50% or more, preferably 70% or more, and more preferably 90% or more. When light in almost all of the visible light range is transmitted, the toner is colorless and transparent.

[0033] Here, "white toner" refers to the CIEL (Cipher Emissions Index) value obtained by measuring the surface of a transfer material with a spectrophotometer in accordance with JIS Z 8781-4:2013 when only white toner is transferred onto the transfer material. * a * b * Lightness L in the color system * is 80 or more, and a * and b * are -10≦a * ≦10, -10≦b * It refers to a toner having a color (white) that satisfies the condition of ≦10.

[0034] In this specification, "color toner" refers to a toner that belongs to a group of toners that includes the above-mentioned chromatic toners, black toner and gray toner contained in the above-mentioned achromatic toners, and the above-mentioned clear toner, and the color toner does not include white toner.

[0035] [Image formation method overview] The image forming method of this embodiment includes a toner image forming step S01 for forming a toner image and a toner image fixing step S02 for fixing the toner image on a recording medium. The toner image forming step S01 is a step for forming a toner image on a recording medium, the toner image including a white toner image and a color toner image disposed on the white toner image. The toner image fixing step S02 is a step for fixing the toner image obtained in the toner image forming step S01 onto the recording medium. In the image forming method of this embodiment, a resin film is used as the recording medium. Details of the resin film will be described later.

[0036] The white toner and color toners that form the toner images contain an amorphous polyester resin as a main component. The vinyl resin content (Vw, % by mass) of the binder resin component contained in the white toner and the vinyl resin content (Vc, % by mass) of the binder resin component contained in the color toner satisfy the relationship shown in formula (1). Furthermore, the color toner contains an ester wax as a release agent.

[0037] [Image forming method] The toner image forming step S01 is performed using white toner and color toner, and may include, for example, a charging step, an exposing step, a developing step, and a transferring step. The charging step, the exposing step, the developing step, and the transferring step in the toner image forming step S01, as well as the fixing step as the toner image fixing step S02, will be described below.

[0038] <Charging process> In the charging step, the electrophotographic photosensitive member is charged. The charging method is not particularly limited, and may be a known method such as a charging roller method in which the electrophotographic photosensitive member is charged by a charging roller.

[0039] <Exposure process> In the exposure step, an electrostatic latent image is formed on an electrophotographic photoreceptor (electrostatic latent image carrier). The electrophotographic photoreceptor is not particularly limited, but examples thereof include drum-shaped ones made of organic photoreceptors such as polysilane or phthalopolymethine. The electrostatic latent image is formed, for example, by uniformly charging the surface of the electrophotographic photoreceptor in a charging step and then imagewise exposing the surface of the electrophotographic photoreceptor using an exposure means. The exposure means is not particularly limited, and those commonly used in electrophotography can be used.

[0040] <Developing process> The development process is a process in which the electrostatic latent image formed in the exposure process is developed with a dry developer containing toner to form a toner image. The toner image is formed using a dry developer containing toner, for example, using a developing unit consisting of an agitator that charges the toner by frictional agitation and a rotatable magnet roller. Specifically, in the developing unit, for example, the toner and carrier are mixed and agitated, and the toner is charged by the friction and held on the surface of the rotating magnet roller, forming a magnetic brush. Because the magnet roller is located near the electrophotographic photosensitive member (electrostatic latent image carrier), a portion of the toner constituting the magnetic brush formed on the surface of the magnet roller migrates to the surface of the electrophotographic photosensitive member by electrical attraction. As a result, the electrostatic latent image is developed with toner, forming a toner image on the surface of the electrophotographic photosensitive member.

[0041] <Transfer process> In the transfer process, the toner image formed in the development process is transferred to a recording medium. The toner image is transferred to the recording medium by peeling and charging the toner image onto the recording medium. Examples of transfer devices that can be used include a corona transfer device using corona discharge, a transfer belt, and a transfer roller. For example, the transfer process can be performed using an intermediate transfer member, where the toner image is primarily transferred onto the intermediate transfer member, and then the primarily transferred toner image is secondarily transferred onto the recording medium. In addition to the above-described embodiment, the transfer process can also be performed by directly transferring the toner image formed on the electrophotographic photoreceptor (electrostatic latent image carrier) to an image support. Examples of recording media used in general image formation methods include plain paper ranging from thin to thick paper, high-quality paper, coated printing paper such as art paper or coated paper, commercially available Japanese paper and postcards, plastic film for overhead projectors, and cloth. In the image formation method of this embodiment, a resin film is used as the recording medium. The toner image transferred onto the recording medium includes a white toner image and a color toner image, with the color toner image being positioned on top of the white toner image formed as the bottom layer.

[0042] <Fixing process> The fixing process involves conveying a recording medium onto which an unfixed image, including a white toner image and a color toner image, to a fixing nip portion provided between a heated fixing rotor and a pressure member, where the unfixed image is thermally fixed. Examples of the fixing process include a roller fixing method comprising a fixing rotor roller (also referred to as a "fixing roller") as a fixing rotor and a pressure roller. The pressure roller is a pressure member that is provided in pressure contact with the fixing roller to form the fixing nip portion. Other examples of the fixing process include a belt fixing method in which the fixing rotor is comprised of a fixing belt.

[0043] [Image forming equipment] While an example of a typical image forming apparatus using YMCK toner will be described below, the image forming method of this embodiment uses white toner to form the bottom layer that serves as the base for the toner image in addition to color toners such as YMCK toner. Therefore, the image forming apparatus used in the image forming method of this embodiment differs in that it uses a similar apparatus with additional image forming units, etc., that take into account the use of white toner. However, since the basic principles are the same, the following description will be used in this case. Furthermore, when clear toner is used, a similar apparatus with additional image forming units, etc., that take this into account can be used.

[0044] 2 is a diagram schematically illustrating an example of the configuration of an image forming apparatus 100 used in the image forming method. The image forming apparatus 100 shown in FIG. 2 is a so-called tandem type color image forming apparatus.

[0045] Image forming apparatus 100 has an original image reading device SC, four image forming units for forming toner images, and a transfer device for transferring the toner images formed in the image forming units onto recording medium P. Image forming apparatus 100 also has a paper feed / transport device for transporting recording medium P, and a heat roll type fixing device 50 as fixing means for fixing unfixed toner images carried on recording medium P onto recording medium P. Note that original image reading device SC is a reading device for reading original images. The configuration of image forming apparatus 100 will be described in further detail below.

[0046] The document image reading device SC reads image information of the document, converts it into image data of each color of YMCK, and sends the image data of the corresponding color to the exposure device 3, which will be described later.

[0047] The four image forming units are devices for forming images in four colors, yellow (Y), magenta (M), cyan (C), and black (K), respectively, and are arranged, for example, in the order of YMCK from the top in FIG. 1. Each image forming unit has a photoreceptor 1, a charging device 2, an exposure device 3, a developing device 4, a primary transfer roller 5, and a cleaning device 6. When a white toner image is formed using white toner, a fifth image forming unit for forming an image with white toner may be further provided, and a white image may be formed in the image forming unit for forming an image with white toner.

[0048] The photoreceptor 1 is, for example, a drum-shaped organic photoreceptor, and the charging device 2 is, for example, a non-contact charging device that uses corona discharge. The exposure device 3 is, for example, a laser oscillation device, and the developing device 4 is a developing device for a two-component developer that contains a two-component developer of one of the colors YMCK. The primary transfer roller 5 is, for example, a charging roller that is freely urged toward the photoreceptor 1 via an intermediate transfer belt 7. The cleaning device 6 is, for example, a blade cleaning device that has an elastic blade made of rubber that contacts the surface of the photoreceptor 1.

[0049] The transfer device has an endless intermediate transfer belt 7, multiple rollers 8 that tension the intermediate transfer belt 7, a secondary transfer roller 9, and a cleaning device 10. The rollers 8 include one or more drive rollers and may also include driven rollers other than the drive rollers. The secondary transfer roller 9 is, for example, a charging roller that can form a nip between the intermediate transfer belt 7 and the recording medium P being conveyed therethrough. The cleaning device 10 is, for example, a blade cleaning device that has an elastic blade that contacts the surface of the intermediate transfer belt 7.

[0050] The paper feed and transport device has a paper feed cassette 11, paper feed rollers 12, transport rollers 13, registration rollers 14, discharge rollers 15, and a paper output tray 16. The paper feed cassette 11 is for storing recording media P. The paper feed rollers 12 are for removing the recording media P from the paper feed cassette 11. The transport rollers 13 are for transporting the recording media P to the nip portion of the secondary transfer roller 9. The registration rollers 14 are for controlling the position of the recording media P being transported. The discharge rollers 15 are for ejecting the recording media P discharged from the fixing device 50 to the outside of the apparatus. The paper output tray 16 is for storing the recording media P discharged to the outside of the apparatus. The recording media P is not particularly limited, but is, for example, a resin film such as an OHP sheet.

[0051] In the image forming apparatus 100 configured as described above, in the image forming section, the surface of the rotationally driven photoreceptor 1 is charged by application of a voltage from the charging device 2. The exposure device 3 irradiates the charged surface of the photoreceptor 1 with laser light corresponding to image data of the corresponding color of YMCK, forming an electrostatic latent image. Toner particles are supplied from the developing device 4 to the surface of the photoreceptor 1 on which the electrostatic latent image has been formed, and the toner particles adhere to the electrostatic latent image, developing the electrostatic latent image.

