NO301410B1 - Recording medium and ink jet recording method using this - Google Patents

Abstract

A recording medium comprises a surface layer composed mainly of aluminum oxide particles and a lower layer having ink absorptivity. A recording medium comprises a surface layer composed mainly of aluminum oxide particles and a lower layer having ink absorptivity, and having a Stöckigt sizing degree according to JIS-P-8122 of 0 to 15 sec. An ink jet recording method performs recording by imparting small droplets of an aqueous ink to a recording medium, wherein said aqueous ink contains an acidic dye and/or a direct dye, and said recording medium comprises a surface layer composed mainly of aluminum oxide particles and a lower layer having ink absorptivity. A recording medium comprising a surface layer composed mainly of aluminum oxide particles containing polyaluminum hydroxide and/or polyaluminum chloride and a lower layer having ink absorptivity. A recording medium comprises a surface layer composed mainly of aluminum oxide particles having particle sizes of 5 mu m or less provided on a liquid absorptive base paper.

Description

Field of the invention

The present invention relates to a recording medium suitable for use in the ink jet recording method, in particular a recording medium which has excellent absorption capacity and color forming properties for an aqueous ink and provides excellent sharpness for the obtained recorded image.

The present invention also relates to a recording medium that can provide a recorded image with little "in-room" discoloration of the image and excellent storage stability for the image, and a recording method that can provide the above-mentioned recorded image.

The present invention also relates to a recording medium with excellent water resistance and light resistance for the recorded image at the same time that the recording medium has different properties as mentioned above.

State of the art

According to the state of the art, the following have been known as recording media for ink (color) ray registers: (1) a recording medium obtained by making paper, generally consisting mainly of pulp, into a sheet with a low degree of gluing, such as filter paper or tracing paper, (2 ) a recording medium having an ink-absorbing layer by using a porous inorganic pigment provided on a substrate (base) paper with low color absorbency, such as plain paper of fine quality, etc. as described in Japanese Laid-Open Patent Publication No. 56-148585, etc.

On the other hand, within the ink-jet recording system for which the formation of a high-quality, high-resolution colored image is particularly required, the recording medium to be used has the following properties: (1) good color-forming properties for the ink attached to the recording medium,

(2) good correct spherical shape for the Talekk point,

(3) good color absorbency so that the attached ink

will not flow out even when several small ink drops may be attached at the same point, (4) good ink fixing ability so that the small ink drops that are attached will not stick out even when they can be rubbed immediately after being attached; (5) good image storability for the image formed, such as water resistance or light resistance etc.

However, no recording medium that satisfies all of the above-required properties has been known to date.

Recently, more precisely, the problem of "in-room" discoloration of the registered image, which is inherent in coated paper, has been subjected to a closer investigation.

The problem of lightfastness, which has been the problem according to the state of the art, is a problem concerning fading of the image when exposed to, for example, UV rays or visible light, etc., and this problem occurs for any image printed on any type of paper from paper for PPC in general or fine quality paper to coated paper for ■ inkjet. The problem of "in-room" discoloration as mentioned here is, however, a problem that is separate from the light resistance that occurs for the image when this is also stored in, for example, a place where no direct sunlight shines, but which does not occur for an image that has been printed on an uncoated paper, such as paper for PPC, etc. (PPC="Plain Paper Copier")

For example, the method described in Japanese Laid-Open Patent Publication No. 60-49990 is a method for improving lightfastness, and no effect can be observed for the "in-room" decolorization. The problem of "in-room" discoloration is thus a problem inherent to coated paper, and it can be argued that it is a problem caused by the pigment that forms the coated layer.

For example, paper coated using high-active silicon dioxide, as described in Japanese Laid-Open Patent Publication No. 56-185690, can provide an image with high optical density while presenting a distinct problem in terms of "in-

room" decolourisation. If, on the other hand, fillers are generally used for paper with a low specific surface area, such as calcium, kaolin, talc or silicon dioxide etc, there is a problem that the image density is lowered even if "in-room"

the discoloration can be suppressed.

In particular, the problems of "in-room" discoloration and image density are thus irreconcilable, and they have represented problems that have not been solved by means of methods according to the state of the art.

Summary of the invention

It is therefore an object of the present invention to provide a recording medium which can provide an image of high quality and high resolution and with a high density for the recorded image, and which nevertheless has excellent ink absorption capacity and the color-forming property of a dye.

The invention also aims to provide a recording medium which can provide a recorded image with good storage duration, in particular a recorded image with low deterioration due to "in-room" discoloration, and an ink jet recording method for forming such an image.

It is a further object of the present invention to provide a recording medium which has excellent water resistance and light resistance for the recorded image while having various properties as mentioned above.

The above and other objects of the present invention can be achieved by means of the inventions as defined below.

