Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/087—Binders for toner particles
  • G03G9/08702—Binders for toner particles comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G9/08706—Polymers of alkenyl-aromatic compounds
  • G03G9/08708—Copolymers of styrene
  • G03G9/08711—Copolymers of styrene with esters of acrylic or methacrylic acid
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G7/00—Selection of materials for use in image-receiving members, i.e. for reversal by physical contact; Manufacture thereof
  • G03G7/0006—Cover layers for image-receiving members; Strippable coversheets
  • G03G7/002—Organic components thereof
  • G03G7/0026—Organic components thereof being macromolecular
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/087—Binders for toner particles
  • G03G9/08742—Binders for toner particles comprising macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • G03G9/08755—Polyesters

Definitions

• the present invention relates to an image forming method.
• the present invention relates to an image forming method capable of forming an image having sufficient adhesive strength to a recording medium and excellent heat sealing resistance.
• an electrophotographic image forming method may be mentioned.
• a base material for soft packaging may be deformed or melted by heating during fixing.
• the electrophotographic image forming method there is a demand for the development of a toner having excellent low-temperature fixability to be able to suppress heating during fixing.
• a polypropylene film or a polyethylene film is used as a film on which an image is formed.
• the printing method described in Japanese Unexamined Patent Publication No. 2022-54448 is to form an image at a specific fixing temperature on a film having a print surface with a specific surface tension, using the toner containing the crystalline polyester as described above.
• a bag-making step in which a printed product of a soft packaging material, which is one of packaging material applications, is processed into a packaging form suitable for a product, after printing. For this reason, a heat sealing process in which a film is melted by heat and pressure to be bonded may be adopted for bonding of a film as a soft packaging material.
• Printing for soft packaging applications includes, "front printing” in which the print surface is on the outer side of a bag and “back printing” in which the print surface is on the inner surface of a bag, when the film is formed into a bag shape.
• the "back printing” in which the print surface is present on the inner surface of a bag requires a lamination step for bag making.
• the lamination step is a step of bonding a laminate film coated with an adhesive onto an image after printing.
• the "front printing” in which the print surface is present on the outer side of a bag can be subjected to bag making without the above-described lamination step. For this reason, the "front printing” has an advantage of improving productivity.
• an image printed by "front printing” may be referred to as a "front-printed image”
• an image printed by "back printing” may be referred to as a "back-printed image”.
• the present invention has been conceived in consideration of the above problems and circumstances.
• Objects of the present invention include providing an electrophotographic image forming method capable of forming an image having sufficient adhesive strength to a resin film as a recording medium such as a base material for soft packaging and excellent heat sealing resistance at the time of bag making.
• a white toner layer is formed as a bottom layer as a base, and a colored toner layer(s) is formed on the white toner layer.
• the present inventor focused on the content of vinyl resin in the binder resin of each of the white toner and the colored toner used to form the toner image. As a result, they found that the heat sealing resistance of the front-printed image is improved when the content of vinyl resin in the colored toner is larger than that in the white toner, which led to the present invention. That is, the above-described object(s) according to the present invention are achieved, for example, by the following means.
• an image forming method reflecting one aspect of the present invention includes:
• the white toner and the colored toner each contain an amorphous polyester resin as a main component.
• the "main component" of each of the white toner and the colored toner refers to the resin having the highest content in the binder resin that constitutes each toner.
• Amorphous polyester resin has the characteristic of being able to lower the softening point while maintaining a relatively high glass transition temperature. Therefore, the white toner and the colored toners are easily thermally melted, and have good low-temperature fixability.
• such a toner has the property of being easily melted by heat and easily wet-spreading on the resin film serving as a recording medium during fixing, so that the contact area between the toner and the resin film increases, and the adhesiveness is improved.
• the colored toner contains a vinyl resin at a specific content ratio in addition to the amorphous polyester resin as the main component.
• vinyl resin has the property of having high elasticity that is not easily reduced even at a high temperature. Therefore, by including such a vinyl resin in the binder resin constituting the colored toner, excessive plasticization of the binder resin is suppressed even when heat and pressure are applied.
• the present inventor focused on the content of vinyl resin in the binder resin constituting the toner. As a result, it was found that the heat sealing resistance of the front-printed image was improved by increasing the vinyl resin content of the colored toner compared to the white toner.
• a white toner image is formed in the lowermost layer (hereinafter, simply referred to as the "lower layer") as a base, and a colored toner image is formed on the white toner image.
• the lower layer the lowermost layer
• the colored toner image as the upper layer is directly subjected to the heat of the heat seal bar. For this reason, the heat of the heat seal bar is more easily transmitted to the colored toner image as the upper layer and the colored toner image is more easily plasticized than the white toner image as the lowermost layer.
• the adhesive strength between the layers in the toner image weakens, causing image separation to occur starting from the interface between the layers. Therefore, it is believed that by reducing the difference in elasticity between the upper and lower layers at high temperature, inter-layer separation due to heat is suppressed, and heat sealing resistance is improved. It was also discovered that by making the colored toner that forms the upper layer, to which heat is easily transmitted, contains more vinyl resin than the white toner that forms the lower layer, the difference in elasticity between the upper and lower layers was reduced, and the heat sealing resistance of the front-printed image was increased.
• the colored toner contains an ester wax as a release agent.
• the ester wax has a high affinity with the amorphous polyester resin. Particles of the wax in an image formed with such a colored toner have a small particle diameter and are uniform, and are present in a greater amount on the front surface side of the image. Therefore, an image formed from such a colored toner has a reduced adhesive strength to a heat seal bar, and the heat sealing resistance is further improved.
• FIG. 1 An image forming method including a toner image forming step S01 of forming a toner image and a toner image fixing step S02 of fixing the toner image on a recording medium.
• the toner image forming step S01 is a step of forming, on a recording medium, a toner image including a white toner image and a colored toner image disposed on the white toner image.
• the toner image fixing step S02 is a step of fixing the toner image obtained in the toner image forming step S01 onto a recording medium.
• FIG. 1 is a flowchart illustrating an embodiment of the image forming method of the present embodiment.
• a toner image including a white toner image and a colored toner image is formed with the white toner and the colored toner. More specifically, the white toner image formed as the lowermost layer on the recording medium is formed from the white toner. The colored toner image is formed from the colored toner.
• the white toner and the colored toner that form the toner image each contain an amorphous polyester resin as a main component.
• the "main component" of the white toner and the colored toner refers to a resin having the highest content in the binder resin constituting the respective toners.
• Vw the content (% by mass) of the vinyl resin in the binder resin component contained in the white toner
• Vc the content (% by mass) of the vinyl resin in the binder resin component contained in the colored toner
• Vw and Vc satisfy the relationship of the following formula (1).
• the colored toner includes ester wax as a release agent.
• the “content (% by mass) of the vinyl resin in the binder resin component contained in the white toner” may be referred to as the “content Vw (% by mass) of the vinyl resin in the white toner”.
• the content (% by mass) of the vinyl resin in the binder resin component contained in the colored toner may be referred to as “the content Vc (% by mass) of the vinyl resin in the colored toner”.
• the white toner and the colored toner may be collectively referred to simply as "toner”. Vc > Vw ⁇ 0
• an image having sufficient adhesive strength to a resin film as a recording medium and excellent heat sealing resistance during bag making can be formed.
• the resin film as a recording medium is suitably used as a soft packaging material, which is one of packaging material applications.
• the image forming method of the present embodiment can form an image in which image separation is unlikely to occur even in the front printing in which the heat seal bar and an image are in direct contact with each other in the heat sealing process in the bag-making step.
• each toner used in the image forming method of the present embodiment contains an amorphous polyester resin as a main component, the toner is easily melted by heat and has good low-temperature fixability.
• the toner since the toner has a characteristic of easily wet-spreading on a resin film that is a recording medium during fixing, a contact area between the toner and the resin film increases, and adhesiveness is improved.
• the difference in elasticity between the upper layer and the lower layer can be reduced by a vinyl resin contained at a larger amount in the colored toner forming the upper layer to which heat is easily transferred in the heat sealing process than in the white toner forming the lower layer.
• the heat sealing resistance of the front-printed image can be improved by reducing the difference in elasticity between the upper layer and the lower layer constituting the image.
• the colored toner contains ester wax as a release agent.
• the adhesive strength to a heat seal bar is reduced, and the heat sealing resistance is further improved. That is, particles of the wax in an image formed of the colored toner have a small diameter and are uniform, and are present at a larger amount on the front surface side of the image. Therefore, the adhesive strength of such an image to the heat seal bar decreases, and the heat sealing resistance is further improved.
• the term "chromatic toner” basically refers to toner having three attributes of hue, brightness and saturation, such as yellow toner, magenta toner, and cyan toner.
• the term “achromatic toner” refers to a coupler that basically does not have hue and saturation but has only brightness, such as a black toner, a white toner, or a gray toner.
