JP2005284214A - Wet electrophotographic recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wet electrophotographic recording sheet having excellent weather resistance and keeping favorable color appearance after printed. <P>SOLUTION: In the wet electrophotographic recording sheet consisting of a sheet-like substrate, brightness is 90.0 to 100.0%, L value is 92.0 to 97.0, (a) value is 2.50 to 6.00 and (b) value is -5.00 to -10.00, and rates of change in the brightness and the (b) after the lapse of three hours at 105°C are ≤5% and ≤3 respectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wet electrophotographic recording sheet, and more particularly to a wet electrophotographic recording sheet that has excellent weather resistance and good color feel after printing in a wet electrophotographic printing system. is there.

  The use of electrophotographic printing is 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 that enables various types of small lot printing and variable information printing. Progress and technical progress is remarkable. In recent years, with the increase in printing speed, the number of printed copies has started to reach the area that has been covered by printing such as offset and gravure.

  Electrophotographic printing has the advantage of being able to handle variable information, but offset and gravure printing are inferior in terms of quality and price because they have achieved very high quality printing at a low price due to many years of accumulated technology. It was. For this reason, technological development for higher image quality, higher speed, lower power consumption, and lower costs is being promoted from both sides of printing machines and printing sheets. Printed materials are required to have higher definition and better color reproducibility, but this is in conflict with speeding up and cost reduction, as well as the performance of toner and printing machines, as well as electrophotography. As for recording sheets for printing, more stringent quality demands such as toner fixing property, transfer property, color reproducibility and running property are gathered.

  Among such electrophotographic printing methods, the dry electrophotographic method is a method typified by an office copier, and the toner for forming an image uses a solid powder toner made of a pigment and a synthetic resin. In the image forming method, printing is performed by a method in which toner is adsorbed to an electrostatic image generated by corona charging, and this toner is heat-pressed to a transfer object. However, in this method, if the toner is made finer, it is likely to be scattered to the surrounding environment, and if this is inhaled, a health problem is caused, so that the working environment is deteriorated and the printed matter is stained. For this reason, there is a limit to miniaturizing the solid powder toner, and it is difficult to obtain high resolution. Furthermore, since the thickness of the transfer object is not uniform, the charge density on the transfer object surface varies due to corona discharge, and an undesired image called fog occurs in the non-image area, or at a somewhat high temperature. There are many problems such as having to melt and solidify.

  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 have been tremendous, with extremely high image quality, and the weak weather resistance has been greatly improved with the advent of pigment-type inks. However, compared with offset printing or the like, there is a problem 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 the most 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 1/10 or more compared to the dry electrophotographic method. This is because the pigment can be used as a coloring material and there is no problem of weather resistance, and the printing finish is close to that of offset printing.

  Wet toner does not use charge or the like when transferring an image from a blanket roll to a sheet. The image is transferred by utilizing the fact that the wet toner has higher adhesion to the printing sheet than the blanket roll. That is, the transfer capability of the wet toner from the blanket roll to the printing sheet is important. If the adhesive ability is increased more than necessary, the toner fixing property is improved, but it becomes difficult to peel off from the blanket roll, so that the toner adhesive 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. Therefore, there is a generally known method called “sapphire treatment” as means for imparting wet electrophotographic printability without selecting the type of sheet. This is a technique of applying polyethyleneimine to a sheet. In order to provide wet electrophotographic printing suitability without using sapphire treatment, there are also methods in which an imine compound is incorporated or applied at the paper production stage. However, these are also basically the same method as the sapphire treatment.

  In addition to this, the amount of ash in the base paper is defined and zirconium is applied to the surface (for example, refer to Patent Document 1), or the surface smoothness and the sizing agent are devised (for example, Patent Document). See 2.) There is an example. These are effective for plain paper (non-coated) type printing paper. In the case of a coated sheet, there is an example of solving the problem by defining the type of pigment or binder and the blending amount of the binder (see, for example, Patent Document 3). However, in actuality, the sheet obtained by these means has a low wet electrophotographic printing suitability as compared with the sheet treated with an imine compound.

  However, a sheet treated with an imine compound has extremely poor weather resistance. Although these sheets depend on the amount of the compound adhering to the sheets, the sheets are discolored after about one month, and the color feeling and appearance of the printed matter are remarkably lowered. Further, the wet electrophotographic printing surface is less glossy than the general offset printing surface. Nevertheless, when the color has deteriorated in this way, the color feel as a printed matter has been remarkably inferior.