According to the present invention, a recording medium is provided which comprises a surface layer which is mainly composed of aluminum oxide particles, and the recording medium is characterized by the fact that it also comprises a lower layer with ink absorption capacity, that the aluminum oxide particles have a BET surface area of 60-170 m/g and an average particle size of 5 µm or less, and that the amount of the applied surface layer is in the range from 0.3 to 7 g/m 2 as the total amount of the pigment.

The present invention also provides an ink jet registration method which provides registration by applying small drops of an aqueous ink to a recording medium according to the invention, the aqueous ink containing an acidic color

fabric and/or a direct dye.

The present invention also provides a recording medium which comprises a surface layer which is mainly composed of aluminum oxide particles and which contains polyaluminium oxide and/or polyaluminium chloride.

The present invention also provides a recording medium comprising a surface layer which is mainly composed of aluminum oxide particles with a particle size of 5 µm or less and applied to a liquid-absorbing backing paper.

During the development of the present invention, investigations were carried out regarding the relationship between the pigment which forms the coated (coated) layer which becomes the ink (colour) receiving layer, and "in-room" decolourisation on the basis of the recognition that "in -room" discoloration is a phenomenon that does not occur on uncoated paper, but only occurs on coated paper, and as a result of these investigations it was found that the problem of "in-room" discoloration can hardly occur when a specific pigment is used as : the pigment that forms the color-receiving layer, especially the recording surface that captures the dye.

Description of the preferred embodiments

The present invention is described in more detail below with reference to preferred embodiments.

The first specific feature of the recording medium according to the present invention is that the surface layer, which is the recording surface, is mainly formed of aluminum oxide particles.

The aluminum oxide particles, as mentioned here, are produced using the method commonly referred to as the Bayer method, whereby aluminum hydroxide obtained by hot sodium hydroxide treatment of bauxite, which is a natural ore, is calcined. They can also be used which are produced by the method where metallic aluminum pellets are subjected to an arc discharge in water, after which the aluminum hydroxide obtained is calcined, or by means of the method where aluminum chloride is gasified at high temperature and oxidized in the gas phase, or by means of the method where inorganic aluminum salt (alum etc.) is split.

It has been known that the crystal structures of the aluminum oxide particles are subjected to transitions depending on the temperature for heat treatment, from aluminum hydroxide of the poisonsitt^ type, the boehmite type to aluminum oxide of the type fc, a, ri»9, a. According to the present invention, of course, any of these manufacturing methods and crystal structures be available.

Cleanliness. for aluminum oxide particles may be different depending on the production method, the degree of purification, but those that can be used according to the present invention are not limited to an aluminum oxide containing 99.99% aluminum oxide (A^O^) which is generally referred to as high purity alumina, but also those containing 80 - 90% A^Og or higher may be sufficiently applicable.

The aluminum oxide particles to be used according to the present invention have a spe-

specific BET surface area within the range 60 - 170 m 2 /g, more preferably 90 - 170 m 2 /g. If the specific BET surface area of the aluminum oxide particles is higher than 170 m 2 /g, the "in-room" discoloration of the recorded image will be undesirably noticeable.

According to what the inventors of the present invention know, the "in-room" discoloration of recorded images is due to oxidative splitting of the dye, and when the dye is captured on the surface layer of the recording medium, the dye will be correspondingly exposed to oxidation on contact with air. Especially when the dye is captured together with an element with a large specific surface area, the contact area with air is maximized, whereby a very strong "in-room" discoloration is caused.

According to the present invention

a pigment with a specific surface area 2 is therefore used

of 170 m /g or less.

In contrast, according to the state of the art, when such pigment as silicon dioxide or calcium carbonate used for ink jet recording paper with a specific surface area of 170 m 2 /g is used for the color receiving layer, the dye in the fixed color due to poor absorption ability for the pigment of the dye penetrate deep into the paper layer together with the solvent in the dye, whereby the dye's color-forming property and the image density become insufficient even if the problem of "in-room" decolorization can be solved.

This is the first reason why a pigment with a BET surface area of 170 m 2 /g or less has not been used according to the prior art for the coated paper as described above.

According to what the present inventors know, however, even a pigment with a specific BET surface area of 170 m 2 /g or less can provide a sufficient inhibitory effect against "in-room" discoloration and also excellent image density when aluminum oxide particles are used.

The reason why only aluminum oxide particles among various inorganic pigments can produce an image with excellent optical density as described above remains to be explained, but according to what the present inventors assume, this could be due to aluminum oxide particles having positive charges on their surface and can also easily absorb electrically acidic dyes and/or direct dyes and that the paper, when such aluminum oxide particles are used, can pick up more dye near the surface, namely on the surface layer of the dye-receiving layer, and also because the dyes and aluminum oxide particles are electrically bonded, why the dyes occurring near the surface layer is stabilized so that they are only split with difficulty, etc.

If, on the other hand, aluminum oxide particles that do not satisfy the requirement for a specific BET surface area of 60 m 2 /g or more are used, the density of the formed image becomes insufficient, and it is therefore desirable to use those that have a specific BET surface area of 60 m 2 /g or more .