• the term “clear toner” refers to a toner that causes a layer formed with the clear toner in an electrophotographic image to be in a so-called transparent state in which the layer transmits light in substantially the entire visible light region or light in part of the region so that the other side of the layer can be seen through.
• the light transmittance is not particularly limited as long as it is a transmittance to the extent that the other side can be seen through, but is 50% or more, preferably 70% or more, and further preferably 90% or more.
• the layer transmits light in substantially the entire visible light region, it is colorless and transparent.
• the "white toner” refers to a toner having a color (white) satisfying the condition that a lightness L* is 80 or more, and a* and b* are -10 ⁇ a* ⁇ 10 and -10 ⁇ b* ⁇ 10, respectively, in the CIE L*a*b* color system in the case where only the white toner is transferred onto a transfer material and the surface thereof is measured with a spectral color difference meter in accordance with JIS Z 8781-4:2013.
• colored toner in the present specification refers to toner belonging to a toner group including the chromatic toner, the black toner and the gray toner included in the achromatic toner, and the clear toner, and the colored toner does not include the white toner.
• the image forming method is an image forming method including a toner image forming step S01 of forming a toner image and a toner image fixing step S02 of fixing the toner image onto a recording medium.
• the toner image forming step S01 is a step of forming, on a recording medium, a toner image including a white toner image and a colored toner image disposed on the white toner image.
• the toner image fixing step S02 is a step of fixing the toner image obtained in the toner image forming step S01 onto a recording medium.
• a resin film is used as the recording medium in the image forming method according to the present embodiment. Details of the resin film will be described later.
• the white toner and the colored toner forming the toner image each contain an amorphous polyester resin as a main component. Further, the content Vw (% by mass) of the vinyl resin in the binder resin component contained in the white toner and the content Vc (% by mass) of the vinyl resin in the binder resin component contained in the colored toner satisfy the relationship of the formula (1). Further, the colored toner includes ester wax as a release agent.
• the toner image forming step S01 is performed using white toner and colored toner, and may include, for example, a charging step, an exposure step, a developing step, and a transfer step.
• the charging step, the exposure step, the developing step, and the transfer step in the toner image forming step S01 and the fixing step as the toner image fixing step S02 are described below.
• an electrophotographic photoreceptor is charged.
• the charging method is not particularly limited, and may be, for example, a known method such as a charging roller method in which the electrophotographic photoreceptor is charged with a charging roller.
• an electrostatic latent image is formed on the electrophotographic photoreceptor (electrostatic latent image bearing member).
• the electrophotographic photoreceptor is not particularly limited, but examples thereof include a drum-shaped photoreceptor formed of an organic photoreceptor such as polysilane or phthalopolymethine. Formation of an electrostatic latent image is performed, for example, by uniformly charging the surface of the electrophotographic photoreceptor in the charging step and exposing the surface of the electrophotographic photoreceptor to light in an image pattern by an exposure device.
• the exposure device is not particularly limited, and a device generally used in an electrophotographic system can be used.
• the developing step is a step of developing the electrostatic latent image formed in the exposure step with a dry developer containing a toner to form a toner image.
• Formation of a toner image is performed using a dry developer containing toner, for example, by a developing device including a stirrer that triboelectrically stirs toner to charge the toner, and a rotatable magnet roller.
• a developing device including a stirrer that triboelectrically stirs toner to charge the toner, and a rotatable magnet roller.
• the toner and the carrier are mixed and stirred, and the toner is charged by friction at that time and is held on the surface of the rotating magnet roller to form a magnetic brush.
• the magnet roller Since the magnet roller is disposed in the vicinity of the electrophotographic photoreceptor (electrostatic latent image bearing member), part of the toner constituting the magnetic brush formed on the surface of the magnet roller is moved to the surface of the electrophotographic photoreceptor by an electrical attraction force. As a result, the electrostatic latent image is developed with the toner to form a toner image on the surface of the electrophotographic photoreceptor.
• the toner image formed in the developing step is transferred to a recording medium.
• the transfer of the toner image to the recording medium is performed by separating the toner image from the electrophotographic photoreceptor and charging it.
• the transfer device for example, a corona transfer device using corona discharge, a transfer belt, a transfer roller, or the like can be used.
• the transfer step can also be performed by a mode in which an intermediate transfer member is used, the toner image is primary-transferred onto the intermediate transfer member, and then the primary -transferred toner image is secondary-transferred onto a recording medium.
• the toner image formed on the electrophotographic photoreceptor can be directly transferred to an image support member.
• the recording medium in a general image forming method can include various kinds of media such as plain paper ranging from thin paper to cardboard, wood-free paper, coated printing sheets such as art paper and coated paper, commercially available Japanese paper and postcard sheets, a plastic film for OHP, and fabric.
• a resin film is used as the recording medium.
• the toner image transferred onto the recording medium includes the white toner image and the colored toner image, and the colored toner image is disposed on the white toner image formed as the lowermost layer.
• the recording medium to which the unfixed image including the white toner image and the colored toner image is transferred is nipped and conveyed to a fixing nip part provided between a heated fixing rotating member and the pressure member to be thermally fixed.
• a system for the fixing step include a roller fixing system constituted by a fixing rotating roller (also referred to as a "fixing roller") as the fixing rotating member and a pressure roller.
• the pressure roller is a pressure member provided in a state of being pressed against the fixing roller so that the fixing nip part is formed.
• the system for the fixing step also include a belt fixing system in which the fixing rotating member is formed of a fixing belt.
• the image forming apparatus used in the image forming method of the present embodiment is different from the general one in which an image forming unit or the like with the use of the white toner taken into account is additionally provided, but the same as the general one in the basic principle, and therefore the description in this case is the same as the following description. Further, in the case of using the clear toner, a similar apparatus in which an image forming unit or the like is additionally provided in consideration of this is used.
• FIG. 2 is a diagram schematically illustrating a configuration example 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.
• the image forming apparatus 100 includes a document image reading device SC, four image forming sections for forming a toner image, and a transfer device for transferring the toner image formed by the image forming sections onto a recording medium P. Further, the image forming apparatus 100 includes a sheet feeding and conveying device for conveying the recording medium P, and a heat roll type fixing device 50 as a fixing section for fixing the unfixed toner image held on the recording medium P to the recording medium P.
• the document image reading device SC is a reading device for reading a document image.
• the document image reading device SC reads image information of a document, converts the image information into image data of each color of YMCK, and sends the image data of the colors to their corresponding exposure devices 3 described later.
• the four image forming sections are devices for forming images in four colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively, and are disposed, for example, in the order of YMCK from the top of FIG. 1 .
• Each of the image forming sections includes 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. Note that in a case where a white toner image is formed with white toner, a fifth image forming section for forming an image with white toner is further provided, and the image forming section for forming an image with white toner is configured to form a white image.
• the photoreceptor 1 is, for example, a drum-shaped organic photoreceptor
• the charging device 2 is, for example, a non-contact charging device using corona discharge.
• the exposure device 3 is, for example, a laser oscillation device
• the developing device 4 is a developing device for a two-component developer, the developing device that houses a two-component developer of one of the colors of YMCK.
• the primary transfer roller 5 is, for example, a charging roller that is freely biased toward the photoreceptor 1 via an intermediate transfer belt 7.
• the cleaning device 6 is, for example, a blade cleaning device including an elastic blade made of rubber that comes in contact with the surface of the photoreceptor 1.
• the transfer device includes an endless intermediate transfer belt 7, a plurality of rollers 8 around which the intermediate transfer belt 7 is stretched, a secondary transfer roller 9, and a cleaning device 10.
• the roller 8 includes one or more drive rollers, and may include driven rollers other than the drive rollers.
• the secondary transfer roller 9 is, for example, a charging roller capable of forming a nip part between the secondary transfer roller 9 and the intermediate transfer belt 7 via the recording medium P to be conveyed thereto.
• the cleaning device 10 is, for example, a blade cleaning device including an elastic blade that comes in contact with the surface of the intermediate transfer belt 7.
• the sheet feeding and conveying device includes a sheet feed cassette(s) 11, a sheet feed roller(s) 12, a conveyance roller(s) 13, a registration roller(s) 14, an ejection roller(s) 15, and a sheet ejection tray 16.
• the sheet feed cassette 11 is for storing recording media P.
• the sheet feed roller 12 is used to take out the recording medium P from the sheet feed cassette 11.
• the conveyance roller 13 is for conveying the recording medium P to the nip part of the secondary transfer roller 9.
• the registration roller 14 is for controlling the position of the recording medium P being conveyed.
• the ejection roller 15 is for ejecting the recording medium P ejected from a fixing device 50 to the outside of the apparatus.
• the sheet ejection tray 16 is for storing the recording medium P ejected to the outside of the apparatus.
