WO2006033310A1

WO2006033310A1 - Information medium and method for manufacturing the same

Info

Publication number: WO2006033310A1
Application number: PCT/JP2005/017201
Authority: WO
Inventors: Satoshi Matsubaguchi; Yoshihisa Usami
Original assignee: Fujifilm Corporation
Priority date: 2004-09-24
Filing date: 2005-09-12
Publication date: 2006-03-30
Also published as: TW200615343A

Abstract

The present invention provides a disc-shaped information medium comprising a printable layer which comprises an undercoat layer and a colorant receiving layer, wherein: the colorant receiving layer comprises microparticles, a binder and a cross-linking agent; a thickness of the colorant receiving layer progressively decreases from an inner circumferential side to an outer circumferential side thereof; and a relationship between a thickness (Tin) at an inner peripheral portion of the colorant receiving layer and a thickness (Tout) at an outer peripheral portion of the colorant receiving layer satisfies the equation of (Tin - Tout) ≥ 1 µm. The present invention further provides a method for producing the disc-shaped information medium.

Description

DESCRIPTION INFORMATION MEDIUM AND METHOD FOR MANUFACTURING THE SAME

[0O01]

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an information medium provided with a printable layer on which characters and photographs can be printed, and a method for manufacturing thereof. [0O02] Description of the Related Art

CDs (compact disks) and DVDs (digital versatile disks) are widely accepted as standardized irrformation recording media in the marketplace.

Examples of CDs include CD-ROMs from which information can only be read, write-once type CD-Rs on which information is capable of being recorded only once, and rewritable CD-RWs on which information be rewritten numerous times.

The CD-ROMs have, for example, a structure in which a row of pits are formed at a track pitch of 1.6 μm on a transparent substrate having a diameter of 120 mm and a thickness of 1.2 mm, and have a recording capacity of about 650 MB. Information can be reproduced by irradiating the CD-ROMs with laser light having a wavelength of 770 to 790 nm at a linear velocity of 1.2 to 1.4 m/s. [0O03]

The DVDs include DVD-ROMs₅ DVD-Rs₅ and DVD-RWs similarly to the CDs.

The DVD-ROMs have a recording density about 6 to 8 times that of the CDs and have, for example, a structure in which two substrates having a thickness of about 0.6 mm are applied to each other, wherein, for example, pits are formed at a track pitch of 0.74 μm and information can be reproduced by irradiating the DVD-ROMs with laser light having a wavelength of 635 to 650 nm at a constant linear velocity of about 3.5 m/s. [0O04]

In the fields of CDs and DVDs₅ information media have been recently developed which are provided with a printable layer formed on the surface opposite to the information-reproducible surface, such that an image can be printed by an ink jet printer (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2002-245671). An ultraviolet ray-curable resin is generally used for the printable layer of such an information medium. However, this printable layer made of an ultraviolet ray-curable resin cannot provide as high image quality as an ink jet recording sheet.

In addition, a printable layer fonned of an ultraviolet curable resin is formed thickly, in order to obtain an absorptive capacity that is sufficient to absorb all the droplets of ink. However, due to of the need for a large amount of energy to be applied at the time of ultraviolet curing, and due to stress generated by contraction during the curing, the disc may be warped. As a result, problems such as deterioration in recording property are produced.

Furthermore, the ultraviolet ray-curable resin causes skin irritation and there is therefore a problem concerning the safety of the material. Moreover, the ultraviolet ray-curable resin has problems concerning handling. For example, it must be stored at ordinary temperature in a dark place, has a short life, and has an unpleasant odor and thus adversely affects working environment.

[0005]

SUMMARY OF THE INVENTION

The present invention is achieved in consideration of the above-described problems. The present invention provides a disk-shaped information medium which is provided with a printable layer having high handling safety and little warpage. Further, the present invention provides a method for manufacturing the disk-shaped information medium. [0006]

Namely, the present invention provides a disc-shaped information medium comprising a printable layer which comprises an undercoat layer and a colorant receiving layer, wherein: the colorant receiving layer comprises microparticles, a binder and a cross-linking agent; a thickness of the colorant receiving layer progressively decreases from an inner circumferential side to an outer circumferential side thereof; and a relationship between a thickness (Ti_n) at an inner peripheral portion of the colorant receiving layer and a thickness (T_out) at an outer peripheral portion of the colorant receiving layer satisfies the equation of (Tj_n - T_out) > 1 μm. [0007]

The present invention further provides a method for producing the disc-shaped information medium, wherein the method comprises forming a coating layer by applying, onto the undercoat layer, a coating solution containing the microparticles and the binder using an extrusion die coater with increasing of the flow rate at a discharging port of the extrusion die coater from an inner circumferential portion to the outer circumferential portion of the medium so as to form the colorant receiving layer. The flow rate preferably accords with the linear velocity of the extrusion die coater.

[0008]

DETAILED DESCRIPTION OF THE INVENTION Disc-shaped Information Medium

The disc-shaped information medium of present invention (hereinafter sometimes referred as the "information medium") is characterized by comprising a printable layer which comprises an undercoat layer and a colorant receiving layer, wherein: the colorant receiving layer comprises microparticles, a binder and a cross-linking agent; a thickness of the colorant receiving layer progressively decreases from an inner circumferential side to an outer circumferential side thereof; and a relationship between a thickness (Tj_n) at an inner peripheral portion of the colorant receiving layer and a thickness (T_out) at an outer peripheral portion of the colorant receiving layer satisfies the equation of (Tj_n - T_out) > 1 μm. [0009]

The information medium of the invention may be applied to a magnetic medium, an optical medium, and a semiconductor medium and may have any form including a disk shape and one stored in a cartridge. In the case of one stored in a cartridge, the information medium is preferably removable. The information medium of the invention is preferably a disk-like optical information recording medium (optical disk).

In the case where the information medium is an optical disk, it may be any one of disks including CDs, DVDs and optical disks using a bluish violet laser to record and reproduce information.

In the case of a medium using a bluish violet laser to record, it may be any one of an applied type such as DVDs and a type provided with a recording layer and a cover layer on a substrate having a thickness of 1.1 mm wherein laser light is introduced from the cover layer side.

The printable layer is generally formed on the side opposite to the surface from which laser light is introduced. However, the printable layer can be formed on the side from which laser light is introduced if it is formed on an area other than an area from which the laser is introduced.

The information medium of the invention is preferably a write-once type, though it may be any of a ROM type, a rewritable type and a write-once type. [0010] Printable layer

The information medium of the invention is provided with a printable layer containing at least a base layer and a colorant receiving layer. Hereinafter, each of the base layer and the colorant receiving layer of the printable layer will be explained. [0011] Colorant receiving layer

The colorant receiving layer in the invention contains at least microparticles, a binder and a cross-linking agent and may further contain a compound represented by the following Formula (1) and/or a compound represented by the following Formula (2) and various additives. [0012]

The thickness of the colorant receiving layer gradually decreases from an inner circumferential side to an outer circumferential side thereof. Further, a relationship between a thickness (Tj_n) at an inner peripheral portion of the colorant receiving layer and a thickness (T_out) at an outer peripheral portion of the colorant receiving layer satisfies the equation of (Tj_n - T_out) ≥ 1 μm. The present invention is capable of suppressing warping caused by internal stress generated during formation of the colorant receiving layer by providing the gradation in the layer thickness of the colorant receiving layer which satisfies this equation.

The difference between the thickness at an inner peripheral portion of the colorant receiving layer and the thickness at an outer peripheral portion of the colorant receiving layer (Tj_n - T_out) is preferably equal to or larger than 2 μm, and is more preferably equal to or larger than 5 μm. The effect of suppressing warping cannot be expressed when the difference (Tj_n - T_out) is smaller than 1 μm. [0013]

A difference between the thickness of the inner peripheral portion and the thickness of the outer peripheral portion (Tj_n - T_out) is preferably 20 μm or less, is more preferably 15 μm or less, and is still more preferably 10 μm or less. [0014]

The smallest thickness of the colorant receiving layer of the medium of the invention, that is observed in the outer peripheral portion, is preferably in a range of 25 to 65 μm.

The thickness of the colorant receiving layer is more preferably in a range of 30 to 60 μm, is further preferably in a range of 35 to 55 μm, and is particularly preferably in a range of 35 to 50 μm.

When the thickness of the colorant receiving layer is less than 25 μm, an absorption capacity sufficient to absorb all liquid droplets of ink cannot be obtained, causing blurring. Also, when the thickness exceeds 65 μm, mechanical properties such as warping and vertical deviation of the information medium may deteriorate. [0015]

It is necessary that the colorant receiving layer of the present invention that the thickness of the colorant receiving layer gradually decreases from an inner circumferential side to an outer circumferential side thereof. Namely, the colorant receiving layer of the present invention is required to have a gradation. The gradation may have an arbitrary shape, and examples thereof include step-shapes and slope shapes. An angle of gradation may or may not be a constant value. [0016]

In order to adjust the thickness of the colorant receiving layer in the above-described range, a method and a condition for coating a colorant receiving layer coating solution which will be explained later may be appropriately set such that the dry thickness of the colorant receiving layer is in the above-described range. [0017] Microparticles

The colorant receiving layer in the invention contains microparticles. Examples of the microparticles include a vapor phase method silica, pseudo boehmite, aluminum oxide, titanium dioxide, barium sulfate, calcium silicate, zeolite, kaolinite, halloysite, mica, talc, calcium carbonate, magnesium carbonate, calcium sulfate and boehmite. Among these microparticles, a vapor phase method silica, pseudo boehmite and aluminum oxide are preferable. [0018] Vapor phase method silica

Silica microparticles are roughly classified into wet method particles and dry method (vapor phase method) particles in general by its production method. In the wet method, a method in which a silicate is decomposed by an acid to produce active silica, the active silica is then moderately polymerized, and the polymerized silica is aggregated and precipitated to obtain silica hydrate is mainly used. As the vapor phase method which are currently and dominantly used, there are a method in which a silicon halide is subjected to high-temperature vapor phase hydrolysis (flame hydrolysis method), and a method (arc method) in which quarts sand and cokes are heated, reduced and vaporized by an arc in an electric furnace and the vaporized materials are oxidized with air. The "vapor phase method silica" means silica anhydride microparticles obtained by the vapor phase method. [0019]

The vapor phase method silica is suitable to form a three-dimensional structure having high percentage of void, though it is different from silica hydrate in density of silanol groups on the surfaces of particles and presence or absence of voids, and exhibits properties different from those of silica hydrate. The reason for this is not clarified, but is thought as follows. In the case of silica hydrate, the density of silanol groups on the surface of microparticles is as many as 5 to 8 groups/nm² and therefore silica microparticles easily densely aggregate. Meanwhile, in the vapor phase method silica, the density of silanol groups on the surfaces of microparticles is as small as 2 to 3 groups/nm² and therefore silica microparticles thin flocculate and, as a result, form a structure having high percentage of void. [0020]

The vapor phase method silica has high ink absorbing ability and high retention efficiency due to its large specific surface area. Also, because this silica has a low refractive index, it can impart transparency to the colorant receiving layer by dispersing it till it has a proper diameter and can provide a high color density and a good color developing property. [0021]

An average primary particle diameter of the vapor phase method silica particles is preferably 30 nni or less, more preferably 20 nm or less, still more preferably 10 nm or less, and most preferably 3 to 10 nm. The vapor phase silica particles tend to adhere to each other due to hydrogen bond of their silanol groups. Therefore, when the average primary particle diameter is 30 nm or less, the vapor phase method silica can form a structure having high percentage of void and can effectively improve an ink absorbing property. [0022]

A solid content of the aforementioned vapor phase method silica particles in the colorant receiving layer is preferably 40% by mass or more, and more preferably 50% by mass or more based on a total solid amount of the colorant receiving layer. When the content exceeds 50% by mass, it becomes possible to form a better porous structure, enabling a colorant receiving layer having sufficient ink absorbing ability. The solid content of the vapor phase method silica particles in the colorant receiving layer herein means the content of the vapor phase method silica particles calculated on the basis of components other than water in the composition of the colorant receiving layer. [0023] Other inorganic pigment microparticles such as silica hydrate microparticles, colloidal silica, titanium dioxide, barium sulfate, calcium silicate, zeolite, kaolinite, halloysite, mica, talc, calcium carbonate, magnesium carbonate, calcium sulfate, boehmite and pseudo boehmite may also be additionally used. When other inorganic pigment microparticles and the vapor phase method silica are used in combination, a content of the vapor phase method silica in a total amount of inorganic pigment .microparticles is preferably 50 % by mass or more, and more preferably 70 % by mass or more. [0024] Pseudo boehmite

The pseudo boehmite is a stratified compound which is represented by Al₂CVxH₂O (1 < x < 2) and whose crystal has a (020) plane forming a huge plane and has a lattice constant d of 0.67 nm. Here, the pseudo boehmite has a structure including excess water between layers of the (020) plane. The pseudo boehmite well absorbs ink and is fixed. It can also improve ink absorbing ability and prevent blurring over time.

