JP2014095776A - Wet type electrophotographic recording sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic recording sheet that is excellent in toner fixability and transferability, and in particular, excellent in prevention of ghost after continuous printing and handleability after printing.SOLUTION: A wet type electrophotographic recording sheet transfers an image from a heated blanket roll to a recording sheet, and includes, as a base material, resin-coated paper having a resin layer at least on one surface of base paper. The resin-coated paper has a toner image receiving layer comprising an inorganic fine particle layer that contains inorganic fine particles as a main component and contains 10 mass% or more of a cationic compound relative to the inorganic fine particles, and an outermost layer that contains a colloidal silica as a main component on a side separated further from the base material than the inorganic fine particle layer.

Description

  The present invention relates to a wet electrophotographic recording sheet printed using a wet electrophotographic system. Specifically, when printing using a wet electrophotographic method using a wet toner, the toner is excellent in toner fixing property and transfer property, and in particular, ghosting does not occur during continuous printing, and it is excellent in curling after printing. This relates to a recording sheet for use.

  Applications for printing using the electrophotographic system are not limited to terminal PC printers, fax machines, or copiers, but are being put to practical use in the field of so-called on-demand printing, which enables various types of small lot printing and variable information printing. The technological progress is remarkable. In recent years, with the improvement of printing speed and image quality, the number of printed copies has begun to be used even in areas conventionally used for printing such as offset and gravure.

  Since electrophotographic printing is a plateless printing method, it is advantageous to handle variable information. On the other hand, although offset and gravure printing cannot handle variable information, it is suitable for performing high-quality printing in large quantities at low cost. Therefore, in the electrophotographic system, technological development is being promoted from the viewpoints of printing machines, toners, and recording sheets for higher image quality, higher speed, lower power consumption, and lower costs. There is also a demand for quality such as toner fixability, transferability, and color reproducibility.

  Among the electrophotographic printing methods, the dry electrophotographic method is a method typified by an office copier, and a solid powder toner composed of a pigment and a synthetic resin is used as a toner for forming an image. In the image forming method, printing is performed by adsorbing toner to an electrostatic image appearing on a photoreceptor, and transferring and heating the toner to a transfer object. However, in this method, if the toner is made finer with the aim of improving the image quality, it becomes easy to scatter in the surrounding environment, which causes health problems when humans inhale it and problems such as soiling the printed matter. Due to the limit of the toner miniaturization, problems such as a large amount of toner consumption and an unnatural appearance as a printed product are pointed out. In addition, there is a problem that the recording sheet undulates due to high-temperature fixing and power consumption increases.

  On the other hand, the wet electrophotographic method is a very promising method. This is because the wet electrophotographic method disperses the toner in the liquid medium, so that the scattering of the powder is not a problem, and the toner can be reduced to about 1/10 that of the dry electrophotographic method. This is because, in addition to the fineness of the image, the pigment can be used as the coloring material, so that there is no problem of weather resistance, and the swell of the image is not conspicuous and the printed matter is close to high-quality offset printing.

  The wet toner is dried prior to transfer to the recording sheet or after the toner is transferred to the recording sheet, thereby removing the solvent in the wet toner and forming an image. When removing the solvent in the wet toner prior to transfer to the recording sheet, a blanket roll heated to approximately 60 to 120 ° C. is used. The solvent component is removed by the heat of the blanket roll, and the toner is melted by heat to cause stickiness, and the image is transferred onto the recording sheet. On the other hand, when the toner is dried after being transferred, the recording sheet on which the wet toner containing the solvent is transferred is heated to remove the solvent on the recording sheet, and the toner is melted and fixed.

  As described above, in the wet electrophotographic system, when transferring an image to a recording sheet, the effect of electric charge is not used. In the former method, that is, in the method of transferring an image from a heated blanket roll to the recording sheet, a wet toner is used. The image is transferred such that the adhesion between the toner and the recording sheet is higher than the adhesion between the wet toner and the blanket roll. That is, the transfer capability of the wet toner from the blanket roll to the recording sheet is important. If the adhesion capability of the toner itself is increased more than necessary for the purpose of improving the adhesion between the recording sheet and the toner, the fixing to the sheet is improved. However, at the same time, the adhesiveness between the blanket roll and the toner is also increased, and the toner is difficult to peel off from the blanket roll, so that the toner adhesion ability cannot be increased more than necessary. For this reason, in the case of wet electrophotographic printing in which an image is transferred from a heated blanket roll to a recording sheet, sufficient toner strength is not obtained even after printing, or toner particles are not transferred to the sheet sufficiently. There was a shortcoming. When sufficient toner strength cannot be obtained, the image of the printed matter is significantly deteriorated by subsequent handling. If the toner transfer is not sufficient and incomplete, a toner residue remains on the surface of the blanket roll and appears as an afterimage (ghost) in an image to be printed later. The occurrence of such a ghost is, for example, because the influence on the blanket roll surface is different between the image area and the non-image area during continuous printing, so the surface of the blanket roll is non-image area where the blanket roll surface and the recording sheet are in direct contact. It may appear even if it is adversely affected, and the wet toner transfer property of an image to be printed later may be reduced and a ghost may occur.

  Therefore, as a means for obtaining sufficient toner fixing strength, there is a method of applying a fixing agent to a sheet. For example, in the HP Indigo machine of Hewlett-Packard Company, there is a process of coating with polyethyleneimine called “sapphire processing”, but yellowing occurs during the storage period of the recording sheet, and the toner is peeled off by handling after printing. There was a problem. Further, in order to provide wet electrophotographic printing aptitude without using such treatment, for example, Japanese Patent Application Laid-Open No. 10-20537 (Patent Document 1), Japanese Patent Application Laid-Open No. 2003-173038 (Patent Document 2), and a special table. A recording sheet having a coating layer containing a polyamide-based polymer or a polyethyleneimine-based polymer having an amino group as a terminal group on a support, which is described in JP-A-2004-503805 (Patent Document 3) or the like is known. Yes. However, it has been extremely difficult to obtain sufficient toner fixability and transferability.

