JP2003080822A - Ink jet recording sheet and image forming method thereof - Google Patents

Abstract

[PROBLEMS] To provide an ink jet recording sheet which can be repeatedly printed in ink jet recording and has excellent reusability, and an image forming method thereof. A white ink-receiving layer is provided on a colored base material layer, and the ink-receiving layer is formed by laminating fine particles in a radiation-curable compound containing two or more ethylenic double bonds in one molecule. An ink receiving layer which is made porous and which is made transparent by attaching a colorless ink to the ink receiving layer is provided. In particular, the fine particles are inorganic or organic fine particles having an average particle size of 0.1 to 5.0 μm, the colorless ink contains water as a main component, and the fine particles forming the ink receiving layer have a refractive index of 1.30 to 1. A value of 60 is preferred.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet recording sheet, and more particularly to an inkjet recording sheet that can be reused many times and an image forming method thereof.

[0002]

2. Description of the Related Art The ink jet recording system is one in which minute droplets of ink are ejected according to various operating principles and adhered to a recording sheet such as paper to record images, characters, etc., but at high speed and low noise. It has features of easy multicoloring, great flexibility of recording patterns, no need for development and fixing, and as a recording device for various figures and color images including Chinese characters.
It is rapidly spreading in various applications. Furthermore, images formed by the multi-color inkjet method can obtain records that are comparable to those of multi-color printing by the plate-making method and printing by the color photographic method. Since it is cheaper than the technology, it is being widely applied to the field of full-color image recording.

However, in recent years, with the spread of printers and copying machines in offices and homes,
The amount of misprints and miscopies has increased, leading to the large amount of paper (recording media) that is not originally needed being discarded, which is a serious social problem from the perspective of waste disposal and resource depletion. . Although high-resolution displays and the like have been commercialized, they have not come into wide use in terms of cost and size. Therefore, like so-called test copy and test print, the recorded image can be temporarily held on the recording sheet, and thereafter, the recorded image can be erased by any means, and the recording sheet can be reused. However, there has been a demand for an inkjet recording sheet that can prevent the disposal of a large amount of paper and promote effective utilization of resources.

Several proposals have hitherto been made to solve these problems. For example, JP-A-7-3
No. 04984, JP-A-6-145566, and the like provide inks that form an image with an ink containing a specific near-infrared absorbing dye and irradiate near-infrared light to erase the image. In addition, it has been proposed to use an ink whose color is erased by a chemical treatment, but even if the ink is erased, the ink remains in the receiving layer, and the recording characteristics are deteriorated by reuse, which is not preferable.

Further, by using hydroxypropyl cellulose in JP-A-8-324103 and polyvinyl acetal in JP-A-9-99605 as a binder of the ink receiving layer, the aqueous solution used for recording by washing with water. It is said that the ink can be washed out and reused. However, since these are hydrophilic resins, their water resistance is weak and there is a problem that deterioration of the ink receiving layer occurs when they are reused many times.

Further, Japanese Patent Application Laid-Open No. 10-157280 discloses a technique of forming a layer containing a hydrophilic polymer binder and a matting agent on a colored layer and making it transparent with water ink. However, there is a problem that the hydrophilic binder is likely to be deteriorated by reuse.

[0007]

The present invention relates to an inkjet recording sheet, and more particularly to an inkjet recording sheet which can be reused many times and an image forming method thereof.

[0008]

As a result of intensive studies, the inventors of the present invention have come to invent the ink jet recording sheet of the present invention and the image forming method thereof.

That is, the ink jet recording sheet of the present invention is an ink jet recording sheet provided with a white ink receiving layer on a colored substrate layer, and the ink receiving layer has two or more ethylenic diamines in one molecule. An ink jet recording sheet comprising a radiation-curable compound containing a heavy bond and one or more kinds of fine particles laminated and porous.

It is preferable that the fine particles are inorganic fine particles or organic fine particles and have an average particle diameter of 0.1 to 5.0 μm.

Further, the refractive index of the fine particles is 1.30 to 1.
It is preferably 60.

It is preferable to record with a colorless ink containing water as a main component.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The ink jet recording sheet of the present invention and the image forming method thereof are described in detail below.

In the ink jet recording sheet of the present invention,
A white ink receiving layer is provided on a colored substrate layer, and the ink receiving layer is laminated with one or more fine particles in a radiation curable compound containing two or more ethylenic double bonds in one molecule. By being made porous, it was possible to provide an inkjet recording sheet having excellent ink absorbency. Although it is possible to perform recording with a colored ink used in ordinary inkjet recording, the present invention proposes an image forming method for a reusable inkjet recording sheet by recording with a colorless ink containing water as a main component.

