JP2010205316A - Information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording medium having a label layer on which the user can repeatedly erase the writing and written trace without affecting the information recorded on the information recording layer. <P>SOLUTION: This invention relates to an information recording medium, including: an information recording layer 102 in which information can be recorded or reproduced by radiating light; and a label layer 106. The label layer contains an electron-donating color developing organic compound, an electron-accepting compound and a solvent, and is used for writing with water-erasable ink and for water-erasing the written trace of the water-erasable ink. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an information recording medium. Specifically, the present invention relates to writing using an ink whose label layer can be decolored by water, and an information recording medium used for decoloring the written mark.

Conventionally, information recording media have been widely used for recording electronic data, and these information recording media are provided with a label portion that indicates recorded contents, indexes, and the like.
The label section has a different form depending on the type of information recording medium. For example, a mode in which a user or the like attaches a sticker to an MO, a DVD-RAM, or the like housed in a hard case is common.
For information recording media such as CDs and DVDs, a method of label printing directly on the disk surface is common.

  For example, in a writable information recording medium such as a CD-R, DVD-R, or Blu-ray disc, the user can write characters on the label layer provided on the disc surface according to the contents of the information recording medium. There is a demand for writing, erasing written characters and the like, and further repeatedly writing and erasing. Therefore, for example, Patent Document 1 proposes a marking pen for writing on the label layer. The marking pen ink composition contains a microcapsule pigment that contains a reversible thermochromic composition, and the writing mark by the ink composition can be erased by heating.

  In addition, the user generally writes on the label layer with an oil-based writing tool, and as a method of erasing the written trace, for example, a method of erasing with an alcohol-based general-purpose solvent is known.

JP 2008-299895 A

However, when the marking pen ink composition described in Patent Document 1 is erased by heating, heat may be transmitted not only to the label layer but also to the information recording layer. In the case of performing the above, there is a possibility that data recorded on the information recording layer may be damaged.
In addition, when erasing a place written with an oil-based writing instrument using a general-purpose solvent, the general-purpose solvent may penetrate into the information recording layer from the disk edge, and information recording data may be lost. There was a problem.
Therefore, a method capable of erasing writing and writing traces without affecting the information recorded on the information recording layer repeatedly by the user, and an information recording medium having a label layer for use in the method The provision of

  As a result of intensive research conducted by the inventors of the present application, the ink is obtained by writing on the label layer with an ink that can be decolored by water, including an electron-donating color-forming organic compound, an electron-accepting compound, and a solvent. It was found that the place written by can be erased with water, and even if these operations are repeated several times, the information recording layer is not affected.

  The gist of the present invention is an information recording medium having an information recording layer capable of recording or reproducing information by irradiating light, and a label layer, wherein the label layer is an electron-donating colored organic compound. An information recording medium comprising: an electron-accepting compound; and a solvent, and used for writing with an ink that can be decolored with water and for decoloring with water the writing mark with the ink.

Further, the label layer preferably has a surface scratch hardness of 100 g or more as measured by the following method.
(Scratch hardness measurement method)
The label layer surface and the needle are brought into contact with each other while a predetermined load is applied to a sapphire needle having a tip radius of 0.2 mm, the load of which can be adjusted, and the needle is moved at a speed of 100 mm / min. The scratch mark of the needle is visually confirmed, and if the scratch mark is not confirmed, it is determined that the needle has a hardness equal to or higher than the load.

  Further, the label layer contains at least one monofunctional monomer that does not contain an aromatic ring in the structure and other than urethane acrylate, and / or polyfunctional monomer that does not contain an aromatic ring in the structure and other than urethane acrylate. It is preferable that it is formed using a mixture containing and having a total content of the monofunctional monomer and / or the polyfunctional monomer of 50% by weight or more. Moreover, it is preferable that the said mixture contains the epoxy resin monomer which does not contain an aromatic ring in a structure, and does not contain an ultraviolet curable oligomer other than a urethane type oligomer, and / or an aromatic ring in a structure.

  The hue of the label layer is such that the L * value of the L * a * b * color system is 60 or more, the absolute value of the a * value is 15 or less, and the absolute value of the b * value is 15 or less. Preferably, the L * value is 60 or more and 90 or less.

  Another gist of the present invention is an information recording medium having an information recording layer capable of recording or reproducing information by irradiating light, and a label layer, the label layer having an electron donating color. A water-soluble organic compound, an electron-accepting compound, and a solvent, and can be written with an ink that can be erased with water. The information recording medium is characterized in that there is no recurrence color due to the ink.

According to the information recording medium of the present invention, the user can easily write on the label layer using ink that can be erased by water, and the characters written on the label layer can be clearly displayed. It can be held in. Further, the written mark can be erased with water, and rewriting can be performed on a position where the written mark is erased. Therefore, the user can surely perform writing on the label layer of the information recording medium and erasing of the written trace by an easy method.
In the present invention, since water is used for erasing the written mark, the information recorded on the information recording layer is not affected at the time of erasing.

It is explanatory drawing for demonstrating an example of the layer structure of the information recording medium of this invention.

  The following examples and the like are examples (representative examples) of the embodiments of the present invention, and the present invention is not specified in these contents without departing from the gist thereof. In addition, when describing with (meth) acrylate in this-application specification, an acrylate and a methacrylate shall be shown.

1. Information Recording Medium The information recording medium of the present invention has at least an information recording layer capable of recording or reproducing information by irradiating light and a label layer.

  If the information recording medium of this invention has an information recording layer and a label layer, there will be no restriction | limiting in the kind unless the effect and objective of this invention are impaired. The present invention can be applied to various disk shapes such as CD-ROM, CD-R, CD + R, CD + RW, CD-RW, DVD-ROM, DVD-R, DVD + R, DVD + RW, DVD-RW, DVD-RAM, and Blu-ray. It can be applied to an information recording medium or the like.

  The layer structure of the information recording medium of the present invention is not particularly limited as long as the object and effect of the present invention are not impaired. For example, a structure in which a substrate / recording layer / reflection layer / protective layer / label layer, such as CD-R and CD-RW, are laminated in this order and information is recorded or reproduced from the substrate side may be used. Further, for example, a configuration in which a protective layer / recording layer / reflective layer / substrate / label layer, such as a Blu-ray disc, are laminated in this order and information is recorded or reproduced from the protective layer side may be used. Further, for example, a recording layer and a reflective layer are provided between two substrates, represented by DVD-R, DVD-RW, etc., on a substrate opposite to the light incident surface for recording or reproducing information. A laminated type structure in which a label layer is laminated may be used.

