JP2005195677A - Electrophotographic coated paper and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic coated paper that is free of the occurrence of blister during fixing and superior in the stability of the size of paper, which is used for an indirect contact dry system electrophotographic full-color copying machine and a printer, and to provide an image forming method which uses the coated paper. <P>SOLUTION: In the electrophotographic coated paper, a coating layer, comprising a pigment and an adhesive as its main components, is formed on each side of the base material comprising wooden fiber as its main constituent, the coating layer being in the range of 5 to 15 g/m<SP>2</SP>in the amount of solid content per side, the rate of change in the moisture content, before and after the coated paper is left for 30 sec in a 120°C oven after a moisture adjustment has been made according to the conditions stipulated by JIS-P8111 is 0.3 mass% or lower. The image forming apparatus uses the coated paper. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an indirect dry electrophotographic copying machine or a printer, in particular, an electrophotographic coated paper used in a full-color image forming apparatus, and an image forming method using the same.

  In recent years, with the advancement of electrophotographic recording devices, using coated paper that has been used for commercial printing such as offset printing, digital signals can be colored on demand on glossy coated paper by electrophotography. So-called on-demand printing is becoming popular. For this reason, color copying machines and color printers are increasing in speed and quality.

  For high image quality, instead of PPC paper and printer paper that have been used normally, coated paper with high white paper gloss that has been used in the field of commercial printing (coating paper for commercial printing). However, because of the vividness of the obtained image, cases used in color copying machines and color printers are increasing.

  However, when commercial printing coated paper is used in full-color copying machines and printers, running troubles occur at the transfer section or the fixing section. That is, in the transfer unit, immediately after the paper is charged and the toner is transferred to the paper, the charged paper causes electrostatic adsorption to the transfer member in the paper transport direction, causing a running trouble. Further, in the fixing unit, when the toner is melt-fixed, an adhesive force is generated between the melted toner and the fixing member, and in the case of coated paper (coated paper) having high white gloss, the paper is the fixing member. Cannot be removed immediately, leaving traces of defective separation, or being unable to peel and causing jamming at the fixing portion. These phenomena occur remarkably in coated paper with a low basis weight of the paper, so-called lightweight coated paper.

  Also, normally, high white glossy coated paper for commercial printing is smoothed by calendaring after coating (coating) in order to impart white paper gloss. Is crushed and air permeability is reduced, so that blisters are likely to occur during fixing. Blisters are fine voids generated on the surface of the toner image area. The cause is that the water inside the paper becomes water vapor due to heating during fixing, and the water vapor is not discharged when the paper has low air permeability. The water vapor pressure in the inside increases, and eventually the toner layer is broken through and discharged.

  Further, in these coated papers for printing, changes in paper dimensions occur when moisture in the paper changes. In the case of an indirect dry electrophotographic full-color copying machine and printer, the moisture content of the paper changes when the toner is thermally fixed on the paper. Therefore, there is a problem that curling occurs on the output paper. From the viewpoints of paper permeability that is not enough to avoid the blister phenomenon, dimensional stability when paper moisture changes related to problems such as curling, etc., coated paper for printing by conventional manufacturing methods is None of them could withstand the use of indirect dry electrophotographic full-color copiers and printers.

  On the other hand, in particular, in order to suppress the occurrence of blisters at the time of fixing, proposals have been made in which the air permeability of the coated paper is specified to be a certain value or less (for example, Patent Document 1 and Patent Document 2 regarding air permeability of 4000 seconds or less). Etc.) and proposals for coating layer pigment specifications for that purpose (for example, see Patent Document 3). However, when the proposed coated paper is left in a high humidity condition for a long time and used in an indirect dry electrophotographic full-color copying machine or printer, the generation of blisters cannot be sufficiently eliminated. As an adverse effect of lowering the air permeability, there is a case where the problem that the strength of the coating layer is lowered may occur.

  Further, since the proposed coated paper has low air permeability, that is, high air permeability, a large amount of moisture passes through the coating layer at high humidity, and also escapes from the coated paper due to heat and pressure in the fixing process. Since there is a lot of moisture, there is a problem (especially curling and undulation) that the dimensional stability of the paper is deteriorated due to a change in moisture of the coated paper, particularly when the coated paper is used under high humidity conditions.

Japanese Patent No. 2218894 Japanese Patent No. 2676291 Japanese Patent No. 2745431

  An object of the present invention is to solve the above problems. That is, the present invention provides an indirect dry electrophotographic full-color copying machine and printer for use in electrophotographic coatings that are free from blisters during fixing and have excellent dimensional stability (especially curling and undulation) due to moisture changes. It is an object of the present invention to provide a working paper and to provide an image forming method using the coated paper.

  In such a situation, the present inventors have conducted intensive research. As a result, the electrophotographic coated paper having a coating layer having a specific configuration on both surfaces of the substrate and satisfying predetermined physical properties is electrophotographic. It has been found that even when an unfixed toner image is formed by this method and fixing is performed using various fixing devices, the generation of blisters is suppressed, and the dimensional stability (especially curling and undulation) of the paper is excellent. It has also been found that the above problems can be solved at a higher level by heating the electrophotographic coated paper upstream of the fixing device so as to have a surface temperature of 50 ° C. or higher.

That is, the present invention
<1> A coating layer mainly composed of a pigment and an adhesive is provided on both sides of a base material mainly composed of wood fibers in a range of 5 to 15 g / m ² in terms of solid content per side,
An electrophotographic coating characterized by having a moisture change rate of 0.3% by mass or less before and after being left to stand in an oven at 120 ° C. for 30 seconds after humidity is adjusted according to the conditions specified in JIS-P8111. It is craft paper.
<2> The electrophotographic coated paper according to <1>, wherein the air permeability is 7000 seconds or less.

<3> An image forming method in which an unfixed toner image is formed on a paper surface by an electrophotographic method, and a fixed image is obtained by heating and pressing the image.
In the image forming method, the electrophotographic coated paper according to <1> or <2> is used as the paper.
<4> The sheet on which an unfixed toner image is formed is inserted into a nip portion formed between the rolls of a fixing device including a pair of rolls, and heated and pressurized. <3> The image forming method described in 1.

<5> The sheet on which the unfixed toner image is formed is inserted into a nip portion formed between an endless belt and a roll of a fixing device including an endless belt and a roll, and the fixed image is heated and pressed. An image forming method to obtain,
The fixing device has an elastic layer near the surface and is rotatably supported, an endless belt having an outer peripheral surface in contact with the surface of the heat fixing roll to form the nip portion, and the endless belt A pressure applying member that is in contact with an inner peripheral surface of the belt and has a pressure contact surface that presses the endless belt along the surface of the heat fixing roll to form the nip portion. The image forming method according to <3>.

<6> A heated fixing belt is brought into contact with the paper on which an unfixed toner image is formed and pressed against the toner image, and the toner image is heated and pressed, and then the fixing belt and the toner image are placed on the surface. The sheet held on the sheet is moved in close contact, and after the toner image is cooled to a predetermined temperature or lower, the sheet holding the toner image is introduced into a fixing device that peels from the fixing belt. The image forming method according to <3>, wherein an image is obtained.
<7> After an unfixed toner image is formed on the paper, prior to introduction into the fixing device, the paper is preheated so that the surface temperature on the side on which the toner image is formed is 50 ° C. or higher. <3> The image forming method according to <3>.

  INDUSTRIAL APPLICABILITY According to the present invention, there is no generation of blisters at the time of fixing, excellent dimensional stability of paper due to moisture change, and in particular, it is used in indirect dry electrophotographic full-color copying machines and printers that do not generate curling or undulations. An electrophotographic coated paper can be provided, and an image forming method capable of forming a recorded image with no blistering and excellent dimensional stability of the paper can be provided by using the coated paper. .

Hereinafter, the present invention will be described in detail.
[Coated paper for electrophotography]
In the electrophotographic coated paper of the present invention, the coating layer mainly composed of a pigment and an adhesive has a solid content of 5 to 15 g / m ^{2 on} one side on both sides of a base material mainly composed of wood fibers. Provided in the
It is an essential requirement that the moisture change rate before and after being left in an oven at 120 ° C. for 30 seconds after conditioning according to the conditions specified in JIS-P8111 is 0.3% by mass or less.