The ink receiving layer formed on the colored substrate layer is composed of a radiation curable compound in which inorganic or organic fine particles having an average particle diameter of 0.1 μm to 5.0 μm are laminated and porous. The particle size of the inorganic or organic particles is 0.1 μm
By controlling as described above, the ink receiving layer can be made white. When recording with a water-soluble ink, this white recording sheet exhibits light transmittance and transparency only in the recording portion. With inorganic or organic fine particles of 0.1 μm or less, whitening of the ink receiving layer is difficult, and the color of the colored substrate layer can be seen through, resulting in poor contrast of the recorded image. Also, the ink absorbency is poor. If the average particle size of the inorganic or organic fine particles exceeds 5.0 μm, the image quality will deteriorate.
By making the fine particles laminated and porous in a radiation curable compound, an inkjet recording sheet having excellent water resistance can be obtained.

The term "multilayer porosity" here refers to a structure in which inorganic or organic fine particles are stacked on a colored substrate using a radiation-curable compound as an adhesive, and voids are formed between the inorganic or organic fine particles. That is, the presence of the ink makes the entire ink receiving layer porous. Due to the fine voids formed in the ink receiving layer, an inkjet recording sheet having excellent ink absorbency can be obtained.

When light enters a transparent medium having a small refractive index from a transparent medium having a large refractive index, total reflection occurs when the incident angle exceeds a certain angle. In order to make transparent with a colorless ink, unless the refractive index of the inorganic or organic fine particles that diffusely reflect is larger than the refractive index of the colorless ink, the transparency becomes insufficient, which is not preferable. The main component of the colorless ink is preferably water in terms of safety and cost. At this time, the refractive index of the irregularly reflecting inorganic or organic fine particles is 1.30.
Preference is given to using pigments which are ˜1.60. 1.
When the refractive index is smaller than 30, a part of incident light is reflected, and sufficient transparency cannot be obtained. On the other hand, when a pigment of 1.60 or more is used, even if the colorless ink fills the holes, it does not become transparent because the refractive index is too different, and thus an image cannot be formed or an image with low contrast is obtained. Can only be formed.

Various kinds of inorganic or organic fine particles having a refractive index of 1.30 to 1.60 can be used. For example, urea-formalin resin (refractive index 1.5
4 to 1.56), melamine-formalin resin (1.5
7), benzoguanamine-formalin resin (1.5
7), organic fine particles such as melamine-benzoguanamine-formalin resin (1.57), polystyrene resin (1.59), polymethylmethacrylate resin (1.49) and polyethylene resin (1.55). To be

The inorganic fine particles include heavy and light calcium carbonate (refractive index 1.49 to 1.60), magnesium carbonate (1.50) and kaolin (1.5).
5), baked clay (same as 1.60), talc (same as 1.5)
7), calcium silicate (1.50 to 1.60), silica (1.40 to 1.50), and aluminum hydroxide (1.53). It is not limited to these.

The ink receiving layer is preferably a hydrophilic polymer which is wet with the colorless ink and has a hydrophilic surface sufficient for the colorless ink to penetrate into the spaces between the inorganic or organic fine particles. . The term "hydrophilic" as used herein refers to a material having a contact angle of less than 90 degrees at the time when the spread of water drops is stopped when water drops are placed on the surface at room temperature. However, among the above-mentioned various members, even if it is a polymer generally called hydrophobic such as polyethylene and polystyrene, a surfactant,
If hydrophilicity is imparted by a method such as addition of a wetting agent, coating, or plasma treatment, it can be used in the ink receiving layer of the present invention. Further, as described below, it is also possible to use a colorless ink whose permeability is improved by adding a surfactant.

