JP2013254221A - Wet type electrophotographic printing paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wet type electrophotographic printing paper of a plain paper type that is inexpensive and uncoated, has good transferability of the liquid toner from a transfer drum to the paper and fixability of the liquid toner to the paper in printing using an electrophotographic method using liquid toner, and can be suitably used for printing in an offset printing method or a letterpress printing method that are common commercial printing.SOLUTION: In non-coated wet type electrophotographic printing paper according to the present invention, base paper contains an internally added filler and an internally added sizing agent, and a surface paper strength enhancing agent and an externally added sizing agent are coated on the surface of the base paper. The externally added sizing agent includes an alkyl ketene dimer; the internal added sizing agent is an alkenyl succinic anhydride; and the wet type electrophotographic printing paper has the Gurley air permeability of 40 seconds or less, and the Bekk smoothness of 10 seconds or more.

Description

  The present invention relates to a printing paper used for wet electrophotographic printing. More specifically, when printing using an electrophotographic method using liquid toner, the transfer property of the liquid toner from the transfer drum to the paper, the fixing property of the liquid toner to the paper and the running property are good, and offset printing. The present invention relates to a non-coated plain paper type paper or paperboard wet electrophotographic printing paper that can be suitably used for printing in a printing system or letterpress printing system.

  The main commercial printing is an offset printing system using cast paper, art paper, coated paper, finely coated paper, non-coated plain paper or paperboard. However, in recent years, an on-demand printing method that can handle variable information such as a dry electrophotographic method, a wet electrophotographic method, or an ink jet method has been developed in order to cope with a variety of small lot printing. Among these on-demand printing systems, the wet electrophotographic system is rapidly increasing in demand because an image close to offset printing can be obtained. In order to further expand the field of wet electrophotographic printing in the future, in addition to the suitability of the paper described below, there is not a dedicated paper but a paper that can be easily used at low cost and is generally available for commercial printing. It is important to be able to use it.

  In the wet electrophotographic system, liquid toner developed on a photoreceptor is transferred to a transfer drum, a solvent in the liquid toner is volatilized by heat, and transferred from the transfer drum to paper by heat and pressure to perform printing. Wet electrophotographic printing paper is required to have transferability of liquid toner from the transfer drum to the paper, toner fixability, and paper runnability. If the transfer property of the liquid toner from the transfer drum to the paper is insufficient, problems such as deterioration in operability at the time of printing or occurrence of contamination when the print information is changed for each sheet occur. If the fixability of the liquid toner is weak, the toner may be lost from the printed surface due to rubbing between the printed surfaces after printing.

  As a method for improving the fixability of the liquid toner, a so-called sapphire treatment in which an imine compound is formed on or applied to a sheet has been performed. The sapphire-treated paper is effective for fixing the liquid toner, but has problems such as high manufacturing cost, deterioration in performance with time, and discoloration unlike ordinary paper.

Therefore, several proposals have been made on plain paper type wet electrophotographic printing paper which does not perform sapphire treatment. In order to improve the fixability of the liquid toner, a paper having a surface smoothness measured by Parker Print Surf of 4.7 microns or more and a limited type of internal sizing agent has been proposed (for example, Patent Document 1). See). Also, for the purpose of improving the fixability of liquid toner, the Gurley air permeability is 200 seconds or more, the Bristow method absorption coefficient is 3.2 ml / m ² · ms ^1/2 or less, and measured by Parker Print Surf. Paper having a surface roughness of 6.5 to 10 μm has been proposed (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 10-171148 JP 2001-75303 A

  However, the method described in Patent Document 1 is an attempt to improve the fixability of the liquid toner by roughening the smoothness of the surface, but the obtained paper does not necessarily satisfy the fixability of the liquid toner. Absent. In addition, there is a limitation in the types of sizing agents, and there is a problem that alkyl ketene dimers cannot be used. The paper having a high air permeability of 200 seconds or more as in Patent Document 2 has a problem that the transfer property of the liquid toner from the transfer drum to the paper is deteriorated. To date, there are almost no non-coated plain paper type wet electrophotographic papers that have good transferability of liquid toner from the transfer drum to the paper and good fixability of the liquid toner to the paper. .

  An object of the present invention is that when printing is performed using an electrophotographic system using liquid toner, the transfer property of the liquid toner from the transfer drum to the paper and the fixability of the liquid toner to the paper are good, and the general It is an object of the present invention to provide an inexpensive non-coated plain paper type wet electrophotographic printing paper that can be suitably used for commercial printing offset printing or letterpress printing.

  As a result of intensive studies on the printability of wet electrophotographic printing paper, the present inventors have found that the problem can be achieved by controlling the air permeability and smoothness.

  In the wet electrophotographic printing paper according to the present invention, the base paper contains an internal additive and an internal sizing agent, and the surface of the base paper is coated with a surface paper strength enhancer and an external sizing agent. In the wet electrophotographic printing paper, the external additive sizing agent includes an alkyl ketene dimer, the internal additive sizing agent is alkenyl succinic anhydride, and the Gurley air permeability is 40 seconds or less, and The Beck smoothness is 10 seconds or more.

  In the wet electrophotographic printing paper according to the present invention, the surface paper strength enhancer is at least one of a starch-based surface paper strength enhancer, a polyvinyl alcohol-based surface paper strength enhancer, or a polyacrylamide-based surface paper strength enhancer. It is preferable to include. The transfer property and fixability of the liquid toner can be further improved.

