Recording medium and ink-jet recording method employing the same

A recording medium contains, within an ink absorbent substrate per se or in an ink receiving coat layer formed on a substrate, basic magnesium carbonate together with a cationic surfactant and/or a nonionic surfactant. The recording medium is suitably used for color ink jet recording of the both-ways serial printing type and eliminates substantially the tone difference between forward and backward printings and the discoloration during indoor storage.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a recording medium useful for color 
recording, and particularly for ink-jet color recording. The present 
invention also relates to a recording method employing the recording 
medium. 
2. Related Background Art 
Coated paper which has an ink-receiving layer which contains a porous 
inorganic pigment formed on an ink-absorbent paper base has been used for 
recording mediums for ink-jet recording as described in Japanese Patent 
Application Laid-Open No. 56-148585. The porous inorganic pigment 
contained in the coating layer is exemplified by silica having superior 
color-developing properties as described in Japanese Patent Application 
Laid-open No. 56-185690, and by many other materials including calcium 
carbonate, alumina, and so forth. 
The aforementioned coated paper is required to have the performance of 
providing images in high density and high sharpness with high resolution, 
and is further required to be responsive to high-speed print output. 
In serial type color ink-jet printers, in order to achieve high-speed print 
output, increasing the driving-frequency of the head is essential, and 
also important is the capability of the head to conduct printing both in 
the forward movement direction and in the backward movement direction. A 
color ink-jet system is considered as an example in which four ink heads 
respectively for the colors of black (Bk), yellow (Y), magenta (M) and 
cyan (C) are arranged in the order of Bk, Y, M, and C from the back side 
to the front side along the forward direction of the head movement. Here, 
the direction of the movement of the ink heads starting from the home 
position is defined to be "forward" direction, and the reversed direction 
to be "backward" direction. The order of the colors of dots plotted with 
the color inks to provide colors of red (R), green (G), and blue (B) in 
the forward movement of the head is reversed in the backward movement. 
With the coated paper derived in the above cited prior art techniques, 
reversal of the dotting order of color inks results in change of color 
tone at mixed color portions, which hinders printing in back-and-forth 
directions. 
The above prior art techniques have further disadvantages as mentioned 
below. For example, when the silica having a large specific surface area 
as disclosed in Japanese Patent Application Laid-Open No. 56-185690 is 
used for obtaining a sharp image with high density, the dye applied on a 
recording medium changes its color over time to deteriorate the recorded 
image even when it is stored in ordinary environmental conditions, like 
posting on an indoor wall. On the contrary, with a pigment such as calcium 
carbonate, kaolin, and talc having a small specific surface area, the 
above-mentioned indoor discoloration is retarded, however the derived 
image density is low without sharp image quality. Therefore, the 
suppression of the indoor discoloration is not consistent with high image 
density, and this inconsistency could not be removed by prior techniques. 
The inventors of the present invention became aware of the fact that the 
indoor discoloration of the recorded image results only when coated paper 
is used, and does not result when non-coated paper such as ordinary PPC 
paper is used, and also that this indoor discoloration differs 
intrinsically from the dye discoloration caused by projection of UV light 
or visible light, and arises even in the absence of the light. 
The inventors considered that the indoor discoloration results from 
oxidative decomposition of the dye which is caused by interaction of the 
dye, the pigment and an oxidative gas with each other. Accordingly, it may 
be assumed that a larger specific surface area of the used pigment causes 
more rapid oxidative decomposition reactions. From this assumption, the 
fact is understood that the higher degree of indoor discoloration is 
caused on coated paper having larger specific surface area of the pigment 
used. 
On the other hand, the image density will be higher if the active surface 
for dye absorption is larger in the vicinity near the surface layer of the 
coat layer. 
The inventors of the present invention already proposed a recording medium 
free from the aforementioned problems of indoor discoloration and 
insufficient image density, as shown in EP 405 417 A1, etc. This recording 
medium, however, does not satisfactorily solve the problem of color tone 
change in printing in the back and forth directions. 
SUMMARY OF THE INVENTION 
A primary object of the present invention is to provide a recording medium 
which does not cause changes in printed-image quality even when the 
dotting order of ink colors is changed, and to provide a recording method 
employing the recording medium. 