  The electrophotographic coated paper of the present invention is characterized by having a coating layer mainly composed of a pigment and an adhesive on both surfaces of a base material mainly composed of wood fibers. By having such a coating layer, formation of a glossy image is realized. And while realizing such a high-gloss image, it is realized by the present invention that a blister or coated paper with little dimensional change can be obtained by heating and pressing in the fixing step.

  As described above, in general, in the fixing process, the moisture inside the coated paper is vaporized by heat or pressure, and because it has a coating layer, it is vaporized to a high pressure. Since it is ejected from the pores of the working layer, the toner image layer that is still in the softened state is destroyed, and an image defect called blister is created. In addition, the moisture in the coated paper suddenly changes in the fixing process in this way, so that the hydrogen bond between the wood fibers of the base material, particularly the cellulose fibers, is re-formed and the dimensions shrink. Curling occurs.

  Therefore, in the image forming method based on the electrophotographic method, the toner is thermally melted to form an image, so that the moisture change due to dehumidification of the paper at the time of fixing and the subsequent moisture absorption is large, and the conventional printing coated paper is used. In such a case, the dimensional change is larger than that in normal offset printing, and the occurrence of blisters and the occurrence of curling and undulation accompanying the dimensional change are likely to be significant.

  The present inventors have studied in detail about the blisters described above and the occurrence of troubles associated with dimensional changes, and have found that they are largely related to the moisture that the coated paper can contain. In particular, it was found that the amount of moisture change before and after drying for 30 seconds in an oven at 120 ° C. greatly affects the occurrence of these troubles for coated paper conditioned under the conditions specified in JIS-P8111.

  FIG. 1 shows the moisture change rate of the coated paper for printing before and after being left in an oven at 120 ° C. for 30 seconds after humidity adjustment according to the conditions specified in JIS-P8111 and the high humidity condition (28 ° C. 85% RH environment) Blister generation situation (blister grade) when forming a secondary color (Blue) solid image using DocuColor 1250 manufactured by Fuji Xerox Co., Ltd. for 48 hours. It is a graph which shows the relationship. As can be seen from the graph shown in FIG. 1, the larger the moisture change rate, the more blisters are generated, and as the moisture change rate is kept low and approaches 0.3% by mass, the blister level is reduced. It has been found. Based on such examination results, the present inventors have repeatedly attempted to make it difficult to remove moisture in the coated paper by heating, and finally completed the present invention.

  In the electrophotographic coated paper of the present invention, the moisture change rate before and after being left in an oven at 120 ° C. for 30 seconds after conditioning according to the conditions specified in JIS-P8111 (hereinafter simply referred to as “the present invention”). In some cases, it is referred to as “moisture change rate”.), It is essential that it is 0.3% by mass or less, more preferably 0.1% by mass or less. When the water change rate in the present invention exceeds 0.3% by mass, the occurrence of blisters becomes remarkable as described above, and the water change in the fixing process also becomes large. Becomes prominent.

The water change rate in the present invention is more specifically as follows.
After adjusting the humidity according to the conditions specified in JIS-P811, the moisture content is measured by a dry drying method using a part of the sample [A (mass%)] and left in an oven at 120 ° C. for 30 seconds. After that, the water content is measured again in the same manner [B (mass%)]. The mass difference [A-B (% by mass)] was determined and used as the moisture change rate in the present invention.

The method for reducing the moisture change rate in the present invention is not particularly limited, and may be adjusted by selecting an appropriate method as appropriate. Examples of the method include the following methods.
For example, there is a method in which a material that hardly separates water molecules absorbed by humidity adjustment by heat is contained in the base material. As such a material, a polymer that slightly crosslinks and insolubilizes a water-soluble polymer and absorbs water to form a gel is preferable. Specifically, polyacrylates, starch-acrylic acid graft polymer, acrylic acid-vinyl alcohol copolymer, isobutylene-maleic acid copolymer, polyacrylic acid-acrylamide copolymer, carboxymethyl cellulose, pyrrolidone carboxylic acid Examples thereof include heterocarboxylates such as salts, sodium aspartate, and the like. However, the present invention is not limited thereto, and any material having a structure in which water molecules are not easily separated by heat may be used.

Among these, the base material contains at least one component selected from the group consisting of polyacrylates, starch-acrylic acid graft polymers, acrylic acid-vinyl alcohol copolymers, and isobutylene-maleic acid copolymers. This is particularly preferable as a method for reducing the moisture change rate in the present invention.
Such a material may be present in the coating layer, but is preferably contained in the substrate. When added to the coating layer, water is easily retained, so that the surface electrical resistivity of the coated paper is likely to be lowered, and transfer failure may occur in the toner transfer process.

  As the base material of the electrophotographic coated paper of the present invention, it is essential to use a base material mainly composed of wood fibers. Here, “wood fibers” refers to wood-derived fibers such as virgin pulp. Of course, it is a concept that naturally includes pulp substitutes derived from wood and waste paper pulp contained in recycled paper. Further, “mainly composed of wood fibers” means that 50% by mass or more of the base material is wood fibers, preferably 70% by mass or more, and more preferably 80% by mass or more. .

  The fiber used for the base material of the electrophotographic coated paper of the present invention is not particularly limited, but wood pulp fibers used for the base paper of ordinary general coated paper, for example, kraft pulp fibers, It is preferable to use sulfite pulp fiber, semi-chemical pulp fiber, chemiground pulp fiber, groundwood pulp fiber, refiner ground pulp fiber, thermomechanical pulp fiber and the like. Moreover, the fiber which chemically modified the cellulose or hemicellulose in these fibers can also be used as needed. Of course, these correspond to the wood fibers defined in the present invention.

  Further, cotton pulp fiber, hemp pulp fiber, kenaf pulp fiber, bagasse pulp fiber (corresponding to the wood fiber defined in the present invention), viscose rayon fiber, regenerated cellulose fiber, copper ammonia rayon fiber, cellulose acetate fiber, polychlorinated Vinyl fiber, polyacrylonitrile fiber, polyvinyl alcohol fiber, polyvinylidene chloride fiber, polyolefin fiber, polyurethane fiber, polyvinyl chloride, polyvinyl alcohol copolymer, fluorocarbon fiber, glass fiber, carbon fiber, alumina fiber These fibers such as metal fibers and silicon carbide fibers can be used alone or in combination.

If necessary, fibers obtained by impregnating or thermally fusing pulp fibers with a synthetic resin such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, or polyester can also be used.
Also, high-quality and medium-quality waste paper pulp can be blended. The amount of waste paper pulp is determined according to the purpose of use and purpose. For example, when waste paper pulp is blended from the viewpoint of resource protection, it is 10% by weight or more, preferably 30% by weight or more in the total fiber. Can be blended.

  It is preferable to use a filler for the base material (base paper) used in the present invention in order to improve the coating suitability and to adjust the opacity and whiteness after coating. Fillers that can be used here include heavy calcium carbonate, light calcium carbonate, kaolin, calcined clay, pyroferrite, sericite, talc, and other inorganic fillers such as silicic acid and titanium dioxide, and urea resin, styrene, etc. Organic pigments can be mentioned, but are not limited to these. The blending amount of these fillers is not particularly limited, but is preferably 3% by mass or more and more preferably 5% by mass or more for the purpose of reducing the water content.

  Moreover, various chemicals such as a sizing agent can be used for the base material used in the present invention by internal or external addition. Types of sizing agents can include sizing agents such as rosin sizing agents, synthetic sizing agents, petroleum resin sizing agents, and neutral sizing agents. Suitable sizing agents such as sulfate bands and cationized starch, fibers Can be used in combination with other fixing agents. From the viewpoint of paper storage stability after copying in electrophotographic copying machines and printers, etc., neutral sizing agents such as alkenyl succinic anhydride sizing agents, alkyl ketene dimers, alkenyl ketene dimers, neutral rosins, petroleum sizes, Olefin resins and styrene-acrylic resins are preferred. As the surface sizing agent, modified cellulose such as oxidized modified starch, enzyme modified starch, polyvinyl alcohol and carboxymethyl cellulose can be used alone or in combination.

