JP2008122987A - Wet electrophotographic recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording sheet for wet electrophotography having an excellent wet toner fixability and transferability when printed by wet electrophotographic method using wet toner. <P>SOLUTION: The recording sheet for wet electrophotography has one or more coating layer at least on one side of a sheet base. The recording sheet for wet electrophotography is characterized in that at least one of materials other than pigment in a coating layer has a solubility parameter which differs from the solubility parameter of fused resin component of the wet toner by 8 or less, and is included by 0.5 to 50.0 mass% of the whole of coating layer solid content. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a recording sheet for wet electrophotography, and more specifically, for wet electrophotography having excellent toner fixability and transferability when printed using a wet electrophotographic system using a wet toner. It relates to a recording sheet.

  Applications for printing using the electrophotographic method are not limited to terminal PC printers, fax machines, or copiers, but are being put to practical use in the field of so-called on-demand printing that enables various types of small lot printing and variable information printing. The technological 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 from both sides of printing machines and printing paper is being promoted. 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 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 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 relatively expensive special paper 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, that is, the dots can be formed. This is because, in addition to being able to be made fine, a pigment can be used as a coloring material, so there is no problem of weather resistance or water resistance.

  Wet toner does not use charge or the like when transferring an image from a blanket roll to a sheet. The image is transferred using the fact that the wet toner printing sheet has higher adhesiveness than the blanket roll. That is, the ability to remove the wet toner from the blanket roll is important, and the adhesion ability cannot be increased more than necessary.

  For this reason, in the case of wet electrophotographic printing, there are disadvantages that, depending on the type of sheet, sufficient toner strength cannot be obtained even if printing is performed, or toner particles are not sufficiently transferred to the sheet. In order to solve such problems, the amount of ash in the base paper is specified, and zirconium is applied to the surface (for example, JP-A-10-171146), or surface smoothness and sizing agent are devised. There are some examples (for example, JP-A-10-171148). These are effective for plain paper (non-coated) type printing paper.

  However, in the case of a coating sheet for printing, the above method cannot be applied, and there is no commercially available printing paper that has sufficient toner suitability for the wet electrophotographic printing method. In order to solve this problem, there is an example which attempts to solve the problem by defining the kind of pigment or binder and the blending amount of the binder (for example, JP-A-9-281739). However, in practice, the fixability and transferability of wet toners are greatly influenced by the physical and chemical properties of the sheet surface, which are complexly related to various substances. It can be said that it is difficult to sufficiently improve sex.

  As a means for imparting wet electrophotographic printing suitability regardless of the type of sheet, there is a generally known means called sapphire treatment, but this method requires a post-process in creating the sheet. Therefore, it is not worth the cost. In addition, there is a drawback that the sheet becomes yellow over time.

  In order to solve these problems, there is an example in which creation of an electrophotographic recording sheet having wet toner suitability is achieved by controlling the area where the wet toner on the surface of the coating layer can interact (for example, a special feature). No. 2002-343237). However, this method is difficult to apply to a coating layer containing a plastic pigment, which is a very useful pigment for enhancing the glossiness of white paper and printing. This is because the plastic pigment has poor wettability with the adhesive resin component of the wet toner, and cannot be involved in adhesion regardless of the specific surface area. For this reason, in the prior art, when it has a coating layer containing a plastic pigment, it has been difficult to control the surface of the coating layer to have suitability for wet toner.

  In the future, when the quality of printed materials is increased, and high-speed printing and operability in subsequent processes are considered, there is a strong demand for recording sheets for wet electrophotography that have excellent fixability with wet toner.

  Accordingly, an object of the present invention is to provide a recording sheet for wet electrophotography having excellent toner fixing property and transferability when printed 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 wet electrophotographic recording sheet of the present invention.

That is, the wet electrophotographic recording sheet in the first invention is a wet electrophotographic recording sheet in which one or more coating layers are provided on at least one side of a sheet-like substrate, and M ₁ in the following formula ₁ is M _1. It is characterized by satisfying the condition of ≧ 25.
M ₁ = A × S (Formula 1)
A: Average specific surface area of the pigment used for the uppermost coating layer (m ² / g)
S: PPS smoothness (μmH20) of the wet electrophotographic sheet
In the present invention, _{M 1} in the above equation 1 is preferably satisfies the condition _{M 1} ≧ 40.

In the present invention, the coating amount of the uppermost layer is preferably 5 to 40 g / m ² .

Furthermore, liquid electrophotography recording sheet in the second invention, in the liquid electrophotographic recording sheet provided with a least one layer of the coating layer on one side of a sheet-like substrate, the M ₂ of the following Equation 2, M ₂ It is characterized in that the condition of ≧ 2.5 is satisfied.
M ₂ = A × S / X (Formula 2)
A: Average specific surface area of the pigment used for the uppermost coating layer (m ² / g)
S: PPS smoothness (μmH20) of the wet electrophotographic sheet
X: part by mass of binder component per 100 parts by mass of pigment used in the uppermost coating layer In the present invention, it is preferable that M ₂ in Formula 2 satisfies the condition of M ₂ ≧ 4.

  In the present invention, A, S, and X in Formula 2 are characterized by satisfying the conditions of A ≧ 25, 0.8 ≦ S ≦ 1.2, and X ≦ 10, respectively.