A sol-like pseudo boehmite (pseudo boehmite sol) is preferably used as a raw material because a smooth layer is easily obtained. [0025]

An average primary particle diameter of the pseudo boehmite particles is preferably 50 nm or less, more preferably 30 nm or less and particularly preferably in a range of 3 to 20 nm. When the average primary particle diameter is within the above range, a structure having high percentage of void can be formed and the ink absorbing ability of the colorant receiving layer can be further improved. The average primary particle diameter can be measured with, for example, an electron microscope.

The BET specific surface area of each of the pseudo boehmite particles is preferably in a range of 40 to 500 m and more preferably in a range of 200 to 500 m . [0026]

Moreover, an aspect ratio of each of the pseudo boehmite particles is preferably in a range of 3 to 10. As for a porous structure of the pseudo boehmite, an average pore radius thereof is preferably in a range of 1 to 30 nm, and more preferably 2 to 15 nm. A pore volume of the pseudo boehmite is preferably in a range of 0.3 to 2.0 ml/g (cc/g), and more preferably 0.5 to 1.5 ml/g (cc/g). Here, the pore radius and pore volume are measured by a nitrogen absorption and desorption method. For example, they may be measured with a gas absorption and desorption analyzer, for example, OMNISOAPTM369 (trade name, manufactured by Beckman Coulter, Inc.). [0027]

A solid content of the aforementioned pseudo boehmite particles in the colorant receiving layer is preferably 50 % by mass or more, and more preferably 60 % by mass or more based on a total solid amount of the colorant receiving layer. When the content exceeds 60 % by mass, it becomes possible to form a better porous structure, enabling a colorant receiving layer having sufficient ink absorbing ability. The solid content of the pseudo boehmite particles in the colorant receiving layer herein means the content of the pseudo boehmite particles calculated on the basis of components other than water in the composition of the colorant receiving layer. [0028]

The pseudo boehmite is preferably used in a form of a dispersion liquid in which it is dispersed in an aqueous solvent. A content of the pseudo boehmite in the dispersion liquid is preferably 60 % by mass or less, more preferably 5 to 60 % by mass, and most preferably 10 to 50% by mass.

The pseudo boehmite can be dispersed particularly effectively when the content is in the above range. For example, thickening and gelation caused by, for example, a reduction in the distance between the pseudo boehmite particles can be effectively suppressed. [0029]

A mass ratio of the vapor phase method silica (S) to the pseudo boehmite (A), namely (S:A), is preferably in a range of 95:5 to 5:95, more preferably in a range of from 80:20 to 20:80, and most preferably in a range of 70:30 to 30:70.

When the vapor phase method silica is used in combination with the pseudo boehmite within the above range of the content ratio, blurring of all inks of plural colors over time can be effectively prevented regardless of hue. Even when a multicolor image is formed, a clear image with high resolution can be formed and kept. [0030] Aluminum oxide

Examples of aluminum oxide used in the invention include anhydrous alumina such as α-alumina, δ-alumina, θ-alumina and χ-alumina and active aluminum oxide, δ- Alumina is preferable among them.

From the viewpoint of a production method, alumina microparticles produced by a vapor phase method, namely, vapor phase method alumina microparticles obtained by hydrolyzing a gaseous metal chloride in a presence of water generated in an oxy-hydrogen reaction or at a temperature that is characteristic in such a reaction are preferable because the microparticles have a high specific surface area. [0031]

The form of the aluminum oxide can be, for example, fine particles, microparticles., ultra fine particles, powders, impalpable powders, or ultra fine powders having predetermined particle diameters. An average primary particle diameter of these particles is preferably 200 nm or less, more preferably 5 to 100 nm, and particularly preferably 5 to 20 nm. When the average primary particle diameter of the alumina microparticles is in the above range, a structure having high percentage of void can be formed and the ink absorbing ability of the colorant receiving layer can be further improved. It is noted that the average primary particle diameter can be measured with, for example, an electron microscope. [0032]

The aluminum oxide in the invention is preferably used in a form of a dispersion liquid. A content of aluminum oxide in the dispersion liquid is preferably 60% by mass or less, more preferably 5 to 60% by mass, and most preferably 10 to 50% by mass. When the content of aluminum oxide is in the above range, aluminum oxide can be more effectively dispersed. When the content of aluminum oxide in the dispersion solution is 60% by mass or less, it is possible to effectively suppress thickening and gelation caused by, for example, a reduction in the distance between the aluminum oxide microparticles in the dispersion liquid.

Primary to tertiary amino groups and salts thereof and/or a cationic polymer having a quaternary ammonium base may be added as an aggregation inhibitor to the dispersion liquid. An amount of the aggregation inhibitor to be added is preferably 1 to 10% by mass, and more preferably 1 to 5% by mass based on the total amount of aluminum oxide microparticles. When the amount of the inhibitor is less than 1% by mass, dispersibility may deteriorate. Meanwhile, when the amount exceeds 10% by mass, decreased color density may be obtained at the time that an image is printed on the colorant receiving layer. [0033]

A solid content of the aforementioned aluminum oxide in the colorant receiving layer is preferably 50% by mass or more, and more preferably 60% by mass or more based on a total solid amount of the colorant receiving layer. When the content exceeds 60% by mass, it becomes possible to form a better porous structure, enabling a colorant receiving layer having sufficient ink absorbing ability. The solid content of the aluminum oxide in the colorant receiving layer herein means the content of the aluminum oxide calculated on the basis of components other than water in the composition of the colorant receiving layer. [0034]

In the invention, the aluminum oxide may be combined with other microparticles. When aluminum oxide is combined with other microparticles in the invention, the content of aluminum oxide in all microparticles is preferably 30% by mass or more, and more preferably 50% by mass or more.

The microparticles may be any of organic microparticles and inorganic microparticles, and among them, inorganic microparticles are preferable from the viewpoint of ink absorbing ability and image stability. [0035] Binder

As mentioned above, the colorant receiving layer in the invention contains a binder. The binder is preferably a water-soluble resin. [0036]

Examples of the water-soluble resin include polyvinyl alcohol resins, which have hydroxyl groups as hydrophilic structural units (e.g., a polyvinyl alcohol (PVA), acetoacetyl modified PVA, cation modified PVA₅ anion modified PVA, silanol modified PVA. and polyvinylacetal), cellulose resins (e.g., methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC)₅ hydroxyethylmethyl cellulose and hydroxypropylmethyl cellulose], chitins, chitosans, starch, resins having ether bonds [e.g., a polyethylene oxide (PEO)₅ polypropylene oxide (PPO), polyethylene glycol (PEG) and polyvinyl ether (PVE)] and resins having carbamoyl groups [e.g., a polyacrylamide (PAAM), polyvinylpyrrolidone (PVP) and polyacrylic acid hydrazide.

As the water-soluble resin, polyacrylates, maleic acid resins, alginates and gelatins having carboxy groups as dissociable groups may also be utilized. [0037]

Among the above resins, polyvinyl alcohol (PVA) resins are particularly preferable. Examples of the polyvinyl alcohol resins include those described in Japanese Patent Application Publication (JP-B) Nos. 4-52786, 5-67432 and 7-29479, Japanese Patent No. 2537827, JP-B No. 7-57553, Japanese Patent Nos. 2,502,998 and 3,053,231, JP-A No. 63-176173, Japanese Patent No. 2,604,367, JP-A Nos. 7-276787, 9-207425, 11-58941, 2000-135858, 2001-205924, 2001-287444, 62-278080 and 9-39373, Japanese Patent No. 2,750,433, JP-A Nos. 2000-158801, 2001-213045, 2001-328345, 8-324105 and 11-348417.

Examples of the water-soluble resin other than the polyvinyl alcohol resins include compounds described in JP-ANo. 11-165461, paragraph Nos. [0011] to [0014]. [0038]

These water-soluble resins may be used singly or in combination of two or more of them.

In the invention, a content of the water-soluble resin is preferably 9 to 40% by mass, and more preferably 12 to 33% by mass based on a total solid mass of the colorant receiving layer. [0039]

The polyvinyl alcohol resin may be used in combination with any of the aforementioned other water-soluble resins. When other water-soluble resin is used in combination with, the polyvinyl alcohol resin, the content of the polyvinyl alcohol resin is preferably 50°A> by mass or more, and more preferably 70% by mass or more based on a total amount of the water-soluble resins. [0040]

The polyvinyl alcohol resin has a hydroxyl group in the structural unit thereof. This hydroxyl groups and the silanol groups on the surfaces of silica microparticles form hydrogen bond, which makes it easy to form a three-dimensional network structure in which secondary particles of the silica microparticles are chain units. It is thought that the formation of the three-dimensional network structure makes it possible to form a colorant receiving layer having a porous structure with high percentage of void.

In the ink jet recording, the porous colorant receiving layer thus obtained can rapidly absorb ink due to capillarity to form good circular dots free from ink blurring. [0041]

Polyvinyl alcohol having a degree of saponification of 70 to 99% is more preferable, and polyvinyl alcohol having a degree of saponification of 80 to 99% is particularly preferable from the viewpoint of transparency. [0042] Ratio of microparticles to water-soluble resin

The ratio by mass (PB ratio (x/y)) of the microparticles (x) relative to the water-soluble resin as the binder (y) largely affects a structure and strength of the colorant receiving layer. That is, when the mass ratio (PB ratio) is increased, percentage of void, pore volume and surface area (per unit mass) are increased, but the density and strength tend to be decreased. [0043]

In the colorant receiving layer in the invention, the mass ratio (PB ratio (x/y)) is preferably 1.5/1 to 10/1 from the viewpoint of prevention of defects caused by a too large PB ratio such as a reduction in layer strength and cracks at the time of drying, and prevention of deteriorated ink: absorbing ability caused by a too small PB ratio, namely caused by voids being easily clogged with a resin and therefore percentage of void being reduced. [0044]

When the information medium of the invention is conveyed through a conveyor system of an ink jet recording printer, stress may be applied to the information medium. Accordingly, it is preferable that the colorant receiving layer has a sufficient film strength. In consideration of such cases, the PB ratio (x/y) is preferably 4/1 or less. On the other hand, the PB ratio (x/y) is preferably 3/1 or more from the viewpoint of assuring of high-speed ink absorbing ability in an ink jet recording printer. [0045]

Specific examples of methods for forming the colorant receiving layer include one in which a coating solution prepared by dispersing the vapor phase method silica microparticles having an average primary particle diameter of 20 nm or less and the water-soluble resin in an aqueous solution in a PB ratio (x/y) of 3/1 to 4/1 is applied onto a base layer and the coating layer is dried, a three-dimensional network structure in which secondary particles of the silica microparticles constitute network chains is formed, whereby a light-transmittable porous film having an average pore diameter of 30 nm or less, a percentage of void of 50 to 80%, a specific pore volume of 0.5 ml/g or more, and a specific surface area of 100 m2/g or more is capable of being easily formed. [0046] Cross-linking agent