(1) Label layer The label layer in the information recording medium of the present invention contains an electron-donating color-forming organic compound, an electron-accepting compound, and a solvent, and can be decolored with water (hereinafter referred to as “decoloring”). It is also a layer used for decoloring with water of writing marks by the ink and writing marks of the ink. The label layer may be used for displaying information that can be visually discriminated.
The information displayed on the label layer includes the type of information recording medium (eg, CD, DVD, etc., whether recording / rewriting is possible, format information, etc.), recording capacity, brand name of the information recording medium, Etc. Further, an indication that the label layer can be written with the decolorable ink or that the written mark can be erased with water may be displayed.

  For example, as shown in the schematic cross-sectional view of FIG. 1, a substrate 101 / information recording layer 102 / reflective layer 103 / protective layer 104 / label layer 106 are laminated in this order, and light for recording or reproducing information (laser light). ) In the information recording medium having the configuration in which the irradiation of 107 is performed from the substrate 101 side, the label layer 106 may serve to protect the information recording layer 102 and the reflective layer 103 from physical damage or the like.

Writing on the label layer is usually performed with a writing instrument containing the above-mentioned decoloring ink in the pen tip, etc. There are no particular restrictions on the type of writing instrument, but decoloring properties are used so as not to wear the surface of the label layer. It is preferable that the ink can be applied.
Also, there is no particular limitation on the method of erasing the written marks with the erasable ink, for example, a method of wiping the written marks with a sponge or cloth soaked in water, a method of flowing running water through the label layer, a label layer For example, a method of immersing in water.

  The label layer may be a single layer or may be a laminate of two or more layers. When the label layer is a layer in which two or more layers are laminated, the outermost layer is a layer that can be written with a decolorable ink.

In the label layer, the area where writing with the decolorable ink and the decoloring with the water of the written mark are performed (hereinafter also referred to as “writing area”) may be the entire surface of the label layer. May be a partial region.
In the writing area, ruled lines, squares, or the like may be printed so that the user can easily write when writing characters or patterns. As a printing method for ruled lines, squares, etc., it can be performed by screen printing or the like using the same material as the material of the label layer described later. The thickness of these ruled lines and squares is usually 1 mm or less, more preferably 0.5 mm or less. However, if it is too thin, the adhesiveness may decrease, so 0.05 mm or more is preferable, and 0.1 mm or more is more preferable.
When forming the label layer, the ruled lines and squares may be masked with a screen and the mixture for forming the label layer may be removed, that is, the label layer may be formed in a shape with the ruled lines and mass areas removed. .

  The hue of the label layer is preferably a hue close to an achromatic color in order to make it easy to see whatever color the decolorizable ink is. Specifically, the L * value of the L * a * b color system is preferably 60 or more, more preferably 65 or more. The absolute value of the a * value is preferably 15 or less, more preferably 10 or less. Further, the absolute value of the b * value is preferably 15 or less, more preferably 10.

In particular, it is preferable to make the hue of the label layer gray so that the written mark can be made less noticeable after the written mark is erased with the decolorable ink. In this case, the L * value of the L * a * b color system is usually 60 or more, preferably 65 or more, and usually 90 or less, preferably 85 or less. In this case, the a * value and b * value are preferably the same as described above.
As described above, when only a partial region of the label layer is used as a writing region, only the writing region may have the hue.

  In order to obtain the above-mentioned hue, for example, an inorganic pigment such as titanium oxide white or carbon black, a colored organic pigment, or a colorant such as a dye is included in a mixture for forming a label layer to be described later, and the color is adjusted. The above hue can be obtained. When a label layer is formed by laminating two or more layers, the outermost layer may have the above hue, and the underlying layer may have the above hue, and the underlying layer may be visible. A layer having transparency to light may be stacked.

The label layer preferably has a surface scratch hardness of 100 g or more, more preferably 150 g or more, as measured by the following method. By setting the scratch hardness on the surface of the label layer to the lower limit value or more, it is difficult for the components of the color erasable ink to enter the label layer, and the erasability of the written mark becomes good.
(Scratch hardness measurement method)
The label layer surface and the needle are brought into contact with each other while a predetermined load is applied to a sapphire needle having a tip radius of 0.2 mm, the load of which can be adjusted, and the needle is moved at a speed of 100 mm / min. The scratch mark of the needle is visually confirmed, and if the scratch mark is not confirmed, it is determined that the needle has a hardness equal to or higher than the load.

  The thickness of the label layer is usually 5 μm or more, preferably 10 μm or more. Further, it is usually 50 μm or less, preferably 30 μm or less. If the thickness of the label layer is too thin, the writing pressure resistance at the time of writing may be insufficient, and if it is too thick, the warp tends to increase due to the shrinkage of the label layer. In addition, as mentioned above, when a label layer consists of two or more layers, it is preferable that the whole film thickness after each layer lamination | stacking is the said range.

  In particular, the label layer can be written with an ink that contains an electron-donating color-forming organic compound, an electron-accepting compound, and a solvent and can be decolored by water (ie, “decolorable ink”). It is preferable that the writing mark is not recolored by the ink after the decoloring of the writing mark by the ink with water and the drying of the water. Decoloration of written traces with water and confirmation of the presence or absence of recurrence after drying of water is done by writing on the label layer with decoloring ink, and after completely drying the written part, decoloring ink with water The writing mark is erased until is completely erased. Thereafter, the water on the label layer is lightly cut, dried at room temperature while containing the water, and then visually checked for a difference in hue between the written mark and the surrounding area.

(Label layer formation method)
The method for forming the label layer of the information recording medium is not particularly limited as long as the object and effect of the present invention are not impaired. Of these, screen printing is preferred because of its high productivity and high versatility.
Hereinafter, a case where the label layer is formed by a screen printing method will be described as an example, but the present invention is not limited thereto.

  When forming a label layer by a screen printing method, a mixture for forming a label layer containing an ultraviolet curable resin monomer described later is applied onto a layer that is a lower layer of the label layer, such as a protective layer or a substrate, and a coating film Form. Next, the ultraviolet ray curable resin monomer is cured by irradiating the coating film with ultraviolet rays to obtain a label layer. In addition, when a label layer consists of two or more layers, it forms by repeating the said application | coating and hardening several times.

  There is no restriction | limiting in particular as a light source used for ultraviolet irradiation, What can irradiate light with a normal wavelength of 200 nm or more and a normal wavelength of 450 nm or less is used. Specific examples of the light source include a mercury lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, and a metal halide lamp.

Further, the irradiation energy amount of ultraviolet rays may be an amount capable of curing the ultraviolet curable resin, and is usually 150 mJ / cm ² or more, preferably 250 mJ / cm ² or more. Moreover, it is 2000 mJ / cm < ² > or less normally, Preferably it is 1000 mJ / cm < ² > or less.