The wet electrophotographic recording sheet in the third invention is a wet electrophotographic recording sheet in which one or more coating layers are provided on at least one side of a sheet-like substrate, wherein N ₁ in the following Equation 3 is N ₁ ≧ 15. It satisfies the following conditions.
N ₁ = B × R × T (Formula 3)
B: Average specific surface area of the inorganic pigment used for the uppermost coating layer (m ² / g)
R: Volume ratio of inorganic pigment used in the uppermost coating layer in all pigments T: PPS smoothness (μmH20) of the wet electrophotographic sheet
In the present invention, it is preferable that N ₁ in Formula 3 satisfies the condition of N ₁ ≧ 20.

In the present invention, the coating amount of the uppermost layer is preferably 5 to 40 g / m ² .

The fourth liquid electrophotographic recording sheet in the invention, in wet electrophotographic recording sheet provided with a least one layer of the coating layer on one side of a sheet-like substrate, the N ₂ in the following Equation 4, N ₂ It is characterized by satisfying the condition of ≧ 1.5.
N ₂ = B × R × T / Y (Formula 4)
B: Average specific surface area of the inorganic pigment used for the uppermost coating layer (m ² / g)
R: Volume ratio of inorganic pigment used in the uppermost coating layer in all pigments T: PPS smoothness (μmH20) of the wet electrophotographic sheet
Y: Effective mass part for the pigment used for the uppermost layer of the electrophotographic sheet In the present invention, it is preferable that N ₂ in Formula 4 satisfies the condition of N ₂ ≧ 2.5.

  The wet electrophotographic recording sheet in the fifth invention is a wet electrophotographic recording sheet in which at least one coating layer is provided on at least one side of a sheet-like substrate, and at least of materials other than pigments in the coating layer. One is characterized in that the difference between the melt resin component of the wet toner and the solubility parameter is within 8 and 0.5 to 50.0% by mass of the entire solid content of the coating layer is contained.

  In the said invention, it is preferable that at least 1 of materials other than the pigment in a coating layer is 1.0-15.0 mass% of the whole solid content of a coating layer.

  Further, in the present invention, at least one of the materials other than the pigment in the coating layer has a difference in solubility parameter between the molten resin component of the wet toner and the solubility parameter within 5 and 1.5 to the total solid content of the coating layer. The content is preferably 5.0% by mass.

  The wet electrophotographic recording sheet according to the sixth invention is a wet electrophotographic recording sheet in which one or more coating layers are provided on at least one side of a sheet-like substrate. At least one is characterized in that the difference in solubility parameter between the molten resin component of the wet toner is within 8 and 20 to 100% by mass of the total adhesive component is used.

  In the present invention, at least one of the adhesive components in the coating layer has a difference in solubility parameter of 5 or less between the molten resin component of the wet toner and is used in an amount of 30 to 50% by mass of the entire adhesive component. It is preferable to be characterized by this.

  FIG. 1 is a schematic view showing the surface of a coating layer of glossy kaolin.

  FIG. 2 is a schematic view showing the surface of a matte kaolin coating layer.

  FIG. 3 is a schematic view showing the surface of a heavy calcium carbonate coating layer that has been subjected to the same calendering treatment as FIG.

  FIG. 4 is a schematic view showing micro unevenness of heavy calcium carbonate.

Hereinafter, the wet electrophotographic recording sheet of the present invention will be described in detail.
[First and second inventions]
As a result of repeated research on the fixability and transferability of toner on a wet electrophotographic recording sheet in the wet electrophotographic method, the present inventor is completely different from the other printing methods in the fixability and transferability of the wet toner. I found that the properties of coated paper are necessary.

  That is, the present inventors have found that the pigment surface area on the coated paper surface greatly affects the fixability and transferability of the wet toner. This can be based on the specific surface area of the pigment, but is not simply proportional to the specific surface area of the pigment.

  This is because the interaction between the wet toner and the pigment occurs only on the very surface of the coated paper. For example, even with coated paper using the same pigment, the surface area that can interact with the wet toner varies greatly depending on the degree of supercalendering of the coated paper (FIGS. 1 and 2). For example, FIG. 1 is a schematic view showing the surface of a coating layer of glossy kaolin. FIG. 1 shows the state of kaolin neatly arranged by the calendar process. In this case, only a part of the upper side can interact with the wet toner. On the other hand, FIG. 2 is a schematic view showing the surface of the matte kaolin coating layer, which shows the surface of the matte kaolin coating layer. In addition, since the gaps between the pigments are larger than those in FIG. 1, more portions appear on the surface of the coating layer. Further, since the orientation is different between kaolin and heavy calcium carbonate, the surface area capable of interacting with the wet toner is greatly different even when the same calender treatment is performed (FIGS. 1 and 3). FIG. 3 is a schematic view showing the surface of a heavy calcium carbonate coating layer that has been subjected to the same calendering treatment as FIG. FIG. 3 shows the state of calcium carbonate that has been calendered in the same manner as in FIG. 1, but because the pigment is indefinite, it is not aligned as in FIG. 1, and the surface area that can interact with the wet toner is increased. .

  An important factor for fixing the wet toner is the surface area of the pigment on the surface of the coating layer that can come into contact with the wet toner. The wet toner in contact with the pigment is adsorbed on the pigment surface by physical and chemical interaction with the pigment. Therefore, it can be said that FIGS. 1 and 2 and FIGS. 3 and 3 are more advantageous for fixing the toner than FIGS. Parker print surf smoothness (which will be abbreviated as PPS smoothness in the present invention) is a measurement method that simply and widely expresses these states. The PPS smoothness is closely related to the surface state of the pigment and the porosity, and in the present invention, the state of the surface pigment of the coated paper in question can be well represented.