  As a means to improve the fixability of the wet toner without using a fixing agent, or to improve the transferability of the toner on the surface of the blanket roll, a recording sheet of calcium carbonate or kaolin that easily absorbs the solvent used in the wet toner is used. For example, JP 2004-77667 A (Patent Document 4), JP 2005-250168 A (Patent Document 5), International Publication No. 2004/049074 Pamphlet (Patent Document 6). Japanese Patent Laid-Open No. 2009-169408 (Patent Document 7) and the like. Japanese Patent Laid-Open No. 9-114122 (Patent Document 8) proposes a recording sheet having a toner fixing layer made of a mixture of a water-soluble resin and colloidal silica. Although these methods work very effectively as methods for improving toner fixing properties, further improvements have been demanded.

  As a further improvement example of the toner fixability, a recording sheet for a wet electrophotographic system using a wet toner contains inorganic fine particles on the substrate and has a fine pore radius of 100 nm or less measured by a nitrogen adsorption method. Japanese Patent Application Laid-Open No. 2012-32758 (Patent Document 9) describes a method for improving toner fixing property by having a toner image-receiving layer having a pore volume of 0.3 mL / g or more. Further, in JP 2012-173717 A (Patent Document 10), an inorganic fine particle layer mainly containing inorganic fine particles and a top layer mainly containing cationic colloidal silica are provided on the base material. In addition, by having a toner image-receiving layer comprising at least two layers, it has excellent toner fixability and transferability, and particularly has excellent continuous printability that does not generate ghost even during continuous printing. A sheet has been proposed.

  In addition, paper is generally widely used as a base material for electrophotographic recording sheets. However, as a base material suitable for outputting digital photo images, a paper support is used as a base paper on at least one surface thereof. Non-absorbent supports such as resin-coated paper and resin film coated with a polyolefin resin layer are used. In particular, polyolefin resin-coated paper has a base paper that has higher elasticity and a smoother surface than resin films. Therefore, it is preferable to obtain a higher toner transfer property as described in Japanese Patent Application Laid-Open No. 2012-32758 (Patent Document 9).

  However, regarding the handling of the recording sheet based on the resin-coated paper as described above, since the sheets may stick to each other after printing, it is difficult to roll up the recording sheet bundle after printing, An excellent recording sheet has been demanded.

Japanese Patent Laid-Open No. 10-20537 JP 2003-173038 A Special table 2004-503805 gazette JP 2004-77667 A JP-A-2005-250168 International Publication No. 2004/049074 Pamphlet JP 2009-169408 A JP-A-9-114122 JP 2012-32758 A JP 2012-173717 A

  The present invention is excellent in toner fixability and transferability when printed using a wet electrophotographic system using a wet toner, and particularly has no ghosting during continuous printing, and has excellent curling properties after printing. An object is to provide a recording sheet for wet electrophotography.

  An object of the present invention described above is a wet electrophotographic recording sheet for transferring an image from a heated blanket roll to a recording sheet, and a resin-coated paper having a resin layer on at least one surface of a base paper as a base material And having an inorganic fine particle layer mainly containing inorganic fine particles and containing 10% by mass or more of a cationic compound with respect to the inorganic fine particles on the resin-coated paper, and being further away from the substrate than the inorganic fine particle layer This was achieved by a wet electrophotographic recording sheet having a toner image-receiving layer comprising an uppermost layer mainly containing colloidal silica on the side.

  According to the present invention, it is possible to provide a wet electrophotographic recording sheet which is excellent in toner fixing property and transfer property, and in particular, does not generate ghost during continuous printing and has excellent curling properties after printing.

  Hereinafter, the wet electrophotographic recording sheet of the present invention will be described in detail.

<Base material>
The wet electrophotographic recording sheet of the present invention has a resin-coated paper in which at least one surface of a base paper is coated with a resin as a base material. In the present invention, the thickness of the resin-coated paper is preferably 50 to 300 μm, more preferably 80 to 260 μm.

  The polyolefin resin-coated paper preferably used in the present invention will be described in detail. The water content of the polyolefin resin-coated paper used in the present invention is not particularly limited, but is preferably in the range of 5.0 to 9.0% by mass, more preferably in the range of 6.0 to 9.0% by mass. It is. The moisture content of the polyolefin resin-coated paper can be measured using any moisture measuring method. For example, an infrared moisture meter, an absolute dry weight method, a dielectric constant method, a Karl Fischer method, or the like can be used.

  The base paper constituting the polyolefin resin-coated paper is not particularly limited, and commonly used paper can be used. However, for example, a smooth base paper used for a photographic support is preferable. As the pulp constituting the base paper, natural pulp, regenerated pulp, synthetic pulp or the like is used alone or in combination. This base paper is blended with additives such as sizing agent, paper strength enhancer, filler, antistatic agent, fluorescent whitening agent, and dye generally used in papermaking.

  Further, a surface sizing agent, a surface paper strength agent, a fluorescent brightening agent, an antistatic agent, a dye, an anchor agent, and the like may be applied on the surface.

Further, the thickness of the base paper is not particularly limited, but preferably has a good surface smoothness such as a paper that is compressed during or after paper making by applying pressure, etc., and its basis weight is 30 to 250 g. / M ² is preferred.

  The polyolefin resin for coating the base paper includes olefin homopolymers such as low density polyethylene, high density polyethylene, polypropylene, polybutene, and polypentene, or copolymers composed of two or more olefins such as ethylene-propylene copolymer, and the like. A mixture having various densities and melt viscosity index (melt index) can be used alone or as a mixture thereof.

  In addition, in the resin of the polyolefin resin-coated paper, white pigments such as titanium oxide, zinc oxide, talc and calcium carbonate, fatty acid amides such as stearic acid amide and arachidic acid amide, zinc stearate, calcium stearate, aluminum stearate, Fatty acid metal salts such as magnesium stearate, antioxidants such as hindered phenol compounds, blue pigments and dyes such as cobalt blue, ultramarine blue, cecilian blue, phthalocyanine blue, magenta such as cobalt violet, fast violet, manganese purple Various additives such as pigments, dyes, fluorescent brighteners, and UV absorbers can be added in appropriate combinations.