Therefore, with the technology up to now, it has been difficult to produce a wet electrophotographic recording sheet that is excellent in weather resistance and has a good color feeling after printing.
JP-A-10-171146 Japanese Patent Laid-Open No. 10-171148 JP-A-9-281739

  An object of the present invention is to provide a wet electrophotographic recording sheet that is excellent in weather resistance in a wet electrophotographic printing system and that has a good color feeling after printing.

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

  That is, in a wet electrophotographic recording sheet comprising a sheet-like substrate, the whiteness is 90.0 to 100.0%, the L value is 92.0 to 97.0, the a value is 2.50 to 6.00, The b value is -5.00 to -10.00, the change in whiteness after 3 hours at a temperature of 105 ° C is 5% or less, and the change in b value is 3 or less. It is a feature.

  In the present invention, the whiteness is 96.0 to 99.0, the L value is 93.0 to 96.0, the a value is 4.00 to 5.00, and the b value is −7.00 to −9.00. Preferably there is.

  From the above results, the wet electrophotographic recording sheet of the present invention can provide a wet electrophotographic recording sheet that is excellent in weather resistance and has a good color feeling after printing.

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

  As a result of earnest research on the weather resistance, color feeling, and printability of the wet electrophotographic recording sheet in the wet electrophotographic method, the present inventor has excellent weather resistance and the color feeling after printing continues to be good. Has found that it is necessary to give color and weather resistance completely different from those of commonly used wet electrophotographic recording sheets.

  There is a feeling that imine compounds are essential for wet electrophotographic recording sheets. However, amino groups present in these compounds are susceptible to chemical reactions, and as a result, colored molecules are formed. Therefore, as long as it depends on the imine compound, light resistance cannot be imparted.

  In order to impart light resistance, it is first necessary not to use an imine compound in which an amino group or an amide group exists at a high concentration. The high concentration mentioned here refers to a compound in which 0.05 mol or more of all elements in the molecule is a nitrogen atom. In addition, when an adhesive system such as SBR latex having a large amount of double bonds in the molecule is used, the light resistance is also inferior even if not as high as that of an imine compound. Therefore, the amount used is preferably 6% by mass or less. The adhesive used is preferably a polyhydric hydroxyl group. The material used as the main component of the sheet is also preferably a high purity compound such as cellulose that does not contain nitrogen atoms.

By the way, there is a concern that without the imine compound, the wet electrophotographic recording sheet is not suitable, but this is reduced by reducing the amount of the hydrophobic compound used as much as possible and using a lot of hydrophilic compounds. Can be achieved. When providing a coating layer, it is good to use the usage-amount of a latex binder as 8 mass% or less of a coating layer, and to make the usage-amount of a hydrophilic binder into 1/2 or more of a latex binder. Furthermore, when a base material on the sheet is filled with a filler or covered with a pigment, a material having a small particle size or a large specific surface area can be selected to provide suitability for a wet electrophotographic recording sheet. Here, the small particle size means 1 μm or less, and the large specific surface area means 20 m ² / g or more.

  Here, if the change in whiteness after 5 hours at a temperature of 105 ° C. is 5% or less and the change in b value is 3 or less, the value of the printed matter is printed at least 3 months after printing. It can be kept just as it is immediately after. If the change in whiteness is 5% and the change in b value is 3 or less, it will look almost the same as immediately after printing for human senses, but it will be understood that it is different from this point. It is not preferable. The amount of change in whiteness referred to here indicates how much whiteness has changed from here on the basis of the value of whiteness before the change. The same applies to the amount of change in the b value, and these are expressed as absolute values.

  Furthermore, the whiteness of the sheet is 90.0 to 100.0%, the L value is 92.0 to 97.0, the a value is 2.50 to 6.00, and the b value is -5.00 to -10.00. If you leave it, the color of the printed material looks excellent. Since this becomes stable for a long period of 3 months or more, the value of the wet electrophotographic printed matter can be increased as compared with the prior art. When the value is lower than the lower limit values of the whiteness and L value shown here, it cannot be said that the color feeling is vivid, so the effect of imparting weather resistance is lowered, which is not preferable. On the other hand, when the L value is higher than the upper limit, the paper is too bright and the image is difficult to see, which is also not preferable. When the a value and the b value are out of the range shown here, the sheet appears to be colored, causing a problem in color reproduction of the image.

