JP2013011752A - Sheet for wet electrophotographic printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive non-coating plain paper-type sheet for wet electrophotographic printing, the sheet favorable in transfer property for a liquid toner from a transfer drum to the sheet, fixing property for a liquid toner to the sheet and traveling property during printing by a wet electrophotographic process and capable of being suitably used for general commercial printing.SOLUTION: The sheet for wet electrophotographic printing is a non-coating sheet having a support medium containing pulp and filler. When a flat surface of a prism is pressed to at least one surface of the sheet for wet electrophotographic printing under the conditions (Condition 1) of 3.4 MPa of pressure and 0.02 second of clamping time to classify the surface state of the sheet into a contact part including a minute non-contact part having an area of less than 0.16 mmand a non-contact part having an area of 0.16 mmor more, 'a total area rate (I) of the non-contact part', which represents a proportion of the total area of the non-contact part with respect to the measured area, is 0.05% or more and 1.8% or less. The sheet has a thickness of 70 to 300 μm.

Description

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

  The main commercial printing is offset printing using cast paper, art paper, coated paper, finely coated paper, uncoated plain paper type paper or paperboard. However, in recent years, an on-demand printing method capable of handling 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 methods, the wet electrophotographic method is rapidly increasing in demand because an image close to offset printing can be obtained. In order to further grow the field of wet electrophotographic printing in the future, in addition to the suitability of the paper described below, there is a paper that can be suitably used for general commercial printing that is inexpensive and easily available, instead of dedicated paper. 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, and printing is performed by transferring the liquid toner from a transfer drum to paper by pressure or the like. Wet electrophotographic printing paper is required to have transferability of liquid toner from the transfer drum to the paper, fixability of liquid toner, and paper runnability. If the transferability of the liquid toner is insufficient, problems such as deterioration in operability at the time of printing or occurrence of stains 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 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. For the purpose of improving the fixability of 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).

  In the wet electrophotographic system, paper may be supplied in the form of a sheet. When supplying in sheet form, unlike dry electrophotography, if the paper thickness is outside the proper range, the bending suitable for the printing press cannot be obtained, and as a result, the paper peels off from the transfer drum. Transport failure or storage failure of the delivery unit occurs.

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

  However, the paper obtained by the method described in Patent Document 1 does not satisfy the fixability of the liquid toner. Furthermore, there is a problem that an alkyl ketene dimer cannot be used as an internal sizing agent. Further, in a paper having a high air permeability of 200 seconds or more as in Patent Document 2, there arises a problem that transferability of the liquid toner from the blanket to the paper is deteriorated.

  An object of the present invention is to solve the above-mentioned problems, and to transfer liquid toner from a transfer drum to paper, fixability of liquid toner to paper, when printing using an electrophotographic method using liquid toner, and An inexpensive non-coated plain paper type wet electrophotographic printing paper that has good running properties and can be suitably used for printing in a general commercial printing offset printing method or letterpress printing method is supplied. That is.

The present inventors have found that the problem can be achieved by limiting the irregularities on the surface of the paper to a specific size. That is, the wet electrophotographic printing paper according to the present invention is a non-coated wet electrophotographic printing paper in which the support contains pulp and filler, on at least one surface of the wet electrophotographic printing paper (condition 1). ), The flat surface of the prism is pressed and classified into a contact portion including a minute non-contact portion having an area of less than 0.16 mm ² and a non-contact portion having an area of 0.16 mm ² or more. “Total area ratio (I) of non-contact parts” (hereinafter, the total area ratio (I) may be referred to as MA value (I)) indicating the ratio of the total area of the non-contact parts to 0.05% is 0.05%. It is not less than 1.8% and has a thickness of 70 to 300 μm.
(Condition 1) Pushing pressure 3.4 MPa and clamping time 0.02 seconds