  Furthermore, the base material used in the present invention includes inorganic substances such as sodium chloride, potassium chloride, calcium chloride, sodium sulfate, zinc oxide, titanium dioxide, tin oxide, aluminum oxide, and magnesium oxide for the purpose of adjusting the electrical resistivity of the paper. Alternatively, organic materials such as alkyl phosphoric acid ester, alkyl sulfuric acid ester acid, sulfonic acid sodium salt, and quaternary ammonium salt can be used alone or in combination.

Further, a paper strength enhancer can be internally or externally added to the base material used in the present invention as required. As paper strength enhancers, starch, modified starch, vegetable gum, carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, urea-formaldehyde resin, melamine-formaldehyde resin, dialdehyde starch, polyethyleneimine, epoxidized polyamide, polyamide-epichlorohydrin resin , Methylolated polyamide, chitosan derivatives and the like, and these materials can be used alone or in combination.
For the substrate used in the present invention, in addition to the above-mentioned materials, various auxiliary agents blended in a normal base paper for coated paper, such as a dye and a pH adjuster, may be appropriately used.

Next, the coating layer in the electrophotographic coated paper of the present invention will be described. In the electrophotographic coated paper of the present invention, from the viewpoint of giving the same texture as conventional coated paper and reducing the production cost, the coating layer mainly composed of a pigment and an adhesive is Formed on both sides of the substrate.
Examples of the pigment contained in the coating layer include pigments used in ordinary general coated paper, such as heavy calcium carbonate, light calcium carbonate, titanium dioxide, aluminum hydroxide, satin white, talc, calcium sulfate, and barium sulfate. , Zinc oxide, magnesium oxide, magnesium carbonate, amorphous silica, colloidal silica, white carbon, kaolin, calcined kaolin, delaminated clay, aluminosilicate, sericite, bentonite, smectite and other mineral pigments and polystyrene resin Examples thereof include fine particles, urea formaldehyde resin fine particles, fine hollow particles, and other organic pigments, and these can be used alone or in combination.

The adhesive used for the coating layer in the electrophotographic coated paper of the present invention may be a synthetic adhesive or a natural adhesive, and is not particularly limited.
Synthetic adhesives include, for example, various copolymers such as styrene-butadiene, styrene-acrylic, ethylene-vinyl acetate, butadiene-methyl methacrylate, vinyl acetate-butyl acrylate, polyvinyl alcohol, and maleic anhydride Examples thereof include a copolymer and an acrylic acid-methyl methacrylate copolymer. One or more of these synthetic adhesives can be used, and two or more can be used in combination depending on the purpose. These synthetic adhesives are preferably used in an amount of about 5 to 50% by mass, more preferably about 10 to 30% by mass per 100% by mass of the pigment.

Natural adhesives include oxidized starches, esterified starches, enzyme-modified starches, cold water soluble starches obtained by flash drying them, casein, soy protein, and other commonly known adhesives. Can be mentioned. These natural adhesives are preferably used in the range of about 0.1 to 50% by mass, more preferably about 2 to 30% by mass per 100% by mass of the pigment.
Moreover, various auxiliary | assistant mix | blended with the pigment for normal coated papers, such as a dispersing agent, a thickener, a water retention agent, an antifoamer, and a water-proofing agent, are used suitably as needed.

The coating layer in the electrophotographic coated paper of the present invention is formed by mixing the above-mentioned components to prepare a coating composition, which is applied to both surfaces of the substrate with an appropriate coating apparatus. Is done.
The prepared coating composition is a coating apparatus used for general coated paper production, such as a blade coater, air knife coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, gravure coater, etc. Is applied to both surfaces of the substrate by on-machine or off-machine. At this time, it may be applied once, but it may be divided into multiple layers to form a single coating layer. As the coating thickness of the coating layer, it is essential that the solid content (dry weight) per side of the substrate is in the range of 5 to 15 g / m ^{2 on} one side, and 5 to 13 g / m ² . It is desirable to set it as a range, and it is more desirable to set it as the range of 6-11 g / m < ² >.

  After the application of the coating layer, a smoothing process is appropriately performed. For the smoothing process at this time, a smoothing device that is usually used, for example, a super calendar, a machine calendar, a soft nip calender, or the like is used, and it is desirable to finish so that the gloss of the blank paper is 15% or more.

The coated paper for electrophotography of the present invention preferably has a basis weight (JIS P-8124) of 60 g / m ² or more and 260 g / m ² or less. If the basis weight is less than 60 g / m ² , the amount of heat received by the fixing process increases, and the vapor pressure is likely to increase. There are some concerns about the occurrence of blisters.

Furthermore, in the electrophotographic coated paper of the present invention, it is desirable to adjust the air permeability (J Tappi No. 5, Oken air permeability) to be 7000 seconds or less. When the air permeability exceeds 7000 seconds, the escape of water vapor is reduced due to heat and pressure in the fixing process, so that the vapor pressure tends to increase, and the 28 ° C. 85% R.S. H. If the equilibrium moisture content in is 8 mass% or less, there is little concern about blistering, but it may be difficult to suppress blistering. The upper limit of the air permeability is more preferably 5000 seconds or less.
The lower limit of the air permeability is preferably 400 seconds or longer. When the air permeability is less than 400 seconds, the paper gloss tends to be low, the strength of the coating layer tends to be low, and there is a concern that paper dust is generated.

  When the electrophotographic coated paper of the present invention is shipped as a product, the product moisture content immediately after opening is within an appropriate range, specifically, preferably 3 to 6.5% by mass, more preferably 4.5. It is preferable to adjust the water content by a paper machine, a coater dryer, a calendar process, or the like so as to be within a range of about ˜5.5 mass%. Moreover, it is desirable to wrap using moisture-proof wrapping paper such as polyethylene laminate paper or material such as polypropylene so that moisture absorption and desorption does not occur during storage.

[Image forming method]
The image forming method of the present invention is an image forming method in which an unfixed toner image is formed on the surface of a paper by an electrophotographic method, and a fixed image is obtained by heating and pressurizing the toner image.
As the paper, the electrophotographic coated paper of the present invention is used.

  In the image forming method of the present invention, the image forming process itself for forming a toner image can be performed by applying all known image forming processes on condition that the electrophotographic coated paper of the present invention is used as the paper. it can. For example, a latent image forming step for forming a latent image on the surface of the latent image carrier, a developing step for developing the latent image using an electrophotographic developer, and a transfer for transferring the developed toner image onto a sheet as a transfer target. And a fixing step of fixing the toner image on the surface of the paper.

  As another method, a color toner image is superposed on a sheet as a transfer medium after overlapping the color toner image using a belt or the like between the latent image carrier and the transfer object, and heated. If a method of fusing and fixing is adopted, a full color image can be formed, and the method can be applied in the present invention.

In particular, in the present invention, even if it is applied to a conventionally known image forming method using various fixing devices, since the electrophotographic coated paper of the present invention is used, blisters, curls and undulations in the fixing process are used. Can be prevented.
Examples of image forming apparatuses applicable in the image forming method of the present invention will be given below.

<Image forming apparatus I>
FIG. 2 is a schematic configuration diagram showing an example of an image forming apparatus preferably used in the image forming method of the present invention. The image forming apparatus shown in FIG. 2 includes a photoconductor 11 that rotates in the direction of arrow A. Around the photoconductor 11 is a roll-type charger 12, an exposure device 13, four colors of cyan, magenta, yellow, and black. The developing device 14 containing the developing devices 14a, 14b, 14c, and 14d that respectively store the developer, the belt-like intermediate transfer member 15, the cleaner 16, and the light neutralizer 17 are arranged in this order. The intermediate transfer member 15 is stretched by support shaft rolls 18a, 18b, and 18c. The spindle roll 18 a is in pressure contact with the photoconductor 11 through the intermediate transfer body 15. The spindle roll 18 c is pressed against the transfer roll 19 through the intermediate transfer body 15. Further, the toner image is transferred from the peripheral surface of the intermediate transfer body 15 to the transfer body 7 by the transfer roll 19.