  FIG. 4 is a schematic view showing the micro unevenness of heavy calcium carbonate, and is a schematic diagram showing the unevenness of calcium carbonate at the nano level. As shown in FIG. 4, the pigment also has a large number of nano level irregularities, and the effective surface area greatly changes. A good indicator of this is the specific surface area of the pigment. If the specific surface area is used, factors related to fixing of the wet toner such as particle diameter and porosity can be considered together. Here, the specific surface area is measured by the BET method.

First, in the wet electrophotographic recording sheets according to the first and second inventions, when the PPS smoothness is S μmH20 and the specific surface area is Am ² / g, the surface area index M ₁ that can interact with the wet toner is as follows. It can be expressed as Equation 1.
M ₁ = A × S (Formula 1)
Here, when the coated paper is manufactured so as to satisfy the condition of M ₁ ≧ 25, a coated paper excellent in wet toner fixing property and transferability can be obtained. When M ₁ ≧ 40, further excellent fixing property and transfer property can be obtained.

The coating amount of the uppermost layer that accepts the wet toner can cover the surface of the sheet-like substrate without gaps by applying 5 to 40 g / m ² . However, when it exceeds 40 g / m ² , the problem of the strength of the coating layer occurs.

  By the way, a binder component is usually added to the coating layer. The binder component covers the surface of the pigment and prevents the interaction between the wet toner and the pigment. A plastic binder has a particularly strong hindering action, which poses a serious problem in producing a wet electrophotographic recording sheet. Therefore, a more excellent wet electrophotographic recording sheet can be obtained by considering the blending amount of the plastic binder.

Here, the pigment surface area index M ₂ capable of interacting with the wet toner in consideration of the coating with the binder, where X is part by mass of the binder component with respect to 100 parts by mass of the pigment, can be expressed as Equation 2 below. it can.
M ₂ = A × S / X (Formula 2)
Here, when the coated paper is produced so as to satisfy M ₂ ≧ 2.5, it is possible to obtain a coated paper particularly excellent in wet toner fixing property and transferability, and when the condition of M ₁ ≧ 4 is exceeded. Extremely excellent fixability and transferability can be obtained.

As can be seen from the above formulas 1 and 2, in the wet electrophotographic recording sheet, so-called mat coated paper is relatively easy to fix and transfer, but the gloss type has excellent fixability and transfer. Difficult to get. However, by setting each parameter so as to satisfy A ≧ 25, 0.8 ≦ S ≦ 1.2, and X ≦ 10, the wet electrophotography having excellent wet toner fixability and transferability while having high gloss. Recording sheets can be obtained.
[Third and fourth inventions]
As a result of repeated research on the fixability of toner on a wet electrophotographic recording sheet in the wet electrophotographic method, the present inventor has a coating paper property completely different from other printing methods in the fixability of the wet toner. I found it necessary. That is, it was found that the surface area of the pigment on the coated paper greatly affects the fixability of the wet toner. This can be based on the specific surface area of the pigment, but it is not simply proportional to the specific surface area of the pigment. This is because the interaction between the wet toner and the pigment occurs only on the very surface of the coated paper. For example, even with coated paper using the same pigment, the surface area that can interact with the wet toner varies greatly depending on the degree of supercalendering of the coated paper. Further details are as described with reference to FIGS.

  However, the plastic pigment has a very poor affinity with the adhesive resin component of the wet toner, and the plastic pigment has little to do with fixing of the toner, so it must be considered except for this.

Here, assuming that the PPS smoothness is T μmH20, the average volume ratio of the inorganic pigment is R, and the average specific surface area of the inorganic pigment is Bm ² / g, the surface area index N ₁ that can interact with the wet toner is Can be expressed as
N ₁ = B × R × T (Formula 3)
Here, when the coated paper is manufactured so as to satisfy N ₁ ≧ 15, a coated paper excellent in wet toner fixing property can be obtained. When N ₁ ≧ 20, a further excellent fixing property can be obtained.

The volume ratio R of the inorganic pigment is calculated using the specific gravity. Here, d _n is the inorganic pigment n gravity, Z _n is the blending ratio relative to the total pigment of the pigment n, d _m is the specific gravity of the plastic pigments m, Z _m is putting as the blending ratio relative to the total pigment of the pigment m, It can be expressed as the following formula 5.
R = (Z1 / d1 + Z2 / d2 + ... + Zn / dn) / (Z1 / d1 + Z2 / d2 + ... + Zn / dn + Z1 '/ d1' + Z2 '/ d2' + ... + Zm / dm) (Formula 5)
For example, in the case of a coating layer of calcium carbonate 50% by mass (specific gravity 2.7), kaolin 30% by mass (specific gravity 2.7), and plastic pigment 20% by mass (specific gravity 1.0), the following formula 6 is obtained. .
R = (50 / 2.7 + 30 / 2.7) / (50 / 2.7 + 30 / 2.7 + 20 / 1.0) = 0.60 (Formula 6)
The coating amount of the wet toner receiving layer is preferably 5 g / m ² or more, so that the surface of the sheet-like substrate can be covered without any gap. However, when it exceeds 40 g / m ² , the problem of the strength of the coating layer occurs. If it is less than 5 g / m ² , uneven acceptance of wet toner occurs.