(Mixture for forming the label layer)
The mixture used for forming the label layer usually contains an ultraviolet curable resin monomer. As the ultraviolet curable resin monomer, any of a radical polymerization type resin monomer and a cationic polymerization type resin monomer can be used. However, since the reaction rate of the radical polymerization type ultraviolet curable resin monomer is generally high, A polymerizable ultraviolet curable resin monomer is preferred.

  When a radical polymerization type ultraviolet curable resin monomer is used, the mixture can usually contain a radical polymerization type resin monomer and a radical photopolymerization initiator, and if necessary, a radical polymerization type resin oligomer. Further, it may contain other various additives. It is also possible to use a cationic polymerization type resin monomer in combination, and in this case, it is preferable to use a cationic polymerization initiator in combination with the mixture.

-UV curable resin monomer In the present invention, as a resin monomer, a monofunctional monomer that does not contain an aromatic ring in the structure and other than urethane acrylate, and / or does not contain an aromatic ring in the structure, and other than urethane acrylate It is preferable to contain one or more polyfunctional monomers in the mixture.

  A monofunctional monomer that does not contain an aromatic ring in the structure and that is other than urethane acrylate, and / or a mixture that contains a polyfunctional monomer that does not contain an aromatic ring in the structure and is other than urethane acrylate in a mixture in a predetermined amount or more. By forming the label layer using, the decoloring property when the written mark is decolored with water after writing on the label layer using the decolorizable ink described later can be made sufficient. This is because an ordinary color-erasable ink contains an aromatic compound having a phenolic hydroxyl group as an electron-accepting compound (developer). In general, a resin having an aromatic ring has an affinity with the aromatic compound having a phenolic hydroxyl group, and when the resin having an aromatic ring is contained in a large amount in the label layer, the affinity Therefore, the aromatic compound having a phenolic hydroxyl group is less likely to move to the aqueous phase, and the decoloring property tends to be lowered. In addition, label layers formed using urethane acrylate monomers generally tend to have the components of the decolorizable ink enter the interior due to the organic solvent in the decolorable ink, resulting in a decrease in the decolorization of the writing marks due to the decolorable ink. Also based on the tendency to. By using the above monofunctional and / or polyfunctional monomers, ink characteristics (mixture characteristics), printability, and coating film characteristics (label layer characteristics) can be adjusted.

  The mixture preferably contains a resin oligomer other than urethane acrylate and / or an epoxy resin monomer that does not contain an aromatic ring in the structure. Because the type and amount of resin oligomer and epoxy resin monomer contained in the mixture can adjust the hardness of the label layer, the adhesion between the label layer and other layers, the water resistance and moisture resistance of the label layer, etc. Depending on these, it is preferable to appropriately use a resin oligomer or an epoxy resin monomer.

  The total content of the monofunctional monomer and / or polyfunctional monomer in the mixture is preferably 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more. The total content of the ultraviolet curable oligomer in the mixture is usually 1% by weight or more, preferably 5% by weight or more, and usually 40% by weight or less, preferably 20% by weight or less. Thereby, the characteristics described above can be obtained.

  Among the polyfunctional monomers that do not contain an aromatic ring in the structure and are other than urethane acrylate and / or polyfunctional monomers that do not contain an aromatic ring in the structure and other than urethane acrylate, Examples of the cationic polymerizable monomer include an epoxy resin monomer that does not include an aromatic ring in the structure, a vinyl ether compound, and the like. These may be used alone or in combination of two or more in any ratio and combination. As the monofunctional monomer that does not contain the aromatic ring in the structure and other than urethane acrylate, and / or the polyfunctional monomer that does not contain the aromatic ring in the structure and other than urethane acrylate, (meth) acrylate type Monomers are preferred.

  Examples of monofunctional (meth) acrylates that do not contain an aromatic ring in the structure include isoamyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, butoxyethyl (meth) acrylate, isobornyl (meth) acrylate, tetrahydrofur Furyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, chlorohydroxypropyl (meth) acrylate, diethylene glycol mono (meth) acrylate, tri Ethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, dipropylene glycol mono (meth) acrylate, polyp Pyrene glycol mono (meth) acrylate, glycerin mono (meth) acrylate, glycerin di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol penta (meth) acrylate, dimethyl (meth) acrylamide, diethyl (meth) acrylamide , Acroylmorpholine, N-vinylpyrrolidone, 2-ethoxyethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, ethyl carbitol (meth) acrylate, glycidyl (meth) acrylate, 1,6-hexanediol (meta ) Acrylate and the like.

  Examples of polyfunctional (meth) acrylates that do not contain an aromatic ring in the structure include 1,3-butylene glycol, 1,4-butanediol, 1,5-pentanediol, and 3-methyl-1,5-pentane. Diol, 1,6-hexanediol, neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, tricyclodecane dimethanol, ethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, Di (meth) acrylates such as polypropylene glycol, dimethylol tricyclodecane, dicyclopentadienyl; trimethylolpropane tri (meth) acrylate, acrylated isocyanurate, pentaerythritol tetra (meth) acrylate, etc. It is below.

  Moreover, as an epoxy resin monomer which does not contain an aromatic ring in a structure, an alicyclic epoxy resin, an aliphatic epoxy resin, etc. are mentioned. Specific examples of the epoxy resin monomer include hydrogenated bisphenol A diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, glycerin diglycidyl ether, and polybutadiene diglycidyl ether. Can be mentioned. The number average molecular weight of the epoxy resin monomer is usually 10,000 or less.

  Specific examples of the vinyl ether compound monomer include triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, cyclohexane-1,4-dimethylol divinyl ether, 1,4-butanediol divinyl ether, and the like.

  Among these, di (meth) acrylate is particularly preferable because the decoloring property of the decoloring ink is good. Particularly preferable examples include di (meth) acrylates of ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, and glycerin diglycidyl ether.

  Examples of ultraviolet curable oligomers that do not contain an aromatic ring and are other than urethane oligomers include acrylic oligomers, epoxy oligomers, polyester oligomers, and ether oligomers. These may be used alone or in combination of two or more in any ratio and combination. In the mixture, by containing a resin oligomer other than an aromatic ring and not containing a urethane-based oligomer, as in the case of the monomer described above, the written mark is erased with water. The decoloring property can be made sufficient.