Another object of the present invention is to provide a recording medium 
which is superior in storability of the recorded images especially with 
less deterioration by indoor discoloration as well as in image density and 
is particularly suitable for ink-jet printing, and also to provide a 
recording method employing the recording medium. 
According to an aspect of the present invention, there is provided a 
recording medium containing basic magnesium carbonate, and a cationic 
surfactant and/or a nonionic surfactant. 
According to another aspect of the present invention, there is provided an 
ink-jet recording method in which ink is ejected through an orifice of an 
ink jet recording head onto a recording medium in response to a recording 
signal, the recording medium containing basic magnesium carbonate, and a 
cationic surfactant and/or a nonionic surfactant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The surfactant in the present invention functions to control the dynamic 
ink permeability of a recording medium, especially of one containing basic 
magnesium carbonate. 
Usually, a coating layer composed of a particulate pigment, a binder, and 
an additive such as a waterproofing (dye fixing) agent tends to vary 
remarkably in permeation characteristics including the permeation rate and 
the running of ink depending on whether the layer is wet or dry. The wet 
and dry states have significant influence when paper having ink-absorbency 
is used as the base material; and the wet and dry states have much more 
significance where pigment light coated paper pigment or internal additive 
type paper having fiber of the base paper exposed at the surface of a 
recording medium is used as the recording medium. This is considered to be 
due to the relative change of the surface tension of the ink to the 
recording medium between a dry state and a wet state. This difference is 
assumed to be caused mainly by the characteristics of the materials 
constituting the coating layer including a pigment, a water-soluble resin, 
a binder, and the like, or the characteristics of pulp fiber, a sizing 
agent, and the like of the base paper. 
In particular, the permeation rate and the permeation characteristics are 
liable to vary in the case where basic magnesium carbonate is used as the 
pigment. Such variation can be effectively controlled by using the 
specified surfactant in combination with the pigment. 
In the present invention, the incorporation into the recording medium of a 
cationic surfactant and/or a nonionic surfactant selected from among a 
variety of surfactants is assumed to lower the surface tention of the ink 
to suppress the variation of dynamic permeability of the ink to the 
recording medium between a dry state and a wet state, especially of the 
recording medium containing basic magnesium carbonate. 
The effect of the addition of surfactant of the present invention is 
particularly remarkable in the case where basic magnesium carbonate is 
used as the particulate pigment. More preferably, spherical basic 
magnesium carbonate particles are used for achieving a high image density. 
This is considered to be due to the fact that the spherical agglomerate of 
the basic magnesium carbonate leads to a denser packed state in the 
formation of the coating layer in comparison with the usual plate-shaped 
or column-shaped agglomerate of basic magnesium carbonate, and 
consequently the dye is caught nearer to the surface of the coating layer 
when compared at the same ink permeation rate. In other words, the active 
surface of the basic magnesium carbonate particles is considered to be 
more effectively utilized in the case where they are sphere-shaped than in 
the case where they are in other shapes. 
Known spherical basic magnesium carbonate materials are however constituted 
of agglomerates having an average particle diameter ranging from about 3 
to about 20 .mu.m with broad particle-size distribution. Therefore, in a 
recording medium formed by applying a known spherical basic magnesium 
carbonate on a substrate, the void formed by the basic magnesium carbonate 
on the surface of the recording medium is not so uniform as that formed by 
fine particles of silica or alumina (having an average particle diameter 
of less than 3 .mu.m). Accordingly, the variation of dynamic permeating 
property of ink may affect image qualities such as optical density, 
feathering, ink-running, etc. more greatly in the former recording medium. 
The difference in image quality caused by the change of the dotting order 
of the color inks can be effectively decreased particularly effectively by 
combined use of a cationic surfactant and/or a nonionic surfactant with 
basic magnesium carbonate as the main pigment in the present invention. 
The present invention is described below in more detail by reference to the 
preferred embodiment. 
In the recording medium of the present invention, the surfactant and the 
pigment may be contained in the substrate (base material), or may be 
contained in a coating layer formed on the substrate. The content of the 
surfactant in the present invention is preferably in the range of from 
0.05 to 2.0% by weight, more preferably from 0.1 to 1.5% by weight based 
on the basic magnesium carbonate in order to achieve the above-mentioned 
effect more sufficiently. The content of the basic magnesium carbonate in 
the recording medium of the present invention is preferably in the range 
of from 0.2 to 50 g/m.sup.2, more preferably from 0.2 to 20 g/m.sup.2 to 
achieve the above-mentioned effect more sufficiently. 