The radiation-curable compound in the ink jet recording sheet of the present invention preferably contains two or more ethylenic double bonds in one molecule and is hydrophilic.
Here, examples of the ethylenic double bond include a vinyl group, an acryloyl group, a methacryloyl group, an alicyclic epoxy group, and the like. An unsaturated polyester having such a functional group at a terminal or a side chain, a modified unsaturated polyester,
Acrylic polymers, acrylic oligomers, acrylic monomers, methacrylic polymers, methacrylic oligomers, methacrylic monomers, polymers having vinyl unsaturated bonds, oligomers and monomers, epoxy compounds, etc. are radiation-curable compounds in the present invention. be able to. For example, the refractive index of polyester resin is 1.52
~ 1.57, the refractive index of epoxy resin is 1.55 to 1.6
0, the refractive index of the acrylic resin is about 1.52 to 1.57, and both are within the range of 1.30 to 1.60 of the material forming the ink receiving layer of the present invention.
A compound having an acryloyl group is particularly preferable because it has excellent radiation curability. In order for the radiation-curable compound having the above structure to have hydrophilicity, a polar group such as a hydroxyl group, a carboxyl group, a secondary amine, a tertiary amine, a quaternary ammonium base, or ethylene is included in the molecule. It is necessary to contain hydrophilic units such as oxide, diethylene oxide, morpholine and pyrrolidone. Here, when the radiation-curable resin compound is monofunctional, crosslinking of the radiation-curable compound is difficult to proceed, the hardness of the ink receiving layer becomes insufficient, and the dissolution and swelling during printing is completely completed. This is not preferable because the water resistance of the ink receiving layer cannot be prevented, and when the printed portion is touched with a hand immediately after printing, a sticky feeling is felt. Further, when the radiation curable compound is not hydrophilic, the ink absorbability is significantly reduced, and ink overflow, bleeding, etc. occur.

As such a radiation curable compound, a commercially available one can be preferably used. Hereinafter, typical commercially available radiation-curable compounds corresponding to the above matters will be exemplified, but the present invention is not limited thereto.

Kayarad PEG400DA, Kayarad R-167, PET-30, Sartomer SR-230,
Sartomer SR-268, Sartomer SR-344, Sartomer SR-444 (above, Nippon Kayaku, Kayarad and Sartomer series), NK ester A-200,
NK ester A-400, NK ester A-600, N
K ester A-TMM-3, NK ester A-TMM-
3L (above, Shin Nakamura Chemical, NK ester series),
Aronix M-240, Aronix M-245, Aronix M-205, Aronix M-210 (above, Toa Gosei Aronix series), 3EG-A, 4
EG-A, 9EG-A, BP-4EA, PE-3A (above, Kyoeisha Oil and Fat Chemicals, Light acrylate series), PE-200, PE-300, PE-400, E
P-22, BPE4, TMP-3, PET-3, C-1
615, C-1615M (above, Dai-ichi Kogyo Seiyaku, New Frontier series)

Among the hydrophilic radiation-curable compounds described above, the compound containing an ethylene oxide segment in the molecule is particularly preferable from the viewpoint of ink absorbability.
A plurality of ethylene oxide segments may be continuous segments, or other segments may be sandwiched therebetween.

The amount of the radiation-curable compound compounded with respect to 100 parts by mass of the inorganic or organic fine particles is 10 to 70 parts by mass, and more preferably 20 to 50 parts by mass. Here, if the amount of the radiation-curable compound is less than 10 solid parts by mass, the binder property of the radiation-curable compound is inferior, the strength of the ink receiving layer is lowered, and the water resistance is inferior, which is not preferable. On the other hand, if the amount exceeds 70 parts by mass, the amount of void-free coating film formed by the radiation-curable compound becomes too large, resulting in poor ink absorbability.

Further, 1 is contained in the ink receiving layer of the present invention.
For the purpose of adjusting the curability of a hydrophilic radiation-curable compound containing two or more ethylenic double bonds in the molecule and stabilizing the ink absorbability, it is necessary within a range that does not impair the effects of the present invention. Accordingly, a monofunctional hydrophilic radiation-curable compound can be added. As the monofunctional hydrophilic radiation curing, commercially available products can be preferably used,
For example, N, N-dimethylacrylamide, acryloylmorpholine, N, N-dimethylaminopropylacrylamide, N, N-dimethylaminoethyl acrylate, dimethylaminoethyl acrylate methyl chloride quaternary salt, N, N-dimethylaminopropyl acrylamide methyl chloride Quaternary salt (above, manufactured by Kojin), Kayarad R-12
8H, Kayarad R-564 (above, Nippon Kayaku, Kayarad series), Aronix M-101, Aronix M-102, Aronix M-114, Aronix M-150, Aronix M-154, Aronix M.
-5300, Aronix M-5400, Aronix M-5500, Aronix M-5600, Aronix M-5700 (above, Toagosei product, Aronix series), NK ester AMP-10G, NK ester A.
MP-20G, NK ester AMP-60G, NK ester AMP-90G (above, Shin Nakamura Chemical Co., Ltd. make, NK ester series) etc. can be mentioned.