The colorant receiving layer contains a cross-linking agent which can cross-link the binder. Wlien the cross-linking agent is contained, the colorant receiving layer can be formed as a porous layer cured by cross-linking reaction between the cross-linking agent and die binder. [0047]

A boron compound, is preferable to cross-link a polyvinyl alcohol which is particularly preferable as the water-soluble resin. Examples of the boron compound include borax, boric acid, borates (e.g., orthoborates, InBO₃, ScBO₃, YBO₃, LaBO₃, Mg₃(BO₃)₂, Co₃(BOs)₂, diborates (e.g., Mg₂B₂O₅ and CO₂B₂O₅), methaborates (e.g., LiBO₂, Ca(BO₂)₂, NaBO₂ and KBO₂), tetraborates (e.g., Na₂B₄O₇-IOH₂O) and pentaborates (e.g., KB₅08-4H₂O, Ca₂B₆O₁₁-TH₂O and CsB₅O₅). Among these boron compounds, borax, boric acid and borates are preferable, and boric acid is particularly preferable from the viewpoint of rapid initiation of cross-linking reaction. [0048]

As the cross-linking agent for the v^ater-soluble resin, a compound other than the boron compound may also be used. Examples of such a cross-linking agent include aldehyde compounds such as formaldehyde, glyoxal, succinaldehyde, glutaraldehyde, dialdehyde starch and dialdehyde derivatives of vegetable gum; ketone compounds such as diacetyl, 1,2-cyclopentanedione and 3-hexene-2,5-dione; active halogen compounds such as bis(2-chloroethyl)urea, bis(2-chloroethyl)sulfone and sodium salt of 2,4-dichloro-6-hydroxy-s-triazine; active vinyl compounds such as divinylsulfone, 1 ,3 -bis(vinylsulfonyl)-2-propanol,

N,N'-ethylenebis(vinylsulfonylacetamide), divinyl ketone, l,3-bis(acryloyl)urea and 1,3,5-triacryloyl-hexahydro-s-triazine; N-methylol compounds such as dimethylolurea and methyloldimethylhydantoin; melamine compounds such as uϊmethylolmelamine, alkylated methylolmelamine, melamine, beazoguanamine and melamine resins; epoxy compounds such as ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, diglycerin polyglycidyl ether, spiroglycol diglycidyl ether and polyglycidyl ether of a phenol resin; [0049] isocyanate compounds such as 1,6-hexamethylene diisocyanate and xylylene diisocyanate; aziridine compounds described in U.S. Patent Nos. 3,017,280 and 2,983,611; carbodiimide compounds described in U.S. Patent No. 3,100,704; ethyleneimino compounds such as l,6-hexarnethylene-N,N'-bisethyleneurea; halogenated carboxyaldehyde compounds such as mucochloric acid and mucophenoxychloric acid; dioxane compounds such as 2,3-dihydroxydioxane; metal-containing compounds such as titanium lactate, aluminum sulfate, chrome alum, potassium alum, zirconyl acetate and chromium acetate; polyamine compounds such as tetraethylenepentamine; hydrazide compounds such as dihydrazide adipate; low molecular-weight molecules and polymers containing two or more oxazoline groups; anhydrides of polyvalent acids, acid chlorides and bissulfonate compounds described in U.S. Patent Nos. 2,725,294, 2,725,295, 2,726,162 and 3,834,902 and active ester compounds described in U.S. Patent Nos. 3,542,558 and 3,251,972.

One of these cross-linking agents may be used singly or in combination of two or more of them. [0050]

When a gelatin is used in addition to the polyvinyl alcohol, following compounds, which are known as a film hardening agent for gelatin, can be used as a cross-linking agent in addition to the boron compound. Examples of such a

IS cross-linking agent for gelatin include aldehyde compounds such as formaldehyde, glyoxal, and glutaraldehyde; ketone compounds such as diacetyl and cyclopentanedione; active halogen compounds such as bis(2-chloroethylurea)-2-liydroxy-4₅6-dichloro-l,3,5-triazine and sodium salt of 2,4-dichloro-6-S-triazine; active vinyl compounds such as divinylsulfonic acid, 1,3- vinylsulfonyl-2-propanol, N₅N' -ethylenebis(vmylsnlfonylacetamide), and

1,3,5-triacryloyl-hexahydro-S-triazine; N-methylol compounds such as dimethylolurea and methyloldimethylhydantoin; [0051] isocyanate compounds such as 1 ,6-hexamethylene diisocyanate; aziridine compounds described in U.S. Patent Nos. 3,017,280 and 2,983,61 1; carbodiimide compounds described in U.S. Patent No. 3,100,704; epoxy compounds such as glycol triglycidyl ether; ethyleneimino compounds such as l,6-hexarnetliylene-N,N'-bisethyleneurea; halogenated carboxyaldehyde compounds such as mucochloric acid and mucophenoxychloric acid; dioxane compounds such as 2,3-dihydroxydioxane; chrome alum, potassium alum, zirconium sulfate, chromium acetate; and the like.

When the boron compound and other cross-linking agents are used in combination, a content of the boron compound in all cross-linking agents is preferably 50 % by mass or more, and is preferably 70 % by mass or more based on a total amount of the all cross-linking agents.

The boron compound may be used singly or in combination of two or more of them. [0052]

The cross-linking agent is preferably supplied simultaneously with application of a coating solution which at least contains the micropartlcles and the binder and which forms the porous colorant receiving layer (namely, a colorant receiving layer coating solution), or before the coating layer formed by applying the colorant receiving layer coating solution exhibits a decreasing rate of dry speed. This operation is effective to prevent generation of cracks when the coating layer is dried.

That is, by applying the cross-linking agent-containing solution to the coating layer at a timing of simultaneously with the application of the coating solution or at a timing of before the coating layer exhibits a decreasing rate of dry speed, the cross-linking agent-containing solution penetrates into the coating layer and quickly reacts with the binder in the coating layer to allow the binder to be made gel state (cured), whereby a strength of the coating layer is rapidly and remarkably improved. [0053] Further, examples of methods of forming a colorant receiving layer used in the invention include a method in which a solution (first solution), which contains the binder and the compound represented by Formula (1) and/or the compound represented by Formula (2), is added to an aqueous dispersion containing the vapor phase method silica and a dispersant and re-dispersed to obtain a coating solution, the coating solution is applied to a surface of the base layer, and a solution (second solution) containing the cross-linking agent is applied to the coating layer simultaneously with the application of the coating solution or during the course of drying of the resultant coating layer and before the coating layer exhibits a decreasing rate of dry speed. When this method is used, the cross-linking agent is preferably added to both the first and second solutions. [0054]

When the cross-linking agent is applied, its solution is prepared by dissolving the cross-linking agent in water and/or an organic solvent.

A concentration of the cross-linking agent in the cross-linking agent solution is preferably 0.1 to 10% by mass, and more preferably 0.5 to 8% by mass based on the mass of the cross-linking agent solution.

Water is generally used as the solvent of the cross-linking agent solution, and an aqueous mixture solvent containing water and an organic solvent miscible with water may also be used.

Any solvent which dissolves the cross-linking agent may be used as the organic solven. Examples of the organic solvent include alcohols such as methanol, ethanol, isopropyl alcohol and glycerin; ketones such as acetone and methyl ethyl ketone; esters such as methyl acetate and ethyl acetate; aromatic solvents such as toluene; ethers such as tetrahydrofuran; and halogenated carbon-including solvents such as dichloromethane. [0055] Mordant

The colorant receiving layer in the invention preferably contains a mordant to improve water resistance of a formed image and prevent blurring of the formed image over time.

A cationic polymer (cationic mordant) is preferable as the mordant. Presence of the mordant in the colorant receiving layer can improve water resistance and prevent blurring over time because the mordant interacts with liquid ink having an anionic dye as a colorant to stabilize the colorant. [0056]

However, if the mordant is directly added to the coating solution for forming the colorant receiving layer, the mordant and the vapor phase silica having an anionic charge may aggregate. Use of a method, in which the mordant is used as another solution, and in which the solution is separately applied, does not cause such aggregation of the inorganic pigment microparticles. Therefore, in the invention, the mordant is preferably contained in a solution other than the dispersion of the vapor phase method silica (for example, a cross-linking agent solution). [0057]

As the cationic mordant, a polymer mordant containing as a cationic group any of primary to tertiary amino groups and a quaternary ammonium base is preferably used. A cationic non-polymer mordant may also be used.

Preferable examples of the polymer mordant include a homopolymer of a monomer (mordant monomer) containing any of primary to tertiary amino groups and salts thereof and a quaternary ammonium base, and a copolymer or a condensed polymer of the mordant monomer and any other monomer (hereinafter referred to as "non-mordant monomer"). These polymer mordants may be used in any form including a water-soluble polymer and water-dispersible latex particles. [0058]

Examples of the mordant monomer include trimethyl-p-vinylbenzylammoniurα chloride, trimethyl-m-vinylbenzylammonium chloride, triethyl-p-vinylbenzylammonium chloride, triethyl-m-vinylbenzylammonium chloride., N,N-dimethyl-N-ethyl-N-p-vinylbenzylammonium chloride.,

N,N-diethyl-N-methyl-N-p-vinylbenzylammonium chloride,,

N,N-dimethyl-N-n-propyl-N-p-vinylbenzylammonium chloride,

N_jN-dimethyl-N-n-octyl-N-p-vinylbenzylammonium chloride.,

N,N-dimethyl-N-benzyl-N-p-vinylbenzylammonium chloride,

N,N-diethyl-N-benzyl-N-p-vinylbenzylammonium chloride .,

N,N-dimethyl-N-(4-methyl)benzyl-N-p-vinylbenzylammonium chloride,

N,N-dimethyl-N-phenyl-N-p-vinylbenzylammonium chloride; [0059] trimethyl-p-vinylbenzylammonium bromide, trimethyl-m-vinylbenzylammoniurn bromide, trimethyl-p-vinylbenzylammonium sulfonate, trimethyl-m-vinylbenzylammonium sulfonate, trimethyl-p-vinylbenzylammoniurn acetate, trimethyl-m-vinylbenzylammonium acetate,

N,N,N-triethyl-N-2-(4-vinylphenyl)ethylammonium chloride ,

N₅N,N-triethyl-N-2-(3 -vinylphenyl)ethylammonium chloride,

N,N-diethyl-N-methyl-N-2-(4-vinylphenyl)ethylammonium chloride,

N₅N-diethyl-N-methyl-N-2-(4-vinylphenyl)ethylammonium acetate; and [0060] quaternary products of N,N-dimethylaminoethyl(meth)acrylate,

N,N-diethylaminoethyl(meth)acrylate, N,N-dimetliylaminopropyl(meth)acrylate,

N,N-diethylaminopropyl(meth)acrylate, N₅N-dimethylaminoethyl(meth)acrylamide, N₅N-diethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide or N,N-diethylaminopropyl(meth)acrylamide, and methyl chloride, ethyl chloride, methyl bromide, ethyl bromide, methyl iodide or ethyl iodide, and sulfonates, alkylsulfonates, acetates and alkylcarboxylates obtained by substituting the anions of these products. [0061]

Specific example of these salts include trimethyl-2-(methacryloyloxy)ethylammonium chloride, triethyl-2-(methacryloyloxy)ethylammonium chloride, trimethyl-2-(acryloyloxy)ethylammonium chloride, triethyl-2-(acryloyloxy)ethylammonium chloride, trimethyl-3-(methacryloyloxy)propylammonium chloride, triethyl-3-(methacryloyloxy)propylammonium chloride, trimethyl-2-(methacryloylamino)ethylammonium chloride, triethyl-2-(methacryloylamino)ethylammonium chloride, trimethyl-2-(acryloylamino)ethylammonium chloride, triethyl-2-(acryloylamino)ethylammonium chloride, trimethyl-3-(methacryloylamino)propylammonium chloride, triethyl-3-(methacryloylamino)propylammonium chloride, trimethyl-3-(acryloylamino)propylammonium chloride, triethyl-3 -(acryloylamino)propylammonium chloride; [0062]

N,N-dimethyl-N-ethyl-2-(methacryloyloxy)ethylammonium chloride,

N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium chloride,

N,N-dimethyl-N-ethyl-3 -(acryloylamino)propylammonium chloride, trimetliyl-2-(methacryloyloxy)ethylammonium bromide, trimethyl-3-(acryloylamino)propylammonium bromide, trimethyl-2-(metliacryloyloxy)ethylammoniuni sulfonate and trimethyl-3 -(acryloylamino)propylammonium acetate.