  By the way, a binder component is usually added to the coating layer. The binder component covers the surface of the pigment and interferes with the interaction between the wet toner and the pigment. A plastic binder has a particularly strong hindering action, which poses a major problem in producing wet electrophotographic coated paper. Therefore, a more excellent wet electrophotographic coated paper can be obtained by considering the blending amount of the plastic binder.

Here, assuming that the effective mass part of the binder component with respect to the pigment is Y part, the pigment surface area index N ₂ capable of interacting with the wet toner in consideration of the coating of the pigment with the binder can be expressed as the following Equation 4. it can.
N ₂ = B × R × T / Y (Formula 4)
Here, when the coated paper is manufactured so as to satisfy N ₂ ≧ 1.5, a coated paper particularly excellent in wet toner fixing property can be obtained. When N ₂ ≧ 2.5, extremely excellent fixability can be obtained.

In addition, the effective mass part Y of the binder component with respect to the pigment is calculated as the following formula 7 using the specific gravity of the pigment. Here, X is the number of parts by mass of the binder based on 100 parts by mass of the pigment. Further, _{d n} is the specific gravity of the pigment n, the _{Z n} put as the blending ratio relative to the total pigment of the pigment n (the _{Z n} to maximum 1).
Y = (d ₁ × Z ₁ + d ₂ × Z ₂ +... + D _n × Z _n ) × X / 2.7 (Formula 7)
For example, when 30 parts by mass of a plastic hollow pigment (mixing ratio 0.3, specific gravity 0.5) and 70 parts by mass of calcium carbonate (mixing ratio 0.7, specific gravity 2.7), 15 parts of binder with respect to 100 parts by mass of pigment The effective mass part Y is as shown in the following formula 8.
Y = (0.5 × 0.3 + 2.7 × 0.7) × 15 / 2.7≈11.3 (Formula 8)
It becomes.
[Fifth and sixth inventions]
As a result of repeated research on the fixability of the toner to the wet electrophotographic recording sheet in the wet electrophotographic method, the present inventor has found that the wet toner has a completely different fixability and transferability from those of other printing methods. I found that paper properties are necessary. That is, it was found that the wettability of the wet toner on the coated paper surface greatly affects the fixability.

  This involves a wet toner adhesion mechanism. Most of the liquid components of the wet toner are petroleum solvents. Petroleum solvents are lost due to heat evaporation during printing and absorption into the sheet, so they do not participate in adhesion or transfer. It is a resin that acts as an adhesive that plays a leading role in adhesion and transfer. This resin is melted by the heat of the roll when an image is formed with a blanket roll. When it comes into contact with the sheet, it is transferred, solidified, and fixed to the sheet. In order for this action to work smoothly, the interaction between the sheet surface and the molten resin needs to be sufficient.

  The height of the interaction between the sheet surface and the molten resin is related to the wettability between the sheet surface and the molten resin. It is essential for the molten resin to smoothly enter the micro unevenness of the sheet. As a result, the interaction between both molecules works in a wide range, that is, the toner is sufficiently transferred to the sheet. Furthermore, the anchor effect is strong and the toner is sufficiently fixed when the molten resin is solidified.

Usually, the wettability of the molten resin to the pigment component of the coating layer of the sheet is sufficient, but other blends contained in the general coating layer act as a factor inhibiting this. For example, a plastic adhesive repels molten resin components and inhibits entry into micro unevenness. On the other hand, polyvalent hydroxyl groups such as starch are unlikely to cause such inhibition. There is a solubility parameter as an index for judging the wettability of such various materials and molten resin components. It is also called SP value for short. The solubility parameter is an amount specific to each substance defined by Equation 1 below.
δ = (ΔH / V) ^1/2 (Equation 9)
When SP value of the material typically used for the coating layer of the coating sheet is exemplified, water 23.4, SBR latex 8.0 to 9.0, polystyrene 9.1, starch 15 to 16, polyvinyl alcohol ( PVA) 18.4, ethylene vinyl alcohol (EVA) 11-13. However, these values vary greatly depending on the functional group to be modified. For example, ether 14.5, ester 15.5, carbonyl 19.6, amine 21.1, alcohol 26.7, amide 29.0, and the SP value varies greatly depending on their abundance ratio. The SP value of PVA varies depending on the degree of saponification, and the modified starch and modified cellulose vary depending on the modification method and degree.

  Many of the resins used as the molten resin component of the wet toner have an amino group or a carboxyl group at a high content in the molecule, and the SP value is often around 20.

  The closer the value of the solubility parameter between substances, the better the wettability described above. The further away, the less compatible and repels. In order to allow smooth penetration of the molten resin component into the micro unevenness of the sheet surface, the difference between the average value of the solubility parameter of the molten resin component and the solubility parameter of the material other than the pigment is preferably within 8 or less. More preferably, the difference is 5 or less.

  All the materials other than the pigment need not be within this range, and may be contained in an amount of 0.5 to 50% by mass or more of the coating layer. Preferably it is 1.0-15.0 mass%, More preferably, it is 1.5-5.0. If it is less than 0.5% by mass, the repellency will be severe, and if it exceeds 50% by mass, the viscosity of the coating solution will be extremely high at the application stage of the coating layer. Becomes higher. Further, since there are too many components other than the pigment and the surface of the pigment is hardly exposed, the fixability and transferability become unsuitable. The most balanced range of the penetration effect and the sheet manufacturing operability is 1.5 to 5.0% by mass. When the solubility parameter difference is within 5 and the content is 1.5 to 5.0% by mass, a higher effect is exhibited.

