Information recording media for laser marking

Abstract

To provide an information recording media capable of being laser marked and excellent in coloring properties.　This laser marking-use information recording media 1 is configured so that a first base material 2, a coloring layer 4, and a second base material 7 are laminated in that order. The first base material 2 is a layer that transmits ultraviolet rays. The coloring layer 4 is a layer containing a leuco dye and a developer.

Description

Laser marking information recording medium

[0001] The present invention relates to an information recording medium for laser marking.

[0002] Laser marking is a type of marking method using laser light emitted from a printing device such as a laser marker. Laser marking techniques for various objects have been proposed. For example, if the object itself absorbs laser light, the surface of the object is scraped or altered by the irradiation of the laser light. This allows for marking in the scraped areas by utilizing the difference in color between the object's surface and the object's interior. Furthermore, in areas where the object's surface has been altered, marking can be achieved by utilizing the discoloration caused by the alteration. Even for objects with low sensitivity to laser light, adding an inorganic material that has laser sensitivity and changes color when heated to the object can impart or improve suitability for laser marking (laser marking suitability).

[0003] However, with this method, the surface of the object or the material exposed on the surface is scraped off by the energy of the laser light, resulting in damage to the surface of the object. This means that the printed area is damaged by the laser light, resulting in a decrease in print quality. Furthermore, there are problems with the density of the drawn characters being low, resulting in poor color development and contrast.

[0004] In response to this, information recording media have been studied that can improve contrast and have excellent color development properties by adding a dye and a color developer to the color-developing layer, and that can suppress surface damage during laser marking by laminating a surface protective layer on the color-developing layer (see, for example, Patent Documents 1 and 2).

[0005] JP 2006-69086 JP 8-25809

[0006] However, the laminated recording material of Patent Document 1 essentially requires the addition of an inorganic material or a specific copper phosphonate to increase sensitivity to laser light. Furthermore, the laser marking material of Patent Document 2 requires a color developer with a melting point of 200° C. or higher. Thus, there has been a problem in that only specific information recording media that can be laser marked and have excellent color development properties have been disclosed, and they have not yet been fully investigated.

[0007] Furthermore, the laminated recording materials and laser marking materials described in Patent Documents 1 and 2 use a color developer having a phenol skeleton, i.e., a phenol-based color developer. Phenol-based color developers have been conventionally used, but in recent years, there has been a trend toward avoiding their use due to environmental considerations. As a result, there has been an increasing demand for information recording media for laser marking that are laser markable, have excellent color development properties, and use a non-phenol-based color developer as the color developer. However, there has been a problem in that no such information recording media have yet been specifically provided.

[0008] Furthermore, when the color-forming layer contains a color developer, there is generally a problem with print storage stability, in that the color density decreases during storage due to the influence of external factors such as chemicals. In particular, when the information recording medium includes a substrate or a laminate layer, components in the substrate or laminate layer (e.g., oil-soluble components such as monomer components and plasticizers) migrate to the color-forming layer, resulting in a problem with moist heat resistance, in that the color density decreases during storage, particularly when stored in a high-temperature, high-humidity environment. For this reason, there has been a problem in that a specific information recording medium for laser marking that is laser-markable and has excellent color development and moist heat resistance has not yet been provided.

[0009] Furthermore, printing devices that irradiate laser light have different wavelengths of irradiated laser light depending on the type of device, and laser marking information recording media that can be printed with infrared laser light such as carbon dioxide laser light, YAG laser light, YVO4 laser light, etc. have been known for some time. However, there has been a problem in that a laser marking information recording medium that can be printed with ultraviolet laser light with a wavelength of more than 351 nm and not more than 400 nm, such as THG (Third Harmonic Generation) laser light, and that has excellent color development properties has not yet been specifically provided.

[0010] Therefore, an object of the present invention is to provide an information recording medium that can be laser-marked and has excellent color development. In particular, a first object of the present invention is to provide an information recording medium for laser marking that can be laser-marked, has excellent color development, and further contains a non-phenolic color developer as a color developer. A second object of the present invention is to provide an information recording medium for laser marking that can be laser-marked and has excellent color development and moist heat resistance. A third object of the present invention is to provide an information recording medium for ultraviolet laser marking that can be laser-marked using an ultraviolet laser beam with a wavelength of more than 351 nm and not more than 400 nm as a light source, and has excellent color development.