In the wet electrophotographic printing paper according to the present invention, the flat surface of the prism is pressed against at least one surface of the wet electrophotographic printing paper in accordance with (Condition 2), and the contactless surface has an area of less than 0.16 mm ^2. The ratio of the total area of the non-contact part to the measurement part area when classified into the contact part including the part and the non-contact part having an area of 0.16 mm ² or more “total area ratio of the non-contact part (II) (Hereinafter, the value of the total area ratio (II) may be referred to as MA value (II)) is preferably 0.8% or less. Image reproducibility can be further improved by increasing the pressure at which the paper and the transfer drum are brought into contact with each other.
(Condition 2) Pressing pressure 3.4 MPa and clamping time 0.10 seconds

  In the wet electrophotographic printing paper according to the present invention, a surface size solution is applied to the surface of the support, and the surface size solution is a starch-based surface paper strength enhancer, a polyvinyl alcohol-based surface paper strength enhancer, or a poly It is preferable to include at least one of acrylamide-based surface paper strength enhancers. While maintaining the surface strength necessary for general commercial printing such as offset printing or letterpress printing, the transferability and fixability of the liquid toner can be further improved.

  In the wet electrophotographic printing paper according to the present invention, when the filler contains 20 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, The ash content is preferably 4 to 35% by mass, and the calcium carbonate content is preferably 4% by mass or more. The fixability of the liquid toner can be further improved.

  In the wet electrophotographic printing paper according to the present invention, the pulp preferably contains hardwood bleached kraft pulp (LBKP), and the Canadian standard freeness (CSF) of the LBKP is preferably 300 to 600 ml. The MA value (I) can be easily controlled within an appropriate range, and the transferability and fixability of the liquid toner can be improved.

  In the wet electrophotographic printing paper according to the present invention, the blending ratio of the mechanical pulp in the pulp is preferably 20% by mass or less. The MA value (I) can be easily controlled within an appropriate range, and the transferability and fixability of the liquid toner can be improved.

The wet electrophotographic printing paper according to the present invention preferably has a density (JIS P 8118: 1998) of 0.77 to 0.95 g / cm ³ . The MA value (I) can be easily controlled within an appropriate range, and the transferability and fixability of the liquid toner can be improved.

  In the wet electrophotographic printing paper according to the present invention, the blending ratio of the bulking agent in the pulp is preferably 0.2 to 1.5% by mass. The MA value (I) can be easily controlled within an appropriate range.

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

  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 wet electrophotographic printing paper according to the present embodiment is a non-coated wet electrophotographic printing paper in which the support contains pulp and filler. According to (Condition 1), at least one surface of the wet electrophotographic printing paper is used. When the flat surface of the prism is pressed and classified into a contact part including a minute non-contact part having an area of less than 0.16 mm ² and a non-contact part having an area of 0.16 mm ² or more, The “total area ratio (I) of non-contact portion” indicating the ratio of the total area of the contact portion is 0.05% or more and 1.8% or less, and the thickness is 70 to 300 μm.
(Condition 1) Pushing pressure 3.4 MPa and clamping time 0.02 seconds

  By setting the thickness of the paper within a certain range, it is possible to maintain the running property and cushioning property of the paper, and to improve the transferability of the liquid toner from the transfer drum to the paper. The wet electrophotographic printing paper according to this embodiment has a thickness of 70 to 300 μm. More preferably, it is 80-250 micrometers. When the thickness is less than 70 μm, poor running such as corner breakage and jamming occurs. Further, the cushioning property is insufficient, the adhesion between the paper and the transfer drum is insufficient, and the transfer of the liquid toner is deteriorated. When the thickness exceeds 300 μm, the paper is not bent appropriately and cannot be stored in the sorter after printing. Further, in the vacuum system using air, there is a case where the sheet is not conveyed by feeding the sheet.

  When the MA value (I) exceeds 1.8%, the surface of the paper has many large dents and the adhesion between the paper and the transfer drum is insufficient. As a result, the transfer of the liquid toner is deteriorated, and the image reproducibility is further deteriorated. More preferably, the MA value (I) is 1.5% or less. More preferably, the MA value (I) is 1.3% or less. The lower limit of the MA value (I) is 0.05%. The lower limit value of the MA value (I) is more preferably 0.1%. In order for the MA value (I) to be less than 0.05%, for example, it is necessary to make the pulp fibers used for the support thin or to make the amount of filler added a considerable amount, resulting in a decrease in paper strength. It is generated and cannot be produced in real.

