JP2009169408A - Electrophotographic recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording sheet capable of exhibiting quickly a fixing strength to toner, when printing using wet type toner by a wet type electrophotographic system. <P>SOLUTION: This electrophotographic recording sheet is provided with one layer or more of coating layers on at least one face of a sheet-like base material, the maximum peak of a void volume by mercury porosimetry is within a range of 0.1 to 1.1 μm of pore diameter, in the recording sheet, and a total A of void volume within the range has an A/B ratio of 32% or more with respect to a total B of void volume within a range of 0.002-100 μm of pore diameter. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic recording sheet that is printed using a wet electrophotographic method. More specifically, the present invention relates to an electrophotographic recording sheet that improves the speed at which toner fixing strength is developed after printing.

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

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

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

  On the other hand, another promising printing method that can handle variable information is an inkjet method. The ink jet method is a method in which fine ink droplets are ejected onto the surface of an object to be transferred to form an image. Recent technological advances are remarkable, the image quality is extremely high, and the weather resistance, which has been a weak point, has been greatly improved by the appearance of pigment-type inks. However, compared to offset printing and gravure printing, there are problems that the printing speed is slow and a relatively expensive dedicated sheet must be used to obtain high image quality.

  Therefore, when considering variable information in the on-demand printing area and satisfying conditions such as high image quality, high speed, and cost, the wet electrophotographic method is a very promising method among various printing methods. This is because the wet electrophotographic method disperses the toner in the liquid medium, so that the scattering of the powder is not a problem and the toner can be reduced to about 1/10 compared to the dry electrophotographic method. This is because, in addition to making the dots finer, pigments can be used as the color material, so there is no problem with weather resistance, the image is not prominent, and the printed matter is close to high-quality offset printing.

  Wet toner does not use the effect of charge when transferring an image from a blanket roll to a recording sheet. The image is transferred so that the adhesiveness of the wet toner to the printing sheet is higher than that of the blanket roll. That is, the transfer capability of the wet toner from the blanket roll to the printing sheet is important. If the toner adhesion ability is increased more than necessary, the fixing to the sheet is improved, but at the same time, it becomes difficult to peel off from the blanket roll, so that the toner adhesion ability cannot be increased more than necessary.

  For this reason, in the case of wet electrophotographic printing, there are drawbacks that sufficient toner strength cannot be obtained even if printing is performed, and that toner particles are not sufficiently transferred to the sheet. Furthermore, the time until the toner exhibits sufficient strength is also required to be shortened. Therefore, as a means for obtaining sufficient toner fixing strength, there is a method of applying a fixing agent to a sheet. For example, a Hewlett-Packard HP indigo machine has a technique called “sapphire processing”. In order to provide wet electrophotographic printability without using such a treatment, there is a method in which a specific compound, for example, an imine compound is applied or applied at the paper manufacturing stage.

  In addition to this, the amount of ash in the base paper is specified, and zirconium is applied to the surface (see, for example, Patent Document 1), or surface smoothness and sizing agent are devised (for example, Patent Document 2). See) There is an example. These are effective for recording sheets of plain paper (non-coated paper) type. In practice, however, the recording sheet obtained by these means needs to be improved because the printability of the wet electrophotographic method is lower than that obtained by processing with an imine compound.

  For these reasons, in actual wet electrophotographic printing, a sheet treated with a fixing agent is often used. However, many fixing agents are unstable in terms of physical properties, and many have a short time from application to a sheet until the effect disappears.

As another method for improving the fixability of the wet toner without using a fixing agent, calcium carbonate that easily absorbs the solvent used in the wet toner is blended in a certain ratio in the coating layer of the recording sheet, and the oil absorption is performed. There has been proposed a method for improving the performance by setting the performance to a certain level or more (see, for example, Patent Document 3). Although this method works very effectively as a method for improving toner fixability, in recent years, there is a strong demand for shortening the time required for cutting and processing after printing, and until sufficient toner fixability is exhibited. There was still room for improvement in terms of speed. Although the toner fixing property is improved with time, if the paper is processed with insufficient fixing, there may be a problem that the toner is peeled off from the recording sheet, and further improvement has been demanded.
JP-A-10-171146 Japanese Patent Laid-Open No. 10-171148 JP 2004-77667 A

  An object of the present invention is to provide an electrophotographic recording sheet that quickly develops fixing strength with toner when printing is performed using a wet electrophotographic system using a wet toner.