  When the whiteness of the sheet is 96.0 to 99.0%, the L value is 93.0 to 96.0, the a value is 4.00 to 5.00, and the b value is −7.00 to −9.00. The color feel of the printed material looks very good, and the value of the printed material can be further increased.

  The whiteness referred to here is that of the JIS standard, and the L value, a value, and b value are Hunter L, a, and b systems.

  The wet electrophotographic recording sheet in the present invention is not limited to use as a wet electrophotographic recording sheet, but may be used in other printing methods such as a dry electrophotographic recording sheet, an offset printing sheet, and a thermal transfer sheet. it can.

  As the base material of the wet electrophotographic recording sheet used in the present invention, plant fibers such as wood pulp, cotton, hemp, bamboo, sugarcane, corn, kenaf, animal fibers such as wool, silk, rayon, cupra, lyocell, etc. Cellulose recycled 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 A fiber, metal fiber, carbon fiber or other inorganic fiber in the form of a sheet or a resin film layer provided thereon is used.

  Production methods for making each fiber into a sheet form include general paper making processes, wet methods, dry methods, chemical bonds, thermal bonds, spun bonds, spun laces, water jets, melt blows, needle punches, stitch blows, flash spinning, tow One or more are appropriately selected from each process such as restoration.

  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.

  Base materials include 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 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, thermal paper, Inkjet paper, thermal transfer paper, synthetic paper, and other paper and paperboard, non-woven fabric, or various resins, plastics, and metals formed into a film are also included.

  The substrate before coating 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 oxide, silica, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate , Calcined kaolin, plastic pigments and the like.

  Binders used in the coating layer include starch purified from natural plants, hydroxyethylated starch, oxidized starch, etherified starch, phosphate esterified starch, enzyme-modified starch and those obtained by flash drying. Cold water soluble starch, natural polysaccharides such as dextrin, mannan, chitosan, arabinogalactan, glycogen, inulin, pectin, hyaluronic acid, carboxymethylcellulose, hydroxyethylcellulose, oligomers thereof, and modified products thereof.

  Further, natural proteins such as casein, gelatin, soybean protein, collagen, and modified products thereof, and synthetic polymers and oligomers such as polylactic acid and peptides can be mentioned.

  In addition, copolymer latex such as styrene-butadiene, acrylic, polyvinyl acetate, ethylene vinyl acetate, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, polyacrylamide, urea, or melamine / formalin resin, Examples thereof include water-soluble synthetic compounds such as polyethyleneimine and polyamidepolyamine / epichlorohydrin. One or more of these can be used. In addition, the use of a known natural or synthetic organic compound is not particularly limited.

  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 method for coating the coating layer is not particularly limited, and various film transfer coaters such as size press, gate roll, shim sizer, air knife coater, rod coater, blade coater, direct fountain coater, Each system such as a spray coater or cast coater is appropriately used.

  Furthermore, in order to obtain the density, smoothness, air permeability, and appearance required for coated and dried coated sheets in a series of operations, various finishing processes such as calendering are performed as necessary. The

  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)
According to the following content, the recording sheet for wet electrophotography of Examples 1-18 and Comparative Examples 1-7 was produced.

<Sheet substrate>
LBKP (freeness 330-440 mlcsf) 70 parts NBKP (freeness 390-490 mlcsf) 30 parts light calcium carbonate (expressed in ash content in base paper, specific surface area 30 m ² / g) 8 parts commercially available cationized starch 1.0 parts commercially available Cationic polyacrylamide yield improver 0.03 parts Red dye 0.01 parts Pulp and internal chemicals were adjusted according to the above formulation to produce a base paper with a basis weight of 87.9 g / m ² .

A wet electrophotographic recording sheet was obtained by attaching a sizing solution of oxidized starch: fluorescent brightening agent 99: 1 to both sides of the base paper by a size press at 0.80 g / m ^{2 on} both sides.

(Comparative Example 1)
A base paper was made with the same composition as in Example 1, and a coating solution of polyethyleneimine: fluorescent whitening agent 29: 1 was attached to this base paper with a gate roll coater on both sides at 0.30 g / m ² for wet electrophotography. A recording sheet was obtained.