Further, in the ink receiving layer of the present invention, a fluorescent whitening agent, an ultraviolet absorber, an antioxidant, a light stabilizer, a radical polymerization initiator, a surface active agent are added to the extent that the effects of the present invention are not impaired. Agents, lubricants, cationic dye fixing agents, pigment dispersants,
Thickener, fluidity improver, defoamer, foam suppressor, release agent, foaming agent, penetrant, coloring dye, coloring pigment, antiseptic, antifungal agent,
Various additives such as a water resistance agent, a wet paper strength enhancer, and a dry paper strength enhancer can also be added. Here, the fluorescent whitening agent added to the ink receiving layer is not particularly limited, but a fluorescent whitening agent containing a thiophene skeleton excellent in radiation resistance and weather resistance is particularly preferable.

Radiation for curing the radiation-curable compound in the ink receiving layer of the ink jet recording sheet of the present invention is generally ultraviolet rays, α rays, β rays, γ rays, X rays.
Rays, electron rays, and the like are included, but since α rays, β rays, γ rays, and X rays are accompanied by the problem of danger to the human body, they are easy to handle, and ultraviolet rays are widely used industrially. And electron beams are effective.

In the present invention, when an electron beam is used,
The irradiation electron dose is preferably in the range of about 0.1 to 10 Mrad. Here, if it is less than 0.1 Mrad, sufficient curing effect cannot be obtained and curing is insufficient, and if it exceeds 10 Mrad, the support is deteriorated, which is not preferable. As an electron beam irradiation method, a scanning method, a curtain beam method, or the like can be used, and the electron beam acceleration voltage is preferably about 100 to 300 KV. In addition, when the atmosphere has a high oxygen concentration during electron beam irradiation, curing of the radiation-curable compound is hindered, so replacement with an inert gas such as nitrogen, helium, or carbon dioxide is performed to reduce the oxygen concentration to 6
Irradiation is generally performed in an atmosphere in which the amount is suppressed to 00 ppm or less, more preferably 400 ppm or less.

When ultraviolet rays are used in the present invention, a sensitizer needs to be added to the adhesive layer. Specific examples thereof include acetophenones such as di- or trichloroacetophenone, benzophenone. , Michler's ketone, benzyl, benzoin, benzoin alkyl ether, benzyl dimethyl ketal, tetramethyl thiuram monosulfide, thioxanthones, azo compounds, etc., polymerization reaction type of UV curable resin, stability, and compatibility with UV irradiation equipment Etc. are selected from the viewpoint. The amount of the sensitizer used is usually about 1 to 5 mass% with respect to the ultraviolet curable compound. In addition, a storage stabilizer such as hydroquinone may be used in combination with the sensitizer. As the light source, for example, a low pressure mercury lamp, a medium pressure mercury lamp,
A high pressure mercury lamp, a xenon lamp, a tungsten lamp, etc. are used.

The coating amount of the ink receiving layer in the present invention is 1 to 30 g / m ^{2 as} dry solid content, more preferably 5 to 20.
There is g / m ² . The ink-receiving layer may be prepared by dissolving or dispersing the above-mentioned inorganic or organic fine particles or a radiation-curable compound in water or an organic solvent, or when the radiation-curable compound is a diluting monomer or oligomer, it is a solvent-free, conventional solvent. It can be coated on a mirror-finished metal roll or a high-gloss synthetic resin film using a known coating method and transferred onto a colored substrate. Moreover, you may apply | coat directly on a colored base material. Examples of such a coating method include a blade method, an air doctor method, a squeeze method, an air knife method, a reverse roll method, a gravure roll and transfer roll method, a bar method, and a curtain method.

The colored base material layer used in the present invention may be a member having absorption in at least a part of the visible light region. However, it is essential that the colorant in the colored substrate is not fluidized by the colorless ink in any color.
This is because if the colorant oozes out into the visible light diffuse reflection layer due to the adhesion of the ink, the surface of the recording material is contaminated and it becomes difficult to use it repeatedly. Specifically, various resin films in which carbon black or other inorganic pigments or organic pigments are dispersed, or paper whose surface is colored by a normal printing method or a coating method can be used. .