  By the way, among the various components in the coating layer, since the adhesive covers the surface of the pigment, the effect of inhibiting the penetration of the molten resin component into the micro unevenness is particularly strong. If this adhesive has a solubility parameter with a difference of 8 or less from the molten resin component, the suitability for wet toner is further enhanced. Preferably it is within 5. In order to obtain an effective coating layer, 20 to 100% by mass of the entire adhesive component is preferably in this range. Preferably it is 30-50 mass%. When the amount is less than 20% by mass, the effect to the extent that it is even better cannot be obtained. When considering the strength of the coating layer and the operability during production, it is preferable to use a plastic adhesive having a solubility parameter that is 30 to 50% by mass of the adhesive component. It can be said that the component is the most balanced range. When the solubility parameter difference is within 5 and the content is 30 to 50% by mass, the highest effect is exhibited.

The coating amount of the wet toner receiving layer is preferably 5 g / m ² or more, so that the surface of the sheet-like substrate can be covered without any gap. However, when it exceeds 40 g / m ² , the problem of the strength of the coating layer occurs. Therefore, it is important to effectively provide the coating layer having the coating amount in this range as the uppermost layer in order to effectively use the present invention.

  The wet electrophotographic recording sheet in each of the above inventions is not limited to use as a wet electrophotographic recording sheet, but other printing such as a dry electrophotographic recording sheet, an offset printing sheet, an inkjet sheet, and a thermal transfer sheet. It can also be used in the scheme.

  Subsequently, items common to the wet electrophotographic recording sheets in the above inventions will be described below.

  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 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 In addition, a sheet in which inorganic fibers such as metal fibers and carbon fibers are formed 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 various fillers such as light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, titanium dioxide, aluminum hydroxide, adhesives, sizing agents, fixing agents, retention agents, paper strength enhancers. Etc. are suitably blended according to each step and each material.

  Furthermore, a resin coat layer may be provided on these fiber sheets.

  Other base materials include fine paper, medium paper, color fine paper, 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, heat sensitive Also included are 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 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 used in the coating layer is not particularly limited. For example, as the inorganic pigment, various natural kaolin pigments such as various kaolins, talc, heavy calcium carbonate (pulverized calcium carbonate), Light calcium carbonate (synthetic calcium carbonate), composite synthetic pigment of calcium carbonate and other hydrophilic organic compounds, satin white, lithopone, titanium oxide, silica, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate, calcined kaolin, etc. Examples of organic pigments include plastic pigments.

  Binders used in coating liquids include starch purified from natural plants, hydroxyethylated starch, oxidized starch, etherified starch, phosphate esterified starch, enzyme-modified starch, and flash dried. 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 And 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.

  Further, as a thickener used in the coating solution, water-soluble polymers such as carboxymethylcellulose, sodium alginate, methylcellulose, hydroxyethylcellulose, casein, sodium polyacrylate, polyacrylate, 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 paper in a series of operations, various finishing treatments such as calendering are performed as necessary. The

Examples Hereinafter, examples of the present invention will be described. However, 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.
[First invention]
Examples 1 to 13 and Comparative Examples 1 to 3
Wet electrophotographic recording sheets of Examples 1 to 13 and Comparative Examples 1 to 3 were prepared with the following composition.
<Base paper>
LBKP (freeness 330 to 440 mlcsf) 70 parts NBKP (freeness 390 to 490 mlcsf) 30 parts light calcium carbonate (* represented by ash content in base paper) * 8 parts commercial cationized starch 1.0 parts commercial cationic polyacrylamide yield 0.03 parts of improver pulp and internally added chemicals were prepared in the above-mentioned composition, and a base paper having a basis weight of 70 g / m ² was made.

To this base paper, 0.80 g / m ² of oxidized starch was adhered on both sides by a size press to obtain a base paper for coating.
<Coating solution>
The pigment composition is listed in Table 1. Other blends are as follows.
Styrene butadiene latex binder (average particle size 100 nm, gel content 40%, Tg 5 ° C.) 10 parts Commercial phosphate esterified starch 3 parts Commercial polyacrylic acid dispersant Suitable amount Commercial carboxymethyl cellulose thickener (CMC) 0. Adjust to pH 9.6 with 1 part sodium hydroxide

  Prepare various coating liquids as described above, apply to the base paper for coating according to the coating amount shown in Table 2 using a fountain / blade coater, and perform supercalendering to obtain a recording sheet for wet electrophotography. It was.

The wet electrophotographic recording sheets obtained in Examples 1 to 13 and Comparative Examples 1 to 3 were measured by the following measuring methods, and the evaluation results are listed in Table 2.
1. Printing Printing was performed using “E-print 1000” manufactured by Indigo as a transfer machine for wet electrophotography. As a print image to be used for evaluation, an image having a solid print portion for each of four colors of black, cyan, magenta, and yellow was output. As a printing area of the solid printing portion, at least a square with a side of 3 cm or more was used.