• the recording medium P is not particularly limited, but is, for example, a resin film such as an OHP sheet.
• the surface of the photoreceptor 1 driven to rotate is charged by the application of voltage from the charging device 2 in the image forming section.
• the exposure device 3 irradiates the charged surface of the photoreceptor 1 with laser light corresponding to image data of the corresponding color of Y, M, C or K to form 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 is formed, and the toner particles adhere to the electrostatic latent image to develop the electrostatic latent image.
• the toner images of the respective colors of YMCK formed in the respective image forming sections and held on the surfaces of the respective photoreceptors 1 are transferred onto the rotating intermediate transfer belt 7 so as to be sequentially superimposed on top of one another by application of voltage from the primary transfer rollers 5.
• a combined colored toner image is thus formed on the intermediate transfer belt 7.
• the white toner image and the colored toner image(s) may be formed by the following one pass method or two pass method.
• the one pass method is a method in which the white toner image and the colored toner image are formed on the intermediate transfer belt 7 and collectively transferred onto the recording medium P.
• the two pass method is a method in which the base image (white toner image) is formed on and fixed to the recording medium P, and then the upper layer image (colored toner image) is formed on and fixed to the base image, that is, the base image and the upper layer image are formed on and fixed to the recording medium P in two steps.
• the primary transfer roller 5 may contact the photoreceptor 1 only during the primary transfer.
• the primary transfer roller 5 in the image forming section for a black image constantly contacts the photoreceptor 1, and the primary transfer rollers 5 for the other colors contact the photoreceptors 1 only during the primary transfer.
• Adhered substances such as the residual toner on the surface of the photoreceptor 1 after the primary transfer are removed from the surface by the cleaning device 6.
• the recording medium P stored in the sheet feeding cassette 11 is taken out from the sheet feeding cassette 11 by the sheet feed roller 12, and is conveyed to the secondary transfer roller 9 via the conveyance roller 13 and the registration roller 14.
• the 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 biased toward the intermediate transfer belt 7 only during the secondary transfer.
• Adhesive substances such as the residual toner on the surface of the intermediate transfer belt 7 after the secondary transfer are removed from the surface by the cleaning device 10.
• the colored toner image on the recording medium P is fixed to the surface of the recording medium P by heat and pressure of the fixing device 50. In this way, a fixed colored toner image is formed on the recording medium P.
• the recording medium P with the colored toner image formed is conveyed onto the sheet ejection tray 16 via the ejection roller 15. By repeating the above-described steps, toner images fixed onto the recording media P are formed one after another.
• FIG. 3 is a diagram schematically illustrating a configuration example of an image forming apparatus for performing the image forming method using a recording medium P stored in a roll shape.
• An image forming apparatus 200 has substantially the same configuration as the image forming apparatus 100 except that the image forming apparatus 200 further includes a storage section 201 that stores a roll-shaped recording medium P, a first conveyance unit 202, a second conveyance unit 203, and a storage section 204.
• the first conveyance unit 202 is for conveying the continuous sheet of the recording medium P to the upstream part of the sheet feeding and conveying device.
• the second conveyance unit 203 is for conveying the recording medium P with the toner image formed and fixed.
• the storage section 204 is for storing the recording medium P conveyed from the conveyance unit 203 to be a roll shape.
• the recording medium P is, for example, a continuous PET sheet used for a soft packaging material.
• the recording medium P is conveyed to the secondary transfer roller 9 from the storage section 201 via the first conveyance unit 202.
• the recording medium P on which the toner image is fixed by the fixing device 50 is stored to be a roll shape in the storage section 204 via the second conveyance unit 203. Except for the above, a toner image is formed on a recording medium P in the same manner as the image forming apparatus 100 forms a toner image on a recording medium P.
• the toner used in the image forming method contains toner particles containing a binder resin.
• the toner particles are obtained by adding an external additive to toner base particles, and an aggregate of the toner particles is referred to as a toner.
• toner base particles can be used as toner particles as they are, but in the present embodiment, toner particles obtained by adding an external additive to the toner base particles are used as toner particles.
• the toner base particles contain a binder resin.
• the toner base particles may contain other constituent components, such as a release agent (wax), a colorant, and a charge control agent, if necessary.
• the colored toner contains at least an amorphous polyester resin and a vinyl resin, as the binder resin.
• the white toner contains at least an amorphous polyester resin as the binder resin.
• the white toner may contain a vinyl resin as the binder resin.
• the colored toner and the white toner may further contain a conventionally known fixing resin, such as a crystalline polyester resin, as the binder resin.
• the amorphous polyester resin is the main component of the binder resin contained in the toner.
• the amorphous polyester resin has the characteristic of being able to lower the softening point while maintaining a relatively high glass transition temperature. For this reason, the toner containing the amorphous polyester resin as the main component is easily thermally melted, and the low-temperature fixability is improved.
• such a toner has the property of being easily melted by heat and easily wet-spreading on the resin film serving as a recording medium during fixing, so that the contact area between the toner and the resin film increases, and the adhesiveness is improved.
• the content of the amorphous polyester resin in the binder resin component is not particularly limited as long as the amorphous polyester resin has the highest content in the binder resin component constituting the toner.
• the content of the amorphous polyester resin in the binder resin component is preferably 60 to 100% by mass, further preferably 70 to 100% by mass, and especially preferably 80 to 100% by mass.
• the amorphous polyester resin is a polyester resin that does not have a melting point and has a relatively high glass transition temperature (Tg) when differential scanning calorimetry (DSC) is performed.
• the glass transition temperature (Tg) is preferably 30 to 80°C, especially preferably 40 to 64°C.
• the glass transition temperature (Tg) can be measured by a differential scanning calorimeter (DSC). Since the monomer constituting the amorphous polyester resin is different from the monomer constituting the crystalline polyester resin, the amorphous polyester resin can be distinguished from the crystalline polyester resin by, for example, analysis such as NMR.
• the glass transition temperature can be controlled by the composition of the resin by those skilled in the art.
• the amorphous polyester resin is obtained by polycondensation reaction of a di-or higher-valent carboxylic acid (polyvalent carboxylic acid) and a di-or higher-valent alcohol (polyhydric alcohol).
• the amorphous polyester resin is not particularly limited, and amorphous polyester resin conventionally known in the present technical field can be used.
• Examples of the polyvalent carboxylic acid and the polyhydric alcohol used in preparation of the amorphous polyester resin include, but are not particularly limited to, the following.
• polyvalent carboxylic acid examples thereof preferably used include unsaturated aliphatic polyvalent carboxylic acid, aromatic polyvalent carboxylic acid, and derivatives thereof. Saturated aliphatic polyvalent carboxylic acid may be used in combination if amorphous resin can be formed.
• Examples of the unsaturated aliphatic polyvalent carboxylic acid include unsaturated aliphatic dicarboxylic acid, unsaturated aliphatic tricarboxylic acid, and unsaturated aliphatic tetracarboxylic acid, and lower alkyl esters and acid anhydrides thereof can also be used.
• Examples of the unsaturated aliphatic dicarboxylic acid include methylenesuccinic acid, fumaric acid, maleic acid, 3-hexenedioic acid, 3-octenedioic acid, and succinic acid substituted with an alkenyl group having a carbon number of 2 to 20.
• Examples of the unsaturated aliphatic tricarboxylic acid include 3-butene-1,2,3-tricarboxylic acid, 4-pentene-1,2,4-tricarboxylic acid, and aconitic acid.
• Examples of the unsaturated aliphatic tetracarboxylic acid include 4-pentene-1,2,3,4-tetracarboxylic acid.
• aromatic polyvalent carboxylic acid examples include aromatic dicarboxylic acid, aromatic tricarboxylic acid, aromatic tetracarboxylic acid, and aromatic hexacarboxylic acid, and ower alkyl esters and acid anhydrides thereof can also be used.
• aromatic dicarboxylic acid examples include phthalic acid, terephthalic acid, isophthalic acid, t-butylisophthalic acid, tetrachlorophthalic acid, chlorophthalic acid, and nitrophthalic acid.
• Examples of the aromatic dicarboxylic acid also include p-phenylenediacetic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and anthracenedicarboxylic acid.
• Examples of the aromatic tricarboxylic acid include 1,2,4-benzene tricarboxylic acid (trimellitic acid), 1,2,5-benzene tricarboxylic acid (trimesic acid), 1,2,4-naphthalene tricarboxylic acid, and hemimellitic acid.
• Examples of the aromatic tetracarboxylic acid include pyromellitic acid, and 1,2,3,4-butanetetracarboxylic acid.
• Examples of the aromatic hexacarboxylic acid include mellitic acid.
• polyvalent carboxylic acids may be used alone or in combination of two or more kinds thereof.