[0052] The YMCK toner images formed in each image forming unit and carried on the surface of the photoreceptor 1 are transferred successively onto the rotating intermediate transfer belt 7 in an overlapping manner by application of a voltage from the primary transfer roller 5. As a result, a composite color toner image is formed on the intermediate transfer belt 7. Note that when forming the white toner image and the color toner images, either a one-pass method or a two-pass method may be used. The one-pass method is a method in which a white toner image and a color toner image are formed on the intermediate transfer belt 7 and then transferred simultaneously to the recording medium P. The two-pass method is a method in which a base image (white toner image) is formed on the recording medium P and fixed, and then an upper image (color toner image) is formed on the base image and fixed. In other words, the base image and upper image are formed and fixed on the recording medium P in two separate steps. The primary transfer roller 5 may contact the photosensitive member 1 only during primary transfer. For example, the primary transfer roller 5 in the image forming section for black images is always in contact with the photosensitive member 1, and the primary transfer rollers 5 for other colors are in contact with the photosensitive member 1 only during primary transfer.

[0053] After the primary transfer, the cleaning device 6 removes any adhering matter such as transfer residual toner from the surface of the photoreceptor 1 .

[0054] The recording medium P accommodated in the paper feed cassette 11 is taken out of the paper feed cassette 11 by the paper feed roller 12 and transported to the secondary transfer roller 9 via the transport roller 13 and the registration roller 14. The color toner image (i.e., a colored toner image) on the intermediate transfer belt 7 is transferred onto the recording medium P by application of a voltage from the secondary transfer roller 9. The secondary transfer roller 9 is, for example, urged toward the intermediate transfer belt 7 only during secondary transfer.

[0055] After the secondary transfer, the cleaning device 10 removes any adhering matter such as transfer residual toner from the surface of the intermediate transfer belt 7 .

[0056] The color toner image on the recording medium P is fixed to the surface of the recording medium P by the application of heat and pressure by the fixing device 50. In this way, a fixed color toner image is formed on the recording medium P. The recording medium P on which the color toner image has been formed is transported onto the paper discharge tray 16 via the discharge rollers 15. By repeating the above process, fixed toner images are formed one after another on the recording medium P.

[0057] Next, an image forming apparatus for carrying out an image forming method using a recording medium P stored in a roll form will be described with reference to Fig. 3. Fig. 3 is a diagram schematically illustrating an example of the configuration of an image forming apparatus for carrying out an image forming method using a recording medium P stored in a roll form.

[0058] Image forming apparatus 200 has substantially the same configuration as image forming apparatus 100, except that it further includes a storage section 201 that stores roll-shaped recording medium P, a first conveying unit 202, a second conveying unit 203, and a storage section 204. The first conveying unit 202 is for conveying successive sheets of recording medium P to the upstream portion of the paper feed conveying device. The second conveying unit 203 is for feeding back the recording medium P on which a fixed toner image has been formed. The storage section 204 is for storing the recording medium P conveyed from the conveying unit 203 in roll form. The recording medium P is, for example, a series of PET sheets used for flexible packaging.

[0059] In the image forming apparatus 200 configured as described above, the recording medium P is continuously transported from the storage section 201 toward the secondary transfer roller 9 via the first transport unit 202. Then, the recording medium P, on which the toner image has been fixed by the fixing device 50, is stored in a roll form in the storage section 204 via the second transport unit 203. Apart from being configured as described above, a toner image is formed on the recording medium P in the same manner as in the formation of a toner image by the image forming apparatus 100.

[0060] [Toner (white toner and color toner)] Next, the white toner and color toners used in the image forming method of this embodiment will be described in detail.

[0061] The toner used in the image forming method contains toner particles containing a binder resin. In the present invention, the toner particles refer to toner base particles to which an external additive has been added, and an aggregate of toner particles is called a toner. Generally, the toner base particles can be used as they are, but in the present invention, the toner particles are used to which an external additive has been added.

[0062] The toner base particles contain a binder resin, and may also contain other components such as a release agent (wax), a colorant, and a charge control agent, as necessary.

[0063] <Binder resin> In the toner used in the image forming method, the color toner contains at least an amorphous polyester resin and a vinyl resin as a binder resin. The white toner contains at least an amorphous polyester resin as a binder resin. The white toner may contain a vinyl resin as a binder resin. The color toner and the white toner may further contain a conventional fixing resin such as a crystalline polyester resin as a binder resin.

[0064] (amorphous polyester resin) Amorphous polyester resin is the main component of the binder resin contained in the toner. Amorphous polyester resin has the property of being able to lower the softening point while maintaining a relatively high glass transition temperature. Therefore, toner containing amorphous polyester resin as the main component is easily thermally melted and has good low-temperature fixability. Furthermore, such toner is easily thermally melted and has the property of easily wetting and spreading on the resin film, which is the recording medium, during fixing, thereby increasing the contact area between the toner and the resin film and improving adhesion.

[0065] There is no particular limitation on the content of the amorphous polyester resin in the binder resin component, as long as it is the resin with the highest content among the binder resins constituting the toner. For example, although not particularly limited, the content of the amorphous polyester resin in the binder resin component is preferably 60 to 100% by mass, more preferably 70 to 100% by mass, and particularly preferably 80 to 100% by mass.

[0066] Amorphous polyester resins are polyester resins that have no melting point and a relatively high glass transition temperature (Tg) when subjected to differential scanning calorimetry (DSC). The glass transition temperature (Tg) is preferably 30 to 80°C, and more preferably 40 to 64°C. The glass transition temperature (Tg) can be measured using a differential scanning calorimeter (DSC). Furthermore, since the monomers constituting amorphous polyester resins are different from the monomers constituting crystalline polyester resins, they can be distinguished from crystalline polyester resins by analysis such as NMR. Furthermore, those skilled in the art can control the glass transition temperature by adjusting the resin composition.

[0067] Amorphous polyester resins are obtained by polycondensation reaction of divalent or higher carboxylic acids (polycarboxylic acids) and divalent or higher alcohols (polyhydric alcohols). There are no particular limitations on the amorphous polyester resins, and any amorphous polyester resins known in the art can be used.

[0068] Examples of the polycarboxylic acid and polyhydric alcohol used in the preparation of the amorphous polyester resin are not particularly limited, but include the following:

[0069] (Polycarboxylic Acid) As the polycarboxylic acid, it is preferable to use an unsaturated aliphatic polycarboxylic acid, an aromatic polycarboxylic acid, or a derivative thereof. A saturated aliphatic polycarboxylic acid may be used in combination as long as it can form an amorphous resin.

[0070] Examples of unsaturated aliphatic polycarboxylic acids include unsaturated aliphatic dicarboxylic acids, unsaturated aliphatic tricarboxylic acids, and unsaturated aliphatic tetracarboxylic acids. Lower alkyl esters and acid anhydrides of these can also be used. Examples of unsaturated aliphatic dicarboxylic acids include methylene succinic acid, fumaric acid, maleic acid, 3-hexenedioic acid, 3-octenedioic acid, and succinic acids substituted with alkenyl groups having 2 to 20 carbon atoms. Examples of unsaturated aliphatic tricarboxylic acids include 3-butene-1,2,3-tricarboxylic acid, 4-pentene-1,2,4-tricarboxylic acid, and aconitic acid. Examples of unsaturated aliphatic tetracarboxylic acids include 4-pentene-1,2,3,4-tetracarboxylic acid.

[0071] Examples of aromatic polycarboxylic acids include aromatic dicarboxylic acids, aromatic tricarboxylic acids, aromatic tetracarboxylic acids, and aromatic hexacarboxylic acids. Lower alkyl esters and acid anhydrides of these compounds can also be used. Examples of aromatic dicarboxylic acids include phthalic acid, terephthalic acid, isophthalic acid, t-butylisophthalic acid, tetrachlorophthalic acid, chlorophthalic acid, and nitrophthalic acid. Examples of aromatic dicarboxylic acids include p-phenylenediacetic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and anthracenedicarboxylic acid. Examples of aromatic tricarboxylic acids include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid (trimesic acid), 1,2,4-naphthalenetricarboxylic acid, and hemimellitic acid. Examples of aromatic tetracarboxylic acids include pyromellitic acid and 1,2,3,4-butanetetracarboxylic acid. Examples of aromatic hexacarboxylic acids include mellitic acid.

[0072] The above polycarboxylic acids may be used alone or in combination of two or more.

[0073] (Polyhydric alcohol) As the polyhydric alcohol, from the viewpoint of charging property and toner strength, it is preferable to use unsaturated aliphatic polyhydric alcohols, aromatic polyhydric alcohols, and derivatives thereof, and saturated aliphatic polyhydric alcohols may be used in combination as long as an amorphous resin can be formed.

[0074] Examples of unsaturated aliphatic polyhydric alcohols include unsaturated aliphatic diols, and derivatives thereof can also be used. Examples of unsaturated aliphatic diols include 2-butene-1,4-diol, 3-butene-1,4-diol, 2-butyne-1,4-diol, 3-butyne-1,4-diol, and 9-octadecene-7,12-diol.

[0075] Examples of aromatic polyhydric alcohols include bisphenols such as bisphenol A and bisphenol F, and alkylene oxide adducts of bisphenols such as their ethylene oxide adducts and propylene oxide adducts. Examples of aromatic polyhydric alcohols include 1,3,5-benzenetriol, 1,2,4-benzenetriol, and 1,3,5-trihydroxymethylbenzene. Derivatives of the aromatic polyhydric alcohols described above can also be used as the aromatic polyhydric alcohol. Among these, it is preferable to use bisphenol A compounds such as ethylene oxide adducts and propylene oxide adducts of bisphenol A, particularly from the viewpoint of easily optimizing thermal properties.

[0076] The number of carbon atoms in the trihydric or higher polyhydric alcohol is not particularly limited, but it is preferable that the number of carbon atoms is 3 to 20, as this makes it easier to optimize the thermal properties.

[0077] The above-mentioned polyhydric alcohols may be used alone or in combination of two or more.