In the image forming apparatus shown in FIG. 2, an image is formed as follows.
The photosensitive member 11 charged by the charger 12 is exposed by the exposure device 13 on the basis of image information of four colors of cyan, magenta, yellow, and black, and a latent image of each color is formed on the surface of the photosensitive member 11. The latent image on the surface of the photoconductor 11 is developed by a developing unit corresponding to each of the developing units 14a, 14b, 14c, and 14d built in the developing device 14 to form a toner image. The developed toner image is electrostatically transferred to the outer peripheral surface of the belt-shaped intermediate transfer body 15 at a portion facing the support shaft roll 18a.

The toner remaining on the surface of the photoconductor 11 after the toner image on the surface of the photoconductor 11 is transferred to the transfer target (paper) 7 is removed by the cleaner 16. Further, the residual charge remaining on the surface of the photoconductor 11 is neutralized by the light neutralizer 17. The photoreceptor 11 is prepared for the next image formation.
This operation is performed for each of the four colors cyan, magenta, yellow, and black, and an unfixed full-color toner image is formed on the outer peripheral surface of the intermediate transfer member 15 by sequentially laminating the outer peripheral surface of the intermediate transfer member 15. The

The full-color toner image formed on the outer peripheral surface of the intermediate transfer member 15 is pressed against the support roller 18c and the transfer roller 19 via the intermediate transfer member 15 as the intermediate transfer member 15 advances in the arrow P direction. It moves to the part (nip part) where it is done. When the toner image on the outer peripheral surface of the intermediate transfer body 15 passes through the nip portion, the toner image is transferred to the surface of the transfer medium 7 that is inserted and travels in the direction of arrow B.
The unfixed image on the surface of the transfer medium 7 obtained in this way is fixed by a fixing device located downstream of the transfer process. Any fixing device can be used as long as it is a fixing device that fixes by applying heat and pressure.

  Examples of the fixing device used in the image forming method of the present invention include a contact-type heat fixing device. For example, a heating roll in which a rubber elastic layer is formed on the outer periphery of a core metal and a surface layer of a fixing member is further provided as necessary. And a hot roll type fixing device comprising a pressure roll having a rubber elastic layer formed on the outer periphery of the core metal and optionally having a fixing member surface layer, and a combination of the roll and the roll, Examples thereof include a combination with a belt and a fixing device in place of the combination of a belt and a belt.

  For the base material (core) of the fixing member, a material having excellent heat resistance, strong strength against deformation, and good thermal conductivity is selected. In the case of a roll type fixing device, for example, aluminum, iron, copper, etc. In the case of a belt-type fixing device, for example, a polyimide film, a stainless steel belt, or the like is selected. A rubber elastic layer usually made of silicone rubber, fluororubber or the like is provided on the surface of the base material in the roll type fixing device.

The base material and rubber elastic layer of the fixing member may contain various additives depending on the purpose, for example, carbon black or metal oxide for the purpose of improving wear resistance, resistance value control, etc. Ceramic particles such as SiC may be contained.
The following are examples of some preferred fixing devices.

<Fixing device I>
First, an example of a heat roll type fixing device (fixing device I) will be described in detail. The fixing device of this example is shown in a schematic configuration diagram in FIG. 3 and is employed in the above <image forming apparatus I> shown in FIG.
The fixing device of this example mainly includes a heat roll 1 having a roll shape and a pressure-bonding roll 2 disposed so as to face the heat roll 1. The heat roll 1 is provided with a heating source 3 for heating it, an elastic layer 5 is formed on the outer periphery of the core 8, and a fixing member surface layer 4 that forms the surface of the heat roll 1 thereon. Is formed.

When the transfer body 7 on which the toner image 6 is formed is inserted in the nip portion between the pressure roll 2 and the heat roll 1 as it advances in the direction of the arrow B, heating and pressurization are performed during the passage. Then, the toner image is fixed.
The fixing device of this example further includes a cleaning member (not shown) for removing the toner adhering to the surface of the heat roll 1, a heating source 3 ′ for heating the pressure-bonding roll 2, and a transfer target, as necessary. You may have the nail | claw (a finger, not shown) etc. which peel 7 from the heat roll 1. FIG. The heating source 3 in the fixing device shown in FIG. 3 is controlled by a temperature control device (not shown) so that the surface temperature of the heat roll 1 is constant.

  The heat roll 1 and / or the pressure roll 2 are preferably provided with elastic layers 5 and 5 ′ having a single layer or a laminated structure. For the elastic layers 5 and 5 ′, heat-resistant rubber such as silicone rubber or fluorine rubber is used, and the rubber hardness (JIS-A) is preferably 60 or less. When the fixing member has the elastic layers 5 and 5 ′, the fixing member is deformed following the unevenness of the toner image 6 on the transfer body 7, and the smoothness of the image surface after fixing can be improved. Is advantageous.

  The thickness of the elastic layers 5 and 5 ′ is preferably in the range of 0.1 to 3 mm, and more preferably in the range of 0.5 to 2 mm. If the thickness of the elastic layers 5 and 5 ′ exceeds 3 mm and is too thick, the heat capacity of the fixing member increases, and it takes a long time to heat the fixing member to a desired temperature, and energy consumption increases. It is not preferable. On the other hand, if the thickness is less than 0.1 mm, the deformation on the surface of the fixing member cannot follow the unevenness of the toner image, and uneven melting may occur. Also, distortion of the elastic layer effective for peeling is obtained. It is not preferable because it is difficult to be made.

<Fixing device II>
Next, an example of a belt-roll nip type fixing device (fixing device II) will be described in detail. The fixing device of this example is shown in a schematic configuration diagram in FIG.
The fixing device of this example includes a heat fixing roll 21 having a built-in heat source, an endless belt 25 stretched around three support rolls 22, 23, 24 and pressed against the heat fixing roll 21, and the endless belt 25. A main portion is configured by the pressure applying member 31 that is in contact with the inner surface side and presses the endless belt 25 along the surface of the heat fixing roll 21.

  The heat fixing roll 21 has a cylindrical core 32 inside, and is driven to rotate in the direction of arrow C by a motor 38. The core 32 is made of aluminum having an outer diameter of 47 mm, an inner diameter of 42 mm, and a length of 350 mm. The surface of the core 32 is directly coated with an HTV silicone rubber having a hardness of 45 ° (JIS-A) as a base layer 23a with a thickness of 2 mm, and further an RTV silicone rubber with a thickness of 50 μm as a top coat layer 23b is dipped thereon. It is coated. Thereby, the coating layer 23 is formed, and the coating layer 23 is finished in a surface state close to a mirror surface.

The rubber hardness of the underlayer 23a is a spring type A type manufactured by Teclock.
It is the result of adding a load of 9.8 N (1,000 gf) and measuring with a hardness meter in accordance with JIS-K6301. The core 32 can be made of a metal having a high thermal conductivity even if it is not aluminum, and the cover layer 23 can be made of other materials as long as it is an elastic body having high heat resistance. .

  Inside the core 32, a halogen lamp 35 having an output of 850 W is disposed as a heating source. A temperature sensor 30 is disposed on the surface of the heat fixing roll 21 and measures the temperature of the surface of the heat fixing roll 21. Then, the halogen lamp 35 is feedback-controlled by a temperature controller (not shown) based on a measurement signal from the temperature sensor 30, so that the surface of the heat fixing roll 21 is adjusted to 150 ° C.

An oil supply device 9 is disposed in the vicinity of the heat fixing roll 21. The oil supply device 9 always supplies a predetermined amount of the release agent from the tank 9a for storing the release agent to the surface of the heat fixing roll 21 through the sponge-like sucking member 9b and the rolls 9c and 9d. This prevents a part of the toner 36 from being offset to the heat fixing roll 21 when fixing an unfixed toner image with the toner 36 on the sheet (paper) 37. As a release agent supplied by the oil supply device 9, dimethyl silicone oil (trade name “KF-96” manufactured by Shin-Etsu Chemical Co., Ltd.) having a viscosity of 1000 mm ² / s (1000 cSt) is used.