  In the wet electrophotographic printing paper according to the present invention, the filler includes 14 to 100% by mass of calcium carbonate with respect to the total amount of the total filler, and the total mass of the wet electrophotographic printing paper is 100% by mass. When the calcium carbonate content is 4% by mass or more, and the ash content is preferably 4 to 35% by mass. The transfer property and fixability of the liquid toner can be further improved.

  In the wet electrophotographic printing paper according to the present invention, the Gurley stiffness in the transport direction is preferably 1.0 mN or more. When supplying in the form of a single wafer, it is possible to reduce conveyance defects.

  The present invention has good transferability of liquid toner from a transfer drum to paper and fixability of liquid toner to paper when printing using an electrophotographic system using liquid toner, and general commercial printing. It is possible to provide an inexpensive non-coated plain paper type wet electrophotographic printing paper that can be suitably used for printing in the offset printing method or the relief printing method.

  Next, the present invention will be described in detail with reference to embodiments, but the present invention is not construed as being limited to these descriptions. As long as the effect of the present invention is exhibited, the embodiment may be variously modified. The second embodiment is a reference form.

  In the non-coated plain paper type wet electrophotographic printing, the present inventors have improved the air permeability of the paper and smoothness in order to improve the transferability and fixability of the liquid toner to the paper. It was found that it is very important to keep the value within a certain range. Furthermore, when the alkyl ketene dimer is used as a sizing agent, the transferability of the liquid toner may be deteriorated, but it has been found that the adverse effect of the alkyl ketene dimer can be eliminated by increasing the air permeability.

  Increasing the air permeability of the paper means increasing the gaps in the paper. By increasing the gaps, the liquid toner can easily come into contact with the surface of the paper, and the solvent content of the liquid toner can be reduced. It is considered that the transferability and fixability of the liquid toner are improved because it is easily absorbed into the paper. Gurley air permeability (JIS P8117: 2009 “Paper and paperboard—Air permeability and air resistance test method (intermediate region) —Gurley method”)) is an index of air permeability of paper. It is measured by the time to exit, and the smaller the value, the higher the air permeability. Further, the rougher the surface of the paper, the worse the adhesion between the liquid toner and the paper and the worse the transferability and fixability of the liquid toner. Beck smoothness (JIS P8119: 1998 “Smoothness test method using Beck smoothness tester”), which is an index of paper smoothness, is measured by the time when 10 cc of air leaks from the paper surface. The smaller the value, the lower the smoothness. It is considered that the transferability and fixability of the liquid toner are improved by keeping the air permeability and smoothness of the paper within appropriate ranges.

  A sizing agent is usually used for printing paper to control water absorption. In wet electrophotographic printing paper, it is preferable not to use a sizing agent from the viewpoint of improving the transferability and fixability of the liquid toner. However, the surface sizing liquid during papermaking or the dampening water absorbency during offset printing is preferred. In order to control bleeding or to prevent bleeding when writing with a pen or the like, a sizing agent is required. Of the types of sizing agents, alkyl ketene dimers are often used in anticipation of such effects as making the paper surface slippery and reducing deterioration in size. However, alkyl ketene dimers are known to inhibit the transfer of liquid toner to paper. Therefore, when using an alkyl ketene dimer, it is necessary to keep the air permeability of the paper low.

  In the wet electrophotographic printing paper according to the first embodiment, the base paper contains an internal filler and an internal sizing agent, and a surface paper strength enhancer and an external sizing agent are applied to the surface of the base paper. In the non-coated wet electrophotographic printing paper, the external additive sizing agent includes an alkyl ketene dimer, the internal additive sizing agent is alkenyl succinic anhydride, and the Gurley air permeability is 40 seconds or less, And Beck smoothness is 10 seconds or more. By adopting such a configuration, it is possible to obtain a printing paper that maintains the transferability and fixability of the liquid toner and can be suitably used for printing in an offset printing method or a relief printing method.

  In the wet electrophotographic printing paper according to the first embodiment, the Gurley air permeability is 40 seconds or less. More preferably, it is 30 seconds or less. If the Gurley air permeability exceeds 40 seconds, the transferability and fixability of the liquid toner are insufficient. However, the Gurley air permeability is preferably 5 seconds or more. More preferably, it is 10 seconds or more. If the Gurley air permeability is less than 5 seconds, there may be a problem of double feeding in sheet feeding in the vacuum system using air.

  In the wet electrophotographic printing paper according to the first embodiment, the Beck smoothness is 10 seconds or more. More preferably, it is 20 seconds or more. When the Beck smoothness is less than 10 seconds, the transferability and fixability of the liquid toner are insufficient. However, the Beck smoothness is preferably 150 seconds or less. More preferably, it is 120 seconds or less. When high smoothness exceeding 150 seconds is required, it becomes very difficult to control the Gurley air permeability to 80 seconds or less, and the transferability and fixability of the liquid toner may be insufficient.

  Here, as a method of controlling the Gurley air permeability to 40 seconds or less, for example, a method of controlling freeness due to beating of pulp, a method of controlling the linear pressure of a paper machine press, or a method of controlling the linear pressure of a calendar Alternatively, there is a method of controlling by combining these. In addition, it can be controlled by using a bulking agent, a combination of various coating liquids on the surface of the base paper and a combination of coating amounts, or a combination of filler types and blending amounts. Pulp freeness (Canadian standard freeness) (JIS P 8121: 1995 “Pulp freeness test method”) is, for example, 300 to 600 cc when hardwood bleached kraft pulp (LBKP) is used as the pulp. It is preferable. More preferably, it is 350-550cc. If the freeness is less than 300 cc, the Gurley air permeability may be too high. If it exceeds 600 cc, the Gurley air permeability may be too low. In addition, the paper layer strength may decrease, and problems may occur during printing.