According to what the present inventors know, "in-room" decolorization and improvement of the image density cannot be reconciled with each other when silicon dioxide is used as the pigment that forms the recording surface (surface layer), because the relationships between the specific surface area of the silicon dioxide and the image density and between the specific surface area and "in-room" discoloration are strong, whereby it has been difficult to improve the inhibition of "in-room" discoloration and improve the image density at the same time.

The tendency for these two properties to conflict with each other can thus be similar also when aluminum oxide particles are used instead of silicon dioxide, but when aluminum oxide particles are used, the increasing tendency for the image density in relation to the pigment's specific surface area is more marked than when silicon dioxide is used, and this offers the advantage that a desired image density can be achieved with particles with a lower specific surface area (170 m 2 /g or less) compared to the use of silicon dioxide. This is the reason why both prevention of "in-room" discoloration and improvement of the image density can be improved by means of the present invention.

The aluminum oxide particles to be used according to the present invention have an average particle size of 5 µm or less and more preferably 3 µm or . less, and even more preferably 1 nm or less.

When the aluminum oxide particles with the specific surface area as specified above are used, the density and "in-room" storability can thus be improved to a considerable extent, but still the image density and "in-room" storability have a compromise.

In other words, according to what the present inventors know, in order to achieve further excellent "in-room" storability while simultaneously maintaining high image density, it is preferred to use the above aluminum oxide particles with an average particle size of 5 µm or less, more preferably 3 µm or less and even more advantageously 1 µm or less.

An average particle size above 5 µm is insufficient to inhibit "in-room" discoloration. The average particle size mentioned here is the particle size in the state where the color-receiving layer is formed. In general, according to the present invention, particles that do not form secondary particles are preferred because the primary particle size for aluminum oxide particles is from 1 nm to 1 µm. In addition, with regard to the color absorbency, the average primary particle size of aluminum oxide particles should preferably be 0.5 µm or less. The particles which have sizes above 0.5 µm have insufficient color absorption capacity.

Moreover, according to what the present inventors know, the "in-room" storability improves as the particle size becomes smaller even though the correlation between the aluminum oxide particles' particle size and the image density is small.

This may be believed to be due to the fact that the apparent surface area of the recording surface is greater when a pigment with larger particle sizes is used during the formation of the recording surface, compared to when particles with smaller particles are laminated, whereby the absorbed dye is exposed to oxidation.

In the recording medium according to the state of the art, in order to improve the color absorption ability, secondary particles are formed, and a pigment with such a large particle size has been used. According to the present invention, there is no problem with regard to color absorption even when forming a surface layer with particles of sub-micrometer size without the formation of secondary particles due to the special structure of the color receiving layer, as described below.

The other specific feature of the present invention is that the recording medium according to the invention consists of a surface layer containing the above-mentioned aluminum oxide particles, and a lower layer with color absorption capacity.

The overlay as mentioned here is a layer that forms the recording surface and as such cannot absorb and retain the entire amount of color that has been attached, but it has the function of primarily absorbing the dye in the color and causing most of the color solvent to penetrate to migrate to the color absorbing lower layer.

For this reason, the recording medium according to the present invention includes the embodiment that it has a recording surface in which the pigment that forms the surface layer, and the fiber-containing material in the base paper is present in a mixture, and/or the embodiment that it has a recording surface that is covered with a surface layer with a maximum thickness of 20 µm, more preferably 15 µm or less.

The amount of the surface layer coated as mentioned here is within the range of 0.3 - 7 g/m 2 as the total amount of pigment. When the coated amount is less than 0.3 g/m 2 , no effect occurs compared to the case where no surface layer is provided, while if the coated amount is over 7 g/m 2 or the maximum thickness of the surface layer is over 20 µm, similarly as is the case with the above-mentioned recording medium (2), such problems as a noticeable decrease in color absorbency, decrease in hindrance of "in-room" decolorization, or formation of paper powder occur even if the above-mentioned aluminum oxide particles are used.

According to the present invention, a more preferred amount of the pigment is coated on the surface layer within

2 2

the range 1-7 g/m and more preferably 2-7 g/rri.

The maximum thickness of the surface layer, as mentioned here, refers to the maximum value in the longitudinal direction of the surface layer in the cross-section of the recording medium, and the amount of pigment for the coating is the amount of pigment that is coated in the form of the surface layer. The amount of applied pigment in the surface layer is determined in accordance with the method according to JIS-P-8128 and can be obtained as the value of the amount of ash in the entire recording medium from which the amount of ash in the backing paper has been removed.

According to the present invention, the surface layer is mainly formed from the above-mentioned aluminum oxide particles, but also inorganic pigments which are known according to the state of the art, such as silicon dioxide, aluminum silicate, magnesium silicate, calcium silicate, calcium carbonate, clay, kaolin, talc or diatomaceous earth etc., or organic pigments, such as urea resin etc, can be used mixed into the pigment in an amount within a range not exceeding 20% by weight.