[0078] The amorphous polyester resin is a polycondensate of a polycarboxylic acid and a polyhydric alcohol, and preferably contains 10 mol % or less of structural units derived from bisphenol A derivatives relative to 100 mol % of all structural units derived from alcohols. This configuration improves the compatibility of the crystalline polyester and finely disperses it, resulting in good low-temperature fixability.

[0079] The method for producing the amorphous polyester resin is not particularly limited, and the resin can be produced by polycondensing (esterifying) the polycarboxylic acid and polyhydric alcohol described above using a known esterification catalyst.

[0080] Examples of catalysts that can be used in the production include alkali metal compounds such as sodium and lithium; compounds containing Group 2 elements such as magnesium and calcium; metal compounds such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium, and germanium; phosphorous compounds; phosphate compounds; and amine compounds. Considering availability, it is preferable to use dibutyltin oxide, tin octoate, tin dioctoate, salts thereof, tetra-n-butyl titanate (tetrabutyl orthotitanate), tetraisopropyl titanate (titanium tetraisopropoxide), tetramethyl titanate, and the like. These may be used alone or in combination of two or more.

[0081] The polycondensation (esterification) temperature is not particularly limited, but is preferably within the range of 150 to 250° C. The polycondensation (esterification) time is not particularly limited, but is preferably 0.5 to 15 hours. During polycondensation, the reaction system may be reduced in pressure as necessary.

[0082] The weight-average molecular weight (Mw) of the amorphous polyester resin is not particularly limited, but is preferably in the range of 5,000 to 100,000, and more preferably in the range of 5,000 to 50,000. If the weight-average molecular weight (Mw) is 5,000 or more, the heat-resistant storage stability of the toner can be improved, and if it is 100,000 or less, the low-temperature fixability can be further improved. Furthermore, the number-average molecular weight (Mn) of the resin is not particularly limited, but is preferably in the range of 1,500 to 25,000. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) can be measured by gel permeation chromatography (GPC).

[0083] Furthermore, the amorphous polyester resin preferably has an acid value of 5 to 50 mgKOH / g. By setting the acid value within this range, the amorphous polyester resin, vinyl resin, and ester wax are easily dispersed uniformly. Therefore, the ester wax is less likely to be exposed on the surface of the toner particles, thereby suppressing the occurrence of image noise (fogging).

[0084] (vinyl resin) In the color toner, the binder resin contains a vinyl resin in addition to the amorphous polyester resin described above. Similarly, the white toner may contain a vinyl resin in addition to the amorphous polyester resin described above, as long as the relationship of formula (1) above is satisfied. That is, the white toner may contain a vinyl resin as the binder resin, as long as the content Vw (mass%) of the vinyl resin in the binder resin component contained in the white toner is smaller than the content Vc (mass%) of the vinyl resin in the binder resin component contained in the color toner.

[0085] In the image forming method of this embodiment, the color toner forming the upper layer, which is more susceptible to heat conduction during heat sealing, contains more vinyl resin than the white toner forming the lower layer. This reduces the difference in elasticity between the upper layer made of color toner and the lower layer made of white toner, improving the heat seal resistance of the surface-printed image. In other words, by reducing the difference in elasticity between the upper and lower layers at high temperatures, peeling between the layers due to heat is suppressed, improving heat seal resistance.

[0086] There are no particular limitations on the specific values ​​of the vinyl resin content ratio Vw (mass%) of the white toner and the vinyl resin content ratio Vc (mass%) of the color toners, as long as they satisfy the relationship of formula (1) above. That is, the white toner may contain or not contain a vinyl resin (i.e., Vw = 0 mass%). On the other hand, the color toner must contain a vinyl resin in addition to the amorphous polyester resin as the main component. The vinyl resin content ratio Vc (mass%) of the color toner is greater than the vinyl resin content ratio Vw (mass%) of the white toner (i.e., the relationship Vc > Vw is satisfied).

[0087] The vinyl resin content ratio Vc (mass %) of the color toner is not particularly limited, but preferably satisfies the relationship of the following formula (2). By configuring in this way, the color toner has good low-temperature fixability and heat resistance. For example, if the vinyl resin content ratio Vc of the color toner exceeds 50 mass %, the low-temperature fixability of the color toner may be reduced. On the other hand, if the vinyl resin content ratio Vc of the color toner is less than 20 mass %, the heat resistance of the color toner may be reduced. 50≧Vc≧20 (2)

[0088] As shown in the above formula (2), the vinyl resin content Vc of the color toner is preferably 20 to 50% by mass, more preferably 25 to 45% by mass, and particularly preferably 25 to 35% by mass.

[0089] The vinyl resin content ratio Vw (mass %) of the white toner is not particularly limited, but is preferably 0 to 30 mass %, more preferably 0 to 20 mass %, and particularly preferably 0 to 10 mass %. White toner is highly filled with inorganic pigments such as titanium oxide, and as a result, the amount of binder resin used tends to be relatively small. Therefore, by setting the vinyl resin content ratio Vw (mass %) of the white toner within the above-mentioned range, the excellent low-temperature fixability of the amorphous polyester resin, which is the main component of the binder resin, is not impaired.

[0090] It is also one of the preferred embodiments that the vinyl resin content ratio Vc (mass %) of the color toner and the vinyl resin content ratio Vw (mass %) of the white toner satisfy the relationship of the following formula (3). 30≧Vc-Vw≧10 (3)

[0091] The above formula (3) represents the difference (Vc-Vw) between the vinyl resin content percentage Vc (mass%) of the color toner and the vinyl resin content percentage Vw (mass%) of the white toner. When the difference in vinyl resin content percentage (Vc-Vw) is 10 to 30 mass%, the difference in elasticity between the upper and lower layers at high temperatures is particularly small, resulting in extremely effective improvement in heat seal resistance. Note that when the difference in vinyl resin content percentage (Vc-Vw) is less than 10 mass%, the image becomes more brittle and may be more likely to peel when the film serving as a recording medium is folded. On the other hand, when the difference in vinyl resin content percentage (Vc-Vw) exceeds 30 mass%, the difference in elasticity between the upper and lower layers becomes too great, making it difficult to achieve sufficient effectiveness in suppressing thermal delamination. While not particularly limited, for example, the difference in vinyl resin content percentage (Vc-Vw) is more preferably 15 to 30 mass%, and particularly preferably 20 to 30 mass%.

[0092] There are no particular limitations on the method for measuring the vinyl resin content Vw (mass%) of the white toner and the vinyl resin content Vc (mass%) of the color toner. For example, if the ratio of the resin components in the binder resins of the white toner and color toners that form the toner image is known, the vinyl resin content (mass%) in the binder resin components can be determined from that ratio. When the color toner contains multiple types of toner, such as yellow toner, magenta toner, and cyan toner, the vinyl resin content Vc (mass%) for each color toner can be determined individually. As described above, when the color toner contains multiple types of toner, it is sufficient that the content Vc (mass%) of each color toner satisfies the relationship of the above formula (1).

[0093] There are no particular limitations on the type of vinyl resin contained in the binder resin. Vinyl resin is a resin obtained by polymerization using at least a vinyl monomer. Examples of vinyl resins include acrylic resin, styrene-acrylic resin, and ethylene-vinyl acetate resin. Among them, styrene-acrylic resin is preferred from the viewpoint of plasticity during thermal fixation. The following describes styrene-acrylic resin as a vinyl resin.

[0094] Styrene-acrylic resins are formed by addition polymerization of at least a styrene monomer and a (meth)acrylic acid ester monomer. Hereinafter, styrene monomers and their derivatives may be collectively referred to as "styrene-based monomers." Furthermore, (meth)acrylic acid ester monomers and their derivatives may be collectively referred to as "(meth)acrylic acid ester monomers." In this specification, "(meth)acrylic acid ester monomers" collectively refers to "acrylic acid ester monomers" and "methacrylic acid ester monomers." For example, "methyl (meth)acrylate" collectively refers to "methyl acrylate" and "methyl methacrylate."

[0095] Examples of styrene-based monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, p-ethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, 2,4-dimethylstyrene, 3,4-dichlorostyrene, and derivatives thereof.

[0096] Examples of (meth)acrylic acid ester monomers include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, ethyl β-hydroxyacrylate, propyl γ-aminoacrylate, stearyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and derivatives thereof. These may be used alone or in combination of two or more.

[0097] In addition, the following can also be used as polymerizable monomers for forming styrene-acrylic resins in addition to the above-mentioned styrene-based monomers and (meth)acrylic acid ester-based monomers. Examples of olefins include ethylene, propylene, and isobutylene. Examples of vinyl esters include vinyl propionate, vinyl acetate, and vinyl benzoate. Examples of vinyl ethers include vinyl methyl ether and vinyl ethyl ether. Examples of vinyl ketones include vinyl methyl ketone, vinyl ethyl ketone, and vinyl hexyl ketone. Examples of N-vinyl compounds include N-vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone. Examples of other monomers include vinyl compounds such as vinylnaphthalene and vinylpyridine, and acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide.

[0098] In addition, as the polymerizable monomer for forming the styrene-acrylic resin, in addition to the above-mentioned styrene-based monomer and (meth)acrylic acid ester-based monomer, for example, a monomer having an ionic dissociable group such as a carboxy group or a phosphate group as shown below can also be used.

[0099] Examples of vinyl monomers having a carboxy group include (meth)acrylic acids such as acrylic acid, methacrylic acid, α-ethylacrylic acid, and crotonic acid, and their α-alkyl or β-alkyl derivatives; unsaturated dicarboxylic acids such as fumaric acid, maleic acid, citraconic acid, and itaconic acid; and unsaturated dicarboxylic acid monoester derivatives such as succinic acid monoacryloyloxyethyl ester, succinic acid monoacryloyloxyethylene ester, phthalic acid monoacryloyloxyethyl ester, and phthalic acid monomethacryloyloxyethyl ester. Examples of vinyl monomers having a phosphoric acid group include acidophosphooxyethyl methacrylate.