(Example 2) to (Example 19), (Comparative Example 2) to (Comparative Example 9)
A sheet obtained in the same manner as in Example 1 was used as a base paper, and the following coating solution was applied.

<Coating fluid>
Commercially available fine heavy calcium carbonate (1 μm or less is 91% by mass) 90 parts Commercially available organic hollow pigment (styrene type) 10 parts Commercially available styrene butadiene latex binder (average particle size 100 nm, gel content 40%, Tg 5 ° C.) 5 parts commercially available Phosphate esterified starch 9 parts Commercial calcium stearate 0.6 parts Commercial carboxymethylcellulose thickener (CMC) 0.1 parts Sodium hydroxide prepared to pH 9.6

A fluorescent whitening agent, a red dye, a blue dye, a yellow dye, a green dye, and a black dye are appropriately added to the coating liquid so as to have the hue shown in Table 1, and the concentration is 50% by mass and the operation speed is 1000 m / min. Using a fountain / blade coater, coating was performed at a coating amount of 10 g / m ² on one side and 20 g / m ^{2 on} both sides. After coating, supercalender treatment was performed on each of the front and back 4 nips at a linear pressure of 200 KN / cm and a temperature of 80 ° C. to obtain a wet electrophotographic recording sheet. In Comparative Example 3, a sapphire treatment was performed using a 3% polyethyleneimine solution instead of dampening water using this rear rotary offset printing press.

  The wet electrophotographic recording sheets obtained in Examples 1 to 18 and Comparative Examples 1 to 7 were evaluated for weather resistance and color feeling by the following measurement methods. The results are shown in Table 1.

1. Weather resistance After being placed in an oven at a temperature of 105 ° C. for 3 hours, it was taken out. The whiteness and b value of the sample that was not placed in the oven and the sample were measured with a Spectro Color Meter PF-10 manufactured by Nippon Denshoku Industries Co., Ltd. The measurement results are shown in Table 1.

2. Color Sensing Wet Electrophotographic Sheet Transfer Machine, “HP-indigo press 1000 (formerly E-print 1000)” manufactured by HP, a solid printing section for four colors of black, cyan, magenta, and yellow for women of ISO400 An image like that is output. As a printing area of the solid printing portion, at least a square with a side of 3 cm or more was used. In all Examples and Comparative Examples, wet electrophotographic printability was good. Ten samples were taken from each sheet, and 5 sheets were placed in an oven at 105 ° C. for 3 hours. The color sensation of the sample before being put into the oven and the sample after being put in was visually judged and evaluated according to the following criteria in four stages.
A: The color feeling is very good.
○: Excellent color.
Δ: Normal color.
X: Color is inferior.

<Evaluation results>
As in Comparative Example 1 and Comparative Example 3, those containing an imine compound and having a weather resistance inferior to the range of the present invention are severely deteriorated in color feeling and cannot maintain good color feeling. On the other hand, as in Examples 1 and 2, a sheet having high weather resistance can maintain a good color feeling.

  As in Comparative Examples 2, 4, 5, 6, 7, 8, and 9, when the hue is out of the range defined in the present invention, it is not possible to have an excellent color feeling, but Examples 2, 3, 6, 7, As long as it is within the range such as 10, 11, 12, 15, 16, and 19, excellent color feeling can be provided.

  When the hue is in a preferable range as in Examples 4, 5, 8, 9, 13, 14, 17, and 18, the printed matter can have a very excellent color feeling.

  The present invention can be applied to a wet electrophotographic recording sheet by a wet electrophotographic method that can handle variable information in an on-demand printing area.

Claims (2)

  In a wet electrophotographic recording sheet comprising a sheet-like substrate, the whiteness is 90.0 to 100.0%, the L value is 92.0 to 97.0, the a value is 2.50 to 6.00, and the b value. Is from -5.00 to -10.00, the change in whiteness after 3 hours at a temperature of 105 ° C. is 5% or less, and the change in b value is 3 or less. A wet electrophotographic recording sheet.   The whiteness is 96.0 to 99.0%, the L value is 93.0 to 96.0, the a value is 4.00 to 5.00, and the b value is −7.00 to −9.00. The wet electrophotographic recording sheet according to claim 1, wherein the recording sheet is a wet electrophotographic recording sheet.