The substrate employed in the present invention is preferably ink-absorbent 
base paper, but is not limited thereto. For example, a film of a polymer 
such as polyester may be used as the substrate material. The preferred 
embodiment of the present invention is described below by taking the cases 
employing an ink-absorbent paper as the substrate. 
The recording medium of the present invention is constituted from a 
substrate, basic magnesium carbonate, a cationic surfactant and/or a 
nonionic surfactant, and preferable other additives such as a binder, a 
dye fixing agent, and a fluorescent whitener. 
The basic magnesium carbonate for use in the present invention is not 
specially restricted. The object of the present invention can be achieved 
satisfactorily with a commercially available magnesium carbonate. However, 
use of spherical basic magnesium carbonate is more preferable. 
The spherical basic magnesium carbonate in the present invention is the one 
having a shape disclosed in Japanese Patent Application Laid-Open Nos. 
60-54915, 61-63526, and 63-89418, but the process of its production is not 
limited to the process described therein. 
The term "spherical" in the present invention concerns the shape of 
agglomerate of the primary particles, and does not necessarily mean a 
complete sphere shape. The preferred shape of the sphere is one having the 
ratio of the major axis length (a) to the minor axis length (b) in the 
range of 0.7.ltoreq.b/a.ltoreq.1.0. 
However, in the production of such spherical basic magnesium carbonate, the 
complete spherical shape of the product cannot always be obtained, 
depending on the reaction conditions modified for controlling the particle 
diameter, the specific surface area, the oil absorption, and other pigment 
properties. For example, particles lacking a portion of the sphere, or 
particles agglomerating in a flower-petal shape may be formed. In the 
present invention, particles with less than 1/4 in volume of the assumed 
complete sphere are also included. 
In the case where the primary particles constructing the agglomerate are 
relatively large and consequently the peripheral line tracing the 
outermost particles is remarkably rugged, the peripheral line is drawn so 
as to form a shape of a circle or an ellipse having the largest ratio of 
the aforementioned b/a within the allowable b/a ratio defined above. 
Further, in the present invention, the basic magnesium carbonate containing 
the above-defined spherical particles in an amount of not less than 85% of 
the total particles is included in the spherical basic magnesium 
carbonate. A particle, which looks as if glued with another particle but 
more than half of the outline is discerned, is regarded as one 
agglomerated particle. 
The average particle diameter of the spherical basic magnesium carbonate is 
in the range of from 0.5 to 20 .mu.m, preferably from 1 to 12 .mu.m. An 
excessively fine particle size causes lower ink absorbency, while an 
excessively large particle size may cause falling-off of the particles 
from the recording medium. 
Here, the particle diameter means the major axis length "a" described 
above. The average particle diameter means a simple average of 100 or more 
of the major axis diameters "a" measured by electron microscopy. In the 
particle size distribution of the spherical basic magnesium carbonate, 95% 
or more in number of the particles have preferably a size of not larger 
than 25 .mu.m, more preferably not larger than 15 .mu.m, and still more 
preferably not larger than 10 .mu.m. 
An excessively large ratio in number of particles having larger size is 
undesirable because the dispersibility of particles is lowered to result 
in formation of larger agglomerate in slurry preparation, which adversely 
effects the coating suitability and printing suitability. 
The specific surface area is measured by the BET method. The particles have 
the surface area particularly preferably in the range of from 10 m.sup.2 
/g to 70 m.sup.2 /g. With an excessively small specific surface area, the 
image density cannot be high, while with an excessively large specific 
surface area, resistance to indoor discoloration of the recording medium 
is low. 
The surfactant for use in the present invention is exemplified below 
without limiting the invention in any way. The cationic surfactant is the 
one having a primary to quaternary ammonium group, a pyridinium group, or 
the like as the hydrophilic group, specific examples including: 
cetyltrimethylammonium chloride, 
stearyltrimethylammonium chloride, 
behenyltrimethylammonium chloride, 
octadecyltrimethylammonium chloride, 
hexadecyltrimethylammonium chloride, 
dodecyltrimethylammonium chloride, 
dioctyldimethylammonium chloride, 
distearyldimethylammonium chloride, 
lauryldimethylbenzylammonium chloride, 
myristyldimethylbenzylammonium chloride, 
stearyldimethylbenzylammonium chloride, 
tetradecyldimethylbenzylammonium chloride, 
octadecyldimethylbenzylammonium chloride, 
oxyethyldodecylamine, and the like. 