  Specifically, examples of the acrylic oligomer include alkyl (such as (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate ( (Meth) acrylate polymer, the above monomers, vinyl carboxylic acid compounds such as maleic acid, itaconic acid, crotonic acid, fumaric acid, glycidyl (meth) acrylate, allyl glycidyl ether, glycidyl ethyl acrylate, crotonyl glycidyl ether, croton Copolymer with a compound selected from glycidyl group-containing vinyl compounds such as glycidyl acid, hydroxyethyl (meth) acrylate, vinyl acetate, (meth) acrylonitrile, (meth) acrylic acid chloride, N- (meth) acryloylmorpholine Is mentioned.

As the epoxy oligomer, an epoxy oligomer obtained by reacting an acrylate with an epoxy resin, polyarylate, or the like can also be used as a resin oligomer component.
As a polyester-type oligomer, oligomers, such as ester of polyester diol and acrylic acid which consist of adipic acid and 1, 6- hexanediol, are mentioned, for example.
Examples of the ether oligomer include esters of polypropylene glycol and acrylic acid.

  In addition, the ultraviolet curable oligomer as used in the field of this invention means that whose number average molecular weight is usually several thousand to less than 10,000. In general, a monomer alone cannot match all the characteristics required for a label layer, and therefore, a label layer suitable for the characteristics required can be obtained by appropriately mixing the types and amounts of oligomers. That is, a label layer having good properties such as hardness, adhesion, water resistance and moisture resistance can be obtained.

-Non-photosensitive resin A non-photosensitive resin may be mixed in the mixture of the present invention. The non-photosensitive resin preferably does not contain an aromatic ring in the structure. Non-photosensitive resins that do not contain an aromatic ring in the structure include, for example, cellulose acetate resins, nitrocellulose resins, polyvinyl alcohol resins, polyvinyl butyral resins, saturated polyester resins, hydroxyethyl cellulose, polybutadiene resins, poly Examples include high molecular substances such as methyl methacrylate resin, acrylic acid / methacrylic acid copolymer, polyvinyl chloride resin, vinyl acetate / vinyl chloride copolymer, and ethylene / vinyl acetate copolymer.
The total content of the non-photosensitive resin mixture is usually 1% by weight or more, preferably 5% by weight or more, and usually 40% by weight or less, preferably 20% by weight or less.

-Photopolymerization initiator Examples of radical photopolymerization initiators that generate radicals by ultraviolet rays used in the mixture include, for example, benzoin such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, or ethers thereof; benzophenone compounds such as benzophenone Benzyl compounds such as benzyl, benzyl methyl ketal and benzyl ethyl ketal; hydroxyalkyl phenyl ketone compounds such as 1-phenyl-2-hydroxy-2-methyl-2-propane; and the like. These can be used singly or in combination of two or more in any ratio and combination.
On the other hand, when a cationic polymerization resin is used alone or in combination with a radical photopolymerization resin, a triarylsulfonium salt (TAS) or a diaryliodonium salt is used as a photoacid generator for generating a cation by ultraviolet rays in the cationic polymerization resin. (DAI) can be used. These may be used alone or in combination of two or more in any ratio and combination and may be used in combination with a radical photopolymerization initiator.

  The content of the photopolymerization initiator in the mixture is usually 0.5% by weight or more, preferably 1% by weight or more, and usually 15% by weight or less, preferably 10% by weight or less. By setting it within the above range, the curability of the resin monomer, the resin oligomer and the like can be made sufficient.

  A sensitizer can be used in combination with the photopolymerization initiator. Examples of the sensitizer include trimethylamine, methyldimethanolamine, triethanolamine, p-diethylaminoacetophenone, ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, N, N-dimethylbenzylamine and 4, 4′-bis (diethylamino) benzophenone and the like can be mentioned. These may be used alone or in combination of two or more in any ratio and combination.

Other In addition, the mixture may contain an additive for the purpose of improving various properties and the like within a range not impairing the object and effect of the present invention. Examples of additives include thermal polymerization inhibitors; antioxidants represented by hindered phenols, hindered amines, phosphites, etc .; plasticizers; silane cups represented by epoxy silanes, mercaptosilanes, (meth) acrylic silanes, etc. Ring agents; and the like. These may be used alone or in combination of two or more in any ratio and combination.
These are selected from those having excellent solubility in ultraviolet curable resins (resin monomers, resin oligomers, resins, etc.) and those that do not inhibit ultraviolet transparency.

  In addition, when forming a label layer by a screen printing method, the trace of a screen mesh may remain on the coating-film surface. When this screen mesh mark remains, the glossiness of the label layer tends to be low. In addition, when writing with the above-described decolorizable ink, the decolorable ink may enter the concave portions of the surface irregularities, and the decoloring property of the decolorable ink may be reduced when the written marks are erased with water. . Therefore, it is preferable that the label layer forming composition contains a surfactant as a leveling agent. Moreover, when a mixture contains surfactant, the defoaming effect | action in the application | coating process of a mixture can also be anticipated.

  Examples of the surfactant include polysiloxanes and acrylic copolymers. These may be used alone or in combination of two or more in any ratio and combination. The surfactant is usually 10% by weight or less, preferably 7% by weight or less, more preferably 6% by weight or less in the mixture. Moreover, it is 0.5 weight% or more normally, Preferably it is 1.0 weight% or more.

Moreover, in order to adjust the hue of the label layer, pigments, dyes, and the like can be contained in the mixture as long as the effects and objects of the present invention are not impaired. These are appropriately selected according to the hue of the label layer. As described above, when the writing area of the label layer is set to an achromatic gray color, for example, an inorganic pigment such as titanium oxide white and carbon black is blended. Toned and used.
In addition, as a colored pigment, for example, an organic pigment such as isoindoline, benzimidazolone, quinacridone, dioxazine, copper phthalocyanine, or the like can be used by blending and toning with a hue close to an achromatic color described in the present application.

  Specifically, Pigment White 6 (titanium oxide), Pigment Black 7 (carbon black), Pigment Yellow 110, Pigment Yellow 151, Pigment Red 202, Pigment Violet 37, and Pigment Blue 37 are listed from the color index. These may be used alone or in combination of two or more in any ratio and combination.

  As the dye, an oil-soluble dye such as methine, perinone, anthraquinone, phthalocyanine, or the like can be used by blending and toning in a timely manner in a hue close to an achromatic color described in the present application. Specifically, Disperse Yellow 82, Solvent Red 135, Disperse Violet 57, Solvent Blue 67, etc. are mentioned from a color index. These may be used alone or in combination of two or more in any ratio and combination.