• polyhydric alcohol examples thereof preferably used include unsaturated aliphatic polyhydric alcohol, aromatic polyhydric alcohol, and derivatives thereof from the viewpoints of the chargeability and the toner strength, and saturated aliphatic polyhydric alcohol may be used in combination therewith if amorphous resin can be formed.
• Examples of the unsaturated aliphatic polyhydric alcohol include unsaturated aliphatic diol, and derivatives thereof can also be used.
• Examples of the unsaturated aliphatic diol 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.
• aromatic polyhydric alcohol examples include bisphenols such as bisphenol A and bisphenol F, and alkylene oxide adducts of bisphenols such as ethylene oxide adducts and propylene oxide adducts of these bisphenols.
• aromatic polyhydric alcohol also include 1,3,5-benzenetriol, 1,2,4-benzenetriol, and 1,3,5-trihydroxymethylbenzene.
• derivatives of the above-described aromatic polyhydric alcohols can also be used. Among these, it is preferable to use a bisphenol A compound such as an ethylene oxide adduct or a propylene oxide adduct of bisphenol A, particularly from the viewpoint that the thermal properties are easily optimized.
• the number of carbon atoms of the trihydric or higher polyhydric alcohol is not particularly limited, but the number of carbon atoms is preferably 3 to 20 because thermal properties thereof are easily optimized in particular.
• polyhydric alcohols may be used alone or in combination of two or more kinds thereof.
• the amorphous polyester resin is polycondensate of polyvalent carboxylic acid and polyhydric alcohol, and the content of structural units derived from a bisphenol A derivative is preferably 10% by mole or less with respect to 100% by mole of all the structural units derived from the alcohol. According to such a constitution, the compatibility of the crystalline polyester is increased, and the crystalline polyester is finely dispersed, whereby the low-temperature fixability is improved.
• the method for producing the amorphous polyester resin is not particularly limited, and the resin can be produced by polycondensation (esterification) of the polyvalent carboxylic acid and the polyhydric alcohol described above using a known esterification catalyst.
• Examples of the catalyst usable in the production include alkali metal compounds such as sodium and lithium, compounds containing a Group 2 element such as magnesium and calcium, metal compounds such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium, and germanium, phosphite compounds, phosphate compounds, and amine compounds.
• alkali metal compounds such as sodium and lithium
• compounds containing a Group 2 element such as magnesium and calcium
• metal compounds such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium, and germanium
• phosphite compounds such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium, and germanium
• phosphite compounds such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium, and germanium
• phosphite compounds such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium, and germanium
• the temperature of the polycondensation (esterification) is not particularly limited, but is preferably 150 to 250°C.
• the time of the polycondensation (esterification) is not particularly limited, but is preferably 0.5 to 15 hours. During the polycondensation, the pressure in the reaction system may be reduced as necessary.
• the weight average molecular weight (Mw) of the amorphous polyester resin is not particularly limited, but is preferably in a range of 5,000 to 100,000, and further preferably in a range of 5,000 to 50,000. If the weight average molecular weight (Mw) is 5,000 or more, the heat-resistant storage property of the toner can be improved, whereas if the weight average molecular weight (Mw) is 100,000 or less, the low-temperature fixability can be further improved.
• the number average molecular weight (Mn) of the resin is not particularly limited, but is preferably 1,500 to 25,000.
• the weight average molecular weight (Mw) and the number average molecular weight (Mn) can be measured by gel permeation chromatography (GPC).
• the amorphous polyester resin preferably has an acid number of 5 to 50 mgKOH/g. Within this range, the amorphous polyester resin, the vinyl resin and the ester wax are likely to be uniformly dispersed. Therefore, the ester wax is less likely to be exposed on the surface of the toner particles, and thus occurrence of image noise (fog) is suppressed.
• the binder resin contains vinyl resin in addition to the amorphous polyester resin described above.
• it may contain vinyl resin in addition to the amorphous polyester resin described above as long as the relationship of the formula (1) is satisfied. That is, the white toner may contain vinyl resin as the binder resin as long as the content Vw (% by mass) of the vinyl resin in the binder resin component contained in the white toner is smaller than the content Vc (% by mass) of the vinyl resin in the binder resin component contained in the colored toner.
• the colored toner for forming the upper layer to which heat is easily transmitted in the heat sealing process contains a greater amount of vinyl resin than the white toner for forming the lower layer.
• the difference in elasticity between the upper layer formed of the colored toner and the lower layer formed of the white toner is reduced, and the heat sealing resistance of the front-printed image can be improved. That is, by reducing the difference in elasticity between the upper layer and the lower layer at a high temperature, the inter-layer separation due to heat is suppressed, and the heat sealing resistance can be improved.
• Specific values of the content Vw (% by mass) of the vinyl resin in the white toner and the content Vc (% by mass) of vinyl resin in the colored toner are not particularly limited as long as the values satisfy the relationship of the above formula (1). That is, the white toner may or may not contain vinyl resin o (i.e., Vw may be 0% by mass). On the other hand, it is essential that the colored toner contains vinyl resin in addition to the amorphous polyester resin as the main component.
• the content Vc (% by mass) of the vinyl resin in the colored toner is greater than the content Vw (% by mass) of the vinyl resin in the white toner (i.e., the relationship of Vc > Vw is satisfied).
• the content Vc (% by mass) of the vinyl resin in the colored toner is not particularly limited, but preferably satisfies the relationship of the following formula (2).
• Such a configuration improves the low-temperature fixability and heat resistance of the colored toner.
• the content Vc of the vinyl resin in the colored toner exceeds 50% by mass, the low-temperature fixability of the colored toner may decrease.
• the content Vc of the vinyl resin in the colored toner is less than 20% by mass, the heat resistance of the colored toner may decrease. 50 ⁇ Vc ⁇ 20
• the content Vc of the vinyl resin in the colored toner is preferably 20 to 50% by mass, further preferably 25 to 45% by mass, and especially preferably 25 to 35% by mass, as indicated by the formula (2) above.
• the content Vw (% by mass) of the vinyl resin in the white toner is not particularly limited, but is, for example, preferably 0 to 30% by mass, further preferably 0 to 20% by mass, and especially preferably 0 to 10% by mass.
• the white toner is highly filled with an inorganic pigment such as titanium oxide, and as a result, the amount of the binder resin used tends to be relatively small. Therefore, by setting the content Vw (% by mass) of the vinyl resin in the white toner to be in the numerical value range described above, excellent low-temperature fixability of the amorphous polyester resin, which is the main component of the binder resin, is not impaired.
• the content Vc (% by mass) of the vinyl resin in the colored toner and the content Vw (% by mass) of the vinyl resin in the white toner satisfy the relationship of the following formula (3). 30 ⁇ Vc ⁇ Vw ⁇ 10
• the formula (3) above represents the difference (Vc - Vw) between the content Vc (% by mass) of the vinyl resin in the colored toner and the content Vw (% by mass) of the vinyl resin in the white toner.
• the difference (Vc - Vw) in content of vinyl resin therebetween is 10 to 30% by mass, the difference in elasticity between the upper layer and the lower layer at high temperature becomes particularly small, and heat sealing resistance can be extremely effectively improved.
• the difference (Vc - Vw) in the content of the vinyl resin is less than 10% by mass, the brittleness of the image increases, and the image may be easily peeled off (separated) when the film as the recording medium is bent.
• the difference (Vc - Vw) in the content of the vinyl resin exceeds 30% by mass, the difference in elasticity between the upper layer and the lower layer becomes excessively large, and a sufficient effect of suppressing the inter-layer separation due to heat may be hardly obtained.
• the difference (Vc - Vw) in the content of the vinyl resin is further preferably 15 to 30% by mass and especially preferably 20 to 30% by mass.
• the method for measuring the content Vw (% by mass) of the vinyl resin in the white toner and the content Vc (% by mass) of the vinyl resin in the colored toner For example, when the ratio of the resin component in the binder resin of each of the white toner and the colored toner forming the toner image has been found, the content (% by mass) of the vinyl resin in the binder resin component can be obtained from the ratio.
• the content Vc (% by mass) of the vinyl resin for each of the colored toners is obtained individually.
• the content Vc (% by mass) in each colored toner satisfies the relationship of the formula (1).
• the kind of the vinyl resin contained in the binder resin is not particularly limited.
• the vinyl resin is a resin obtained by polymerization using at least a vinyl monomer.
• the vinyl resin include acrylic resin, styrene acrylic resin, and ethylene-vinyl acetate resin. Among these, from the viewpoint of plasticity at the time of heat fixing, styrene acrylic resin is preferable.
• the styrene acrylic resin as the vinyl resin will be described.
• the styrene acrylic resin is formed by addition-polymerizing at least a styrene monomer and a (meth) acrylic acid ester monomer.
• styrene monomers and derivatives thereof may be collectively referred to as "styrene-based monomer”.