[0011] As a result of extensive research to achieve the above-mentioned object, the inventors have discovered that by having a laminated structure in which a color-forming layer is sandwiched between a first substrate and a second substrate, and further adding a color developer to the color-forming layer, it is possible to obtain an information recording medium that is capable of laser marking without suffering surface damage when irradiated with laser light, and that also has excellent color-forming properties.

[0012] In particular, the inventors have found that an information recording medium containing a specific non-phenolic color developer as the color developer can be laser-marked and has excellent color development properties.

[0013] The inventors have also found that by providing a specific intermediate layer, it is possible to provide an information recording medium for laser marking that is laser markable, has excellent color development properties, and is also more excellent in moist heat resistance.

[0014] Furthermore, it was found that by using the above-mentioned laminated structure, it is possible to provide an information recording medium for laser marking that is capable of laser marking without surface damage even when an ultraviolet laser beam having a wavelength of more than 351 nm and not more than 400 nm is used as a light source, and that has excellent color development properties. The present invention was completed based on these findings.

[0015] That is, the present invention provides an information recording medium for laser marking, which is an information recording medium having a first substrate, a color-developing layer, and a second substrate laminated in this order, wherein the first substrate is a layer that transmits ultraviolet light, the color-developing layer contains a leuco dye and a color developer, and the color developer contains a non-phenolic color developer.

[0016] The non-phenolic color developer preferably contains at least a compound represented by the following formula (1) and / or a compound represented by the following formula (2). (In formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and a plurality of R 1 may be the same or different. 1 is a hydrocarbon group having 1 to 4 carbon atoms, and a plurality of A 1 may be the same or different. m represents an integer of 0 to 4, and multiple m's may be the same or different. (The symbols in formula (2) are the same as those in formula (1) above.)

[0017] It is preferable that a laminate layer be further provided between the color-developing layer and the second substrate.

[0018] The present invention also provides an information recording medium for laser marking, which is an information recording medium having a first substrate, a color-developing layer, an intermediate layer, and a second substrate laminated in this order, wherein the first substrate is a layer that transmits ultraviolet light, the color-developing layer contains a leuco dye and a color developer, and the intermediate layer contains a resin having a water-soluble portion and / or a crosslinking agent.

[0019] The intermediate layer preferably contains a resin having a water-soluble portion and a crosslinking agent.

[0020] The resin having a water-soluble portion is preferably a core-shell type resin having at least a carboxy group as the water-soluble portion.

[0021] It is preferable that a laminate layer be further provided between the intermediate layer and the second substrate.

[0022] The present invention also provides an information recording medium for ultraviolet laser marking, which is an information recording medium having a first substrate, a color-developing layer, and a second substrate laminated in this order, wherein the first substrate is a layer that transmits ultraviolet light, the color-developing layer contains a leuco dye and a color developer, and which can develop color when irradiated with ultraviolet laser light having a wavelength of more than 351 nm and not more than 400 nm.

[0023] The ultraviolet laser light is preferably a THG laser light.

[0024] It is preferable that a laminate layer be further provided between the color-developing layer and the second substrate.

[0025] It is preferable that an anchor layer be further provided between the first substrate and the color-forming layer.

[0026] The second substrate is preferably a layer that transmits ultraviolet light.

[0027] The laser-markable information recording medium of the present invention can provide an information recording medium that is laser-markable, has excellent color development properties, and further contains a non-phenolic color developer as a color developer. It can also provide an information recording medium that is laser-markable, has excellent color development properties, and is more resistant to moist heat. It can also provide an information recording medium that can be printed by irradiation with ultraviolet laser light having a wavelength of more than 351 nm and not more than 400 nm, and has excellent color development properties.

[0028] 1 is a cross-sectional view of a laser-markable information recording medium according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view of a laser-markable information recording medium according to another embodiment of the present invention.