  The pressure applying member 31 is formed by laminating an elastic layer 31b and a low friction layer 31c on the surface of the base plate 31a, and is pressed against the heat fixing roll 21 by a compression coil spring 26 disposed on the base plate 31a side. Has been. The base plate 31a is made of stainless steel having a width (traveling direction of the endless belt 25) of 20 mm, a length (perpendicular to the traveling direction of the endless belt 25) of 320 mm, and a thickness of 5 mm. The elastic layer 31b is made of a silicone sponge (silicone rubber foam) having a rubber hardness of 23 ° and a thickness of 5 mm. Here, the rubber hardness is a result obtained by adding a load of 2.94N (300 gf) with an Asker C type sponge rubber hardness meter manufactured by Kobunshi Kagaku. Further, as the low friction layer 31c, “FGF-400-4” (trade name) manufactured by Chuko Kasei Co., Ltd., which is a glass fiber sheet impregnated with polytetrafluoroethylene, is used.

  Since the elastic layer 31 b is provided here, the contact surface of the low friction layer 31 c in contact with the endless belt 25 can be aligned with the outer peripheral surface of the heat fixing roll 21. That is, if the pressure applying member 31 is pressed toward the heat fixing roll 21 with a load of a certain level or more, the elastic layer 31 b is deformed and the contact surface of the low friction layer 31 c is pressed along the outer peripheral surface of the heat fixing roll 21. It is designed to be deformed. Therefore, when the pressure applying member 31 is pressed against the heat fixing roll 21 by the compression coil spring 26, the endless belt 25 is pressed against the heat fixing roll 21 without a gap, and a belt nip portion is formed.

The surface of the low friction layer 31c is coated with dimethyl silicone oil (trade name “KF-96” manufactured by Shin-Etsu Chemical Co., Ltd.) having a viscosity of 1000 mm ² / s (1000 cSt). The friction coefficient with the pressure applying member 31 is reduced. In a state where dimethyl silicone oil is applied, the friction coefficient μ2 between the pressure applying member 31 and the endless belt 25 is smaller than the friction coefficient μ1 between the endless belt 25 and the heat fixing roll 21 ( μ1> μ2). Thus, by setting the friction coefficients on both surfaces of the endless belt 25, the endless belt 25 is driven as the heating and fixing roll 21 rotates and travels while sliding on the pressure applying member 31.

  The endless belt 25 is formed of a polyimide film with a thickness of 75 μm, a width of 300 mm, and a circumferential length of 188 mm. The endless belt 25 is wound with a tension of about 78.4 N (8 kgf) around support rolls 22, 23, and 24 that are arranged at positions away from the heat fixing roll 21. The support rolls 22, 23, and 24 are made of stainless steel, and their diameters are 18 mm, 18 mm, and 23 mm, respectively.

The endless belt 25 is pressed against the heat fixing roll 21 without a gap by the pressure applying member 31 being pressed toward the heat fixing roll 21. At this time, the contact pressure of the pressure applying member 31 is set to about 5.5 × 10 ⁴ Pa (0.56 kgf / cm ² ). The heat fixing roll 21 is rotated in the direction of the arrow C by the motor 38 at a peripheral speed V = 220 mm / sec, and the endless belt 25 is driven to rotate at a speed of 220 mm / sec by this rotation.

  Next, the operation of the fixing device of this example will be described. In the fixing device of this example, on the right side in FIG. 4, a toner image by the toner 36 is transferred to the surface of the sheet 37 by a transfer device (not shown), and the sheet 37 is conveyed toward the belt nip portion. The sheet 37 enters the position where the pressure applying member 31 is disposed in the belt nip portion. The image of the toner 36 is fixed on the surface of the sheet 37 by the pressure acting on the belt nip portion and the heat applied through the heat fixing roll 21 by the halogen lamp 35.

<Fixing device III>
Next, an example of a belt-belt nip type fixing device (fixing device III) will be described in detail. The fixing device of this example is shown in a schematic configuration diagram in FIG.
In the fixing device of this example, the fixing belt 43 that circulates in the direction of the arrow E and the pressure belt 45 that circulates in the direction of the arrow F by being driven thereby form a nip portion for fixing. . When the paper 47 is loaded, the pressure roll 41 and the pressure roll 42 are pressed against each other from the circumference of the fixing belt 43 and the pressure belt 45 to form the entrance of the nip portion. Yes. Before entering the nip portion, the surface of the fixing belt 43 is sufficiently heated by the first, second, and third heating portions.

The first heating unit is a cooling unit after passing through the inlet of the nip unit, and heat taken from the fixing belt 43 by the cooling plate 52 provided for cooling the fixing belt 43 is made of aluminum by the heat pipe 53. It is configured to be used for heating the fixing belt 43.
The second heating unit is configured by an aluminum heating roll 48 that is in contact with the back surface (inner peripheral surface) of the fixing belt 43. A heater 55a is arranged inside the heating roll 48, and the temperature is controlled by temperature control means (not shown) based on the detection data of the temperature sensor 44a arranged to sense the surface temperature of the heating roll 48. Yes.

The third heating unit is configured by an aluminum heating roll 49 that contacts the surface (outer peripheral surface) of the fixing belt 43. A heater 55b is arranged inside the heating roll 49, and the temperature is controlled by temperature control means (not shown) based on the detection data of the temperature sensor 44b arranged to sense the surface temperature of the heating roll 49. Yes.
The fixing belt 43 is sequentially preheated by the first heating unit by the rotation in the direction of arrow E, heated from the back side by the second heating unit, and from the front side by the third heating unit, respectively, to a temperature necessary for fixing. The nip is reached in a heated state. A temperature sensor 44c for detecting the surface temperature of the fixing belt 43 is disposed immediately before the nip portion. Based on the detected data, a control unit (not shown) controls the second heating unit and / or the third heating unit. The heating condition of the heating unit is feedback controlled.

  The nip formed between the fixing belt 43 and the pressure belt 45 by the sheet 47 having an unfixed toner image formed on the surface thereof traveling in the direction of the arrow D and the pressure roll 41 and the pressure roll 42 arranged opposite to each other. When it is inserted into the entrance of the part, heat and pressure are applied there, and the toner constituting the toner image is melted. When the toner is melted, it acts as an adhesive, and the fixing belt 43 and the paper 47 are in an adhesive state. After that, the cooling plate 52 removes heat from the fixing belt 43 and cools the cooling belt. Is done. This deprived heat is used in the first heating section as described above. The temperature of the fixing belt 43 at the peeling portion corresponding to the exit of the section (nip portion) where the fixing belt 43 and the pressure belt 45 are in contact with each other is such that the toner is solidified to some extent and is easily separated from the fixing belt 43. It cools in the said cooling part so that it may become below. At the peeling portion, the paper 47 is peeled off from the fixing belt 43, proceeds in the direction of arrow D, and is discharged outside the apparatus.

In this example, the cooling unit was cooled so that the surface temperature of the fixing belt 43 was 100 ° C. or less. The temperature is more preferably adjusted to 90 ° C. or lower.
The surface of the fixing belt 43 at the entrance of the nip portion is heated in the three heating portions so that the temperature becomes equal to or higher than the melting temperature of the toner. In this example, the surface of the fixing belt 43 is heated to 175 ° C. More specifically, the first heating unit is heated to approximately 115 to 120 ° C, the second heating unit is heated to approximately 160 to 170 ° C, and the third heating unit is heated to 175 ° C.

In the fixing device of this example, the fixing belt 43 is strongly heated by the three heating portions as described above, and the heating efficiency is high, so that high-speed fixing can be realized. Further, since the heat of the sheet 47 to be cooled after fixing and the heat of the fixing belt 43 are transferred to the first heating unit and reused, not only the sheet peelability is good but also the thermal efficiency is good. .
In this example, the above configuration realizes continuous high-speed fixing of 60 sheets per minute (A4 horizontal feed).