  As a result of intensive studies to solve the above problems, the present inventors have invented the following electrophotographic recording sheet.

  That is, in an electrophotographic recording sheet in which one or more coating layers are provided on at least one side of a sheet-like substrate, the maximum peak of void volume by the mercury intrusion method of the recording sheet is from 0.1 to 1. The total void volume within the range of 1 μm (A) is 32% or more of the total void volume within the range of pore diameters of 0.002 to 100 μm (B). This is a characteristic electrophotographic recording sheet.

  The electrophotographic recording sheet of the present invention can solve the problem of toner peeling in processing such as cutting and folding of the printed sheet by developing toner fixing properties very quickly.

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

  The present inventor has studied a technique for shortening the time required to exhibit a sufficient fixing power with respect to the fixability of toner on an electrophotographic recording sheet in the electrophotographic system. As a result, it has been found that by appropriately designing the size of the capillary of the coating layer mainly composed of pigment, the intended performance is remarkably improved.

  The electrophotographic recording sheet of the present invention is a recording sheet for electrophotography in which at least one coating layer is provided on at least one side of a sheet-like substrate, and the maximum peak of void volume by the mercury intrusion method of the recording sheet is narrow. The pore diameter is in the range of 0.1 to 1.1 μm, preferably 0.3 to 0.9 μm. The total void volume in the range (A) is 32% or more, preferably 32% to 40%, with respect to the total void volume (B) in the pore diameter range of 0.002 to 100 μm. It is characterized by being. The void volume here refers to the void volume of the coating layer on the side in contact with the toner. Only when this condition is satisfied, the coating layer contains a solvent which is one of the components constituting the wet toner. Absorbs very quickly and enhances the function of the adhesive inherent in wet toners.

The mercury intrusion method of the present invention is a method widely used for measuring the pore structure (pore diameter and pore volume) of a porous body. The measurement principle uses that mercury has a large surface tension, and mercury cannot enter the pores of the porous body unless pressure is applied. That is, using the surface tension of mercury of 480 (dyn / cm) and a contact angle of 140 °, the relationship between the pressure applied to mercury and the pore diameter at which mercury can enter at that time is expressed by the following general formula (1).
P = −4σcos θ / D (1)
(note)
P: pressure required for mercury to enter the pores (psi)
σ: Surface tension of mercury (480 dyn / cm)
θ: contact angle of mercury (140 °)
D: pore diameter (μm)
By substituting the values of σ and θ into the above formula (1), the general formula (2) for obtaining the pore diameter is obtained.
D (μm) = 213 / P (psi) (2)

  In order to obtain the pore distribution using the above principle, the pressure P applied to the mercury is gradually changed, and the volume V of mercury entering the pores at that time is measured to determine the mercury pressure P and the mercury concentration. Draw the relationship with the penetration amount V, determine the differential coefficient (dV / dP) of this relationship curve as the vertical axis, and convert the pressure P into the pore diameter according to the above equation (2) as the horizontal axis. Is required. When the pore distribution of the electrophotographic recording sheet is determined by this method, a pore distribution curve having the maximum peak is obtained. In the present invention, it has a peak appearing in a pore range of 0.1 to 1.1 μm.

  In the present invention, the void volume is determined by the following method. A measuring instrument using the mercury intrusion method, for example, a porosimeter, is used to change the pressure of mercury and press-fit it into an electrophotographic recording sheet, to obtain a pore distribution curve at that time, and a pore diameter of 0.002 μm to The total void volume (B) in the range of 100 μm is obtained. Furthermore, the total (A) of void volumes within a range having a peak appearing in a pore diameter range of 0.1 to 1.1 μm is obtained. In the present invention, the A / B ratio is set to 32% or more.