The pigment for forming the surface layer, as described above, should preferably contain 80% by weight of aluminum oxide particles or more, and when aluminum oxide particles are contained in an amount below 80% by weight, the image density will be lower, and furthermore, the problem of "in-room " storability will not be avoided depending on the type of pigment used in combination.

As described above, for the recording medium according to the present invention, a recording medium which can satisfy the respective required properties can be obtained by providing a relatively very small amount of the surface layer because this is used in combination with a color absorbing lower layer as described below.

It appears from the above that the present invention is distinctive in its construction in relation to, for example, an example according to the state of the art which comprises a color-receiving layer in an amount as high as 15 g/m<2> using aluminum particles with a particle size of 30 µm on a polyethylene terephthalate film, as shown in example 2 in Japanese Laid-Out Patent Publication No. 58-110287, or in relation to an example comprising aluminum particles that have been internally filled in pulp fibers during sheet production,

as described in Japanese Patent Laid-Open Patent Publication No. 58-110288.

Specific examples of a preferred recording medium with a color-absorbing lower layer according to the present invention may include: (1) an embodiment where a surface layer is provided on a liquid-absorbing backing paper and where the backing paper also functions as the color-absorbing lower layer, and (2) the embodiment where a pigment layer with excellent color absorption capacity is provided on a base paper on which a surface layer is provided etc

Below, the respective embodiments will be described in detail.

The embodiment (1) is the most preferred embodiment according to the present invention with regard to the problems of "in-room" discoloration, paper powder etc., and stability in production or price.

The surface layer according to this embodiment consists of a pigment containing the above-mentioned aluminum oxide particles and a binder. Examples of the binder that can be used according to the present invention may include water-soluble polymers such as polyvinyl alcohol, starch, oxidized starch, cationized starch, casein, carboxymethylcellulose, gelatin, hydroxyethylcellulose or acrylic resin, etc., and aqueous dispersion type polymers such as SBR latex or polyvinyl acetate emulsion etc., which are known in the state of the art, which can be used alone or as a mixture of two or more of these types.

According to this embodiment, a preferred application ratio (weight ratio) between all pigments and the binder can be from 1:4 to 20:1, more preferably from 1:2 to 4:1. If the binder amount is over 1:4, the color absorption capacity exhibited by the coated layer is reduced, while if the binder amount is less than 20:1, the powder waste for the above-mentioned pigment from the coated layer will be undesirably high.

The base paper on which the above-mentioned surface layer is provided must be color absorbent with a preferred degree of bonding according to Stockigt within the range of 0 - 15 s, more preferably 0 - 10 s, and even more preferably 0 - 8 s. When a base paper with a degree of bonding according to until Stockigt of over 15 is used, the color absorption capacity of the recording medium as a whole becomes undesirably deficient.

The recording medium having the above-mentioned coated layer provided on the base paper should preferably have a Stockigt bonding degree within the range of 0 - 5 s, more preferably 0 - 10 s, and even more preferably 0 - 5 s. If it exceeds 15 s, most of the color absorption ability will be dependent on the coated layer within the above-mentioned area, whereby the color absorption ability will be deficient.

According to the present invention, the pulp that makes up the backing paper is not particularly limited, but this can mainly be composed of wood pulp as represented by LBKP or NPKP as known in the state of the art, but synthetic fibers or glass fibers can also be mixed in this if desired.

Specific examples of the fillers in the backing paper that can be used according to the present invention may include clay, talc, kaolinite, titanium oxide or calcium carbonate etc. generally used, and especially according to the present invention these fillers are contained in an amount of 1 - 20 g/m 2 , more preferably 2-10 g/m<2>, calculated ash content.

According to what the present inventors know, in particular the outlining and dot shapes of small color drops attached to the recording medium are strongly affected by the ash content of the backing paper of this paper type, and when the ash content is below 1 g/m 2 , the attached small color drops will be strongly attached outwards along the fiber direction on the backing paper surface, whereby the dot shapes will be poor and, moreover, the separation of the small color drops will be greater than necessary. If, on the other hand, the ash content is higher than 20 g/m 2 , the recording medium itself will lose firmness, and in addition to this, powder waste from the backing paper will find an unwanted place.

Among the above-mentioned fillers, calcium carbonate is also particularly preferred because the point shape and the color-forming properties are good.

The ash content of the backing paper according to the above embodiment (1) can be determined, for example, by removing the color-receiving layer from the recording medium using a good solvent for the binder and determining only the ash content of the backing paper in accordance with the method of JIS-P-8128 , expressed as the mass of ash content per area unit of the paper at this time. In ordinary paper for color jet, for example, polyvinyl alcohol is used as the binder, and in this case the applied layer is removed by dipping the recording medium into calm warm water, after which the ash content of the base paper can be determined.

The backing paper to be used for the above embodiment (1) can be produced using the above-mentioned materials, possibly together with sheet-forming aids, gluing agents, yield-increasing agents or paper strength-enhancing agents, etc. which are known within the state of the art, should this be desired.

In addition, a preferred basis weight for the base paper to be used for embodiment (1) can lie within the range 60 - 120 g/m 2. As the recording medium according to embodiment (1) absorbs color through the base paper, thus if the base paper's basis weight is less than 60 g/m , problems occur, such as the formation of folds or wrinkles etc, when high density printing is carried out. If the therein-2

against is higher than 120 g/m , the paper becomes too firm, whereby a problem arises with regard to the transportability of the registration device.

The recording medium according to the embodiment absorbs color only with the pigment layer and therefore has excellent color absorption ability and dot shape and is thus suitable for making high-resolution and high-quality images.

The special feature of the recording medium according to embodiment (2) is that the color-receiving layer comprises a layer structure of two or more layers and contains a color-retaining layer primarily formed of pigment with a larger particle size than the above-mentioned aluminum oxide particles.

The color-retaining layer is preferably formed mainly by a pigment with an (average) particle size of 5 - 30 µm, more preferably a silicon-type pigment, and furthermore preferably a synthetic silicon dioxide, and is arranged lower than the layer containing the aluminum oxide particles which make up the recording surface, as described above.

According to the above embodiment (2), images with further improved dot shape and without giving a rough feeling can be obtained without the occurrence of powder waste while also utilizing the advantage when a pigment with a larger particle size is used, by using a pigment with a larger particle size which the color-holding layer and where the small irregularities on the surface are filled with a pigment with smaller particle sizes of the layer that forms the recording surface.

The specific surface area for the pigment that forms the color-retaining layer should preferably be greater than for the pigment that primarily forms the surface layer, more preferably 200 m/g or higher, also with regard to the color absorption capacity. In addition, with regard to the color-forming property and the color absorption capacity, a structure is preferred where the color absorption rate for the surface layer is low to such an extent that small drops of color can be squeezed out with suitable sizes and where the color-holding layer's color absorption capacity is high. For this purpose, a ratio between pigment and binder in the surface layer may constitute the recording surface of preferably 1:3 - 5:1, more preferably 1:2 - 3:1, and even more preferably 1:1 - 10:1, as the collected by the color-receiving layer, is preferably used. Moreover, any of the binders known in the art can be used to form the color-retaining layer. Amount of the total color-receiving layer that has been applied can preferably lie within the range 2-50 g/m 2 , more preferably 8-30 g/m 2 , the applied amount of the color-retaining layer preferably being greater than that of the surface layer.

In order to improve the color absorption capacity of the recording medium according to embodiment (2), moreover, preferably porous silicon dioxide particles with spherical particle shapes, as described in Japanese Laid-Open Patent Publication No. 62-183382, can preferably be used as the pigment that forms the color-holding layer. In particular, when the above-mentioned spherical silicon dioxide having an average particle size of 5 - 30 µm is used for the color-retaining layer, a color-receiving layer with a higher void volume compared to that obtained by using amorphous pigment according to the prior art can be formed, whereby a recording medium with excellent color absorbency can be achieved.

When the recording medium according to the present invention is produced according to the respective embodiments as described above, a coating solution containing the components as described above is coated on the substrate surface in accordance with the method known in the art, such as by means of the roller coating method , the knife coating method, the air coating method,

the sluice roll coating method or the glue press method etc.

After an aqueous coating solution comprising eg pigment and a binder has been coated on the substrate, the coating can also be dried according to the method known in the state of the art, by for example using a hot air drying oven or heating drum etc., to obtain the recording medium according to the present invention.

In order to make the surface of the dye-receiving layer smooth or to increase the surface strength of the dye-receiving layer, a super-calender can also be used in the steps.

The recording medium according to the present invention prepared as described above has high image density, excellent color absorption capacity and yet excellent properties without in situ discoloration taking place.

In order to further improve the water resistance and light resistance of the recorded image, while maintaining the above-mentioned various recording characteristics, it is necessary to incorporate a polyaluminum oxide and/or a polyaluminum chloride into the pigment layer containing the aluminum oxide particles.

The polyaluminium hydroxide mentioned here is a compound which has two or more compounds represented by [Al(OH)2_2) in the molecule, including for example compounds represented by

[Al(OH) 3]nAlCl3 (n _> 2) ,

and the above compounds are commercially available under the trade name paho.#2S from Asada Kagaku Kogyo.

The polyaluminum chloride is a compound that has two or more compounds represented by [AlCl^^1 in the molecule, including, for example, compounds represented by the formula:

[Al2(OH)1Cl6_1]m(m > 1),

and the compounds are commercially available under the trade name PAC from Taki Kagaku Kogyo.

The recording medium according to the present invention should preferably contain these compounds in an amount within the range 0.01 - 5 g/m 2 . If the amount is less than 0.01 g/m 2 , the water resistance becomes insufficient, while if the amount is above 5 g/m 2 m 2 problems arise, such as a reduction in color absorption and image density.

According to the prior art, as the dye fixing agent available in color ray recording medium, those disclosed in Japanese Laid-Open Patent Publication Nos. 56-84992, 59-20696, 59-33176, 60-11389, 61-58788 and 61 -252189 etc, and all of these are of the amine type, but they cannot sufficiently satisfy both water resistance and light resistance even if they are improved.

The recording medium according to the present invention for which an aluminum type compound is used which is different from the amine type according to the state of the art, as the dye fixing agent, has the effect of improving the water fastness of the dye and also has no detrimental effect on the light fastness.

Although the polyaluminum compound can be used together with an amine-type dye fixing agent, as described above, mixed into it, furthermore, in this case, the amine-type water-resistant agent should preferably be 70% by weight or less, more preferably 25% by weight or less,

of the polyaluminum compound. If it is contained in an amount above 70% by weight, the bad effect due to the use of the amine-type agent which provides water resistance will manifest itself in the fact that it undesirably reduces the light resistance.

According to the present invention, the color-receiving layer can also contain fluorescent whitening agents, surface-active agents, defoamers, pH-regulating agents, anti-fungal agents, UV-absorbing agents or anti-oxidation agents, etc. if this should be necessary.

When the color ray recording system for the recording medium according to the present invention with the structure described above is used, for example in accordance with the registration method according to the present invention by means of which registration is carried out with a multi-coloured, aqueous color, such as yellow (Y) , magenta (M), cyan (C), black (Bk) etc, no discoloration takes place in situ on the image obtained, so that a registered image with excellent storability is obtained.

The method according to the present invention is a recording method for which the recording medium according to the present invention as described above is used, and the actual color obtained by means of the color ray recording method for the specific recording medium, as described above, by the recording method, may also be known. For example, its recording agent may be water-soluble dyes, as represented by direct dyes, acid dyes, basic dyes, reactive dyes or food dyes, etc. Preferred examples of dyes that are particularly suitable for the color used for the color ray recording system and that can provide images that satisfy the required properties in combination with the above-mentioned recording medium, such as color-forming properties, sharpness, stability or lightfastness among others, may include:

Direct dyes such as

Cl. Direct Black 17, 19, 32, 51, 71, 108, 146, CI. Direct Blue 6, 22, 25, 71, 86, 90, 106, 199,

CI. Direct Red 1, 4, 17, 28, 83,

CI. Direct Yellow 12, 24, 26, 86, 98, 142,

CI. Direct Orange 34, 39, 44, 46, 60,

CI. Direct Violet 47, 48,

CI. Direct Brown 109,

CI. Direct Green 59, etc.

Acidic dyes such as

CI. Acid Black 2, 7, 24, 26, 31, 52, 63, 112, 118, CI. Acid Blue 9, 22, 40, 59, 93, 102, 104, 113, 117, 120, 167, 229, 234, CI. Acid Red 1, 6, 32, 37, 51, 52, 80, 85, 87, 92, 94, 115, 180, 256, 317, 315, CI. Acid Yellow 11, 17, 23, 25, 29, 42, 61, 71,

CI. Acid Orange 7, 19,

CI. Acid Violet 49, etc.

and otherwise can

CI. Basic Black 2,

CI. Basic Blue 1, 3, 5, 7, 9, 24, 25, 26, 28, 29, CI. Basic Red 1, 2, 9, 12, 13, 14, 37,

CI. Basic Violet 7, 14, 27,

CI. Basic Black 1, 2, etc.

also used.

The above examples of dyes are particularly preferred for the color that can be used for the registration method according to the present invention, and the dyes for the color to be used according to the present invention are not limited to these dyes.

Such water-soluble dyes are generally used in the color according to the state of the art in an amount of 0.1 - 20% by weight of the color, and the same ratio can also be used according to the present invention.

The solvent to be used for the aqueous

color for use according to the present invention, is water or a solvent mixture of water with a water-soluble organic solvent, particularly preferably a solvent mixture of water and a water-soluble organic solvent. As the water-soluble organic solvent, one containing a polyhydric alcohol with anti-drying effect on the color is preferred. As water, it is preferred to use deionized water instead of water in its general form, which contains different ions.

The content of the water-soluble organic solvent in the color can generally lie within the range 0-95, preferably 2-80, and more preferably 5-50, wt%.

A preferred water content may be 20 - 98%, more preferably 50 - 90%, based on the total weight of the dye.

The color to be used according to the present invention can also, if desired, include surface-active agents, viscosity-regulating agents or surface tension-regulating agents etc. in addition to the above components.

Method of recording by adding the above color to the above recording medium in the method of the present invention is the ink jet recording method, and this method can be based on any system provided that it is a system capable of effectively removing the color from the nozzle and add the color to the recording medium which is the injection target.