• (meth) acrylic acid ester monomers and derivatives thereof may be collectively referred to as "(meth) acrylic acid ester-based monomer”.
• the term “(meth) acrylic acid ester monomer” collectively refers to "acrylic acid ester monomer” and “methacrylic acid ester monomer”.
• methyl (meth) acrylate” collectively refers to "methyl acrylate” and "methyl methacrylate”.
• styrene-based monomer examples include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, p-ethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, 2,4-dimethylstyrene, 3,4-dichlorostyrene, and derivatives thereof.
• Examples of the (meth) acrylic acid ester-based monomer 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 ⁇ -hydroxyacrylate, propyl ⁇ -aminoacrylate, stearyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and derivatives thereof. These may be used alone or in combination of two or more kinds thereof.
• the polymerizable monomer for forming the styrene acrylic resin the following can also be used together with the aforementioned styrene-based monomer and (meth) acrylic acid ester-based monomer.
• olefins include ethylene, propylene, and isobutylene.
• vinyl esters include vinyl propionate, vinyl acetate, and vinyl benzoate.
• vinyl ethers include vinyl methyl ether and vinyl ethyl ether.
• vinyl ketones include vinyl methyl ketone, vinyl ethyl ketone, and vinyl hexyl ketone.
• 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.
• the polymerizable monomer for forming the styrene acrylic resin for example, the following monomers having an ionic dissociable group such as a carboxy group and a phosphate group can also be used together with the aforementioned styrene-based monomers and (meth) acrylic acid ester-based monomers.
• vinyl-based monomer having a carboxy group examples include (meth) acrylic acid and ⁇ -alkyl derivatives or ⁇ -alkyl derivatives such as acrylic acid, methacrylic acid, ⁇ -ethylacrylic acid and crotonic acid; unsaturated dicarboxylic acid 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.
• vinyl-based monomer having a phosphate group examples include acidophosphooxyethyl methacrylate.
• the polymerizable monomer for forming the styrene acrylic resin for example, the following polyfunctional vinyls can also be used together with the aforementioned styrene-based monomer and (meth) acrylic acid ester-based monomer.
• the 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.
• the binder resin may contain, for example, crystalline polyester resin in addition to the amorphous polyester resin and the vinyl resin described above.
• the crystalline polyester resin is a resin obtained by polycondensation reaction between a carboxylic acid having a valency of two or more (polyvalent carboxylic acid) and an alcohol having a valency of two or more (polyhydric alcohol).
• the crystalline polyester resin is one kind of crystalline resin.
• the crystalline resin refers to a resin having a clear endothermic peak, not a stepwise endothermic change, in differential scanning calorimetry (DSC).
• the clear endothermic peak means a peak having a half value width of the endothermic peak of 15°C or less when measured at a temperature increase rate of 10°C/min in differential scanning calorimetry (DSC).
• the toner used in the image forming method it is preferable that least one of the white toner and the colored toner further contain the crystalline polyester resin as the binder resin.
• the crystalline polyester resin has good affinity for 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 melt property at the time of fixing can be improved, and the low-temperature fixability can be further improved.
• the crystalline polyester resin is an optional component of the binder resin, and the content thereof is not particularly limited.
• the content of the crystalline polyester resin in the binder resin is preferably 1 to 30% by mass, and further preferably 5 to 20% by mass.
• polyvalent carboxylic acid and the polyhydric alcohol used in the preparation of the crystalline polyester resin include, but are not particularly limited to, the following.
• Examples of the polyvalent carboxylic acid include dicarboxylic acid.
• the dicarboxylic acid is preferably aliphatic dicarboxylic acid, and may further include aromatic dicarboxylic acid.
• the number of carbon atoms of the main chain including a carboxy group is preferably 4 to 12 from the viewpoint that excellent crystallinity is obtained in the crystalline polyester resin.
• short-chain aliphatic dicarboxylic acid is further preferably used from the viewpoint of ensuring the low-temperature fixing ability.
• the short-chain aliphatic dicarboxylic acid is a linear aliphatic dicarboxylic acid having 6 to 10 carbon atoms in the main chain including a carboxy group.
• Such dicarboxylic acids may be used alone or in combination of two or more kinds thereof.
• Examples of the aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid. Examples thereof further 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.
• the lower alkyl esters and acid anhydrides of the compounds mentioned above can also be used.
• the aforementioned aliphatic dicarboxylic acids it is preferable to use succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid.
• succinic acid glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid.
• adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid are further preferably used.
• aromatic dicarboxylic acid examples include terephthalic, isophthalic, orthophthalic, t-butylisophthalic, 2,6-naphthalenedicarboxylic, and 4,4'-biphenyldicarboxylic acids.
• Examples of the polyhydric alcohol component include diol.
• the diol is preferably aliphatic diol, and may further include other diol. From the viewpoint of obtaining excellent crystallinity in the crystalline polyester resin, among the aliphatic diols, a linear aliphatic diol having 2 to 15 carbon atoms in the main chain is preferably used, and an aliphatic diol having 2 to 10 carbon atoms in the main chain is further preferably used. Further, from the viewpoint of ensuring the low-temperature fixability, it is especially preferable to use short-chain aliphatic diols among these aliphatic diols.
• the short-chain aliphatic diol is an aliphatic diol in which the number of carbon atoms of the main chain is 2 to 6. These diols may be used alone or in combination of two or more kinds thereof.
• Examples of the aliphatic diol 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, and 1,20-eicosanediol.
• 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 further preferably used.
• a diol having a double bond can also be used as the diol other than the aliphatic diol.
• the diol having double bond include 2-butene-1,4-diol, 3-hexene-1,6-diol, and 4-octene-1,8-diol.
• the method for producing the crystalline polyester resin is not particularly limited, and the crystalline polyester resin can be produced by using a general polyester polymerization method in which a dicarboxylic acid component and a diol component are reacted in the presence of a catalyst.
• a general polyester polymerization method in which a dicarboxylic acid component and a diol component are reacted in the presence of a catalyst.
• Examples of the catalyst that can be used in the production of the crystalline polyester resin include a titanium catalyst and a tin catalyst.
• Examples of the titanium catalyst include titanium tetraethoxide, titanium tetrapropoxide, titanium tetraisopropoxide, and titanium tetrabutoxide.
• Examples of the tin catalyst include dibutyltin dichloride, dibutyltin oxide, and diphenyltin oxide.
• the ratio of the diol and the dicarboxylic acid in the monomers of the crystalline polyester resin can be expressed as the equivalence ratio [OH]/[COOH] of the hydroxy groups [OH] of the diol to the carboxy groups [COOH] of the dicarboxylic acid.
• the equivalence ratio [OH]/[COOH] of the hydroxy groups [OH] of the diol to the carboxy groups [COOH] of the dicarboxylic acid is preferably within the range of 1.5/1.0 to 1.0/1.5, further preferably within the range of 1.2/1.0 to 1.0/1.2.
• toner base particles In addition to the binder resin, internal additives such as a colorant, a release agent, and a charge control agent may be contained in the toner base particles as necessary.
• the coloring agent generally known dyes and pigments can be used.
• the term "colored toner” in the present specification refers to a toner belonging to a toner group including the chromatic toner, the black toner and the gray toner included in the achromatic toner, and the clear toner, and the colored toner does not include the white toner.
• the "white toner” refers to a toner having a color (white) satisfying the above-described specific conditions.
• the white color of the white toner is set as a reference color, and the chromatic colored toner, the black toner, the gray toner, and the clear toner which are recognized as being different from the white color are referred to as the "colored toner" for convenience.
• any of various known colorants can be used, and 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 can be used as appropriate.
• the colorant for the chromatic toner e.g., colored toner
• a known colorant such as a dye or an organic pigment
• examples of the organic pigment include C. I. Pigment Reds 5, 48:1, 48:2, 48:3, 53:1, 57:1, 81:4, 122, 139, 144, 149, 166, 177, 178, 222, 238, 269, C .I. Pigment Yellows 14, 17, 74, 93, 94, 138, 155, 180, 185, C. I. Pigment Oranges 31, 43, and C. I. Pigment Blues 15:3, 60, 76, and examples of the dye include C. I.
• Solvent Yellows 19 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, 162, and C.
• Solvent Blues 25 36, 69, 70, 93, 95.
• the colorant for the white toner known colorants such as an inorganic pigment or an organic pigment can be used as appropriate.
• the inorganic pigment 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 smectite.
• the organic pigment include polystyrene resin particles and urea formalin resin particles.
• the aforementioned ones may be used alone or in combination of two or more kinds thereof.
• the content of the colorant is preferably 1 to 20 parts by mass, and further preferably 4 to 15 parts by mass, with respect to 100 parts by mass of the binder resin.
• the colored toner contains ester wax as a release agent.
• the colored toner may also 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 agent.