  When the MA value (I) does not fall within the desired range depending on the dry state in the paper making process, it is preferable to adjust the MA value (I) appropriately by calendaring or the like. In addition, as a concrete means for making the MA value (I) 0.05% or more and 1.8% or less, for example, Canadian Standard Freeness (CSF) when making a paper base to be described later is within a specific range. In other words, the filler is within a specific range, and the calendar process is performed.

  In the wet electrophotographic printing, a liquid toner having a particle diameter smaller than that of the powder toner used in the dry electrophotographic method is used. For this reason, it is possible to obtain a high-resolution printed matter having a higher resolution than printing by the dry electrophotographic method. In order to obtain such a high-quality printed matter, it is preferable that the surface state of the paper is smooth so that the transferability and fixability of the liquid toner are sufficient. However, the image quality of an image drawn with minute liquid toner depends on minute irregularities having a depth of 4 to 6 μm generated on the surface of the paper. Therefore, in the wet electrophotographic printing paper, the surface to be the printing surface is required to have a surface state with few minute irregularities. In this embodiment, the unevenness on the surface of the paper is defined by the non-contact area ratio (MA value) at a constant pressure. The reason for this is that, according to this method, the surface condition which is finer than the so-called air leak method such as Parker Print Surf (PPS) or Beck smoothness or the stylus method or a direct surface state for image quality evaluation is obtained. This is because it can be grasped. In this embodiment, PST2600 (manufactured by FIBRO system ab) is used as means for measuring the MA value (I). Next, a measurement method will be described.

First, the paper is backed with the prism at a specific clamping pressure (pressing pressure) and a specific time (in condition 1, the pressing pressure is 3.4 MPa and the clamping time is 0.02 seconds). Clamp with plate. Next, light is applied to the paper surface obliquely from above through a prism pressed against the paper surface. Read the reflected light with the upper CCD camera. Then, the contact / non-contact area between the prism surface and the paper surface is calculated from the measured image by the dedicated image analysis platform and dedicated program of PST2600 attached to a commercially available personal computer. Since the non-contact area is classified according to the area, data correlating with the lack of the image line portion due to poor walling can be obtained. If there are many non-contact portions with a large area, the printing ink is difficult to fix and tends to cause chipping of the print portion. Based on the above principle, it is possible to perform surface state measurement more directly than the so-called air leak method smoothness measurement method. In the present embodiment, the MA value (I) is a ratio of the total area of non-contact parts having an area of 0.16 mm ² or more to the measurement part area, and is obtained from the following (Equation 1).
(Expression 1) MA value (I) [%] = (total area [mm ² ] / measurement area [mm ² ] of non-contact part having an area of 0.16 mm ² or more) × 100
In Equation 1, the measurement part area is an area of an actual measurement part to which light is applied in the pressing surface of the prism.

In the wet electrophotographic printing paper according to the present embodiment, the flat surface of the prism is pressed against at least one surface of the wet electrophotographic printing paper according to (Condition 2), and has a small non-contact area having an area of less than 0.16 mm ^2. The ratio of the total area of the non-contact part to the measurement part area when classified into the contact part including the part and the non-contact part having an area of 0.16 mm ² or more “total area ratio of the non-contact part (II) Is preferably 0.8% or less.
(Condition 2) Pressing pressure 3.4 MPa and clamping time 0.10 seconds

  The measurement method of MA value (II) is the same as the measurement method of MA value (I) except that the clamping condition is changed to condition 2. Keeping the MA value (II) low under the condition that the clamping time is long as in Condition 2 means that the image reproducibility can be improved by increasing the pressure at which the paper and the transfer drum are in contact with each other. To do. The MA value (II) is more preferably 0.6% or less.