  The image forming apparatus or the fixing apparatus applicable to the image forming method of the present invention has been described above by giving one image forming apparatus or three fixing apparatuses. However, the present invention is limited to the apparatuses of these embodiments. Instead, various conventionally known image forming apparatuses or fixing apparatuses can be applied. The individual elements described in each of these examples can also be applied in other examples.

  In the image forming method of the present invention, after an unfixed toner image is formed on the paper (electrophotographic coated paper of the present invention) and then introduced into the fixing device, the paper is loaded with the toner image. It can be preheated (hereinafter sometimes referred to as “preheating”) so that the surface temperature of the formed side is 50 ° C. or higher. When the surface temperature of the paper is set to 50 ° C. or higher by preheating, moisture taken into the paper, which is the electrophotographic coated paper of the present invention, becomes water vapor, and is in a state in which molecular motion is likely to occur. As a result, it is possible to particularly prevent the occurrence of blisters because the moisture content is reduced or water vapor easily escapes from the paper in the fixing step.

  Note that if the toner constituting the unfixed toner image is melted by preheating, it may affect the final image. Therefore, this preheating is below the melting temperature of the used toner. It is desirable to carry out at the temperature of. Furthermore, the temperature is preferably 10 ° C. or more lower than the melting temperature of the used toner, more preferably 20 ° C. or more.

  The preheating method may be a non-contact method using radiant heat or a method using heat conduction for contact heating with the paper, but the temperature of the paper surface is 50 ° C. at the outlet of the preheating device for preheating. It is necessary to make it above. As a method for measuring the temperature of the paper surface, a contact method such as a thermocouple may be used, or a non-contact method such as an infrared radiation method may be used.

  Below, an example of the preheating apparatus which can be used when performing preheating in the image forming method of this invention is given. Of course, the preheating device usable in the present invention is not limited to the following examples. Such a preheating device may be installed upstream or downstream of the transfer process, but it is of course a requirement that it be installed upstream of the fixing process.

<Preheating device I>
FIG. 6 is a schematic configuration diagram showing an example of a preheating device (preheating device I) that can be used when preheating is performed in the image forming method of the present invention.
The preheating device in this example is mainly stretched by a heating roll 63, a drive roll 64, and a tension roll 65, and a heating belt 62 that rotates in the direction of arrow G by the driving force of the tension roll 65, and an outer periphery thereof. The pressing roll 61 and the charger 66, and the counter plate 68 and the heating plate 69 disposed on the inner periphery of the heating belt 62 are configured.

  The heating plate 69 and the heating roll 63 include a heat source (not shown), and the heating belt 62 is heated from the inner periphery. At this time, the heating plate 69 is not in contact with the heating belt 62 due to radiant heat, and the heating roll 63 is of course in contact with the heating belt 62 to apply heat to the heating belt 62. The pressing roll 61 and the counter plate 68 are in contact with each other via the heating belt 62, and a nip portion is formed between them. When the heating belt 62 rotates in the direction of the arrow G and reaches the nip portion, the temperature of the surface of the heating belt 62 reaches a temperature sufficient for preheating due to the heating of the heating plate 69 and the heating roll 63. The counter plate 68 also includes an auxiliary heat source (not shown).

  In addition, a charger 66 is disposed upstream of the nip portion formed by the pressing roll 61 and the counter plate 68 in the rotation direction of the heating belt 62 (in the direction of arrow G). The charger 66 uses a corotron charger, and charges the surface of the heating belt 62 so that the paper 67 on which the unfixed toner image is formed is brought into close contact with the surface of the heating belt 62, thereby improving transportability. is there.

  When the sheet 67 on which the unfixed toner image is formed on the surface in the previous process is sent to the preheating device of this example, the sheet 67 proceeds in the direction of arrow H, and the surface on which the unfixed toner image is formed is the pressing roll 61. It is inserted through a nip formed by the pressing roll 61 and the opposing plate 68 so as to be on the side (facing the upper surface). In the nip portion, the sheet 67 is heated and dehumidified by the heating belt 62 that has been previously set to a predetermined temperature by the heating plate 69 and the heating roll 63. At this time, the heat held by the heating belt 62 is maintained by an auxiliary heat source included in the counter plate 68.

  When the sheet 67 is conveyed in the direction of arrow G while being in close contact with the heating belt 62, it is sufficiently preheated in the conveyance process (that is, the surface on which the toner image is formed becomes 50 ° C. or more), and the driving roll 64 Due to the influence of the radius of curvature of the heating belt 63 due to the above, self-stripping properties are imparted and peeled off from the surface of the heating belt 62. Then, it is sent to a fixing process by a fixing device.

<Toner or developer>
Next, the toner or developer that can be used in the image forming method of the present invention is not particularly limited, but the following can be preferably used.
(toner)
In general, a polyester resin or a styrene-acrylic resin is mainly used as a resin component of a toner suitable for use in the image forming method of the present invention. The pigment component of the suitable toner is not particularly limited, and conventionally known pigment components can be used without any problem.

  Any suitable production method such as a pulverization method or a polymerization method may be adopted as the preferred toner production method, but a resin particle dispersion in which resin particles are dispersed and a colorant dispersion in which colorants are dispersed. The emulsion aggregation method in which the resin particles and the colorant are aggregated to a toner particle size, and the obtained aggregate is heated and fused to a temperature equal to or higher than the glass transition point of the resin is preferable.

In the present invention, the preferable volume average particle diameter of the toner is preferably in the range of 2 to 8 μm, and more preferably in the range of 3 to 7 μm. When the volume average particle diameter of the toner is less than 2 μm, the chargeability tends to be insufficient and the developability may be lowered. On the other hand, when the toner exceeds 8 μm, the resolution of the image may be lowered. Therefore, it is not preferable respectively.
Here, the volume average particle diameter of the toner means a particle diameter at which the cumulative volume becomes 50% from the small diameter side. For example, Coulter Counter TA-II (manufactured by Nikka Machine Co., Ltd.), Multisizer II (manufactured by Nikka Kisha Co., Ltd.). ) Or the like.

The preferred toner particle size distribution is preferably 1.28 or less, more preferably 1.25 or less, as a volume average particle size distribution index GSDv. In particular, a toner having a sharp particle size distribution can be obtained by producing by an emulsion aggregation method. If GSDv exceeds 1.28, the sharpness and resolution of the image are lowered, which is not preferable.
Here, the volume average particle size distribution index GSDv of the toner is a ratio (D _84v / D _16v ) of the particle diameter D _16v at which the cumulative volume is 16% to the particle diameter D _84v at which the cumulative volume is 84% from the small diameter side. It can be measured using the same device as the volume average particle diameter.

In the present invention, the preferable toner particles preferably have an average shape factor SF1 defined by the following formula (1) in a range of 100 ≦ SF1 ≦ 140, and in a range of 110 ≦ SF1 ≦ 135. More desirable.
SF1 = ML ² × 100π / 4A (1)
(In the above formula, ML represents the maximum length of toner particle diameter, and A represents the projected area of toner particles.)

The shape factor SF1 is used as a factor representing the shape of the toner and the like, and the area, length, shape, and the like of the toner particles can be quantitatively analyzed with high accuracy from an image captured by an optical microscope or the like. This is based on a statistical method of image analysis, and can be measured by, for example, Image Analyzer LUZEX III manufactured by NIRECO.
In the present invention, the average value of the shape factor SF1 is obtained by averaging the values of the shape factor SF1 obtained by image analysis of 200 toner particles to be measured.

  As apparent from the above formula (1), the shape factor SF1 is obtained by multiplying the value obtained by squaring the maximum length of the toner particle diameter by the square of the toner particle area by π / 4, and further multiplying by 100. As the toner particle shape is closer to a sphere, the value is closer to 100, and conversely, the longer the toner particle is, the larger the value is. That is, the difference between the maximum diameter and the minimum diameter of the toner, that is, the shape factor SF1 is an index representing distortion. If it is a perfect sphere, SF1 = 100.

