JP2007264288A - Electrophotograph transfer paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotograph transfer paper which has at least one or more coat layers and is superior in appearance after printing and in image quality on the surface. <P>SOLUTION: This electrophotograph transfer paper has at least one or more layers coated on the base paper and is characterized by its formation index of ≥100, for the formed total when measured by using a three-dimensional analyzer made by MKsystem Co. This is a printing paper 105 g/m<SP>2</SP>or higher but ≤169 g/m<SP>2</SP>in weight and used to print in an electrophotograph printer at a printing speed of ≥20 sheets per minute for standard A 4 size paper in the length direction. The coated layer has an amount of coating of ≥10 g/m<SP>2</SP>and its 75° mirror surface glossiness is ≥60% by JIS P8142, and the surface electric resistance of the paper is ≥1×10<SP>11</SP>Ω by JIS K6911. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic transfer paper. More specifically, it can be printed by electrophotographic printers, fax machines, copiers, and on-demand printers. In particular, it is a transfer for electrophotography that gives a high-quality image without fine gloss unevenness and density unevenness with solid images. Provide paper.

  Output by electrophotography is rapidly expanding due to the spread of printing from personal computers and on-demand printing. Up to now, high-quality output media has been preceded by the sublimation thermal transfer system, which has been used in the field of medical image processing, etc. It was a point.

  Recently, coupled with dramatic improvements in resolution and ink droplet miniaturization technology, the inkjet printing method is approaching photographic image quality, and several photo systems have been put on the market due to their low running costs. . However, although the inkjet method is inexpensive, the problem that the printing process takes time has not been solved.

  The electrophotographic method, which is relatively inexpensive and has a short print processing time, has attracted attention as a full-color output method that emphasizes visuals as well as text-centered outputs. In the electrophotographic method, an original latent image is formed on a semiconductor material, which is made visible by toner and transferred onto an image receiving material. The toner is generally fixed on the image receiving material by heat.

  The output by the electrophotographic system is increasing in speed and image quality year by year, and accordingly, the requirements for various physical properties required for the paper are also changing. The physical properties required of paper are limited to, for example, dry electrophotography, for example, surface resistivity / volume resistivity relating to static electricity attenuation used for image formation, and thermal conductivity (smoothness, density) relating to heating efficiency of toner fixing. , Air permeability for reducing blisters during heating or internal bond strength of paper, rigidity for double feeding and jamming problems during high-speed conveyance of paper, and friction coefficient between paper.

  Among these, when attention is paid to a printed image after printing, it is known that the surface / volume resistance value related to transfer and the smoothness that causes uneven unevenness are important.

  In an electrophotographic printer, a large amount of heat is applied to transfer toner to an electrophotographic transfer paper and fix the toner. The principle of toner transfer is based on a method of attracting toner through paper using an electrostatic force having a potential opposite to that of the toner. At this time, if static electricity leaks in the paper, the static electricity that attaches the toner weakens, and the toner does not transfer to the paper sufficiently. Since the static electricity leakage of this paper has been experimentally shown to be inversely proportional to the surface resistivity and volume resistivity, the surface resistivity and volume resistivity are used as a measure of the degree of static electricity leakage. Has been.

  With respect to the surface resistivity and the volume resistivity, various conditions are prescribed in each patent, and it is described that a clear image cannot be obtained unless each patent satisfies the prescribed value. (For example, patent document 1).

  However, in practice, when various papers are prototyped and a print test is performed on papers whose surface resistivity and volume resistivity are changed, it can be confirmed that there are upper and lower resistance limits for each printer. Generally, the lower the resistance value, the better, that is, the upper limit tended to be lower until several years ago, but the lower limit is now becoming higher with the recent increase in the speed of electrophotographic printers. This is considered to be due to the fact that the toner particle size becomes smaller as the resolution becomes higher, and the transfer potential necessary for toner transfer becomes lower. The lower the transfer potential, the less the static electricity diffusion on the paper surface, and the higher the required surface / volume resistance value. Here, there are many patents regarding the ranges of the surface resistivity and the volume resistivity, and there are factors in which the prescribed values differ for each patent. From the above results, it can be confirmed that the meaning of the definition is ambiguous in the description of the surface resistivity and the volume resistivity ignoring the relation with the printing speed.

  Further, even when the surface / volume resistance value of the electrophotographic transfer paper is within an appropriate range, printing unevenness (hereinafter abbreviated as printing unevenness) may occur. This is believed to be related to the smoothness and texture of electrophotographic paper. In general, the better the formation, the smoother the unevenness. There is a patent that defines the formation coefficient of a base paper of an electrophotographic transfer paper having at least one coating layer (for example, Patent Document 2). However, it can be said that the aperture at the time of formation measurement is rough and the formation value is low, and the printing speed of the evaluation machine is low, and the quality is insufficient for an electrophotographic printer that is currently increasing in speed and resolution. In addition, the coating amount and the 75-degree specular gloss (hereinafter abbreviated as “white gloss”) of the coating layer according to JISP8142 are also low, and it is impossible to obtain the same quality as the mainstream A2 coat as a coated paper in the so-called offset printing field.

Usually, since the electrostatic capacity and heat capacity of the paper depend on the paper thickness or basis weight, the printing speed varies with the paper thickness or basis weight, and the printing speed decreases with these increases. The adjustment of the printing speed with respect to the paper thickness or basis weight varies depending on the company or each printer of the electrophotographic printer, but for paper of 105 g / m ² or more, a printing mode in which the printing speed is specially reduced, that is, a cardboard mode is provided. There are many cases. Here, it is difficult to increase the printing speed of thick paper.

  Further, when a coating layer is provided, the coating layer has a higher density than the base paper layer, so that the thermal conductivity is high, and the static electricity decay rate is also increased. Accordingly, similarly, the thicker the coating layer, the lower the printing speed must be, and it becomes difficult to increase the printing speed.

With the widespread use of electrophotographic transfer paper, a level of printing equivalent to so-called offset printing has been required for the quality after printing. However, it is difficult to increase the printing speed for the above reasons. While the speed of the electrophotographic printer was slow, there was no problem with using commercially available A2 coated paper for offset printing. However, with the recent increase in the speed of electrophotographic printers, there are various problems in addition to uneven printing. It is likely to occur. In particular, since the A2 coated paper for offset printing usually has a white paper gloss of 60% or more, the coating amount corresponding to this is required to be 10 g / m ² or more on one side, but it has a high thermal conductivity and a static electricity decay rate. Therefore, it can be said that speeding up becomes difficult.

Therefore, with the recent increase in image quality of electrophotographic transfer paper, there has been a demand for better quality after printing, but on the other hand, printing unevenness becomes more noticeable as the speed of printers increases. Yes. There is a need for an electrophotographic transfer paper that can output a more uniform image even with a high-speed printer.
Japanese Patent No. 3232514 JP-A-8-123066

  Accordingly, an object of the present invention is to provide an electrophotographic transfer paper that is excellent in the appearance of the printed matter after printing and the image quality of the printed surface in the electrophotographic transfer paper having at least one coating layer.

  As a result of intensive studies in view of the above, the present inventor has invented the electrophotographic transfer paper of the present invention.

  That is, the electrophotographic transfer paper of the present invention is characterized in that the formation index is 100 or more in the electrophotographic transfer paper in which at least one coating layer is provided on the base paper.

Further, it is characterized by being 105 g / m ² or more and 169 g / m ² or less.

Further, the coating layer is coated so that the coating amount is 10 g / m ² or more and the 75-degree specular gloss of the coating layer according to JISP8142 is 60% or more.

Furthermore, the surface electrical resistance value of the transfer paper according to JISK6911 is 1 × 10 ¹¹ Ω or more.

  By using the electrophotographic transfer paper of the present invention, it is possible to print an image excellent in the appearance of the printed matter after printing with the electrophotographic printer and the image quality of the printing surface.

Hereinafter, the electrophotographic paper will be described in detail. The present inventor has a sheet gloss is 60% to 80% and basis weight 105g / m ² ~169g / m electrophotographic paper transfer paper printing speed of ² of the sheet 20 sheets of A4 lateral / min or more of an electrophotographic printer Various We proceeded with the study by printing.

First, as a result of studying the surface / volume resistance value, the printing speed is relatively fast, and therefore printing unevenness may occur unless the surface resistivity in a 23 ° C. and 50% environment is 1.0 × 10 ¹¹ Ω or more. Was revealed.

  However, just controlling the surface resistance value did not reduce printing unevenness, and other factors were suggested, and as a result of diligent research, it was confirmed that the formation of electrophotographic transfer paper was deeply involved. did.

  The measurement method of formation is not standardized, and several types of formation measurement devices are sold by each company. There are two types of devices, one using β rays and the other using light transmitted light. Further, there are evaluation methods for using light transmitted light, and processing the variation of light transmitted light as an image, There is something to process the cycle. Further, even in the same light transmission image analysis type, evaluation criteria vary depending on each company, such as a higher formation index and a better formation, and a lower formation index.

  In the present invention, the formation was measured using “3-D SHEET ANALYZER” manufactured by M / Ksystem, which can measure the formation even with relatively thick paper. In this apparatus, the formation becomes better as the formation coefficient becomes higher. Usually, the formation of only paper made of wood pulp or the like is measured. However, since the formation can be measured even with relatively thick paper, it can also be applied to coated paper. Normally, when the amount of light transmitted is used, the coefficient changes depending on the thickness, but this apparatus has a function of automatically adjusting the amount of light, and the influence of the thickness can be eliminated to some extent.

  Actually, the means for increasing the formation coefficient of the base paper is roughly divided into a base paper blending method and a paper making method. Examples of the blending method include a method of using a pulp having a short fiber length and adjusting the amount of the yield improver. As a papermaking method, the J / W ratio is controlled, the wire used for papermaking is changed, and a hybrid former or a gap former with a dewatering board with a pressure adjusting mechanism is used alone. Or it is achieved by combining.

In addition, the formation coefficient of the paper after coating also changes depending on the composition of the coating liquid. For example, in the case of a coating liquid with poor water retention, that is, the coating liquid is likely to soak into the base paper, the formation is more likely to deteriorate. Tend. Therefore, when the preparation concentration of the coating liquid is low or when a binder with low water retention is used, the formation coefficient of the paper after coating is lowered. The concentration of the coating solution is not particularly specified, but it can be said that a concentration of a certain level or higher is desirable so that the water retention is at least 60 g / m ² or less. Also, the higher the concentration, the better from the viewpoint of drying load and drying history.

With respect to the coating amount, it is first important to cover, that is, to sufficiently cover the base paper with the coating solution, and next, it is necessary to determine the coating amount so that the white gloss can be sufficiently expressed. Generally, covering requires 5 g / m ² or more on one side, and 8 g / m ² or more on one side depending on the state of the base paper. The effect of the coating amount, the pigment system containing the coating liquid, and the smoothing treatment are significant for the development of white paper gloss. Among these, regarding the smoothing treatment, there is no particularly difficult part regarding the expression of 60% or more of the blank paper gloss as long as the coating amount of 7 to 8 g / m ² is satisfied due to the recent improvement of the calendar apparatus. However, in the method of developing white paper gloss by reducing the coating amount and performing the smoothing process, another problem such as double feeding tends to occur in the electrophotographic printer. Therefore, although depending on the pigment system, the coating amount is preferably 10 g / m ² or more, and the load of the smoothing treatment should be as small as possible.

  Examples of the internal filler used when producing the electrophotographic transfer paper of the present invention include kaolin, clay, and styrene acrylic hollow pigment in addition to light calcium carbonate and heavy calcium carbonate.

  Examples of the internal sizing agent used when producing the base paper of the electrophotographic transfer paper of the present invention include a rosin sizing agent in the case of acidic papermaking, and an alkyl ketene dimer and alkenyl in the case of neutral papermaking. Examples include succinic anhydride, neutral rosin sizing agent, and cationic styrene acrylic.

  The base paper surface of the electrophotographic transfer paper of the present invention has a binder such as starch and polyvinyl alcohol, a styrene / acrylic acid copolymer, a styrene / methacrylic acid copolymer, and a styrene / methacrylic acid copolymer. , Surface sizing agents such as acrylonitrile / vinyl formal / acrylic ester copolymer, styrene / maleic acid copolymer, dimensional stabilizers such as ethylene-urea resin, inorganic conductive agents such as sodium chloride and potassium chloride, organic conductive It is possible to impregnate agents, surfactants, pigments and dyes.

  As an apparatus for applying the binder, the surface sizing agent, and the like, a conventional size press, a gate roll size press, a film transfer type size press, a rod coater, a bill blade, a short dwell coater, or the like can be used. Among these coating apparatuses, a system that impregnates the above-mentioned size press liquid into the paper layer is desirable.

  The pulp that can be used when the base paper of the electrophotographic transfer paper of the present invention is manufactured as a neutral paper includes NBKP, LBKP, NBSP, LBSP, GP, TMP, and other non-wood pulp such as kenaf and bagasse, Used paper pulp is used, and it is used alone or in combination as required.

  Examples of other additives include pH adjusters, metal sequestering agents, antifungal agents, viscosity modifiers, surface tension modifiers, lubricants, surfactants, and rust inhibitors.