[0100] Furthermore, as the polymerizable monomer for forming the styrene-acrylic resin, the following polyfunctional vinyls can also be used in addition to the above-mentioned styrene-based monomers and (meth)acrylic acid ester-based monomers: Examples of polyfunctional vinyls include ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, neopentyl glycol dimethacrylate, and neopentyl glycol diacrylate.

[0101] (crystalline polyester resin) The binder resin may contain, for example, a crystalline polyester resin in addition to the amorphous polyester resin and vinyl resin described above. Crystalline polyester resins are resins obtained by a polycondensation reaction between a divalent or higher carboxylic acid (a polycarboxylic acid) and a divalent or higher alcohol (a polyhydric alcohol). Crystalline polyester resins are a type of crystalline resin. A crystalline resin is a resin that exhibits a clear endothermic peak rather than a stepwise endothermic change in differential scanning calorimetry (DSC). Specifically, a clear endothermic peak means a peak whose half-width is 15°C or less when measured in differential scanning calorimetry (DSC) at a heating rate of 10°C / min.

[0102] In the toner used in the image forming method, at least one of the white toner and the color toner preferably further contains a crystalline polyester resin as a binder resin. For example, the crystalline polyester resin has a good affinity with the amorphous polyester resin described above. Therefore, by further containing the crystalline polyester resin, the dispersibility of the toner particles is improved. In addition, the sharp melting property during fixing can be improved, and the low-temperature fixing property can be further improved.

[0103] The crystalline polyester resin is an optional component in the binder resin, and there are no particular restrictions on its content, etc. For example, from the viewpoint of obtaining better low-temperature fixability, the content of the crystalline polyester resin in the binder resin is preferably 1 to 30% by mass, more preferably 5 to 20% by mass.

[0104] Examples of the polycarboxylic acid and polyhydric alcohol used in the preparation of the crystalline polyester resin are not particularly limited, but include the following:

[0105] Examples of polycarboxylic acids include dicarboxylic acids. The dicarboxylic acid is preferably an aliphatic dicarboxylic acid, and may further contain an aromatic dicarboxylic acid. From the viewpoint of obtaining excellent crystallinity in the crystalline polyester resin, the dicarboxylic acid preferably has 4 to 12 carbon atoms in the main chain including the carboxy group. Furthermore, from the viewpoint of ensuring low-temperature fixability, it is more preferable to use short-chain aliphatic dicarboxylic acids among these aliphatic dicarboxylic acids. A short-chain aliphatic dicarboxylic acid is a linear aliphatic dicarboxylic acid having 6 to 10 carbon atoms in the main chain including the carboxy group. Such dicarboxylic acids may be used alone or in combination of two or more.

[0106] Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid. Other examples include 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, and 1,18-octadecanedicarboxylic acid. Lower alkyl esters and acid anhydrides of the compounds listed above can also be used. Among the above aliphatic dicarboxylic acids, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid are preferred. Furthermore, among the above aliphatic dicarboxylic acids, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid are more preferred.

[0107] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, t-butylisophthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid.

[0108] Examples of polyhydric alcohol components include diols. The diol is preferably an aliphatic diol, and other diols may also be included. From the viewpoint of obtaining excellent crystallinity in the crystalline polyester resin, it is preferable to use a linear aliphatic diol having 2 to 15 carbon atoms in the main chain, and it is more preferable to use an aliphatic diol having 2 to 10 carbon atoms in the main chain. Furthermore, from the viewpoint of ensuring low-temperature fixability, it is particularly preferable to use a short-chain aliphatic diol among these aliphatic diols. A short-chain aliphatic diol is an aliphatic diol having 2 to 6 carbon atoms in the main chain. Such diols may be used alone or in combination of two or more.

[0109] Examples of aliphatic diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,15-pentadecanediol, 1,18-octadecanediol, 1,2 Among these, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol are preferably used, and ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol are more preferably used.

[0110] As the diol other than the aliphatic diol, a diol having a double bond can also be used, such as 2-butene-1,4-diol, 3-hexene-1,6-diol, and 4-octene-1,8-diol.

[0111] The method for producing the crystalline polyester resin is not particularly limited, and the crystalline polyester resin can be produced by a general polyester polymerization method in which a dicarboxylic acid component and a diol component are reacted in the presence of a catalyst. For example, it is preferable to produce the crystalline polyester resin by selectively using a direct polycondensation method or a transesterification method depending on the type of monomer.

[0112] Examples of catalysts that can be used in the production of crystalline polyester resins include titanium catalysts and tin catalysts. Examples of titanium catalysts include titanium tetraethoxide, titanium tetrapropoxide, titanium tetraisopropoxide, and titanium tetrabutoxide. Examples of tin catalysts include dibutyltin dichloride, dibutyltin oxide, and diphenyltin oxide.

[0113] The ratio of the diol and dicarboxylic acid in the monomer of the crystalline polyester resin can be expressed as the equivalent ratio [OH] / [COOH] of the hydroxy group [OH] of the diol to the carboxy group [COOH] of the dicarboxylic acid. The equivalent ratio [OH] / [COOH] of the hydroxy group [OH] of the diol to the carboxy group [COOH] of the dicarboxylic acid is preferably within a range of 1.5 / 1.0 to 1.0 / 1.5, and more preferably within a range of 1.2 / 1.0 to 1.0 / 1.2.

[0114] In addition to the binder resin, the toner base particles may contain internal additives such as a colorant, a release agent, and a charge control agent, if necessary.

[0115] (coloring agent) Generally known dyes and pigments can be used as colorants. As mentioned above, the term "color toner" in this specification refers to a toner belonging to a group of toners that includes the above-mentioned chromatic toners, black toner and gray toner included in the above-mentioned achromatic toners, and the above-mentioned clear toner, and does not include white toner. On the other hand, the term "white toner" refers to a toner having a color (white) that satisfies the above-mentioned specific conditions. For this reason, the white color of white toner is used as a reference color, and chromatic toners, black toner, gray toner, and clear toner that are recognized as being different from the white color will be referred to as "color toner" for convenience.

[0116] For example, various known colorants can be used as colorants for black toner, such as carbon blacks such as furnace black and channel black, magnetic materials such as magnetite and ferrite, dyes, and inorganic pigments including non-magnetic iron oxide.

[0117] As a colorant for a chromatic toner (for example, a color toner), any known colorant such as a dye or an organic pigment can be used. Specifically, as an organic pigment, for example, CI Pigment Red 5, 48:1, 48:2, 48:3, 53:1, 57:1, 81:4, 122, 139, 144, 149, 166, 177, 178, 222, 238, 269, CI Pigment Yellow 14, 17, 74, 93, 94, 138, 155, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251 Examples of suitable dyes include CI Solvent Red 1, 49, 52, 58, 68, 11, 122, CI Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, 162, CI Solvent Blue 25, 36, 69, 70, 93, and 95.

[0118] Any known inorganic or organic pigment can be used as a colorant for a white toner. 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. Examples of organic pigments include polystyrene resin particles and urea formalin resin particles.

[0119] The colorant for obtaining the toner of each color may be used alone or in combination of two or more. The content of the colorant is preferably 1 to 20 parts by mass, more preferably 4 to 15 parts by mass, per 100 parts by mass of the binder resin.

[0120] (mold release agent) The color toner contains an ester wax as a release agent. The color toner may contain a release agent other than the ester wax, but the content of the ester wax is preferably 50% by mass or more of the total content of the release agents. The content of the release agent is preferably 1 to 30 parts by mass, more preferably 5 to 20 parts by mass, per 100 parts by mass of the binder resin. Hereinafter, a release agent such as the ester wax may be referred to as an "ester-based release agent."

[0121] The ester wax may be any of monoester wax, diester wax, triester wax, tetraester wax, and wax having five or more ester bonds.

[0122] The ester wax is not particularly limited, but examples include the following: monoesters obtained by reacting a higher fatty acid with a higher alcohol; diesters obtained by reacting a higher fatty acid with a dihydric alcohol or a higher alcohol with a dicarboxylic acid; triesters of trimethylolpropane and a higher fatty acid; triesters of glycerin and a higher fatty acid; tetraesters of pentaerythritol and a higher fatty acid; esters obtained by reacting a hydroxy acid such as citric acid with a higher fatty acid or a higher alcohol; and esters obtained by reacting a carboxylic acid or alcohol having an aromatic group such as a cyclic acid with a higher fatty acid or a higher alcohol.

[0123] The hydrocarbon chain of the higher fatty acid and higher alcohol preferably has 13 to 30 carbon atoms, more preferably 17 to 22. The dihydric alcohol and dicarboxylic acid are preferably compounds having two hydroxyl groups or two carboxyl groups at both ends of a hydrocarbon group having 1 to 30 carbon atoms.

[0124] Each hydrocarbon group may be substituted with a linear or branched alkyl group, alkenyl group, alkynyl group, aromatic hydrocarbon ring group, aromatic heterocyclic group, non-aromatic hydrocarbon ring group, non-aromatic heterocyclic group, etc. Furthermore, each hydrocarbon group may be substituted with an alkoxy group, cycloalkoxy group, aryloxy group, alkylthio group, cycloalkylthio group, arylthio group, alkoxycarbonyl group, aryloxycarbonyl group, or sulfamoyl group. Furthermore, each hydrocarbon group may be substituted with an acyl group, acyloxy group, amido group, carbamoyl group, ureido group, sulfinyl group, alkylsulfonyl group, arylsulfonyl group, or heteroarylsulfonyl group. Furthermore, each hydrocarbon group may be substituted with an amino group, halogen atom, fluorohydrocarbon group, cyano group, nitro group, hydroxy group, thiol group, silyl group, deuterium atom, etc.