The nonionic surfactant includes: 
polyoxyethylene alkyl ether, 
polyoxyethylene alkylphenol ether, 
polyoxyethylene alkylphenyl ether, 
polyoxyethylene aliphatic ester, 
sorbitan ester ether, 
sorbitan ester; and the like, but is not limited thereto. 
In the present invention, other conventionally used inorganic or organic 
pigments may be used in combination with the spherical basic magnesium 
carbonate within the range in which the object of the present invention is 
achievable. 
The inorganic pigment includes silica, alumina, aluminum silicate, 
magnesium silicate, hydrotalcite, calcium carbonate, titanium oxide, clay, 
talc, and the like, but is not limited thereto. The organic pigment is 
exemplified by plastic pigments such as urea resins, urea-formalin resins, 
polyethylene resins, polystyrene resins, and the like, but is not limited 
thereto. The mixing ratio of the pigment is preferably in the range of 
from 10 to 60% by weight based on the basic magnesium carbonate. 
The binder for use in the present invention includes, for example, 
water-soluble polymers such as polyvinyl alcohol, starch, oxidized starch, 
cationic starch, casein, carboxymethylcellulose, gelatin, 
hydroxyethylcellulose, acrylic resins, and the like; water-dispersible 
polymers such as SBR latex, polyvinyl acetate emulsion, and the like; and 
combination of two or more thereof. 
The preferred mixing ratio of the pigment and the binder (P/B) in the 
present invention is not lower than 1/4 by weight in view of further 
improvement of ink absorbency of the ink-receiving layer, and not higher 
than 10/1 by weight in view of prevention of pigment-falling-off of the 
ink-receiving layer, more preferably being in the range of from 6/1 to 
1/1. 
Further in the present invention, the ink receiving layer may contain an 
additive, if necessary, such as a dye-fixing agent (waterproofing agent), 
a fluorescent whitener, a surfactant, an anti-foaming agent, a pH 
controlling agent, a mildewproofing agent, a UV absorbing agent, an 
anti-oxidizing agent, a dispersing agent, a viscosity-reducing agent, and 
the like. Such additives are arbitrarily selected from known compounds 
depending on the object. 
The dye-fixing agent is explained as an example of the additives. The 
additional use of the following dye-fixing agent improves the 
water-resistance of the formed image. 
##STR1## 
The above compounds are merely examples, and do not limit the present 
invention. The waterproofing effect of the dye-fixing agent depends on the 
kind of the dye used for ink-jet recording. Accordingly, the combination 
with the dye for recording have to be sufficiently examined. 
The recording medium of the present invention is prepared by applying an 
aqueous coating liquid containing a pigment, a binder, and other additives 
by a known method such as a roll-coater method, a blade-coater method, an 
air-knife-coater method, a gate-roll-coater method, a size-press method, 
and the like onto the surface of a substrate, and then drying the coated 
matter by means of a hot-air drying oven, a hot drum, or the like. The 
recording medium may be further subjected to a supercalender treatment for 
the purpose of smoothing the surface of the ink-receiving layer or raising 
the surface strength of the ink-receiving layer. 
The total amount of the coating of the pigment in the ink-receiving layer 
is preferably in the range of from 0.2 to 50 g/m.sup.2, more preferably 
from 0.2 to 20 g/m.sup.2. In using a small amount of the coating, a part 
of the substrate may be exposed on the surface. At the coating amount of 
less than 0.2 g/m.sup.2, no effect is achieved in color development of the 
dye in comparison with the case of mediums having no ink-receiving layer, 
while at the coating amount of more than 50 g/m.sup.2, pigment-falling-off 
occurs at the coating layer, which is undesirable. Meanwhile, the amount 
of the coating is in the range of from 0.5 to 100 .mu.m in terms of layer 
thickness. 
The ink itself for the ink-jet recording on the recording medium described 
above may be any known ink, which can be used without any inconvenience. 