  When the maximum peak of the void volume by the mercury intrusion method of the recording sheet exceeds 1.1 μm in pore diameter, the size of the capillary tube is not sufficiently small, so that the image formed by the toner and the coating layer of the recording sheet The speed at which the solvent of the wet toner is removed from the interface is reduced. In addition, even if the maximum peak is in the specified range, the total void volume in the pore diameter range of 0.1 to 1.1 μm is larger than the total void volume in the pore diameter range of 0.002 to 100 μm. If the ratio is less than 32%, the expected effect cannot be obtained. This is because a capillary having a pore diameter of 1.1 μm or less removes the solvent of the wet toner from the wet toner very effectively. On the other hand, it can be said that it is difficult at present to produce an electrophotographic recording sheet having a maximum void volume peak with a pore diameter of less than 0.1 μm at a realistic cost.

  In order to adjust the ratio between the maximum peak pore diameter and the void volume, it is necessary to select the particle size and shape of the pigment forming the coating layer, the kind of the binder, and the blending amount. In order to make the maximum peak appear on the low pore diameter side, or to increase the void volume ratio on the low pore diameter side, control of the pigment particle size distribution such as finer pigment and removal of coarse particle components, porous shape It is effective to select a pigment shape such as a spindle shape or a needle shape and to appropriately reduce the amount of the binder.

By setting the coating amount of the uppermost layer to 3 g / m ² or more, the surface of the sheet-like substrate can be covered to some extent and the intended performance can be exhibited, but it is preferably 7 g / m ² or more. However, a coating amount exceeding 30 g / m ² is not necessary because it impedes productivity in recording sheet production.

  The electrophotographic recording sheet in the present invention is not limited to use as a wet electrophotographic recording sheet, but can also be used in other printing systems such as dry electrophotography, offset printing, gravure printing, thermal transfer, and inkjet.

  The base material of the electrophotographic recording sheet used in the present invention includes plant fibers such as wood pulp, cotton, hemp, bamboo, sugar cane, corn, kenaf, animal fibers such as wool and silk, rayon, cupra, lyocell, etc. Cellulose regenerated fibers, semi-synthetic fibers such as acetate, polyamide fibers, polyester fibers, polyacrylonitrile fibers, polyvinyl alcohol fibers, polypropylene fibers, polyvinylidene chloride fibers, polyurethane fibers, and other chemical fibers, glass fibers, The thing which made the inorganic fiber, such as a metal fiber and carbon fiber, the sheet form, or the thing which provided the resin film layer on it is used.

  In the case of using a fiber sheet-like base material, as a manufacturing method for making each fiber into a sheet, a general paper making process, a wet method, a dry method, a chemical bond, a thermal bond, a spun bond, a spun lace, a water jet, a melt blow, One or more are appropriately selected from each process such as needle punching, stitch blowing, flash spinning, and tow opening.

  These fibers include light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, titanium dioxide, aluminum hydroxide and other fillers, binders, sizing agents, fixing agents, retention agents, paper strength enhancers, etc. These various compounding agents are suitably blended according to each step and each material. Furthermore, a resin coat layer may be provided on these fiber sheets.

  In addition, the base materials are high quality paper, medium quality paper, color quality, book paper, cast paper, fine coated paper, lightweight coated paper, coated paper, art paper, medium coated paper, gravure paper, Indian paper, coated paper Ivory, uncoated ivory, art post, coated post, uncoated card, special board, coated ball, tracing paper, type paper, PPC paper, NIP paper, continuous slip paper, foam paper, copy paper, carbonless paper, heat sensitive Examples include paper, paperboard such as paper, inkjet paper, thermal transfer paper, synthetic paper, non-woven fabric, or various resins, plastics, and metals formed into a film.

  The base material for providing the coating layer may be subjected to various surface treatments and calendar treatments in order to obtain the required density, smoothness and air permeability.