  The method for controlling the Beck smoothness to 10 seconds or more is a smoothing process using a known calendar device such as a paper machine press, a machine calendar, a super calendar, or a soft calendar.

In the wet electrophotographic printing paper according to the first embodiment, the surface paper strength enhancer and the external additive sizing agent are applied to the surface of the base paper. The externally added sizing agent includes an alkyl ketene dimer. The external sizing agent is applied to the surface of the base paper, for example, as a coating solution containing the external sizing agent. The coating amount of the external sizing agent is preferably 0.001 to 0.030 g / m ² per one side of the paper in terms of solid content. More preferably, it is 0.005-0.010 g / m < ² >.

  For example, the first embodiment can be modified as follows. In the wet electrophotographic printing paper according to the modified embodiment of the first embodiment, it is preferable that the base paper further contains an internal sizing agent, and the internal sizing agent contains an alkyl ketene dimer. By using an alkyl ketene dimer as the internally added sizing agent and the externally added sizing agent, it is possible to further enhance effects such as the effect of making the paper surface slippery and the deterioration of the size property being small. The content of the internally added sizing agent is preferably 0.01 to 0.10% by mass with respect to the total solid content of the pulp constituting the base paper. More preferably, it is 0.01-0.05 mass%.

  Moreover, it is possible to use together sizing agents other than alkyl ketene dimer as a sizing agent. As the sizing agent that can be used in combination, conventionally known sizing agents can be used, such as rosin sizing agents, alkenyl succinic anhydrides, styrene-acrylic sizing agents, styrene-maleic acid sizing agents, higher fatty acid amide sizing agents, Olefin sizing agent and acrylate sizing agent. As a particularly preferred form, an alkyl ketene dimer is used as the external additive sizing agent, and at least one of rosin sizing agent or alkenyl succinic anhydride is used as the internal additive sizing agent.

  The surface paper strength enhancer is not particularly limited. For example, starch-based surface strength enhancer, polyvinyl alcohol-based surface strength enhancer, polyacrylamide-based surface strength enhancer, urea formaldehyde-based surface strength enhancer. , A melamine formaldehyde surface paper strength enhancer and a polyamide epoxy surface paper strength enhancer. These can be used alone or in combination of two or more. In the wet electrophotographic printing paper according to this embodiment, the surface paper strength enhancer is at least one of a starch-based surface paper strength enhancer, a polyvinyl alcohol-based surface paper strength enhancer, or a polyacrylamide-based surface paper strength enhancer. It is preferable to include. Starch-based surface strength enhancing agents are, for example, oxidized starch, cationized starch, amphoteric starch, grafted starch, phosphate esterified starch, and self-modified starch. Autogenous denaturation is, for example, denaturation by enzymatic or thermochemical action. Examples of the polyvinyl alcohol surface paper strength enhancer include polyvinyl alcohol and modified polyvinyl alcohol. Polyvinyl alcohol includes a fully saponified type, a partially saponified type, and an intermediate saponified type. Examples of the polyacrylamide surface paper strength enhancer include anionic polyacrylamide, nonionic polyacrylamide, and cationic polyacrylamide. Offset printing which is general commercial printing by using at least one of starch-based surface paper strength enhancer, polyvinyl alcohol-based surface strength enhancer or polyacrylamide-based surface strength enhancer in combination. Alternatively, the transferability and fixability of the liquid toner can be further improved while maintaining the surface strength necessary for letterpress printing. In particular, a polyvinyl alcohol-based surface strength enhancer or a polyacrylamide-based surface strength enhancer is preferred, and a combination of a starch-based surface strength enhancer and a polyvinyl alcohol-based surface strength enhancer or a starch-based surface strength enhancer The combined use with a polyacrylamide surface paper strength enhancer is particularly preferred.

The surface on which the surface paper strength enhancer is applied is one side or both sides of the base paper. In the present embodiment, it is preferable to have both sides. The coating amount of the surface paper strength enhancer on the surface of the base paper is preferably 0.05 to 3.00 g / m ² per one side of the paper in terms of solid content. More preferably 0.50~2.50g / ^{m 2.} If it is less than 0.05 g / m ² , problems such as paper peeling at the time of printing including wet electrophotographic printing, powder falling, and peeling of the paper surface layer during paper processing may occur. If it exceeds 3.00 g / m ² , the air permeability may increase, thereby causing problems such as insufficient transferability, insufficient fixability, and stickiness of the liquid toner. Polyvinyl alcohol-based surface strength enhancers are effective in improving the transferability and fixability of liquid toners, but air permeability tends to be low. In terms of minutes, it is preferably 0.05 to 0.75 g / m ² per side of the paper. More preferably, it is 0.05-0.4 g / m < ² >.

  The surface paper strength enhancer is applied to the surface of the base paper, for example, as a coating solution containing the surface paper strength enhancer. The content of the surface paper strength enhancer in the coating solution is preferably 1 to 20% by mass. More preferably, it is 4-15 mass%.