[0029] [Laser-markable information recording medium] The laser-markable information recording medium of the first aspect of the present invention has a laminated structure in which at least a first substrate, a color-developing layer, and a second substrate are laminated in this order. The first substrate is a layer that transmits ultraviolet light. The color-developing layer contains at least a leuco dye and a color developer, and the color developer contains at least a non-phenolic color developer.

[0030] A laser-markable information recording medium according to a second aspect of the present invention has a laminated structure in which at least a first substrate, a color-forming layer, an intermediate layer, and a second substrate are laminated in this order. The first substrate is a layer that transmits ultraviolet light. The color-forming layer contains at least a leuco dye and a color developer. The intermediate layer contains at least a resin having a water-soluble portion and / or a crosslinking agent.

[0031] A laser-markable information recording medium according to a third aspect of the present invention has a laminated structure in which at least a first substrate, a color-developing layer, and a second substrate are laminated in this order. The first substrate is a layer that transmits ultraviolet light. The color-developing layer contains at least a leuco dye and a color developer. The laser-markable information recording medium can develop color when irradiated with ultraviolet laser light having a wavelength of more than 351 nm and not more than 400 nm.

[0032] In this specification, "the information recording medium for laser marking of the present invention" is a general term that includes the information recording medium for laser marking of the first aspect, the information recording medium for laser marking of the second aspect, and the information recording medium for laser marking of the third aspect.

[0033] The laser-markable information recording medium of the present invention preferably further comprises an anchor layer, and more preferably further comprises a laminate layer. Furthermore, it is more preferable that the laser-markable information recording medium further comprises an anchor layer and a laminate layer. The anchor layer is a layer provided between the first substrate and the color-forming layer. The laminate layer is a layer provided between the color-forming layer and the second substrate when there is no intermediate layer, and is a layer provided between the intermediate layer and the second substrate when there is an intermediate layer. The laser-markable information recording medium may also comprise layers other than those described above. Examples of the other layers include a printing layer, an adhesive layer, a backcoat layer, an overcoat layer, a heat-insulating layer, and a protective layer.

[0034] Hereinafter, one embodiment of the laser marking information recording medium of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments.

[0035] FIG. 1 is a schematic cross-sectional view showing one embodiment of a laser-markable information recording medium of the present invention. As shown in FIG. 1 , the laser-markable information recording medium 1 of this embodiment has a laminated structure in which a color-forming layer 4 and a second substrate 7 are laminated in this order on a sheet-like first substrate 2, with the color-forming layer 4 sandwiched between the first substrate 2 and the second substrate 7. Furthermore, at least the first substrate 2 is a layer that transmits ultraviolet light. By satisfying this configuration, the laser-markable information recording medium 1 of this embodiment is capable of laser marking and achieves good color development. For example, it is believed that laser light irradiated onto the first substrate 2 can pass through the first substrate 2 and therefore efficiently affect the color-forming layer 4. Furthermore, it is believed that the color-forming layer 4, which contains a leuco dye and a color developer, absorbs the laser light and uses its energy to produce vivid color development. Furthermore, because laser light is generally high-energy, when the color-forming layer 4 absorbs the laser light, some kind of impact phenomenon such as foaming, gasification, or abrasion can occur. However, because the color-forming layer 4 is protected by the first substrate 2 and the second substrate 7, it is believed that laser marking is possible without causing damage. Furthermore, because the first substrate 2 is a layer that transmits ultraviolet light, it is believed that damage such as holes caused by the first substrate 2 itself absorbing a large amount of laser light can be avoided. Furthermore, with a laminated structure in which the color-forming layer 4 is sandwiched between substrates, substrates generally tend to be stronger than layers formed by coating (coating layers), and therefore resistance to abrasion and wear can also be improved.