  In the present invention, the pigment that can be used when the coating layer is provided on the sheet-like substrate is not particularly limited, and for example, purification of various kaolins, talc, heavy calcium carbonate (ground calcium carbonate), etc. Natural mineral pigments, light calcium carbonate (synthetic calcium carbonate), composite synthetic pigments of calcium carbonate and other hydrophilic organic compounds, satin white, lithopone, titanium dioxide, silica, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate , Calcined kaolin, plastic pigments and the like.

  As binders used in the coating layer, various copolymer latexes such as styrene-butadiene, acrylic, polyvinyl acetate, ethylene-vinyl acetate, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, poly Examples thereof include water-soluble compounds such as acrylamide, urea or melamine / formalin resin, polyethyleneimine, and polyamidepolyamine / epichlorohydrin. Furthermore, starch purified from natural plants, hydroxyethylated starch, oxidized starch, etherified starch, phosphate esterified starch, enzyme-modified starch, cold water soluble starch obtained by flash drying them, dextrin, mannan, chitosan, arabi Examples thereof include natural polysaccharides such as nogalactan, glycogen, inulin, pectin, hyaluronic acid, carboxymethylcellulose, and hydroxyethylcellulose, oligomers thereof, and modified products thereof. Examples thereof include natural proteins such as casein, gelatin, soybean protein and collagen, and modified products thereof, and synthetic polymers and oligomers such as polylactic acid and peptides. These can be used alone or in combination.

  The thickeners used in the coating solution include water-soluble polymers such as carboxymethylcellulose, sodium alginate, methylcellulose, hydroxyethylcellulose, casein, and sodium polyacrylate, polyacrylate, and styrene maleic anhydride copolymer. And synthetic polymers such as silicates and inorganic polymers such as silicates.

  In addition, various auxiliary agents that are usually used such as a dispersant, an antifoaming agent, a water-proofing agent, and a coloring agent, and those obtained by cationizing these auxiliary agents are suitably used as necessary.

  In the present invention, the coating method is not particularly limited, and various film transfer coaters such as a size press having a puddle, a metering size press, a gate roll, and a shim sizer, an air knife coater, a rod coater, a blade coater, Each system such as a direct fountain coater, spray coater, cast coater is appropriately used.

  Furthermore, the recording sheet coated and dried in a series of operations is subjected to various finishing processes such as a calendar process as required in order to obtain the required density, smoothness, air permeability, and appearance. However, excessive calendering processing impairs the capillary structure of the coating layer, so it needs to be performed appropriately.

  Examples of the present invention will be described below, but the present invention is not limited to these examples. Further, “parts” and “%” shown in the examples indicate parts by mass and mass% unless otherwise specified.

(Example 1) to (Example 8) and (Comparative Example 1) to (Comparative Example 2)
An electrophotographic recording sheet was prepared according to the following contents.

<Sheet substrate>
LBKP (Drainage 400 mlcsf) 70 parts NBKP (Drainage 480 mlcsf) 30 parts Light calcium carbonate (indicated by ash content in base paper) 8 parts Commercial cationized starch 1.0 parts Commercial cationic polyacrylamide yield improver 0.03 parts Pulp and internal chemicals were prepared with the above composition, and a base paper was made with a basis weight of 72.0 g / m ² .

To this base paper, 0.80 g / m ² of oxidized starch was adhered on both sides by a size press to obtain a sheet-like substrate.

<Coating solution>
The composition of the coating liquid is as follows.
Pigment The number of blending parts is listed in Table 1. Commercial styrene butadiene latex binder 11 parts Commercial phosphate esterified starch 2 parts Commercial calcium stearate lubricant 0.6 parts Commercial carboxymethyl cellulose thickener (CMC) 0.1 parts Sodium hydroxide Adjusted to pH 9.6

The above coating solution was applied at a coating amount of 14 g / m ² on one side and 28 g / m ^{2 on} both sides using a blade coater. After the coating, a soft calender treatment comprising a metal roll and an elastic roll was performed so that the metal rolls contacted with the front and back surfaces one by one to obtain an electrophotographic recording sheet. Examples 1 to 8 and Comparative Examples 1 and 2 were performed at a calendar linear pressure of 80 kN / m, and Examples 9 and 10 were 200 kN / m.