[0125] Specific examples of the ester wax include behenyl behenate, triglycerol behenate, pentaerythritol tetrastearate, stearyl stearate, pentaerythritol tetrabehenate, ethylene glycol stearate, ethylene glycol behenate, neopentyl glycol stearate, neopentyl glycol behenate, 1,6-hexanediol stearate, 1,6-hexanediol behenate, glycerin stearate, glycerin behenate, stearyl citrate, behenyl citrate, stearyl phosphate, behenyl phosphate, etc. The ester wax may be a natural wax such as carnauba wax.

[0126] The melting point of the ester wax is preferably 65 to 90°C. If the melting point of the ester wax is lower than 65°C, a portion of the release agent (ester wax) may melt and ooze onto the surface of the toner particles during toner storage or while the toner is loaded in an image-forming device. Oozing of the release agent onto the surface of the toner particles can cause image noise, which is undesirable from a practical standpoint. Furthermore, if the melting point of the release agent (ester wax) is low, the release agent (ester wax) may not fully crystallize on the image surface and remain molten, resulting in poor document offset resistance. On the other hand, if the melting point of the ester wax is higher than 90°C, the release agent (ester wax) may not melt sufficiently during heat sealing, making it difficult for it to ooze onto the image surface, resulting in poor heat-sealing resistance. Furthermore, if the melting point of the ester wax is high, low-temperature fixability may also be impaired. Although not particularly limited, the melting point of the ester wax is more preferably 70 to 80°C.

[0127] There are no particular limitations on the release agents other than the ester wax, and various known waxes can be used, for example. For example, hydrocarbon waxes include branched-chain hydrocarbon waxes and long-chain hydrocarbon waxes. Examples of branched-chain hydrocarbon waxes include polyolefin waxes such as polyethylene wax and polypropylene wax, and microcrystalline waxes. Examples of long-chain hydrocarbon waxes include paraffin wax and sazol wax. Examples of release agents other than ester waxes include dialkyl ketone waxes such as distearyl ketone; and amide waxes such as ethylenediamine behenylamide and trimellitic acid tristearylamide.

[0128] The white toner may contain at least one of the ester waxes and other release agents other than the ester waxes described above as a release agent. The content of the release agent and the like conform to the preferred embodiments for the color toners.

[0129] (charge control agent) The toner particles may contain a charge control agent as needed. Various known compounds can be used as the charge control agent. Examples of the charge control agent include, but are not limited to, nigrosine dyes, metal salts of naphthenic acid or higher fatty acids, alkoxylated amines, quaternary ammonium salt compounds, azo metal complexes, and salicylic acid metal salts or their metal complexes.

[0130] The content of the charge control agent is not particularly limited, but is preferably 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the total amount of the binder resin.

[0131] [Other characteristics of white toner and color toner] The white toner and color toner used in the image forming method of the present embodiment are not particularly limited, but the difference in storage modulus at 90° C. between the white toner and the color toner is 1.0×10 4 Pa~1.0×10 5It is preferable that the toner layer has a thickness of Pa. By configuring in this manner, sufficient adhesion can be obtained between the white toner image and the color toner image that constitute the toner image, and the heat seal resistance can be further improved.

[0132] The storage modulus of the white and color toners at 90°C can be measured using the following method. For the measurement sample, 0.2 g of toner containing external additives was weighed and pressure-molded using a compression molding machine at 25 MPa to produce cylindrical pellets with a diameter of 10 mm. A rheometer (TA Instruments' "ARES G2") was used, with an 8 mm diameter parallel plate on top and a 20 mm diameter parallel plate on the bottom, to measure the temperature drop at a frequency of 1 Hz. The sample was set at 100°C, the gap was set to 1.4 mm, and any excess sample was scraped off. The gap was then set to 1.2 mm. The sample was then cooled to the desired temperature while applying axial force, and allowed to stand for 3 hours. The temperature was then lowered to the starting temperature of 30°C, the axial force was stopped, and the storage modulus (G') was measured by increasing the temperature from 30°C to 150°C at a rate of 3°C / min. Detailed measurement conditions are shown below. The "storage modulus" is an index of the hardness of a material, and the smaller the value, the softer the material.

[0133] [Measurement conditions] Frequency: 1Hz Ramp rate: 3℃ / min ·Axicial force: 0g, sensitivity: 10g ·Initial strain:3.0%, Strain adjust:30.0%, Minimum strain:0.01%, Maximum strain:10.0% ·Minimum torque:1g·cm, Maximum torque:80g·cm Sampling interval: 1.0℃ / pt

[0134] [Average particle size of toner particles] The average particle size of the toner particles is, for example, preferably in the range of 3 to 9 μm, more preferably in the range of 3 to 8 μm, in terms of volume-based median diameter. When producing toner particles by employing, for example, the emulsion aggregation method described below, this average particle size can be controlled by the concentration of the aggregating agent used, the amount of organic solvent added, the fusion time, the polymer composition, etc.

[0135] When the volume-based median diameter is within the above range, the transfer efficiency is increased, improving the image quality of halftones and the image quality of thin lines and dots.

[0136] The volume-based median diameter of toner particles was measured and calculated using a measuring device connected to a computer system equipped with the data processing software "Software V3.51" (manufactured by Beckman Coulter, Inc.). Specifically, 0.02 g of toner was first added to 20 mL of surfactant solution, and the mixture was then ultrasonically dispersed for 1 minute to prepare a toner dispersion. The surfactant solution used can be, for example, a neutral detergent containing surfactant components diluted 10 times with pure water to disperse the toner particles. The toner dispersion prepared as described above was then pipetted into a beaker containing an "ISOTON II" (manufactured by Beckman Coulter, Inc.) in the sample stand until the concentration indicated on the measuring device reached 8%. Maintaining this concentration range ensures reproducible measurements. Then, in the measuring device, the number of measured particles is set to 25,000, the aperture diameter is set to 50 μm, the measurement range of 1 to 30 μm is divided into 256 parts, and the frequency value is calculated. The particle diameter of the largest 50% of the volume cumulative fraction is taken as the volume-based median diameter.

[0137] [Average circularity of toner particles] From the viewpoint of improving transfer efficiency, the toner particles preferably have an average circularity within a range of 0.930 to 1.000, more preferably within a range of 0.940 to 0.995.

[0138] The average circularity of toner particles is measured using an "FPIA-3000" (manufactured by Sysmex Corporation). Specifically, the sample (toner particles) is first soaked in an aqueous solution containing a surfactant and then dispersed by ultrasonic dispersion treatment for 1 minute. Then, using an "FPIA-2100" (manufactured by Sysmex Corporation), images are taken using the measurement conditions HPF (high magnification imaging) mode at an appropriate density of 3,000 to 10,000 HPF detections, and the circularity of each toner particle is calculated according to the following formula (T). The circularity of each toner particle is then added together and divided by the total number of toner particles to calculate the average circularity of the toner particles.

[0139] Formula (T): Circularity = (perimeter of a circle with the same projected area as the particle image) / (perimeter of the projected particle image)

[0140] [Softening point of toner] The softening point of the toner is preferably in the range of 80 to 120° C. from the viewpoint of obtaining low-temperature fixability, and more preferably in the range of 90 to 105° C. The softening point of the toner is measured using a flow tester shown below.

[0141] Specifically, 1.1 g of sample (toner) was placed in a petri dish at 20°C and 50% RH, flattened, and left for at least 12 hours. After leaving for at least 12 hours, a molding machine "SSP-10A" (Shimadzu Corporation) was used to apply a pressure of 375 MPa for 30 seconds to produce a cylindrical molded sample with a diameter of 1 cm. Next, the molded sample was extruded from the cylindrical die hole (1 mm diameter x 1 mm) using a 1 cm diameter piston at the end of preheating under the following conditions in a flow tester "CFT-500D" (Shimadzu Corporation) at 24°C and 50% RH. The offset temperature T was then measured using the temperature rise melting temperature measurement method with an offset value set to 5 mm. offset The conditions for extruding the molded sample are a load of 196 N (20 kgf), a starting temperature of 60° C., a preheating time of 300 seconds, and a temperature rise rate of 6° C. / min.

[0142] (Toner manufacturing method) There are no particular limitations on the method for producing the toner used in the image forming method. For example, the toner can be produced by a kneading and pulverizing method, a suspension polymerization method, an emulsion polymerization aggregation method, an emulsion aggregation method, a dissolution suspension method, a polyester elongation method, a dispersion polymerization method, or other known methods. For example, the emulsion polymerization aggregation method or the emulsion aggregation method can be suitably used as the toner production method.

[0143] In the emulsion polymerization aggregation method, first, a dispersion of binder resin particles (hereinafter also referred to as "binder resin particles") is prepared by emulsion polymerization. Next, the prepared dispersion of binder resin particles is mixed with a dispersion of colorant particles (hereinafter also referred to as "colorant particles") and a dispersion of a release agent such as wax. Then, toner particles are aggregated until they reach a desired particle size, and further, the shape is controlled by fusing the binder resin particles together to produce toner particles.

[0144] In the emulsion aggregation method, first, a binder resin solution dissolved in a solvent is dropped into a poor solvent to prepare a resin particle dispersion. Next, the prepared resin particle dispersion is mixed with a dispersion of a colorant and a dispersion of a release agent such as wax, and the mixture is aggregated to a desired toner particle size. Further, the shape of the toner particles is controlled by fusing the binder resin particles together, thereby producing toner particles.