The recording agent therefor may be a water-soluble dye such as direct 
dyes, acidic dyes, basic dyes, reactive dyes, and food dyes. Any dye for 
ink-jet recording use may be employed without any particular limitation, 
The particularly preferred embodiment of the recording method of the 
present invention is an ink-jet recording which employs a direct dye 
and/or an acidic dye as the recording agent. Although the relation thereof 
with the recording medium is not exactly known, the effect is assumed to 
be due to a chemical reaction with the basic magnesium carbonate contained 
or the cationic and/or nonionic surfactant in the recording medium, 
thereby sufficiently reducing the difference in color tone between the 
image formed by forward movement of head and the one formed by backward 
movement of the head, and yet retaining sufficient recording image density 
and sufficient resistance against indoor discoloration. 
The aforementioned water-soluble dye is used conventionally in an amount 
ranging from about 0.1 to 20% by weight in an ink. In the present 
invention the dye may also be used in an amount in the same range. 
The solvent for the aqueous ink of the present invention is water, or a 
mixed solvent of water and a water-soluble organic solvent. Particularly 
suitable is a mixed solvent of water and a water-soluble organic solvent, 
the water-soluble organic solvent containing a polyhydric alcohol which is 
effective to prevent drying of ink. 
The method of recording by applying the ink on the aforementioned recording 
medium is preferably any ink-jet recording method, in which the ink is 
ejected through a nozzle to apply the ink onto the recording medium as an 
ejected-ink-receiving body. 
In particular, the recording medium of the present invention is effectively 
used in the recording method in which an ink receives thermal energy to 
change its volume abruptly by phase transition and is ejected by the 
action caused by this volume change, as described in Japanese Patent 
Application Laid-Open No. 54-59936. 
A recording apparatus is described below which is suitable for recording on 
the recording medium of the present invention. 
An example of the constitution of the heads, which is a main portion of the 
apparatus, is shown in FIG. 1, FIG. 2, and FIG. 3. 
A head 13 is formed by bonding a plate of glass, ceramics, or plastics 
having a groove 14 for ink passage with a heat-generating head 15. (The 
type of the head is not limited to the one shown in the drawing.) The 
heat-generating head 15 is constituted of a protection layer 16 formed of 
silicon oxide or the like, aluminum electrodes 17-1 and 17-2, a 
heat-generating resistance layer 18 formed of nichrome or the like, a heat 
accumulation layer 19, and a substrate plate 20 having a high 
heat-releasing property made of alumina or the like. 
Ink 21 reaches the ejection orifice 22 (a fine pore), forming a meniscus by 
action of pressure P not shown in the figure. 
On application of an electric signal to the electrodes 17-1 and 17-2, the 
region designated by a symbol "n" of the heat-generation head 15 abruptly 
generates heat to form a bubble in the ink 21 at the position adjacent 
thereto. The pressure generated by the bubble pushes out the meniscus 23 
and ejects the ink 21 from the orifice 22, as recording droplets 24, and 
the droplets are propelled to a recording medium 25. FIG. 3 illustrates 
exterior appearance of a multi-head constructed by juxtaposing a 
multiplicity of heads shown in FIG. 1. The multi-head is prepared by 
bonding a glass plate 27 having multi-grooves 26 with a heat-generation 
head 28 similar to the one described in FIG. 1. 
Incidentally, FIG. 1 is a cross-sectional view of the head 13 along an ink 
flow path, and FIG. 2 is a cross-sectional view of the head at the line 
A-B in FIG. 1. 
FIG. 4 illustrates an example of the ink-jet recording apparatus having 
such a head mounted therein. 
In FIG. 4, a blade 61 operating as a wiping member is held at one end by a 
blade-holding member, forming a fixed end in a shape of a cantilever. The 
blade 61 is placed at a position adjacent to the recording region of the 
recording head, and in this example, is held so as to protrude into the 
moving path of the recording head. A cap 62 is placed at a home position 
adjacent to the blade 61, and is constituted such that it moves in the 
direction perpendicular to the moving direction of the recording head to 
come into contact with the ejection nozzle face to cap the nozzles. An ink 
absorption member 63 is provided at a position adjacent to the blade 61, 
and is held so as to protrude into the moving path of the recording head 
in a manner similar to that of the blade 61. The aforementioned blade 61, 
the cap 62, and the absorption member 63 constitute an ejection-recovery 
section 64, the blade 61 and the absorption member 63 remove water, dust, 
and the like from the ink ejecting nozzle face. 