[0036] FIG. 2 is a schematic cross-sectional view showing another embodiment of the laser-markable information recording medium of the present invention. As shown in FIG. 2 , the laser-markable information recording medium 1 of this embodiment comprises an anchor layer 3, a color-forming layer 4, an intermediate layer 5, a laminate layer 6, and a second substrate 7 laminated in this order on a sheet-like first substrate 2, with the color-forming layer 4 sandwiched between the first substrate 2 and the second substrate 7. The first substrate 2 and the anchor layer 3, the anchor layer 3 and the color-forming layer 4, the color-forming layer 4 and the intermediate layer 5, the intermediate layer 5 and the laminate layer 6, and the laminate layer 6 and the second substrate 7 are in direct contact with each other. In this specification, the laminate comprising the first substrate 2, the anchor layer 3, the color-forming layer 4, and the intermediate layer 5 is sometimes referred to as the "first laminate," and the laminate layer 6 and the second substrate 7 is sometimes referred to as the "second laminate." The presence of the anchor layer 3 further improves adhesion between the first substrate 2 and the color-forming layer 4, thereby preventing peeling between the layers. Furthermore, by providing the laminate layer 6, the adhesion between the intermediate layer 5 and the second substrate 7 is further improved, and peeling between the layers can be suppressed. Furthermore, in the manufacturing method described below, the first laminate and the second laminate can be laminated by various lamination methods, and therefore the laser marking information recording medium 1 can be efficiently manufactured.

[0037] (First Substrate) The first substrate 2 is a layer that transmits ultraviolet light and can function as a support for the laser-marking information recording medium 1 and can protect the color-developing layer, etc. From the perspective of further improving the transmittance of laser light, the first substrate 2 is preferably a layer that transmits at least a portion of ultraviolet light in the wavelength range of 10 to 400 nm, and more preferably a layer that transmits at least a portion of ultraviolet light with a wavelength of more than 351 nm and not more than 400 nm. By using such a first substrate 2, the transmittance of laser light can be further improved, and the suitability for laser marking can be further improved. The first substrate 2 may be a single layer or multiple layers.

[0038] Examples of the first substrate 2 include a resin film. Examples of the resin constituting the resin film include polyethylene (low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and very low-density polyethylene), polypropylene (random copolymer polypropylene, block copolymer polypropylene, and homopolypropylene), polybutene, polymethylpentene, ionomer, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid ester (random and alternating) copolymer, ethylene-vinyl acetate copolymer (EVA), ethylene-propylene copolymer, cyclic olefin polymer, ethylene-butene copolymer, and ethylene-hexene copolymer. Examples of the resin include polyolefin resins such as polymers; polyurethane; polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate, and polybutylene terephthalate (PBT); polystyrene; polycarbonate; polyimide resins; polyether ether ketone; polyetherimide; polyamides such as aramid and wholly aromatic polyamide; polyphenyl sulfide; fluororesins; polyvinyl chloride; polyvinylidene chloride; cellulose resins such as triacetyl cellulose (TAC); silicone resins; acrylic resins such as polymethyl methacrylate (PMMA); polysulfone; polyarylate; and polyvinyl acetate. The above resins can be used alone or in combination of two or more. The resin film can be stretched or unstretched.

[0039] The thickness of the first substrate 2 is not particularly limited, and is, for example, preferably 5 μm to 150 μm, more preferably 10 μm to 100 μm. When the thickness is within the above range, the coating property and supportability can be more excellent.

[0040] From the viewpoint of further improving physical strength, the thickness of the first substrate 2 may be 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, or 50 μm or more. When the first substrate 2 is irradiated with laser light, because the first substrate 2 is a layer that transmits ultraviolet light, even if the thickness is within the above range, the laser light can efficiently act on the color-forming layer 4, and both color development and physical strength can be achieved.

[0041] The haze of the first substrate 2 is not particularly limited, but from the viewpoint of further improving visibility and / or laser marking suitability, it is preferably 30% or less, more preferably 20% or less, even more preferably 10% or less, even more preferably 5% or less, and particularly preferably 3% or less. The haze can be measured by a conventional method, for example, by a method conforming to JIS K7136:2000. When the haze is within the above range, the transparency of the first substrate 2 is increased, thereby further improving the visibility when viewing the color-developing portion of the color-developing layer 4 through the first substrate 2. Furthermore, when the haze is within the above range, the transmittance of laser light can be further improved, thereby further improving color development and further suppressing damage to the first substrate 2, thereby further improving laser marking suitability.