[0145] By employing the emulsion aggregation method as a toner manufacturing method, the dispersibility of colorant particles in the dispersion of the colorant contained in the toner base particles is excellent. Furthermore, even when the colorant particles and the binder resin particles are aggregated and fused together, the toner base particles can be formed while the colorant particles maintain excellent dispersibility.

[0146] Furthermore, emulsion polymerization aggregation can also be used to obtain toner base particles having a core-shell structure. Specifically, when producing toner base particles having a core-shell structure, core particles are first produced by aggregating, associating, and fusing binder resin particles for the core particles with colorant particles. Then, binder resin particles for the shell layer are added to a dispersion of the produced core particles, and the binder resin particles for the shell layer are aggregated and fused to the surface of the core particles. In this way, a shell layer is formed so as to cover the surface of the core particles, and toner base particles having a core-shell structure are obtained.

[0147] When producing the toner used in the image forming method of this embodiment, the blending of the raw materials of the binder resin may be appropriately adjusted so that the vinyl resin content ratio Vc (mass %) of the color toner is greater than the vinyl resin content ratio Vw (mass %) of the white toner.

[0148] [Recording media (resin film)] The recording medium is a member for holding a toner image, and the recording medium used in the image forming method of this embodiment is a resin film.

[0149] The resin constituting the resin film is not particularly limited, and resins constituting known resin films can be used. Examples of resins constituting the resin film include polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), and polyethylene (PE). Other examples of resins include biaxially oriented polypropylene (OPP), unstretched polypropylene (CPP), biaxially oriented nylon (ONY), and unstretched nylon (CNY). Further examples include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), high-impact polystyrene (HIPS), and PLA (polylactic acid).

[0150] The image forming method of this embodiment uses the white toner and color toner described above, thereby forming an image that has sufficient adhesive strength to the resin film as a recording medium and also has excellent heat-sealing resistance during bag production. Therefore, the recording medium used in the image forming method of this embodiment is preferably a resin film that is easily deformed. For example, from the viewpoint of easily achieving high adhesion to the toner, a film whose main component is a resin containing an aromatic ring is even more preferable. Examples of resins containing an aromatic ring include polyethylene terephthalate (PET), polystyrene (PS), and high impact polystyrene (HIPS). Among these resins, a film whose main component is polyethylene terephthalate (PET) is particularly preferable. The "main component" of the film refers to a component whose content is 60% by mass or more of the total mass of the film. The main component of the film preferably accounts for 80% by mass or more, and more preferably 90% by mass or more, of the total mass of the film.

[0151] The recording medium may be in the form of a sheet of a predetermined size, but is preferably in the form of a roll that is wound up after the toner image is fixed. Winding up after image formation is suitable for efficient mass production of packaging, and allows the recording medium (resin film) after image formation to be stored in roll form and used in subsequent packaging processes. The recording medium may be surface-treated or not. Examples of surface treatment methods include corona treatment and plasma treatment. From a cost perspective, no surface treatment is preferred, while a surface treatment is preferred in terms of image adhesion.

[0152] If the thickness of the recording medium is too thick, it may not be suitable for processing as a flexible packaging material, and if it is too thin, the risk of breakage increases, which may result in insufficient processability as a flexible packaging material. From the viewpoint of achieving sufficient processability as a flexible packaging material, the thickness of the recording medium is preferably 20 to 70 μm, and more preferably 30 to 55 μm.

[0153] The embodiments to which the present invention can be applied are not limited to the above-described embodiments, and can be modified as appropriate within the scope of the invention. [Example]

[0154] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the following examples, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass," respectively.

[0155] [Toner production] <Preparation of Amorphous Polyester Resin Particle Dispersion (A)> (Preparation of amorphous polyester resin) Bisphenol A ethylene oxide 2.2 mole adduct: 40 mole parts Bisphenol A propylene oxide 2.2 mole adduct: 60 mole parts Dimethyl terephthalate: 60 parts by mole Dimethyl fumarate: 15 parts by mole Dodecenyl succinic anhydride: 20 parts by mole Trimellitic anhydride: 5 mole parts A reaction vessel equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube was charged with the above monomers other than dimethyl fumarate and trimellitic anhydride, and 0.25 parts by mass of tin dioctylate per 100 parts by mass of the above monomers. After reacting for 6 hours at 235°C under a nitrogen gas stream, the temperature was lowered to 200°C, and dimethyl fumarate and trimellitic anhydride were added and reacted for 1 hour. The temperature was then raised to 220°C over 5 hours, and polymerization was continued under a pressure of 10 kPa until the desired molecular weight was reached, yielding a pale yellow, transparent amorphous polyester resin.

[0156] The amorphous polyester resin had a weight average molecular weight of 35,000, a number average molecular weight of 8,000, a glass transition temperature (Tg) of 59°C, and an acid value of 16.2 mgKOH / g.

[0157] (Preparation of Amorphous Polyester Resin Particle Dispersion (A)) Next, the obtained amorphous polyester resin was dispersed using a disperser that was a modified high-temperature, high-pressure emulsifying disperser "Cavitron CD1010" (manufactured by Eurotech). Specifically, an amorphous polyester resin dispersion was prepared so that the composition ratio was 80% by mass of ion-exchanged water and 20% by mass of amorphous polyester resin. At this time, the pH was adjusted to 8.5 with ammonia, the rotor rotation speed was set to 60 Hz, and the pressure was set to 5 kg / cm. 2 The Cavitron was operated under the conditions of a pressure of 490 kPa and a heating temperature of 140°C by a heat exchanger. Subsequently, ion-exchanged water was added to the dispersion to adjust the solid content to 20% by mass, thereby preparing amorphous polyester resin particle dispersion (A). The volume-based median diameter (D50) of this dispersion was measured using a "Microtrac (registered trademark, the same applies hereinafter) UPA-150" (manufactured by Nikkiso Co., Ltd.) and was found to be 160 nm.

[0158] <Preparation of vinyl resin particle dispersion (B)> (First stage polymerization) A 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device was charged with 8 parts by mass of sodium dodecyl sulfate and 3,000 parts by mass of ion-exchanged water, and the internal temperature was raised to 80° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream. After the temperature was raised, a solution prepared by dissolving 10 parts by mass of potassium persulfate in 200 parts by mass of ion-exchanged water was added, and the liquid temperature was again raised to 80° C., and a mixed liquid of the following monomers was added dropwise over 1 hour.

[0159] Styrene (St): 480.0 parts by mass n-Butyl acrylate (BA): 250.0 parts by mass Methacrylic acid (MAA): 68.0 parts by mass

[0160] After the dropwise addition of the mixed liquid, the mixture was heated at 80° C. for 2 hours with stirring to polymerize the monomers, thereby preparing a vinyl resin particle dispersion liquid (1-a).

[0161] (Second stage polymerization) A 5 L reaction vessel equipped with a stirrer, temperature sensor, cooling tube, and nitrogen inlet was charged with 1,100 parts by mass of ion-exchanged water and 55 parts by mass (solids equivalent) of the vinyl resin particle dispersion (1-a) prepared by the first-stage polymerization described above, and heated to 87°C. Separately, the following monomers, chain transfer agent, and release agent were dissolved at 80°C to obtain a mixed liquid. The resulting mixed liquid was mixed and dispersed for 10 minutes using a mechanical disperser "CLEARMIX" (manufactured by M Technique Co., Ltd.) with a circulation path, to prepare a dispersion containing emulsified particles (oil droplets).

[0162] Styrene (St): 256.0 parts by mass 2-Ethylhexyl acrylate (2-EHA): 95.0 parts by mass Methacrylic acid (MAA): 30.0 parts by mass n-Octyl-3-mercaptopropionate (chain transfer agent): 3.9 parts by mass Behenyl behenate (mold release agent, melting point 73°C): 136.8 parts by weight Microcrystalline wax (mold release agent, melting point 80°C): 7.2 parts by weight

[0163] The prepared dispersion was added to the 5 L reaction vessel, and a polymerization initiator solution prepared by dissolving 5.5 parts by mass of potassium persulfate in 100 parts by mass of ion-exchanged water was added. The system in the reaction vessel was heated and stirred at 87°C for 1 hour to carry out polymerization, thereby preparing a vinyl resin particle dispersion (1-b).

[0164] (Third stage polymerization) To the vinyl resin particle dispersion (1-b) obtained by the second-stage polymerization, a solution of 8 parts by mass of potassium persulfate dissolved in 140 parts by mass of ion-exchanged water was added, followed by dropwise addition of a mixture of the following monomers and chain transfer agent over 90 minutes at a temperature of 84°C.

[0165] Styrene (St): 367.2 parts by mass n-Butyl acrylate (BA): 165.0 parts by mass Methacrylic acid (MAA): 34.3 parts by mass Methyl methacrylate (MMA): 52.5 parts by weight n-Octyl-3-mercaptopropionate: 8.0 parts by mass

[0166] After the dropwise addition was completed, polymerization was carried out by heating and stirring for 2 hours, and then the mixture was cooled to 28°C to prepare vinyl resin particle dispersion (B). The volume-based median diameter (D50) of this dispersion was measured using a Microtrac UPA-150 (manufactured by Nikkiso Co., Ltd.) and found to be 130 nm. The weight-average molecular weight (Mw) of the vinyl resin contained in the resulting dispersion was 34,000.

[0167] <Preparation of Crystalline Polyester Resin Particle Dispersion (C)> (Preparation of crystalline polyester resin) Dodecanedioic acid: 50 parts by mole 1,9-nonanediol: 50 parts by mole The above monomers were placed in a reaction vessel equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube, and the atmosphere inside the reaction vessel was replaced with dry nitrogen gas. Next, 0.25 parts by mass of titanium tetrabutoxide (Ti(On-Bu)4) was added per 100 parts by mass of the above monomers. After stirring and reacting for 3 hours at 170°C under a nitrogen gas flow, the temperature was further increased to 210°C over 1 hour, the pressure inside the reaction vessel was reduced to 3 kPa, and the reaction was continued under reduced pressure for 13 hours with stirring to obtain a crystalline polyester resin.