In particular, the color jet system by means of which color can be discharged through the nozzle due to influencing force due to state changes due to the sudden volume change of the color that has received the influence of heat energy, according to the method described in Japanese Laid-Open Patent Publication No. 54- 59936, effectively applied.

The recording medium according to the present invention, as described above, is suitable as a recording medium for color ray recording, especially when using aqueous ink, and exhibits the following effects: (1) Because it is highly absorbent to aqueous ink, it obtains essentially the same condition which dried immediately after the supply of colour, and a part of the recording device, hands or fingers, when they come into contact with the medium, will not be contaminated, or the recorded image will not be contaminated. (2) When it is used for color ray registration, in addition to the above-mentioned effect (1), the point gets a high density with a shape that is approximately similar to a real sphere, without excessive slippage of the point or the occurrence of spring formation from the point, whereby a sharp high resolution image can be formed. (3) As it has excellent color characteristics, it is suitable for color printing. (4) There are small problems regarding image storability inherent in coated paper, and in the color ray recording method using the recording medium according to the present invention and a color with multiple colors, there is no problem of in situ discoloration that has occurred when the obtained image is stored on the wall or in the drawer in an office where indirect solar radiation has occurred for one to several months. (5) The recording medium according to the present invention is also excellent in terms of water resistance and light resistance for the recorded image at the same time that the recording medium exhibits the above-mentioned properties (1) - (4).

The present invention is described in more detail below with reference to examples and comparative examples, and in these, parts and percentages are based on weight if nothing else is indicated.

Examples 1 to 4

Using a substrate with a Stockigt bonding degree of 5 s, a basis weight of 66 g/m 2 and containing calcium carbonate in an amount of 9.0% (5.9 g/m 2 ), calculated on the ash content in accordance with JIS -P-8128, a coating solution having the composition shown below was applied by the stick application method until the amount applied as a coating with drying was 5 g/m 2 , and the coating was dried at 110°C for 3 minutes to obtain a recording medium according to the present invention.

The composition of the coating solution

The pigments used are listed below in Table 1.

Comparative example 1

A recording medium was prepared in the same manner as in Example 1, except that a paper for PPC was used as the base paper having a gluing degree according to Stockigt of 24 s and a basis weight of 66 g/m 2 (paper for Canon NP dry).

Examples 5 - 8 and comparison examples 2 and 3

Using a paper with a bonding degree according to Stockigt of 0 s, a basis weight of 65 g/m 2 and calcium carbonate in an amount of 2.4% (1.6 g/m 2 ), calculated on the ash content, as the base paper, a coating solution with the same composition as in example 1 applied by means of the rod coating method up to a coating quantity on drying of 7 g/m 2 , and dried at 110° C to obtain the registration medians according to the present invention and according to the comparative example.

As the pigments, the mixtures of alumina with other pigments as shown in Table 2 were used.

The color-ray recording adaptability of the above recording medium was judged by performing the color-ray recording with a color of the composition given below by means of a color-ray printing apparatus with color nozzle heads provided with 128 nozzles with a nozzle interval of 1 mm/16 nozzles, in accordance with the four colors Y, M, C and Bk. Color composition