  The coating liquid containing the surface paper strength enhancing agent and the coating liquid containing the external sizing agent may be individually applied to the surface of the base paper, or may be simultaneously applied as a mixed liquid in which both are mixed. When applying individually, the order to apply is not specifically limited. Further, these coating liquids may be appropriately blended with known auxiliaries such as a conductive agent, a cationizing agent, a coloring dye, a coloring pigment, and a fluorescent brightening agent as long as the intended effect of the present invention is not impaired. Good. The means for applying these coating liquids to the base paper surface is not particularly limited, and a known coating machine such as a size press, a gate roll size press, a shim sizer, a rod coater, or an air knife coater may be used. it can.

  In the wet electrophotographic printing paper according to the first embodiment, the base paper contains a filler. As the filler, conventionally known pigments can be used, such as calcium carbonate, talc, kaolin, calcined kaolin, titanium dioxide, and synthetic silica. These may be used alone or in combination of two or more. Among these fillers, calcium carbonate is preferably used in that the fixability of the liquid toner can be further improved. Furthermore, light calcium carbonate is more preferable among calcium carbonates. Since calcium carbonate has a function as an anti-slip agent, it is preferable to use talc, which can be expected to have an effect as a lubricant, in combination with calcium carbonate. The blending ratio of calcium carbonate and talc is preferably 14:86 to 95: 5. More preferably, it is 20: 80-90: 10. The slipperiness of the paper surface can be kept within an appropriate range. Since titanium dioxide has a high effect of preventing image see-through of printing paper, it is preferable to further use titanium dioxide in combination. It is preferable that the compounding quantity of titanium dioxide is 0.5-5 mass% as an ash from the point of an image back-through prevention effect and the point of cost. More preferably, it is 1-3 mass%.

  In the wet electrophotographic printing paper according to the first embodiment, the filler includes 14 to 100% by mass of calcium carbonate with respect to the total amount of the total filler, and the total mass of the wet electrophotographic printing paper is 100% by mass. When the calcium carbonate content is 4% by mass or more, and the ash content is preferably 4 to 35% by mass. The transfer property and fixability of the liquid toner can be further improved.

  The ash content is preferably 4 to 35% by mass when the total mass of the wet electrophotographic printing paper is 100% by mass. More preferably, it is 6-33 mass%. If the ash content is less than 4% by mass, the transferability and fixability of the liquid toner may be weakened. If the ash content exceeds 35% by mass, the effect of improving the transferability and fixability of the liquid toner is saturated and the surface strength is lowered, which may cause problems such as paper peeling and powder falling.

  Since calcium carbonate easily absorbs the residual solvent of the liquid toner transferred to the surface of the paper, the transferability and fixability of the liquid toner can be further improved by adding calcium carbonate. It is preferable that calcium carbonate is 14-100 mass% with respect to the total amount of all the fillers. More preferably, it is 20-100 mass%. When the content of calcium carbonate with respect to the total amount of filler is less than 14% by mass, the transferability and fixability of the liquid toner may be weakened. The content of calcium carbonate in the entire paper is preferably 4% by mass or more. If it is less than 4% by mass, the transferability and fixability of the liquid toner may be weakened. However, the content of calcium carbonate with respect to the entire paper is preferably set to 35% by mass or less because there is a risk that the surface strength of the base paper is reduced or the papermaking wire is quickly worn. More preferably, it is 25 mass% or less.

  In the wet electrophotographic printing paper according to the first embodiment, the Gurley stiffness (JAPAN TAPPI No. 40: 2000) in the transport direction when the wet electrophotographic printing machine is supplied in the form of a sheet is 1 It is preferably 0.0 mN or more. More preferably, it is 1.5 mN or more. Gurley stiffness is an indicator of paper and paperboard runnability. In the wet electrophotographic system, paper may be supplied in the form of a sheet. When supplying in the form of a single sheet, if the rigidity of the paper in the conveyance direction is weak, a conveyance failure occurs when the paper is supplied. By supplying a Gurley stiffness of 1.0 mN or more, the sheet was supplied in the form of a single sheet. In this case, it is possible to supply a printing sheet with little conveyance failure. If the Gurley stiffness is less than 1.0 mN, a problem of conveyance failure may occur when the paper is supplied to the transfer drum. The Gurley stiffness is preferably 40 mN or less. More preferably, it is 30 mN or less.

  As the base paper, paper containing raw pulp is mainly used. Examples of the raw material pulp include chemical pulp such as LBKP (hardwood bleached kraft pulp), NBKP (softwood bleached kraft pulp), GP (crushed wood pulp), PGW (pressurized groundwood pulp), RMP (refiner mechanical pulp), TMP ( Thermo-mechanical pulp), CTMP (chemi-thermomechanical pulp), CMP (chemi-mechanical pulp), mechanical pulp such as CGP (chemi-ground pulp), wood pulp such as DIP (deinked pulp) and kenaf, bagasse, bamboo, cotton, etc. Non-wood pulp. These can be used alone or in admixture at any ratio. In addition, a synthetic fiber can be further blended within a range that does not impair the intended effect of the present invention. From the viewpoint of environmental conservation, ECF (Elemental Chlorine Free) pulp, TCF (Totally Chlorine Free) pulp, DIP, and pulp obtained from planted trees are more preferable.

  The raw material pulp is made into a pulp slurry having a suitable degree of freeness by using a disintegrator and a beater. The pulp slurry is prepared by blending a filler and an internal sizing agent. Paper materials include wet paper strength enhancers, internal paper strength enhancers such as dry paper strength enhancers, bulking agents, yield improvers, drainage improvers, sulfuric acid bands, cationizing agents, colored dyes, colored pigments, It is possible to further mix known auxiliaries such as a fluorescent brightening agent and a fluorescent decoloring agent as long as the effects of the present invention are not impaired.