[0168] The crystalline polyester resin had a weight average molecular weight of 23,000, a number average molecular weight of 6,500, an acid value of 19.1 mgKOH / g, and a melting point of 73.2°C.

[0169] (Preparation of Crystalline Polyester Resin Particle Dispersion (C)) Next, the obtained crystalline polyester resin was dispersed using a disperser that was a modified high-temperature, high-pressure emulsifying disperser "Cavitron CD1010" (manufactured by Eurotech). Specifically, a crystalline polyester resin dispersion was prepared so that the composition ratio was 80% by mass of ion-exchanged water and 20% by mass of crystalline polyester resin. At this time, the pH was adjusted to 8.5 with ammonia, the rotor rotation speed was set to 60 Hz, and the pressure was set to 5 kg / cm. 2 The Cavitron was operated under the conditions of a pressure of 490 kPa and a heating temperature of 140°C by a heat exchanger. Subsequently, ion-exchanged water was added to the dispersion to adjust the solid content to 20% by mass, thereby preparing crystalline polyester resin particle dispersion (C). The volume-based median diameter (D50) of this dispersion was measured using a Microtrac UPA-150 (manufactured by Nikkiso Co., Ltd.) and found to be 190 nm.

[0170] <Preparation of Ester-Based Mold Release Agent Particle Dispersion (D)> Ester wax: 100 parts by weight Anionic surfactant: 10 parts by weight Ion-exchanged water: 400 parts by weight The above materials were mixed and heated to 80°C, and thoroughly dispersed using an IKA Ultra-Turrax (registered trademark, the same applies hereinafter) T50. The ester wax used had a melting point of 74°C, an acid value of 0.1 mgKOH / g, and was primarily composed of behenyl behenate. The anionic surfactant used was Neogen (registered trademark) RK, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. After dispersion treatment using a pressure-discharge Gaulin homogenizer, ion-exchanged water was added to the dispersion to adjust the solid content to 15% by mass, thereby preparing an ester-based release agent particle dispersion (D). The volume-based median diameter of the release agent particles in this dispersion was measured using a laser diffraction particle size distribution analyzer LA-750 (manufactured by HORIBA), and was found to be 220 nm.

[0171] <Preparation of hydrocarbon-based release agent particle dispersion (E)> A hydrocarbon-based release agent particle dispersion (E) was prepared in the same manner as in the preparation of the ester-based release agent particle dispersion, except that the release agent was changed to paraffin wax (hydrocarbon-based wax) with a melting point of 75°C and an acid value of 0 mgKOH / g. The volume-based median diameter of the release agent particles in this dispersion was measured using a laser diffraction particle size distribution analyzer "LA-750" (manufactured by HORIBA) and was found to be 150 nm.

[0172] <Preparation of Cyan Colorant Particle Dispersion (F)> Sodium dodecyl sulfate: 90 parts by weight CI Pigment Blue 15:3: 200 parts by weight Ion-exchanged water: 1600 parts by weight The solution containing the above components was thoroughly dispersed using a homogenizer "Ultra Turrax T50" (manufactured by IKA), and then treated with an ultrasonic disperser for 20 minutes to prepare a cyan colorant particle dispersion (F).

[0173] The volume-based median diameter of the cyan colorant particles in the obtained cyan colorant particle dispersion (F) was 180 nm.

[0174] <Preparation of White Colorant Particle Dispersion (G)> 210 parts by mass of rutile-type titanium dioxide (manufactured by Ishihara Sangyo Kaisha) as a colorant was added to a surfactant aqueous solution prepared by dissolving sodium alkyldiphenyl ether disulfonate in 480 parts by mass of ion-exchanged water to a concentration of 1% by mass. The mixture was then dispersed using an ultrasonic homogenizer. The solid content was adjusted to 30% by mass. This resulted in the preparation of a white colorant dispersion (G) in which the white colorant was dispersed in an aqueous medium.

[0175] The volume-based median diameter of the white colorant particles in the resulting white colorant particle dispersion (G) was 200 nm.

[0176] <Toner Production> (Production of Color Toner 1 (Cyan Toner)) <Agglomeration / fusion process and aging process> Amorphous polyester resin particle dispersion (A): 215 parts by mass (solid content) Cyan colorant particle dispersion (F): 7 parts by mass (solid content) Ion-exchanged water: 1500 parts by weight Trimellitic anhydride: 5 mole parts The above materials were placed in a 4-liter reaction vessel equipped with a thermometer, pH meter, and stirrer, and 1.0% nitric acid was added at 25°C to adjust the pH to 3.0. Subsequently, while dispersing at 3,000 rpm using a homogenizer "Ultra Turrax T50" (manufactured by IKA), 100 parts by mass of a 2% aqueous aluminum sulfate (flocculant) solution was added over 30 minutes. After the dropwise addition was completed, the mixture was stirred for 10 minutes to thoroughly mix the raw materials and flocculant.

[0177] Amorphous polyester resin particle dispersion (A): 85 parts by mass (solid content) Vinyl resin particle dispersion (B): 162 parts by mass (solid content) Ester-based release agent particle dispersion (D): 10 parts by mass (solid content) The reactor was then fitted with a stirrer and mantle heater, and the temperature was raised at a rate of 0.2°C / min up to 40°C, and then at a rate of 0.05°C / min after exceeding 40°C, while the stirrer's rotation speed was adjusted to ensure sufficient agitation of the slurry mixture in the reactor. During the temperature increase, particle size was measured every 10 minutes using a Coulter Multisizer 3 (aperture diameter 50 μm, manufactured by Beckman Coulter). When the volumetric median diameter reached 5.0 μm, the temperature was maintained and a premixed liquid of the above materials was added over a 20-minute period.

[0178] After maintaining the temperature at 50°C for 30 minutes, 8 parts by mass of a 20% by mass EDTA (ethylenediaminetetraacetic acid) aqueous solution was added to the reaction vessel, followed by the addition of a 1 mol / L aqueous sodium hydroxide solution to adjust the pH of the raw material dispersion to 9.0. Thereafter, the temperature was increased to 85°C at a rate of 1°C / min while adjusting the pH to 9.0 every 5°C, and the temperature was maintained at 85°C.

[0179] ≪Cooling process≫ Thereafter, when the shape factor measured using a particle size analyzer "FPIA-2100" (manufactured by Malvern Instruments) reached 0.960, the mixture was cooled at a temperature decreasing rate of 10°C / min to obtain toner particle dispersion (1).

[0180] <Filtration, washing, and drying processes> The toner particle dispersion (1) was then filtered, and the resulting solid was thoroughly washed with ion-exchanged water. The solid was then dried at 40°C to obtain toner particles (1). The resulting toner particles (1) had a volume-based median diameter of 6.0 μm. The resulting toner particles (1) also had an average circularity of 0.961.

[0181] <External additive addition process> To 100 parts by mass of the resulting toner particles (1), 1.6 parts by mass of hydrophobic silica (number average primary particle diameter: 12 nm) and 0.6 parts by mass of hydrophobic titanium oxide (number average primary particle diameter: 20 nm) were added. The mixture was then mixed for 20 minutes using a Henschel mixer (manufactured by Nippon Coke & Engineering Co., Ltd.) at a rotor peripheral speed of 35 mm / sec to obtain color toner 1 with a volume-based median particle diameter of 6.0 μm. The final resin ratio in the binder resin component of color toner 1 was amorphous polyester resin:vinyl resin:crystalline polyester resin = 65:35:0 (mass ratio). Table 1 shows the content (mass %) of each resin in the binder resin component of color toner 1 and the type of release agent.

[0182] [Table 1]

[0183] (Preparation of Color Toners 2 to 7 (Cyan Toner)) Color toners 2 to 7 were produced in the same manner as color toner 1, except that the type and amount of dispersion liquid used were changed so that the content (mass%) of each resin in the binder resin component of the color toner was the value shown in Table 1. When producing color toners 3 to 4 and 6 to 8, which contain a crystalline polyester resin as the binder resin component, crystalline polyester resin particle dispersion (C) was added as the raw material initially added to the reaction vessel in the "aggregation / fusion process and aging process." That is, when using crystalline polyester resin particle dispersion (C) as a raw material for producing the toner, it was added to the reaction vessel from the beginning to produce the color toner. For color toner 7, ester-based release agent particle dispersion (D) and hydrocarbon-based release agent particle dispersion (E) were used in combination as the release agent particle dispersion. For color toner 9, hydrocarbon-based release agent particle dispersion (E) was used. Table 1 shows the content (mass %) of each resin in the binder resin component of color toners 2 to 9, and the type of release agent.

[0184] (Preparation of White Toners 1 to 4) White toners 1 to 4 were produced in the same manner as color toners 1 to 9, except that white colorant particle dispersion (G) was used and the type and amount of dispersion used were changed so that the content (mass%) of each resin in the binder resin component would be the value shown in Table 2. Table 2 shows the content (mass%) of each resin in the binder resin component of white toners 1 to 4, and the type of release agent.

[0185] [Table 2]

[0186] <Preparation of developer> The following ferrite carrier was used to prepare each of the developers by mixing color toners 1 to 9 and white toners 1 to 4 to a toner concentration of 6% by mass. The ferrite carrier used was a ferrite carrier coated with a copolymer resin of cyclohexyl methacrylate and methyl methacrylate (monomer mass ratio = 1:1) and having a volume-based median diameter of 30 μm.