  Further, in order to improve the scratch resistance of the label layer, etc., silicon oxide (silica), talc, titanium oxide, clay, calcium carbonate, calcium silicate, barium sulfate, mica, diatomaceous earth silica, aluminum hydroxide, Inorganic fine particles such as alumina, zirconium oxide and zirconium hydroxide can be added. The particle size of the inorganic fine particles may be 0.01 μm or more, preferably 0.5 μm or more, and usually 10 μm or less, preferably 5 μm or less. The content of the particles is preferably in a range that does not impair the erasability after writing of the erasable ink on the label layer.

(2) Information Recording Layer Information writing (recording) and / or reading (reproduction) on the information recording medium of the present invention is preferably performed with a laser beam converged to about 1 μm. As the laser beam, for example, a semiconductor laser beam can be suitably used. Recording of information on the information recording layer is usually performed by melting, evaporation, sublimation, deformation, modification, etc. of the material of the recording layer in the laser light irradiation portion (recording portion). The recorded information is reproduced by reading the difference in reflectance between the laser light irradiated portion and the non-irradiated portion.
As the laser beam, a semiconductor laser beam is preferably used.

  The information recording layer is formed of a material capable of recording electronic information (information recorded by a digital signal, such as information recorded by a digital signal) by laser light irradiation, and is usually an information recording made of an organic substance. It is formed as an information recording layer made of a layer or an inorganic substance.

  When the information recording layer is made of an organic material, an organic dye is mainly used. Examples of organic dyes include macrocyclic azaannulene dyes (phthalocyanine dyes, naphthalocyanine dyes, porphyrin dyes, etc.), polymethine dyes (cyanine dyes, merocyanine dyes, squarylium dyes, etc.), anthraquinone dyes, azurenium dyes, azo dyes. Examples thereof include dyes, metal-containing azo dyes, and metal-containing indoaniline dyes. These may be used alone or in combination of two or more in any ratio and combination. Among these, metal-containing azo dyes, cyanine dyes, and phthalocyanine dyes are preferable. In particular, metal-containing azo dyes are preferable because they are excellent in durability and light resistance.

  Examples of the method for forming the information recording layer made of an organic material include dry film forming methods such as vacuum vapor deposition and sputtering, and wet film forming methods generally used such as a cast method, a spin coating method, and an immersion method. Of these, the wet film forming method is preferable from the viewpoint of mass productivity and cost, and the spin coating method is particularly preferable.

  When the information recording layer is formed of an inorganic substance, for example, a rare earth transition metal alloy such as Tb / Te / Co or Dy / Fe / Co which is recorded by a magneto-optical effect is used. Further, chalcogen alloys such as Ge · Te and Ge · Sb · Te that change phase may be used. These layers may be a single layer or may be composed of two or more layers.

Examples of the method for forming the information recording layer made of an inorganic substance include vapor deposition, ion plating, and sputtering. Of these, the sputtering method is particularly preferable from the viewpoint of mass productivity and cost.
The thickness of the information recording layer varies depending on the type of the recording layer, but the lower limit is usually 5 nm, preferably 10 nm, and the upper limit is usually 500 nm, preferably 300 nm.
The information recording layer may be a phase change recording layer capable of recording / erasing.

(3) Reflective layer The reflective layer usually has a function of reflecting light applied to the information recording medium. When the guide layer or pit for recording / reproduction is provided on the substrate, the reflective layer has an uneven shape corresponding thereto.
Examples of the material for forming the reflective layer include those having a sufficiently high reflectance at the wavelength of the reproduction light, for example, metals such as Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, and Pd. Can be used alone or as an alloy. Among these, Au, Al, and Ag have high reflectivity and are suitable as a material for the reflective layer. Further, those containing Ag as a main component are particularly preferable from the viewpoints of low cost and high reflectance.

  Examples of the method for forming the reflective layer include vapor deposition, ion plating, and sputtering. Of these, the sputtering method is particularly preferable from the viewpoint of mass productivity and cost. The lower limit of the thickness of the reflective layer 103 is usually 30 nm, preferably 50 nm, and the upper limit is usually 150 nm, preferably 120 nm.

(4) Protective layer A protective layer may be formed in the information recording medium of the present invention. The protective layer is usually formed of a material that is transparent to laser light, and examples thereof include ultraviolet (UV) curable resins. As a specific example of the ultraviolet (UV) curable resin, acrylate resins such as urethane acrylate, epoxy acrylate, and polyester acrylate can be used. Since most of these materials are laser light transmitting materials, they can be suitably used. These ultraviolet (UV) curable resins may be used alone or in a combination of two or more. Further, the protective layer may be a single monolayer film or a multilayer film having two or more layers.

As a method of forming the protective layer with an ultraviolet (UV) curable resin, an ultraviolet (UV) curable resin is usually used as it is or after dissolving in an appropriate solvent to prepare a coating solution, and then the coating solution is used as a reflective layer. It can be formed by coating on and curing by irradiating with ultraviolet (UV) light. In this case, a spin coating method, a casting method, or the like can be employed as a coating method. The protective layer can also be formed by various wet film formation methods such as the above-described various coating methods and screen printing methods, various dry film formation methods such as vacuum deposition methods, sputtering methods, ion plating methods, and the like. It is formed by a method appropriately selected according to the method. Among these, a wet film forming method, particularly a spin coating method is preferable, and a spin coating method is generally used.
The lower limit of the thickness of the protective layer 104 is usually 1 μm, preferably 3 μm, and the upper limit is usually 15 μm, preferably 10 μm.

(5) Substrate A substrate is usually used for the information recording medium of the present invention. The substrate is required to be transparent to the wavelengths of the recording light and the reproducing light depending on the incident directions of the recording light and the reproducing light with respect to the information recording layer. It is formed with the material which has.

  As a material for forming the substrate, for example, polycarbonate resin, acrylic resin, methacrylic resin, polystyrene resin, vinyl chloride resin, epoxy resin, polyester resin, amorphous polyolefin resin, and other polymer materials, Inorganic materials such as glass are used. These may be used alone or in combination of two or more in any ratio and combination. Among these, the polycarbonate resin is particularly preferable because it is excellent in terms of high light transmission, low optical anisotropy, and high mechanical strength. Amorphous polyolefin is preferable from the viewpoint of chemical resistance, moisture absorption resistance, optical properties, and the like.

  For example, as shown in the schematic cross-sectional view of FIG. 1, in a configuration in which the substrate 101 is formed in contact with the information recording layer 102, a recording / reproducing guide groove or pit may be provided on the substrate 101. . In this case, the substrate 101 can be molded by a molding method such as injection molding. Such guide grooves or pits are preferably provided at the time of forming the substrate 101. For example, the guide grooves or pits may be provided on the substrate 101 using an ultraviolet (UV) curable resin.