  Paper is made with a paper machine to make a base paper. The paper making method is not particularly limited, and various types such as long net paper machine, long net multilayer paper machine, circular net paper machine, circular net multilayer paper machine, long net circular net combination multilayer paper machine, twin wire paper machine, etc. Can be manufactured with equipment. The papermaking method is not particularly limited, and either acidic papermaking or neutral papermaking can be selected. However, when a high amount of calcium carbonate is added as a filler, neutral papermaking is preferable.

The basis weight of base paper is not particularly limited, is preferably 40~350g / ^{m 2,} more preferably 80~300g / ^{m 2.}

  The method for producing a wet electrophotographic printing paper according to the first embodiment includes a stock preparation step, a paper making step, a surface size step, and a calendar step. The paper stock preparation step is a step of preparing a paper stock by blending a pulp slurry obtained by appropriately beating the raw material pulp with a filler and, if necessary, an internally added sizing agent and an auxiliary agent. The paper making process is a process of making a base paper by making paper with a paper machine. The surface sizing step is a step of applying a coating solution containing a surface paper strength enhancer and a coating solution containing an external sizing agent to the surface of the base paper. A calendar process is a process of smoothing the surface of a paper using a calendar device. In this manner, the wet electrophotographic printing paper according to the present embodiment can be manufactured at low cost because it does not perform processing steps such as a coating step.

  The first embodiment is a form in which an externally added sizing agent is essential, but the present invention is not limited to the means for applying the sizing agent to the base paper. In the wet electrophotographic printing paper according to the second embodiment, the base paper contains a filler and an internal sizing agent, and the surface of the base paper is coated with a surface paper strength enhancer for non-coating wet electrophotography. In the printing paper, the internal sizing agent contains an alkyl ketene dimer, the Gurley air permeability is 40 seconds or less, and the Beck smoothness is 10 seconds or more. The difference between the wet electrophotographic printing paper according to the first embodiment and the wet electrophotographic printing paper according to the second embodiment is that a sizing agent containing an alkyl ketene dimer is applied to the base paper as an external sizing agent. Or (first embodiment) or applied to the base paper as an internal sizing agent (second embodiment). Therefore, the wet electrophotographic printing paper according to the second embodiment is the configuration of the base paper, the type and content of the filler, the type and content of the sizing agent, the type and content of the surface paper strength enhancer. This is equivalent to the wet electrophotographic printing paper according to the first embodiment. In addition, as with the wet electrophotographic printing paper according to the first embodiment, by appropriately controlling the Gurley air permeability and Beck smoothness, the effect of improving the transferability and fixability of the liquid toner to the paper Play. Moreover, there exists an effect which makes driving | running | working property favorable by controlling Gurley rigidity appropriately.

  The wet electrophotographic printing paper manufacturing method according to the second embodiment includes an internal sizing agent as an essential component in the stock preparation step, and does not apply a coating solution containing an external sizing solution in the surface sizing step. Except this, it is the same as the manufacturing method of the wet electrophotographic printing paper according to the first embodiment.

  The wet electrophotographic printing paper according to the first embodiment, the modified embodiment and the second embodiment is not limited to use as a wet electrophotographic printing paper, but is a recording paper for a dry electrophotographic copying machine / printer, an inkjet system Can be used as recording paper.

  Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” and “%” represent “parts by mass” and “mass%”, respectively, unless otherwise specified. The number of added parts is a value in terms of solid content.

  The obtained wet electrophotographic printing paper was tested based on the following evaluation method.

(Gurley air permeability)
Measured according to JIS P8117: 2009.

(Beck smoothness)
Measured according to JIS P8119: 1998.

(Total ash)
Measured according to JIS P8251: 2003 “Paper, paperboard and pulp-ash content test method—525 ° C. combustion method”.

(Gurley stiffness)
JAPAN TAPPI No. 40: Measured according to 2000.

(Freeness)
Measured according to JIS P8121: 1995.

  About the obtained wet electrophotographic printing machine, running property, liquid toner transferability, and liquid toner fixability were evaluated by the following methods. For the evaluation, “HP Indigo 5500 Digital Press” manufactured by HP was used as a wet photographic printer, and a black, cyan, magenta and yellow four-color single-color printing solid was used using a paper having a width of 320 mm and a length of 460 mm. The image containing it was printed.

(Runability)
The total number of conveyance failures when 1000 sheets were printed twice was measured.
A: The number of conveyance defects is 0 (practical level).
○: The number of conveyance failures is 1 (practical level).
(Triangle | delta): The frequency | count of conveyance defect is 2 times (practical upper and lower limit level).
X: The number of conveyance failures is 3 or more (practical level).

(Liquid toner transferability)
The remaining state of the toner on the transfer drum after printing 6000 sheets was visually evaluated.
A: The transfer drum is free from toner contamination and is good (practical level).
○: The transfer drum is almost free of toner contamination and is good (practical level).
Δ: Toner is slightly stained on the transfer drum, but there is no practical problem (practical lower limit level).
X: The toner is very dirty on the transfer drum (impractical level).