In the wet electrophotographic printing paper according to the present embodiment, a surface size liquid is applied to the surface of the support, and the surface size liquid is a starch-based surface paper strength enhancer, a polyvinyl alcohol-based surface paper strength enhancer, or polyacrylamide. It is preferable that at least any one of the system surface paper strength enhancers is included. While maintaining the surface strength necessary for general commercial printing such as offset printing or letterpress printing, the transferability and fixability of the liquid toner can be further improved. The surface to which the surface sizing liquid is applied is one side or both sides of the support. In the present embodiment, it is preferable to have both sides. The coating amount of the surface sizing liquid is preferably 0.1 to 6.0 g / m ² on both sides of the paper in terms of solid content. More preferably, it is 1.0-5.0 g / m < ² >. If it is less than 0.1 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 6.0 g / m ² , problems such as insufficient transferability of liquid toner, insufficient fixability, and stickiness may occur due to an increase in air permeability. In addition, it is preferable that the application amount of the surface size liquid per one side of the paper is 0.05 to 3.00 g / m ² in terms of solid content. More preferably 0.50~2.50g / ^{m 2.} The polyacrylamide surface paper strength enhancer is preferable in that the cushioning property is maintained because the paper surface is not hardened, and the MA value (I) can be reduced. The coating amount of the polyacrylamide surface paper strength enhancer is preferably 0.5 to 6.0 g / m ² on both sides of the paper in terms of solid content. More preferably 1.0~6.0g / ^{m 2.} In addition, the polyvinyl alcohol-based surface strength enhancer is effective for improving the transferability and fixability of the liquid toner, but in order to deteriorate the air permeability, the coating amount of the polyvinyl alcohol-based surface strength enhancer is In terms of conversion, it is preferably 0.1 to 1.5 g / m ² per both sides of the paper. More preferably 0.2 to 1.0 g / ^{m 2.}

  In addition to the surface paper strength enhancer, the surface sizing liquid can be suitably formulated with a surface sizing agent, a conductive agent, a coloring dye, a coloring pigment, a fluorescent whitening agent, and the like according to each product. Moreover, the method of apply | coating a surface size liquid is not specifically limited, For example, it can apply | coat using a size press, a gate roll size press, a shim sizer, a rod coater, and an air knife coater.

  In the wet electrophotographic printing paper according to this embodiment, the Gurley stiffness in the vertical direction (JAPAN TAPPI No. 40: 2000) is preferably 1.0 mN or more. More preferably, it is 1.5 mN or more. Gurley stiffness is an indicator of the hardness of paper or paperboard. If the Gurley stiffness is less than 1.0 mN, there may be a problem of conveyance failure when the sheet is peeled from the transfer drum. Further, if the Gurley stiffness is too high, the delivery storage property after printing deteriorates, so it is preferably 35 mN or less. More preferably, it is 30 mN or less.

In the wet electrophotographic printing paper according to the present embodiment, the density (JIS P 8118: 1998 “Paper and paperboard—Test method of thickness and density”) is preferably 0.77 to 0.95 g / cm ^3. . The MA value (I) can be easily controlled within an appropriate range. By setting the density of the paper within a certain range, the cushioning property is maintained, and the transfer property of the liquid toner from the transfer drum to the paper can be improved. The density is more preferably 0.79 to 0.90 g / cm ³ . If the density is less than 0.77 g / cm ³ , the air gap in the paper becomes too large, and in the vacuum system using air, there may be a problem of double feeding when feeding the sheet. If it exceeds 0.95 g / cm ³ , the cushioning property is insufficient and the desired MA value (I) is not achieved, and the adhesion between the paper and the transfer drum is insufficient. As a result, the transferability and adhesion of the liquid toner may be inferior.

  As the support, paper mainly containing pulp and filler is used. Examples of the pulp include chemical pulp such as LBKP (hardwood bleached kraft pulp), NBKP (softwood bleached kraft pulp), GP (ground wood pulp), PGW (pressure ground wood pulp), RMP (refiner mechanical pulp), TMP (thermo). Mechanical pulp), CTMP (chemothermomechanical pulp), CMP (chemimechanical pulp), mechanical pulp such as CGP (chemiground 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 (Total Chlorine Free) pulp, waste paper pulp, and pulp obtained from planted trees are preferable. Mechanical pulp lowers the density of paper, but due to the nature of the pulp itself, it tends to increase the MA value (I) in order to harden the paper. Therefore, in the wet electrophotographic printing paper according to this embodiment, the blending ratio of mechanical pulp in the pulp is preferably 20% by mass or less. More preferably, it is 10 mass% or less.