  The main production method of polyolefin resin-coated paper is produced by a so-called extrusion coating method in which a polyolefin resin is cast in a molten state on a traveling base paper, and is preferably at least one side of the base paper, more preferably the base paper. Are coated with resin. Further, before the resin is coated on the base paper, the base paper is preferably subjected to activation treatment such as corona discharge treatment and flame treatment. The thickness of the resin coating layer is suitably 5 to 50 μm.

An undercoat layer is preferably provided on the side of the substrate used in the present invention on which the toner image-receiving layer is applied. This undercoat layer is applied and dried in advance on the surface of the substrate before the toner image-receiving layer is applied. This undercoat layer contains a water-soluble polymer or polymer latex that can form a film. Preferred are water-soluble polymers such as gelatin, polyvinyl alcohol, polyvinyl pyrrolidone and water-soluble cellulose, and particularly preferred is gelatin. Adhesion amount of the water-soluble polymer is preferably ^{10~500mg / m 2, 20~300mg / m} 2 is more preferable. Further, the undercoat layer preferably contains a surfactant and a hardener. By providing the undercoat layer on the substrate, it effectively works to prevent cracking when the toner image-receiving layer is applied, and a uniform coated surface is obtained.

  Various types of back layers may be provided on the opposite surface on which the toner image-receiving layer is provided in order to prevent curling, to prevent sticking when superimposed immediately after printing, and to further improve toner transferability. A toner image receiving layer may be provided on both sides.

<Toner image-receiving layer>
The toner image-receiving layer in the present invention comprises at least two layers: a layer mainly containing inorganic fine particles and an uppermost layer mainly containing colloidal silica on the side farther from the substrate than the inorganic fine particle layer.

<Inorganic fine particle layer>
The inorganic fine particle layer of the recording sheet of the present invention mainly contains inorganic fine particles. Here, “mainly contained” means that the inorganic fine particles are contained in an amount of 50% by mass or more, more preferably 60% by mass or more with respect to the solid content coating amount of the inorganic fine particle layer.

  Examples of the inorganic fine particles used in the inorganic fine particle layer in the present invention include various known fine particles such as amorphous synthetic silica, alumina, alumina hydrate, calcium carbonate, magnesium carbonate, and titanium dioxide. Amorphous synthetic silica, alumina, or alumina hydrate is preferred in that As the amorphous synthetic silica, gas phase method silica and wet method silica, which will be described later, are particularly preferably used from the viewpoint of toner fixing property and transferability.

  Amorphous synthetic silica can be roughly classified into wet method silica, gas phase method silica, and others depending on the production method. Wet method silica is further classified into precipitation method silica, gel method silica, and sol method silica according to the production method. Precipitated silica is produced by reacting sodium silicate and sulfuric acid under alkaline conditions, and the silica particles that have grown are agglomerated and settled, and are then commercialized through the steps of filtration, washing, drying, pulverization and classification. Precipitated silica is commercially available, for example, from Tosoh Silica Co., Ltd. as a nip seal and from Tokuyama Co., Ltd. as a Toxeal. Gel silica is produced by reacting sodium silicate and sulfuric acid under acidic conditions. During the ripening, the fine particles dissolve and reprecipitate so as to bind other primary particles, so that the distinct primary particles disappear and form relatively hard aggregated particles having an internal void structure. For example, it is commercially available as nip gel from Tosoh Silica Co., Ltd. and as syloid and silo jet from Grace Japan Co., Ltd. The sol method silica is also called colloidal silica, which is obtained by heating and aging a silica sol obtained through metathesis of sodium silicate acid or the like through an ion exchange resin layer. For example, it is commercially available as Snowtex from Nissan Chemical Industries, Ltd. Yes.

  Vapor phase silica is also called a dry method as opposed to a wet method, and is generally made by a flame hydrolysis method. Specifically, a method of making silicon tetrachloride by burning with hydrogen and oxygen is generally known, but silanes such as methyltrichlorosilane and trichlorosilane can be used alone or silicon tetrachloride instead of silicon tetrachloride. Can be used in a mixed state. Vapor phase silica is commercially available as Aerosil from Nippon Aerosil Co., Ltd. and QS type from Tokuyama Co., Ltd.

In the present invention, gas phase method silica can be preferably used. The average primary particle diameter of the vapor phase silica used in the present invention is preferably 30 nm or less. More preferably, an average primary particle diameter of 3 to 15 nm (especially 3 to 10 nm) and a specific surface area by the BET method of 200 m ² / g or more (preferably 250 to 500 m ² / g) are used. The average primary particle diameter as used in the present invention is an average particle diameter obtained by measuring the diameter of a circle equal to the projected area of each of the 100 primary particles existing within a certain area by observation with an electron microscope. It is. The BET method referred to in the present invention is one of the powder surface area measurement methods by the vapor phase adsorption method, and is a method for obtaining the total surface area, that is, the specific surface area of a 1 g sample from the adsorption isotherm. Usually, as the adsorbed gas, a large amount of nitrogen gas is used, and the method of measuring the adsorbed amount from the change in pressure or volume of the gas to be adsorbed is most often used. The most prominent expression for expressing the isotherm of multimolecular adsorption is the Brunauer, Emmett, and Teller formula, called the BET formula, which is widely used for determining the surface area. The adsorption amount is obtained based on the BET equation, and the surface area is obtained by multiplying the area occupied by one adsorbed molecule on the surface.

  Vapor phase silica may be dispersed in the presence of either a cationic or anionic compound. The average secondary particle size of the vapor phase method silica is preferably 5 μm or less, more preferably 500 nm or less, and still more preferably 10 to 300 nm. As a dispersion method, gas phase method silica and a dispersion medium are premixed by ordinary propeller stirring, turbine type stirring, homomixer type stirring, etc., and then a media mill such as a ball mill, a bead mill, a sand grinder, a high pressure homogenizer, an ultrahigh pressure, etc. It is preferable to perform dispersion using a pressure disperser such as a homogenizer, an ultrasonic disperser, a thin film swirl disperser, or the like. The average secondary particle diameter as used in the present invention can be determined by photography using a transmission electron microscope. For simplicity, a laser scattering particle size distribution meter (for example, LA920 manufactured by Horiba, Ltd.) Can be measured as a number median diameter.