As the resin film, polyester, polystyrene, polyvinyl chloride, poly (meth) acrylic acid ester, cellulose derivative such as cellulose acetate, polyolefin such as polyethylene and polypropylene, polycarbonate, polyamide, polyesteramide, polyether, polyimide, Examples thereof include polyamide imide and polyether ester, and further, copolymers, blends and cross-linked products thereof can be used. Among these, polyester is preferable from the viewpoint of mechanical strength and workability, and polyethylene terephthalate is particularly preferable.

If necessary, an antioxidant, a heat stabilizer, a lubricant, an ultraviolet absorber, etc. may be added to the colored substrate layer. In addition, corona treatment or undercoat treatment may be performed for the purpose of improving the adhesiveness with other layers.

The method of coating or impregnating the ink receiving layer according to the present invention includes various blade coaters, roll coaters, air knife coaters, bar coaters, rod blade coaters,
Various devices such as a curtain coater, a short dwell coater, and a size press can be used on-machine or off-machine. Further, after coating or impregnation, it is also possible to finish using a calender device such as a machine calender, a TG calender, a super calender and a soft calender.

The ink of the present invention preferably contains water as a main component from the viewpoint of safety and cost. Therefore, the water component in the ink may evaporate, and the image may disappear immediately after printing. Therefore, an ink absorbing layer may be provided between the ink receiving layer and the colored substrate layer in order to retain the printed colorless ink. The ink absorbing layer is composed of a water-absorbing polymer or a water-soluble polymer which is insoluble in water, and the content thereof can be determined according to the desired image holding time.

Specifically, its refractive index is 1.30 at room temperature.
Examples of the resin of 1.60 include starch, corn starch, sodium alginate, gum arabic, gelatin, casein, dextrin, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, cellulose sulfate, as a water-soluble polymer or a water-insoluble water-absorbing polymer. Cyanoethyl cellulose, polyvinyl alcohol, acrylic acid-polyvinyl alcohol copolymer, vinyl acetate-methyl acrylate copolymer, polyvinyl methyl ether, sodium polyacrylate, methyl vinyl ether-maleic anhydride copolymer, ethylene-
Maleic anhydride copolymer, sodium polystyrene sulfonate, polyvinyl benzyl trimethyl ammonium chloride, polydiallyl dimethyl ammonium chloride, polydimethylaminoethyl methacrylate hydrochloride, polyvinyl pyridine, polyvinyl imidazole, polyethyleneimine, polyamidoamine, polyacrylamide, Examples thereof include polyethylene oxide and polyvinylpyrrolidone. Particularly, polyacrylic acid salts such as sodium polyacrylate, polysulfonates, polyvinyl alcohol / polyacrylate copolymers, poly N-
At least one water-absorbing polymer such as a vinylacetamide-based or amino acid-based synthetic polymer, a starch graft polymerization system, a carboxymethylcellulose system, a cellulose graft polymerization system, or a carboxymethylcellulose-based semisynthetic polymer may be contained. preferable. With such a water-absorbing polymer, it is possible to dramatically increase the image holding time even with a small amount.

In principle of the present invention, the substances constituting the ink receiving layer, that is, the above-mentioned polymers, porous particles, binders, water-absorbing polymers, etc., do not themselves absorb in the visible light region. Although preferable, depending on the thickness of the diffuse reflection layer,
If it is sufficiently thin, it is possible to use a substance that absorbs in the visible light region.

The image holding time can be increased by adding a wetting agent to the colorless ink.
Specific wetting agents, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, polyethylene glycol, polyhydric alcohols such as glycerin, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, Alkyl ether derivatives of polyhydric alcohols such as diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether and triethylene glycol monomethyl ether, aryl ether derivatives of polyhydric alcohols such as ethylene glycol monophenyl ether, lactic acid , Carboxylic acids with hydroxyl groups such as malic acid And its salts, and N- methyl-2-pyrrolidone, there is a nitrogen-containing heterocyclic compounds of 2-pyrrolidone and the like. A mixture of the above polyhydric alcohols, alkyl ether derivatives of polyhydric alcohols, aryl ether derivatives of polyhydric alcohols, carboxylic acids having a hydroxyl group or salts thereof, and nitrogen-containing heterocyclic compounds. Can also be used.