(Liquid toner fixability)
After printing, an adhesive tape (Cello Tape (registered trademark) R, manufactured by Nichiban Co., Ltd.) was attached to each color solid portion of the printed sample after 24 hours, and the adhesive tape was peeled off at a speed of about 5 mm / second by 180 ° peeling. The fixing degree of the liquid toner on the paper surface after peeling was visually evaluated.
A: There is no adhesion of liquid toner to the adhesive tape, and the print density of the peeled-off adhesive tape remains unchanged (practical level).
◯: Some liquid toner is taken on the adhesive tape, but the print density of the adhesive tape peeling trace is hardly changed (practical level).
(Triangle | delta): Although liquid toner is taken up to the adhesive tape and the printing density of the peeling trace of an adhesive tape has fallen a little, there is no problem practically (practical lower limit level).
X: A large amount of liquid toner adheres to the adhesive tape, and a white portion is generated in the peeling trace of the adhesive tape (practically impossible level).

  Next, with respect to the obtained wet electrophotographic printing paper, the printing durability as an offset printing suitability was evaluated by the following method.

(Press life)
Using “Lilithon 40 (L-40)” manufactured by Komori as an offset printing machine, printing four colors with black, indigo, red and yellow ink at a printing speed of 8500 sheets / hour, and improving printing durability evaluated.
(Double-circle): There is almost no dirt of a blanket and it is good (practical level).
○: There is some dirt on the blanket, but there is almost no omission in the image area, which is good (practical level).
(Triangle | delta): There are many stain | pollution | contaminations of a blanket and there is omission of an image line part (practical use lower limit level).
X: The blanket is severely soiled and the image area is often missing (practically impossible).

Example 1
100 parts of LBKP bleached with ECF as a pulp was beaten to 450 ml of freeness to obtain a pulp slurry, and 1.0 part of cationized starch (Neotack 30T: manufactured by Nippon Food Processing Co., Ltd.) as an internal paper strength enhancer and a filler As calcium carbonate (TP121: manufactured by Okutama Kogyo Co., Ltd.) and 15 parts of talc (talc NTL: manufactured by Nippon Talc Co., Ltd.), and alkenyl succinic anhydride (AS1523: manufactured by Seiko PMC Co.) as an internal sizing agent, Then, 1 part of a sulfuric acid band was added to prepare a paper stock. This stock was made with an on-top twin-wire paper machine to obtain a base paper. Next, in a gate roll apparatus, as a surface sizing solution, a 12% solution of oxidized starch (Ace A: manufactured by Oji Cornstarch) as a surface paper strength enhancer and an alkyl ketene dimer (SE2380: manufactured by Seiko PMC) as an external sizing agent The mixed solution in which the 0.1% solution was mixed was applied so that the coating amount per both sides of the base paper was 2 g / m ² solid mass (1 g / m ² per side) and dried. Then, it planarized with the machine calendar and obtained the printing paper for wet electrophotography with a basic weight of 105 g / m < ² >. The Gurley air permeability was 28 seconds, and the Beck smoothness was 40 seconds. The content of calcium carbonate with respect to the total mass of the paper was 4.4%.

(Example 2)
In Example 1, except that the freeness was changed to 300 ml, the press linear pressure adjustment and the machine calendar adjustment were changed to Gurley air permeability of 36 seconds and Beck smoothness of 103 seconds, and the basis weight was changed to 82 g / m ² . Wet electrophotographic printing paper was obtained under the same conditions as described in Example 1. The content of calcium carbonate with respect to the total mass of the paper was 4.6%.

(Example 3)
In Example 1, except that the freeness was changed to 550 ml, the press linear pressure adjustment and the machine calendar adjustment were changed to Gurley air permeability 12 seconds and Beck smoothness 18 seconds, and the basis weight was changed to 205 g / m ² . Wet electrophotographic printing paper was obtained under the same conditions as described in Example 1. The content of calcium carbonate with respect to the total mass of the paper was 4.7%.

(Reference Example 4)
In Example 1, the internal sizing agent was changed to 0.05 part of alkyl ketene dimer (size pine K-287: manufactured by Arakawa Chemical Industries, Ltd.), and the Gurley air permeability was 22 seconds by adjusting the press line pressure and adjusting the machine calendar. A wet electrophotographic printing paper was obtained under the same conditions as described in Example 1 except that the Beck smoothness was changed to 47 seconds. The content of calcium carbonate with respect to the total mass of the paper was 4.3%.

(Example 5)
In Example 1, the surface sizing solution was externally added with a 10% solution of oxidized starch (Ace A: manufactured by Oji Cornstarch) and a 2% solution of modified polyacrylamide (ST-5000: manufactured by Seiko PMC) as a surface paper strength enhancer. The sizing agent was changed to a mixture of 0.1% liquid alkyl ketene dimer (SE2380: manufactured by Seiko PMC), and Gurley permeability was adjusted to 29 seconds and Beck smoothness to 33 seconds by adjusting the press linear pressure and machine calendar. Except for the change, wet electrophotographic printing paper was obtained under the same conditions as described in Example 1. The content of calcium carbonate relative to the total mass of the paper was 4.5%.

(Reference Example 6)
In Example 1, the internal sizing agent was changed to 0.2 parts by mass of a neutral rosin sizing agent (CC1401: manufactured by Seiko PMC Co., Ltd.). A wet electrophotographic printing paper was obtained under the same conditions as described in Example 1 except that the smoothness was changed to 20 seconds. The content of calcium carbonate with respect to the total mass of the paper was 4.2%.