  The electrophotographic recording sheets obtained in Examples 1 to 8 and Comparative Examples 1 and 2 were measured by the following measuring method, and the evaluation results are listed in Table 1.

Measurement of pore diameter and void volume by mercury porosimetry was obtained using Autopore III9420 manufactured by MICROMERITICS. The pore measurement range was about 0.0018-100 μm. From these values and charts, the following measured values A and B were obtained.
Measured value A: the position of the maximum peak of void volume. [Μm]
Measurement value B: Ratio of the total void volume in the range of pore diameters of 0.1 to 1.1 μm to the total void volume in the range of pore diameters of 0.002 to 100 μm. [%]

  As a wet electrophotographic transfer machine, “HP indigo press 3050” manufactured by Hewlett-Packard Company was used to evaluate the fixability of the wet electrophotographic toner. As a print image to be used for evaluation, a solid print image is output for each of four colors of black, cyan, magenta, and yellow and a heavy color obtained by superimposing all four colors. A tape peeling test was performed on the solid printed portions of black, cyan, magenta, yellow, and heavy colors printed. This is a very suitable method for evaluating the adhesive strength between the image area and the transfer sheet, and how long after printing is finished, can it proceed to processing such as guillotine, cutter cutting, folding, and bookbinding? It becomes the index which shows. It can be said that those which show strong fixability in a short time are excellent.

<Tape peeling>
A cellophane adhesive tape having a width of 18 mm was applied to the print sample so that there was no unevenness in the printed portion of each color, and the tape was slowly peeled off at a speed of about 5 mm / second at 180 ° peeling. The degree of fixing of the toner after peeling to the sheet was visually determined, and a four-step evaluation was performed according to the following criteria. Table 1 shows the lowest evaluation among the image portions. Immediately after the end of printing, it was carried out under four conditions, one hour later, four hours later, and one day later.
A: The toner does not peel at all for each color.
○: Most of the toner remains on the sheet for each color.
(Triangle | delta): The toner peeled off from the sheet | seat with one part color, and there exists a part which fell out white in the printing part.
X: For each color, the toner is peeled off from the sheet, and a white portion of the printed portion is noticeable.

<Evaluation results>
In the tape peeling test immediately after printing, peeling of the image was observed particularly in the heavy-colored image area, but in most of the examples, good toner fixing strength was exhibited after 1 hour, and all the tests were performed after 4 hours. In the examples, sufficient fixing strength was shown. In the examples, calcium carbonate, kaolin, and polystyrene-based organic pigments are used in various ways. Although the toner fixing strength develops to some extent depending on the type of material and the shape of the particles, the measured values A and It can be seen that by designing the measurement value B as defined in the present invention, the expression of the fixing strength at an early stage after printing is improved. Among them, Examples 9 and 10 were obtained by increasing the linear calender pressure and smoothing, and compared with Examples 1 and 2 in which the composition of the coating layer was the same, the speed at which the fixing strength was expressed was slightly slower. It showed good enough fitness. On the other hand, in Comparative Example 1, the toner fixing strength was not sufficient even after 4 hours, indicating that it is not appropriate to proceed to cutting or folding immediately after printing. In Comparative Example 2, it was determined that the toner strength was insufficient even after one day and the wet toner was not suitable.

  It can be applied to electrophotographic recording sheets in wet electrophotographic printing.

Claims (1)

  In an electrophotographic recording sheet in which at least one coating layer is provided on at least one side of a sheet-like substrate, the maximum peak of the void volume by the mercury intrusion method of the recording sheet has a pore diameter of 0.1 to 1.1 μm The total void volume in the range (A) is 32% or more with respect to the total void volume (B) in the pore diameter range of 0.002 to 100 μm. Recording sheet for electrophotography.