JPH08150774A - Sheet for recording and its preparation - Google Patents

Abstract

PURPOSE: To provide a sheet for recording with excellent transparency of an ink receiving layer, drying properties of an ink and image qualities, improved initial absorbing speed and adhesiveness of the ink and remarkably improved resistance to blocking and disturbance of the image caused by release of the ink. CONSTITUTION: A substrate sheet 2 and an ink receiving layer 3 provided at least on one face of the substrate sheet 2 are provided and the ink receiving layer 3 is formed by dispersing water-absorptive polymer fine particles with a particle diameter of 0.3μm or smaller the surfaces of which are coated with inorg. ultrafine particles in a hydrophobic matrix polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording sheet,
In particular, the present invention relates to a recording sheet having an ink receiving layer that enables good recording by an ink jet printer using a water-soluble ink.

[0002]

2. Description of the Related Art Conventionally, a wire dot recording system, as an output print of a computer or a word processor,
Various systems such as a thermal color recording system, a thermal melt transfer recording system, a thermal sublimation transfer recording system, an electrophotographic recording system and an inkjet recording system have been developed. Among them, the ink jet recording method is characterized in that plain paper can be used as a recording sheet, printing cost is low, the apparatus is compact, and high speed recording is possible without noise. Therefore, attention has been paid to its use as a printer that outputs image information such as characters and figures created by a computer or the like quickly and accurately. Also, since it is easy to colorize and the picture is clear, the image information created by the computer can be printed by the inkjet printer.
To record on a transparent recording sheet with OHP (Oh
There is also an increasing demand for using it as a manuscript (bar head projector) or the like at conferences, presentations at various academic conferences, and the like.

In general, an ink jet printer ejects recording ink from a nozzle by a pressure of a fine piezoelectric element (piezo element) or an air pressure (bubble jet) generated by heating of a thermal head for recording. Recording is performed by attaching to the sheet. For this reason, as a recording ink used for inkjet recording, an ink that is difficult to dry is used in order to prevent defective ejection of ink from the nozzle due to an increase in viscosity due to drying of the ink. Generally, the ink component is generally a dye, resin, additive, etc. dissolved in water and alcohol.

Therefore, the recording sheet for recording with the ink jet printer is required to absorb the moisture of the adhered ink and dry and solidify the ink. For this reason, a recording sheet is used in which an ink receiving layer is formed on a resin film to enhance ink absorption.

In particular, the following characteristics are required for the ink receiving layer of a recording sheet for an ink jet printer.

Excellent ink absorbency, no bleeding, that is, good ink dryness, excellent image clarity, excellent scratch resistance, that is, even if the recording surface is rubbed easily The sheet and the image are water resistant, and the image will not bleed or run off even if water adheres.

From this point of view, the conventional recording sheet has an ink receiving layer on a base sheet and uses a water-soluble polymer as the receiving layer, and is filled with silica or the like. It has been proposed to add a demulcent or to use a water-absorbent gel dispersed in a water-insoluble polymer binder.

[0008]

However, the ink-receiving layer formed by coating the water-soluble polymer shows tackiness after absorbing the ink, and when overlaid immediately after recording,
Ink drying is insufficient, and blocking and image disorder often occur, and it cannot be said that the ink composition has sufficient performance.

When a charging agent such as silica is added, the ink absorbency is improved and the drying property is improved, but the ink adsorption force becomes too strong, so that a suitable dot spread can be obtained. As a result, the drawing line becomes a thin line, which causes a problem that the required image cannot be obtained.

Further, Japanese Patent Application Laid-Open No. 58-112284 proposes a recording sheet using a highly absorbent resin such as an ionic water-absorbent gel in the ink receiving layer, which satisfies both the ink absorbability and the image quality. ing.

However, the super-absorbent resin used in this product generally has a huge particle size of several tens of μm to several hundreds of μm, and when it is used for an OHP sheet, for example, a sufficient light absorption is obtained. There is a problem that transparency cannot be obtained.

The present invention was devised under such circumstances, and its purpose is to provide transparency of the ink receiving layer,
A recording sheet having excellent drying property and image quality of the ink, improved initial absorption speed and tackiness of the ink, and significantly improved blocking and image disturbance due to ink release, and a recording sheet of such a recording sheet. It is to provide a manufacturing method.

[0013]

In order to achieve such an object, a recording sheet of the present invention comprises a base sheet and an ink receiving layer provided on at least one surface of the base sheet. The ink receiving layer is configured such that the water-absorbent polymer fine particles having a particle diameter of 0.3 μm or less, the surface of which is coated with inorganic ultrafine particles, are dispersed in the hydrophobic matrix polymer.

Further, the present invention is a method for producing a recording sheet comprising a base sheet and an ink receiving layer provided on at least one surface of the base sheet, wherein the ink receiving layer is a hydrophobic layer. In a water-soluble matrix polymer, it is formed by applying a coating solution in which water-absorbing polymer particles having their surfaces coated with inorganic ultrafine particles are dispersed on a substrate sheet, wherein the water-absorbing polymer particles are Formed by polymerizing a polymerizable monomer dissolved in a solution containing a hydrophobic matrix polymer, the inorganic ultrafine particles are coated on the water-absorbing polymer particles in the process of polymerizing the polymerizable monomer. It is configured to be performed by adding the inorganic ultrafine particles or by adding the inorganic ultrafine particles after the polymerization of the polymerizable monomer is completed.

[0015]

The ink receiving layer used in the present invention is formed by dispersing fine particles of water-absorbing polymer whose surface is coated with ultrafine inorganic particles in a hydrophobic matrix polymer. In other words, the properties, that is, the blocking due to the discharge of the ink and the disorder of the image are remarkably improved, and the ink has excellent properties in the drying property, the image quality and the transparency.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view of a recording sheet of the present invention. In FIG. 1, a recording sheet 1 is a base sheet 2
And an ink receiving layer 3 formed on one surface of the base sheet 2.

In the base sheet 2, the recording sheet 1 is OHP.
When used as an application sheet, transparency, heat resistance,
A film-shaped or plate-shaped thermoplastic having dimensional stability and rigidity is preferable.
Specifically, polyethylene terephthalate resin, polycarbonate resin, acrylic resin, polyvinyl chloride resin,
Extrusion sheets and films made of polypropylene resin, polystyrene resin, polyethylene resin, cellulose triacetate resin, or the like, or stretched films thereof may be used. The thickness of the base sheet 2 is 5 to 250 μm.
The degree is preferably about 50 to 180 μm.

When the use of the recording sheet 1 is not limited to OHP, the base sheet 2 may be synthetic paper such as polystyrene, fine paper, art paper, coated paper or cast paper. It is also possible to use various colored or white papers such as coat paper, wallpaper, backing paper, synthetic resin-impregnated paper, emulsion-impregnated paper, synthetic rubber latex-impregnated paper, synthetic resin-internally added paper, and paperboard.

When the adhesion between the base sheet 2 and the ink receiving layer formed on the surface of the base sheet 2 is insufficient, the base sheet 2 is formed on the base sheet 2 for the purpose of improving the adhesion. Various underlayers (anchor-coat layers) may be interposed, or various easy-adhesion treatments such as corona discharge treatment may be performed.

The ink receiving layer 3 formed on the base sheet 2 has a particle size of 0.1 μm or less (particularly 0.001 to 0.001 μm).
0.1 μm), more preferably 0.05 μm or less (particularly 0.005 to 0.05 μm), the surface is coated with inorganic ultrafine particles, and the particle size is 0.3 μm or less, especially 0.001 to
It is composed of a hydrophobic matrix polymer in which 0.2 μm water-absorbing polymer particles are dispersed.

The particle size of the dispersed water-absorbing polymer is 0.3.
By controlling the thickness to be equal to or less than μm, the light transmittance and the transparency can be improved. Further, by dispersing the water-absorbent polymer fine particles whose surfaces are coated with the ultrafine inorganic particles in the hydrophobic matrix polymer, the above-mentioned problems of tackiness and strength of the sheet can be solved, and a sheet having sufficient performance can be obtained.

The production of the ink receiving layer 3 in the present invention is as follows.
In a solution of a hydrophobic matrix polymer dissolved in a hydrophobic solvent, a monomer dissolved in the solution is polymerized to form water-absorbing polymer fine particles, and fine particles having a predetermined particle diameter as described above are used. It has the feature that the dispersed matrix polymer solution can be adjusted freely.

Further, the solution thus obtained is used as it is as a coating liquid (coating liquid).

The particle size of the water-absorbing polymer fine particles is to change the place where the fine particles are produced by the polymerization of the monomer, that is, the free volume, because the spreading of the polymer molecular chains in the hydrophobic matrix polymer solution is different. It is possible to control by. As this method, for example,
A mixed solvent of a good solvent and a poor solvent is used as a solvent for dissolving the hydrophobic matrix polymer, and the molecular form of the hydrophobic matrix polymer is adjusted by changing the volume ratio of the good solvent and the poor solvent in this mixed solvent. , A method of changing the free volume can be cited, but the method is not limited to this. As long as it is a solvent in which the free volume corresponding to the particle diameter of the target absorbent polymer particles is formed by the solubility of the hydrophobic matrix polymer used, it is not a mixed solvent of a good solvent and a poor solvent, but one type. Can be used.

The free volume generated by the fine particles in the solution can also be changed by changing the molecular weight of the hydrophobic matrix polymer or the concentration of the hydrophobic matrix polymer solution. In the present invention, by adjusting the free volume of the hydrophobic matrix polymer solution in this way, the particle size necessary for imparting sufficient light transmittance and transparency to the ink receiving layer 3, that is, the particle size of 0. 3μ
The formation of fine particles of absorbent polymer having a size of m or less is achieved.

The solution used for dissolving the hydrophobic matrix polymer is
It is necessary to use a solvent that dissolves in the monomer stage and insoluble in the water-absorbing polymer fine particles obtained by polymerization.

As the polymerizable monomer (monomer) for synthesizing the water-absorbent polymer fine particles obtained by the above-mentioned production method, -OH group, -COOH group, -N are included in the molecule.
It is represented by a compound having a hydrophilic group such as H ₂ group and oxyethylene group, and examples thereof include acrylic acid, alkali metal salts or ammonium salts of acrylic acid, methacrylic acid, itaconic acid, 2-hydroxyethyl acrylate, 2-hydroxyethyl. Methacrylate, acrylamide, N-vinyl-2-pyrrolidone, vinylmethyl ether, vinylethyl ether, vinyl-2-methoxyethyl ether,
Vinyl sulfonic acid, an alkali metal salt of vinyl sulfonic acid, and the like are preferably used.

As the hydrophobic matrix polymer, various conventionally known ones can be used. For example, polymethyl acrylate, polymethyl methacrylate, polybutyl acrylate, polybutyl methacrylate, polystyrene, poly α-methylstyrene, polyvinyl butyral, polyvinyl acetal, polybutadiene, polyisoprene, polyvinyl. Examples thereof include polymers such as methyl ketone and polymethyl isopropenyl ketone, and copolymers thereof.

Furthermore, in the synthesis of the water-absorbing polymer fine particles, the above-mentioned polymerizable monomers may be used alone or as a mixture of two or more kinds. In addition, it is desirable to add a polyfunctional monomer in order to partially crosslink. By cross-linking the water-absorbent polymer particles in this manner, in particular,
The ink absorption speed at the initial stage of printing is improved, and the strength and adhesiveness of the recording sheet are also improved.

The cross-linking method includes a method of adding a polyfunctional monomer together with the polymerizable monomer at the time of polymerizing the water-absorbent polymer fine particles, a method of continuously adding the water-absorbing polymer particles as the polymerization progresses, and a water-absorbing method. Examples thereof include a method of adding the polymer fine particles after polymerizing them.

The polyfunctional monomers used here include divinylbenzene, methylenebisacrylamide,
Bifunctional monomers such as ethylene glycol diglycidyl ether and ethylene glycol dimethacrylate, triaryl cyanurate, trifunctional monomers such as trimethylolpropane trimethacrylate, tetraallyloxyethane, tetramethylol 4 such as methane tetraacrylate
Known compounds such as functional monomers are used.

The weight ratio of the polymerizable monomer to the polyfunctional monomer is 1 / 0.001 to 1 / 0.1, more preferably 1 / 0.005 to 1 / 0.05. This value is 1
If it exceeds /0.001, the effect of the addition of the polyfunctional monomer does not appear, and if this value is less than 1 / 0.1, the crosslinking becomes too dense and the ink absorption rate and water absorption amount remarkably decrease. .

The particle size of the water-absorbent polymer fine particles can be adjusted to a predetermined particle size by adjusting the free volume of the fine particles generated in the solution of the hydrophobic matrix polymer as described above, and sufficient light transmission can be obtained. It is possible to produce a water-absorbent fine particle polymer having a particle size necessary for its properties and transparency.

As a method for coating the surface of the water-absorbent polymer fine particles with the inorganic ultrafine particles, the inorganic ultrafine particles are added during the polymerization of the water-absorbent polymer fine particles, and the inorganic ultrafine particles are localized on the surface of the polymer fine particles. There is a method of coating and a method of coating by adding inorganic ultrafine particles after synthesis of the water-absorbent polymer particles, which can be appropriately selected. Among these, for the method of adding the inorganic ultrafine particles after synthesizing the water-absorbing polymer particles, a method of adding after adsorbing the amphipathic polymer to the inorganic ultrafine particles, a method of utilizing heterocoagulation, and a surface charge of the inorganic ultrafine particles A method that uses electrostatic interaction of ionic groups of water-absorbent polymer particles, when synthesizing water-absorbent polymer particles in advance, it is copolymerized with a heavy synthetic monomer having an inorganic component, and has affinity with inorganic ultrafine particles. A known method such as a method of increasing the value can be used.

Such inorganic ultrafine particles include silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ),
Titanium oxide (TiO ₂ ), iron oxide (Fe ₂ O ₃ ), indium oxide (In ₂ O ₃ ), zirconium oxide (ZrO
₂ ), tin oxide (SnO ₂ ) and the like. Among these, silicon oxide and aluminum oxide are particularly preferably used.

The solution thus obtained does not require any post-treatment because the water-absorbent polymer fine particles whose surfaces are coated with inorganic ultrafine particles are dispersed in the hydrophobic matrix polymer solution. It can be applied as it is to a substrate sheet as a coating liquid (coating liquid), a coating film is formed by removing the solvent, and the recording sheet of the present invention can be obtained.

The content weight ratio of the hydrophobic matrix polymer and the water-absorbent polymer fine particles is 1/50.
10/1, more preferably 1 / 40-8 / 1. If this value exceeds 10/1, the absorption capacity of the ink receiving layer is reduced, and image bleeding and disturbance appear, and
When the value becomes less than 1/50, the adhesiveness of the ink receiving layer increases, and fingerprints and the like easily adhere, and the sheets adhere to each other due to stacking. Inconvenience occurs.

The weight ratio of the water-absorbent polymer fine particles to the inorganic ultrafine particles is 50/1 to 10/1, and more preferably 40/1 to 20/1. The content weight ratio of the ultrafine inorganic particles was too large, and this value was 10/1.
If the value is out of the range, the fixing property of the ink becomes strong, an appropriate spread of dots cannot be obtained, and a fine line image is formed, and also the transparency of the sheet is deteriorated because the inorganic ultrafine particles cannot be dispersed and aggregate. . If the content ratio of the inorganic ultrafine particles is too small and this value deviates from the range of 50/1, the effect of adding the inorganic ultrafine particles is significantly reduced.

The method of applying the solution may be various conventionally known methods, for example, a gravure coat or a gravure river.
Score, roll coat, Meyer bar coat, bra
Any method such as a dough coat, a knife coat, an air knife coat, a comma coat, a slot die coat, a slide die coat, a dip coat and the like may be used. The thickness of the coating film applied on the substrate sheet 2 using these methods is preferably 1 to 50 μm, and more preferably 3 to 30 μm when dried. When the film thickness is less than 1 μm, the ink absorption amount becomes insufficient, while when it exceeds 50 μm, the economic demerit is simply increased, which is not preferable.

Ink receiving layer 3 thus formed
Further, the sheet for recording of the present invention can also be obtained by irradiating ionizing radiation with an ultraviolet lamp, an electron irradiating device, a γ-ray irradiating device or the like to crosslink the water-absorbing polymer or its composition to form a water-absorbing gel. Can be obtained. When ultraviolet rays are used as the ionizing radiation, a suitable photoinitiator,
It is preferable to add a sensitizer and the like. By irradiating the coating film with the ionizing radiation in this manner, the ink drying property during printing can be further improved.

An antistatic layer, a curl preventive layer or the like may be provided on the surface (rear surface) of the base sheet 2 opposite to the surface on which the ink receiving layer 3 is formed.

Next, the present invention will be described in more detail by showing more concrete examples. (Example 1) As a hydrophobic matrix polymer, 6 g of polyvinyl butyral (BL-S, manufactured by Sekisui Chemical Co., Ltd.) having a degree of polymerization of about 300 was dissolved in 120 g of a good solvent, methyl ethyl ketone (MEK). Next, to this solution, 20 g of acrylic acid, 0.5 g of α, α′-azobisisobutyronitrile (AIBN) as an initiator, and 0.03 of trimethylolpropane trimethacrylate as a crosslinking agent.
After adding 2 g, radical polymerization reaction was carried out at 60 ° C. for 8 hours in a nitrogen stream to obtain a polyvinyl butyral solution in which fine particles of crosslinked polyacrylic acid were dispersed.

When the obtained crosslinked polyacrylic acid fine particles were observed with a scanning electron microscope, a uniform particle size of 0.3 μm was obtained. Into this solution, as inorganic ultrafine particles, silicon oxide ultrafine particles having an average particle diameter of 12 nm (AEROSI
L200, Nippon Aerosil Co., Ltd.) 1g MEK30
When the solution dispersed in g was added and stirred at room temperature for 12 hours, a polyvinyl butyral solution in which crosslinked polyacrylic acid fine particles whose surface was coated with silicon oxide ultrafine particles were dispersed was obtained.

Using this solution as it is as a coating liquid, a dry thickness of about 20 nm was obtained by using a Meyer bar on a sheet base material (Lumilar Q80D, manufactured by Toray Industries, Inc.) made of polyethylene terephthalate having a thickness of 100 μm. The recording sheet of Example 1 was prepared by applying the coating solution as described above and drying at 80 ° C. for 30 minutes. (Example 2) A recording sheet was prepared in the same manner as in Example 1 except that 0.5 g of silicon oxide ultrafine particles was dispersed in 15 g of MEK as the inorganic ultrafine particles. (Example 3) Aluminum oxide ultrafine particles (Aluminium Oxi) having an average particle diameter of 13 nm as inorganic ultrafine particles
de C, manufactured by Nippon Aerosil Co., Ltd.) 1 g MEK50
A recording sheet was prepared in the same manner as in Example 1 except that the solution dispersed in g was used. (Example 4) Silicon oxide ultrafine particles 1 as inorganic ultrafine particles
ME in which 1 g of hydroxypropyl cellulose (SL, manufactured by Nippon Soda Co., Ltd.), which is an amphiphilic polymer, was dissolved
A recording sheet was prepared in the same manner as in Example 1 except that the solution was added to 50 g of K and stirred and dispersed at room temperature for 12 hours. (Example 5) A recording sheet was prepared in the same manner as in Example 1 except that trimethylolpropane trimethacrylate as a cross-linking agent was not added. Then, the obtained sheet was accelerated with an electron beam irradiation device (Curetron, manufactured by Nisshin High Voltage Co., Ltd.) at an acceleration voltage of 180K.
A recording sheet was produced by irradiating the coating film with an electron beam of V, 20 Mrad, and crosslinking. (Example 6) 18 g of acrylic acid as a polymerizable monomer,
A recording sheet was produced in the same manner as in Example 1 except that the copolymer fine particles were synthesized using 2 g of triethoxyvinylsilane. (Example 7) A polymerization reaction was carried out in the same manner as in Example 1 above, and 1 hour after the initiation of the polymerization reaction, a solution prepared by dispersing 1 g of silicon oxide ultrafine particles as MEK 30 g as inorganic ultrafine particles was added, followed by 7 hours at 60 ° C. A radical polymerization reaction was carried out in order to prepare a polyvinyl butyral solution in which ultrafine silicon oxide particles were localized on the surface of polyacrylic acid particles. Using this solution, a recording sheet was prepared in the same manner as in Example 1 above. (Comparative Example 1) A recording sheet was prepared in the same manner as in Example 1 using the polyvinyl butyral solution in which the polyacrylic acid fine particles dispersed in the same manner as in Example 1 were dispersed as it was as a coating solution. did.

With respect to the recording sheets (Examples 1 to 8 and Comparative Example 1) thus produced, the drying property, image quality,
The transparency and tackiness were evaluated under the following conditions.

A test pattern was printed with a dry desk writer C (manufactured by Hured Packer), and immediately after that, a sensory test was conducted by touching the printed surface.

[0048] Evaluation criteria: ◎ ... test by the print after already completely dried and are ○ ... partially dried to have × ... until completely dry take more than 3 minutes image quality desk writer C (manufactured by Hewlett Packer Co., Ltd.) A pattern was printed and visually evaluated.

Evaluation criteria: ⊚: No ink bleeding, no flow, moderate dot spread ◯: Moderate size dot is obtained, but ink bleeding is slightly ×: Ink bleeding is markedly transparent A test pattern was printed by a desk writer C (manufactured by Hured Packer Co., Ltd.), and visually evaluated by whether or not the transparency for practical use was obtained.

A test pattern was printed with an adhesive desk writer C (manufactured by Hured Packer Co., Ltd.), and after drying the printed surface, 40 g /
Place plain paper with a cm ² weight on the recording sheet,
Image distortion and paper sticking due to ink release were evaluated.

Evaluation criteria: ◯: Image is not distorted and paper is not stuck. Δ: Image is not distorted, but some sticking of paper is seen. ×: Distorted image, sticking of paper is seen. The results are shown below. It shows in Table 1.

[0052]

[Table 1]

[0053]

The effect of the present invention is clear from the results shown in Table 1. That is, according to the present invention, the ink receiving layer provided on at least one surface of the substrate sheet has a particle size of 0.3 μm or less in which the surface is coated with the inorganic ultrafine particles in the hydrophobic matrix polymer. Since the water-absorbent polymer fine particles are formed by being dispersed, the transparency of the ink receiving layer, the drying property of the ink, and the image quality are excellent, and the initial absorption speed and the tackiness of the ink are improved to prevent blocking due to the release of the ink. The effect is that image distortion is remarkably improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a recording sheet of the present invention.

[Explanation of symbols]

 1 ... Recording sheet 2 ... Substrate sheet 3 ... Ink receiving layer

Claims (9)

[Claims] 1. A substrate sheet, and an ink receiving layer provided on at least one surface of the substrate sheet, wherein the ink receiving layer covers the surface with inorganic ultrafine particles in a hydrophobic matrix polymer. A recording sheet, wherein the water-absorbent polymer fine particles having a particle diameter of 0.3 μm or less are dispersed and formed. 2. The inorganic ultrafine particles are silicon oxide or
The recording sheet according to claim 1, wherein the recording sheet is aluminum oxide. 3. The weight ratio of the hydrophobic matrix polymer and the water-absorbent polymer fine particles coated with the inorganic ultrafine particles is 1/50 to 10/1, wherein the weight ratio is 1/50 to 10/1. Recording sheet described. 4. The recording medium according to any one of claims 1 to 3, wherein a weight ratio of the water-absorbent polymer fine particles to the inorganic ultrafine particles is 50/1 to 10/1. Sheet. 5. The recording sheet according to claim 1, wherein the ink receiving layer is crosslinked by irradiation with ionizing radiation. 6. A method for producing a recording sheet comprising a base sheet and an ink receiving layer provided on at least one surface of the base sheet, wherein the ink receiving layer is a hydrophobic matrix polymer. In, is formed by applying a coating liquid in which the water-absorbent polymer fine particles whose surface is coated with inorganic ultrafine particles are dispersed on a substrate sheet, wherein the water-absorbent polymer fine particles are a hydrophobic matrix polymer. Formed by polymerizing a polymerizable monomer dissolved in a solution containing, the coating of the inorganic ultrafine particles to the water-absorbent polymer particles,
Production of a recording sheet characterized by being carried out by adding inorganic ultrafine particles in the process of polymerizing the polymerizable monomer, or by adding inorganic ultrafine particles after the polymerization of the polymerizable monomer is completed. Method. 7. The inorganic ultrafine particles are silicon oxide or
The recording sheet manufacturing method according to claim 6, wherein the recording sheet is aluminum oxide. 8. The method for producing a recording sheet according to claim 7, wherein a crosslinking agent is added when the water-absorbent polymer fine particles are polymerized and formed. 9. The polymerization ratio of the polymerizable monomer and the cross-linking agent when polymerizing the water-absorbent polymer fine particles is 1/0.
It is 001 to 1 / 0.1, The manufacturing method of the recording sheet of Claim 8 characterized by the above-mentioned.