Examples of other copolymerizable monomers include N-vinylimidazole and N-vinyl-2-methylimidazole. [0063] The non-mordant monomer means a monomer which contains no basic or cationic moiety such as a primary to tertiary amino group or a salt thereof or a quaternary ammonium base and which does not interact or hardly interacts with the dye contained in ink jet ink.

Examples of the non-mordant monomer include alkyl (meth)acrylates; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate; aralkyl esters such as benzyl (meth)acrylate; aromatic vinyls such as styrene, vinyltoluene and α-methylstyrene; vinyl esters such as vinyl acetate, vinyl propionate and vinyl versatate; allyl esters such as allyl acetate; halogen-containing monomers such as vinylidene chloride and vinyl chloride; vinyl cyanides such as (meth)acrylonitrile; and olefins such as ethylene and propylene. [0064]

As the alkyl (meth)acrylate, alkyl (meth)acrylates with an alkyl moiety having 1 to 18 carbon atoms are preferable. Examples of the preferable alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate and stearyl (meth)acrylate.

Among these compounds, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and hydroxyethyl methacrylate are preferable.

The non-mordant monomers may be used singly or in combination of two or more of them. [0065]

Furthermore, preferable examples of the polymer mordant include polydiallyldimethylammonium chloride, polymethacryloyloxyethyl-β-hydroxyethyldimethylammonium chloride, polyethylenimine, polyallylamine, polyallylamine hydrochloride, polyamide-polyamine resin, cationic starch, dicyandiamido-formalin condensate, dimethyl-2-hydroxypropylammonium salt polymer, polyamidine and polyvinylamine. [0066]

The molecular weight of the polymer mordant is preferably 1,000 to 200,000, and more preferably 3,000 to 60,000 in terms of weight average molecular weight. When the molecular weight is in the range of 1,000 to 200,000, water resistance of the medium is prevented from being insufficient and deterioration in handling aptitude of the medium caused by excessively increased viscosity is prevented. [0067] As the cationic non-polymer mordant, for example, water-soluble metal salts such as aluminum sulfate, aluminum chloride, aluminum polychloride or magnesium chloride are preferable. [0068] Compounds represented by Formulae (1) and (2)

The colorant receiving layer in the information medium of the invention preferably contains a compound represented by the following Formula (1) and/or a compound represented by the following Formula (2). These compounds represented by Formulae (1) and (2) or solvents having high boiling points. [0069]

RO(CH₂CH₂O)_nH Formula (1)

In Formula (1), R represents a saturated hydrocarbon group having 1 to 12 carbon atoms, an unsaturated hydrocarbon group having 1 to 12 carbon atoms, a phenyl group or an acyl group, and n represents an integer from 1 to 3.

RO(CH₂CH(CH₃)O)_nH Formula (2)

In Formula (2), R represents a saturated hydrocarbon group having 1 to 12 carbon atoms, an unsaturated hydrocarbon group having 1 to 12 carbon atoms, a phenyl group or an acyl group, and n represents an integer from 1 to 3. [0070]

Inclusion of the compound represented by Formula (1) and/or the compound represented by Formula (2) in the colorant receiving layer can suppress drying shrinkage of the colorant receiving layer when a three-dimensional network structure (porous structure) is formed. It is thought that this is because the compounds represented by Formulae (1) or (2) moderately inhibit hydrogen bondings between silanol groups on the surfaces of the vapor phase method silica particles and hydroxyl groups of polyvinyl alcohol. Thereby, cracks of the colorant receiving layer when a three-dimensional network structure is formed can be prevented, and therefore production yield and quality of the information medium can be improved. [0071]

In Formulae (1) and (2), R represents a saturated hydrocarbon group having 1 to 12 carbon atoms, an unsaturated hydrocarbon group having 1 to 12 carbon atoms, a phenyl group or an acyl group, and is preferably a saturated hydrocarbon group having 1 to 4 carbon atoms. The number of carbon atoms in the saturated hydrocarbon group is 1 to 12, preferably 1 to 8, and more preferably 1 to 4. Examples of the saturated hydrocarbon group include alkyl groups and alicyclic hydrocarbon groups. The saturated hydrocarbon groups may have a substituent. Specific examples of the saturated hydrocarbon group include a methyl group, an ethyl group, a propyl group, a butyl group, and a hexyl group. Among these, a methyl group, an ethyl group, a propyl group, and a butyl group are preferable. [0072]

The number of carbon atoms of the unsaturated hydrocarbon group is 1 to 12, preferably 1 to 8, and more preferably 1 to 4. Examples of the unsaturated hydrocarbon group include alkenyl groups and alkynyl groups. The unsaturated hydrocarbon group may have a substituent. Specific examples of the unsaturated hydrocarbon group include a vinyl group, an allyl group, an ethynyl group, a 1,3-butadienyl group, and a 2-propynyl group, and among these, an allyl group is preferable. [0073]

The acyl group preferably has 1 to 8 carbon atoms and more preferably 1 to 4 carbon atoms. The acyl group may have a substituent. Specific examples of the acyl group include an acetyl group, a propionyl group, a butyryl group, and a valeryl group, and among these, a butyryl group is preferable. [0074]

In Formulae (1) and (2), n represents an integer from 1 to 3, and is preferably 2 or 3. [0075]

The compounds represented by Formulae (1) or (2) are preferably water-soluble compounds. Here, "water-soluble" compounds mean those soluble in water in an amount of 1 mass% or more. [0076]

Specific examples of the compounds represented by Formulae (1) or (2) include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoallyl ether, ethylene glycol monphenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, diethylene glycol monododecyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether and propylene glycol monobutyl ether. Among these compounds, diethylene glycol monobutyl ether and triethylene glycol monobutyl ether are preferable.

[0077]

It is sufficient that the colorant receiving layer contains at least one of the compounds represented by Formulae (1) or (2). Therefore, the colorant receiving layer may contain one or more compounds represented by Formulae (1) or (2), or may contain a combination of the compound represented by Formula (1) and the compound represented by Formula (2). When the compound represented by Formula (1) (amount: x) is combined with the compound represented by Formula (2) (amount: y), the mixing ratio (mass ratio) x:y is not limited, but is preferably 100:1 to 100:100, and more preferably 100:10 to 100:50.

Further, a total content of the compounds represented by Formulae (1) or (2) in the colorant receiving layer is preferably 0.1 to 5.0 g/m², and more preferably 0.2 to 3.0 g/m². [0078] Other components

The colorant receiving layer may contain the following components in accordance with necessity.

The colorant receiving layer may contain an anti-color fading agent such as an ultraviolet absorbent, an antioxidant, or a singlet oxygen quencher for the purpose of suppressing deterioration of the colorant.

Examples of the ultraviolet absorbent include cinnamic acid derivatives, benzophenone derivatives and benzotriazolylphenol derivatives. Specific examples of the ultraviolet absorbent include butyl α-cyano-phenylcinnamate, o-benzotriazolephenol, o-benzotriazole-p-chlorophenol, o-benzotriazole-2,4-di-t-butylphenol and o-benzotriazole-2,4-di-t-octylphenol. Hindered phenol compounds may also be used as the ultraviolet absorbent, and specifically, phenol derivatives having a branched alkyl group or groups at at least one of the second and sixth positions. [0079]

Benzotriazole ultraviolet absorbents, salicylic acid ultraviolet absorbents, cyanoacrylate ultraviolet absorbents and oxalic acid anilide ultraviolet absorbents may also be used. These ultraviolet absorbents are described in JP-A Nos. 47-10537, 58-111942, 58-212844, 59-19945, 59-46646, 59-109055 and 63-53544, JP-B Nos. 36-10466, 42-26187, 48-30492, 48-31255, 48-41572, 48-54965 and 50-10726, U.S. Patent Nos. 2,719,086, 3,707,375, 3,754,919 and 4,220,711. [0080] A fluorescent whitening agent may also be used as the ultraviolet absorbent. Examples of the fluorescent whitening agent include cumarin fluorescent whitening agents. Specific examples of the cumarin fluorescent whitening agents are described, for example, in JP-B Nos. 45-4699 and 54-5324. [0081]

Examples of the antioxidant include those described in European Patent Application Laid-open Nos. 223,739, 309,401, 309,402, 310,551, 310,552 and 459,416, German Patent Laid-open No. 3,435,443, JP-A Nos. 54-48535, 60-107384, 60-107383, 60-125470, 60-125471, 60-125472, 60-287485, 60-287486, 60-287487, 60-287488, 61-160287, 61-185483, 61-211079, 62-146678, 62-146680, 62-146679, 62-282885, 62-262047, 63-051174, 63-89877, 63-88380, 66-88381, 63-113536, [0082]

63-163351, 63-203372, 63-224989, 63-251282, 63-267594, 63-182484, 1-239282, 2-262654, 2-71262, 3-121449, 4-291685, 4-291684, 5-61166, 5-119449, 5-188687, 5-188686, 5-110490, 5-1108437 and 5-170361, JP-B Nos. 48-43295 and 48-33212 and U.S. Patent Nos. 4,814,262 and 4,980,275. [0083]

Specific examples of the antioxidant include

6-ethoxy- 1 -phenyl-2,2,4-trimethyl- 1 ,2-dihydroquinoline, 6-ethoxy- 1 -octyl-2,2,4-trimethyl- 1 ,2-dihydroquinoline, 6-ethoxy- 1 -phenyl-2,2,4-trimethyl- 1 ,2,3 ,4-tetrahydroquinoline,

6-ethoxy- 1 -octyl-2,2,4-trimethyl- 1 ,2,3 ,4-tetrahydroquinoline, nickel cyclohexanoate, 2,2-bis(4-hydroxyphenyl)propane, 1 , 1 -bis(4-hydroxyphenyi)-2-ethylhexane,

2-methyl-4-methoxy-diphenylamine and l-methyl-2-phenylindole. [0084]

The anti-color fading agents may be used singly or in combination of two or more of them. The anti-color fading agent may be water-solubilized, dispersed, emulsified or included in microcapsules.

An amount of the anti-color fading agent to be added is preferably 0.01 to 10% by mass based on a total amount of the colorant receiving layer coating solution. [0085]

The colorant receiving layer may further contain various inorganic salts in view of improving dispersibility of the inorganic pigment microparticles, and/or an acid or an alkali serving as a pH control agent.

The colorant receiving layer may further contain metal oxide microparticles having electronic conductivity in view of suppressing frictional electrification and peeling electrification of a surface of the colorant receiving layer, and any matting agent in view of decreasing frictional characteristics of a surface of the colorant receiving layer.

[0086]

Formation of colorant receiving layer

A- method for forming the colorant receiving layer in the invention is not particularly limited as far as the formed colorant receiving layer satisfies the above-described layer thickness range.