As described above, the following fixing evaluation was performed on the solid print portions of each color of black, cyan, magenta, and yellow printed by “E-print 1000”.
2. Tape stripping After printing, a cellophane adhesive tape “Cello Tape (registered trademark) No. 405” made by Nichiban Co., Ltd. with a width of 18 mm is pasted on a print sample that has passed for 24 hours so that there is no unevenness in the printing part of each color, The tape was slowly peeled off at a speed of about 5 mm / second. The degree of fixing of the toner after peeling to the paper was visually determined, and a five-step evaluation was performed according to the following criteria. “Δ” or more is regarded as the symmetry of the invention.
A: Most of the toner remains on the paper for each color.
○: The toner remains in each color, but it can be seen that the print density of the printing portion after the tape is peeled is lowered.
(Triangle | delta): The toner peeled off from paper with one part color, and there is a part which has fallen white in the printing part.
X: For each color, the toner is peeled off from the paper, and the white portion of the printed portion is noticeable.
3. For rubbing evaluation, the horizontal method of JIS P8147 “Testing method for friction coefficient of paper and paperboard” was applied. For each of the examples and comparative examples, a blank wet electrophotographic recording sheet was attached to the horizontal plate, and the recording sheet having a printing portion printed by the printing machine was attached to the weight. Then, when the transfer paper with the printing portion was attached to the weight, the printed surface of the printing portion was rubbed against the blank recording sheet attached to the horizontal plate.

  As described above, after the test piece is attached to the horizontal plate and the weight, the weight is slid on the horizontal plate under the conditions described in JIS P8147. In the “friction test”, the weight is slid on the horizontal plate only once with one test piece combination. In this evaluation, the weight is slid on the horizontal plate 50 times with one test piece combination. Let The test piece used was 24 hours after printing.

Thereafter, the printing unit attached to the weight was observed, and the degree of toner dropout due to rubbing between the papers was observed. The remaining condition of the toner in the printing portion was visually determined, and a four-step evaluation was performed according to the following criteria. “Δ” or more is regarded as the symmetry of the invention.
A: A decrease in the density of the printed portion is hardly recognized for each color.
○: It can be seen that the print density decreases slightly for each color.
Δ: It can be seen that the print density decreases for each color.
X: It can be seen that the print density decreases for each color, and there is a part that is partially whitened.
4). Eraser peeling 24 hours after printing, the printed part of each color was reciprocated five times with a uniform force using the corners of the unused eraser “dragonfly pencil, PE-01A”. The degree of fixing of the toner after reciprocation to paper was visually determined, and a four-step evaluation was performed according to the following criteria. “O” or more was regarded as the symmetry of the invention.
A: The toner does not peel from the paper for each color.
○: Some toner is peeled from the paper, but less than 20%.
Δ: Less than 50%, the toner is peeled off from the paper, and some parts are white.
X: For each color, the toner is easily peeled off from the paper, and the white portions are conspicuous.
5. Transferability After printing using “E-print1000” manufactured by Indigo as a transfer machine for wet electrophotography, cleaning was performed with a print cleaner, and transferability was determined based on how the print cleaner was stained. “Δ” or more was the subject of the invention.
A: Not dirty at all.
○: Very small dirt adheres.
Δ: Small dirt adheres.
X: It becomes dirty clearly.
6). White Paper Gloss About the white paper gloss, gloss was evaluated with a gloss meter at a 75 ° -75 ° reflectance. In particular, when A, S, and X satisfy the conditions of A ≧ 25, 0.8 ≦ S ≦ 1.2, and X ≦ 10, respectively, “◯” or more is the subject of the invention.

○ (Good): 70% or more △ (Normal): 70% or less

<Evaluation results>
As in Comparative Examples 1 to 3, coated paper that does not satisfy M ₁ ≧ 25 cannot have suitability for wet toner. On the other hand, the wet electrophotographic recording sheet satisfying M ₁ ≧ 25 as in all the examples is suitable for the wet toner. As can be seen from comparison between Examples 1 and 2 and Examples 3 to 6, when M ₁ ≧ 40, the toner has better wet toner suitability. As can be seen from a comparison of Examples 7 to 13, when the coating amount is less than 4 g / m ² or more than 40 g / m ² , some undesired physical properties appear. Therefore, the coating amount is preferably 5 to 40 g / m ² .
[Second invention]
Examples 14-23
For the same coating base paper as obtained in Examples 1 to 13 and Comparative Examples 1 to 3, the following coating solution was prepared, and the coating amount was 15 g / m ² using a fountain / blade coater. Coating was performed on the coating base paper, and supercalender treatment was performed to obtain wet electrophotographic recording sheets of Examples 14-23.
<Coating solution>
The pigment formulation and binder formulation are listed in Table 3. As the binder, a styrene-butadiene latex binder (average particle size 100 nm, gel content 40% by mass, Tg 5 ° C.) and commercially available phosphated starch were used. Other formulations are as follows.
Commercially available polyacrylic acid-based dispersant Appropriate amount Commercially available carboxymethylcellulose-based thickener (CMC) 0.1 part Adjusted to pH 9.6 with sodium hydroxide

  The wet electrophotographic recording sheets obtained in Examples 14 to 23 were measured by the measurement method described above, and the evaluation results are listed in Table 4.