  In the present invention, wet process silica can also be used. As the wet method silica used here, precipitation method silica or gel method silica is preferable, and precipitation method silica is particularly preferable. As the wet process silica particles used in the present invention, wet process silica particles having an average primary particle diameter of 50 nm or less, preferably 3 to 40 nm and an average secondary particle diameter of 5 μm or less are preferable, and further 500 nm or less. It is particularly preferable to use wet method silica fine particles finely pulverized to about 20 to 200 nm.

  The wet process silica may be dispersed and pulverized in the presence of either a cationic or anionic compound. As a pulverization method, a wet dispersion method in which silica dispersed in an aqueous medium is mechanically pulverized can be preferably used. A preferred method of pulverizing the wet method silica fine particles used in the present invention will be described by taking dispersion as an example in the presence of a cationic compound. First, silica particles and a cationic compound are mixed in a dispersion medium mainly composed of water, and at least one dispersion device such as a sawtooth blade type dispersion machine, a propeller blade type dispersion machine, or a rotor stator type dispersion machine is used. Use to obtain a silica pre-dispersion. If necessary, an appropriate low boiling point solvent or the like may be added to the aqueous dispersion medium. The higher the solid content concentration of the silica pre-dispersion liquid, the more preferable, but when the concentration is too high, it becomes impossible to disperse, so the preferable range is 15 to 40% by mass, and more preferably 20 to 35% by mass. Next, the silica pre-dispersion is subjected to mechanical means having a stronger shearing force to pulverize the silica particles, whereby a wet process silica fine particle dispersion is obtained. As a mechanical means, a known method can be adopted, for example, a media mill such as a ball mill, a bead mill, a sand grinder, a high pressure homogenizer, a pressure disperser such as an ultra high pressure homogenizer, an ultrasonic disperser, a thin film swirl disperser, etc. Can be used.

  As the cationic compound used for the dispersion of the gas phase method silica and the wet method silica, a cationic polymer can be preferably used. As the cationic polymer, polyethyleneimine, polydiallylamine, polyallylamine, alkylamine polymer, JP-A 59-20696, JP-A 59-33176, JP-A 59-33177, JP 59-1555088, JP 60-11389, JP 60-49990, JP 60-83882, JP 60-109894, JP 62-198493 JP-A-63-49478, JP-A-63-115780, JP-A-63-280681, JP-A-1-40371, JP-A-6-234268, JP-A-7-125411 A polymer having a primary to tertiary amino group or a quaternary ammonium base described in JP-A-10-193976 Used Mashiku. In particular, diallylamine derivatives are preferably used as the cationic polymer. In terms of dispersibility and dispersion viscosity, the weight average molecular weight of these cationic polymers is preferably 2000 to 100,000, and particularly preferably 2000 to 30,000.

  As the alumina used in the present invention, γ-alumina which is a γ-type crystal of aluminum oxide is preferable, and among them, a δ group crystal is preferable. γ-alumina can make primary particles as small as about 10 nm. Usually, secondary particles of thousands to tens of thousands of nanometers are averaged by ultrasonic, high-pressure homogenizer, counter collision type jet crusher, etc. The particle size is preferably 5 μm or less, more preferably 500 nm or less, and more preferably about 20 to 300 nm.

The alumina hydrate used in the present invention is represented by a constitutive formula of Al ₂ O ₃ .nH ₂ O (n = 1 to 3). The alumina hydrate used in the present invention can be obtained by a known production method such as hydrolysis of aluminum alkoxide such as aluminum isopropoxide, neutralization of aluminum salt with alkali, hydrolysis of aluminate, and the like. The average secondary particle diameter of the alumina hydrate used in the present invention is preferably 5 μm or less, further 500 nm or less, more preferably 20 to 300 nm.

  The alumina and alumina hydrate used in the present invention may be dispersed in the presence of either a cationic or anionic compound. As the cationic compound, those dispersed by a known dispersing agent such as acetic acid, lactic acid, formic acid, nitric acid are preferably used.

  Two or more kinds of inorganic fine particles may be used in combination from the inorganic fine particles described above. For example, combined use of finely divided wet method silica and vapor phase method silica, combined use of finely divided wet method silica and alumina or alumina hydrate, and combined use of vapor phase method silica and alumina or alumina hydrate. It is done.

  In the present invention, the inorganic fine particle layer preferably contains a binder together with the inorganic fine particles. Examples of the binder include polyvinyl alcohol, gelatin, polyethylene oxide, polyvinyl pyrrolidone, polyacrylic acid, polyacrylamide, polyurethane, dextran, dextrin, Examples include carrageenan (κ, ι, λ, etc.), agar, pullulan, chitosan derivatives, casein, soy protein, water-soluble polyvinyl butyral, hydroxyethyl cellulose, carboxymethyl cellulose, and the like. Two or more of these binders can be used in combination. In using the binder, it is important that the binder does not swell due to humidity during storage or the like and does not block the voids. From this viewpoint, a binder having a relatively low swelling property is preferably used. A preferred binder is fully or partially saponified polyvinyl alcohol.

  Particularly preferred among the polyvinyl alcohols are those having a degree of saponification of 80% or more or those completely saponified. Those having an average degree of polymerization of 200 to 5000 are preferred.

  In the present invention, if necessary, a hardening agent can be used together with the binder constituting the inorganic fine particle layer. Specific examples of the hardener include aldehyde compounds such as formaldehyde and glutaraldehyde, ketone compounds such as diacetyl and chloropentanedione, bis (2-chloroethyl) urea, 2-hydroxy-4,6-dichloro-1 , 3,5-triazine, a compound having a reactive halogen as described in US Pat. No. 3,288,775, divinyl sulfone, a compound having a reactive olefin as described in US Pat. No. 3,635,718, N-methylol compounds as described in US Pat. No. 2,732,316, isocyanates as described in US Pat. No. 3,103,437, US Pat. No. 3,017,280, US Pat. No. 2,983 Aziridine compounds as described in US Pat. No. 611, carbodiimide compounds as described in US Pat. No. 3,100,704 , Epoxy compounds as described in U.S. Pat. No. 3,091,537, halogen carboxaldehydes such as mucochloric acid, dioxane derivatives such as dihydroxydioxane, chromium alum, zirconium sulfate, borax, boric acid and borates. There exist inorganic crosslinking agents etc., and these can be used 1 type or in combination of 2 or more types.

  When a part having a saponification degree of 80% or more or completely saponified polyvinyl alcohol is used as the binder, borax, boric acid and borates are preferable, and boric acid is particularly preferable.

  Moreover, the binder which has a keto group can also be used as a binder which comprises an inorganic fine particle layer. The binder having a keto group can be synthesized by a method of copolymerizing a monomer having a keto group and another monomer, a method of introducing a keto group by a polymer reaction, or the like. Particularly preferred is a modified polyvinyl alcohol having a keto group. Examples of the modified polyvinyl alcohol having a keto group include acetoacetyl-modified polyvinyl alcohol.

  The acetoacetyl-modified polyvinyl alcohol can be produced by a known method such as a reaction between polyvinyl alcohol and diketene. The degree of acetoacetylation is preferably from 0.1 to 20 mol%, more preferably from 1 to 15 mol%. The saponification degree is preferably 80 mol% or more, more preferably 85 mol% or more. The degree of polymerization is preferably 500 to 5000, more preferably 2000 to 4500. It is also possible to use a fully or partially saponified polyvinyl alcohol or cation-modified polyvinyl alcohol and a binder having a keto group.

  In the present invention, the binder having a keto group contained in the inorganic fine particle layer is preferably crosslinked with a crosslinking agent. Such crosslinkers include aliphatic polyamines, alicyclic polyamines, heterocyclic polyamines, aromatic polyamines, polyamide polyamines, polyether polyamines, dicyandiamide derivatives, hydrazine compounds, polyhydrazide compounds, aldehydes, methylol compounds, activity And compounds such as vinyl chloride compounds, epoxy compounds, and polyvalent metal salts. In particular, polyhydrazide compounds and polyvalent metal salts are preferred. Moreover, since it has the same structure as ordinary polyvinyl alcohol except for the portion modified with acetoacetyl or diacetone acrylamide, a hardener can be used in combination. It is particularly preferable to use borax, boric acid, or borate in combination.

  Further, the content of the binder in the inorganic fine particle layer in the present invention is preferably in the range of 1% by mass to less than 50% by mass with respect to the total solid content of the inorganic fine particle layer, and particularly 5 to 40% by mass in the inorganic fine particle layer. It is preferable for forming fine pores and forming a porous layer.

  The inorganic fine particle layer of the present invention contains a cationic compound. As the cationic compound, a cationic polymer and a water-soluble polyvalent metal compound can be preferably used. As a result of the study, the present inventor has found that a recording sheet excellent in curling property can be obtained by adding 10% by mass or more of a cationic compound to the inorganic fine particles in the inorganic fine particle layer. The post-printing property which is an effect of the present invention means that it is easy to handle and bundle the recording sheets after printing, particularly when the recording sheets are taken out from the paper discharge unit. . When the curlability is poor, it is difficult to make the recording sheet bundle uniform by sticking the recording sheets to each other.

  As a method of incorporating the cationic compound into the inorganic fine particle layer, the above-mentioned method of adding as a dispersant when dispersing the inorganic fine particles, the method of adding to the coating solution when preparing the coating solution, the uppermost layer after forming the inorganic fine particle layer A method of applying or spraying a cationic compound before the formation is provided, but is not particularly specified, and any method may be used.

  When adding a cationic compound at the time of dispersion | distribution of an inorganic fine particle, the range of 1-10 mass% with respect to an inorganic fine particle is preferable from a stability viewpoint of a dispersion liquid. In this case, in order to form the inorganic fine particle layer of the present invention, a cationic compound is added so as to be 10% by mass or more before forming the uppermost layer after forming the coating liquid or after forming the inorganic fine particle layer. Good.

  Examples of the cationic polymer include polymers having a primary to tertiary amino group and a quaternary ammonium base that are used when the above-described inorganic fine particles are dispersed.

  As a water-soluble polyvalent metal compound, a water-soluble polyvalent metal salt is a water-soluble metal selected from calcium, barium, manganese, copper, cobalt, nickel, aluminum, iron, zinc, zirconium, chromium, magnesium, tungsten, and molybdenum. Salt. Specifically, for example, calcium acetate, calcium chloride, calcium formate, calcium sulfate, barium acetate, barium phosphate, manganese chloride, manganese acetate, manganese formate dihydrate, manganese ammonium sulfate hexahydrate, cupric chloride , Ammonium copper (II) chloride dihydrate, copper sulfate, cobalt chloride, cobalt thiocyanate, cobalt sulfate, nickel sulfate hexahydrate, nickel chloride hexahydrate, nickel acetate tetrahydrate, nickel ammonium sulfate hexa Hydrate, nickel amidosulfate tetrahydrate, nickel phenolsulfonate, aluminum sulfate, aluminum sulfite, aluminum thiosulfate, polyaluminum chloride, basic polyaluminum hydroxide, aluminum sulfate nonahydrate, aluminum chloride hexahydrate , Ferrous bromide, ferrous chloride, ferric chloride, sulfuric acid Iron, ferric sulfate, zinc bromide, zinc chloride, zinc nitrate hexahydrate, zinc sulfate, zinc phenolsulfonate, zirconium acetate, zirconium chloride, zirconium chloride octahydrate, zirconium hydroxychloride, chromium acetate, Examples include magnesium sulfate, magnesium chloride hexahydrate, magnesium citrate nonahydrate, sodium phosphotungstate, sodium tungsten citrate, 12 tungstophosphoric acid n-hydrate, and the like. Some of them have an inappropriately low pH, and in that case, the pH can be appropriately adjusted and used. In the present invention, the term “water-soluble” means that 1% by mass or more dissolves in water at room temperature and normal pressure. In the present invention, a water-soluble metal salt composed of zirconium and aluminum is preferable. As a water-soluble metal salt composed of zirconium, for example, ZA-30 is commercially available from Daiichi Rare Element Chemical Co., Ltd. The water-soluble metal made of aluminum is, for example, Takibaine # 1500 from Taki Chemical Co., Ltd., Polyaluminum Hydroxide (Paho) from Asada Chemical Co., Ltd., and Riken Green Co., Ltd. It is also sold under the name of Purachem WT and from other manufacturers for the same purpose, and various grades are easily available.

  The cationic compound to be contained in the inorganic fine particle layer in the present invention can be used in combination of two or more, and among them, a cationic polymer having a molecular weight of 20,000 or less is used in an amount of 60% by mass or more based on the total cationic compound. Alternatively, it is particularly preferable to use a cationic compound having a molecular weight of 20,000 or less and a water-soluble polyvalent metal compound in combination. Thereby, a recording sheet superior in toner fixing property can be obtained.

  The content of the cationic compound is 10% by mass or more based on the inorganic fine particles contained in the inorganic fine particle layer. 10-25 mass% is especially more preferable.

  The inorganic fine particle layer further includes preservatives, surfactants, colored dyes, colored pigments, UV absorbers, antioxidants, pigment dispersants, antifoaming agents, leveling agents, fluorescent whitening agents, viscosity stabilizers, pH A regulator or the like can also be added.

Dry coating amount of the inorganic fine particle layer in the present invention is preferably in the range of 0.1 to 50 g / ^{m 2,} the range of 5~35g / ^{m 2} is more preferable.

  The inorganic fine particle layer in the present invention may be composed of two or more layers. In this case, the structures of the image receiving layers may be the same or different from each other.

<Top layer>
The uppermost layer laminated on the inorganic fine particle layer of the present invention mainly contains colloidal silica. Here, to contain mainly means to contain colloidal silica 50 mass% or more with respect to the solid content coating amount of the uppermost layer, More preferably, it contains 60 mass% or more.

  Colloidal silica used in the present invention is, for example, from Nissan Chemical Industries, Ltd. Snowtex ST-20, ST-30, ST-40, ST-C, ST-N, ST-20L, ST-O, ST- OL, ST-S, ST-XS, ST-XL, ST-YL, ST-ZL, ST-OZL, etc., using a commercially available anionic colloidal silica such as the Quartron PL series of Fuso Chemical Industry Co., Ltd. can do. Commercially available cationic colloidal silica that has already been cationized with a water-soluble polyvalent metal compound such as aluminum can also be used. For example, Snowtex ST-AK-L, ST-UP of Nissan Chemical Industries, Ltd. -AK, ST-AK, ST-PS-M-AK, ST-AK-YL, etc.

  The average primary particle size of the colloidal silica used in the uppermost layer of the present invention is preferably 5 to 100 nm, and more preferably 30 to 60 nm in order to obtain good toner fixing property and transferability.

The solid content coating amount of colloidal silica contained in the uppermost layer laminated on the inorganic fine particle layer is preferably 0.05 to 5 g / m ² , and excellent wet toner fixability and excellent wet toner suppressing ghost generation. In order to obtain transferability, the range of 0.5 to 3 g / m ² is more preferable.

  In the present invention, the uppermost layer may contain a binder in order to maintain the properties as a film. As the binder, the same binder as the above-mentioned inorganic fine particle layer can be used, and various water-soluble polymers or polymer latexes are preferably used. As the water-soluble polymer, for example, polyvinyl alcohol, polyethylene glycol, starch, dextrin, carboxymethyl cellulose, polyvinyl pyrrolidone, polyacrylic acid ester and the like and derivatives thereof are used. Particularly preferred organic binders are completely or partially saponified. Of polyvinyl alcohol.

  In the present invention, when the uppermost layer contains a binder having a keto group, it is preferably crosslinked with a crosslinking agent. Such crosslinkers include aliphatic polyamines, alicyclic polyamines, heterocyclic polyamines, aromatic polyamines, polyamide polyamines, polyether polyamines, dicyandiamide derivatives, hydrazine compounds, polyhydrazide compounds, aldehydes, methylol compounds, activity And compounds such as vinyl chloride compounds, epoxy compounds, and polyvalent metal salts. In particular, polyhydrazide compounds and polyvalent metal salts are preferred. Moreover, since it has the same structure as ordinary polyvinyl alcohol except for the portion modified with acetoacetyl or diacetone acrylamide, a hardener can be used in combination. It is particularly preferable to use borax, boric acid, or borate in combination.

  Further, the content of the binder in the uppermost layer in the present invention is preferably in the range of 0 to 40% by mass with respect to the total solid content of the uppermost layer, and particularly 0 to 20% by mass forms fine pores in the uppermost layer. And is preferable for forming a porous layer.

  The top layer further includes preservatives, surfactants, colored dyes, colored pigments, UV absorbers, antioxidants, pigment dispersants, antifoaming agents, leveling agents, fluorescent whitening agents, viscosity stabilizers, pH adjustments. An agent or the like can also be added.

  In the present invention, various known coating methods can be used as the coating method used for coating the toner image-receiving layer. For example, there are a spray gun method, a slide bead method, a slide curtain method, an extrusion method, a slot die method, a gravure roll method, an air knife method, a blade coating method, a rod bar coating method, and the like. The effect of the present invention can be achieved by either sequential coating in which the toner image-receiving layer and the uppermost layer are coated one by one, or simultaneous multilayer coating of both layers, but simultaneous multilayer coating is preferred from the viewpoint of production efficiency.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, the content of this invention is not restricted to an Example. In addition, a part and% show a mass part and mass%.

<Preparation of recording sheet 1>
<Production of polyolefin resin-coated paper>
A 1: 1 mixture of hardwood bleached kraft pulp (LBKP) and hardwood bleached sulfite pulp (LBSP) was beaten to 300 mL with Canadian Standard Freeness to prepare a pulp slurry. As a sizing agent, alkylketene dimer is 0.5% to pulp, polyacrylamide is 1.0% to pulp, and cationized starch is 2.0% to pulp. Polyamide epichlorohydrin resin is 0 to pulp. 0.5% added and diluted with water to give a 0.2% slurry. This slurry was made with a long paper machine to a basis weight of 170 g / m ² , dried and conditioned to a moisture content of 6.0% by mass, and used as a base paper for polyolefin resin-coated paper. A polyethylene resin composition in which 10% of anatase-type titanium is uniformly dispersed with respect to a resin of 100% of low density polyethylene having a density of 0.918 g / cm ³ is melted at 320 ° C. on a base paper made at a thickness of 35 μm. Extrusion-coating was performed, and the surface was extrusion-coated using a cooling roll having a finely roughened surface. Melted at similarly 320 ° C. The blend resin composition of the low density polyethylene resin 30 parts of a density 0.962 g / cm 70 parts high density polyethylene resin of ³ and a density 0.918 g / cm ³ on the other surface, the thickness Extrusion-coating to a thickness of 30 μm, and extrusion coating using a cooling roll having a roughened surface was used as the back surface.

The surface of the polyolefin resin-coated paper was subjected to a high-frequency corona discharge treatment, and then an undercoat layer having the following composition was applied and dried so that gelatin was 50 mg / m ² to prepare a substrate.

<Underlayer>
Lime-processed gelatin 100 parts Sulfosuccinic acid-2-ethylhexyl ester salt 2 parts Chromium alum 10 parts

<Preparation of inorganic fine particle layer and top layer>
The following inorganic fine particle layer coating solution 1 and the following uppermost layer coating solution 1 are applied to the surface of the substrate using a slide bead coating device, the dry coating amount of the inorganic fine particle layer is 8 g / m ² , and the uppermost layer of colloidal silica solid content. Was simultaneously applied so as to be ² g / m ² . After the coating, it was cooled at 10 ° C. for 20 seconds, and then dried by blowing heated air at 30 to 55 ° C.

<Preparation of silica dispersion 1>
3 parts of diallyldimethylammonium chloride homopolymer (molecular weight 9000) and 100 parts of gas phase method silica (average primary particle diameter 7 nm, specific surface area 300 m ² / g) are added to water to prepare a preliminary dispersion, which is then treated with a high-pressure homogenizer. Thus, a silica dispersion having a solid content concentration of 20% was produced. The average secondary particle diameter was 130 nm when measured using a particle size distribution analyzer (LA920, manufactured by Horiba, Ltd.).

<Inorganic fine particle layer coating solution 1>
Silica dispersion 1 (as solids) 103 parts polyvinyl alcohol (saponification degree 88%, average polymerization degree 3500) 35 parts boric acid 6 parts diallyldimethylammonium chloride homopolymer (as solids) 8 parts (Daiichi Kogyo Seiyaku ( Co., Ltd., Charol DC902P, molecular weight 9000, solid content concentration 51.5%)
It adjusted with water so that solid content concentration might be 11%. The amount of inorganic fine particles based on the total solid content is 66%.

<Top layer coating solution 1>
Cationic colloidal silica sol (as solid content) 100 parts (manufactured by Nissan Chemical Industries, Ltd., ST-AK-L, average particle size 40-45 nm)
Polyvinyl alcohol (saponification degree 88%, average polymerization degree 3500) 8 parts Surfactant 0.2 parts (Nonionic; manufactured by Nippon Surfactant Co., Ltd., NIKKOL BT-9)
It adjusted with water so that colloidal silica solid content concentration might be 8%.

<Preparation of recording sheet 2>
A recording sheet 2 was produced in the same manner as the recording sheet 1 except that the uppermost layer of the recording sheet 1 was not provided.

<Preparation of recording sheet 3>
A recording sheet 3 was produced in the same manner as the recording sheet 1 except that the inorganic fine particle layer coating solution 1 of the recording sheet 1 was changed to the following inorganic fine particle layer coating solution 2.

<Inorganic fine particle layer coating solution 2>
Silica dispersion 1 (as solid content) 103 parts Polyvinyl alcohol (saponification degree 88%, average polymerization degree 3500) 35 parts boric acid 6 parts diallyldimethylammonium chloride homopolymer (as solids) 6 parts (Daiichi Kogyo Seiyaku ( Co., Ltd., Charol DC902P, molecular weight 9000, solid content concentration 51.5%)
It adjusted with water so that solid content concentration might be 11%. The amount of inorganic fine particles based on the total solid content is 67%.

<Preparation of recording sheet 4>
A recording sheet 4 was produced in the same manner as the recording sheet 1 except that the inorganic fine particle layer coating solution 1 of the recording sheet 1 was changed to the following inorganic fine particle layer coating solution 3.

<Inorganic fine particle layer coating solution 3>
Silica dispersion 1 (as solid content) 103 parts Polyvinyl alcohol (saponification degree 88%, average polymerization degree 3500) 35 parts boric acid 6 parts diallyldimethylammonium chloride homopolymer (as solid content) 15 parts (Daiichi Kogyo Seiyaku ( Co., Ltd., Charol DC902P, molecular weight 9000, solid content concentration 51.5%)
It adjusted with water so that solid content concentration might be 11%. The amount of inorganic fine particles with respect to the total solid content is 63%.

<Preparation of recording sheet 5>
A recording sheet 5 was prepared in the same manner as the recording sheet 1 except that the inorganic fine particle layer coating solution 1 of the recording sheet 1 was changed to the following inorganic fine particle layer coating solution 4.

<Inorganic fine particle layer coating solution 4>
Silica dispersion 1 (as solids) 103 parts polyvinyl alcohol (saponification degree 88%, average polymerization degree 3500) 35 parts boric acid 6 parts diallyldimethylammonium chloride homopolymer (as solids) 21 parts (Daiichi Kogyo Seiyaku ( Co., Ltd., Charol DC902P, molecular weight 9000, solid content concentration 51.5%)
It adjusted with water so that solid content concentration might be 11%. The amount of inorganic fine particles with respect to the total solid content is 61%.

<Preparation of recording sheet 6>
A recording sheet 6 was prepared in the same manner as the recording sheet 1 except that the inorganic fine particle layer coating solution 1 of the recording sheet 1 was changed to the following inorganic fine particle layer coating solution 5.

<Inorganic fine particle layer coating solution 5>
Silica dispersion 1 (as solids) 103 parts polyvinyl alcohol (saponification degree 88%, average polymerization degree 3500) 35 parts boric acid 6 parts diallyldimethylammonium chloride homopolymer (as solids) 23 parts (Daiichi Kogyo Seiyaku ( Co., Ltd., Charol DC902P, molecular weight 9000, solid content concentration 51.5%)
It adjusted with water so that solid content concentration might be 11%. The amount of inorganic fine particles with respect to the total solid content is 60%.

<Preparation of recording sheet 7>
A recording sheet 7 was produced in the same manner as the recording sheet 1 except that the inorganic fine particle layer coating solution 1 of the recording sheet 1 was changed to the following inorganic fine particle layer coating solution 6.

<Inorganic fine particle layer coating solution 6>
Silica dispersion 1 (as solids) 103 parts polyvinyl alcohol (saponification degree 88%, average polymerization degree 3500) 35 parts boric acid 6 parts diallyldimethylammonium chloride homopolymer (as solids) 8 parts (Daiichi Kogyo Seiyaku ( Co., Ltd., Charol DC303P, molecular weight 30000, solid concentration 41.5%)
It adjusted with water so that solid content concentration might be 11%. The amount of inorganic fine particles based on the total solid content is 66%.

<Preparation of recording sheet 8>
A recording sheet 8 was produced in the same manner as the recording sheet 1 except that the inorganic fine particle layer coating solution 1 of the recording sheet 1 was changed to the following inorganic fine particle layer coating solution 7.

<Inorganic fine particle layer coating solution 7>
Silica dispersion 1 (as solid content) 103 parts Polyvinyl alcohol (saponification degree 88%, average polymerization degree 3500) 35 parts boric acid 6 parts Takibaine # 1500 (as solids content) 10 parts (manufactured by Taki Chemical Co., Ltd.) (Aluminum chloride aqueous solution, solid content concentration 23.5%)
It adjusted with water so that solid content concentration might be 11%. The amount of inorganic fine particles based on the total solid content is 65%.

<Preparation of recording sheet 9>
A recording sheet 9 was produced in the same manner as the recording sheet 1 except that the inorganic fine particle layer of the recording sheet 1 was not provided.

<Preparation of recording sheet 10>
A recording sheet 10 was produced in the same manner as the recording sheet 1 except that the inorganic fine particle layer coating solution 1 of the recording sheet 1 was changed to the following inorganic fine particle layer coating solution 8.

<Inorganic fine particle layer coating solution 8>
Silica dispersion 1 (as solid content) 103 parts Polyvinyl alcohol (saponification degree 88%, average polymerization degree 3500) 35 parts boric acid 6 parts It adjusted with water so that solid content concentration might be 11%. The amount of inorganic fine particles based on the total solid content is 69.4%.

  Table 1 shows the results of evaluating the recording sheets 1 to 10 according to the following evaluation method.

<Fixability: Tape peeling test>
Indigo “E-print 1000” was used as a wet electrophotographic transfer machine, and the fixability of the wet electrophotographic toner was evaluated. As a print image to be used for evaluation, a solid print image was output for each of four colors of black, cyan, magenta, and yellow, and a heavy color obtained by superimposing the four colors. A tape peeling test was performed on the solid print portion of each color printed. In the tape peeling test, a cellophane adhesive tape having a width of 18 mm was applied to the printed portion of each color so as not to be uneven, and the tape was slowly peeled off at a speed of about 5 mm / second at 180 ° peeling. The degree of fixing of the toner after peeling to the sheet was visually determined, and a four-step evaluation was performed according to the following criteria. Immediately after the end of printing, 1 hour later, 4 hours later, and 1 day later, the test was performed under four conditions.

A: The toner does not peel at all for each color.
○: Most of the toner remains on the sheet for each color.
(Triangle | delta): The toner peeled off from the sheet | seat with one part color, and there exists a part which fell out white in the printing part.
X: For each color, the toner is peeled off from the sheet, and a white portion of the printed portion is noticeable.

<Transferability>
After printing using an Indigo press wet electrophotographic transfer machine as a wet electrophotographic transfer machine, the blanket roller was cleaned with a print cleaner, and transferability was judged by how the print cleaner was stained. “Δ” or more was the subject of the invention. The results are shown in Table 1.

○: Not dirty at all.
Δ: Slightly dirty.
X: Dirty.

<Continuous printability>
“HP Indigo Digital Press 5500” manufactured by Hewlett-Packard Company was used as a wet electrophotographic transfer machine, and the occurrence of ghosts after continuous printing was evaluated. At the time of continuous printing, an image in which a white paper portion (non-image portion) and a solid patch of gray and black were arranged was printed, and then a solid gray image was printed on the entire surface to evaluate the occurrence of ghost. The results are shown in Table 1.

○: Ghost is hardly recognized.
Δ: A little ghost is confirmed.
X: Ghost is conspicuous.

<Spring properties>
“HP Indigo Digital Press 5500” manufactured by Hewlett-Packard Co. was used as a wet electrophotographic transfer machine, and the creasability of the recording sheet after printing was evaluated. As an evaluation index, the short side and the long side of the A4 size recording sheet bundle output to the paper discharge tray after continuous printing of 10 sheets are aligned, and the ease of aligning the recording sheet bundle is evaluated according to the following criteria. went. The results are shown in Table 1.

○: Recording sheet bundles are aligned. Alternatively, the recording sheets stick together weakly, but the recording sheet bundle is aligned.
X: The recording sheets stick to each other and the recording sheet bundle is not aligned.

  As is apparent from the above results, a wet electrophotographic recording sheet having excellent toner fixability and transferability, particularly free from ghosting during continuous printing, and excellent in spreading after printing is obtained by the present invention. Can do.

Claims (1)

  A wet electrophotographic recording sheet for transferring an image from a heated blanket roll to a recording sheet, comprising a resin-coated paper having a resin layer on at least one surface of a base paper as a base material, on the resin-coated paper An inorganic fine particle layer mainly containing inorganic fine particles and containing 10% by mass or more of a cationic compound with respect to the inorganic fine particles, and mainly containing colloidal silica on the side farther from the substrate than the inorganic fine particle layer. A wet electrophotographic recording sheet having a toner image-receiving layer comprising the uppermost layer.