(Example 7)
In Example 1, the surface sizing solution was externally added with a 10% solution of oxidized starch (Ace A: manufactured by Oji Cornstarch) and a 2% solution of modified polyacrylamide (ST-5000: manufactured by Seiko PMC) as a surface paper strength enhancer. The sizing agent was changed to a mixture of 0.1% liquid alkyl ketene dimer (SE2380: manufactured by Seiko PMC), the surface sizing liquid coating device was changed to a two-roll size press, and the coating amount was changed to the base paper. sided total solid weight 5.5 g / ^{m 2} (per side, 2.75 g / ^{m 2)} of the change, by the press line pressure adjustment and machine calender adjustment, Gurley 30 s, was changed to Bekk smoothness 26 seconds Except for the above, wet electrophotographic printing paper was obtained under the same conditions as described in Example 1. The content of calcium carbonate relative to the total mass of the paper was 4.5%.

(Example 8)
In Example 7, the pulp was changed to 50 parts of EBK-bleached LBKP and 50 parts of bleached DIP. PVA-117 (manufactured by Kuraray Co., Ltd.) was changed to a mixed liquid of 1% liquid and alkyl ketene dimer (SE2380: manufactured by Seiko PMC) as an external sizing agent, and the press linear pressure adjustment and machine calendar adjustment were performed. A wet electrophotographic printing paper was obtained under the same conditions as described in Example 7, except that the Gurley permeability was changed to 35 seconds and the Beck smoothness was changed to 33 seconds. The content of calcium carbonate with respect to the total mass of the paper was 4.6%.

(Reference Example 9)
In Reference Example 6, the filler was changed to 15 parts of calcium carbonate (TP121: manufactured by Okutama Kogyo Co., Ltd.) and 1 part of talc (talc NTL: manufactured by Nihon Talc Co., Ltd.), and the Gurley air permeability was adjusted by adjusting the press line pressure and machine calendar. A wet electrophotographic printing paper was obtained under the same conditions as described in Reference Example 6 except that the time was changed to 22 seconds and Beck smoothness of 35 seconds. The content of calcium carbonate relative to the total mass of the paper was 13.0%.

(Reference Example 10)
In Reference Example 6, the filler was changed to 17 parts of calcium carbonate (TP121: manufactured by Okutama Kogyo Co., Ltd.) and 17 parts of talc (talc NTL: manufactured by Nihon Talc Co., Ltd.), and Gurley air permeability was adjusted by adjusting the press line pressure and machine calendar. A wet electrophotographic printing paper was obtained under the same conditions as described in Reference Example 6 except that the seconds were changed to 23 seconds and the Beck smoothness was changed to 52 seconds. The content of calcium carbonate relative to the total mass of the paper was 15.3%.

(Reference Example 11)
In Reference Example 6, the filler was changed to 5 parts of calcium carbonate (TP121: manufactured by Okutama Kogyo Co., Ltd.) and 1 part of talc (talc NTL: manufactured by Nihon Talc Co., Ltd.), and Gurley air permeability was adjusted by adjusting the press line pressure and machine calendar. A wet electrophotographic printing paper was obtained under the same conditions as described in Reference Example 6 except that the setting was changed to 34 seconds and Beck smoothness of 23 seconds. The content of calcium carbonate with respect to the total mass of the paper was 4.2%.

(Reference Example 12)
In Reference Example 6, the filler was changed to 17 parts of calcium carbonate (TP121: manufactured by Okutama Kogyo Co., Ltd.) alone, and Gurley permeability was changed to 20 seconds and Beck smoothness was changed to 35 seconds by press linear pressure adjustment and machine calendar adjustment. Except for the above, wet electrophotographic printing paper was obtained under the conditions described in Reference Example 6. The content of calcium carbonate relative to the total mass of the paper was 14.8%.

(Reference Example 13)
In Reference Example 6, the filler was changed to 2 parts of calcium carbonate (TP121: manufactured by Okutama Kogyo Co., Ltd.) and 12 parts of talc (talc NTL: manufactured by Nihon Talc Co., Ltd.), and Gurley air permeability was adjusted by adjusting the press line pressure and machine calendar. A wet electrophotographic printing paper was obtained under the same conditions as described in Reference Example 6 except that the time was changed to 37 seconds and the Beck smoothness was changed to 32 seconds. The content of calcium carbonate relative to the total mass of the paper was 1.8%.

(Reference Example 14)
In Reference Example 13, the surface sizing solution was a modified polyacrylamide (ST-5000: manufactured by Seiko PMC) 4% solution as a surface paper strength enhancer, and an alkyl ketene dimer (SE2380: manufactured by Seiko PMC) as an external sizing agent. Change to a mixed solution with 1% liquid, change the coating amount of the surface sizing liquid to 0.7 g / m ² solid mass per side of the base paper (0.35 g / m ² per side), press linear pressure A wet electrophotographic printing paper was obtained under the same conditions as described in Reference Example 13 except that the Gurley permeability was changed to 24 seconds and the Beck smoothness was changed to 31 seconds by adjustment and machine calendar adjustment. The content of calcium carbonate with respect to the total mass of the paper was 1.6%.

(Reference Example 15)
In Reference Example 6, the filler was changed to 3 parts of calcium carbonate (TP121: manufactured by Okutama Kogyo Co., Ltd.) alone and changed to Gurley permeability 30 seconds and Beck smoothness 23 seconds by press linear pressure adjustment and machine calendar adjustment. Except for the above, wet electrophotographic printing paper was obtained under the conditions described in Reference Example 6. The content of calcium carbonate relative to the total mass of the paper was 2.4%.

(Example 16)
In Example 1, the wet electrophotographic printing paper was subjected to the same conditions as described in Example 1 except that the Gurley permeability was changed to 5 seconds and the Beck smoothness was changed to 10 seconds by press linear pressure adjustment and machine calendar adjustment. Obtained. The content of calcium carbonate with respect to the total mass of the paper was 4.4%.

(Reference Example 17)
In Example 1, the internal sizing agent was changed to 0.05 part of alkyl ketene dimer (size pine K-287: manufactured by Arakawa Chemical Industries, Ltd.), and as a surface sizing solution, oxidized starch (ACE A) as a surface paper strength enhancer. : Oji Cornstarch Co., Ltd.) A wet electrophotographic printing paper was obtained under the same conditions as described in Example 1 except that 12% solution was used. The Gurley air permeability and Beck smoothness were the same as in Example 1. The content of calcium carbonate relative to the total mass of the paper was 4.1%.

(Comparative Example 1)
Wet electrophotographic printing under the same conditions as described in Example 1, except that the freeness was changed to 250 ml, and the Gurley permeability was changed to 55 seconds and the Beck smoothness to 68 seconds by adjusting the press linear pressure and machine calendar. Got the paper.

(Comparative Example 2)
Wet electrophotographic printing under the same conditions as described in Example 1 except that the freeness was changed to 620 ml and the Gurley permeability was changed to 15 seconds and the Beck smoothness was changed to 7 seconds by adjusting the press linear pressure and machine calendar. Got the paper.

(Comparative Example 3)
Wet electrophotographic printing under the same conditions as described in Example 8 except that the freeness was changed to 250 ml and the Gurley permeability was changed to 43 seconds and the Beck smoothness was changed to 8 seconds by adjusting the press linear pressure and machine calendar. Got the paper.

(Comparative Example 4)
Wet sizing was carried out under the same conditions as described in Reference Example 4 except that the surface sizing liquid was changed to no application and the press linear pressure adjustment and machine calender adjustment were changed to Gurley air permeability of 26 seconds and Beck smoothness of 31 seconds. A photographic printing paper was obtained.

(Comparative Example 5)
As described in Example 1, except that the freeness was changed to 620 ml, the press linear pressure adjustment and the machine calendar adjustment were changed to Gurley air permeability 6 seconds and Beck smoothness 8 seconds, and the basis weight was changed to 64 g / m ^2. Under the same conditions, a wet electrophotographic printing paper having a Gurley stiffness of 0.903 mN was obtained. The content of calcium carbonate with respect to the total mass of the paper was 4.1%.

  By comparing Examples 1-3, 5, 7, 8, 16, Reference Examples 4, 6, 9-15, 17 and Comparative Examples 1-3, 5, the Gurley permeability was set to 40 seconds or less. It was confirmed that the transferability and fixability of the liquid toner were good by setting the smoothness to 10 seconds or more. Further, by comparing Examples 1 to 3, 5, 7, 8, 16 and Reference Examples 4, 6, 9 to 15, 17 and Comparative Example 4, a surface sizing liquid containing a surface paper strength enhancer was obtained. It was confirmed that by applying to the base paper surface, the liquid toner transferability and fixability can be combined with the offset printing suitability.

  By comparing Reference Examples 6 and 9 to 12 and Reference Examples 13 to 15, the blending ratio of calcium carbonate in the total filler is 14 to 100% by mass, the ash content is 4 to 35% by mass, and calcium carbonate It was confirmed that the transferability and the fixability of the liquid toner were good by making the addition ratio of 4 mass% or more.

  Comparing Example 1 and Reference Example 17, the alkyl ketene dimer has a transfer property and a fixing property of the liquid toner regardless of whether the alkyl ketene dimer is blended as an internal sizing agent or an external sizing agent. It was confirmed that good paper was obtained.

  By comparing Examples 1 to 3, 5, 7, 8, 16 and Reference Examples 4, 6, 9 to 15, 17 and Comparative Example 5 with a Gurley stiffness of 1 mN or more, a single wafer is supplied. It was confirmed that the running performance was good.

  As is apparent from Table 1, the surface paper strength enhancer is applied to the surface of the base paper, and the Gurley air permeability and Beck smoothness are controlled so that the liquid toner has good transferability and fixability, and commercial printing. It was possible to obtain a wet electrophotographic printing paper having the offset printing aptitude which is the main body of the above. Further, by setting the Gurley stiffness to 1 mN or more, it was possible to obtain a wet electrophotographic printing paper with good running performance on a sheet.

Claims (4)

The base paper contains an internal filler and an internal sizing agent,
In a non-coated wet electrophotographic printing paper in which a surface paper strength enhancer and an external additive sizing agent are applied to the surface of the base paper,
The external additive sizing agent includes an alkyl ketene dimer,
The internally added sizing agent is alkenyl succinic anhydride,
A wet electrophotographic printing paper having a Gurley air permeability of 40 seconds or less and a Beck smoothness of 10 seconds or more.   The said surface paper strength enhancer contains at least 1 sort (s) of a starch type surface strength enhancer, a polyvinyl alcohol type surface strength enhancer, or a polyacrylamide type surface strength enhancer. Wet electrophotographic printing paper. As the filler, 14 to 100% by mass of calcium carbonate with respect to the total amount of all fillers,
When the total mass of the wet electrophotographic printing paper is 100% by mass, the content of calcium carbonate is 4% by mass or more, and the ash content is 4 to 35% by mass. Item 3. The wet electrophotographic printing paper according to Item 1 or 2.   The wet electrophotographic printing paper according to any one of claims 1 to 3, wherein the Gurley stiffness in the transport direction is 1.0 mN or more.