[0042] The total light transmittance of the first substrate 2 in the wavelength range of 300 nm to 400 nm is not particularly limited, but from the viewpoint of further improving suitability for laser marking, it is preferably 40% or more, more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more. The total light transmittance in the wavelength range of 300 nm to 400 nm can be measured by a conventional method, for example, by a method conforming to JIS K7375:2008. When the total light transmittance is within the above range, the transmittance of laser light can be further improved, thereby further improving color development and further suppressing damage to the first substrate 2, thereby further improving suitability for laser marking. Furthermore, the total light transmittance in the wavelength range of more than 351 nm to 400 nm is preferably within the above range, the total light transmittance in the wavelength range of more than 353 nm to 390 nm is preferably within the above range, and the total light transmittance in the wavelength range of more than 353 nm to 360 nm is preferably within the above range.

[0043] (Second Substrate) The second substrate 7 is a layer that can function as a support for the laser marking information recording medium 1 and can also function to protect the color-developing layer, etc. The second substrate 7 may be a single layer or multiple layers.

[0044] The second substrate 7 is not particularly limited and may be, for example, a resin film, high-quality paper, art paper, coated paper, kraft paper, laminated paper obtained by laminating a thermoplastic resin such as polyethylene to the above paper substrate, synthetic paper, or porous material such as nonwoven fabric. Examples of resins constituting the resin film include those exemplified in the section on the first substrate. The resins may be used alone or in combination of two or more. The resin film may be stretched or unstretched.

[0045] The second substrate 7 may be a layer that transmits ultraviolet light. In this case, laser light can be irradiated from the second substrate 7 side as well to cause the laser marking information recording medium to develop color, thereby further improving design freedom. From this perspective, it is preferable that the second substrate 7 be a resin film.

[0046] The thickness of the second substrate 7 is not particularly limited and is, for example, preferably 5 μm to 200 μm, more preferably 10 μm to 150 μm. When the thickness is within the above range, the coating property and supportability can be superior. Furthermore, from the viewpoint of further improving physical strength, the thickness of the second substrate 7 may be 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, 60 μm or more, 80 μm or more, or 100 μm or more. In particular, when the second substrate 7 is a layer that transmits ultraviolet light, even if the thickness is within the above range, laser light can efficiently act on the color-forming layer 4, thereby achieving both color development and physical strength.

[0047] The haze of the second substrate 7 is not particularly limited, but when the second substrate 7 is a resin film, from the viewpoint of further improving transparency and / or laser marking suitability, the haze is preferably 30% or less, more preferably 20% or less, even more preferably 10% or less, still more preferably 5% or less, and particularly preferably 3% or less. The haze is determined in the same manner as for the first substrate 2.

[0048] The total light transmittance of the second substrate 7 in the wavelength region of 300 nm to 400 nm is not particularly limited, but from the viewpoint of further improving the suitability for laser marking, it is preferably 40% or more, more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more. The total light transmittance in the wavelength region of 300 nm to 400 nm is determined in the same manner as for the first substrate 2. Furthermore, the total light transmittance in the wavelength region of more than 351 nm to 400 nm is preferably within the above range, the total light transmittance in the wavelength region of more than 353 nm to 390 nm is preferably within the above range, and the total light transmittance in the wavelength region of more than 353 nm to 360 nm is preferably within the above range.

[0049] (Anchor Layer) The anchor layer 3 is a layer intended to increase the adhesion between the first substrate 2 and the color-forming layer 4. The anchor layer 3 may not be provided if it is not required, in which case the color-forming layer 4 can be directly laminated on the first substrate 2. The material for forming the anchor layer 3 is not particularly limited, and it can be formed using, for example, a resin. The anchor layer 3 may also contain other components. Examples of such other components include surfactants, preservatives, inorganic pigments, organic pigments, and viscosity modifiers.

[0050] Examples of the resin include acrylic resins such as acrylic resin, styrene-acrylic resin, acrylic-urethane resin, acrylic-amide resin, and vinyl acetate-acrylic resin; maleic acid resins such as maleic acid resin, styrene-maleic acid resin, and olefin-maleic acid resin; and styrene butadiene latex (SBR) resin. These resins may be modified resins modified by known methods. These resins may be used alone or in combination of two or more.

[0051] In this specification, "acrylic resin" refers to a resin (acrylic resin) obtained by homopolymerizing an acrylic monomer, and / or a resin obtained by copolymerizing an acrylic monomer with another monomer (a monomer other than the acrylic monomer that is copolymerizable with the acrylic monomer). Here, the other monomer may be one type or two or more types. Furthermore, when simply referring to "acrylic," unless otherwise specified, it means (meth)acrylic acid (salt) and / or (meth)acrylic acid ester. Here, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid, and "(meth)acrylic acid (salt)" means (meth)acrylic acid and / or (meth)acrylic acid salt.

[0052] The salt of the (meth)acrylic acid salt is not particularly limited and examples thereof include ammonium salts such as ammonia; alkanolamine salts such as triethanolamine, diethanolamine, and monoethanolamine; alkylamine salts such as methylamine salt, ethylamine salt, diethylamine salt, and triethylamine salt; polyamine salts such as diethyleneamine salt and diethylenetriamine salt; alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium and calcium; and polyvalent metal salts such as zinc and iron. These salts can be used alone or in combination of two or more.

[0053] The composition forming the resin may be a solid, an emulsion, or a solution, but is preferably an emulsion or a solution from the viewpoint of excellent handling and coatability.

[0054] Examples of the surfactant include anionic surfactants such as sodium dioctylsuccinate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, and alkyl ether sulfate salts; and nonionic surfactants such as acetylene glycol and alkylene oxide adducts of acetylene glycol. These surfactants can be used alone or in combination of two or more.

[0055] The coating amount (dry mass) of the anchor layer 3 is, for example, 0.1 g / m 2 ~5.0g / m 2 is preferable, and more preferably 0.3 g / m 2 ~4.0g / m 2 , more preferably 0.5 g / m 2 ~3.0g / m 2 When the coating amount is within the above range, the adhesion between the layers becomes more appropriate, and peeling between the layers can be further suppressed.

[0056] (Coloring Layer) The coloring layer 4 is a layer that develops color as a result of a chemical reaction between the leuco dye and the color developer caused by the energy of the laser beam, and forms a recorded image on the laser marking information recording medium 1 .

[0057] Here, the color-forming layer 4 provided in the laser-markable information recording medium 1 of the first aspect of the present invention contains at least a leuco dye and a color developer, and the color developer contains at least a non-phenolic color developer. In the first aspect of the present invention, by satisfying all of these configurations for the color-forming layer 4, it is possible to provide a laser-markable information recording medium 1 that is more excellent in suitability for laser marking and that has a reduced environmental impact. The leuco dyes can be used alone or in combination of two or more, and the non-phenolic color developers can be used alone or in combination of two or more.

[0058] Furthermore, the color-forming layer 4 provided in the laser-markable information recording medium 1 of the second and third aspects of the present invention contains at least a leuco dye and a color developer. In the second and third aspects of the present invention, by satisfying all of these configurations for the color-forming layer 4, it is possible to provide an information recording medium 1 for laser marking that is more excellent in suitability for laser marking. The color developer does not need to contain a non-phenolic color developer, but from the standpoint of environmental friendliness, it is preferable that it contains a non-phenolic color developer. The leuco dyes can be used alone or in combination of two or more, and the color developers can be used alone or in combination of two or more.

[0059] The color-forming layer 4 may further contain other components as necessary, such as a binder, a filler, a lubricant, a dispersant, a crosslinking agent, a preservative, a sensitizer, a surfactant, and a viscosity adjuster.

[0060] Examples of the non-phenolic color developer include urea compounds. The urea compound is preferably an N,N'-diarylurea derivative having one or more sulfonate ester structures (-S(=O)2-O-) in the molecule. Specifically, the N,N'-diarylurea derivative preferably includes a compound represented by the following formula (1) and / or a compound represented by the following formula (2). In this specification, "urea compound" refers to a compound having one or more urea bonds (-NH-C(=O)-NH-) in the molecule, and "N,N'-diarylurea derivative" refers to a compound having an N,N'-diarylurea skeleton.

[0061] (In formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and a plurality of R 1 may be the same or different. 1 is a hydrocarbon group having 1 to 4 carbon atoms, and a plurality of A 1 may be the same or different. m represents an integer of 0 to 4, and multiple m's may be the same or different. (The symbols in formula (2) are the same as those in formula (1) above.)

[0062] The compound represented by the formula (1) and / or the compound represented by the formula (2) can be brought into contact with, for example, a leuco dye described below by the energy of a laser beam, and can develop a color.

[0063] In the above formula (1) and the above formula (2), R 1 is a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and a plurality of R 1 may be the same or different. 1 is a hydrocarbon group having 1 to 4 carbon atoms, and a plurality of A 1 may be the same or different. m represents an integer of 0 to 4, and when m is 2 or more, multiple m's may be the same or different.

[0064] In the above formula (1), a plurality of R 1 -SO3- is directly bonded to a carbon atom constituting a benzene ring.1 The substitution positions of —SO— may be the same or different. 1 The substitution position of --SO.sub.3-- is preferably the 2-, 3- or 4-position, more preferably the 3-position.

[0065] In the above formula (2), R 1 -SO3- is directly bonded to a carbon atom that constitutes a benzene ring. 1 The substitution position of --SO.sub.3-- is preferably the 2-, 3- or 4-position, more preferably the 3-position.

[0066] In the formula (1) and the formula (2), the R 1 Among the "hydrocarbon groups having 1 to 12 carbon atoms which may have a substituent," examples of the "hydrocarbon groups having 1 to 12 carbon atoms" include linear alkyl groups having 1 to 12 carbon atoms, branched alkyl groups having 1 to 12 carbon atoms, alicyclic alkyl groups having 3 to 12 carbon atoms, aralkyl groups having 7 to 12 carbon atoms, and aryl groups having 6 to 12 carbon atoms. Furthermore, multiple "hydrocarbon groups having 1 to 12 carbon atoms which may have a substituent" may be the same or different.

[0067] Examples of the "straight-chain alkyl group having 1 to 12 carbon atoms, branched-chain alkyl group having 1 to 12 carbon atoms, and alicyclic alkyl group having 3 to 12 carbon atoms" include straight-chain alkyl groups having 1 to 12 carbon atoms, branched-chain alkyl groups having 1 to 12 carbon atoms, and alicyclic alkyl groups having 3 to 12 carbon atoms, such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, cyclopentyl group, hexyl group, cyclohexyl group, 2-ethylhexyl group, and lauryl group. These alkyl groups may further have a substituent as described below.

[0068] Examples of the "aralkyl group having 7 to 12 carbon atoms" include unsubstituted aralkyl groups such as benzyl, 1-phenylethyl, 2-phenylethyl, and 3-phenylpropyl. These aralkyl groups may further have a substituent as described below. Examples of the "substituted aralkyl group having 7 to 12 carbon atoms" include aralkyl groups having a substituent such as p-methylbenzyl group, m-methylbenzyl group, m-ethylbenzyl group, p-ethylbenzyl group, p-i-propylbenzyl group, p-t-butylbenzyl group, p-methoxybenzyl group, m-methoxybenzyl group, o-methoxybenzyl group, m,p-di-methoxybenzyl group, p-ethoxy-m-methoxybenzyl group, p-phenylmethylbenzyl group, p-cumylbenzyl group, p-phenylbenzyl group, o-phenylbenzyl group, m-phenylbenzyl group, p-tolylbenzyl group, m-tolylbenzyl group, o-tolylbenzyl group, and p-chlorobenzyl group.

[0069] Examples of the "aryl group having 6 to 12 carbon atoms" include unsubstituted aryl groups such as a phenyl group, a 1-naphthyl group, and a 2-naphthyl group. These aryl groups may further have a substituent as described below. