Note: Descriptions are shown in the official language in which they were submitted.
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OJ-G418-US, CA, EP
COATED PAPER SHEET FOR ELECTRO-COAGULATION PRINTING
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coated paper
sheet for electro-coagulation printing. More
particularly, the present invention relates to a coated
paper sheet for electro-coagulation printing, having a
high water resistance and capable of recording clear ink
images thereon without difficulty in the transfer of ink
images.
2. Description of the Related Art
A basic principle of an electro-coagulation
printing method (which may be referred to as an
elcography) is disclosed in U.S. Patent No. 3,892,645 and
Japanese PCT Application Publication No. 4-504,688 (PCT
International Publication W0 90/11897). This printing
system is a non-printing plate system and uses an aqueous
ink having such a property that it is gelled with an
electric charge.
In elcography, the specific aqueous ink as
mentioned above is applied between a positive cylindrical
electrode and a negative electrode, and an electric
differential potential corresponding to an imagewise
signal is applied between the positive and negative
electrodes to generate metal ions, to coagulate portions
of the aqueous ink layer farmed on the cylindrical
electrode by the metal ions, and to cause the coagulated
ink colloid to adhere to the surface of the positive
cylindrical electrode. By controlling the amount and
location of the coagulated ink colloid, a desired colored
ink image can be formed on the positive cylindrical
electrode surface, and a colored image formed from the
electro-coagulated ink can be transferred onto a surface
of a recording material under pressure. The constitution
of a printing machine for the elcographic printing method
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will be explained later by referring to an attached
drawing. An embodiment of the electro-coagulation
printer will be illustrated later.
The elcographic printing method is
characterized by not using a printing plate. A non-
printing plate printing method is advantageous in that no
procedure for providing a printing plate is necessary,
desired images can be easily printed on a recording
material surface in accordance with electric signals
corresponding to the desired images, and thus various
prints recording images different from each other can be
easily prepared for various customers. Especially, the
elcographic printing method is advantageous for various
lots of prints each in a small number and different from
one another.
Also, the elcographic printing method is
advantageous in that since the amount of gelled ink,
which corresponds to the color density of the images, is
proportional to the amount of the electric charge
(pulse), ink images having a fine and sharp color tone
can be recorded.
Since in the elcography, no dots or halftone
dots are used, the color tone of the images can be
controlled by regulating the thickness of the ink layers,
as in gravure printing. The thickness of the ink layers
is proportional to the electric potential-applying time
in accordance with the electric signals, and thus the
color tone of the images can be accurately controlled.
Therefore, the elcographic printing method is suitable
for recording colored images.
Conventional printing paper sheets have a
satisfactory absorption of oil-based inks, but are poor
in absorption and transferring property of the aqueous
inks usable for the elcographic printing. Also, when the
elcography is applied to multi-color printing, the water
component in a first colored aqueous ink applied onto the
coating material surface must be quickly absorbed by the
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coating material, before the second colored ink is
applied onto the first colored ink images. If the second
colored aqueous ink is applied onto the first colored
aqueous ink images before the water component of the
first colored aqueous ink images is fully absorbed by the
coating material, the second colored aqueous ink is not
fully transferred to the coating material and, thus, the
desired colored images cannot be obtained. Japanese
Unexamined Patent Publication No. 10-131,091 discloses an
ink receiving layer containing a pigment comprising
synthetic amorphous silica and/or colloidal silica and
formed on a support. This specific ink receiving layer
can solve the above-mentioned problem to a certain
extent.
Generally, to obtain ink images having a high
resolution, the recording medium must be selected from
high gloss sheets, for example, coated art paper sheets
(coated No. 1 grade) and cast-coated paper sheets, having
a higher surface smoothness than that of other printing
paper sheets for common printings. The conventional
printing paper sheets, for example, coated art paper
sheets and cast-coated paper sheets have excellent
absorbing property for oily inks. However, when these
conventional printing sheets are used for the electro-
coagulation printing, they exhibit an unsatisfactory
absorption of aqueous inks and an insufficient transfer
property for the aqueous ink images. Especially, when
the conventional printing sheets are employed in the
multi-color printing, although the first colored aqueous
ink can be absorbed by the printing sheet, the second
colored aqueous ink cannot be fully transferred to the
printing paper sheet.
Also, from the principle of the electro-
coagulation printing, since the specific aqueous ink is
gelled with metal ions generated due to the differential
electropotential created between the negative and
positive electrodes in accordance with imagewise electric
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signal, and the coagulated ink colloid is transferred to
and fixed on a printing paper surface under pressure, the
adhesive property of the ink colloid to the printing
paper sheet is very low, especially when water is located
between the ink image and the printing paper sheet
surface, the adhesive property is particularly low, and
thus, the ink images are easily removed from the printing
paper sheet surface. Namely, the ink image exhibits a
very poor water resistance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a
coated paper sheet for electro-coagulation printing,
which has excellent ink-transferring property and ink
absorption and can be recorded with ink images with high
clarity and sharpness.
Another object of the present invention is to
provide a coated paper sheet for electro-coagulation
printing especially suitable for mufti-color printing.
The above-mentioned object can be obtained by the
coated paper sheet of the present invention for electro-
coagulation printing.
The coated paper sheet of the present invention for
the electro-coagulation printing comprises a support
paper sheet and a coating layer formed on the support
paper sheet and comprising a pigment and a binder, the
coated paper sheet having a total pore volume of fine
pores having a pore size of 0.01 to 0.40 um, of 0.10 to
0.20 ml/g, as determined by a mercury porosimeter.
In the coated paper sheet of the present invention
for electro-coagulation printing, the coated surface of
the coated paper sheet preferably has a smoothness of
1.0 ~m or less determined by a microtopograph under a
pressure of 3,922,660 Pa (40 kgf/cm2).
In the coated paper sheet of the present invention
for electro-coagulation printing, the pigment in the
coating layer preferably includes at least one member
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selected from the group consisting of calcinated clay,
structured kaolin and delaminated clay in an amount of 20
to 70~ by weight, based on the total weight of the
pigment in the coating layer.