It is also effective to add a water-soluble polymer to the colorless ink because it can prevent evaporation of water in the ink.
As a water-soluble polymer, in natural systems, gum arabic, traggan gum, guar gum, karaya gum, locust bean gum, arabinagalactone, pectin, tainse seed starch and other plant macromolecules, alginic acid, carrageenan, agar, seaweeds such as fungus Polymers, animal polymers such as gelatin, casein, albumin and collagen, microbial polymers such as xanthene gum and dextran, and semi-synthetic systems such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose,
Fibrin-based polymers such as carboxymethyl cellulose, soluble starch, carboxymethyl starch (CMS), dialdehyde starch, starch-based polymers such as sodium starch glycolate, sodium starch phosphate ester, sodium alginate, propylene glycol alginate, etc. Seaweed macromolecules, pure synthetic systems,
Vinyl polymers such as polyvinyl alcohol, polyvinylpyrrolidone and polyvinyl methyl ether, non-crosslinked polyacrylamide, polyacrylic acid and its alkali metal salts, acrylic resins such as water-soluble styrene acrylic resin,
Water-soluble styrene maleic acid resin, water-soluble vinyl naphthalene acrylic resin, water-soluble vinyl naphthalene maleic acid resin, polyvinylpyrrolidone, polyvinyl alcohol, β
Examples include alkali metal salts of formalin condensates of naphthalene sulfonic acid, polymer compounds having a side chain of a salt of a cationic functional group such as quaternary ammonium or amino group, and natural polymer compounds such as shellac.

Various surfactants may be added for the purpose of improving the wettability and penetrability of the colorless ink to the recording material. Examples of the surfactant include anionic surfactants, cationic surfactants, amphoteric surfactants and nonionic surfactants.

Specific examples of the anionic surfactant include:
Soap, N-acyl amino acid salt, alkyl ether acetate, carboxylate such as acylated peptide, alkyl sulfonate, alkylbenzene sulfonate, alkylnaphthalene sulfonate, sulfosuccinate, alkylsulfosuccinate, α -Sulfonates such as olefin sulfonates and N-acyl sulfonates, sulfated oils, alkyl sulfates, alkyl ether carboxylates, alkyl ether sulfates, sulfate ester salts such as alkylamide sulfates,
Phosphate ester salts such as alkyl phosphates, alkyl ether phosphates, alkyl aryl phosphates, fluoroalkyl carboxylates, fluoroalkyl sulfonates,
Examples thereof include fluoroalkyl phosphate ester, carboxylic acid-modified polydimethylsiloxane, and sulfonic acid-modified polydimethylsiloxane.

Specific examples of the cationic surfactant include:
Examples thereof include aliphatic amine salts, alkyl quaternary ammonium salts, fluoroalkyl trimethyl ammonium salts, aromatic amine salts, aromatic quaternary ammonium salts, and heterocyclic quaternary ammonium salts.

Specific examples of the amphoteric surfactant include betaine type such as carboxybetaine and sulfobetaine, aminocarboxylic acid salt, imidazoline and the like. Specific examples of the nonionic surfactant include ethylene oxide adducts of aliphatic alcohols, polyoxyethylene alkyl ether-based compounds, polyoxyethylene polyoxypropylene alkyl ether-based compounds, and alkylamine oxides. Furthermore, it is also possible to add a pH adjusting agent, a heavy metal ion sealing agent, an antiseptic / antifungal agent, an anticorrosive agent and the like, which are used in ordinary colored inks, to the colorless ink.

The pH adjusting agent is adjusted to a pH range in which the colorless ink does not erode the ink chamber of the printer or the head member. Examples of the heavy metal ion sealant include sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uramildiacetate. As the antiseptic / antifungal agent, sodium dehydroacetate, sodium sorbate, sodium 2-pyridinethiol-1-oxide, sodium benzoate, sodium pentachlorophenol and the like can be used in the present invention. Examples of the rust preventive include acid sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, dicyclohexylammonium nitrite and the like.

The colorless ink is mainly composed of water,
A colorless ink raw material in which components other than water such as the above wetting agent or water-soluble polymer are premixed easily mix with water, so water is added at the stage of use as an ink, and the colorless ink is stirred by stirring for a short time. Can be obtained. The colorless ink raw material is very suitable for transportation and storage. Furthermore, the image holding time can be easily controlled by changing the amount of water added.

As the ink jet printer for forming an image with the above-mentioned colorless ink, a conventionally known one can be used. The method of the recording head may be any conventionally known method, for example, a piezoelectric material is used to apply ink pressure by an electric pulse, and the ink is ejected as droplets from a nozzle provided in the recording head to adhere to the recording material. Examples thereof include an inkjet recording head of a type, and an inkjet recording head of a type in which bubbles are generated in the ink by using a heating element and the pressure causes the ink to be ejected as droplets onto a recording material.