Colorant

Y: CI. Direct Yellow 86

M: CI. Acid Red 35

C: CI. Direct Blue 199

Bk: CI. Food Black 2

Assessment was carried out for the items reproduced below. The results are shown in Table 3 below. (1) The dye absorptivity was judged by the dye jet printing apparatus as described above. Sharply printed image without color mixing! the print border between the printed letters printed with the respective colors Y, M, C and Bk was scored as 0, and one that was not so was scored as x. (2) For image density, the image density of a printed material (BK) of solid print by means of the same color jet printing apparatus was judged using a Macbeth RD-918 type reflection densitometer. (3) Room storability was measured by leaving the printed material used under (2) above (Bk) taped to the wall in an office for 6 months. The difference E<*>Aab between the color of the image immediately after printing (before delay) and the color of the image after delay was determined to judge the storability in space. (4) For paper powder when the color-receiving layer surface is scratched with a pencil with a hardness of H, a surface with a lot of formation of paper powder by tearing or cutting the coated layer is judged as x, while a good surface is judged as 0. ; Examples 9 - 11 and Comparative Six Examples 4 and 5 ;Using a fine quality ordinary paper (Ginkan, trade name, produced by Sanoyo Kokusaku Pulp) as the substrate, this was coated with a coating solution I, which is reproduced below, until a coating amount of drying 20 g/m 2 by the bar coating method and dried at 110°C for 5 minutes to form a color-holding layer, and on the color-holding layer a coating solution II, which is reproduced below, was coated to a coating amount by drying 7 g/m 2 by the bar coating method, followed by drying at 110°C for 3 minutes, to form a surface layer for the production of recording media according to the present invention and according to the comparative examples. ;Composition for coating solution I ; ; Composition for coating solution II; Example 9; Example 10 Example 11 Comparative example 4 Comparative example 5 ; Example 12: On the same base paper as in example 9, using a coating solution III as reproduced below, this was coated using the rod coating method up to a coating amount with drying of 20 g/m 2 , followed by drying at 110° C for 5 minutes , to form a color-retaining layer, and on the color-retaining layer with a coating solution IV given below, applied up to a coating amount on drying of 7 g/m^, followed by drying at 110°C for 3 minutes to form a surface layer, whereby a recording medium according to the present invention was obtained. ;Composition for coating solution III ; Composition for coating solution IV; Comparative Example 6 ; On the same base paper used in Example 10, a coating solution reproduced below was applied by the rod coating method to a coating amount of 15 g/m , followed by drying at 140° C. for 5 minutes to form a lower layer with low color absorption capacity. On the lower layer, coating was applied using the coating solution used in Example 10 in the same manner as in Example 10, followed by drying, to obtain a recording medium 6 for comparison. ;Composition for coating solution ; ; The evaluation of the respective recording media according to the above examples 9-12 and comparative examples 4-6 was carried out for the following items. The results are shown in Table 4 below. (1) The color absorption ability judged by the above color jet printing apparatus. The recorded image with very strong line clarity at the mixed color portion of colors compared to the single color portion and with the formation of color bleeding is judged as x, one without line clarity as 0 and one with weak line formation as A. In addition, one without line clarity even at the overlapped portion was of three colors judged to (2) Room storability is measured by printing a fixed pattern of Bk using the above printing apparatus and by leaving the printed product to stand for 6 months pasted on the wall in an office. The difference between the color of the image and the color of the image immediately after printing (AE<*>ab) is determined to judge the discoloration in space. (3) For the color characteristic, the color of the printed products by solid printing (YrMrC) using the above printing apparatus was measured using a high-speed color analyzer (manufactured by Murakami Shikisai Kagaku). (4) For the image density, the O.D. for the printed product at fixed printing (Bk) using the above-mentioned printing apparatus measured using the Macbeth densitometer RD-914.

Examples 13 - 16 and comparative examples 7 - 9

Except for the use of the coating compositions set forth below (Table 5), recording media were prepared in the same manner as in Example 1.

Composition for coating solution

When using the above-mentioned recording media, registration was assessed in the same way as in example 1. The results are shown in Table 6.

Water resistance and light resistance were assessed as described below.

Water resistance was judged by immersing the printed product according to (1) in running water (20°C) for 5 minutes, and the ratio of the image density of the M-printed part after immersion to the image density before immersion (residual O.D. ratio) was determined.

Light fastness was judged by irradiating the printed product according to (1) using Xenon Fade-Ometer (manufactured by Ci-35 Atlas Co.) under the conditions of a black plate temperature of 63°C and a humidity of 70% RH in 100 hours, and the ratio between the image density on the M-printed part after irradiation in relation to the image density before irradiation was determined.

Claims (11)

1. Recording medium comprising a surface layer which is mainly composed of aluminum oxide particles, characterized in that it also comprises a lower layer with ink absorption capacity, that the aluminum oxide particles have a BET surface area of 60-170 m<2>/g and an average particle size of 5 pm or less, and that the amount of the applied surface layer is in the range from 0.3 to 7 g/m<2>as the total amount of the pigment. 2. Recording medium according to claim 1, characterized in that the aluminum oxide particles have an average particle size of 1 pm or less. 3. Recording medium according to claim 1 or 2, characterized in that the aluminum oxide particles comprise 80% by weight or more of all pigments in the surface layer. 4. Recording medium according to any one of claims 1-3, characterized in that the lower layer is a paper with a gluing degree according to Stockigt in accordance with JIS-P-8122 of 0-15 s. 5. Recording medium according to any one of claims 1-4, characterized in that the lower layer is a base paper with fibrous material and that the aluminum oxide particles of the surface layer are in a mixture with the paper fiber-like material of the base paper. 6. Recording medium according to any one of claims 1-5, characterized in that it has a gluing degree according to StOckigt in accordance with JIS-P-8122 of 0-15 s. 7. Recording medium according to any one of claims 1-6, characterized in that the ink-receiving layer comprises an ink-holding layer formed mainly of a pigment which is provided between a base paper and the said surface layer which is mainly composed of aluminum oxide particles. 8. Recording medium according to any one of claims 1-7, characterized in that the surface layer, which is mainly composed of aluminum oxide particles, contains polyaluminium hydroxide and/or polyaluminium chloride. 9. Recording medium according to claim 8, characterized in that the polyaluminium hydroxide and/or the polyaluminium chloride is contained in an amount in the range 0.01-5 g/m<2>. 10. Ink jet recording method which is performed by applying small drops of an aqueous ink to a recording medium, characterized in that a recording medium according to any one of claims 1-9 is used as recording medium and that an ink containing an acidic dye and/or a direct dye is used. 11. Ink jet registration method according to claim 10, characterized in that small ink droplets formed by allowing heat energy to act on the ink are applied.