(Developer)
The developer that can be used in the image forming method of the present invention is not particularly limited, and can have an appropriate component composition depending on the purpose.
The developer includes a one-component developer composed of toner alone and a two-component developer using a combination of toner and carrier.

The carrier used in the two-component developer is not particularly limited. For example, a known carrier such as a resin-coated carrier described in JP-A Nos. 62-39879 and 56-11461 can be used. Can be used.
The mixing ratio of the toner and the carrier in the two-component developer is not particularly limited and can be appropriately selected depending on the purpose.
Since the image forming method of the present invention uses the electrophotographic coated paper of the present invention, it has no image defects and has excellent dimensional stability.

Hereinafter, the present invention will be described more specifically with reference to examples. Of course, the present invention is not limited to the examples described below. In the examples, “parts” and “%” represent “parts by mass” and “mass%”, respectively, unless otherwise specified.
Note that the method for evaluating the sheet characteristics will be described later.

[Manufacture of electrophotographic coated paper]
(Example of coated paper for electrophotography I)
Filtration degree of 500 ml obtained by beating a pulp slurry obtained by mixing 80 parts by mass of LBKP (hardwood bleached kraft pulp) and 20 parts by mass of NBKP (softwood bleached kraft pulp) with Niagara Beata (manufactured by Kumagai Riki Kogyo Co., Ltd.) In the pulp slurry, 10 parts by weight of light calcium carbonate (Tamapearl TP-121, manufactured by Okutama Kogyo Co., Ltd.), cationized starch (trade name: MS4600, manufactured by Nippon Food Chemical Co., Ltd.) 0.2 part by mass and 0.05 part by mass of alkenyl succinic anhydride (Fibran 81, manufactured by Oji National Corporation) were added. These mixtures were diluted with white water to prepare a paper slurry having a solid content concentration of 0.3%.

The obtained paper slurry was stirred for 2 hours, and then paper was made using an oriented sheet former (manufactured by Kumagai Rikyu Kogyo Co., Ltd.). Next, polyacrylic acid sodium salt (Sunfresh ST- 500MPSA (manufactured by Sanyo Chemical Industries Co., Ltd.) was applied with a size press device so that the coating amount was 3.0 g / m ² in terms of dry weight. A smoothing treatment was performed so as to be seconds, and a base material having a basis weight of 84 g / m ² was obtained.

  On the other hand, 100% by mass of a pigment component [20% by mass of light calcium carbonate (trade name: Tama Pearl T-123, manufactured by Okutama Kogyo Co., Ltd.) and 80% by mass of kaolin (Ultra White 90, manufactured by Engelhard Co., Ltd.)] On the other hand, as an adhesive, oxidized starch (Ace A, manufactured by Oji Cornstarch Co., Ltd.) 3% by mass (solid ratio to pigment; hereinafter the same in this example) and a synthetic adhesive (LX430 and 2507H, blending ratio 20:80, A coating composition comprising 14% by mass of Nippon Zeon Co., Ltd.) and 0.3% by mass of a dispersant (Aron T-40, manufactured by Toa Gosei Co., Ltd.) and coating the obtained base material A product was prepared.

The obtained coating composition was coated on both sides of the obtained base material with a blade coater so that the dry weight would be 10 g / m ^{2 on} one side, and after drying, a white paper was printed with a super calendar at a roll temperature of 50 ° C. Smoothing was performed so that the gloss was 50%, and a coated paper for electrophotography having a basis weight of 104 g / m ² was obtained. The moisture change rate (the moisture change rate before and after being left in an oven at 120 ° C. for 30 seconds after conditioning according to the conditions defined in JIS-P8111) of the obtained coated paper is 0. 15% by mass.

(Example of coated paper for electrophotography II)
In the same manner as described in the electrophotographic coated paper example I, a paper slurry having a solid content concentration of 0.3% was prepared. The obtained paper slurry was stirred for 2 hours, and then paper was made using an oriented sheet former (manufactured by Kumagaya Rikkoku Kogyo Co., Ltd.). Then, the starch-acrylic acid graft copolymer (Sun Wet, manufactured by Sanyo Chemical Industries Co., Ltd.) was applied with a size press device so that the coating amount was 3.5 g / m ² in terms of dry weight. A smoothing treatment was performed so as to be seconds, and a base material having a basis weight of 94 g / m ² was obtained.

  On the other hand, 100% by mass of pigment component [40% by mass of light calcium carbonate (trade name: Tama Pearl T-123, manufactured by Okutama Kogyo Co., Ltd.), 50% by mass of kaolin (Ultra White 90, manufactured by Engelhard Co., Ltd.), Organic pigment (Nipol MH5055, manufactured by Nippon Zeon Co., Ltd.) 10% by mass], as an adhesive, oxidized starch (Ace A, manufactured by Oji Cornstarch Co., Ltd.) 3% by mass (solid ratio to pigment; hereinafter in this example) The same), synthetic adhesive (0623A and 0640, blending ratio 15:85, manufactured by JSR Corporation) 14% by mass, and dispersant (Aron T-40, manufactured by Toagosei Co., Ltd.) 0.2% by mass. The coating composition which mix | blends and coats to the obtained said base material was prepared.

The obtained coating composition was coated on both sides of the obtained base material with a blade coater so that the dry weight was 5 g / m ^{2 on} one side, and after drying, a white paper was printed with a super calendar at a roll temperature of 50 ° C. Smoothing was performed so that the gloss was 30%, and a coated paper for electrophotography having a basis weight of 104 g / m ² was obtained. The moisture change rate in the present invention of the obtained coated paper was 0.20% by mass.

(Example of coated paper for electrophotography III)
In the same manner as described in the electrophotographic coated paper example I, a paper slurry having a solid content concentration of 0.3% was prepared. The resulting stock slurry was stirred for 2 hours, and then paper was made using an oriented sheet former (manufactured by Kumagai Rikkoku Kogyo Co., Ltd.). Next, an acrylic acid-vinyl alcohol copolymer (Sumikagel) was applied to the obtained wet paper. , Manufactured by Sumitomo Chemical Co., Ltd.) with a size press so as to be 2.5 g / m ^2, and after drying, a smoothing treatment is performed using a machine calendar so that the Oken smoothness becomes 30 seconds. And a base material having a basis weight of 84 g / m ² was obtained.
Thereafter, in the same manner as in the electrophotographic coated paper example I, an electrophotographic coated paper having a basis weight of 104 g / m ² was obtained. The moisture change rate in the present invention of the obtained coated paper was 0.18% by mass.

(Electrophotographic coated paper example IV ... for comparison)
In the electrophotographic coated paper example I, the same procedure as in the electrophotographic coated paper example I was performed except that the operation of applying polyacrylic acid sodium salt with a size press device was not performed during the production of the substrate. Each operation was performed by the method to obtain an electrophotographic transfer paper having a basis weight of 104 g / m ² . The moisture change rate in the present invention of the obtained coated paper was 0.90% by mass.

(Example of electrophotographic coated paper V ... for comparison)
OK Top Coat N (basis weight 104.7 g / m ² , manufactured by Oji Paper Co., Ltd.), which is a commercially available coated paper for printing, was used as electrophotographic coated paper example V. The moisture change rate of the coated paper in the present invention was 0.65% by mass.

<Evaluation of paper characteristics>
With respect to the electrophotographic coated paper of each example produced as described above, the paper characteristics were evaluated. Including those already described, they are summarized in Table 1 below. The method for evaluating the paper characteristics is as described later.

<Evaluation method of paper characteristics>
(1) Basis weight It measured by the method prescribed | regulated to JISP-8124.
(2) Blank paper glossiness The measurement was performed at an incident angle of 75 ° in accordance with JIS P-8142.
(3) Air permeability J Tappi No. Measured by the method specified in 5 (Oken air permeability).
(4) Moisture change rate in the present invention After adjusting the humidity according to the conditions specified in JIS-P8111, the moisture content was measured by an absolutely dry method using a part of the sample [A (mass%)], After leaving it in an oven at 120 ° C. for 30 seconds, the water content is measured again in the same manner [B (mass%)]. The mass difference [A-B (% by mass)] was determined and used as the moisture change rate in the present invention.