<Evaluation results>
As can be seen from a comparison of Examples 14 and 15, when the value of M ₂ ≧ 2.5 satisfies the specified value in addition to M ₁ ≧ 25, it has very good wet toner suitability. Further, when M ₂ ≧ 4.0 is satisfied as in Examples 16 to 20, it is extremely good. On the other hand, as can be seen by comparing Examples 21 to 23, a wet electrophotographic recording sheet excellent in white paper gloss can be obtained by satisfying A ≧ 25, 0.8 ≦ S ≦ 1.2, and X ≦ 10. .
[Third invention]
Examples 24-33 and Comparative Examples 4-6
Wet electrophotographic recording sheets of Examples 24-33 and Comparative Examples 4-6 were prepared with the following composition.
<Base paper>
LBKP (freeness 330 to 440 mlcsf) 70 parts NBKP (freeness 390 to 490 mlcsf) 30 parts light calcium carbonate (* represented by ash content in base paper) * 8 parts commercial cationized starch 1.0 parts commercial cationic polyacrylamide yield 0.03 parts of improver pulp and internally added chemicals were prepared in the above-mentioned composition, and a base paper having a basis weight of 70 g / m ² was made.

To this base paper, 0.80 g / m ² of oxidized starch was adhered on both sides by a size press to obtain a base paper for coating.
<Coating solution>
The pigment composition is listed in Table 5. Other blends are as follows.
Styrene butadiene latex binder (average particle size 100 nm, gel content 40%, Tg 5 ° C.) 10 parts Commercial phosphate esterified starch 3 parts Commercial polyacrylic acid dispersant Suitable amount Commercial carboxymethyl cellulose thickener (CMC) 0. Adjust to pH 9.6 with 1 part sodium hydroxide

  The various coating liquids described above were prepared and applied to the coating base paper with a coating amount described in Table 6 using a fountain / blade coater, and subjected to supercalendering to obtain a wet electrophotographic recording sheet. It was.

  The wet electrophotographic recording sheets obtained in Examples 24 to 33 and Comparative Examples 4 to 6 were measured by the measurement method described above, and the evaluation results are listed in Table 6.

<Evaluation results>
As in Comparative Examples 4 to 6, coated paper that does not satisfy N ₁ ≧ 15 cannot have suitability for wet toner. On the other hand, the wet electrophotographic recording sheet satisfying N ₁ ≧ 15 as in all the examples is suitable for the wet toner. As can be seen from comparison between Examples 24 and 25 and Example 26, when N ₁ ≧ 20, the wet toner suitability is further improved. As can be seen from a comparison of Examples 27 to 33, when the coating amount is less than 4 g / m ² or more than 40 g / m ² , some unfavorable physical properties appear. Therefore, the coating amount is preferably 5 to 40 g / m ² .
[Fourth Invention]
Examples 34-40
For the same coating base paper as obtained in Examples 24 to 33 and Comparative Examples 4 to 6, the following coating solution was prepared, and the coating amount was 15 g / m ² using a fountain / blade coater. The above coating base paper was coated and subjected to supercalendering to obtain wet electrophotographic recording sheets of Examples 34-40.
<Coating fluid>
The pigment formulation and binder formulation are listed in Table 7. As the binder, a styrene-butadiene latex binder (average particle size 100 nm, gel content 40% by mass, Tg 5 ° C.) and commercially available phosphated starch were used. Other formulations are as follows.
Commercially available polyacrylic acid-based dispersant Appropriate amount Commercially available carboxymethylcellulose-based thickener (CMC) 0.1 part Adjusted to pH 9.6 with sodium hydroxide

  The wet electrophotographic recording sheets obtained in Examples 34 to 40 were measured by the measurement method described above, and the evaluation results are listed in Table 8.

<Evaluation results>
As can be seen from a comparison of Examples 34 and 35, when N ₁ ≧ 15 and N ₂ ≧ 1.5 also satisfy the specified value, the toner has very good wet toner suitability. Further, when N ₂ ≧ 2.5 is satisfied as in Examples 36 to 40, a very good wet electrophotographic recording sheet can be obtained.
[Fifth Invention]
Examples 41-56 and Comparative Examples 7-10
Wet electrophotographic recording sheets of Examples 41 to 66 and Comparative Examples 7 to 10 were prepared with the following composition.
<Base paper formulation>
LBKP (freeness 330-440 mlcsf) 70 parts NBKP (freeness 390-490 mlcsf) 30 parts <internally added chemicals>
Light calcium carbonate (* expressed as ash content in base paper) * 8 parts commercial cationized starch 1.0 parts commercial cationic polyacrylamide yield improver 0.03 parts Pulp, internal additive prepared with the above formulation, basis weight 70 g Paper of / m ² was made.

The base paper was coated with 0.80 g / m ² of oxidized starch on both sides by a size press to obtain a base paper for coating.
<Composition of coating liquid>
The formulations other than those described in Table 9 are shown below. Others are as shown in Table 9. As the solvent, water or ethyl alcohol and a mixed solvent thereof were used. Note that the solubility parameter values of the dispersant, CMC, and sodium hydroxide are small and can be assumed to have no effect.
Commercially available calcium carbonate pigment 100 parts Commercially available polyacrylic acid dispersant Suitable amount Commercially available styrene butadiene latex (average particle size 100 nm, gel content 40%, Tg 5 ° C.) 10 parts Commercially available carboxymethylcellulose thickener (CMC) 0.01 Adjusted to pH 9.6 with sodium hydroxide

The various coating solutions described above were prepared, applied with a fountain / blade coater at a coating amount of 7 g / m ² , and subjected to supercalendering to obtain a recording sheet for wet electrophotography. The ease of coating at the time of coating was evaluated sensuously. “Δ” or more was the subject of the invention.
“◎”: The coating can be applied very smoothly after preparation.
“◯”: After the preparation, it can be applied smoothly.
“△”: After preparation, if any measures are taken, coating is performed.
"X": Coating is impossible or almost impossible.