  The lower limit of the substrate thickness is usually 1.1 mm, preferably 1.15 mm, and the upper limit of the thickness is usually 1.3 mm, preferably 1.25 mm.

2. Ink The ink used for writing on the label layer in the information recording medium of the present invention contains an electron-donating color-forming organic compound, an electron-accepting compound, and a solvent, and can be decolored with water. Usually, it is used in a writing instrument such as a pen.

・ Electron-donating color-forming organic compounds Electron-donating electron-donating color-forming organic compounds react when they come into molecular contact with the electron-accepting compounds described later, and develop colors specific to each electron-donating color-forming organic compound. To do. In addition, application of water causes the electron-accepting compound to dissolve in the aqueous phase and dissociate, and thus changes from a colored state to a colorless state.
Examples of the electron donating color-forming organic compound include triphenylmethane phthalide, phenosadine, phenothiazine, fluoran, indolylphthalide, spiropyran, azaphthalide, diphenylmethane, chromenopyrazole, leuco. Any conventionally known ones such as auramine, azomethine, rhodamine lactam, naphtholactam, triazene and the like can be used. These may be used alone or in combination of two or more in any ratio and combination.

  Specific examples of the electron donating color-forming organic compound include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (4-diethylaminophenyl) -3- (1-ethyl). -2-methylindol-3-yl) phthalide, 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide, 3,3-bis (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- [2-ethoxy-4- (N-ethylanilino) phenyl] -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, 3,6-diphenylaminofur Oran, 3,6-dimethoxyfluorane, 3,6-di-n-butoxyfluorane, 2-methyl-6- (N-ethyl-Np-tolylamino) fluorane, 3-chloro -6-cyclohexylaminofluorane, 2-methyl-6-cyclohexylaminofluorane, 2- (2-chloroanilino) -6-di-n-butylaminofluorane, 2- (3-trifluoromethylanilino)- 6-diethylaminofluorane, 2- (N-methylanilino) -6- (N-ethyl-Np-tolylamino) fluorane, 1,3-dimethyl-6-diethylaminofluorane, 2-chloro-3-methyl-6 -Diethylaminofluorane, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-di-n-butylaminofluorane, 2-xylidino-3-methyl-6-diethylaminofluor Oran, 1,2-Benz-6-diethylaminofluorane, 1,2-Benz-6- (N-ethyl-N-i Butylamino) fluorane, 1,2-benz-6- (N-ethyl-N-isoamylamino) fluorane, 2- (3-methoxy-4-dodecoxystyryl) quinoline, spiro [5H- (1) benzopyrano ( 2,3-d) pyrimidine-5,1 '(3'H) isobenzofuran] -3'-one, 2- (diethylamino) -8- (diethylamino) -4-methyl-, spiro [5H- (1) Benzopyrano (2,3-d) pyrimidine-5,1 '(3'H) isobenzofuran] -3'-one, 2- (di-n-butylamino) -8- (di-n-butylamino)- 4-methyl-, spiro [5H- (1) benzopyrano (2,3-d) pyrimidin-5,1 '(3'H) isobenzofuran] -3'-one, 2- (di-n-butylamino) -8- (diethylamino) -4- Methyl-, spiro [5H- (1) benzopyrano (2,3-d) pyrimidin-5,1 '(3'H) isobenzofuran] -3'-one, 2- (di-n-butylamino) -8 -(N-ethyl-Ni-amylamino) -4-methyl-, spiro [5H- (1) benzopyrano (2,3-d) pyrimidine-5,1 '(3'H) isobenzofuran] -3' -One, 2- (di-n-butylamino) -8- (di-n-butylamino) -4-phenyl, 3- (2-methoxy-4-dimethylaminophenyl) -3- (1-butyl- 2-Methylindol-3-yl) -4,5,6,7-tetrachlorophthalide, 3- (2-ethoxy-4-diethylaminophenyl) -3- (1-ethyl-2-methylindole-3- Yl) -4,5,6,7-tetrachlorophthalide, - (2-ethoxy-4-diethylaminophenyl) -3- (1-pentyl-2-methylindole-3-yl) -4,5,6,7 can be given tetrachloro phthalide like.

  The electron donating color-forming organic compound is usually contained in the ink in an amount of 0.5% by weight or more, preferably 2% by weight or more, more preferably 5% by weight or more. Moreover, it is 20 weight% or less normally, Preferably it is 15 weight% or less. Thereby, the color developability of the ink can be improved.

-Electron-accepting compound A water-soluble developer is suitable as the electron-accepting compound. Specifically, water-soluble thiocyanate such as zinc salt, cobalt salt, nickel salt, zinc salicylate, gallic acid, polyoxyalkylene monoallyl monomethyl ether / maleic anhydride / styrene copolymer, polyoxyethylene alkyl ether Carboxylic acid, polyoxyethylene aryl ether phosphate ester, polyoxyethylene alkyl ether phosphate ester, p-sulfosalicylic acid, P-toluenesulfonic acid, naphthalenesulfonic acid, lactic acid, tartaric acid, citric acid and the like. In addition, bisphenol A, bisphenol S, etc. are mentioned as a water-insoluble developer. Of these, zinc salicylate, gallic acid, P-toluenesulfonic acid, bisphenol A, and bisphenol S are preferable. These may be used alone or in combination of two or more in any ratio and combination.
By using the water-soluble developer, when the handwriting is decolored, that is, when it is brought into contact with water, the water-soluble developer dissolves as an ion and moves to the aqueous phase, and as a result, The leuco dye, which is an electron-donating color-forming organic compound, closes and becomes colorless.

  The electron-accepting compound is usually contained in the ink in an amount of 0.5% by weight or more, preferably 2% by weight or more, more preferably 5% by weight or more. Moreover, it is 30 weight% or less normally, Preferably it is 20 weight% or less. Thereby, the coloring property and decoloring property of the ink can be made sufficient.

・ Solvent The organic solvent used in the ink can be arbitrarily selected, but the electron-donating color-forming compound, the electron-accepting compound, and the solubility of other components used as necessary, and the ink It is preferable to select in consideration of the drying speed, and a volatile organic solvent is preferable.
Examples of the volatile organic solvent include alcohols, cellosolves, glycol ethers, esters, and the like. Specifically, ethanol, isopropyl alcohol, butanol, propylene glycol monomethyl ether, or the like can be used. These may be used alone or in combination of two or more in any ratio and combination.

