EP0854050B1

EP0854050B1 - Recording medium for printer

Info

Publication number: EP0854050B1
Application number: EP19970123044
Authority: EP
Inventors: Kengo Ito; Michiko Kusano; Tetsuo Kozumi
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1997-01-16
Filing date: 1997-12-31
Publication date: 2002-03-06
Anticipated expiration: 2017-12-31
Also published as: EP0854050A3; DE69710862D1; JPH10193779A; JP3750245B2; EP0854050A2

Description

BACKGROUND OF THE INVENTION

Field of the invention

This invention relates to a recording medium for a printer containing an interlayer compound for fixing and holding a water-soluble dye by an intercalation reaction which is based on the ion exchange action.

Description of the Related Art

Among systems for outputting on a recording medium the image information or the letter code information prepared by a personal computer or a word processor, there is an ink jet recording system of emitting an aqueous ink containing a water-soluble dye onto a recording medium for a printer for forming an image from a recording nozzle having an electrical field, heat or the pressure as a driving source.
This ink jet recording system recently has come into widespread use in offices or home because it is only low in noise during recording and in running cost is low and an image can be formed on an ordinary paper sheet while wastes such as used ink ribbons are not produced.
Meanwhile, the dye used in general in this ink jet recording system is held on the dye fixing layer, after it is transferred to the dye fixing layer, by the force of interaction with constituent components of the dye fixing layer, such as the Van del Waals force or hydrogen linkage. Thus, if the solvent, such as water, having stronger affinity to these dyes, is contacted with the image after image formation, the dye tends to be dissolved from the dye fixing layer to the solvent thus causing image blurring. If the heat energy or the water vapor sufficient to counteract the Van del Waals force or the hydrogen linkage between the water-soluble dye making up the image and the constituent elements of the dye fixing layer is supplied to the recording medium for the printer, the water-soluble dye tends to be moved to cause the image blurring. Moreover, if the water-soluble dye making up the image is exposed to light rays of a higher energy, such as ultraviolet light, the image tends to be faded or changed in color tone or or lowered in concentration due to decomposition of the dye itself.
For improving image fixation, such as water-proofness, in this ink jet recording system, it has been proposed to fix and hold the dye on the dye fixing layer by an intercalation reaction which is based on the ion exchange action. There is proposed in Japanese Laying-Open patent Application 7-69725 a dye fixing layer in which an interlayer compound having an ion exchange function is used as a mixture with hydrophilic binder resins, such as a polyvinyl pyrrolidone resin, a polyvinyl butyral resin, hydroxy propyl cellulose resin or polyvinyl alcohol resin.
Also, a proposal has been made of treating the interlayer compound with an organic acid for improving the ink fixation.
Moreover, attempts have been made for modifying the molecular structure of the dye for improving the light-fastness of the image.
However, the above-described systems are insufficient in effectuating dye fixation to the interlayer compound, such that the image perservability, especially light-fastness, remains insufficient, thus presenting difficulties in realising the fixation comparable to that realized with a silver halide photo.
Thus, difficulties are feared to be met in using an image formed on a recording medium by the conventional ink jet recording system in the fields of application in which high image durability is required, such as a certification photo or printed matter for outdoor display. However, even in these fields of application, it has been a desideratum to improve the image durability for realizing image formation by the ink jet recording system.
EP-A-0 732 218 discloses an ink-jet recording element comprising a polymeric film substrat or a resin coated paper substrate, wherein an ink-receiving layer comprising a synthetic clay is coated thereon. The provision of said synthetic clay results in a printed image with both an improved waterfastness and light-fastness.
EP-A-0 633 143 discloses a printing paper containing an intercalation compound that may fix water-soluble dyes to the paper due to the intercalation based on ion-exchanging between them.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to overcome the above-mentioned problems of the prior art and to provide a recording medium for a printer containing an interlayer compound for fixing and holding a water-soluble dye by an intercalation reaction which is based on the ion exchange action, in which the recording medium has superior ink fixation and water-proofness and in which an image formed thereon has improved light-fastness.
For accomplishing the above object, the present inventors have conducted perseverant researches and have found that, if an organic acid is newly added besides the organic acid used for improving the fixation between the interlayer compound and the aqueous ink, the image formed on the recording medium for the printer can be improved significantly in light-fastness.
The preset invention provides a recording medium for a printer containing an interlayer compound used for fixing and holding a water-soluble dye by an intercalation reaction which is based on the ion exchange action, wherein at least one organic acid is contained in an amount of 5 to 100 wt% related to the interlayer compound.
If the organic acid is contained in an amount of 5 to 100 wt%, related to the interlayer compound, not only the ink fixation properties and water-proofness can be improved in forming an image on a recording medium, but also the light-fastness of an image can be improved.
If the content of the organic acid is less than 5 wt%, the image is lowered in water-proofness and light-fastness. If the content of the organic acid exceeds 100 wt%, the proportion of the resin is correspondingly decreased, thus lowering adhesion and water-proofness to lead to lowered ink permeation and loss of luster as the recording medium thus detracting from the image quality.
The organic acid 5 preferably has 1 to 20 carbon atoms.
Preferably, the recording medium for a printer is made up at least of a substrate and a dye fixation layer formed of a binder resin and which is formed on a substrate. The interlayer compound is contained in the dye fixation layer in an amount of 10 to 90 wt% related to the solid content in the dye fixation layer.
If the content of the interlayer compound is less than 10 wt%, the dye fixing effect is lowered, whereas, if the content of the interlayer compound exceeds 90 wt%, the resin content in the solid content making up the dye fixation layer is relatively decreased to lower the flexibility.
As this interlayer compound, a layered inorganic high molecular material, formed of a mineral of the hydrotalcite group, is preferably employed.
Also preferably, the recording medium for a printer is made up of a substrate, a dye fixation layer formed of a binder resin and an ink absorbing layer formed of an ink-absorbing resin. The ink-absorbing resin is formed on the dye fixation layer, while the dye fixation layer is formed on the substrate. An organic acid is contained in the ink absorbing layer in an amount of 10 to 150 wt% related to the weight of the ink-absorbing resin.
If the content of the organic acid is less than 10 wt%, the image is lowered in water-proofness and light-fastness. If the content of the organic acid exceeds 150 wt%, the amount of the resin is correspondingly decreased, thus lowering adhesion and water-proofness to lead to lowered ink permeation and loss of luster as the recording medium thus detracting from the image quality.
In the structure of the recording medium for the printer, it may be a double-layered structure comprised of a substrate and a dye fixation layer of a binder resin formed thereon, or a three-layered structure additionally including an ink absorbing layer of an ink-absorbing resin formed on the dye fixation layer.
It suffices if the interlayer compound is contained in the dye fixation layer while the organic acid is contained in at least one of the dye fixation layer and the ink absorbing layer.
It is seen from above that, since a pre-set amount of the organic acid is contained in the recording medium for a printer according to the present invention, not only the ink fixation properties and water-proofness can be improved when forming an image on the recording medium, but also the image formed on the recording medium can be improved significantly in light-fastness.
That is, the recording medium for a printer according to the present invention has durability comparable to a silver halide photo, such that it can be satisfactorily used as a certification photo or as printed matter for outdoor display purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view showing a structure of a recording medium for a printer embodying the present invention.
Fig.2 is a schematic view showing another structure of a recording medium for a printer embodying the present invention.
Fig.3 is a schematic view showing still another structure of a recording medium for a printer embodying the present invention.
Fig.4 is a schematic view showing yet another structure of a recording medium for a printer embodying the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, preferred embodiments of recording medium for a printer according to the present invention will be explained in detail.
The recording medium for a printer, according to the present invention, contains an interlayer compound for fixing and holding the water-soluble dye by an intercalation reaction based on the ion exchange action and also contains at least one organic acid in an amount of 5 to 100 wt% related to the weight of the interlayer compound.
The organic acid, thus added to the recording medium for a printer, improves the fixation between the interlayer compound and the aqueous ink. Moreover, if added in a pre-set amount to an ink absorbing layer and a dye fixation layer, the organic acid accords superior ink filtration characteristics and water-proofness, while improving the light-fastness of the image formed on the recording medium for the printer.
If the amount of the organic acid is less than 5 wt%, the image is lowered in water-proofness and light-fastness. If the amount of the organic acid exceeds 100 wt%, adhesion to a substrate and to other layers is lowered to deteriorate water-proofness, while the permeation characteristics of the aqueous ink is lowered and the recording medium becomes delustered to detract from the picture quality.
The recording medium for the printer according to the present invention is composed at least of a substrate and a dye fixation layer of a binder resin formed on the substrate. That is, the recording medium for the printer may be of a double layer structure composed of a substrate and the dye fixation layer formed of the binder resin and which is formed on the substrate. Alternatively, the recording medium for the printer may be of a three-layered structure further including an ink absorption layer on the dye fixation layer.
In the latter case, the interlayer compound is contained in the dye fixation layer, whilst the organic layer is contained in at least one of the dye fixation layer and the ink absorption layer.
Specifically, a first embodiment of the recording medium for a printer is of a double-layer structure, made up of a substrate 1 and a dye fixation layer 2, formed in this order, as shown in Fig. 1. An interlayer compound 4 and at least one organic acid 5 are contained in the dye fixation layer 2.
A second embodiment of the recording medium for a printer is of a three-layer structure composed of a substrate 1, a dye fixation layer 2 and an ink absorbing layer 3, formed in this order, and an interlayer compound 4 and at least one organic acid 5 are contained in the dye fixation layer 2, as shown in Fig.2. The ink absorbing layer 3 absorbs water or alcohols, used as solvents for the aqueous ink used, to improve permeation characteristics of the aqueous ink.
Similarly to the second embodiment, a third embodiment of the recording medium for a printer is of a three-layer structure and contains the interlayer compound 4 in the dye fixation layer 2, while containing at least one organic acid 5 in the ink absorbing layer 3.
Similarly to the second embodiment, a fourth embodiment of the recording medium for a printer is of a three-layer structure, and contains an interlayer compound 4 and at least one organic acid 5 in the dye fixation layer 2, while containing at least one organic acid 5 in the ink absorbing layer 3.
In any of the above-described embodiments of the recording medium for a printer, the desired meritorious effect may be achieved. The ink absorbing layer 3, however, is preferably provided for improving ink absorption properties.
The recording medium for the printer according to the present invention is characterized in that 5 to 100 wt% of the organic acid 5 is contained in the interlayer compound 4. If, however, the organic acid 5 is contained in the ink absorbing layer 3, as in the third and fourth embodiments, it is more preferred that the amount of the organic acid 5 in the ink absorbing layer 3 be 10 to 150 wt% based on the weight of the ink absorbing resin.
If the amount of the organic acid 5 is less than 10 wt%, the image is lowered in water-proofness and light-fastness. If the amount of the organic acid 5 exceeds 150 wt%, the proportion of the resin is proportionately lowered, thus leading to the lowering of adhesion, water-proofness and ink infiltration and to a loss of luster as a recording medium to detract from the image quality.
The organic acids may be enumerated by carboxylic acid, sulfonic acid, sulfinic acids, enol, imide, oxime and aromatic sulfonamide. The number of these organic acids is preferably 1 to 20. These organic acids may be used alone or in combination.
The dye fixation layer preferably contains the interlayer compound in an amount of 10 to 90 wt% related to the solid content in the dye fixation layer.
If the amount of the interlayer compound is less than 5 wt%, the dye fixation effect is lowered. Conversely, if the amount of the interlayer compound exceeds 90 wt%, the content of the resin in the solid content making up the dye fixation layer is relatively lowered to deteriorate the flexibility.
For this interlayer compound, it is preferred to use a layered inorganic high molecular material having excellent water absorption or water swelling properties and exhibiting an anion exchange capability. For example, a mineral of the hydrotalcite group having exchange anions is preferably employed. In particular, natural minerals of the hydrotalcite group having the composition of Mg_0.7Al_0.3O_1.15 is preferred. Alternatively, synthesized products having a slightly different composition may also be used.
Like natural products, fine powders of the synthesized product are free of foreign matter, and present a pure white color, with crystals per se being optically transparent. Thus, if the fine powders of the synthesized product are contained in the dye fixation layer as the interlayer compound, an image can be formed which has a color saturation comparable to that of silver halide photos. Alternatively, such a mineral corresponding to the mineral of the hydrotalcite group having, in its ion exchange site, inorganic ions, such as NO₃ ^-, SO₄ ^2-, CLO₄ ^-, Fe(CN)₆ ^-4, ions of heteropolyphosphric acid, or lower carboxylate ions having hydrophilic organic anions, capable of undergoing solvation with a high dielectric constant medium, such as water or alcohol, may be used. In contradistinction from the above ions, higher carboxylate ions tend to give an interlayer which hardly undergoes solvation and hence are not desirable.
For improving dispersibility to binder resins as later explained or improving swelling properties with respect to non-aqueous solvents, such as alcohols, such an interlayer compound having a portion of exchange anions replaced by organic anions for widening the interlayer separation (pillar effect) or partially hyrophobilizing the interlayer may be used. Preferred organic anions may be enumerated by carboxylic acid anions, sulfonic acid anions, ester anions or phosphoric acid ester anions.
The dye fixation layer making up the recording medium for the printer contains a binder resin in addition to the above-mentioned interlayer compounds. As the binder resin, hydrophilic resins having the operation of increasing the dispersibility of the interlayer compound in the dye fixation layer and for permeating the solvent for the aqueous ink, such as water or alcohol, may be used.
As the binder resin, any ordinary thermoplastic resins may be used. These thermoplastic resins may be exemplified by acetalized vinyl alcohols, such as polyvinyl butyral resins, cellulose-based resins, such as hydroxy propyl cellulose resins, polyvinyl pyrrolidone based resins, such as pyrrolidone-vinyl acetate copolymers, polyvinyl alcohol resins and polyvinyl acetal resins. These binder resins may be used alone or in combination. Those binder resins having substituents instigating flocculation in the binder resins or inhibiting image fixation, such as groups more liable to be ion-exchanged and held than the water-soluble dyes, are not preferred.
The layer thickness of the dye fixation layer is usually 2 to 40 µm and preferably 4 to 15 µm.
As the ink absorbing layer, formed on the above-mentioned dye fixation layer, hydrophilic resins, permeated through by solvents for the aqueous ink used in the recording method of the present invention, such as water or alcohol, are used.
As the ink absorbing resins, hydroxy propyl cellulose based resins, polyamide resins, polyvinyl pyrrolidone based resins, polyvinyl alcohol based resins or polyvinyl butyral based resins, may be used. These ink absorbing resins may be used alone or in combination.
The layer thickness of the ink absorbing layer is usually 1 to 5 µm and preferably 0.5 to 1.5 µm. If the layer thickness of the ink absorbing layer is not more than 0.1 µm, absorption of the aqueous ink falls short, whereas, if the layer thickness is above 5 µm, the aqueous ink is absorbed by the ink absorbing layer to lower the permeating properties of the ink in the interlayer compound used for accepting and holding the dye.

EXAMPLES

The present invention will be hereinafter explained with reference to Examples based on experimental results. These Examples are merely illustrative and are not intended fro limiting the invention.

Experiment 1

In the experiment 1, a recording medium for a printer, comprised of an interlayer compound 4 and an organic acid 5 contained in a dye fixation layer 2 provided on a substrate 1, was readied, as shown in Fig.2, while an ink containing a direct dye and an acidic dye as the water-soluble dye, was readied. Using these, an image recorded on a recording medium for a printer was checked as to durability.

Sample 1

First, as a binder resin, 4 g of a polyvinyl alcohol resin (manufactured by NIPPON GOSEI KAGAKU under a trade name of KH-20, were added to and dissolved in a mixed solvent of 14 g of ethyl alcohol and 64 g of water. To this solution was added hydrotalcite treated with an organic acid (4 g of hydrotalcite manufactured by KYOWA KAGAKU under the trade name of KW2200 to which was adsorbed 2.5 g equivalent of malic acid), as an interlayer compound 4, and the resulting mass was subjected to dispersion processing for eight hours in a sand mill to produce a liquid dispersion designed for forming the dye fixation layer. Then, 0.8 g of phthalic acid as the organic acid 5 was dissolved in this liquid dispersion adapted for forming the dye fixation layer.
The liquid dispersion adapted for forming the dye fixation layer, thus produced, was coated on a transparent polyester film substrate 125 µm in thickness (manufactured by TORAY under the trade name of 'Lumilar-T-60) to a dry thickness of 4 µm. The resulting product was dried under a condition of 100°C and one minute for completing the dye fixation layer 2.
Then, 1.6 g of hydroxy propyl cellulose (manufactured by NIPPON SODA under the trade name of HPC-L) were dissolved in 90 g of ethyl alcohol to produce a solution designed for forming an ink absorbing layer. This solution for forming an ink absorbing layer was coated by a wire bar to a dry thickness of 1 µm on the dye fixation layer 2 and dried to form the ink absorbing layer 3. This completed a recording medium for a printer (sample 1).

Samples 2 to 6

A liquid dispersion for the dye fixation layer was prepared using p-toluene sulfonic acid, benzene sulfinic acid, ethyl acetoacetate, phthalimide and benzaldoxim in place of phthalic acid. Five samples (samples 2 to 6) were fabricated in otherwise the same way as in sample 1.

Sample 7

A recording medium for a printer (sample 7) was prepared in the same way as in sample 1, except that the liquid dispersion for forming the dye fixation layer 2 was prepared using a mixed organic acid of phthalic acid/malic acid = 2:1.

Sample 8

A recording medium for a printer (sample 8) was prepared in the same way as in sample 1, except that the amount of addition of dissolved phthalic acid was changed to 0.24 g for preparing the liquid dispersion designed for forming the dye fixation layer 2.

Sample 9

A recording medium for a printer (sample 9) was prepared in the same way as in sample 1, except that phthalic acid was removed from the liquid dispersion adapted for forming the dye fixation layer employed in the sample.

Sample 10

A recording medium for a printer (sample 10) was prepared in the same way as in sample 1, except that the amount of addition of dissolved phthalic acid was changed to 4.4 g, for preparing the liquid dispersion for forming the dye fixation layer 2.

Evaluation of Experiment 1

Printing samples were recorded on the recording mediums for the printer of the samples 1 to 10 prepared as described above, using an ink jet printer manufactured by SEIKO EPSON under the trade name of MJ-800C for forming an image. The luster, water-proofness, ink fixation and light-fastness of the recording mediums for the printer were checked as now explained.

(1) Test for Luster

The luster of the substrate after formation of the dye fixation layer 2 was measured by a gloss-meter manufactured by NIPPON DENSYOKU KOGYO KK under the trade name of VG-1D, under the condition of an incidence reflection angle of 45°, using a transparent polyester substrate prior to formation of the dye fixation layer 2 as a reference. The results are shown in Table 1.

(2) Test for Water-Proofness

After immersing the recording medium for the printer, having the image formed thereon, in water in its entirety for ten minutes, the recording medium was hoisted from the water, and changes n the dye fixation layer 2 were observed visually and evaluated in accordance with the following standard. The results are also shown in Fig.1.
○: no changes seen in the dye fixation layer
×: the dye fixation layer was peeled from the substrate or dissolved such that the product could not be used as the recording medium for a printer

(3) Test on Ink Absorptivity

During image formation, it was checked visually whether the ink was permeated into and absorbed by the dye fixation layer 2 and the state of ink permeation and absorption was evaluated in accordance with the following standards. The results are shown in Table 1.
○: the ink was permeated into and absorbed by the dye fixation layer
×: the ink was not permeated into nor absorbed by the dye fixation layer (4) Test on Ink Fixation
During the test on water-proofness, changes in the image were checked visually and evaluated in accordance with the following standards. The results are shown in Table 1.
○: no changes ae caused in an image
▵: the image suffers from bleeding but is practically not inconvenient
× : the image suffers from significant flowing or bleeding

(5) Test on light-fastness

For each image formed in each sample, *L, *a and *b, provided in JIS Z8105, were measured by a spectrometer manufactured by GRTAG under the trade name of SPM100-11.
Next, each sample carrying the above image was irradiated with an energy of 90 kJ/m² by WEATHER-OMETER manufactured by ATLAS for 72 hours for measuring *L, *a and *b of the image of each sample irradiated with the energy.
After irradiation with the energy, the color difference ▵E in each sample was found in accordance with the following equation (1): color difference ▵E = [(▵*L)2 + (▵*a)2 +(▵*b)2]½ where ▵*L, ▵*a and ▵*b stand for differences of *L, *a and *b before and after test, respectively and
○: ▵E ≤ 5
▵: 5 < ▵E ≤ 5

×: ▵E > 15.

	luster	water-proofness	ink absorption	ink fixation	light-fastness
sample
1	92	○	○	○	○
sample 2	89	○	○	○	○
sample 3	90	○	○	○	○
sample 4	92	○	○	○	○
sample 5	91	○	○	○	○
sample 6	88	○	○	○	○
sample 7	90	○	○	○	○
sample 8	92	○	○	○	○
sample 9	90	×	○	▵	▵
sample 10	53	×	×	×	▵

It is seen from the results of Table 1 that the recording mediums for a printer of samples 1 to 8, containing one or more organic acids in the dye fixation layer containing in turn the interlayer compound 4 are significantly superior in water-proofness, ink fixation and light-fastness to the recording medium for a printer of the sample 9 not containing the organic acid 5. However, it is not desirable that the dye fixation layer contain the organic acid in an amount exceeding 100 wt% based on the weight of the interlayer compound, as in the sample 10, because then the properties as the recording medium for the printer are deteriorated.
It is seen from the above results that, if a pre-set amount of the organic acid is contained in the dye fixation layer 2, not only the ink fixation and water-proofness, but also the light-fastness of an image is improved.

Experiment 2

In the experiment 2, a recording medium for a printer, containing an interlayer compound 4 in a dye fixation layer 2 on a substrate 1 and also containing an organic acid 5 in an ink absorbing layer 3 was readied, while an ink containing a direct dye and an acidic dye as the water-soluble dye was readied. Using these, an image recorded on the recording medium for the printer was checked.

Sample 11

First, as a binder resin, 4 g of a polyvinyl alcohol resin (manufactured by NIPPON GOSEI KAGAKU under a trade name of KH-20, were added to and dissolved in a mixed solvent of 14 g of ethyl alcohol and 64 g of water. To this solution was added hydrotalcite treated with an organic acid (4 g of hydrotalcite manufactured by KYOWA KAGAKU under the trade name of KW2200 to which was adsorbed 2.5 g equivalent of malic acid), as an interlayer compound 4, and the resulting mass was subjected to dispersion processing for eight hours in a sand mill to produce a liquid dispersion adapted for forming the dye fixation layer.
The liquid dispersion adapted for forming the dye fixation layer, thus produced, was coated on a transparent polyester film substrate 125 µm in thickness (manufactured by TORAY under the trade name of 'Lumilar-T-60) to a dry thickness of 4 µm. The resulting product was dried under a condition of 100°C and one minute for completing the dye fixation layer 2.
Then, 1.6 g of hydroxy propyl cellulose (manufactured by NIPPON SODA under the trade name of HPC-L) and 0.96 g of phthalic acid as the organic acid 5 were dissolved in 90 g of ethyl alcohol to produce a solution for forming an ink absorbing layer. This solution for forming an ink absorbing layer was coated by a wire bar to a dry thickness of 1 µm on the dye fixation layer 2 and dried to form the ink absorbing layer 3. This completed a recording medium for a printer (sample 11).

Samples 12 to 16

A solution for the ink absorbing layer 3 was prepared using p-toluene sulfonic acid, benzene sulfinic acid, ethyl acetoacetate, phthalimide and benzaldoxim in place of phthalic acid. Five samples (samples 12 to 16) were fabricated in otherwise the same way as in sample 1.

Sample 17

A recording medium for a printer (sample 17) was prepared in the same way as in sample 11, except that the liquid dispersion for forming the dye fixation layer 2 was prepared using a mixed organic acid of phthalic acid/malic acid = 2:1.

Sample 18

A recording medium for a printer (sample 18) was prepared in the same way as in sample 11, except that the amount of addition of dissolved phthalic acid was changed to 0.24 g for preparing the solution for forming the ink absorbing layer.

Sample 19

A recording medium for a printer (sample 19) was prepared in the same way as in sample 11, except that phthalic acid was removed from the solution for forming the dye fixation layer employed in the sample 11.

Sample 20

A recording medium for a printer (sample 20) was prepared in the same way as in sample 11, except that the amount of addition of dissolved phthalic acid was changed to 3.2 g for preparing the liquid dispersion for forming the dye fixation layer.
Evaluation of Experiment 2 Printing samples were recorded on the recording mediums for the printer of the samples 11 to 20 prepared as described above, using an ink jet printer for forming images. The luster, water-proofness, ink fixation and light-fastness of the recording mediums for the printer were checked, as in experiment 1. The results are shown in Table 2.

	luster	water-proofness	ink absorption	ink fixation	light-fastness
sample 11	92	○	○	○	○
sample 12	90	○	○	○	○
sample 13	89	○	○	○	○
sample 14	90	○	○	○	○
sample 15	92	○	○	○	○
sample 16	91	○	○	○	○
sample 17	92	○	○	○	○
sample 18	90	○	○	○	○
sample 19	90	×	○	▵	▵
sample 20	54	×	×	×	▵

It is seen from the results of Table 2 that the recording mediums for a printer of samples 11 to 18, containing one or more organic acids in the ink absorbing layer 3, are significantly superior in water-proofness, ink fixation and light-fastness to the recording medium for a printer of the sample 19 not containing the organic acid 5. However, it is not desirable that the dye fixation layer contain the organic acid in an amount exceeding 100 wt% based on the weight of the interlayer compound, as in the sample 20, because then the properties as the recording medium for the printer are deteriorated.
It is seen from the above results that, if a pre-set amount of the organic acid is contained in the ink absorbing layer 3, not only the ink fixation and water-proofness, but also the light-fastness of an image is improved.

Experiment 3

In the experiment 3, a recording medium for a printer, containing an interlayer compound 4 and an organic acid 5 in a dye fixation layer 2 on a substrate 1 and also containing an organic acid 5 in an ink absorbing layer 3, was readied, while an ink containing a direct dye and an acidic dye as the water-soluble dye was also readied. Using these, an image recorded on the recording medium for the printer was checked.

Sample 21

In preparing a liquid dispersion for a dye fixation layer, 0.8 g of phthalic acid was dissolved, whereas, for preparing a solution for forming an ink absorbing layer, 0.96 g of phthalic acid was dissolved. Using these, a recording medium for a printer (sample 21) was prepared.

Sample 22

In preparing a liquid dispersion for a dye fixation layer, 0.24 g of phthalic acid was dissolved, whereas, for preparing a solution for forming an ink absorbing layer, 0.16 g of phthalic acid was dissolved. Using these, a recording medium for a printer (sample 22) was prepared in otherwise the same way as in sample 21.

Sample 23

In preparing a liquid dispersion for a dye fixation layer and a solution for forming an ink absorbing layer, phthalic acid was not added. A recording medium for a printer (sample 23) was prepared in otherwise the same way as in sample 21.

Sample 24

In preparing a liquid dispersion for a dye fixation layer, 4.4 g of phthalic acid was dissolved, whereas, for preparing a solution for forming an ink absorbing layer, 3.2 g of phthalic acid was dissolved. A recording medium for a printer (sample 24) was prepared in otherwise the same way as in sample 21.

Evaluation of Experiment 3

Printing samples were recorded on the recording mediums for the printer of the samples 21 to 24 prepared as described above, using an ink jet printer for forming images. The luster, water-proofness, ink absorption, ink fixation and light-fastness of the recording mediums for the printer were evaluated as in experiment 1. The results are shown in Table 3.

luster water-proofness ink absorption ink fixation light fastness

sample 21 93 ○ ○ ○ ○

sample 22 90 ○ ○ ○ ○

sample 23 91 × ○ ▵ ▵

sample 24 48 × × × ▵
It is seen from the results of Table 3 that the recording mediums for a printer of samples 21 and 22, containing one or more organic acids in the dye fixation layer 2 and the ink absorbing layer 3, are significantly superior in water-proofness, ink fixation and light-fastness to the recording medium for a printer of the sample 23 not containing the organic acid 5. However, it is not desirable that the dye fixation layer 2 and the ink absorbing layer 3 contain the organic acid in an excess amount, as in the sample 24, because then the properties as the recording medium for the printer are deteriorated.
It is seen from the above results that, if a pre-set amount of the organic acid is contained in the dye fixation layer 2 and in the ink absorbing layer 3, not only the ink fixation and water-proofness, but also the light-fastness of an image formed on a recording medium is improved.
It may be seen from the results of experiments 1 to 3 that, by containing one or more organic acids in at least one of the dye fixation layer and the ink absorbing layer, water-proofness and fixation of the recording medium and the light-fastness of the image formed thereon may be improved significantly. However, if the content of the organic acid is excessive, the proportion of the resin is correspondingly reduced, thus significantly deteriorating the properties of the recording medium for the printer.

Claims

A recording medium for a printer containing an interlayer compound (4) used for fixing and holding a water-soluble dye by an intercalation reaction which is based on the ion exchange action, wherein the improvement resides in that
at least one organic acid (5) is contained in an amount of 5 to 100 wt% related to the interlayer compound (4).
The recording medium for a printer as claimed in claim 1 wherein said organic acid (5) has 1 to 20 carbon atoms.
The recording medium for a printer as claimed in claim 1 wherein said recording medium for a printer is made up at least of a substrate (1) and a dye fixation layer (2) formed of a binder resin, said dye fixation layer (2) being formed on said substrate (1);
said interlayer compound (4) being contained in the dye fixation layer (2) in an amount of 10 to 90 wt% related to the solid amount in the dye fixation layer (2).
The recording medium for a printer as claimed in claim 1 wherein said interlayer compound (4) is an layered inorganic high molecular material formed of a mineral of the hydrotalcite group.
The recording medium for a printer as claimed in claim 1 wherein said recording medium for a printer is made up of a substrate (1), a dye fixation layer (2) formed of a binder resin and an ink absorbing layer (3) formed of an ink-absorbing resin, said an ink-absorbing resin being formed on the dye fixation layer (2), said dye fixation layer (2) being formed on a substrate (1); and wherein
an organic acid (5) is contained in the ink absorbing layer (3) in an amount of 10 to 150 wt% related to the weight of the ink-absorbing resin.
The recording medium for a printer as claimed in claim 1 wherein said recording medium for a printer is made up of a substrate (1) and a dye fixation layer (2) formed of a binder resin, said dye fixation layer (2) being formed on said substrate (1); and wherein
an interlayer compound (4) and at least one organic acid (5) are contained in said dye fixation layer (2).
The recording medium for a printer as claimed in claim 1 wherein said recording medium for a printer is made up of a substrate (1), a dye fixation layer (2) formed of a binder resin and an ink absorbing layer (3) formed of an ink-absorbing resin, said an ink-absorbing resin being formed on the dye fixation layer (2), said dye fixation layer (2) being formed on said substrate (1); and wherein
an interlayer compound (4) and at least one organic acid (5) are contained in said dye fixation layer (2).
The recording medium for a printer as claimed in claim 1 wherein said recording medium for a printer is made up of a substrate (1), a dye fixation layer (2) formed of a binder resin and an ink absorbing layer (3) formed of an ink-absorbing resin, said an ink-absorbing resin being formed on the dye fixation layer (2), said dye fixation layer (2) being formed on said substrate (1); wherein
an interlayer compound (4) is contained in said fixation layer (2); and wherein
at least one organic acid (5) is contained in said ink absorbing layer (3).
The recording medium for a printer as claimed in claim 1 wherein said recording medium for a printer is made up of a substrate (1), a dye fixation layer (2) formed of a binder resin and an ink absorbing layer (3) formed of an ink-absorbing resin, said an ink-absorbing resin being formed on the dye fixation layer (2), said dye fixation layer (2) being formed on said substrate (1); wherein
an interlayer compound (4) and at least one organic acid (5) are contained in said dye fixation layer (2); and wherein
at least one organic acid (5) is contained in said ink absorbing layer (3).