In the coated paper sheet of the present invention
for electro-coagulation printing, the coated surface of
the coated paper sheet preferably has a gloss of 70$ or
more, determined in accordance with Japanese Industrial
Standard P 8142.
In the coated paper sheet of the present invention
for electro-coagulation printing, the coated paper sheet
having a gloss of 70$ or more is preferably one formed by
a cast coating method.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is an explanatory side view of an embodiment
of the electro-coagulation printer to which the recording
material of the present invention is applied.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The inventors of the present invention have made an
extensive studies concerning what problems would be found
when conventional coated paper sheets for printing were
used for elcography. As a result of the study, the
inventors of the present invention have made the
following finding.
Among the conventional printing paper sheets, the
coated paper printing sheets having a coating layer
formed on a support paper sheet and comprising a pigment,
are provided with a dense surface which is substantially
free from pores and in which even if, they exist, the
size of the pores is small, and they thus exhibit a very
high resistance to penetration of the coagulated ink
colloid into the inside of the printing paper sheet. If
the ink contains water, the printed ink images exhibit a
very low resistance to rubbing and thus are easily
removed by rubbing. Namely the ink images have a poor
water resistance.
As mentioned above, the elcographic printing method
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is a very advantageous printing method. However, this
method is disadvantageous in that when conventional paper
sheets or printing paper sheets are used, the advantages
of elcography cannot be fully obtained. For example,
when a conventional printing paper sheet is used, prints
having excellent printing qualities both in high color
density tone and low color density tone cannot be
obtained.
when a conventional coated printing paper sheet is
used, the resultant printed images, in a low color
density region in which the amount of the coagulated ink
colloid is small, exhibit a sufficient color density and
thus the resultant prints are satisfactory. However, in
a high color density region in which the amount of the
coagulated ink colloid is large, the resultant colored
ink images exhibit a poor transferring property. Also,
when conventional newspaper sheets or form-printing paper
sheets are used, the elcographic printing in the high
color density region, in which the amount of the
coagulated ink colloid is large, can be satisfactory
effected. However, in the low color density region in
which the amount of the coagulated ink colloid is small,
the elcographic printing is disadvantageous in that non-
printed white spots and reduced color density spots are
formed.
An embodiment of an electro-coagulation printer will
be explained by referring to the attached drawing below.
In Fig. 1, a metal cylinder 1 is used as a positive
electrode and it rotates in the direction shown by thick
arrows in Fig. 1. The peripheral surface of the positive
rotary cylindrical metal electrode 1 is cleaned by a
cleaning means 2, and is then coated with a corrosion-
preventive coating agent by a conditioning means 3.
A portion of the surface-conditioned peripheral
surface of the positive rotary cylindrical metal
electrode faces a plurality of needle-shaped negative
electrodes 4a electrically insulated from each other and
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independently from each other embedded in and fixed to a
print head 4. Into the clearance between the peripheral
surface of the positive rotary cylindrical metal
electrode 1 and the needle-shaped negative electrodes 4a,
an electro-coagulatable ink is applied through an ink
feeder 5 to form an ink layer on the peripheral surface
of the positive rotary cylindrical metal electrode 1.
Then differential electric potentials are applied
imagewise between the positive and negative electrodes,
in accordance with electric signals corresponding to the
images to be printed, to generate metal ions from the
positive cylindrical metal electrode.
The ink layer on the positive cylindrical metal
electrode is electrically gelled and coagulated imagewise
by the metal ions. The coagulated ink portions are
cohered imagewise on the peripheral surface of the
positive cylindrical metal electrode 1, and non-
coagulated ink portions are selectively removed from the
coagulated ink portions by a wiper 6.
A recording material 8 is brought, in the direction
shown by the thin arrows into contact with the peripheral
surface of the positive cylindrical metal electrode 1 and
is pressed toward the peripheral surface of the
electrode 1 by a press roll 7. The coagulated colloidal
ink images carried on the peripheral surface of the
electrode 1 are transferred to the recording surface of
the recording material 8.
When multi-colored images are printed, the above-
mentioned electro-coagulation printing procedures are
repeatedly carried out for each of the multiple colored
inks.
The porous structure of the coated paper sheet is
represented by the pore size and total pore volume of
fine pores contained in the coated paper sheet and having
a specific pore size, determined by a mercury porosimeter
in which mercury is pushed into the coated paper sheet.
The surface property and the cushioning property of the
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coated paper sheet can be represented by the smoothness
or surface roughness of the coated paper sheet under
pressure. The smoothness of the coated paper sheet is
determined by a microtopograph under a pressure of
3,922,660 Pa (40 kgf/cmz). This smoothness is referred
to as a press-reflection smoothness in the units of um.
In the present invention, the coated paper sheet
must have a porous structure containing fine pores having
a pore size of from 0.01 to 0.40 Vim, and the total pore
volume of the fine pores is in the range of from 0.10 to
0.20 ml/g, preferably 0.11 to 0.20 ml/g, determined by a
mercury porosimeter (a mercury press-pushing method).
When the total pore volume of the fine pores having
a pore size of 0.01 to 0.40 ~m is less than 0.10 ml/g,
the resultant recording sheet is disadvantageous in that
the ink colloid images with moderate to high color
density are transferred to the coated paper sheet with an
unsatisfactory degree of transfer, while the ink colloid
images with a low color density can be transferred with a
satisfactory degree of transfer, and thus the resultant
printed images are unsatisfactory as a whole.
Especially, in the multi-color printing, the too small
pore volume causes the resultant printing paper sheet to
exhibit a degraded applicability to the electro-
coagulation printing.
When the total pore volume is more than 0.20 ml/g,
the resultant coated paper sheet is advantageous in that
the aqueous ink absorption is enhanced, but is not
preferable in that the color density of the printed ink
images is low and the gloss of the images may be
decreased.
There is no limitation to the means for adjusting
the total pore volume of the fine pore in the coated
paper sheet. It was found by the inventors of the
present invention that the target coated paper sheet
having a total pore volume of 0.10 to 0.20 ml/g can be
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relatively easily obtained by using, as a pigment
component of the coating layer, at least one member
selected from calcinated clay, structured kaolin and
delaminated clay is employed in an amount of 20 to 70~ by
solid weight based on the total solid weight of the
pigment contained in the coating layer.
Among the conventional pigments usable for the
production of the coated paper sheets, the calcinated
clay, structured kaolin and delaminated clay can easily
form bulky coating layer. Therefore, it is assumed that
these pigments contribute to forming a porous coating
layer.
The structured kaolin refers to a kaolin pigment
produced by chemically treating kaolin particles and
comprising secondary particles each formed from a
plurality of primary particles agglomerated with each
other. Usually, the structured kaolin is produced from
clay and may be combined, in a portion thereof, with
titanium dioxide, etc. This composite pigment may be
used for the present invention.
The delaminated clay refers to clay particles
produced by applying a shearing force to laminated clay
particles to delaminate the laminated clay particles.
In the formation of the coating layer containing the
calcinated clay, structured kaolin and/or delaminated
clay, preferably, the coating amount of the layer is
controlled, or after drying the coated layer, the
resultant coated paper sheet is subjected to a smoothing
treatment, to obtain, with a high efficiency the target
coated paper sheet having the desired porous structure,
namely the total pore volume of the fine pores having a
pore size of 0.01 to 0.40 Vim, of 0.10 to 0.20 ml/g.
There is no limitation to the procedure for
smoothing the coated paper sheet surface. Usually, a
support paper sheet is coated, on the one or two surfaces
thereof, with a coating liquid containing the above-
mentioned pigment and a binder, to form one or two
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coating layers, and the resultant coated paper sheet is
subjected to a smoothing treatment under pressure using,
for example, a super calender. The smoothing procedure
may be carried out in the same manner as that for
conventional coated paper sheets.
In the coated paper sheet of the present invention,
the dry coating amount of the coating layer on each
surface of the support paper sheet is preferably adjusted
to 5 to 30 g/m2, more preferably 8 to 25 g/m2.
To adjust the total pore volume of the fine pores
having a pore size of 0.01 to 0.40 um to 0.10 to
0.20 ml/g and the press-reflection smoothness measured by
microtopograph under a pressure of 3,922,660 Pa
(40 kgf/cm2) to 1.0 um or less, the smoothing procedure
is preferably carried out by using a machine calender, a
super calender or soft compact calender, while
controlling the smoothing conditions, for example,
calender roll temperature, calender roll-nipping pressure
or the number of nippings. The smoothing procedures can
be effected without specific difficulty.
Where the coating layer is formed in a dry amount of
less than 5 g/mz on each surface, the resultant coated
paper sheet may have a total pore volume of less than
0.10 ml/g and a press-reflection smoothness of more than
1.0 um. Also, where the dry amount of the coating layer
is more than 30 g/m2 per surface of the support paper
sheet, the resultant coated paper sheet may have an
increased total pore volume. However, the resultant
coated paper may have an unsatisfactory mechanical
strength for printing and too low a producibility.
Where the dry content of at least one member
selected from the calcinated clay, structured kaolin and
delaminated clay is less than 20~ by weight based on the
total dry weight of the pigment, the resultant coated
paper sheet may satisfy the specific porous structure,
and where it is more than 70~ by weight, the resultant
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coated paper sheet may exhibit an insufficient mechanical
strength to printing, and unsatisfactory color density
and gloss of the printed ink images.
The present invention will be further explained
below.
In the electro-coagulation printing system
(elcographic system), the gelled ink must be fully
transferred to and absorbed in the coating layer of the
coated paper sheet, and for this necessity, in the
surface of the coating layer (recording surface or
printing surface), a plurality of pores for rapidly
absorbing the ink (or a water component of the ink)
therein must be formed. Also, the aqueous ink usable for
the electro-coagulation printing system is gelled between
a pair of electrodes, and the content of water contained
in the gelled ink is assumed to be 40 to 60~ by weight,
which is high in comparison with the water content of
usual printing inks and is difficult to be transferred
and fixed to the printing surface. Therefore, the coated
paper sheet, which serves as a recording medium, must
absorb therein the water in the gelled ink and to assist
the transfer and fixing of the gelled ink to the coated
paper sheet.
For this purpose, it was found in the present
invention that in the porous structure of the present
invention, it is important to control the pore size of
the fine pores to 0.01 to 0.40 um and to maintain the
total pore volume at 0.10 to 0.20 ml/g, as determined by
the mercury porosimeter.
In a preferable embodiment of the coated paper sheet
of the present invention for the electro-coagulation
printing, the coated paper sheet has a high smoothness
and a high cushioning property. The two properties
contributes to enhancing the transferred ink-absorbing
property of the printing paper sheet.
In the electro-coagulation printing system, the
transferring property of the ink is very important. The
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images comprising a gelled ink colloid and formed on a
metal cylinder are transferred on a surface of the coated
paper sheet (recording medium) under pressure by using a
press roll. Therefore, the surface smoothness and
cushioning property of the coated paper sheet are
important for receiving the transferred ink images.
From the above-mentioned point of view, the
inventors of the present invention made extensive studies
on a coated paper sheet having enhanced printing
properties for the electro-coagulation printing. As a
result, it was found that a printing surface having a
press-reflection smoothness of 1.0 ~m or less determined
by a microtopograph under a pressure of 3,922,660 Pa
(40 kgf/cmz) contributes to obtaining a good printing
result in which no ink-transfer occurs and ink dots are
in the form of a true circle. The reasons for the
selection of the pressure of 3,922,660 Pa (40 kgf/cm2) in
the determination of the press-reflection smoothness by
the microtopograph is that the ink transfer in the
electro-coagulation printing is effected by the press
with a press roll, and this pressing condition of the
printing has a close relationship to the pressure of
3,922,660 Pa (40 kgf/cm2) in the press-reflection
smoothness measurement by the microtopograph. This
relationship was found for the first time by the
inventors of the present invention. The press-reflection
smoothness under a pressure of 980,665 Pa (10 kgf/cm2),
1,961,330 Pa (20 kgf/cm2) or 2,941,995 Pa (30 kgf/cm2)
has a certain relationship to the printing results in a
high color density of ink images. However, in moderate
to low color densities of ink images, the printing
results are variable in response to the type of the
coated paper sheets, for example, coated art paper
sheets, coated paper sheets (gloss type, dulustered type
or matte type) and light weight coated paper sheets, and
thus a fixed relationship is difficult to find.
Accordingly, the inventors of the present invention
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found that when the coated paper sheet surface has a
press-reflection smoothness of 1.0 ~,m or less determining
by the microtopograph under a pressure of 3,922,660 Pa
(40 kgf/cmz), the coated paper sheet exhibits the above-
mentioned excellent printing property as desired.
If the smoothness is more than 1.0 um, the surface
of the coated paper sheet may have a high roughness even
under pressure and thus may be unsatisfactory in the
printing result, for example, the transfer and absorption
of the gelled ink colloid may be unevenly conducted, and
in a low color density region having a small amount of
ink, of the printed paper sheet, the true circle property
of the ink dots may be degraded, no ink-transfer may
occur, and the color density of the ink images may be
reduced.
There is no specific lower limit of the press-
reflection smoothness of the coated paper sheet of the
present invention. Usually, the cast-coated paper
sheets, which has a very high smoothness among the coated
paper sheets, exhibit a press-reflection smoothness of
about 0.05 um under a pressure of 3,922,660 Pa
(40 kgf/cmz). Therefore, the lower limit of the press-
reflection smoothness of the coated paper sheet of the
present invention under the above-mentioned pressure is
preferably about 0.05 um. However, there is no certain
evidence for a lower limit.
To obtain ink images having a high accuracy, a
coated paper sheet having a high surface smoothness like,
for example, the above-mentioned cast-coated paper sheet
having a gloss of 70~ or more determined in accordance
with Japanese Industrial Standard (JIS) P 8142, is
preferably employed. The inventors of the present
invention made extensive studies on the coated paper
sheets having a high gloss and being satisfactory in
printing properties thereof as recording paper sheets
having a high smoothness. As a result, it was found that
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a cast-coating method by which a high smoothness and a
high gloss can be easily obtained can be advantageously
utilized to produce the recording paper sheet of the
present invention.
The cast-coating method will be explained below.
In principle, a coating layer surface having a high
gloss and a high smoothness can be obtained while
maintaining the bulkiness of the coating layer at a high
level, by bringing a coated coating layer kept in a wet
condition into contact with a mirror-finished casting
metal surface of a cast drum heated to a desired
temperature under pressure, by drying the coating layer
and by separating the dried coating layer surface from
the casting metal surface to transfer the mirror-finished
surface condition having a high gloss to the coating
layer.
Generally, the cast-coated paper sheet can be coated
by one of the following three methods, namely a wet cast-
coating method in which a coated coating layer in a
wetted condition is brought into coated with a mirror-
finished and heated casting drum surface under pressure
and dried and the dried coating layer surface is
separated from the casting drum surface; a re-wet cast-
coating method in which a coated coating layer in a
wetted condition is dried, the dried coating layer is
plasticized with a re-wetting liquid, and brought into
contact with a mirror-finished heated casting drum
surface under pressure and dried and the dried coating
layer surface is separated from the casting drum surface;
and a gel cast-coating method in which a coated coating
layer in a wetted condition is gelled, the gelled coating
layer surface is brought into contact, under pressure,
with a mirror-finished heated casting drum surface, and
dried and the dried casting layer surface is separated
from the casting drum surface. In each casting method, a
cast-coated layer surface having a high gloss and a high
smoothness is obtained.
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In the production of the coated paper sheet of the
present invention, any of the above-mentioned casting
methods may be utilized. Preferably, the re-wet casting
method by which only the surface of the coating layer can
be smoothed, an excellent gloss can be imparted to the
coating layer surface, and the inside portion of the
coating layer can be maintained at a porous condition,
can be advantageously and easily used for the production
of the coated paper sheet of the present invention,
because in the re-wet casting method, only the surface
portion of the coating layer is plasticized.
In the coated paper sheet of the present invention,
the coating layer may contain, in addition to at least
one member selected from calcinated clay, structured
kaolin and delaminated clay, at least one conventional
pigment selected from, for example, conventional clay,
ground calcium carbonate, precipitated calcium carbonate,
titanium dioxide, aluminum hydroxide, silica, satin
white, and talc, which are usually used for the coated
paper sheets.
In the coating layer, the pigment is contained in a
mixture with a binder. There is no limitation to the
type and amount of the binder. The binder usable for the
coating layer may be selected from binders for the
conventional coated paper sheets, for example, starch and
modified starches, for example, phosphate-esterificated
starched, cation-modified starches and engym-modified
starches, polyvinyl alcohol, casein, lances of synthetic
resins, for example, styrene-butadiene copolymers, vinyl
acetate-copolymers, acrylic copolymers, and urethane
copolymers. These binders may be used alone or in a
mixture of two or more thereof.
Usually, in the coating color for forming the
coating layer, the binder is preferably contained in an
amount of 3 to 50~ by dry weight, more preferably 5 to
30~ by dry weight. Optionally, the coating color for the
coating layer further contains an additive comprising at
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least one member selected from dispersing agents, pH-
adjusting agents, for example, sodium hydroxide and
aqueous ammonia solutions, anti-foaming agents,
antiseptic agents, fluorescent whitening agents,
lubricant, dyestuffs, waterproofing agents, fluid-
modifiers and colored pigments.
Particularly, the waterproofing agents are important
additives for enhancing the water resistance of the
recording paper sheet for the electro-coagulation
printing and are not only added to the coating color, but
also are applied to the coating layer surface before or
after an electro-coagulation printing is applied thereto,
and/or are added to an aqueous ink for the electro-
coagulation printing, to protect the coated paper sheets
or the ink images received on the coated paper sheets
from water.
In the electro-coagulation printing, the
conventional waterproofing agent for the coated paper
sheets are not always satisfied to enhance the water
resistance of the recording paper sheets. For the coated
paper sheets for electro-coagulation printing, the
waterproofing agent preferably comprises a member
selected from epoxy compound-containing waterproofing
agents and multi-valent metal compound-containing
waterproofing agents. The epoxy compound usable as a
waterproofing agent for the present invention contains
one or more epoxy groups and are preferably selected from
polyepoxy compounds, for example, diglycerol
polyglycidylether and glycerol polyglycidylether; diepoxy
compounds, for example, polyethylene glycol
diglycidylether, polypropylene glycol diglycidylether,
trimethylolpropane polyglycidylether, polyglycerol
polyglycidylether, and sorbitol polyglycidylether and
glycidylester compounds, for example, diglycidylester of
adipic acid; and polyamide-epoxide resins. Among these
epoxy compounds, the glycerol polyglycidylether,
diglycerol polyglycidylether and polyglycerol
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polyglycidylether are advantageously employed to produce
the coated paper sheets of the present invention having
the desired properties.
The mufti-valent metal compounds for the
waterproofing agents are preferably selected from zinc
compounds, for example, zinc sulfate, zinc acetate, zinc
formate and zinc carbonate; and zirconium compounds, for
example, zirconium acetate, zirconium ammonium carbonate,
zirconium sulfate, zirconium nitrate, zirconium iodide
and zirconium fluoride. Among the above mentioned
compounds, the zirconium compounds, particularly
zirconium ammonium carbonate, is advantageously employed.
The amount of the waterproofing agent to be applied
to coating layer surface and/or the ink images
transferred to the recording surface is not limited to a
specific level. Usually, the coating layer preferably
contains the waterproofing agent in a solid amount of 0.5
to 3.0 g/m2, more preferably 1.0 to 2.5 g/mz. Also, the
waterproofing agent contained in the aqueous ink is
preferably in a solid amount of 0.1 to 20~ by weight,
more preferably 0.5 to 15~ by weight, based on the total
solid weight of the ink. Further, the waterproofing
agent is preferably contained in a solid amount of 1 to
20$ by weight, more preferably 2 to 15$ by weight, based
on the solid weight of the coating color.
There is no limitation to the type of coating
devices for coating the support paper sheets with a
coating color. Usually, the coating is carried out by
using conventional coating devices, for example, air
knife coater, blade coater, rod coater, bar coater, roll
coaters, for example, gate roll coater and size-press
coater and bill blade coater.
Optionally, the support paper sheet is smoothed by
using a machine calender, a soft calender, or a Yankee
dryer before coating. Also, as long as the purpose of
the present invention can be attained, after the support
paper sheet is coated with a coating color for the
CA 02297588 2000-02-02
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coating layer and is dried, the resultant coated paper
sheet is optionally smoothed by using a machine calender,
a soft calender or a super calender.
There is no limitation to the type of pulp for
forming the support paper sheet. Usually, the support
paper sheet usable for the present invention is produced
from chemical pulps, mechanical pulps and waste paper
stocks, which may be used alone or in a mixture of two or
more of the above-mentioned pulps. The support paper
sheet may be a composite paper sheet comprising two or
more paper sheet layers superposed on each other in a
paper-forming procedure. In the formation of the paper
sheet, the pulp slurry optionally contains one or more
additives selected from sizing agents, paper strength-
enhancing agents, chemical stabilizing agents, freeness-
controlling agents, fillers and coloring materials.
EXAMPLES
The present invention will be further explained by
the following examples which are merely representative
and are not intended to restrict the scope of the present
invention in any way.
Example 1
An aqueous pigment slurry was prepared by mixing a
dispersing agent (trademark: ARON T-40, made by TOA GOSEI
K.K.) in an effective component amount of 0.2 part by
weight, sodium hydroxide in an effective component amount
of 0.1 part by weight and an anti-foaming agent
(trademark: NOPCO 8034L, made by SUN NOPCO CO.) in an
amount of 0.1 part by weight into water, and the mixture
was further mixed with a pigment consisting of 30 parts
by weight of calcinated clay (trademark: ALPHATEX, made
by ECC INTERNATIONAL CO.), 30 parts by weight of
precipitated calcium carbonate trademark: TP-121-7K,
made by OKUTAMA KOGYO K.K.) and 40 part by weight of
ground calcium carbonate (trademark: FMT-90, made by
FEIMATEC K.K.), while dispersing the mixture in water for
30 minutes, by stirring by a COWLESS dissolver.
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The aqueous pigment slurry was further added with a
binder consisting of 1 part by weight of oxidized starch
(trademark: ACE A, made by OJI CORN STARCH K.K.) and
12 parts by solid weight of a styrene-butadiene copolymer
latex (trademark: L-1117, made by ASAHI KASEIKOGYO K.K.)
and was diluted with water to provide a coating color
having a solid content of 60$ by weight for a coating
layer.
A fine paper sheet produced by a natural paper-
forming system and having a basis weight of 54 g/m2 was
coated by using a blade coater, on the front and back
surfaces thereof, with the above-mentioned coating liquid
in a dry amount of 15 g/m2 per surface of the paper
sheet, and dried.
The resultant both surface-coated paper sheet was
calendered by a 7-nip super calender provided with metal
rolls heated to a surface temperature of 80°C.
A both surface-coated paper for electro-coagulation
printing was obtained.
Example 2
A both surface-coated paper sheet for electro-
coagulation printing was produced by the same procedures
as in Example 1 with the following exceptions.
An aqueous pigment slurry was prepared by mixing a
dispersing agent (trademark: ARON T-40, made by TOA
GOSEI K.K.) in an effective component amount of 0.2 part
by weight, sodium hydroxide in an effective component
amount of 0.1 part by weight and an anti-foaming agent
(trademark: NOPCO 8034L, made by SUN NOPCO CO.) in an
amount of 0.1 part into water, and the mixture was
further mixed with a pigment consisting of 60 parts by
weight of structured kaolin (trademark: LOTOPRINT, made
by HEUBA K.K.), and 40 parts by weight of precipitated
calcium carbonate trademark: TP-123-CS, made by OKUTAMA
KOGYO K.K.), while dispersing the mixture in water for
30 minutes, by stirring by a COWLESS dissolver.