For example, as mentioned above, the mordant is preferably introduced into the colorant receiving layer during the process of applying the aforementioned cross-linking agent solution. Specifically, the colorant receiving layer is preferably formed by a method (Wet On Wet (WOW) method) in which a coating solution (colorant receiving layer coating solution) containing the compound represented by Formula (1) and/or the compound represented by Formula (2), the microparticles, and the binder is applied to a substrate, and in which a solution (cross-linking agent solution) containing the cross-linking agent and the mordant is applied to the resultant coating layer simultaneously with the application of the coating solution, or during the course of drying of the coating layer and before the coating layer exhibits a decreasing rate of dry speed, followed by curing (cross-linking) the coating layer to which the cross-linking agent solution has been applied. In this method, the colorant receiving layer coating solution fcias a pH of 8.0 to 10.0, showing alkalinity. [0087]

The colorant receiving layer in the information medium of the invention can also be obtained by simultaneously applying the colorant receiving layer coating solution and the cross-linking agent solution to a substrate with a barrier solution including only a material or materials which do not react with the cross-linking agent interposed between these solutions, followed by curing the resultant coating layers. Here, the mordant is contained in at least one of the cross-linking agent solution and the barrier solution. [0088]

In the invention, the mordant and the cross-linking agent (boron compound) are simultaneously applied to the substrate, whereby water resistance of the colorant receiving layer can be improved, as mentioned above. To the contrary, if the mordant, which is cationic, is added to the colorant receiving layer coating solution, which includes the vapor phase method silica having an anionic charge on the surface thereof, the mordant and the silica may aggregate. However, if a method is adopted in which a solution containing the mordant and the colorant receiving layer coating solution are separately prepared and applied, it is unnecessary to take aggregation of the vapor phase silica into account, which increases types of mordant which can be used. [0089]

In the invention, the colorant receiving layer coating solution containing at least the compound represented by Formula (1) and/or the compound represented by Formula (2), the vapor phase silica and the polyvinyl alcohol may be prepared, for example, in the following manner.

The vapor phase silica is added to water (for example, in an amount of 10 to 20 % by mass), and the resultant mixture is stirred with a wet type colloid mill with a rotor which can rotate at a high speed (e.g., trade name: CLEARMIX, manufactured by M Technique Co. Ltd.,) at a high rotation speed of 10,000 rpm (preferably 5,000 to 20,000 rpm) for 20 minutes (preferably 10 to 30 minutes). Thereafter, an aqueous polyvinyl alcohol solution, is added to the mixture (such that the mass of the PVA is about 1/3 of the mass of the vapor phase method silica). Furthermore, the compound represented by Formula (1) and/or the compound represented by Formula (2) are added to and dispersed in the resultant mixture under the same rotation conditions as above, whereby the colorant receiving layer coating solution can be prepared. The resulting coating solution is uniform sol, which is applied to a substrate with the following coating machine so as to form a porous colorant receiving layer having a three-dimensional network: structure.

Although conventionally known various dispersing machines such as a high rotation dispersing machine, a medium agitation type dispersing machine (e.g., a ball mill and a sand mill), an ultrasonic dispersing machine, a colloid mill dispersing machine and a high-pressure dispersing machine may be used in the dispersing treatment, a colloid mill dispersing machine or a high-pressure dispersing machine is preferably used in the invention in order to efficiently fine massive particles and disperse the resultant microparticles. [0090]

A surfactant, a pH control agent, and/or an antistatic agent may be further added to the colorant receiving layer coating solution, if necessary.

Application of the colorant receiving layer coating solution may be carried out, for example, by a contact coating method such as bar coating, roll coating, blade coating, screen coating or pad coating, or a non-contact coating method such as spray coating, spin coating, curtain coating or dip coating. Application by extrusion die coater may be also used. The colorant receiving layer coating solution is adjusted so that an application amount thereof is progressively decreased from the inside to the outer periphery, and the difference between the thickness at an inner peripheral portion of the colorant receiving layer and the thickness at an outer peripheral portion of the colorant receiving layer (Tj_n - T₀Ut) when dry is greater or equal to 1 μm. [0091]

When the colorant receiving layer coating solution is applied by spray coating, the pressure is preferably 1.013 to 2026 liPa, more preferably 50.65 to 1013 hPa, and still more preferably 101.3 to 506.5 hPa. The spread angle of the spray is preferably 1 to 120°, more preferably 10 to 60°, and still more preferably 20 to 50°. The liquid particle diameter is preferably 0.1 to 1,000 μm, more preferably 1 to 500 μm, and still more preferably 10 to 100 μm. The distance between the spray and a work (information medium) is preferably 1 to 1,000 mm, more preferably 10 to 200 mm, and still more preferably 30 to 100 mm. The temperature is preferably 10 to 40 ⁰C, more preferably 15 to 35 ⁰C, and still more preferably 20 to 30 ⁰C. The humidity is preferably 5 to 70% RH, more preferably 10 to 40% RH, and still more preferably 20 to 50% RH.

When the colorant receiving layer coating solution is applied by spray coating, a desired layer thickness distribution can be obtained by increasing the diameters of arrayed plural nozzles, in accordance with the line speed, over the inner to outer peripheral portions of the colorant receiving layer. [0092]

When the colorant receiving layer coating solution is applied by spin coating, the viscosity of each coating solution is preferably 0.1 to 10,000 mPa»s, more preferably 1 to 6,000 mPa^»s, and still more preferably 10 to 3,000 mPa^»s. The viscosity of the first liquid (colorant receiving layer coating solution) is preferably 50 to 10,000 mPa^»s, more preferably 100 to 6,000 mPa^»s, and still more preferably 200 to 3,000 mPa*s to secure sufficient thickness. The viscosity of the second liquid (cross-linking agent solution) is preferably 0.1 to 1,000 mPa^»s, more preferably 1 to 500 mPa^#s, and still more preferably 2 to 300 mPa^«s to secure uniformity of the resultant coating layer. The number of rotations during dispensing is preferably 10 to 1,000 rpm, more preferably 50 to 600 rpm, and still more preferably 100 to 400 rpm. During sweeping, the number of rotations is gradually raised either step by step or smoothly, and is specifically, preferably 100 to 10,000 rpm, more preferably 200 to 5,000 rpm, and still more preferably 300 to 3,000 ipm. As for the shape of a nozzle, the length of the nozzle is preferably 1 to 100 mm, more preferably 5 to 50 mm, and still more preferably 10 to 30 mm. The inside diameter of the nozzle is preferably 0.1 to 5 mm, more preferably 0.3 to 3 mm, and still more preferably 0.5 to 2 mm. The thickness of the nozzle is preferably 0.1 to 1 mm, and more preferably 0.2 to 0.5 mm. The nozzle may be arranged aslant along the flow. The distance between the nozzle and a work is preferably 0.5 to 100 mm, more preferably 1 to 50 mm, and still more preferably 2 to 20 mm. The temperature is preferably 10 to 40 ⁰C, more preferably 15 to 35 ⁰C, and still more preferably 20 to 30 ⁰C. The humidity is preferably 5 to 70% RH, more preferably 10 to 40% RH, and still more preferably 20 to 50% RH.

When the colorant receiving layer coating solution, is applied by spin coating, a process in which the rotation speed is gradually raised during addition of the coating solution can be utilized in order to obtain a desired layer thickness distribution over an inner peripheral portion to an outer peripheral portion of the colorant receiving layer.

When a second solution (cross-linking solution) described below is applied by spin coating, in order to assure an evenness of the coated film a viscosity of the second solution is preferably in a range of 0.1 to 1,000 mPa.s, more preferably in a range of 1 to 500 mPa.s, and still more preferably in a range of 2 to 300 mP.^»s. [0093]

After the colorant receiving layer coating solution is applied to the substrate, the cross-linking agent solution is applied to the resultant coating layer. The cross-linking agent solution may be applied before the coating layer exhibits a decreasing rate of dry speed. That is, the cross-linking agent and the mordant are introduced in the colorant receiving layer during a period starting immediately after the colorant receiving layer coating solution has been applied and ending before the coating layer exhibits a decreasing rate of dry speed. [0094]

Here, the term "before the coating layer exhibits a decreasing rate of dry speed" generally indicates a period starting immediately after the application of the coating solution and ending several minutes just after the application. During this period, the coating layer exhibits a constant rate of dry speed, which means that the content of the solvent in the applied coating layer decreases in proportioa with time. The period in which a constant rate of dry speed is observed is described in Chemical Engineering Handbook (pp. 707-712, published by Maruzen Co., Ltd., October 25, 1980). [0095]

As mentioned above, after the colorant receiving layer coating solution is applied, the coating layer is dried till the coating layer exhibits a decreasing rate of dry speed. The details of drying conditions are described below. [0096]

The colorant receiving layer may be dried by any drying method such as natural drying, hot air drying, low-temperature set diying, infrared/far-infrared drying, high-frequency drying, or oven drying.

In a case of natural drying is employed, a drying time of the coating layer is preferably 0.1 to 10,000 seconds, more preferably 1 to 1,000 seconds, and still more preferably 10 to 500 seconds. A drying temperature is preferably 0 to 40 ⁰C, more preferably 10 to 35 ⁰C, and still more preferably 20 to 30 ⁰C. A drying humidity is preferably 10 to 70% RH, more preferably 20 to 60% RH, and still more preferably 30 to 50% RH. [0097]

In a case of hot air drying is employed, a drying time of the coating layer is preferably 0.1 to 5,000 seconds, more preferably 1 to 1,000 seconds, and still more preferably 10 to 500 seconds. A drying temperature is preferably 40 to 200 ⁰C, more preferably 60 to 150 ⁰C, and still more preferably 80 to 130 ⁰C. A drying humidity is preferably 0.01 to 50% RH, more preferably 0.1 to 30% RH, and still more preferably 1 to 20% RH. [0098]

In a case of low-temperature set drying is employed, a drying temperature of the coating layer is preferably 2 to 25 °C, and more preferably 5 to 15 ⁰C, and still more preferably 80. to 130 ⁰C. A drying humidity is preferably 10 to 50% RH, and more preferably 10 to 30% RH.

It is preferable that the temperature and humidity are raised either gradually or step by step from a low temperature and low humidity environment to a high temperature and high humidity environment in the course of drying. In addition, it is preferable that an air velocity used for drying is 3m/s or more in a direction parallel to the coating layer after the point of time when the coating layer exhibits a decreasing drying rate. [0099]

In the case of infrared/far-infrared drying is employed, a drying time of the coating layer is preferably 0.1 to 1,000 seconds, more preferably 1 to 500 seconds, and still more preferably 10 to 300 seconds. A power is preferably 10 to 2,000 W, more preferably 50 to 1,500 W₅ and still more preferably 100 to 1,000 W.

A drying condition in a case of high-frequency drying is similar to that in the case of infrared/far-infrared drying. [0100] In a case of oven drying is employed, a drying time of the coating layeτ is preferably 0.1 to 1,000 seconds, more preferably 1 to 500 seconds, and still more preferably 10 to 300 seconds. [0101]

Examples of a method of applying the cross-linking agent before the coating layer exhibits a decreasing rate of dry speed include (1) a method in which the cross-linking agent solution is applied onto the coating layer, (2) a method in which, the solution is sprayed, and (3) a method in which a substrate on which the coating layer has been formed is dipped in the cross-linking agent solution. [0102]

In the above method (1), known coating methods may be utilized, and examples thereof include methods which use a curtain flow coater, an extrusion die coater, an air doctor coater, a bread coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater, or a bar coater. Among these, methods which use an extrusion die coater, a curtain flow coater, or a bar coater, are preferable in view of avoiding direct contact of coaters with the coating layer. [0103]

The amount of the cross-linking agent solution containing at least the cross-linking agent and the mordant and applied to the colorant receiving layer is such that the amount of the cross-linking agent applied is generally 0.01 to 10 g/m² and preferably 0.05 to 5 g/m². [0104]

After the cross-linking agent solution is applied, the resultant is generally dried and cured by being heated at a temperature in a range of 40 to 180 ⁰C for a period of 0.5 to 30 minutes to the coating layer. It is preferable that heating is conducted at a temperature in a range of 40 to 150 ⁰C for a period of 1 to 20 minutes.

When borax or boric acid is used as the boron compound to be contained in the cross-linking agent solution, it is preferable that heating is conducted at a temperature in a range of 60 to 100 ⁰C for a period of 5 to 20 minutes. [0105]

Also, the cross-linking agent coating solution may be applied simultaneously with the application of the colorant receiving layer coating solution.

In this case, the colorant receiving layer coating solution and the cross-linking agent solution can be simultaneously applied (multilayer application) to a substrate such that both solutions are in contact with the substrate. Thereafter, the resultant coating layers are dried and cured, whereby the colorant receiving layer can be formed. [0106]

The simultaneous application (multilayer application) may be accomplished by a coating method using an extrusion die coater or curtain flow coater. After the simultaneous application, the formed coating layer(s) is(/are) dried. At this time, the coating layer is dried by heating at a temperature in the range of 40 to 150 ⁰C for a period of 0.5 to 10 minutes and preferably at a temperature in a range of 40 to 100 ⁰C for a period of 0.5 to 5 minutes.

When borax or boric acid is used as the boron compound to be contained in the cross-linking agent solution, it is preferable to heat the coating layer at a temperature in a range of 60 to 100 ⁰C for a period of 5 to 20 minutes. [0107]

When an extrusion die coater is used to carry out the simultaneous application (multilayer application), the two coating solutions simultaneously discharged are formed into layers in the vicinity of the outlet of the extrusion die coater, namely, before they are transferred to a substrate. In this state, they are applied as layers on the substrate. The two layer coating solutions which have been multi-layered easily cause cross-linking reaction at the boundary thereof. Accordingly, these two discharged solutions are mixed and easily thicken in a portion of the extrusion die coater which portion is near the outlet. This may hinder coating operation. Therefore, when these two solutions are simultaneously applied as mentioned above, a barrier layer solution (intermediate layer solution) including only a material or materials which do not react with the cross-linking agent is preferably interposed between the two solutions. In other words, it is preferable that the colorant receiving layer coating solution, the barrier layer solution, and the cross-linking agent solution containing the cross-linking agent and the mordant are simultaneously applied to carry out simultaneous triple layer application. [0108]

The material(s) of the barrier layer solution can be any substance which does not react with the cross-linking agent and which can form a liquid layer. Examples of the barrier layer solution include water, and an aqueous solution containing a trace of a water-soluble resin that does not react with the cross-linking agent. The water-soluble resin is used in view of, for example, viscosity-increasing, and selected in consideration of coatability. Examples of the water-soluble resin include polymers such as hydroxypropylmethyl cellulose, methyl cellulose, hydroxyethylmethyl cellulose, polyvinylpyrrolidone and gelatin.

It is noted that the barrier layer solution may further contain the mordant. [0109]

The colorant receiving layer in the invention may be formed by a method in which: a coating solution, which is obtained by adding to and redispersing in an aqueous dispersion including the microparticles and a dispersing agent each of a solution (first solution) containing the compound represented by Formula (1) and/or the compound represented by Formula (2) and the binder and another solution (second solution) containing the cross-linking agent and the mordant; the coating solution is applied onto the base layer so as to form the coating layer; and the coating layer is cured. A pH of the coating solution used to form the colorant receiving layer in this method is 2.5 to 4.0, and the coating solution shows acidity. Use of this method improves glossiness and density of a printed image and is therefore preferable. [0110]

Specific examples of a drying method and condition for this method include those described in "Chemistry and Technology of Water-Soluble Polymers" edited by C. A. Finchi (1993). [0111]

As the dispersing agent, a cationic polymer may be used. Preferable examples of the cationic polymer include a homopolymer of a monomer having any of primary to tertiary amino groups and salts thereof and a quaternary ammonium base, and a copolymer or a condensed polymer formed of the monomers and any other monomers. The dispersing agent is preferably used in a form of a water-soluble polymer. [0112]

A molecular weight of the dispersing agent is preferably 1,000 to 200,000, and more preferably 3,000 to 60,000 in terms of a weight average molecular weight. When the molecular weight is smaller than 1,000, dispersibility of the dispersing agent may become insufficient. When the molecular weight exceeds 200,000, a viscosity of the aqueous dispersion may increase. An amount of the dispersing agent is preferably 1% to 30% and more preferably 3% to 20% with respect to the amount of vapor phase silica. When the amount is less than 1%, inferior dispersibility may be obtained. When the amount exceeds 30%, color density may decrease at the time that an image is formed on the colorant receiving layer. [0113]

When the aqueous dispersion including the microparticles and the dispersing agent is prepared, an aqueous dispersion of the microparticles may be prepared in advance and added to an aqueous solution of the dispersing agent. Alternatively, the aqueous solution of the dispersing agent may be added to the aqueous dispersion of the microparticles, or the aqueous dispersion and the aqueous solution may be simultaneously mixed. Also, powder of the microparticles rather than the aqueous dispersion thereof may be added to the aqueous solution of the dispersing agent.

After the microparticles is mixed with the dispersing agent, the resultant mixed solution may be stirred with a dispersing machine to fine particles contained therein. Thus, an aqueous dispersion containing particles with an average particle diameter of 50 to 300 nm can be obtained. Although conventionally known various dispersing machines such as a high rotation dispersing machine, a medium agitation type dispersing machine (e.g., a ball mill and a sand mill), an ultrasonic dispersing machine, a colloid mill dispersing machine and a high-pressure dispersing machine may be used as the dispersing machine used to obtain the aqueous dispersion, a colloid mill dispersing machine or a high-pressure dispersing machine is preferably used in order to efficiently fine massive particles and disperse the resultant microparticles. [0114]

Examples of the solvent used in the coating solution include water, an organic solvent, and a mixed solvent thereof. Examples of the organic solvent include alcohols such as methanol, ethanol, n-propanol, iso-propanol and methoxypropanol, ketones such as acetone and methyl ethyl ketone, tetrahydrofuran, acetonitrile, ethyl acetate and toluene. [0115]

A coating solution, which is obtained by adding to and redispersing in an aqueous dispersion including the microparticles and a dispersing agent each of a solution (first solution) containing the compound represented by Formula (1) and/or the compound represented by Formula (2) and the binder and another solution (second solution) containing the cross-linking agent and the mordant, can be applied onto the base layer in the same manner as that for coating the colorant receiving layer coating solution. [0116] Method for producing Disc-shaped Information Medium

The disc-shaped information medium of the present invention is preferably produced in accordance with the following method for producing a disc-shaped information medium.

Namely, the method for producing the disc-shaped information medium of the present invention is characterized by comprising forming a coating layer by applying, onto the undercoat layer, a coating solution containing the microparticles and the binder using an extrusion die coater with increasing of the flow rate at a discharging port of the extrusion die coater from an inner circumferential portion to the outer circumferential portion of the medium so as to form the colorant receiving layer. In one embodiment, the flow rate accords with the linear velocity of the extrusion die coater. [0117]

The coating solution that is coated by using an extrusion dye coater and used in the method for manufacturing the disk-shaped recording medium of the invention may be any solution such as the colorant receiving layer coating solution used in the WOW method or the coating solution which is obtained by adding to and redispersing in an aqueous dispersion including the microparticles and a dispersing agent each of a solution (first solution) containing the compound represented by Formula (1) and/or the compound represented by Formula (2) and the binder and another solution (second solution) containing the cross-linking agent and the mordant.

Methods for applying the cross-linking agent, methods for curing (hardening) the coating layer, and conditions for curing the coating layer may be appropriately selected from the above-described methods accounting for kinds of the coating solution. [0118]

If this kind of coating solution is coated with an extrusion die coater with an application amount (flow rate of the coating solution at a discharging port of the extrusion die coater) being changed by changing the diameter of the discharging port (for different radial positions of the information medium), then it is easy to form a colorant receiving layer that satisfies the above described layer thickness conditions.

Specifically, the extrusion die is set in close proximity when carrying out coating within a radial positional range from 25mm to 55mm, and it is preferable to design the width (slit width) of the discharging port such that the width thereof at the 55mm position is 2 to 11 times the width thereof at the 25mm position. This design allows adjustment of the application amount (flow rate at the discharging port), thereby allowing formation of the colorant receiving material having a desired film thickness. [0119]

The colorant receiving layer is thus formed on the substrate. Thereafter, the colorant receiving layer may be calendered with, for example, a super calender or a gloss calender. Specifically, the colorant receiving layer may be made to pass between a roll nip while the colorant receiving layer is being heated and pressurized. This makes it possible to improve surface smoothness, glossiness, transparency and coating layer strength. However, the calendering treatment sometimes causes a reduction in percentage of void (namely, ink absorbing ability may deteriorate) and it is therefore necessary to conduct calendering with a setting of a condition in accordance with which the degree of reduction in percentage of void is low.

[0120]

A roll temperature for conducting the calendering treatment is preferably 30 to 150 ⁰C, and more preferably 40 to 100 ⁰C.

A linear load between rolls for conducting the calendering treatment is preferably 50 to 400 kg/cm, and more preferably 100 to 200 kg/cm. [0121]

A pore diameter of the colorant receiving layer is preferably 0.005 to 0.030 μm, and more preferably 0.01 to 0.025 μm in terms of median diameter.

The percentage of void and the pore median diameter may be measured with a mercury porosimeter (trade name: PORESIZER™ 9320-PC2, manufactured by Shimadzu Corporation). [0122]

The colorant receiving layer preferably has high transparency. As for a measure of transparency, the haze value of the colorant receiving layer formed on a transparent film substrate is preferably 30% or less, and more preferably 20% or less.

The haze value may be measured with a haze meter (trade name: HGM-2DP, manufactured by Suga Test Instrument Co., Ltd.). [0123]

The information medium of the invention can exhibit a glossiness of 30% or more at 60°. The glossiness may be measured with a digital variable gloss meter (trade name: UGV-50DP, manufactured by Suga Test Instrument Co., Ltd.) or the like. [0124]

As is understood from the above, the disk-shaped information medium having little warpage can be obtained by applying the colorant receiving layer containing the microparticles, the binder and the cross-linking agent in the above-described layer-thickness condition.

In addition, unlike those made of an ultraviolet-curable resin, the colorant receiving layer of the information medium of the invention needs a decreased amount of ultraviolet rays to be irradiated to the information medium and recording characteristics such as jitter can be improved as mentioned above. Also, unlike the ultraviolet-curable resin, the colorant receiving layer does not irritate skin and therefore has high handling safety. [0125] Base layer The information medium of the invention includes a base layer between the colorant receiving layer and the substrate. When the information medium has a highly opaque base layer, it has diffusibility close to that of paper, improving image quality. In particular, when the information medium has a white base layer, color reproducibility can be improved. When the information medium has a base layer with high glossiness, an image formed thereon is like a glossy photograph. When the information medium has a base layer with a highly matting property, an image formed thereon is like a matt photograph. When various colors are used for the base layer, images having a variety of impressions can be formed. In the case of a fluorescent base layer, a fluorescent image can be made. Although there is no particular limitation to a method of forming such a base layer, it is preferable to form a radiation-curable resin layer by screen printing from the viewpoint of productivity. The radiation-curable resin is one cured by an electromagnetic wave such as ultraviolet rays, electron beams, X-rays, γ-rays or infrared rays. Among these radiation rays, ultraviolet rays and electron beams are preferable as the radiation. [0126]

The thickness of the base layer is preferably 0.1 to 100 μm, more preferably 1 to 50 μm, and most preferably 3 to 20 μm. [0127] Intermediate layer

The information medium of the invention may have an intermediate layer between the colorant receiving layer and the base layer. When the intermediate layer has high ink absorbing ability, the amount of ink which the information medium can receive is increased, and color density and image quality can be improved at the time of image printing. Alternatively, the intermediate layer can be provided between the base layer and the substrate. In this case, it is possible to improve adhesion between the base layer and the substrate and to control warpage of the entire information medium. [0128]

The thickness of the intermediate layer is preferably 0.1 to 100 μm, more preferably 1 to 50 μm, and most preferably 3 to 20 μm. [0129] Surface layer

The information medium of the invention may have a surface layer on or above the colorant receiving layer. Providing the surface layer can further improve a surface strength and preservability of a printed image. The surface layer is required to receive ink, or has a characteristic to quickly pass ink through the surface layer. [013O]

The thickness of the surface layer is preferably 0.01 to 100 μm, more preferably 0.1 to 10 μm, and most preferably 0.5 to 5 μm. [013 1]

Hereinafter, the substrate and each of layers used in the invention will be explained. The described layer structures and materials are only examples and the invention is not limited by them. [0132] Substrate

The substrate can be made of any material selected from various materials which are used as substrate materials of conventional optical recording media.

Specific examples of the substrate material include glass; polycarbonates; acrylic resins such as polymethyl methacrylate; vinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymers; epoxy resins; amorphous polyolefins; polyesters; and metals such as aluminum. These materials may be combined, if desired.

Among the above materials, amorphous polyolefins and polycarbonates are preferable and polycarbonates are particularly preferable from the viewpoints of humidity resistance and low cost. The thickness of the substrate is preferably 0.5 to 1.2 mm, and more preferably 0.6 to 1.1 mm. [0133]

A guide groove or grooves for tracking, or an irregularity or irregularities (pre-groove) representing information such as address signals are formed on the substrate.

In a case of a medium in which information is recorded with a bluish violet laser, a track pitch of the pre-groove(s) is preferably in a range of 200 to 800 nm, more preferably in a range of 200 to 500 nm, and still more preferably in a range of 200 to 400 nm.

Further, a depth of the pre-groove(s) (groove depth) is preferably in a range of 10 to 180 nm, and more preferably in a range of 20 to 150 nm.

Moreover, a half breadth of the pre-groove(s) is preferably in a range of 200 to 400 nm, more preferably in a range of 230 to 380 nm, and still more preferably in a range of 250 to 350 nm. [0134]

In a case of DVD-Rs or DVD-RWs, a track pitch of a pre-groove(s) is preferably in a range of 300 to 900 nm, more preferably in a range of 350 to 850 nm, and still more preferably in a range of 400 to 800 nm.

Further, the depth of the pre-groove(s) (groove depth) is preferably in a range of 100 to 160 nm, more preferably in a range of 120 to 150 nm, and still more preferably in a range of 130 to 140 nm.

Moreover, a half breadth of the pre-groove(s) is preferably in a range of 200 to 400 nm, more preferably in a range of 230 to 380 nm, and still more preferably in a range of 250 to 350 nm. [0135]

In a case of CD-Rs or CD-RWs₅ a track pitch of a pre-groove(s) is preferably in a range of 1.2 to 2.0 μm, more preferably in a range of 1.4 to 1.8 μm, and still more preferably in a range of 1.55 to 1.65 μm.

Further, a depth of the pre-groove(s) (groove depth) is preferably in a range of 100 to 250 nm, more preferably in a range of 150 to 230 nm, and still more preferably in a range of 170 to 210 nm.

Moreover, a half breadth of the pre-groove(s) is preferably in a range of 400 to 650 nm, more preferably in a range of 480 to 600 nm, and still more preferably in a range of 500 to 580 nm. [0136] Recording layer

In a case of CD-Rs or DVD-Rs, a recording layer is formed in the following manner. A dye serving as a recording material and a binder are dissolved in a proper solvent and then the resulting coating solution is applied to the surface of the substrate, on which surface the pre-groove is formed, by a spin coating method to form a coating layer, followed by drying.

The temperature in the spin coating method is preferably 23 ⁰C or more, and more preferably 25 ⁰C or more. Although there is limitation to the upper limit of the temperature, trie temperature must be lower than the flash point of the solvent and is preferably 35 ⁰C.

When the temperature is lower than 23 ⁰C, the drying rate of the solvent slows down and therefore an intended dye layer thickness (thickness of the recording layer) my not be obtained. Moreover, the application and drying require more time, reducing productivity. [0137]

Examples of the dye include a cyanine dye, an oxonol dye, a metal complex dye, an azo dye and a phthalocycanine dye. Among these dyes, a phthalocycanine dye is preferable. Dyes described in JP-A Nos. 4-74690, 8-127174, 11-53758, 11-334204, 11-334205, 11-334206, 11-334207, 2000-43423, 2000-108513 and 2000-158818 are also preferably used. [0138]

Examples of the solvent of the coating solution include esters such as butyl acetate, ethyl lactate and 2-πiethoxyethyl acetate; ketones such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone; chlorinated hydrocarbons such as dichloromethane, 1,2-dicliloroethane and chloroform; amides such as dimethylformamide; hydrocarbons such as methylcyclohexane; ethers such as tetrahydrofuran, ethyl ether and dioxane; alcohols such as ethanol, n-propanol, iso-propanol, n-butanol and diacetone alcohol; fluorinated solvents such as 2,2,3,3-tetrafiuoropropanol; ^d glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and propylene glycol monomethyl ether.

These solvents may be used singly or in combination of two or more of them in consideration of solubility of the recording material. Various additives such as an antioxidant, a UV absorbent, a plasticizer and a lubricant may be added to the coating solution according to the purpose. [0139]

When the coating solution includes a binder, examples of the binder include natural organic polymer materials such as a gelatin, cellulose derivative, dextran, rosin and rubber; and synthetic organic polymers such as hydrocarbon resins, e.g., polyethylene, polypropylene, polystyrene and polyisobutylene, vinyl resins, e.g., polyvinyl chloride, polyvinylidene chloride and polyvinyl chloride/polyvinyl acetate copolymer, acrylic resins, e.g., poly(methyl acrylate) and poly(methyl methacrylate), polyvinyl alcohol, chlorinated polyethylene, epoxy resins, butyral resins, rubber derivatives and initial condensates of thermosetting resins such as phenol/formaldehyde resins. When the binder is used as one of materials of the recording layer, the amount of the binder is usually 0.01 to 50 times, and preferably 0.1 to 5 times as much as that of the recording material in terms of mass ratio. The concentration of the recording material in the coating solution prepared in the above manner is generally in the range of 0.01 to 10 % by mass, and preferably 0.1 to 5 % by mass. [0140]

The coating method can be a spin coating method as mentioned above. An apparatus used in this method can be those conventionally known.

The recording layer may be formed as a single layer or multi layers. A thickness thereof is generally in a range of 20 to 500 nm, preferably in a range of 30 to 300 nm, and more preferably in a range of 50 to 100 nm. [0141]

The recording layer may contain various anti-color fading agent(s) to improve light fastness of the recording layer.

A singlet oxygen quencher is generally used as the anti-color fading agent. Examples of the singlet oxygen quencher include those described in publications such as already known patent specifications.

Specific examples of the singlet oxygen quencher include those described in JP-A Nos. 58-175693, 59-81194, 60-18387, 60-19586, 60-19587, 60-35054, 60-36190, 60-36191, 60-44554, 60-44555, 60-44389, 60-44390, 60-54892, 60-47069, 63-209995 and 4-25492, JP-B Nos. 1-38680 and 6-26028, German Patent No. 350,399 and Journal of Japan Chemical Society, the October issue, 1992, page 1141. [0142]

An amount of the singlet oxygen quencher is usually in a range of 0.1 to 50 % by mass, preferably in a range of 0.5 to 45 % by mass, more preferably in a range of 3 to 40 % by mass, and still more preferably in a range of 5 to 25 % by mass based on the amount of the dye. [0143]

In a case of CD-RWs or DVD-RWs, the recording layer is preferably made of an optical recording material whose phase can change, which is constituted of at least Ag, Al₅ Te and Sb, and which can take at least two states including a crystal state and an amorphous state. Such a recording layer can be formed by a known method.

A known dielectric layer may be formed on the recording layer in accordance with necessity. [0144] Optical reflecting layer

After the recording layer is formed, a light reflecting layer is formed on the recording layer by vapor deposition, sputtering or ion plating. When the light reflecting layer is formed, a mask is usually used, whereby an area where the light reflecting layer is formed can be controlled. [0145]

The light reflecting layer contains a light reflecting material having a high reflectance with respect to laser light. The reflectance is preferably 70% or more.

Examples of the light reflecting material having a high reflectance include metals and semimetals such as Mg, Se, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, RIi, Pd, Ir, ?t, Cu, Ag, Au, Zn₅ Cd, Al, Ga, In, Si, Ge, Te, Pb, Po, Sn and Bi, and stainless steel. These light reflecting materials may ^"be used singly, in combination of two or more of them, or can be used as an alloy. Among these materials, Cr, Ni, Pt, Cu, Ag, Au, Al and stainless steel are preferable, Au, Ag₃ Al and alloys of these metals are more preferable, and Au and Ag and alloys of these metals are most preferable.

A thickness of the light reflecting layer is usually in a range of 10 to 300 nm, and preferably in a range of 50 to 200 nm. [0146] Protective layer and Protective substrate

After the light reflecting layer is formed, a protective layer is formed on the light reflecting layer.

The protective layer is formed by a spin coating method. Use of the spin coating method makes it possible to form a protective layer without damaging the recording layer (e.g., dissolution of dyes and chemical reaction between the dye and the protective layer materials). The number of rotations in the spin coating is preferably 50 to 8,000 rpm, and more preferably 100 to 5,000 rpm from the viewpoint of formation of a uniform layer and prevention of any damage to the recording layer.

When a radiation-curable resin (ultraviolet ray-curable resin) is used as the protective layer material, the protective layer is formed by a spin coating method and then irradiated with ultraviolet rays from an ultraviolet ray radiation lamp (metal halide lamp) to cure the ultraviolet ray-curable resin.

The protective layer can be allowed to stand for a fixed time before the resin is cured in order to prevent formation of a protective layer having uneven thickness. [0147]

The protective layer prevents ingress of moisture and generation of scratches. The material of the protective layer is preferably a radiation-curable resin, a visible ray-curable resin, a thermosetting resin or silicon dioxide, and particularly preferably a radiation-curable resin. Examples of the radiation-curable resin include ultraviolet ray-curable resins such as "SD-640" (trade name, manufactured by Dainippon Ink and Chemicals Incorporated), and "SD-347" (trade name, inanufactured by Dainippon Ink and Chemicals Incorporated), "SD-694" (trade name, manufactured by Dainippon Ink and Chemicals Incorporated), or "SKCD 1051" (trade name, manufactured by SKC) may also be used. A thickness of the protective layer is preferably in a range of 1 to 200 μm, and more preferably in a range of 50 to 150 μm.

In a layer structure in which the protective layer is used as a laser optical path, the protective layer must have transparency. Here, the term "transparency" means that the protective layer is transparent (transmittance: 90°/o or more) enough to transmit recording light and reproducing light. [0148]

In a case of DVD-Rs and DVD-RWs₅ an adhesive layer made of an ultraviolet ray-curable resin and a protective substrate having a thickness of about 0.6 mm and made of the similar material as that of the substrate are laminated on the light reflecting layer in place of the protective layer.

That is, after the light reflecting layer is formed, an ultraviolet ray-curable resin (e.g., SD640 as described above) is applied to the light reflecting layer by a spin coating method to form an adhesive layer having a thickness of 20 to 60 μm. Then, a polycarbonate substrate (thickness: 0.6 mm) serving as a protective substrate is put on the formed adhesive layer, and the resultant is irradiated with ultraviolet rays from the substrate side to cure the ultraviolet ray-curable resin and bond these layers and the protective substrate. [0149]

The information medium, which has a laminate including on the substrate the recording layer, the light reflecting layer, and the protective layer or the adhesive layer and the protective substrate (dummy substrate), is manufactured in the above manner.

The information medium of the invention may be applied to information media which have a track pitch narrower than that of conventional DVDs and which can record and reproduce information with laser light having a smaller wavelength than laser light used for current DVDs, by appropriately selecting the track pitch of the pre-groove formed on the substrate or the materials of the recording layer. [0150]

As for the thickness of the information medium of the invention, the lower limit of thickness is preferably 0.3 mm, more preferably 0.5 mm, and still more preferably 0.7 mm. Also, the upper limit of thickness is preferably 100 mm, more preferably 20 mm, and still more preferably 5 mm. When the information medium is too thin, defects may occur by bending it. When the information medium is too thick, inferior removability may be obtained.

[0151]

EXAMPLES

The invention will be explained in more detail by way of examples, which are not intended to limit the invention. In the examples, all designations of parts and % indicate parts by mass and mass percentage (% by mass), respectively. [0152] Examples 1 to 3 and Comparative Example 1 Production of a disk substrate

A polycarbonate substrate (trade name: PANLIGHT AD5503, manufactured by Teijin Limited, thickness: 0.6 mm, outer diameter: 120 mm, inner diameter: 1 5 mm) formed by injected molding machine and having a spiral groove (land) and LPP* on the surface thereof was prepared. A depth of the track, a track width, and a track pitch were 140 nm, 310 nm, and 740 nm, respectively. [0153]

Ig of a die mixture containing an oxonol die (A) and an oxonol die (B) shown below at the mass ratio of 65:35 was dissolved in 100 ml of 2,2,3,3-tetrafluoro-pxopanol so as to prepare a recording layer forming coating solution. The recording layer forming coating solution was coated by spin coating on a grooved surface of the obtained substrate while changing a revolution speed from 300 to 3000 rpm. and was dried so as to form a recording layer. Thicknesses of the recording layer was measured by observing a cross section of the recording layer with an SEM, and was found to be 150 nm at a groove and 110 nm at a land portion. [0154] Oxonol dye (A) Oxonol dye (B)

[0155]

Subsequently, a light reflection layer, which consists of Ag and has a thickness of about 150 nm, was formed on the recording layer by DC sputtering in an Ar atmosphere. The pressure in the chamber was 0.5 Pa. [0156]

Further, a UV curable resin (trade name: SD-318, manufactured by Dainippon Ink and Chemicals Inc.) was dispensed on the light reflection layer, in a ring shape. Furthermore, a separately-prepared disc-shaped protective substrate (diameter: 120 mm, thickness: 0.6 mm) made of polycarbonate was placed thereon with center alignment, and was rotated at a revolution speed of 5000rpm for 3 seconds, and a UV curable resin (trade name: SD-640, manufactured by Dainippon Ink and Chemicals Inc.) was spread out over the entire surface thereof and spun so as to spin off an excessive amount of UV curable resin. When the UV curable resin had spread out over the entire surface, UV light was irradiated thereon by using a high pressure mercury vapor lamp so as to cure the UV curable resin. In this manner, the disc-shaped protective substrate was affixed to the substrate having the recording layer and the light reflection layer formed thereon. The thickness of the affixing layer was 25 μm, and it was affixed without air bubbles entering therebetween. [0157]

Subsequently, a printable layer was formed on a surface of the disc-shaped protective substrate opposite to the laser light incident surface thereof in the following manner. [0158]

A UV curable ink (trade name: WHITE No .3, manufactured by Teikoku Printing Inks Mfg. Co., Ltd.) was further printed on the disc-shaped protective substrate by screen printing. Thereafter, ultra-violet light at 80W/cm² was irradiated thereon by using a metal halide lamp so as to cure the UV curable ink. Two undercoat layers (white layers), each of which having a thickness of 8 μm were formed and thus the total thickness of two undercoat layers was 16 μm. The screen used was a mesh screen of 300 lines per inch made of TETORON® having a yarn diameter of 31 μm and a mesh opening of 38 μm. [0159]

Next, the following process was carried out to form a colorant receiving layer on the base layer. [0160] Preparation of colorant receiving layer coating solution

(1) Vapor phase silica microparticles and (2) deionized water, which are described in the following composition, were mixed and the resultant was stirred for 20 minutes at 10,000 rpm with a high-speed rotary colloid mill (trade name: CLEARMIX, manufactured by M technique Co., Ltd.). Then, a first solution containing (3) polyoxyethylene lauryl ether, (4) an aqueous 9 % polyvinyl alcohol solution and (5) diethylene glycol monobutyl, and a second solution containing (6) boric acid, (7) mordant and (8) deionized water were respectively added to the resultant water dispersion, and the mixture was dispersed in the same conditions as above to prepare a colorant receiving layer coating solution A.

A ratio by mass of the silica microparticles to the water-soluble resin (PB ratio of the component (1): the component (4)) was 3.5:1 and a pH of the colorant receiving layer coating solution A was 3.4, and the colorant receiving layer showed acidity. [0161] Composition of Colorant receiving layer coating solution A

(1) Vapor phase method silica microparticles (inorganic pigment microparticle) (average primary particle diameter: 7 nm) (trade name: AEROSIL® 300, manufactured by Nippon Aerosil Co., Ltd.) 10.0 parts

(2) Deionized water 55.2 parts Composition of First solution

(3) Polyoxyethylene lauryl ether (surfactant) (trade name: EMULGEN 109P (10 %), manufactured by Kao Corporation, HLB value: 13.6) 3.5 parts

(4) 9 % aqueous solution of polyvinyl alcohol (water-soluble resin) (trade name: PVA420, manufactured by Kuraray Co., Ltd., degree of saponification: 81.8 %, degree of polymerization: 2,000) 31.7 parts

(5) Diethylene glycol monobutyl ether (compound represented by Formula (I))

0.5 parts Composition of Second solution

(6) Boric acid (concentration: 6 %) (cross-linking agent) 10.4 parts

(7) Mordant (trade name: PAS-F5000 (concentration: 20 %), manufactured by Nitto Boseki Co.,Ltd.) 2.5 parts

(8) Deionized water 5.3 parts [0162]

Formation of Colorant Receiving Layer

After having conducted corona discharge treatment on a surface of the undercoat layer of the above-described information medium, the colorant receiving layer coating solution A obtained as above was coated on the undercoat layer by using an extrusion die coater. While coating the coating solution A, a slit width (a width of the discharging port) of the extrusion die coater for discharging the coating solution was adjusted as shown in Table 1, thereby adjusting the discharged flow amount of the colorant receiving layer coating solution A.

Thereafter, the colorant receiving layer thus coated was dried in an environment of 5 ⁰C and 10% RH in low-temperature low-humidity storage, until the flowability of the coating solution at the surface was suppressed. The coating layer exhibited a constant drying rate during this drying period. Immediately after this initial drying, the coating layer was further dried with a hot air drier for 10 minutes in an environment of 2O⁰C and 20% RH (air velocity: 4 m/sec). Thus, an information medium that is provided with the colorant receiving layer having a dry film thickness as shown in Table 1 was produced.

[0163]

Evaluation

The information media of Examples 1 to 3 and Comparative Example 1 obtained as described above were evaluated by the following methods. [0164] Evaluation of Warping

Tilt in a radial direction was measured for each of the information media of Examples 1 to 3 and Comparative Example 1. The measurement was conducted at 512 points on an outer peripheral portion (r = 55 mm) of the colorant receiving layer by using a DVD mechanical characteristic evaluation apparatus DLD4000 (trade name, manufactured by Japan E.M. Co.,Ltd.). Average values thereof are shown in Table 1.

It should be noted that, with respect to information media, a tilt level of 0.8 degree or less causes no problem in practical use. [0165]

Table 1

[0166]

As are shown in Table 1, the disc-shaped information media of Examples 1 to 3 showed values of tilt in the radial direction which produce no practical problems and little warping.

In contrast, the disc-shaped information media of Comparative example 1 showed a large value of tilt in the radial direction and warping which cannot be applied to practical use.

Claims

CLAIMS:

1. A disc-shaped information medium comprising a printable layer which comprises an undercoat layer and a colorant receiving layer, wherein: the colorant receiving layer comprises microparticles, a binder and a cross-linking agent; a thickness of the colorant receiving layer progressively decreases from an inner circumferential side to an outer circumferential side thereof; and a relationship between a thickness (Tj_n) at an inner peripheral portion of the colorant receiving layer and a thickness (T_out) at an outer peripheral portion of the colorant receiving layer satisfies the equation of (Tj_n - T_out) ≥ 1 μm.

2. The disk-shaped information medium of claim I₅ wherein: the microparticles comprise at least one type of particle selected from the group consisting of vapor phase method silica, pseudo boehmite, and aluminum oxide particles; the binder is a polyvinyl alcohol; the cross-linking agent is a borate compound; and the colorant receiving layer further comprises a mordant.

3. The disk-shaped information medium of claim 1, wherein the colorant receiving layer further comprises at least one compound selected from the group consisting of compounds represented by the following Formula (1) and compounds represented by the following Formula (2):

RO(CH₂CH₂O)_nH Formula (1)

RO(CH₂CH(CH₃)O)_nH Formula (2) where in Formulae (1) and (2), R represents a saturated hydrocarbon group having 1 to 12 carbon atoms, an unsaturated hydrocarbon group having 1 to 12 carbon atoms, a phenyl group or an acyl group, and n represents an integer from 1 to 3.

4. The disk-shaped information medium of claim 3, wherein the further comprising compound in the colorant receiving layer is at least one compound selected from the group consisting of compounds represented by Formula (1) and compounds represented by Formula (2) in which R in Formulae (1) and (2) represents a saturated hydrocarbon group having 1 to 4 carbon atoms.

5. The disk-shaped information medium of claim 1, wherein the difference between the thickness at the inner peripheral portion of the colorant receiving layer and the thickness at the outer peripheral portion of the colorant receiving layer (Tj_n - T_out) is greater or equal to 5 μm.

6. The disk-shaped information medium of claim I₅ wherein the difference between the thickness at the inner peripheral portion of the colorant receiving layer and the thickness at the outer peripheral portion of the colorant receiving layer (Tj_n - T_out) is from lμm to 10 μm.

7. The disk-shaped information medium of claim 1, wherein the thickness of the outer peripheral portion is in a range of 25 to 65 μm.

8. A method for producing the disc-shaped information medium comprising a printable layer which comprises an undercoat layer and a colorant receiving layer, wherein: the colorant receiving layer comprises microparticles, a binder and a cross-linking agent; a thickness of the colorant receiving layer progressively decreases from an inner circumferential side to an outer circumferential side thereof; and a relationship between a thickness (Tj_n) at an inner peripheral portion of the colorant receiving layer and a thickness (T_out) at an outer peripheral portion of the colorant receiving layer satisfies the equation of (Tj_n - T_out) ≥ 1 μm, and wherein the method comprises forming a coating layer by applying, onto the undercoat layer, a coating solution containing the microparticles and the binder using an extrusion die coater with increasing of the flow rate at a discharging port of the extrusion die coater from an inner circumferential portion to the outer circumferential portion of the medium so as to form the colorant receiving layer.

9. The method of claim 8, wherein: the microparticles comprised in the disc-shaped information medium comprise at least one type of particle selected from the group consisting of vapor phase method silica, pseudo boehmite, and aluminum oxide particles; the binder is a polyvinyl alcohol; the cross-linking agent is a borate compound; and the colorant receiving layer further comprises a mordant.

10. The method of claim 8, wherein the colorant receiving layer further comprises at least one compound selected from the group consisting of compounds represented by the following Formula (1) and compounds represented by the Following Formula (2):

RO(CH₂CH₂O)_nH Formula (1)

11. The method of claim 8, wherein the flow rate at the discharging port of the extrusion die coater from the inner circumferential portion to the outer circumferential portion of the medium accords with the linear velocity of the extrusion die coater.