  A conventionally known pigment can be used as the filler. Examples of the filler include calcium carbonate such as light calcium carbonate and heavy calcium carbonate, talc, kaolin, calcined kaolin, titanium dioxide, and synthetic silica. These may be used alone or in combination. In order to improve the fixability of the liquid toner, calcium carbonate is preferable, and light calcium carbonate is more preferable among the calcium carbonates. Since calcium carbonate has a function as an anti-slip agent and talc has a function as a lubricant, it is preferable to use talc together with calcium carbonate and adjust the blending ratio as appropriate. The mixing ratio of calcium carbonate and talc is preferably 20:80 to 95: 5 in terms of mass ratio. More preferably, it is 25: 75-80: 20. The slipperiness of the paper surface can be kept within an appropriate range. Further, since titanium dioxide has a high effect of preventing image back-through of printing paper, it is preferable to use titanium dioxide in combination. Titanium dioxide is preferably 0.5 to 2% by mass as ash from the viewpoint of preventing image back-through and cost. More preferably, it is 1.0-2.0 mass%.

  In the wet electrophotographic printing paper according to the present embodiment, the filler contains 20 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. Is 4 to 35% by mass, and the content of calcium carbonate is preferably 4% by mass or more. It becomes easy to efficiently absorb the solvent component of the liquid toner into the paper, and the fixability of the liquid toner can be further improved. If the ash content is less than 4% by mass, the paper becomes hard and the cushioning property is impaired, the MA value (I) increases, and the transferability and fixing property of the liquid toner may be weakened. If the ash content exceeds 35% by mass, the effect of improving the fixability of the liquid toner is saturated and the surface strength is lowered, which may cause a problem of paper peeling or powder falling. The ash content is more preferably 8 to 28% by mass. Further, since calcium carbonate easily absorbs the residual solvent of the liquid toner transferred to the surface of the paper, the fixability of the liquid toner can be further improved by adding calcium carbonate. It is preferable that calcium carbonate is 20-100 mass% with respect to the total amount of all the fillers. More preferably, it is 25-100 mass%. When the content of calcium carbonate with respect to the total amount of filler is less than 20% 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. More preferably, it is 5 mass% or more. If it is less than 4% by mass, the effect of improving the fixability of the liquid toner may be small. However, when light calcium carbonate is used as the calcium carbonate, the content of the light calcium carbonate with respect to the entire paper is preferably 25% by mass or less because the surface strength of the support may be reduced. More preferably, it is 20 mass% or less. Further, when heavy calcium carbonate is used as calcium carbonate, the content of heavy calcium carbonate with respect to the entire paper is preferably 25% by mass or less because there is a possibility that the wear of the papermaking wire is accelerated. More preferably, it is 20 mass% or less.

  It is preferable that the support further contains an internal sizing agent. Various types of internal sizing agents can be used, and are not particularly limited. Examples thereof include reinforced rosin sizing agents, neutral rosin sizing agents, acidic rosin sizing agents, weak acidic rosin sizing agents, AKD, and ASA.

  In addition to pulp, fillers and internal sizing agents, the support includes internal paper strength enhancers such as wet paper strength enhancers, bulking agents, yield improvers, drainage improvers, sulfuric acid bands, colored dyes, and colored pigments. Various auxiliary agents such as a fluorescent brightener, a fluorescent decoloring agent, and a pitch control agent can be suitably blended in accordance with each product. As the internal paper strength enhancer, a conventionally known paper strength enhancer can be used. For example, starch based paper strength enhancer, polyacrylamide based paper strength enhancer, polyvinyl alcohol based paper strength enhancer. is there.