• the content of the release agent is preferably 1 to 30 parts by mass, and further preferably 5 to 20 parts by mass, with respect to 100 parts by mass of the binder resin.
• the release agent such as ester wax may be referred to as an "ester-based release agent".
• the ester wax may be any of a monoester-based wax, a diester-based wax, a triester-based wax, a tetraester-based wax, and a wax having five or more ester bonds.
• the ester wax is not particularly limited, but examples thereof are as follows: a monoesterified product obtained by reaction of higher fatty acid with higher alcohol, a diesterified product obtained by reaction between higher fatty acid and dihydric alcohol, or by reaction between higher alcohol and divalent carboxylic acid, a triesterified product of trimethylolpropane and higher fatty acid, a triesterified product of glycerol and higher fatty acid, a tetraesterified product of pentaerythritol and higher fatty acids, an esterified product obtained by reaction of hydroxy acid such as citric acid and higher fatty acid or higher alcohol, and an esterified product obtained by reaction of aromatic carboxylic acid or alcohol such as a ring acid and higher fatty acid or higher alcohol.
• the hydrocarbon chain of the higher fatty acid and the higher alcohol preferably has 13 to 30 carbon atoms, and further preferably 17 to 22 carbon atoms.
• the divalent alcohol and the divalent carboxylic 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.
• 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, or the like. Further, each hydrocarbon group may be substituted with an alkoxy group, a cycloalkoxy group, an aryloxy group, an alkylthio group, a cycloalkylthio group, an arylthio group, an alkoxycarbonyl group, an aryloxycarbonyl group or a sulfamoyl group.
• each hydrocarbon group may be substituted with an acyl group, an acyloxy group, an amido group, a carbamoyl group, a ureido group, a sulfinyl group, an alkylsulfonyl group, an arylsulfonyl group or a heteroarylsulfonyl group.
• each hydrocarbon group may be substituted with an amino group, a halogen atom, a fluorinated hydrocarbon group, a cyano group, a nitro group, a hydroxy group, a thiol group, a silyl group, a deuterium atom, or the like.
• ester wax examples 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 laurate, and behenyl laurate.
• the ester wax may be natural wax such as carnauba wax.
• the ester wax has a melting point of 65 to 90°C.
• the melting point of the ester wax is lower than 65°C, part of the release agent (ester wax) may melt and ooze out to the surface of the toner particles during storage of the toner or when the toner is loaded in an image forming apparatus.
• the release agent ooze out to the surface of the toner particles, image noise may occur, which is not preferable from a practical viewpoint.
• the melting point of the release agent (ester wax) is low, the release agent (ester wax) may not be completely crystallized on the surface of an image and may be in a molten state, resulting in deterioration of document offset resistance.
• the release agent (ester wax) is not sufficiently melted at the time of heat sealing, so that the release agent is less likely to ooze out to the surface of the image and the heat sealing resistance may deteriorate.
• the melting point of the ester wax is high, the low-temperature fixability may also deteriorate.
• the melting point of the ester wax is not particularly limited, but is further preferably 70 to 80°C.
• hydrocarbon wax examples include branched-chain hydrocarbon wax and long-chain hydrocarbon-based wax.
• examples of the branched-chain hydrocarbon wax include polyolefin wax such as polyethylene wax and polypropylene wax, and microcrystalline wax.
• examples of the long-chain hydrocarbon-based wax include paraffin wax and Sasol wax.
• examples of the release agent other than the ester wax include dialkyl ketone-based wax such as distearyl ketone, and amide-based wax such as ethylenediamine behenylamide and trimellitic acid tristearylamide.
• the white toner may contain, as the release agent, at least one of the ester waxes and the release agents other than the ester waxes described above.
• the content and so forth of the release agent are in accordance with the preferable aspects in the colored toner.
• the toner particles may optionally contain a charge control agent.
• a charge control agent various known compounds can be used. Examples of the charge control agent include, but are not particularly limited to, nigrosine dye, metal salt of naphthenic acid or higher fatty acid, alkoxylated amine, quaternary ammonium salt compound, azo metal complex, and salicylic acid metal salt and metal complex thereof.
• the content of the charge control agent is not particularly limited, but is preferably, for example, 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the total amount of the binder resin.
• the white toner and the colored toner used in the image forming method of the present embodiment are not particularly limited, but the difference in storage modulus between the white toner and the colored toner at 90°C is preferably 1.0 ⁇ 10 4 Pa to 1.0 ⁇ 10 5 Pa. Such a configuration can provide sufficient adhesiveness between the white toner image and the colored toner image forming the toner image, further improving heat sealing resistance.
• the measurement of the storage elastic modulus of each of the white toner and the colored toner at 90°C can be performed by the following method.
• a toner with an external additive is weighed to 0.2 g and pressure-molded by applying a 25 MPa force with a compression-molding machine to prepare a cylindrical pellet having a 10 mm diameter.
• a rheometer (“ARES G2" manufactured by TA instrument Co., Ltd) is used, and a set of a parallel plate having a 8 mm diameter on the upper side and a parallel plate having a 20 mm diameter on the lower side is used to perform temperature drop measurement under the condition of a 1 Hz frequency.
• the sample setting is performed at 100°C, and after the gap is set to 1.4 mm, the sample protruded from between the plates is scraped off, the gap is set to 1.2 mm, the temperature is lowered to an appropriate temperature while the axial force is applied, and it is allowed to stand still for three hours. Thereafter, the temperature is lowered to 30°C that is a measurement start temperature, the application of the axial force is stopped, and the temperature increasing measurement of the storage elasticity (G') is performed from 30°C to 150°C at a temperature increase speed of 3°C/min. Detailed measurement conditions are shown below. Note that the "storage modulus" is an indicator of the hardness of a material, and a smaller value thereof indicates a softer material.
• the average particle diameter of the toner particles is, for example, preferably within a range of 3 to 9 ⁇ m, and further preferably within a range of 3 to 8 ⁇ m, in terms of the volume-based median diameter.
• the average particle diameter can be controlled by, for example, the concentration of the aggregating agent to be used, the amount of the organic solvent to be added, the fusion time, the composition of the polymer, and the like when the production is performed by an emulsion aggregation method described later.
• volume-based median diameter When the volume-based median diameter is within the above range, the transfer efficiency is increased, the image quality of halftones is improved, and the image quality of fine lines and dots is improved.
• the volume-based median diameter of the toner particles is measured and calculated by using a measurement apparatus in which a computer system equipped with data-processing software "Software V3.51" is connected to "Multisizer 3" (manufactured by Beckman Coulter, Inc.).
• a computer system equipped with data-processing software "Software V3.51" is connected to "Multisizer 3” (manufactured by Beckman Coulter, Inc.).
• toner 0.02 g of toner is added to and blended with 20 mL of surfactant, and then ultrasonic dispersion is performed for 1 minute to prepare a toner dispersion liquid.
• the surfactant solution for example, a neutral detergent containing a surfactant component diluted 10 times with pure water can be used for the purpose of dispersing the toner particles.
• the toner dispersion liquid prepared as described above is injected into a beaker containing "ISOTONII" (manufactured by Beckman Coulter, Inc.) in a sample stand with a pipette until the display concentration of the measurement apparatus becomes 8%.
• concentration in this range, a reproducible measurement value can be obtained.
• the measurement particle count number is set to 25,000
• the aperture diameter is set to 50 ⁇ m
• the frequency value is calculated by dividing the range of 1 to 30 ⁇ m which is the measurement range into 256 parts
• the particle diameter of 50% from the larger volume integrated fraction is set as the volume-based median diameter.
• the toner particles preferably have an average circularity in the range of 0.930 to 1.000, and further preferably in the range of 0.940 to 0.995, from the viewpoint of improving the transfer efficiency.
• the average circularity of the toner particles is measured using "FPIA-3000" (manufactured by Sysmex Corporation). Specifically, first, a sample (toner particles) is wetted with an aqueous solution containing a surfactant and subjected to ultrasonic dispersion treatment for 1 minute to be dispersed. Thereafter, imaging is performed with an "FPIA-2100" (manufactured by Sysmex Corporation) under measurement conditions of an HPF (high-power field imaging) mode at an appropriate density corresponding to an HPF detection number of 3,000 to 10,000, and the circularity of each toner particle is calculated according to the following formula (T).
• FPIA-3000 manufactured by Sysmex Corporation
• the average circularity of the toner particles is calculated by adding the circularities of the respective toner particles and dividing the sum by the total number of the toner particles.
• Circularity (Perimeter of circle having the same projection area as particle image)/(Perimeter of particle projection image)
• the softening point of the toner is preferably in a range of 80 to 120°C from the viewpoint of imparting the low-temperature fixability to the toner and further preferably in a range of 90 to 105°C from the viewpoint of the low-temperature fixability.
• the softening point of the toner is measured by the flow tester described below.