[Image formation]
(Image Forming Method I)
Image formation was performed by the image forming apparatus I shown in FIG. 2, which incorporates the fixing device I shown in FIG.

(Image Forming Method II)
Image formation was performed with the image forming apparatus I shown in FIG. 2 described above by replacing the fixing device with the fixing apparatus II shown in FIG.

(Image Forming Method III)
Image formation was performed with the image forming apparatus I shown in FIG. 2 described above by replacing the fixing device with the fixing apparatus III shown in FIG.

(Paper heating example)
In the image forming apparatus I shown in FIG. 2, it is downstream of the transfer portion consisting of the support shaft roll 18 c and the transfer roll 19, and upstream of the fixing device I shown in FIG. 3 mainly consisting of the heat roll 1 and the pressure roll 2. 6 is installed, and immediately after the preheating device I, a sheet surface temperature measuring device (infrared radiation thermometer, manufactured by Keyence) is provided to The temperature was monitored.

[Examples 1-6 and Comparative Examples 1-3]
With respect to the electrophotographic coated paper examples I to V, the image forming methods I to III, and the presence / absence of the sheet heating example, each image is formed in accordance with the quality evaluation described later in the combination shown in Table 2 below. Recording tests were conducted, and these were designated as Examples 1 to 5 and Comparative Examples 1 to 3.

<Quality evaluation>
The quality of the following items was evaluated for the images and paper states obtained in the above examples and comparative examples. The results are summarized in Table 2 below.
(1: blister)
For the evaluation of the blister generation level, a recording test during single-sided printing was performed with a secondary color solid image of cyan and magenta when the image area ratio was 200%. Each paper is 28 ° C. and 85% R.S. H. After being left in the environment for 48 hours, it was subjected to a recording test. In the toner, an emulsion aggregation method (a resin particle dispersion in which resin particles are dispersed and a colorant dispersion in which a colorant is dispersed is mixed, and the resin particles and the colorant are aggregated into a toner particle size. And a toner having a shape factor SF1 of 134 and a volume average particle size distribution index GSDv of 1.22.
The obtained recorded images were evaluated based on the following evaluation criteria by tactile sensation, visual observation or observation with an optical microscope.

A: No blisters are generated.
○: Blister is generated but cannot be confirmed visually.
(Triangle | delta): The thing which can confirm a blister visually and is disturbing an image.
X: Blister can be confirmed by touch, and image gloss is lowered.

(2: Curl / Wavy)
Each paper is 28 ° C. and 85% R.S. H. Paper that had been left in the environment for 48 hours was subjected to a recording test. As the formed image, an image identification number N3 (image name: fruit basket) of an ISO / JIS-SCID sample (issued by the Japanese Standards Association) was used.
The curling / waving of the paper when the image was output was evaluated according to the following evaluation criteria.

A: Almost no curling or undulation occurs.
◯: Slight curling and / or undulation occurs but is in an acceptable range.
(Triangle | delta): Curling and / or a wave | undulation generate | occur | produced and it has reached the level which cannot be accepted.
X: The curl is large, and in some cases, it becomes a cylinder.

[Consideration of results]
As is apparent from the results shown in Table 2, the electrophotographic coated paper of the present invention was free from blistering and small in curling and undulation. On the other hand, in Comparative Example 1, since the moisture change rate was large, blisters were remarkably generated, and curling and undulation after fixing were very large. In Comparative Example 2, a commercially available coated paper for printing was used. However, blisters were remarkably generated due to the large moisture change rate, and the curling and undulation after fixing became very large.
Therefore, the electrophotographic coated paper of the present invention can suppress the blister defect of the fixed image in the electrophotographic copying machine and printer as compared with the conventional coated paper, and the occurrence of curling and undulation after fixing. It turns out that it is suppressed.

The moisture change rate of the coated paper for printing before and after being left in an oven at 120 ° C. for 30 seconds after humidity adjustment according to the conditions specified in JIS-P8111 and the high humidity condition (28 ° C., 85% R.D. H. The relationship between the blister generation state (blister grade) when forming a secondary color (Blue) solid image using the DocuColor 1250 manufactured by Fuji Xerox Co., Ltd. for 48 hours under the environment) It is a graph. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus preferably used in an image forming method of the present invention. It is a schematic block diagram which shows an example of the fixing device used for the image forming method of this invention used for the image forming apparatus shown in FIG. It is a schematic block diagram which shows another example of the fixing device used suitably for the image forming method of this invention. FIG. 6 is a schematic configuration diagram illustrating still another example of a fixing device preferably used in the image forming method of the present invention. It is a schematic block diagram which shows an example of the preheating apparatus which can be used when performing preheating in the image forming method of this invention.

Explanation of symbols

  1: Heat roll, 2: Press roll, 3, 3 ′: Heat source, 4: Fixing member surface layer, 5, 5 ′: Elastic layer, 6: Toner image, 7: Transfer object, 8: Core, 9: Oil supply device, 9a: tank, 11: photoconductor, 12: charger, 13: exposure device, 14: developing device, 15: intermediate transfer member, 16: cleaner, 17: photostatic device, 18a, 18b, 18c: Spindle roll, 19: Transfer roll, 21: Heat fixing roll, 22, 23, 24: Support roll, 25: Endless belt, 26: Compression coil spring, 30, 44a, 44b, 44c: Temperature sensor, 31: Pressure Application member 32: Core 35: Halogen lamp 36: Toner 37: Sheet 38: Motor 41: Pressure roll 42: Pressure roll 43: Fixing belt 45: Pressure belt 47, 67: Paper 48: Heating roll 49: Heating roll 51: Heating plate 52: Cooling plate 53: Heat pipe 55a, 55b: Heater 61: Pressing roll 62: Heating belt 63: Heating roll 64: Drive roll 65: Stretching roll 66: Charger 68: Counter plate 69: Heating plate

Claims (7)

A coating layer mainly composed of a pigment and an adhesive is provided on both sides of a base material mainly composed of wood fibers in a range of 5 to 15 g / m ² in terms of solid content per side;
An electrophotographic coating characterized by having a moisture change rate of 0.3% by mass or less before and after being left to stand in an oven at 120 ° C. for 30 seconds after humidity is adjusted according to the conditions specified in JIS-P8111. Craft paper. 2. The electrophotographic coated paper according to claim 1, wherein the air permeability is 7000 seconds or less. An image forming method for forming an unfixed toner image on a paper surface by electrophotography and obtaining a fixed image by heating and pressurizing the toner image,
An image forming method using the electrophotographic coated paper according to claim 1 or 2 as the paper. The paper sheet on which an unfixed toner image is formed is inserted into a nip portion formed between the rolls of a fixing device including a pair of rolls, and heated and pressurized. Image forming method. Image formation for obtaining a fixed image by inserting the paper on which an unfixed toner image is formed into a nip portion formed between an endless belt and a roll of a fixing device including an endless belt and a roll, and heating and pressurizing the sheet. A method,
The fixing device has an elastic layer near the surface and is rotatably supported, an endless belt having an outer peripheral surface in contact with the surface of the heat fixing roll to form the nip portion, and the endless belt A pressure applying member that is in contact with an inner peripheral surface of the belt and has a pressure contact surface that presses the endless belt along the surface of the heat fixing roll to form the nip portion. The image forming method according to claim 3. A heated fixing belt is brought into contact with the paper on which the unfixed toner image is formed and pressed against the toner image, and the toner image is heated and pressurized, and then the fixing belt and the toner image are held on the surface. After the toner image is cooled to a predetermined temperature or less after being moved in close contact with the paper, the paper holding the toner image is introduced into a fixing device that peels from the fixing belt to obtain a fixed image. The image forming method according to claim 3. After an unfixed toner image is formed on the sheet, prior to introduction into the fixing device, the sheet is preheated so that the surface temperature on the side on which the toner image is formed is 50 ° C. or higher. The image forming method according to claim 3.

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