  The method of paper making the support is not particularly limited, and is a long paper machine, a long net multilayer paper machine, a circular net paper machine, a circular net multilayer paper machine, a long net circular combination multi-layer paper machine, a twin wire paper machine. It can be manufactured by various devices such as a machine. The papermaking method is not particularly limited, and for example, either acid papermaking or neutral papermaking may be used. However, when a high amount of calcium carbonate is added as a filler, neutral papermaking is preferable.

The wet electrophotographic printing paper according to the present embodiment is a plain paper type wet electrophotographic printing paper. Here, the plain paper refers to paper on which a coating liquid containing a pigment is not coated. Specifically, for example, high-quality paper, medium-quality paper, and reprint paper. In addition, the paper includes multilayer paperboard or single-layer paperboard. The basis weight of the support is not particularly limited, is preferably 65~280g / ^{m 2,} more preferably from 80~230g / ^{m 2.}

  Examples of the method for controlling the MA value (I) within an appropriate range include a method for controlling freeness by beating pulp, a method for controlling the linear pressure of a paper machine press, a method for controlling the linear pressure of a calendar, and the like. There is a method to control in combination. Furthermore, the combination of use of a bulking agent, the kind of filler, and the compounding quantity can be illustrated. In this embodiment, when the pulp contains LBKP, Canadian Standard Freeness (CSF) (Canadian Standard Freeness) of LBKP (JIS P 8121: 1995 “Pulp Freeness Test Method”) is 300 to 600 ml. Preferably there is. More preferably, it is 330-550 ml. If the freeness is less than 300 ml, the paper becomes hard and the MA value (I) may not fall within the desired range. Further, since the thickness is reduced, it is necessary to change the production conditions so that the desired thickness range is obtained. If it exceeds 600 ml, the paper layer strength may decrease, and printing may cause problems. Moreover, it is preferable that the compounding quantity of a bulking agent is 0.2-1.5 mass parts in conversion of solid content with respect to 100 mass parts of absolutely dry pulp. More preferably, it is 0.3 to 1.1 parts by mass. If it is less than 0.2 parts by mass, the MA value (I) may not be within a desired range. When the amount exceeds 1.5 parts by mass, the paper layer strength is lowered, stains in the paper making process occur, and the paper may not be manufactured substantially.

  In the wet electrophotographic printing paper according to this embodiment, for the purpose of controlling the MA value (I), it is preferable to perform a smoothing process using a known calendar device such as a paper machine press, a machine calendar, a super calendar, or a soft calendar. .

  The wet electrophotographic printing paper according to the present embodiment is not limited to use as a wet electrophotographic printing paper, but can be used as a recording paper for a dry electrophotographic copying machine / printer or an inkjet recording paper.

  Next, the present invention will be described more specifically with reference to examples, but 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.

(Measurement of MA value (I))
PST2600 (manufactured by FIBRO system ab) was used, and the MA value (I) was determined from Equation 1 with a clamping pressure of 3.4 MPa and a clamping time of 0.02 seconds (condition 1).

(Measurement of MA value (II))
PST2600 (manufactured by FIBRO system ab) was used, and the MA value (II) was determined from Equation 1 with a clamping pressure of 3.4 MPa and a clamping time of 0.1 second (condition 2).

(Basis weight)
Measured according to JIS P 8124: 2011 “Paper and paperboard—Method of measuring basis weight”.

(Thickness and density)
Measured according to JIS P 8118: 1998 “Paper and paperboard—Test methods for thickness and density”.

(ash)
Measured according to JIS P 8251: 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 P 8121: 1995 “Method for testing freeness of pulp”.

  The resulting paper was evaluated for wet electrophotographic printing suitability for running property, liquid toner transferability and liquid toner fixability by the following methods. For the evaluation, “HP Indigo 5500 Digital Press” manufactured by HP was used as a wet electrophotographic printing machine, 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 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).
Δ: The number of conveyance failures is 2 (practical lower limit level).
X: The number of conveyance failures is 3 or more (practically impossible 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, a cellophane adhesive tape (registered trademark Cello Tape R, manufactured by Nichiban Co., Ltd.) was attached to each color solid part 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, the obtained wet electrophotographic printing paper was evaluated for printing durability as offset printing suitability by the following method.