-Others In the said ink, surfactant etc. can be used in the range which does not impair the objective and effect of this invention, for example. The surfactant can be mixed to make the electron-donating color-forming organic compound and the electron-accepting compound easy to get wet with water and to improve the decoloring property.
Specific examples of the surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ethyl ester, sorbitan alkyl ester, polyoxyethylene oleate, polyoxyethylene laurate, polyoxyethylene sorbitan A monooleate etc. are mentioned, It can use individually by 1 type or 2 types or more by arbitrary ratios and combinations. These can be used in the ink composition in an amount of usually 1% by weight or more, preferably 2% by weight or more, and usually 30% by weight or less, preferably 20% by weight or less.
Moreover, the said ink can use 1 type of other arbitrary additives, or 2 or more types by arbitrary ratios and combinations.

  The present invention will be described more specifically with reference to examples. However, the present invention is not limited to the description of the following examples without departing from the gist thereof.

(1) Production of information recording medium (production of Bare disk of CD-R)
A polycarbonate resin substrate having a groove with a width of 0.45 μm and a depth of 155 nm and a thickness of 1.2 mm was formed by injection molding. On this substrate, a fluorine alcohol solution of a metal-containing azo dye was applied by spin coating and dried at 90 ° C. for 15 minutes to form an information recording layer having a thickness of 70 nm. Next, silver (Ag) was sputtered on the information recording layer to form a reflective layer having a thickness of 70 nm. Furthermore, an ultraviolet curable resin (“Dai Nippon Ink Co., Ltd.“ SD-394 ”) mainly composed of an acrylate monomer is applied onto the reflective layer by spin coating, and then cured by irradiating with ultraviolet (UV) light. Then, a 7 μm-thick protective layer was formed, and a CD-R BareDisk having a recording / reproducing functional layer was produced.

(Preparation of decolorizable ink)
In the following examples and comparative examples, the label layer was evaluated using the blue color of trade mark: Pencle manufactured by SUNNY as the decolorizable ink.
The ink composition is an ink comprising an electron donating color-forming compound (crystal violet lactone), zinc salicylate, ethanol, isopropyl alcohol, and a surfactant.

なお、上記Ｉｒｇａｃｕｒｅ １８４は、ラジカル光重合開始剤であり、１−ヒドロキシ−シクロヘキシル−フェニル−ケトンを示す。以下同様である。 [Example 1] (Example of UV curable monomer containing no aromatic ring)
Light acrylate 9EG-A represented by the following chemical formula (Kyoeisha Chemical) 90% by weight
Irgacure 184 (Ciba Specialty Chemicals) 10% by weight

The above Irgacure 184 is a radical photopolymerization initiator and represents 1-hydroxy-cyclohexyl-phenyl-ketone. The same applies hereinafter.

The UV curable resin coating solution (mixed solution) having the above blending ratio was applied onto a 100 μm polyester film with a gap 7 μm applicator, and irradiated and cured to about 300 mJ with a UV irradiation device.
Characters were written with the decoloring ink on the coating film coated and cured on the polyester film, and good color development was confirmed. Next, when water was applied, the color was instantly erased and no written marks were left after drying. The results are shown in Table 1.

[Example 2] (Example of UV curable monomer containing no aromatic ring)
Epoxy ester represented by the following chemical formula: 70PA (Kyoeisha Chemical) 90% by weight
Irgacure 184 (Ciba Specialty Chemicals) 10% by weight

  A coating film was formed on the polyester film in the same manner as in Example 1 except that the UV curable resin coating liquid (mixed liquid) having the above blending ratio was used. Characters were written on the coating film with the above decoloring ink to confirm good color development. Next, when water was applied, the color was instantaneously erased, and no written marks remained even after drying, and no written marks were confirmed. The results are shown in Table 1.

[Example 3] (Example of UV curable monomer containing no aromatic ring)
Epoxy ester represented by the following chemical formula 80MFA (Kyoeisha Chemical) 90% by weight
Irgacure 184 (Ciba Specialty Chemicals) 10% by weight

  A coating film was formed on the polyester film in the same manner as in Example 1 except that the UV curable resin coating liquid (mixed liquid) having the above blending ratio was used. Characters were written on the coating film with the above decoloring ink to confirm good color development. Next, when water was applied, the color was instantaneously erased, and no written marks remained even after drying, and no written marks were confirmed. The results are shown in Table 1.

[Example 4] (Example of UV curable monomer containing no aromatic ring)
The mixed liquid of Example 2 was applied onto the above-described CD-R BareDisk using a 300-mesh screen with a screen printing machine, and irradiated and cured to about 300 mJ with a UV irradiation apparatus to form a label layer. Obtained.
In the same manner as in Example 1 above, letters were written on the CD-R label layer with decoloring ink to confirm good color development. Next, when water was applied, the color was instantaneously erased, and no written marks remained even after drying, and no written marks were confirmed. The results are shown in Table 1.

  Subsequently, as a result of testing the surface hardness (scratch hardness) of the label layer with a scratching needle: 0.2 mmR made of sapphire using a scratch test of HEIDON Tribogear-TYPE: 18, scratches were up to 150 g. I couldn't see it. The results are shown in Table 2.

[Example 5] (Example of UV curable monomer containing no aromatic ring)
A white underlay label layer was formed under the same conditions as in Example 4 using the white UV ink (RC INK VID SERIES WHITE) manufactured by Jujosha Co., Ltd. on the BareDisk protective layer of the CD-R described above.
On the base label layer, the mixed solution of Example 2 was applied and cured under the same conditions as in Example 4 to form the outermost label layer.
When characters were written on the CD-R label layer in the same manner as in Example 1 with a decolorizable ink, the written marks were very easy to see and good writing quality was obtained. Next, when water was applied, the color was instantaneously erased, and no written marks remained even after drying, and no written marks were confirmed. The results are shown in Table 1.

[Example 6] (Example of ultraviolet curable ink containing no aromatic ring)
DVD MITE OO CLEAR made by Jujo Co., Ltd. was applied on the BareDisk protective layer of the CD-R using a 300 mesh screen with a screen printer, and irradiated and cured to about 300 mJ with a UV irradiation device. A label layer was formed.
In the same manner as in Example 1 above, letters were written on the CD-R label layer with decoloring ink to confirm good color development. Next, when water was applied, the color was instantaneously erased, and a good decoloring property was confirmed to such an extent that a trace of the description could be seen even after drying. The results are shown in Table 1.

  Subsequently, as a result of testing the surface hardness (scratch hardness) of the label layer with a scratching needle: 0.2 mmR made of sapphire using a scratch test of HEIDON Tribogear-TYPE: 18, scratches were up to 150 g. I couldn't see it. The results are shown in Table 2.