Since the colorless ink of the present invention does not contain a colorant, it is less likely to cause clogging than conventional inks. In a typical inkjet printer, various mechanisms are provided to maintain reliability. For example, to prevent evaporation of solvent from the nozzle when the printer is stopped, a mechanism that caps the nozzle, a mechanism that sucks ink near the nozzle whose viscosity has increased due to solvent evaporation from the outside when the printer is started, a predetermined amount or a predetermined time After printing,
Examples include a mechanism for discharging ink to the drain and a mechanism for constantly vibrating the vicinity of the nozzle to prevent the colorant and the like from aggregating near the nozzle. If a colorless ink having an appropriate composition is used, these reliability mechanisms can be simplified, which leads to downsizing and cost reduction of the printer.

In the image obtained by ejecting the colorless ink onto the recording material of the present invention, as the water content in the colorless ink evaporates, the ink receiving layer becomes opaque and finally the image disappears. It is possible to arbitrarily set the image holding time depending on the ink composition and the prescription of the recording material. After outputting the image,
The point that it disappears naturally and completely without any modification is a big difference from the conventional one.

It is also possible to accelerate image disappearance by a very simple process. That is, it is possible to accelerate the evaporation of the colorless ink by heating the recording material on which the image is formed or by blowing air on the image surface. It is more effective if both heating and air blowing are performed.

The recording material and the colorless ink of the present invention, which have already been described in detail, have a structure that is very suitable for the above reproducing method. The recording material and the ink are used not only in the recording method of the present invention but also in combination with the above-described reproducing method, whereby an effective reuse system that does not waste resources can be realized. Examples using the recording material of the present invention will be described below.

[0052]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. Further, "parts" and "%" shown in the examples represent parts by mass and% by mass, unless otherwise specified.

Example 1 On a black polyethylene terephthalate sheet obtained by dispersing carbon black, organic fine particles (styrene-
Acrylic fine particles, average particle diameter 1.0 μm, refractive index 1.
52) A mixture of 100 parts and 30 parts of a radiation curable compound (pentaerythritol triacrylate) was prepared into an aqueous solution having a solid content concentration of 25%, and was coated and dried by a rod bar so that the dry coating amount was 10 g / m ^2. Then, from the ink receiving layer side, an acceleration voltage of 150 KV and an irradiation dose of 2 Mra
The inkjet recording sheet of Example 1 was obtained by irradiating an electron beam under the condition of d to cure the ink receiving layer. Printing was performed using an ink jet printer (manufactured by EPSON, MJ-700V2C) using water as ink to obtain a printed matter.
The printed part became transparent, the solvent did not bleed into the non-printed part, the printed part was clearly distinguishable from the cloudy non-printed part, and the printing state was confirmed. The printed part did not bleed even when rubbed with a fingertip.

Example 2 On a black polyethylene terephthalate sheet obtained by dispersing carbon black, 100 parts of organic fine particles (polymethyl methacrylate-based fine particles, average particle diameter 5.0 μm, refractive index 1.49), radiation cured. A mixture of 40 parts of a polyfunctional compound (polyethylene glycol 400 diacrylate) and 0.5 part of an ultraviolet curing initiator was prepared into an aqueous solution having a solid content concentration of 35%, and the dry coating amount was adjusted to 15 by a rod bar.
The inkjet recording sheet of Example 2 was obtained by coating and drying so that the coating amount was g / m ² and performing ultraviolet irradiation treatment. Inkjet printer (Made by EPSON, MJ-7
00V2C) and printing using water as ink,
I got a print. The printed part became transparent, the solvent did not bleed into the non-printed part, the printed part was clearly distinguishable from the cloudy non-printed part, and the printing state was confirmed. The printed part did not bleed even when rubbed with a fingertip.

Example 3 Black polyethylene obtained by dispersing carbon black
Inorganic fine particles (average particle size
1.5 μm, refractive index 1.45) 100 parts, radiation curable
Compound (pentaerythritol triacrylate) 30
Part mixture was prepared into an aqueous solution having a solid concentration of 25% and
The dry coating amount is 10 g / m with the dover. ²So that
After coating and drying, from the ink receiving layer side, acceleration voltage 150
Irradiation with an electron beam under the conditions of KV and irradiation dose of 2 Mrad
The ink jet recording layer of Example 1 is prepared by curing the ink-receiving layer.
I got a card. Inkjet printer (made by EPSON,
Printing using water as ink with MJ-700V2C)
Then, a printed matter was obtained. The printing area becomes transparent and the solvent is
The printed part does not bleed, and the printed part becomes a cloudy non-printed part.
They were clearly distinguishable and the print status was confirmed. Printed area is fingertip
It didn't bleed when rubbed with.

Comparative Example 1 On a black polyethylene terephthalate sheet obtained by dispersing carbon black, organic fine particles (polystyrene ultrafine particles, average particle diameter 52 nm, refractive index 1.59) 1
A mixture of 00 parts and 30 parts of a radiation curable compound (pentaerythritol triacrylate) was prepared into an aqueous solution having a solid concentration of 25%, and the dry coating amount was adjusted to 10 by a rod bar.
The inkjet recording sheet of Comparative Example 2 was coated and dried so as to have g / m ^2, and the ink receiving layer was cured by irradiating the ink receiving layer surface side with an electron beam under the conditions of an acceleration voltage of 150 KV and an irradiation dose of 2 Mrad. Got Printing was performed using an inkjet printer (MJ-700V2C manufactured by EPSON) using water as ink to obtain a printed matter. Although the printed area became transparent, the water ink absorption was poor and the peripheral area of the printed area also bleeded, and even when the printed area was rubbed with a fingertip, it bleeded. In addition, the background part became gray close to black and the contrast was low.

Comparative Example 2 An ink jet recording sheet of Comparative Example 2 was prepared and an image was formed in the same manner as in Example 1 except that zinc oxide (refractive index 2.01) fine particles were used instead of the organic fine particles. However, even if colorless ink was attached, the ink receiving layer did not become transparent and an image could not be recognized.

Comparative Example 3 An ink jet recording sheet of Comparative Example 3 was obtained in the same manner as in Example 1 except that the organic fine particles in the ink receiving layer were cationic colloidal silica (average particle size 80 nm, refractive index 1.45). It was Inkjet printer (EPSON
Manufactured by MJ-700V2C) using water as an ink for printing to obtain a printed matter. The printed part does not become transparent,
Further, the water ink absorbability was poor, and the peripheral portion of the print also bleeded, and even when the printed portion was rubbed with a fingertip, it bleeded.

Comparative Example 4 An ink jet recording sheet of Comparative Example 4 was obtained in the same manner as in Example 1 except that the organic fine particles of the ink receiving layer were organic fine particles of crosslinked polystyrene (average particle diameter 12 μm, refractive index 1.59). It was Inkjet printer (EPSON
Manufactured by MJ-700V2C) using water as an ink for printing to obtain a printed matter. Although the water ink absorbability was good, the resolution was poor and the image quality was poor.

Comparative Example 5 An ink jet recording sheet of Comparative Example 5 was obtained in the same manner as in Example 1 except that hydroxymethyl cellulose was used in place of the radiation curable compound of Example 1. Printing was performed using an inkjet printer (MJ-700V2C manufactured by EPSON) using water as ink to obtain a printed matter.
Although the printed part became transparent, the water resistance was poor when printed with water ink, and when the printed part was rubbed with a fingertip immediately after printing, there was a sticky feeling and bleeding was also seen.

[0061]

The ink jet recording sheet of the present invention is
Ink absorption by using inorganic or organic fine particles having an average particle diameter of 0.1 to 5.0 μm on the colored substrate layer and a radiation curable compound containing two or more ethylenic double bonds in one molecule. It was possible to obtain an inkjet recording sheet having excellent properties and excellent reusability.

Claims (4)

[Claims] 1. A radiation-curable compound having an ink-receiving layer having a white ink-receiving layer on a colored substrate layer, wherein the ink-receiving layer contains two or more ethylenic double bonds in one molecule. An ink jet recording sheet, characterized in that one or more kinds of fine particles are laminated and made porous. 2. The inkjet recording sheet according to claim 1, wherein the fine particles are inorganic fine particles or organic fine particles and have an average particle diameter of 0.1 to 5.0 μm. 3. The fine particles have a refractive index of 1.30 to 1.60.
The inkjet recording sheet according to claim 1 or 2, wherein 4. The image forming method for an ink jet recording sheet according to claim 1, wherein recording is performed with a colorless ink containing water as a main component.