(Press life)
Using Lithlon 40 (L-40) (manufactured by Komori Co., Ltd.) 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. To this pulp slurry, 1.0 part of cationized starch (Neotack 30T: manufactured by Nippon Shokuhin Kako Co., Ltd.) and 10.0 parts of calcium carbonate as a filler (TP121: manufactured by Okutama Kogyo Co., Ltd.) and 10.0 parts of talc (talc NTL: manufactured by Nippon Talc Co., Ltd.), 0.2 parts of neutral rosin sizing agent (CC1401: manufactured by Seiko PMC Co.) as an internal sizing agent, sulfuric acid 1.0 part of a band was added to prepare a paper stock. This stock was made with an on-top twin-wire paper machine to obtain a support. Next, with a gate roll coater, 8% solution of oxidized starch (MS3800: manufactured by Nippon Shokuhin Kako Co., Ltd.) as a surface sizing solution is applied to the front and back of the support so that the coating amount per side is 3 g / m ^2. Applied and dried. Thereafter, using a machine calendar, a flattening treatment was performed at a linear pressure of 100 kN / m to obtain a wet electrophotographic printing paper having a basis weight of 127 g / m ² . The content of calcium carbonate relative to the total mass of the paper was 8%.

(Example 2)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the freeness of LBKP was changed to 300 ml. The content of calcium carbonate relative to the total mass of the paper was the same as in Example 1.

(Example 3)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the freeness of LBKP was changed to 550 ml. The content of calcium carbonate relative to the total mass of the paper was the same as in Example 1.

Example 4
In Example 1, except that 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.), wet electrophotography according to Example 1. I got printing paper. The content of calcium carbonate with respect to the total mass of the paper was 13%.

(Example 5)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the filler was changed to 17 parts of calcium carbonate and 17 parts of talc. The content of calcium carbonate relative to the total mass of the paper was 15%.

(Example 6)
In Example 1, a wet electrophotographic printing paper was obtained according to Example 1 except that the filler was changed to 5 parts of calcium carbonate and 1 part of talc. The content of calcium carbonate relative to the total mass of the paper was 4.5%.

(Example 7)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the raw material yield was changed and the basis weight was changed to 70 g / m ² . The content of calcium carbonate with respect to the total mass of the paper was 7%.

(Example 8)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the raw material yield was changed and the basis weight was changed to 250 g / m ² . The content of calcium carbonate with respect to the total mass of the paper was 9%.

Example 9
In Example 1, except that the surface sizing solution was changed to a modified polyacrylamide 6% solution (ST-5000: manufactured by Seiko PMC), and the coating amount was changed to a solid mass of 3 g / m ² in total on the front and back sides. In accordance with Example 1, a wet electrophotographic printing paper was obtained. The content of calcium carbonate relative to the total mass of the paper was 8%.

(Example 10)
In Example 1, the surface sizing liquid was changed to a polyvinyl alcohol 4% liquid (PVA117: manufactured by Kuraray Co., Ltd.), and the coating amount was changed to a solid mass of 1 g / m ² in total on the front and back sides. Thus, a wet electrophotographic printing paper was obtained. The content of calcium carbonate relative to the total mass of the paper was 8%.

(Example 11)
In Example 2, a wet electrophotographic printing paper was obtained according to Example 2 except that 0.8% of a bulking agent (PT8107: manufactured by Seiko PMC Co., Ltd.) was added. The content of calcium carbonate relative to the total mass of the paper was the same as in Example 2.

(Comparative Example 1)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the raw material yield was changed to a basis weight of 60 g / m ² . The content of calcium carbonate with respect to the total mass of the paper was 6%.

(Comparative Example 2)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the raw material yield was changed to a basis weight of 300 g / m ² . The content of calcium carbonate with respect to the total mass of the paper was 9%.

(Comparative Example 3)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the machine calender linear pressure was reduced to 30 kN / m. The content of calcium carbonate relative to the total mass of the paper was the same as in Example 1.

(Comparative Example 4)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that no filler was added.

(Comparative Example 5)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the freeness of LBKP was changed to 250 ml. The content of calcium carbonate relative to the total mass of the paper was the same as in Example 1.

(Comparative Example 6)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the pulp was changed to 70 parts LBKP and 30 parts mechanical pulp. The content of calcium carbonate relative to the total mass of the paper was the same as in Example 1.

(Comparative Example 7)
In Example 1, wet electrophotographic printing paper was obtained according to Example 1 except that the filler was changed to 50 parts of calcium carbonate and 0 parts of talc. The content of calcium carbonate with respect to the total mass of the paper was 46%.

  In each of the wet electrophotographic printing papers of Examples 1 to 11, the liquid toner from the transfer drum to the paper in the wet electrophotographic printing was set by setting the paper thickness and the MA value (I) to the desired ranges. Transferability, fixability of liquid toner to paper, and running property were good. Further, these wet electrophotographic printing papers can be suitably used for printing by a conventional general printing method such as an offset printing method.

  In Comparative Example 1, since the paper thickness was insufficient, jamming frequently occurred during running, which was not suitable for practical use. In Comparative Example 2, since the thickness of the paper was excessive, the paper was not bent appropriately, and as a result, the running performance became unsuitable for practical use. Also, storage after printing was not possible. In Comparative Examples 3, 4, 5, and 6, the MA value (I) does not fall within the desired range, and as a result, 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 poor. became. In Comparative Example 7, a large amount of filler was added in order to reduce the MA value (I), but as a result, the printing durability decreased and the fixability of the liquid toner deteriorated, making it unsuitable for practical use.

  As is clear from Table 1, by limiting the thickness of the paper and the irregularities on the paper surface to a specific size, the liquid toner has good transferability and fixability, and offset printing is the main commercial printing. Wet electrophotographic printing paper having suitability could be obtained.

Claims (8)

In a non-coating wet electrophotographic printing paper in which the support contains pulp and filler,
On at least one surface of the wet electrophotographic printing paper, according to (condition 1), pressed against a flat surface of the prism, the contact portion and the 0.16 mm ² or more, including a small non-contact portion having an area of less than 0.16 mm ² When classified into a non-contact part having a surface area of "total area ratio (I) of non-contact part" indicating the ratio of the total area of the non-contact part to the measurement part area is 0.05% or more and 1.8% A wet electrophotographic printing paper having a thickness of 70 to 300 μm, which is as follows.
(Condition 1) Pushing pressure 3.4 MPa and clamping time 0.02 seconds On at least one surface of the liquid electrophotographic printing paper, according to (condition 2), pressed against a flat surface of the prism, the contact portion and the 0.16 mm ² or more, including a small non-contact portion having an area of less than 0.16 mm ² When it classifies into the non-contact part which has the area of "The total area ratio (II) of a non-contact part" which shows the ratio of the total area of the said non-contact part with respect to a measurement part area is 0.8% or less The wet electrophotographic printing paper according to claim 1, wherein
(Condition 2) Pressing pressure 3.4 MPa and clamping time 0.10 seconds On the surface of the support, a surface size liquid is applied,
The surface sizing liquid contains 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. The wet electrophotographic printing paper described. The filler contains 20 to 100% by mass of calcium carbonate based on the total amount of all fillers,
The ash content is 4 to 35% by mass and the content of calcium carbonate is 4% by mass or more when the total mass of the wet electrophotographic printing paper is 100% by mass. 4. The wet electrophotographic printing paper according to any one of 3 above. The pulp comprises hardwood bleached kraft pulp (LBKP);
The wet electrophotographic printing paper according to any one of claims 1 to 4, wherein the Canadian standard freeness (CSF) of the LBKP is 300 to 600 ml.   The wet electrophotographic printing paper according to any one of claims 1 to 5, wherein a blending ratio of mechanical pulp in the pulp is 20% by mass or less. The wet electrophotographic printing paper according to any one of claims 1 to 6, wherein the density (JIS P 8118: 1998) is 0.77 to 0.95 g / cm ³ .   The wet electrophotographic printing paper according to any one of claims 1 to 7, wherein a proportion of the bulking agent in the pulp is 0.2 to 1.5 mass%.