[0187] <Storage modulus of toner at 90°C (Pa)> The storage modulus (Pa) at 90°C of the prepared color toners 1-9 and white toners 1-4 was measured using the following method. First, 0.2 g of the toner containing external additives was weighed and pressure-molded in a compression molding machine at 25 MPa to produce cylindrical pellets with a diameter of 10 mm. Using a rheometer (TA Instruments' "ARES G2"), a set of parallel plates with an 8 mm diameter on top and a 20 mm diameter on the bottom was used to perform temperature-reduction measurements at a frequency of 1 Hz. The sample was set at 100°C, the gap was set to 1.4 mm, and any excess sample was scraped off. The gap was then set to 1.2 mm. The sample was then cooled to an arbitrary temperature while applying axial force and allowed to stand for 3 hours. The temperature was then lowered to the starting temperature of 30°C, the axial force was stopped, and the storage modulus (G') was measured by increasing the temperature from 30°C to 150°C at a heating rate of 3°C / min. Detailed measurement conditions are shown below.

[0188] [Measurement conditions] Frequency: 1Hz Ramp rate: 3℃ / min ·Axicial force: 0g, sensitivity: 10g ·Initial strain:3.0%, Strain adjust:30.0%, Minimum strain:0.01%, Maximum strain:10.0% ·Minimum torque:1g·cm, Maximum torque:80g·cm Sampling interval: 1.0℃ / pt

[0189] <Image formation using white toner and color toner> Example 1 Using the developer prepared above, an image was formed on a resin film as a recording medium using a commercially available full-color label printer "bizhub PRESS (registered trademark) C71cf" (manufactured by Konica Minolta). The image formed was a solid image in which, from the closest to the resin film, a white toner image made of White Toner 1 and a color toner image made of Color Toner 1 (cyan toner) were arranged. In producing the image, the toner adhesion amount of White Toner 1 was 8 g / m 2 The toner adhesion amount of color toner 1 is set to 8 g / m 2 The full-color label printer used for image formation was modified so that the fixing temperature, toner adhesion amount, and system speed could be freely set. In Example 1, images were formed at a fixing temperature of 185°C and a system speed of 270 mm / sec. A 20 μm-thick biaxially oriented polypropylene film (referred to as PP in the table) was used as the resin film. Table 3 shows the compositions of the white toner and color toners used in Example 1. The difference (Vc - Vw) between the vinyl resin content percentage Vc (mass%) of color toner 1 and the vinyl resin content percentage Vw (mass%) of white toner 1 was calculated. The results are shown in the "Vc - Vw (mass%)" column of Table 3. The difference in storage modulus at 90°C between white toner 1 and color toner 1 used in Example 1 was also calculated. The results are shown in the "Difference in storage modulus at 90°C (Pa)" column of Table 3.

[0190] The image formed on a recording medium (resin film) by the image forming method of Example 1 was evaluated for substrate adhesion and heat seal resistance by the following methods. The results are shown in Table 3. Hereinafter, the image formed on the recording medium may be referred to as a toner image layer. Furthermore, the toner image layer and the recording medium (resin film) on which the toner image layer is formed may be collectively referred to as a printed matter.

[0191] <Substrate adhesion> First, the printed matter was left for one day. Then, 10 mm x 10 mm grid cuts were made at 3 cm intervals on the printed surface of the printed matter on which the toner image layer was formed using a cutter. Cellophane tape (registered trademark) was applied to the printed surface with the cuts and then quickly peeled off. The appearance of the toner image layer (the toner image layer's remaining rate) was observed, and the substrate adhesion was evaluated using the following evaluation criteria. A, B, or C was deemed acceptable (passed) for use. The toner image layer's remaining rate was calculated by photographing the toner image layer on the printed surface with the cellophane tape attached, and then calculating the difference in density of the photographed image after peeling off the cellophane tape relative to the total area. The grid cuts were made with a cutter to cut only the toner image layer without damaging the resin film serving as a recording medium.

[0192] (Criteria for determining substrate adhesion) A: 90% to 100% of the toner image layer remained on the resin film. B: 80% or more and less than 90% of the toner image layer remained on the resin film. C: 60% or more and less than 80% of the toner image layer remained on the resin film. D: Less than 60% of the toner image layer remained on the resin film.

[0193] <Heat seal resistance> First, the prepared printed matter was left for one day. Then, the image printed on the resin film was heat-sealed at 120°C, 0.2 MPa, and 1 second using a heat seal tester "TP-701-B" (manufactured by Tester Sangyo Co., Ltd.). The heat-sealed area where the heat seal had narrowed from the image was visually observed, and the heat-seal resistance was evaluated according to the following evaluation criteria. The visual observation of the heat-sealed area was performed based on whether the image was attached to the heat seal bar and whether there were any wrinkles in the heat-sealed area. Evaluations of A, B, and C were deemed acceptable for use (pass).

[0194] (Criteria for determining heat seal resistance) A: No change was observed in the heat-sealed area. B: Slight wrinkles are observed in the heat-sealed area. C: Significant wrinkles are observed in the heat-sealed area. D: The laminate melted and adhered to the heat seal bar.

[0195] [Table 3]

[0196] [Table 4]

[0197] (Examples 2 to 20, Comparative Examples 1 to 4) Images were formed on resin films in the same manner as in Example 1, except that the white and color toners used and the resin film used as a recording medium were changed as shown in Tables 3 and 4. When a 20 μm-thick biaxially oriented polypropylene film was used as the resin film, it is indicated as PP in Tables 3 and 4. When a 15 μm-thick high-density polyethylene film was used as the resin film, it is indicated as PE in Tables 3 and 4. When a 25 μm-thick polyethylene terephthalate film was used as the resin film, it is indicated as PET in Table 4.

[0198] The images formed on recording media (resin films) by the image forming methods of Examples 2 to 20 and Comparative Examples 1 to 4 were evaluated for substrate adhesion and heat seal resistance in the same manner as in Example 1. The results are shown in Tables 3 and 4.

[0199] As shown in Tables 3 and 4, the images formed by the image forming methods of Examples 1 to 20 were evaluated as having good substrate adhesion and heat seal resistance. Specifically, when an image formed on a resin film is composed of a white toner image at the bottom and a color toner image on top of the white toner image, it was found that the heat seal resistance of the image is improved by increasing the vinyl resin content of the color toner compared to the white toner. In particular, it was confirmed that the heat seal resistance tends to be further improved when the difference in vinyl resin content between the color toner and the white toner (Vc - Vw) is 10 to 30% by mass. Furthermore, by including amorphous polyester resin as the main component in both the white toner and the color toner, substrate adhesion that is satisfactory for use was obtained. Comparison with Comparative Example 4 also revealed that the heat seal resistance of the image is improved by including ester wax as a release agent in the color toner.

[0200] On the other hand, it was found that the heat seal resistance of the image formed on the resin film was insufficient when the vinyl resin content of the color toner was lower than that of the white toner, as in Comparative Examples 1 and 2. Furthermore, when neither the white toner nor the color toner contained vinyl resin as a binder resin, as in Comparative Example 3, the heat seal resistance of the image formed on the resin film was also insufficient. Furthermore, it was found that the heat seal resistance of the image was insufficient when the color toner contained a higher vinyl resin content than the white toner, as in Comparative Example 4, when the color toner did not contain ester wax as a release agent. [Industrial Applicability]

[0201] The image forming method of the present invention can form an image having excellent adhesive strength and heat seal resistance on a resin film used for applications such as a substrate for flexible packaging, etc. Therefore, the present invention is expected to further popularize image formation using electrophotography. [Explanation of symbols]

[0202] 1 photoreceptor 2. Charging device 3 Exposure equipment 4. Developing device 5 Primary transfer roller 6, 10 Cleaning device 7 Intermediate transfer belt 8. Laura 9 Secondary transfer roller 11 Paper cassette 12 Paper feed roller 13 Conveyor roller 14 Registration roller 15 Ejection roller 16. Paper output tray 50 Fixing device 100, 200 Image forming device 201 Storage Unit 202 First transport unit 203 Second transport unit 204 Storage area F film P Recording medium SC Document Image Reader

Claims

1. forming a toner image on a recording medium, the toner image including a white toner image and a color toner image disposed on the white toner image; and fixing the toner image on the recording medium, the recording medium is a resin film, the toner image is formed from a white toner and a color toner, the white toner and the color toner each containing an amorphous polyester resin as a main component, When the content ratio (mass%) of the vinyl resin in the binder resin component contained in the white toner is Vw and the content ratio (mass%) of the vinyl resin in the binder resin component contained in the color toner is Vc, Vw and Vc satisfy the relationship of the following formula (1), and The image forming method according to claim 1, wherein the color toner contains an ester wax as a releasing agent. Vc>Vw≧0 (1)

2. 2. The image forming method according to claim 1, wherein Vc satisfies the relationship of the following formula (2): 50≧Vc≧20 (2)

3. 3. The image forming method according to claim 1, wherein the vinyl resin is a styrene-acrylic resin.

4. 3. The image forming method according to claim 1, wherein at least one of the white toner and the color toner further contains a crystalline polyester resin.

5. 3. The image forming method according to claim 1, wherein the melting point of the ester wax is 65 to 90°C.

6. The difference in storage modulus at 90° C. between the white toner and the color toner is 1.0×10 ４ Pa ~ 1.0 x 10 ５ 3. The image forming method according to claim 1, wherein the toner is Pa.

7. 3. The image forming method according to claim 1, wherein the amorphous polyester resin is a polycondensation product of a polycarboxylic acid and a polyhydric alcohol, and the content of structural units derived from bisphenol A derivatives is 10 mol % or less relative to 100 mol % of all structural units derived from alcohols.

Images