The aqueous pigment slurry was further added with a
CA 02297588 2000-02-02
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binder consisting of 1 part by weight of oxidized starch
(trademark: ACE A, made by OJI CORN STARCH K.K.) and
15 parts by solid weight of a styrene-butadiene copolymer
latex (trademark: SN-lOlB, non-alkali swelling type Tg =
-5°C, made by SUMIKA A & L K.K.) and was diluted with
water to provide a coating color having a solid content
of 60~ by weight for a coating layer.
Example 3
A both surface-coated paper sheet for electro-
coagulation printing was prepared by the same procedures
as in Example 2, with the following exceptions.
In the preparation of the coating color for the
coating layer, the pigment consisted of 40 parts by
weight of a delaminated clay (trademark: NEW CLAY, made
by ENGELHARD CO.) 40 parts by weight of a precipitated
calcium carbonate (trademark: TP-123-CS, made by OKUTAMA
KOGYO K.K.) and 20 parts by weight of a ground calcium
carbonate (trademark: FMT-90, made by FEIMATEC C0.).
Example 4
A both surface-coated recording sheet for electro-
coagulation printing was prepared by the same procedures
as in Example 2, with the following exceptions.
In the preparation of the coating color for the
coating layer, the pigment consisted of 20 parts by
weight of a calcinated clay (trademark: ANSILEX, made by
ENGELHARD C0.) 40 parts by weight of a structured kaolin
(trademark: LOTOPRINT, made by HEUBA K.K.) and 40 parts
by weight of a precipitated calcium carbonate (trademark:
TP-123-CS, made by OKUTAMA KOGYO K.K.).
Example 5
A both surface-coated recording sheet for electro-
coagulation printing was prepared by the same procedures
as in Example 4, with the following exceptions.
In the preparation of the coating color for the
coating layer, the calcinated clay was replaced by the
same delaminated clay as in Example 3.
Also, in the calender treatment, the 7-nip super
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calender having the metal rolls heated to a surface
temperature of 80°C was replaced by a 4 nip soft calender
having metal rolls heated to a surface temperature of
120°C.
Example 6
A both surface-coated recording sheet for electro-
coagulation printing was prepared by the same procedures
as in Example 2, with the following exceptions.
In the preparation of the coating color for the
coating layer, the pigment consisted of 20 parts by
weight of the same calcinated clay as in Example 4,
parts by weight of the same structured kaolin as in
Example 2, 20 parts by weight of the same delaminated
clay in Example 3 and 40 parts by weight of the same
15 precipitated calcium carbonate as in Example 2.
Example 7
A both surface-coated recording sheet for electro-
coagulation printing was prepared by the same procedures
as in Example 5, with the following exceptions.
20 In the coating procedure for the coating layers, the
coating color was coated on both the surfaces of the
coated paper sheets to form front and back coating layers
each in a dry amount of 8 g/mz.
Example 8
A both surface-coated recording sheet for electro-
coagulation printing was prepared by the same procedures
as in Example 5, with the following exceptions.
In the coating procedure for the coating layers, the
coating color was coated on both the surfaces of the
coated paper sheet to form front and back coating layers
each in a dry amount of 23 g/m2.
Example 9
An aqueous pigment slurry having a solid content of
40~ by weight was prepared by mixing 60 parts by weight
of precipitated calcium carbonate (trademark: BRILLIANT
S15, made by SHIRAISHI KOGYO K.K.) with 20 parts by
weight of amorphous silica (trademark: Finesil X-37,
CA 02297588 2000-02-02
~ - 22 -
made by TOKUYAMA SODA K.K.), 20 parts by weight of the
same calcinated clay in Example 4 and 0.5 part by weight
of a dispersing agent comprising sodium polyacrylate
(trademark: ALON A-9, made by TOA GOSEI K.K.), in water.
A casein solution was prepared by mixing 100 parts
by weight of casein with 15 parts by weight of 28~
aqueous ammonium solution and dissolving the casein
mixture in hot water at a temperature of 70°C. A cast-
coating color was prepared by mixing the aqueous pigment
slurry with 5 parts by weight of the caserin solution and
a styrene-butadiene copolymer latex (trademark: L-1392,
made by ASAHI KASEIKOGYO K.K.) in a solid amount of
parts by weight; adjusting the pH value of the mixture
to 10.5 by adding an aqueous ammonia solution; and
15 adding, to the pH-adjusted mixture, a 10~ aqueous zinc
sulfate solution in a solid amount of 1.5 parts by
weight.
The cast-coating color was coated by using an air
knife on the front surface of a paper sheet produced by
an acid paper-forming procedure and having a basis weight
of 60 g/m2, in a dry amount of 25 g/mz, and then dried.
The resultant coated layer was re-wetted with a 2~
aqueous ammonium stearate solution, and brought into
contact under pressure with a mirror-finished casting
drum surface at a surface temperature of 105°C, to smooth
the rewetted coating layer surface and dry the rewetted
coating layer, and then resultant coated sheet was
separated from the casting drum. A cast-coated paper
sheet for electro-coagulation printing was obtained.
Example 10
A cast-coated paper sheet for electro-coagulation
printing was produced by the same procedures as in
Example 9 with the following exceptions.
In the preparation of the aqueous pigment slurry,
the pigment consisted of 50 parts by weight of the same
precipitated calcium carbonate (trademark: Brilliant
S15) as in Example 9, 20 parts by weight of kaolin
CA 02297588 2000-02-02
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(trademark: UW-90, made by ENGELHARD CO.) and 30 parts
by weight of the same calcinated clay (trademark:
ANSILEX) in Example 4.
Example 11
A two surface-coated paper sheet for electro-
coagulation printing was produced by the same procedures
as in Example 1 with the following exceptions.
In .the preparation of the coating color for the
coating layer, the pigment slurry in a solid amount of
100 parts by weight was mixed with an epoxy waterproofing
agent (trademark: DENACOL PC-1000, made by NAGASE KASEI
K.K.) comprising glycerol polyglycidylether in a solid
amount of 2 parts by weight.
Comparative Example 1
A two surface-coated paper sheet for electro-
coagulation printing was produced by the same procedures
as in Example 2 with the following exceptions.
In the aqueous pigment slurry, the pigment consisted
of 15 parts by weight of the same calcinated clay as in
Example 1, 65 parts by weight of kaolin (trademark:
UW-90, made by ENGELHARD C0.) and 20 parts by weight of
the same precipitated calcium carbonate as in Example 2.
Comparative Example 2
A two surface-coated paper sheet for electro-
coagulation printing was produced by the same procedures
as in Example 2 with the following exceptions.
In the aqueous pigment slurry, the pigment consisted
of 75 parts by weight of the same structured kaolin as in
Example 2, and 25 parts by weight of the same ground
calcium carbonate as in Example 1.
Comparative Example 3
A two surface-coated paper sheet for electro-
coagulation printing was produced by the same procedures
as in Example 2 with the following exceptions.
In the aqueous pigment slurry, the pigment consisted
of 40 parts by weight of the same delaminated clay as in
Example 3, 40 parts by weight of the same kaolin as in
CA 02297588 2000-02-02
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Comparative Example 1, and 20 parts by weight of the same
precipitated calcium carbonate as in Example 2. Also,
the coating layer was formed in a dry weight of 3 g/m2 on
each surface of the support paper sheet.
Comparative Example 4
A two surface-coated paper for electro-coagulation
printing was produced by the same procedures as in
comparative Example 3 with the following exceptions.
The coating amount of the coating liquid on each
surface of the paper sheet was changed to 32 g/m2 by dry
weight.
Comparative Example 5
A two surface-coated paper sheet for electro-
coagulation printing was produced by the same procedures
in Example 2, with the following exceptions.
In the preparation of the coating color, the pigment
consisted of 35 parts by weight of kaolin (trademark:
Rastra, made by ENGELHARD CO.), 25 parts by weight of
ground calcium carbonate (trademark: HYDROCurve 90, made
by BIHOKU FUNKAKOGYO K.K.), 25 parts by weight of ground
calcium carbonate (trademark: HYDROCURVE 60, made by
BIHOKU FUNKAKOGYO K.K.) and 15 parts by weight of
precipitated calcium carbonate (trademark: TP-121-MS,
made by OKUTAMA KOGYO K.K.), and the binder consisted of
3 parts by weight of oxidized starch (trademark: ACE A,
made by OJI CORN STARCH K.K.) and 10 parts by solid
weight of a styrene-butadiene copolymer latex (trademark:
T-2550K, made by JSR CO.). Also, the smoothing treatment
was carried out by using a 11 nip super calender.
Comparative Example 6
A two surface-coated paper sheet for electro-
coagulation printing was produced by the following
procedures.
Preparation of a coating color for an undercoat
layer
An aqueous pigment slurry having a solid content of
72~ by weight was prepared by dispersing a mixture of
CA 02297588 2000-02-02
- 25 -
parts by weight of kaolin (trademark: HT, made by
ENGELHARD C0.), with 90 parts by weight of ground calcium
carbonate (trademark: HYDROCURVE 60, made by BIHOKU
FUNKAKOGYO K.K.) and 0.2 part of sodium polyacrylate as a
5 dispersing agent, in water by using a Cowless dissolver.
A coating color having a solid content of 65~ by
weight was prepared by mixing the aqueous pigment slurry
with 10 parts by solid weight of oxidized starch
(trademark: ACE A, made by OJI CORN STARCH K.K.),
10 5 parts by solid weight of a styrene-butadiene copolymer
latex (trademark: T-2550K, made by JSR Co.) and diluting
the mixture with water.
Preparation of a coating color for uppercoat layer
An aqueous pigment slurry having a solid content of
66$ by weight was prepared by dispersing a mixture of
40 parts by weight of kaolin (trademark: UW-90, made by
ENGELHARD C0.), with 20 parts by weight of precipitated
calcium carbonate (trademark: TP-221-GS, made by OKUTAMA
KOGYO K.K.) 40 parts by weight of ground calcium
carbonate (trademark: FMT-90, made by FEIMATEC C0.) and
0.2 part of sodium polyacrylate, as a dispersing agent in
water by using a Cowless dissolver.
A coating color having a solid content of 60~ by
weight was prepared by mixing the aqueous pigment slurry
with 2.5 parts by solid weight of oxidized starch
(trademark: ACE A, made by OJI CORN STARCH K.K.),
11.5 parts by solid weight of a styrene-butadiene
copolymer latex (trademark: T-2550K, made by JSR CO.)
and diluting the mixture with water.
Preparation of an undercoated paper sheet
The coating color for the undercoat layer was coated
on front and back surfaces of the same paper sheet having
a basis weight of 54 g/m2 as in Example 1 by using a
blade coater, and dried, to form front and back undercoat
layers each in a dry amount of 6.5 g/m2.
CA 02297588 2000-02-02
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Coating the undercoated paper sheet with the coating
color for the u~percoat layer
The coating color for the uppercoat layer was coated
on the front and back surfaces of the undercoated paper
sheet by using a blade coater and dried, to form front
and back uppercoat layers each having a dry weight of
8 g/m2. On each of the front and back surfaces of the
paper sheet, a composite coating layer consisting of an
undercoat layer formed on the paper sheet and an
uppercoat layer formed on the undercoat layer, was
formed.
The two surface-coated paper sheet was subjected to
a smoothing treatment by using a 4 nip-soft calender
having metal rolls heated to a surface temperature of
150°C.
A two surface-coated paper sheet for electro-
coagulation printing was obtained.
Comparative Example 7
A two surface-coated paper sheet for electro
coagulation printing was produced by the following
procedures.
Preparation of a coatincr color for an undercoat
layer
An aqueous pigment slurry having a solid content of
72~ by weight was prepared by dispersing a mixture of
parts by weight of kaolin (trademark: UW-90, made by
ENGELHARD CO.), with 70 parts by weight of ground calcium
carbonate (trademark: HYDROCURVE 90, made by BIHOKU
FUNKAKOGYO K.K.) and 0.2 part of sodium polyacrylate, as
30 a dispersing agent, in water by using a Cowless
dissolver.
A coating color having a solid content of 65~ by
weight was prepared by mixing the aqueous pigment slurry
with 8 parts by solid weight of oxidized starch
(trademark: ACE A, made by OJI CORN STARCH K.K.),
13 parts by solid weight of a styrene-butadiene copolymer
latex (trademark: T-2550K, made by JSR CO.) and diluting
CA 02297588 2000-02-02
a _ 27 _
the mixture with water.
Preparation of a coating color for uppercoat layer
An aqueous pigment slurry having a solid content of
66~ by weight was prepared by dispersing a mixture of
55 parts by weight of kaolin (trademark: UW-90, made by
ENGELHARD C0.), with 10 parts by weight of ground calcium
carbonate (trademark: FMT-90, made by FEIMATEC CO.),
20 parts by weight of satin white (trademark: SW-BL,
made by SHIRAISHI KOGYO K.K.) and 15 parts by weight of a
plastic pigment (trademark: HP-1055, made by ROHM AND
HAAS C0.) and 0.2 part of sodium polyacrylate, as a
dispersing agent, in water by using a Cowless dissolves.
A coating color having a solid content of 60~ by
weight was prepared by mixing the aqueous pigment slurry
with 1 part by solid weight of oxidized starch
(trademark: ACE A, made by OJI CORN STARCH K.K.), 1 part
of polyvinyl alcohol (trademark: PVA-105, made by
KURARAY K.K.) and 17 parts by solid weight of a styrene-
butadiene copolymer latex (trademark: T-2550K, made by
JSR C0.) and diluting the mixture with water.
Preparation of an undercoated paper sheet
The coating color for the undercoat layer was coated
on front and back surfaces of the same paper sheet having
a basis weight of 54 g/mz as in Example 1 by using a
blade coater, and dried, to form front and back undercoat
layers each in a dry amount of 10 g/mz.
Coating the undercoated paper sheet with the coating
color for the ugpercoat layer
The coating color for the uppercoat layer was coated
on the front and back surfaces of the undercoated paper
sheet by using a blade coater and dried, to form front
and back uppercoat layers each having a dry weight of
15 g/m2. On each of the front and back surfaces of the
paper sheet, a composite coating layer consisting of an
undercoat layer formed on the paper sheet and an
uppercoat layer formed on the undercoat layer, was
formed.
CA 02297588 2000-02-02
- 28 -
The two surface-coated paper sheet was subjected to
a smoothing treatment by using a 11 nip-super calender
having metal rolls heated to a surface temperature of
80°C.
A two surface-coated paper sheet for electro-
coagulation printing was obtained.
TESTS
Each of the coated paper sheets of Examples 1 to 11
and Comparative Examples 1 to 7 was air-conditioned under
the conditions in accordance with Japanese Industrial
Standard (JIS) P 8111 for 6 hours, and subjected to
printing by an electro-coagulation printer.
The coated paper sheets or the printed coated paper
sheet were subjected to the following tests.
(1) Total pore volume and pore size of coated paper
sheets
A specimen of the coated paper sheet was
subjected to a mercury porosimeter (Model:
PMI 30000 psi, made by PMI CO.) by which the average pore
size and a total pore volume of the specimen were
determined by a mercury press-penetration method. The
total pore volume is a total volume of the pores having a
pore size of 0.01 to 0.40 um.
(2) Smoothness of coated paper sheet
The smoothness of a specimen was measured by a
microtopograph (press-reflection smoothness tester) made
by TOYO SEIKI K.K. under a pressure of 3,922,660 Pa
( 40 kgf /cm2 ) .
(3) Gloss of coated paper sheet
The gloss was measured in accordance with
Japanese Industrial Standard (JIS) P 8142.
(4) Evaluation of printing property of coated paper
sheet
A specimen was printed in a low color density
region and a high color density region of a single color
by an electro-coagulation printer (made by ELCORSY CO.).
The printed ink images were evaluated by the naked eye.
CA 02297588 2000-02-02
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The ink used for printing comprised water as a medium, a
polymeric binder and a coloring pigment.
Evaluation of ink-transfer property in a low color
density region
4: Coagulation ink images are smoothly and uniformly
transferred without forming no ink-transferred
portion. The printed ink images have a high color
density and a high uniformity.
3: Coagulated ink images are smoothly transferred and
uniformly absorbed.
2: No ink-transferred portions are formed and uneven
ink image absorption occurs.
1: Uneven ink image absorption occurs and ink-
transfer property is bad.
Evaluation of ink transfer property in a high color
density region
4: Printed ink images have a high color density and
ink transfer property is good.
3: Ink transfer property is good. Color density of
printed ink image is slightly low.
2: Ink absorption and ink image transfer are slightly
uneven.
1: Ink absorption is certainly uneven and ink image
transfer property is bad.
The test results are shown in Table 1.
CA 02297588 2000-02-02
"" - 30 -
Table 1
I Item Total Coated Ink transfer Water
pore paper ~o erty resist-
sheet
I volume Press- Gloss Low High ance
II reflectionof color color
smooth- coated density density
Example (ml/g) ness paper region region
No. (~) sheet
($)
Example 1 0.11 0.6 40 3 3 3
2 0.13 0.5 75 3 4 3
3 0.12 0.5 65 3 3 3
4 0.15 0.6 70 4 4 3
0.14 0.6 60 4 4 3
6 0.13 0.7 50 _4 3 3
7 0.11 0.8 55 4 3 3
8 0.12 0.4 72 4 4 3
9 0.12 0.06 88 4 3 3
0.13 0.05 87 4 3 3
11 0.11 0.6 40 3 3 4
Comps- 1 0.05 0.5 __75 2 1 1
rative 2 0.09 0.8 70 3 2 2
Example 3 0.07 0.6 65 2 2 3
4 0.05 0.4 70 3 1 1
5 0.22 2.8 40 2 2 3
6 0.065 0.6 75 2 1 1
7 0.05 0.4 83 2 1 1
Table 1 shows that the coated paper sheets of the
present invention are useful for electro-coagulation
5 (elcography) printing in which an ink capable of being
gelled in an electrically changed condition, is gelled
imagewise on an electrode consisting of a metal cylinder,
and the gelled ink images are transferred to a recording
surface of the recording sheet. When the coated paper
10 sheet is used for the electro-coagulation printing, ink
images with a high quality are recorded thereon.