  The wet electrophotographic recording sheets obtained in Examples 41 to 56 and Comparative Examples 7 to 10 were measured by the measurement method described above, and the evaluation results are listed in Table 10. The average value of the solubility parameter of the molten resin component of the ink used for printing is 20.

<Evaluation results>
As in Comparative Examples 7 and 8, if the material other than the pigment having a solubility parameter whose difference from the average solubility parameter of the molten resin component of the wet toner is within 8 is not included, the wet toner is hardly suitable. On the other hand, it can be seen that wet toner suitability can be obtained by including 0.5% by mass or more as in Example 41 and other examples. On the other hand, as can be seen from Example 47 and Comparative Example 10, when it exceeds 50% by mass, the operability becomes worse and the suitability is lost. As can be seen by comparing Examples 42, 43 and 45, 46, preferable results are obtained when the corresponding compound is in the range of 1.5 to 15.0% by mass. From Example 44 and Comparative Example 9, when the difference in solubility parameter is 8 or more, the wet toner suitability is lost. As can be seen by comparing Examples 48 to 56, more preferable results are obtained when the difference in solubility parameter is within 5 and from 1.5 to 15% by mass.
[Sixth Invention]
Examples 57-69
For the same coating base paper as prepared in Examples 41 to 56 and Comparative Examples 7 to 10, the following coating solution was prepared, and the coating amount was 7 g / m ² using a fountain / blade coater. Was coated on the above-mentioned base paper for coating, and supercalender treatment was performed to obtain recording sheets for wet electrophotography of Examples 57 to 69.
<Composition of coating liquid>
Table 11 below shows formulations other than those described. Others are as shown in Table 11. As the modified starch, natural corn starch having a solubility parameter of each value was synthesized by acetylation treatment with DMF / acetic anhydride / pyridine. Commercially available products (100% saponification degree) are used for PVA, etc., and styrene butadiene latex adhesive (average particle size 100 nm, gel content 40%, Tg 5 ° C.) is used as the plastic adhesive. As the solvent, water or ethyl alcohol and a mixed solvent thereof were used. Note that the solubility parameter values of the dispersant, CMC, and sodium hydroxide are small and can be assumed to have no effect.
Commercially available calcium carbonate pigment 100 parts Commercially available polyacrylic acid dispersant Suitable amount Commercially available carboxymethylcellulose thickener (CMC) 0.01 parts Adjusted to pH 9.6 with sodium hydroxide

  The wet electrophotographic recording sheets obtained in the above examples were measured by the measurement method described above, and the evaluation results are listed in Table 12.

<Evaluation results>
When Examples 57 to 59 were compared, a preferable result was obtained when the amount of the corresponding compound in the adhesive content ratio was 20% by mass, and the adhesive content ratio of the corresponding compound was 30 as in Examples 60 to 69. It can be seen that when the difference in solubility parameter is within 5% by mass to 50% by mass, the toner has particularly excellent wet toner suitability. Thus, it can be seen that excellent results can be obtained by producing a wet electrophotographic recording sheet as defined in the present invention.

  As described above, the wet electrophotographic recording sheets according to the first to sixth inventions have excellent toner fixability and transferability when printed using a wet electrophotographic system using a wet toner. Recording sheets can be obtained.

It is the schematic which shows the coating layer surface of a glossy kaolin. It is the schematic which shows the coating layer surface of a matte kaolin. It is the schematic which shows the coating layer surface of the heavy calcium carbonate which carried out the calendar process similar to FIG. It is the schematic which shows the micro unevenness | corrugation of heavy calcium carbonate.

Claims (5)

  In a wet electrophotographic recording sheet in which at least one coating layer is provided on at least one side of a sheet-like substrate, at least one of the materials other than the pigment in the coating layer is a molten resin component of a wet toner and a solubility parameter. A wet electrophotographic recording sheet having a difference of 8 or less and containing 0.5 to 50.0% by mass of the entire solid content of the coating layer.   2. The wet electrophotographic recording sheet according to claim 1, wherein at least one of the materials other than the pigment in the coating layer contains 1.0 to 15.0 mass% of the entire solid content of the coating layer. .   At least one of the materials other than the pigment in the coating layer has a difference in solubility parameter between the molten resin component of the wet toner and the solubility parameter within 5 and contains 1.5 to 5.0% by mass of the entire solid content of the coating layer. The wet electrophotographic recording sheet according to claim 1, wherein the recording sheet is a wet electrophotographic recording sheet.   In a wet electrophotographic recording sheet in which at least one coating layer is provided on at least one side of a sheet-like substrate, at least one of the adhesive components in the coating layer is a difference in solubility parameter from the molten resin component of the wet toner. The wet electrophotographic recording sheet according to any one of claims 1 to 3, wherein the recording material is within 8 and 20 to 100% by mass of the entire adhesive component.   At least one of the adhesive components in the coating layer has a difference in solubility parameter of 5 or less between the molten resin component of the wet toner and 30 to 50% by mass of the entire adhesive component is used. The recording sheet for wet electrophotography according to claim 4.

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