上記配合割合となるＵＶ硬化樹脂塗布液（混合液）を用いた以外は、実施例１と同様にしてポリエステルフィルム上に塗布膜を形成した。塗布膜上に上記消色性インキにて文字を記述し良好な発色を確認した。次に水を塗布したところ消色するものの乾燥すると記載跡が淡く再発色し、筆記跡が残り完全には消色できなかった。結果を表１に示す。 [Example 7] (Example of UV-curable monomer containing aromatic ring)
HOA-MPL (Kyoeisha Chemical) represented by the following chemical formula: 90% by weight
Irgacure 184 (Ciba Specialty Chemicals) 10% by weight

A coating film was formed on the polyester film in the same manner as in Example 1 except that the UV curable resin coating liquid (mixed liquid) having the above blending ratio was used. Characters were written on the coating film with the above decoloring ink to confirm good color development. Next, when water was applied, the color disappeared, but when it was dried, the written marks lightly reappeared, and the written marks remained and could not be completely erased. The results are shown in Table 1.

[Example 8] (Example of ultraviolet curable monomer containing aromatic ring)
NK ester A-BPE-10 (Kyoeisha Chemical) represented by the following chemical formula: 90% by weight
Irgacure 184 (Ciba Specialty Chemicals) 10% by weight

  A coating film was formed on the polyester film in the same manner as in Example 1 except that the UV curable resin coating liquid (mixed liquid) having the above blending ratio was used. Characters were written on the coating film with the above decoloring ink to confirm good color development. Next, when water was applied, the color disappeared, but when it was dried, the written marks lightly reappeared, and the written marks remained and could not be completely erased. The results are shown in Table 1.

[Example 9] (Example of ultraviolet curable monomer containing aromatic ring)
Epoxy ester 3002A (Kyoeisha Chemical) represented by the following chemical formula: 90% by weight
Irgacure 184 (Ciba Specialty Chemicals) 10% by weight

  A coating film was formed on the polyester film in the same manner as in Example 1 except that the UV curable resin coating liquid (mixed liquid) having the above blending ratio was used. Characters were written on the coating film with the above decoloring ink to confirm good color development. Next, when water was applied, the color disappeared, but when it was dried, the written marks lightly reappeared, and the written marks remained and could not be completely erased. The results are shown in Table 1.

上記配合割合となるＵＶ硬化樹脂塗布液（混合液）を用いた以外は、上記実施例４と同様にしてＣＤ−Ｒレーベル層上に消色性インキにて文字を記載し良好な発色を確認した。次に水を塗布したところ消色するものの乾燥すると記載跡が淡く再発色し、はっきり筆記跡が残り完全には消色できなかった。 [Example 10] (Example using urethane acrylate resin)
NK Oligo UA-W2A (Shin Nakamura Chemical Co., Ltd.) represented by the following chemical formula 90% by weight
Irgacure 184 (Ciba Specialty Chemicals) 10% by weight

Except for using the UV curable resin coating liquid (mixed liquid) with the above blending ratio, the characters were written on the CD-R label layer with decolorizable ink in the same manner as in Example 4 to confirm good color development. did. Next, when water was applied, the color disappeared, but when it was dried, the written mark lightly reappeared, and the written mark remained clearly and could not be completely erased.

[Example 11] (Example using ultraviolet curable ink containing urethane acrylate)
DVD OPT-L CLEAR made by Jujo Co., Ltd. was applied on the BareDisk protective layer of the CD-R using a 300-mesh screen with a screen printer, and irradiated and cured to about 300 mJ with a UV irradiation device. A label layer was formed.
In the same manner as in Example 1, letters were written on the CD-R label layer with decoloring ink to confirm good color development. Next, when water was applied, the color disappeared, but when it was dried, the written marks lightly reappeared, and the written marks remained and could not be completely erased. The results are shown in Table 1.

Subsequently, as a result of testing the surface hardness (scratch hardness) of the label layer at a scratching needle: 0.2 mmR made of sapphire using a scratch test of HEIDON tribogear-TYPE: 18, the scratch rate was 100 g. It was seen. The results are shown in Table 2.

The present invention can be directly written on a label layer of an information recording medium using decoloring ink, and can be corrected at the time of erroneous entry or change of recorded contents, such as water or a sponge or cloth containing water. You can erase the writing mark with. These operations can be repeated.
Therefore, in the rewritable information recording medium that is generally used in the current market, the written content can be rewritten in accordance with the change of the recorded content, etc. Can be easily corrected. Therefore, the present invention can be applied to all information recording media.

101 Substrate 102 Information recording layer 103 Reflective layer 104 Protective layer 106 Label layer 107 Light (recording light or reproducing light)

Claims (7)

An information recording medium having an information recording layer capable of recording or reproducing information by irradiating light and a label layer,
The label layer contains an electron-donating color-forming organic compound, an electron-accepting compound, and a solvent, and is used for writing with an ink that can be decolored with water and for decoloring with water the writing mark with the ink. An information recording medium characterized by that. The information recording medium according to claim 1, wherein the label layer has a surface scratch hardness of 100 g or more as measured by the following method.
(Scratch hardness measurement method)
The label layer surface and the needle are brought into contact with each other while a predetermined load is applied to a sapphire needle having a tip radius of 0.2 mm, the load of which can be adjusted, and the needle is moved at a speed of 100 mm / min. The scratch mark of the needle is visually confirmed, and if the scratch mark is not confirmed, it is determined that the needle has a hardness equal to or higher than the load. The label layer is
A monofunctional monomer which does not contain an aromatic ring in its structure and is other than urethane acrylate, and / or contains at least one polyfunctional monomer which does not contain an aromatic ring in its structure and is other than urethane acrylate, 3. The information recording medium according to claim 1, wherein the information recording medium is formed using a mixture in which the total content of the polyfunctional monomer is 50% by weight or more. 4. The mixture according to claim 3, wherein the mixture contains an aromatic ring in the structure and an ultraviolet curable oligomer other than the urethane-based oligomer, and / or an epoxy resin monomer that does not contain the aromatic ring in the structure. The information recording medium described. As for the hue of the label layer, the L * value of the L * a * b * color system is 60 or more, the absolute value of the a * value is 15 or less, and the absolute value of the b * value is 15 or less. The information recording medium according to claim 1, wherein the information recording medium is a recording medium. 6. The information recording medium according to claim 5, wherein the L * value is 60 or more and 90 or less. An information recording medium having an information recording layer capable of recording or reproducing information by irradiating light and a label layer,
The label layer contains an electron-donating color-forming organic compound, an electron-accepting compound, and a solvent, and can be written with an ink that can be erased with water. The information recording medium according to claim 1, wherein after the water is dried, the written mark does not have a recurrent color due to the ink.

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