  In the present invention, the pigment used in the coating liquid as the coating layer is not particularly limited, and examples thereof include purified natural mineral pigments such as various kaolins, talc, and ground calcium carbonate, satin white, and lithopone. Examples include composite synthetic pigments, semi-synthetic pigments such as titanium oxide, precipitated calcium carbonate, and aluminum hydroxide, and synthetic pigments such as plastic pigments.

  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.

  The binder used in the coating solution includes ordinary starch, oxidized starch, etherified starch, esterified starch, enzyme-modified starch and various commercially available starches such as cold water soluble starch obtained by flash drying them, styrene-butadiene series , Acrylic and vinyl acetate copolymers SBR latex, polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, polyacrylamide, urea or melamine / formalin resin, polyethyleneimine, polyamide polyamine / epichlorohydrin, etc. Natural products such as wax, casein, and soy protein, and those obtained by cationizing them.

  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. The coated paper that has been coated and dried in a series of operations is subjected to various calendar treatments as necessary.

Examples Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In addition, unless otherwise indicated, the part and% in an example show a mass part and mass%, respectively.
<Base paper formulation>
LBKP (freeness 440mlcsf) 100 parts

<Internal medicine>
Light calcium carbonate (* indicated by ash content in base paper) * 7 parts commercial cationized starch 1.0 parts commercial cationic polyacrylamide yield improver 0.02 parts Pulp and internal additives were adjusted according to the above formulation.

<Coating fluid>
Polystyrene-based hollow pigment (average particle size 1.0 μm, hollow rate 50%) 7 parts heavy calcium carbonate A (average particle size 1.2 μm) 53 parts heavy calcium carbonate B (average particle size 2.0 μm) 40 parts commercially available Polyacrylic acid-based dispersant 0.1 parts Commercial adhesive (SBR latex) 10 parts Commercial phosphoric acid ester starch 1 part Sodium hydroxide adjusted to pH 9.6

According to the above base paper composition, a pulp slurry is prepared, and a hybrid former using a fixed shoe as a dewatering shoe with a width of 5000 mm and a paper making speed of 900 m / min. (Mitsubishi Heavy Industries; Bellform former) Was used to produce a base paper with a basis weight of 97.9 g / m ² . A 2.5 woven wire was used as the bottom wire, and the J / W ratio at the time of manufacture was 0.95.

With respect to the obtained base paper, the coating liquid was adjusted by the above composition to obtain a coating liquid having a concentration of about 63%. Using the fountain application / blade system coater, the obtained coating solution was coated at a coating speed of 1600 m / min on a single side of 15 g / m ² on a single side and dried to a basis weight of 127.9 g / A coated paper of m ² was obtained.

  For the obtained coated paper, using a super calender device (number of steps: 10 steps, rigid roll: chilled roll having an outer diameter of 400 mm, elastic roll: cotton roll having an outer diameter of 400 mm, linear pressure: 220 kN / m) offline. The calendering process was performed, and the electrophotographic transfer paper of Example 1 was produced.

  An electrophotographic transfer paper of Example 2 was produced in the same manner except that the J / W ratio was 1.2 in Example 1.

  An electrophotographic transfer paper of Example 3 was prepared in the same manner except that the freeness of the pulp was changed to 480 mlcsf in Example 1.

The electrophotographic transfer paper of Example 4 was prepared in the same manner as in Example 1, except that the coating amount on one side was 10 g / m ² and the super calender linear pressure was 250 kN / m.

  The electrophotographic transfer paper of Example 5 was prepared in the same manner as in Example 1 except that the binder formulation in the coating solution formulation was 5 parts of SBR latex and 5 parts of commercially available PVA (degree of polymerization 400).

An electrophotographic transfer paper of Example 6 was prepared in the same manner as in Example 1 except that the basis weight of the base paper was 127.0 g / m ² and the basis weight after coating was 157.0 g / m ² .

Comparative Example 1
An electrophotographic transfer paper of Comparative Example 1 was produced in the same manner except that the J / W ratio was 1.05 in Example 1.

Comparative Example 2
An electrophotographic transfer paper of Comparative Example 2 was produced in the same manner except that the freeness of the pulp was changed to 500 mlcsf in Example 1.

Comparative Example 3
An electrophotographic transfer paper of Comparative Example 3 was prepared in the same manner as in Example 1 except that the coating amount of the coating solution was 8 g / m ² and the supercalender linear pressure was 280 kN / m.

Comparative Example 4
An electrophotographic transfer paper of Comparative Example 4 was produced in the same manner except that the super calender linear pressure was 100 kN / m in Example 1. At this time, the gloss of white paper was 50%.

Comparative Example 5
An electrophotographic transfer paper of Comparative Example 5 was prepared in the same manner as in Example 1 except that the number of blended commercial phosphate esterified starch in the coating solution blended was 0.

Comparative Example 6
An electrophotographic transfer paper of Comparative Example 6 was prepared in the same manner as in Example 1 except that the base paper basis weight was 144.4 g / m ² and the post-coating basis weight was 174.4 g / m ² .

Comparative Example 7
Commercially available general offset A2 coated paper 127.9 g / m ² is shown as Comparative Example 7.

<Ground coefficient>
The formation index of the electrophotographic transfer paper obtained in Examples 1 to 6 and Comparative Examples 1 to 7 was measured using “3-D SHEET ANALYZER” manufactured by M / Ksystem. As measurement conditions, measurement was performed using a 1 mm stop as the diameter of the stop. The formation index was measured for five A4 size electrophotographic transfer papers of each Example and Comparative Example, and the average value was reported.

<Print unevenness>
For printing unevenness after printing of the electrophotographic transfer paper obtained in Examples 1 to 6 and Comparative Examples 1 to 7, “CLC5000” manufactured by Canon was used as an electrophotographic printer. A 10 cm x 10 cm solid part is printed on each electrophotographic transfer paper at three stages of A4 horizontal printing speed of 50 sheets / min, 25 sheets / min, and 12.5 sheets / min, and solid printing unevenness is visually observed. Judged in 5 stages. The criteria are as follows. A level of “3” or more at 25 sheets / minute is a practical level.
“5”: No printing unevenness.
“4”: Printing unevenness is slightly recognized.
“3”: Printing unevenness is recognized, but at a practical level.
“2”: Uneven printing can be recognized immediately.
“1”: Print unevenness is conspicuous.

<Transportability>
As for the transportability during printing of the electrophotographic transfer paper obtained in Examples 1 to 6 and Comparative Examples 1 to 7, “CLC5000” manufactured by Canon as an electrophotographic printer was used, and each A4 size electrophotographic paper was used. Single-sided 500 sheets, single-sided printing and double-sided printing were performed, and the number of paper jams in the printer was measured. The criteria are as follows.
“○”: Within 1 time “△”: Within 5 times “×”: Over 6 times

About electrophotographic transfer paper obtained in Examples 1-6 and Comparative Examples 1-7, evaluation of printing unevenness of images after printing at blank paper gloss, surface resistance value, formation index, transportability, and each printing speed The results are shown in Table 1. From these results, it can be confirmed that an excellent image can be obtained on the printed surface if the formation is good and the white paper gloss value and the surface resistance value are appropriate. Specifically, from Example 1, Example 2 and Comparative Example 1, the fiber mixing on the wire part progresses as the J / W ratio departs from 1.0, confirming the improvement in formation associated therewith. it can. Moreover, from Example 1, Example 3, and Comparative Example 2, it can be confirmed that the lower the pulp drainage, the better the formation. Regarding the coating amount, from Example 1, Example 4, and Comparative Example 3, a coating amount of 10 g / m ² or more is required in order to obtain an excellent image on the printed surface while maintaining the texture and gloss of white paper. It can be confirmed that it is necessary. Regarding the coating liquid, the higher the water retention of the coating liquid, the better. Therefore, Example 5 in which PVA is introduced into the binder is good, but Comparative Example 5 with reduced starch is not sufficient. Regarding the basis weight of the base paper, there is no problem in Example 1 and Example 6 which are design ranges, but in Comparative Example 6 exceeding the design range, sufficient image quality is obtained at A4 horizontal 20 sheets / min or more. Absent. Further, Comparative Example 7 is a general offset A2 coated paper that does not consider the suitability for electrophotography at all, and printing unevenness is conspicuous.

Claims (4)

  An electrophotographic transfer paper having a formation index of 100 or more, wherein the electrophotographic transfer paper is provided with at least one coating layer on a base paper. ^2. The electrophotographic transfer paper according to claim 1, wherein the electrophotographic transfer paper has a basis weight of 105 g / m ² or more and 169 g / m ² or less. The smoothing treatment is performed so that the coating amount of the coating layer is 10 g / m ² or more and the 75-degree specular gloss of the coating layer according to JISP8142 is 60% or more. Or the electrophotographic transfer paper described in 2. Electrophotographic transfer paper according to claim 1, the surface electrical resistance of the transfer paper, characterized in that it is 1 × 10 ¹¹ Ω or more by K6911.