• a sample (toner) is placed in a laboratory dish, leveled, and left to stand for 12 hours or more. After being left for 12 hours or more, the sample is pressurized with 375 MPa force for 30 seconds using a molding machine "SSP-10A" (manufactured by Shimadzu Corp.) to produce a cylindrical molded sample having a 1 cm diameter.
• SSP-10A molding machine
• the prepared molded sample is extruded from the end of preheating under the environment of 24°C and 50%RH using a flow tester "CFT-500D" (manufactured by Shimadzu Corp.) from the hole (1 mm diameter ⁇ 1 mm) of the cylindrical die using a piston having a 1 cm diameter under the following conditions.
• the offset method temperature Toffset measured with the setting of the offset value 5 mm by the melting temperature measurement method of the temperature increase method is defined as the softening point of the toner.
• 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 increase speed of 6°C/min.
• the method for producing the toner used in the image forming method is not particularly limited.
• the method for producing the toner include a kneading pulverization 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, and other known methods.
• the emulsion polymerization aggregation method or the emulsion aggregation method can be suitably adopted as the method for producing the toner.
• a dispersion of fine particles of a binder resin (which hereinafter may be referred to as "binder resin fine particles”) is prepared by the emulsion polymerization method.
• the prepared dispersion of the binder resin fine particles is mixed with a dispersion of fine particles of a colorant (which hereinafter may be referred to as "colorant fine particles”) and a dispersion of a release agent such as wax.
• the toner particles are aggregated until a desired particle diameter is obtained, and shape control is performed by performing fusion between the binder resin fine particles, thereby producing toner particles.
• a binder resin solution dissolved in a solvent is added dropwise to a poor solvent to prepare a resin particle dispersion.
• the prepared resin particle dispersion, a dispersion of a colorant, and a dispersion of a release agent such as wax are mixed, the mixture is aggregated until a desired toner particle diameter is obtained, and shape control is performed by performing fusion between the binder resin fine particles, thereby producing toner particles.
• the dispersibility of the colorant fine particles in the dispersion liquid of the colorant contained in the toner base particles becomes excellent. Further, even when the colorant fine particles and the binder resin fine particles are aggregated and fused, the toner base particles can be formed while the colorant fine particles maintain the excellent dispersibility.
• toner base particles having a core-shell structure can be obtained by the emulsion polymerization aggregation method. Specifically, when the toner base particles having a core-shell structure are produced, first, binder resin fine particles for core particles and fine particles of a colorant are aggregated, associated, and fused to produce core particles. Thereafter, binder resin fine particles for a shell layer are added to the prepared dispersion of the core particles, and the binder resin fine particles for a shell layer are aggregated and fused onto the surfaces of the core particles. Thus, a shell layer is formed so as to cover the surfaces of the core particles, and toner base particles having a core-shell structure can be obtained.
• the combination of the raw materials of the binder resins is appropriately adjusted such that the content Vc (% by mass) of the vinyl resin in the colored toner is higher than the content Vw (% by mass) of the vinyl resin in the white toner.
• the recording medium is a member for holding a toner image.
• the recording medium used in the image forming method of the present embodiment is a resin film.
• the resin constituting a resin film is not particularly limited, and a known resin constituting a resin film is used.
• the resin constituting a resin film include polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), and polyethylene (PE).
• Other examples of the resin include biaxially oriented polypropylene (OPP), non-oriented polypropylene (CPP), biaxially oriented nylon (ONY), and non-oriented nylon (CNY).
• Still other examples of the resin include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), high impact polystyrene (HIPS), and polylactic acid (PLA).
• the recording medium used in the image forming method of the present embodiment is further preferably a resin film that is likely to deform.
• a film containing a resin containing an aromatic ring as the main component is further preferable.
• the resin containing an aromatic ring include polyethylene terephthalate (PET), polystyrene (PS), and high impact polystyrene (HIPS).
• a film containing polyethylene terephthalate (PET) as the main component is especially preferable.
• the "main component" of the film refers to a component having a content of 60% by mass or more with respect to the total mass of the film.
• the main component of the film is preferably 80% by mass or more, and further preferably 90% by mass or more, with respect to the total mass of the film.
• the recording medium may be in the form of a sheet having a predetermined size, but is preferably in the form of being wound into a roll after the toner image is fixed. Winding after image formation is suitable for carrying out efficient mass production of the packaging process, and the recording medium (resin film) after image formation can be stored in a roll form and used for the next packaging process and thereafter.
• the recording medium may be either one that has been surface-treated or one that has not been surface-treated. Examples of the surface treatment method include corona treatment and plasma treatment. It is preferable that the surface treatment is not performed in terms of costs, whereas it is preferable that the surface treatment is performed in terms of adhesiveness of an image.
• the thickness of the recording medium is preferably 20 to 70 ⁇ m, and further preferably 30 to 55 ⁇ m.
• the monomers other than dimethyl fumarate and trimellitic anhydride are poured and t0.25 parts by mass of dioctylate with respect to 100 parts by mass of the total amount of the monomers was poured.
• the mixture was reacted at 235°C for 6 hours, then, the temperature was lowered to 200°C, dimethyl fumarate and trimellitic anhydride were added, and the mixture was reacted for 1 hour.
• the temperature was raised to 220°C over 5 hours, and polymerization was carried out under a pressure of 10 kPa until a desired molecular weight was obtained, to obtain a light yellow transparent amorphous polyester resin.
• 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 number of 16.2 mgKOH/g.
• the obtained amorphous polyester resin was dispersed using a dispersing machine obtained by modifying an emulsification dispersing machine "CAVITRON CD1010" (manufactured by Eurotec Co., Ltd) to a high-temperature and high-pressure type. Specifically, an amorphous polyester resin dispersion was prepared so as to have a composition ratio of 80% by mass of ion exchange water and 20% by mass of the concentration of amorphous polyester resin.
• the pH level was adjusted to 8.5 with ammonia, and the Cavitron was operated under conditions of a rotor rotation speed of 60 Hz, a pressure of 5 Kg/cm 2 (490 kPa), and a heating temperature by a heat exchanger of 140°C. Thereafter, ion exchanged water was added to the dispersion to adjust the solid content to 20% by mass, thereby preparing an amorphous polyester resin particle dispersion (A).
• the volume-based median diameter (D50) of the dispersion was measured using "Microtrac ( ® , the same applies hereinafter) UPA-150" (manufactured by Nikkiso Co., Ltd), and it was 160 nm.
• 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 further added.
• the system in the reaction vessel was heated and stirred at 87°C for 1 hour to perform polymerization, thereby preparing a vinyl resin particle dispersion (1-b).
• a solution of 8 parts by mass of potassium persulfate dissolved in 140 parts by mass of ion exchanged water was further added to the vinyl resin particle dispersion (1-b) obtained by the second stage polymerization. Thereafter, under a temperature condition of 84°C, a mixed solution of the following monomers and a chain transfer agent was added dropwise over 90 minutes.
• the mixture was heated and stirred for 2 hours for polymerization and then cooled to 28°C, thereby preparing a vinyl resin particle dispersion (B).
• the volume-based median diameter (D50) of this dispersion was measured using "Microtrac UPA-150" (manufactured by Nikkiso Co., Ltd), and it was 130 nm.
• the weight average molecular weight (Mw) of the vinyl resin contained in the obtained dispersion was 34,000.
• the crystalline polyester resin had a weight average molecular weight of 23,000, a number average molecular weight of 6,500, an acid number of 19.1 mgKOH/g, and a melting point of 73.2°C.
• the obtained crystal polyester resin was dispersed using a dispersing machine obtained by modifying an emulsifying dispersing machine "CAVITRON CD1010" (manufactured by Eurotec, Co., Ltd) to a high-temperature and high-pressure type.
• a crystalline polyester resin dispersion was prepared so as to have a composition ratio of 80% by mass of ion-exchanged water and 20% by mass of concentration of crystalline polyester resin.
• the pH level was adjusted to 8.5 with ammonia, and the Cavitron was operated under conditions of a rotor rotation speed of 60 Hz, a pressure of 5 Kg/cm 2 (490 kPa), and a heating temperature by a heat exchanger of 140°C.
• ion exchanged water was added to the dispersion to adjust the solid content to 20% by mass, thereby preparing a crystalline polyester resin particle dispersion (C).
• the volume-based median diameter (D50) of this dispersion was measured using "Microtrac UPA-150" (manufactured by Nikkiso Co., Ltd), and it was 190 nm.
• the resultant was subjected to a dispersion treatment with a pressure discharge type Gaulin homogenizer, and then 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 release agent particles in the dispersion was measured with a laser diffraction-type particle size distribution measuring device "LA-750" (manufactured by HORIBA, Ltd) and found to be 220 nm.
• a hydrocarbon-based release agent particle dispersion (E) is 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) having a melting point of 75°C and an acid number of 0 mgKOH/g.
