Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1999-08-16
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, C428S537500, C428S914000
Reexamination Certificate
active
06280831
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to transfer paper for electrophotography, which is used in indirect dry-type electrophotographic full-color duplicators and printers. Precisely, it relates to coated transfer paper for electrophotography having the advantages of high glossiness, no blister in image fixation through simplex and duplex printing, and high-quality image formation.
2. Description of the Related Art
The recent tendency in the art is toward high-speed duplication in duplicators and printers to give high-quality color images. In particular, in the field of on-demand publications, color duplicators and color printers are being much used for producing publications which have heretofore been produced in an ordinary printing method, as being relatively easy to use for producing a small number of publications.
In general, conventional coated paper with high glossiness is produced by applying a pigment having a mean particle size of at most 2 microns onto base paper in an amount of at lest 10 g/M
2
for each side, through coating with various coaters, followed by smoothening the coated surface through calendering. The coated paper with high glossiness is generally used in the field of commercial printing, but is being much used in electrophotographic duplicators and printers, in place of ordinary PPC paper or copying paper, to increase the sharpness of images to be printed thereon.
However, using the coated paper with high glossiness in electrophotographic duplicators and printers is problematic in that it is often blistered while toner images are fixed thereon under heat. Blistering as referred to herein includes the following: While toner images are fixed on paper under heat, water existing in the paper is heated to vaporize, whereby the water vapor pressure in the paper increases. The water vapor is discharged outside the paper, but if not smoothly discharged for some reasons, it will rapidly expand inside the base paper to give local blisters. This is hereinafter referred to as paper blistering.
Another is as follows: The high-pressure water vapor having been formed inside the paper shall be discharged out through the void in the coating layer. However, if toner images are on the paths through which the water vapor is being discharged out, the water vapor will break the toner images to flow outside. In that condition, the coated paper shall have fine blisters or through-holes, is thereby degraded. This is hereinafter referred to as toner blistering. The toner blistering produces serious image defects.
Owing to its coating layer, the coated paper could not ensure sufficient water vapor discharging paths. When having toner images thereon, it is often troubled by paper blistering and toner blistering. In particular, the coated paper with high glossiness requires calendering for increasing its glossiness. However, calendering increases the density of the coating layer, and the calendered coated paper will be much more troubled by paper blistering and toner blistering.
The blistering occurs more frequently in duplex printing than in simplex printing. This is because, in duplex printing, toner adheres first on one surface of the coating layer to form toner images thereon, and thereafter on the other surface thereof also to form toner images thereon. In the latter step of such duplex printing, the water vapor having been formed in the paper is more difficult to go out than that to go out in simplex printing. Conventional coated paper with high glossiness for ordinary printing and that for electrophotographic printing are blistered only a little or are not blistered in simplex printing, but are significantly blistered in duplex printing.
For overcoming blistering of coated paper for electrophotography, some methods have heretofore been proposed. One comprises controlling the center line average height of the surface of the coating layer to be at most 2.0 &mgr;m and controlling the air permeability of the coating layer to be at most 4000 seconds (see JP-A 62-198876); and another comprises controlling the smoothness and the air permeability of the base paper to be coated and specifically defining the amount of the coating layer that contains an organic pigment to thereby control the air permeability of the coating layer to be at most 4000 seconds (see JP-A 5-241366). The air permeability is measured according to an Ohken's air permeability test method stipulated in Japan Tappi No. 5 (this accords with JIS P8117), in which is measured the time (in terms of seconds) as taken by 10 ml of air passing through paper under a pressure of 0.1 kg/cm
2
, and the time thus measured indicates the vapor permeability of the paper tested.
However, those types of coated paper for electrophotography proposed as above are still problematic in that they are often troubled by paper blistering and toner blistering in duplex printing though little in simplex printing. The reason will be because, in simplex printing, water vapor discharge from the toner image-formed surface of the paper is difficult but is easy from the opposite surface thereof, and therefore the printed paper is blistered little. However, in duplex printing, the toner images formed shall cover the both surfaces of the paper, and the vapor permeability of the paper will be not enough for smooth water vapor discharge in that condition.
SUMMARY OF THE INVENTION
Given that situation, the present invention is to overcome the problems as above and to provide transfer paper for electrophotography which has the advantages of high glossiness and high surface smoothness and which is not troubled by paper blistering and toner blistering and is waved or curled little.
We, the present inventors have assiduously studied for solving the problems with transfer paper for electrophotography having the advantages of high glossiness and high surface smoothness, and, asa result, have found that, in transferpaper for electrophotography as prepared by coating the both surfaces of base paper with a coating layer consisting essentially of a pigment and an adhesive to have an increased degree of glossiness, when the air permeation flow rate through the transfer paper is controlled to be not lower than a predetermined value, or in the transfer paper through which the airpermeation flow rate is lower than the predetermined value, when its internal bonding strength is ensured to be not lower than a predetermined value, then the problems with the transfer paper for electrophotography as above are all solved. On the basis of these findings, we have completed the present invention. Specifically, the constitution of the invention is as follows:
(1) Transfer paper for electrophotography, which includes;
a substrate of which the both surfaces are coated with a coating layer consisting essentially of a pigment and an adhesive, and is characterized in that;
the permeation flow rate through it of air having been heated at 180° C. and pressurized to have a pressure of 2 kg/cm
2
is larger than 200 ml/min.
Preferably;
the air permeation flow rate through the transfer paper is larger than 200 and not more than 900 ml/min,
the coating layer on at least one surface of the substrate has a degree of glossiness of at least 50%,
the coating layer has a density of at most 1.20 g/cm
3
, more preferably at most 1.10 g/cm
3
1
,
the pigment to be in the coating layer is at least one selected from organic pigments, delaminated clay, and pillar-shaped pigments,
the coating layer has a multi-layered structure,
the weight of the transfer paper falls between 70 g/m
2
and 220 g/m
2
,
the water content of the transfer paper falls between 3.0% and 6.5%, more preferably between 4.5% and 5.5%.
(2) Transfer paper for electrophotography, which comprises;
a substrate of which the both surfaces are coated with a coating layer consisting essentially of a pigment and an adhesive, and is characterized in that;
the permeation flow rate through it of air having been heated at 180°C. and pressurized to have a pressure of 2 kg/cm
2
falls between 50
Hosoi Kiyoshi
Kato Masaru
Nakanishi Ryosuke
Tokiyoshi Tomofumi
Fuji 'Xerox Co., Ltd.
Hess Bruce H.
Oliff & Berridg,e PLC
Shewareged B.
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