Electrophotographic transfer paper

Details Electrophotographic transfer paper Electrophotographic transfer paper

1998-12-07

2001-08-28

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S212000, C428S218000, C428S219000, C428S341000, C428S914000

Reexamination Certificate

active

06280830

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic transfer paper for use in a dry indirect electrophotographic full-color or monochromatic duplicating machine, printer, etc. which exhibits a high paper gloss and excellent running properties, particularly in a high humidity and temperature atmosphere.
2. Description of the Related Art
In recent years, the trend of more duplicating machines and printers is to be provided in a multi-color system, operate at a higher speed and provide a higher image quality. Also, in the art of on-demand publications, color duplicating machines or printers have been made able to meet the demand for easier publication of copies in a smaller circulation. Thus, there has been a marked trend toward the use of duplicating machines or printers in publishing this kind of printed matters.
A coated paper having a high white paper glossiness commonly known as a glossy coated paper is normally obtained by applying a particulate pigment having an average particle diameter of not more than 2 &mgr;m to a substrate in an amount of not less F than 10 g/m
2
for each side by means of any of various coaters, and then calendering the coated material to smooth the surface thereof. Such a coated paper having the high white paper glossiness has been normally used in the art of commercial printing. Also in duplicating machines and printers, the foregoing coated paper has been used more occasionally instead of conventional PC papers or printer papers to obtain an image which is sharper than ever.
In the operation of the duplicating machines or the printers, a stack of papers is placed on a tray disposed inside the main body thereof or a manual tray disposed outside the main body, and then fed into the printing zone one sheet by one sheet. However, when fed in a high humidity atmosphere as in rainy season, the printing coated paper having the high white paper glossiness can be subject to so-called misfeeding, that is, two sheets of the coated paper can be stuck to each other and thus cannot be fed. This is because the coefficient of friction between the printing coated papers in stack becomes very large in the high humidity atmosphere. Such a coated paper normally has a higher smoothness than other coated papers for use in duplicating machines or printers. Because of the presence of a coating layer, such a coated paper also has a low water absorptivity. Therefore, it is thought that the water content attached to a surface of the coating layer is not easily absorbed by the coating layer but adsorbed by a surface of the coated paper in the high humidity atmosphere. The smoother the coating layer is, the more easily this excessive adsorbed water on the surface of one coated paper can adhere to the surface of another. This is probably because the surface tension and hydrogen bond of the adsorbed water cause the papers to be stuck to each other, raising the coefficient of static friction therebetween and hence preventing the paper from running.
As a method for improving the running properties of coated paper there is proposed a method disclosed in JP-A-62-198875 involving an adjustment of the surface roughness of coated layer and the standard deviation of the coefficient of static friction between papers to not more than 2.0 &mgr;m and not more than 0.05, respectively (The term “JP-A” as used herein means an “unexamined published Japanese patent application”). However, this proposal has no recognition that water present between papers causes a poor running and the poor running is also due to the surface tension of water. Further, a method disclosed in JP-A-8-171226 which eliminates the poor running in the high humidity atmosphere by adjusting the smoothness and the air permeability of coated paper measured by Oken type testers to a range of from 60 to 300 seconds and a range of from 10 to 90 seconds, respectively, has been proposed. Regrettably, under these conditions, a coated paper having a white paper glossiness of not less than 55% cannot be produced.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to solve the foregoing problems and provide an electrophotographic transfer paper to improve the running properties in a high humidity atmosphere over the related art coated paper having a high white paper gloss and a high smoothness.
The inventors made extensive studies to solve the foregoing problems with a coated paper having the high white paper gloss and the high smoothness. As a result, it was found that the use of the following constitutions makes it possible to solve the problems:
(1) An electrophotographic transfer paper comprising a substrate and coating layers formed on both sides of the substrate mainly including a pigment and an adhesive, wherein the paper has a glossiness of not less than 55% (corresponding to 75 degree white paper glossiness in accordance with JIS P-8142) and satisfies the following condition when the paper packed in a package is unpacked and allowed to stand at a temperature of 28° C. in an atmosphere of 85%RH for 5 minutes:
0.8≦
CA/D≦
3.5
wherein CA (&mgr;m) is the difference calculated by subtracting a thickness of paper before allowed to stand from a thickness of paper after allowed to stand and D (g/cm
3
) is the density of the transfer paper (JIS P-8118).
(2) The electrophotographic transfer paper according to Clause (1), in which the density (JIS P-8118) falls within the range of from 0.95 to 1.20 g/cm
3
.
(3) The electrophotographic transfer paper according to Clause (1) or (2), in which the water content of the paper which has just been unpacked falls within the range of from 4 to 6.5%.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The inventors noted that a high smoothness and a high air permeability coated paper having a white paper gloss of not less than 55% which is subject to a poor running due to adhesivity by adsorbed water can be prevented from being misfed in a high humidity atmosphere by controlling excessive adsorbed water present between the papers, which enhances the adhesivity between the papers, to reduce the coefficient of static friction between the papers. The adhesivity between the coated papers in a high humidity atmosphere becomes more remarkable when the coated paper has a higher white paper gloss and a higher smoothness. In general, it can be proposed that the control over the excessive adsorbed water be attained by increasing the permeation of water into the interior of the coat. However, the inventors' experiment shows that if the permeability of the interior of the coat is enhanced simply by increasing void of the coat, the resulting coat exhibits a reduced strength that makes itself easily peelable by a heating roll during the fixing of the toner or by folding the printed paper or scratching the surface of the printed paper. This phenomenon causes a partial omission of image. Thus, the foregoing proposal cannot be put into practical use.
The inventors made further extensive studies. As a result, it was found that the firm adhesion between papers is partly due to the expansion of the coated paper itself. In other words, water is adsorbed by the surface of the coated paper under high humidity conditions. In this case, although papers come in close contact with each other, it is thought that water is only adsorbed by one of the two sheets of coated paper but doesn't affect the other. However, in addition to the foregoing adsorption of water, the penetration of moisture into the fiber portion of the substrate of the coated paper causes the fiber to expand. It is thought that water adsorbed by the surface of the coat on one coated paper facing another enhances the adhesion between papers due to the expansion of fiber. As a result, the two sheets of coated paper are stuck to each other, causing a rise in the coefficient of static friction therebetween. This phenomenon occurs first at the edge of the paper. A range effectd thereby then gradually widens.
As mentioned above, the firm adhesion in the hi

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