• the volume-based median diameter of release agent particles in the dispersion was measured with a laser diffraction-type particle size distribution measuring device "LA-750" (manufactured by HORIBA, Ltd) and found to be 150 nm.
• the mixed solution of the above components was sufficiently dispersed with a homogenizer "ULTRA-TURRAX T50" (manufactured by Ika-Werke GmbH & Co. KG), and then treated for 20 minutes with an ultrasonic disperser, thereby preparing a cyan colorant particle dispersion (F).
• ULTRA-TURRAX T50 manufactured by Ika-Werke GmbH & Co. KG
• the volume-based median diameter of the cyan colorant particles was 180 nm.
• rutile-type titanium oxide manufactured by Ishihara Sangyo Kaisha, Ltd
• a colorant 210 parts by mass of rutile-type titanium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd) as a colorant was put into an aqueous surfactant solution in which sodium alkyl diphenyl ether disulfonate was dissolved in 480 parts by mass of ion exchanged water so as to have a concentration of 1% by mass. Thereafter, dispersion treatment was performed using an ultrasonic homogenizer. The solid content concentration was adjusted to 30% by mass. Thus, a white colorant dispersion liquid (G) in which the white colorant was dispersed in the aqueous medium was prepared.
• G white colorant dispersion liquid
• the volume-based median diameter of the white colorant particles was 200 nm.
• aqueous aluminum sulfate having a concentration of 2% is added thereto over 30 minutes while dispersing was performed with a homogenizer "ULTRA-TURRAX T50" (manufactured by Ika-Werke GmbH & Co. KG at 3,000 rpm. After completion of the dropwise addition, stirring was performed for 10 minutes to sufficiently mix the raw materials and the aggregating agent.
• EDTA ethylenediaminetetraacetic acid
• the obtained toner particles (1) had a volume-based median diameter of 6.0 ⁇ m.
• the average circularity of the obtained toner particles (1) is 0.961.
• Colored toners 2 to 9 were produced in the same manner as the colored toner 1 except that the types/amounts of the dispersions to be used were changed such that the contents (% by mass) of the resins in the binder resin component of each of the colored toners 2 to 9 became the values listed in TABLE I. Note that when the colored toners 3 to 4 and 6 to 8 containing the crystalline polyester resin as the binder resin component were produced, the crystalline polyester resin particle dispersion (C) was added as a starting material to be initially put in the reaction vessel in the "aggregation and fusion step and ripening step".
• the crystalline polyester resin particle dispersion (C) was put into the reaction vessel from the start to produce a colored toner.
• the ester-based release agent particle dispersion (D) and the hydrocarbon-based release agent particle dispersion (E) were used in combination as the release agent particle dispersion for the colored toner 7.
• the hydrocarbon-based release agent particle dispersion (E) was used for the colored toner 9. TABLE I shows the content (% by mass) of each resin in the binder resin component and the type of the release agent for each of the colored toners 2 to 9.
• White toners 1 to 6 were produced in the same manner as the colored toners 1 to 9 except that the white colorant particle dispersion (G) was used, and the types/amounts of the dispersions used were changed such that the contents (% by mass) of the resins in the binder resin component of each of the white toners 1 to 6 became the values listed in TABLE II.
• TABLE II shows the content (% by mass) of each resin in the binder resin component and the type of the release agent for each of the white toners 1 to 6.
• Each of the colored toners 1 to 9 and the white toners 1 to 6 was mixed with the following ferrite carriers so as to have a toner concentration of 6% by mass, thereby each producing a developer.
• the storage modulus (Pa) of each of the produced colored toners 1 to 9 and white toners 1 to 6 at 90°C was measured by the following method. First, as a measurement sample, a toner to which an external additive had been added was weighed to 0.2 g, and pressure-molding was performed by applying a pressure of 25 MPa with a compression-molding machine to produce a cylindrical pellet having a 10 mm diameter. By using a rheometer ("ARESG2" manufactured by TA instrument) and using a set of a parallel plate having a diameter of 8 mm on top and a parallel plate having a diameter of 20 mm on bottom, the temperature decrease measurement was performed under a condition of a frequency of 1 Hz.
• ARESG2 manufactured by TA instrument
• the sample setting was performed at 100°C, and after the gap was set to 1.4 mm, the sample protruded from between the plates was scraped off, the gap was set to 1.2 mm, the temperature was lowered to an appropriate temperature while the axial force was applied, and it was allowed to stand still for three hours. Thereafter, the temperature was lowered to 30°C that was a measurement start temperature, the application of the axial force was stopped, and the temperature increasing measurement of the storage elasticity (G') was performed from 30°C to 150°C at a temperature increase speed of 3°C/min. Detailed measurement conditions are shown below.
• the full color label printer for performing image formation was remodeled so that the fixing temperature, the toner adhesion amount, and the system speed could be freely set, and in Example 1, image formation was performed at a fixing temperature of 185°C and a system speed of 270 mm/sec.
• a biaxially oriented polypropylene film (“PP" in TABLES) having a thickness of 20 ⁇ m was used.
• TABLE III shows the compositions of the white toner and the colored toner used in Example 1. The difference (Vc - Vw) between the content Vc (% by mass) of the vinyl resin in the colored toner 1 and the content Vw (% by mass) of the vinyl resin in the white toner 1 was calculated.
• Example 1 formed on the recording medium (resin film) by the image forming method was evaluated about the adhesiveness to the base material and the heat sealing resistance by the following methods. The results are shown in TABLE III.
• the image formed on the recording medium may be referred to as a "toner image layer”.
• a toner image layer and a recording medium (resin film) on which the toner image layer was formed may be collectively referred to as a "print product”.
• the produced print product was left to stand for one day. Thereafter, of the print product, the print surface on which the toner image layer was formed was cut with a cutter to form a square of 10 mm ⁇ 10 mm at 3 cm intervals.
• Cellophane tape (Cellotape ® ) was stuck to the print surface having the cuts, and when the tape was rapidly peeled off, the state of the appearance of the toner image layer (the residual percentage of the toner image layer) was observed, and the adhesiveness to the base material was evaluated in accordance with the following evaluation criteria. Evaluations of A, B and C were regarded as having no problem in use (passing).
• the residual percentage of the toner image layer was calculated as follows: photographing the toner image layer on the print surface to which the cellophane tape was stuck, and calculating the residual percentage thereof from the gradation difference of the image with the cellophane tape peeled off with respect to the entire area. Note that the above-described cutting of the squares was performed by cutting only the toner image layer with a cutter without damaging the resin film as the recording medium.
• the produced print product was left to stand for one day. Thereafter, the image printed on the resin film was heat-sealed with a heat seal tester "TP-701-B" (manufactured by Tester Sangyo Co., Ltd) at 120°C and 0.2 MPa for 1 second.
• TP-701-B manufactured by Tester Sangyo Co., Ltd
• a heat-sealed portion in which the heat-sealing was performed on the image was visually observed, and the heat sealing resistance was evaluated in accordance with the following evaluation criteria.
• the visual observation of the heat-sealed portion was performed based on the presence or absence of adhesion of the image to the heat seal bar and the presence or absence of wrinkles in the heat-sealed portion. Evaluations of A, B and C were regarded as having no problem in use (passing).
• Examples 2 to 20 and Comparative Examples 1 to 4 images were formed on resin films as recording media in the same manner as in Example 1 except that the white toner, the colored toner and the resin film to be used were changed as illustrated in TABLE III and TABLE IV.
• PP represents that a biaxially oriented polypropylene film having a thickness of 20 ⁇ m was used as the resin film.
• PE represents that a high-density polyethylene film having a thickness of 15 ⁇ m was used as the resin film.
• PET represents that a polyethylene terephthalate film having a thickness of 25 ⁇ m was used as the resin film.
• the images of Examples 1 to 20 formed by the image forming method were excellent in both the evaluations of the adhesiveness to the base material and the heat sealing resistance. That is, it has been found that in a case where an image formed on a resin film is composed of a white toner image as the lowermost layer and a colored toner image on the white toner image, when the content of the vinyl resin in the colored toner is higher than that in the white toner, the heat sealing resistance of the image is improved. In particular, in a case where the difference (Vc - Vw) in the content of the vinyl resin between the colored toner and the white toner is 10 to 30% by mass, a tendency of further improvement of the heat sealing resistance is can be confirmed.
• the white toner and the colored toner each containing an amorphous polyester resin as the main component can provide the adhesiveness to the base material having no problem in use. It has been also found from the comparison with Comparative Example 4 that the colored toner containing an ester wax as the release agent improves the heat sealing resistance of an image.
• the image forming method of the present embodiment can form images excellent in adhesive strength and heat sealing resistance on resin films used as base materials for soft packaging or the like. Therefore, according to the present embodiment, further spread of image formation in the electrophotographic method is expected.

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