A recording head 65 has an ejection energy generation means, and conducts 
recording by ejecting ink toward a recording medium opposing the ejection 
nozzle face. A carriage 66 is provided for supporting and moving the 
recording head 65. The carriage 66 is slideably engaged with a guide rod 
67. A portion of the carriage 66 is connected (not shown in the drawing) 
to a belt 69 driven by a motor 68, so that the carriage 66 is movable 
along the guide rod 67 to the recording region of the recording head and 
the adjacent region thereto. 
The constitution of a paper delivery portion 51 for delivery of a recording 
medium and a paper delivery roller 52 driven by a motor not shown in the 
figure delivers the recording medium to the position opposing to the 
ejecting nozzle face of the recording head, and the recording medium is 
discharged with the progress of recording to a paper discharge portion 
provided with paper-discharge rollers 53. 
In the above constitution, the cap 62 of the ejection-recovery portion 64 
is positioned away from the moving path of the recording head 65 during 
returning of the head to the home position at the end of the recording, 
etc., while the blade 61 is made to protrude into the moving path. 
Therefore, the ejecting nozzle face of the recording head 65 is wiped 
therewith. The cap 62 moves to protrude toward the moving path of the 
recording head 65 when the cap 62 comes into contact for capping with the 
ejecting nozzle face of the recording head 65. 
At the time when the recording head 65 moves from the home position to the 
record-starting position, the cap 62 and the blade 61 are at the same 
position as in the above-mentioned wiping, so that the ejection nozzle 
face of the recording head is wiped also in this movement. 
The recording head moves to the home position not only at the end of the 
recording and at the time of ejection recovery, but also at a 
predetermined interval during movement for recording in the recording 
region. By such movement, the wiping is conducted. 
The present invention is described in more detail by reference to examples. 
In the examples, the terms "part" and "%" are based on weight unless 
otherwise mentioned. 
EXAMPLE 1 AND COMATIVE EXAMPLE 1 
Method for Preparing Recording Medium 
The constitutional elements in the Example and Comparative Example are 
listed below: 
Substrate material: 
Wood-free paper (Ginwa, made by Sanyo Kokusaku Pulp Co, Ltd.) 
Coating material: 
(1) Basic magnesium carbonate (dense magnesium carbonate, made by Konoshima 
Kagaku K.K., average primary particle diameter: 0.47 .mu.m, specific 
surface area: 27 m.sup.2 /g, bulk density: 0.44 g/cc, oil absorption: 79 
ml/100 g), 
(2) Binder (PVA-217, made by Kuraray Co., Ltd., saponification degree: 89 
mol %, polymerization degree: 1700), 
(3) Waterproofing agent (polyallylamine hydrochloride, PAA-HCl-3L, made by 
Nitto Boseki Co., Ltd., average molecular weight: 10,000), 
(4) Cationic surfactant (Coatamine 24P, made by Kao Corporation, 
lauryltrimethylammonium chloride). 
The recording medium was prepared in the manner described below. 
First, 15 parts of the Pigment (1), basic magnesium carbonate, was mixed 
with 85 parts of water, and the mixture was stirred for 15 minutes by 
means of a commercial homogenizer at a stirring rate of 10,000 rpm. To the 
mixture, a separately prepared binder solution (aqueous 10% polyvinyl 
alcohol solution) was added in an amount to give a pigment/binder ratio 
(solid ratio) of 2/1, and stirred for 5 minutes. The aforementioned 
Additive (3) was added thereto in a ratio of 10% (solid ratio) based on 
the Pigment (1), and stirred for 5 minutes. Further thereto, the 
Surfactant (4) was added at a ratio (solid ratio) of 0.5% based on the 
Pigment (1), and stirred further for 5 minutes to provide a coating 
liquid. 
The resulting coating solution was applied on the aforementioned substrate 
material with a wire bar coater. The coated matter was dried at 
110.degree. C. for 5 minutes, and treated with a supercalender. Thus the 
recording medium of the present invention was prepared. 
The recording medium employed in Comparative Example 1 was prepared in the 
same manner as in Example 1 except that the cationic surfactant (5) was 
not used. 
The recording mediums for Examples 2 to 5 and Comparative Example 2 to 6 
were prepared in the same manner as above. 
Table 1 summarizes the constitutional elements and their mixing ratio used 
in Examples 2 to 5 and Comparative Examples 2 to 6. As the substrate 
material, ink-absorbent paper was consistently used which had a basis 
weight of 100 g/m.sup.2, thickness of 100 .mu.m, and a sizing degree of 2 
seconds, and contained calcium carbonate as a filler at a content of 6.5% 
in terms of ash according to JIS-P-8128. The amount of coating was 
adjusted to be 6 g/m.sup.2 as dry coating matter. 
TABLE 1 
EXAMPLE 2 
Pigment: Spherical basic magnesium carbonate (average particle diameter: 
5.0 .mu.m, bulk density: 0.3 g/cc, specific surface area: 30 m.sup.2 /g, 
oil absorption: 70 ml/100 g): 15 parts 
Binder: PVA-217: 6 parts 
Waterproofing agent: Dimethyldiallylammonium chloride-acrylamide copolymer 
(PAS-J41, made by Nitto Boseki Co. Ltd., average molecular weight: 
10,000): 3 parts 
Surfactant: Cation BB (dodecyltrimethylammonium chloride, made by Nippon 
Oil and Fat Co., Ltd.): 0.075 part 
EXAMPLE 3 
Pigment: The same as in Example 2 
Binder: The same as in Example 2 
Waterproofing agent: The same as in Example 2 
Surfactant: Nonion T-208.5 (polyoxyethylene tridecyl ether, made by Nippon 
Oil and Fat Co., Ltd.): 0.070 part 
EXAMPLE 4 
Pigment: The same pigment as in Example 2: 10 parts, and Silica (Fine Sil 
K-40, made by Tokuyama Soda 
Co, Ltd., average particle diameter: 1.5 .mu.m, 
specific surface area: 300 g/m.sup.2): 5 parts 
Binder: The same as in Example 2 
Waterproofing agent: PAA-HCl-3L: 1.5 parts 
Surfactant: The same as in Example 3 
EXAMPLE 5 
Pigment: The same pigment as in Example 2: 10 parts, and alumina (Aluminum 
oxide C, made by Degussa CO., average particle diameter: 20 nm, specific 
surface area: 100 g/m.sup.2): 5 parts 
Binder: The same as in Example 2 
Waterproofing agent: The same as in Example 4 
Surfactant: Electrostripper QN (made by Kao Corporation): 0.05 part 
COMATIVE EXAMPLE 2 
Pigment: The same as in Example 2 
Binder: The same as in Example 2 
Waterproofing agent: The same as in Example 4 
Surfactant: Not used 
COMATIVE EXAMPLE 3 
Pigment: The same as in Example 4 
Binder: The same as in Example 2 
Waterproofing agent: The same as in Example 4 
Surfactant: Not used 
COMATIVE EXAMPLE 4 
Pigment: The same as in Example 5 
Binder: The same as in Example 2 
Waterproofing agent: The same as in Example 4 
Surfactant: Not used 
COMATIVE EXAMPLE 5 
Pigment: Silica (Finesil K-40, made by Tokuyama Soda Co., Ltd.) 
Binder: The same as in Example 2 
Waterproofing agent: The same as in Example 4 
Surfactant: Sanisol (alkylbenzylmethylammonium chloride, made by Kao 
Corporation): 0.075 part 
COMATIVE EXAMPLE 6 
Pigment: The same as in Comparative Example 5 
Binder: The same as in Example 2 
Waterproofing agent: The same as in Example 4 
Surfactant: Not used 
COMATIVE EXAMPLES 7-9 
The recording mediums for comparison were prepared in the same manner as in 
Example 1 except that the anionic surfactants below were used respectively 
in place of the cationic surfactant of Example 1. 
Comparative Example 7: 
Polyoxyethylene octylphenol ether sulfate (made by Matsumoto Yushi K.K.) 
Comparative Example 8: 
Sodium dicetylsulfosuccinate (made by Matsumoto 
Yushi K.K.) 
Comparative Example 9: 
Potassium alkylphosphate (made by Matsumito 
Yushi K.K.) 
With the above recording mediums, color ink-jet recording was conducted by 
use of the inks having the compositions below in an amount of 8 
nQ/mm.sup.2 for single color ink dot in the two ink-dotting orders of 
C.fwdarw.M.fwdarw.Y.fwdarw.Bk and Bk.fwdarw.Y.fwdarw.M.fwdarw.C.fwdarw.Bk. 
Ink composition 
______________________________________ 
Dye 5 parts 
Diethylene glycol 
20 parts 
Water 80 parts 
______________________________________ 
Dyes 
Y: C.I. Direct Yellow 86 
M: C.I. Acid Red 35 
C: C.I. Direct Blue 199 
Bk: C.I. Food Black 2 
The image density of the solid-print portions of the single colors and the 
mixed colors were evaluated. 
Solid printing was conducted with black color ink and the combinations of 
two color inks of yellow and magenta, magenta and cyan, and cyan and 
yellow with the head movement in the forward direction and in the backward 
direction, thus changing the order of the dotting of the ink colors. The 
reflective optical densities of each of the colors of the solid prints 
were measured by means of MacBeth Reflactodensitometer RD-918. The results 
of the measurement are shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
OD (Bk) 
Direction 
OD R(M/Y) 
OD G(C/Y) 
OD B(C/M) 
__________________________________________________________________________ 
Example 1 1.38 forward 
1.40/1.28 
1.40/1.26 
1.42/1.38 
backward 
1.41/1.29 
1.42/1.28 
1.40/1.40 
Comparative Example 1 
1.38 forward 
1.43/1.27 
1.40/1.26 
1.40/1.37 
backward 
1.35/1.35 
1.35/1.35 
1.35/1.45 
Example 2 1.35 forward 
1.36/1.25 
1.35/1.25 
1.34/1.32 
backward 
1.36/1.25 
1.34/1.26 
1.35/1.33 
Example 3 1.35 forward 
1.35/1.24 
1.34/1.26 
1.35/1.32 
backward 
1.35/1.25 
1.35/1.25 
1.34/1.34 
Comparative Example 2 
1.34 forward 
1.36/1.26 
1.34/1.25 
1.35/1.31 
backward 
1.30/1.32 
1.28/1.35 
1.30/1.37 
Example 4 1.40 forward 
1.40/1.28 
1.40/1.27 
1.42/1.35 
backward 
1.40/1.29 
1.41/1.28 
1.43/1.36 
Comparative Example 3 
1.40 forward 
1.40/1.23 
1.40/1.22 
1.40/1.36 
backward 
1.32/1.28 
1.33/1.28 
1.35/1.40 
Example 5 1.42 forward 
1.45/1.30 
1.42/1.30 
1.41/1.40 
backward 
1.47/1.31 
1.41/1.32 
1.40/1.40 
Comparative Example 4 
1.43 forward 
1.45/1.25 
1.41/1.24 
1.42/1.40 
backward 
1.38/1.30 
1.35/1.29 
1.37/1.45 
Comparative Example 5 
1.45 forward 
1.50/1.35 
1.45/1.35 
1.46/1.40 
backward 
1.40/1.40 
1.40/1.40 
1.38/1.50 
Comparative Example 6 
1.45 forward 
1.50/1.35 
1.46/1.35 
1.44/1.39 
backward 
1.40/1.40 
1.38/1.38 
1.37/1.47 
Comparative Example 7 
1.33 forward 
1.35/1.10 
1.36/1.08 
1.37/1.24 
backward 
1.18/1.28 
1.22/1.27 
1.22/1.33 
Comparative Example 8 
1.32 forward 
1.35/1.08 
1.37/1.09 
1.37/1.22 
backward 
1.18/1.28 
1.21/1.26 
1.24/1.35 
Comparative Example 9 
1.32 forward 
1.36/1.10 
1.38/1.08 
1.36/1.24 
backward 
1.17/1.29 
1.25/1.26 
1.24/1.35 
__________________________________________________________________________ 
In Table 2, the term "OD R(M/Y)" means the reflective optical densities of 
magenta color and yellow color at the yellow/magenta solid print portion, 
and the terms "OD G(Y/C)" and "OD B(C/M)" have analogous meaning. The term 
"forward" means the printing with the head moving in the forward 
direction, and the term "backward" means the printing with the head moving 
in the backward or reversed direction. 
As shown clearly in Table 2, the presence of the basic magnesium carbonate 
and a cationic surfactant and/or a nonionic surfactant resolves the 
difference of color tone between the mixed color portions dotted with 
different order of ink colors. 
The present invention provides printed images having consistent color tone 
by use of a serial type color ink-jet printer regardless of the movement 
direction of the head, thus enabling high-speed printing.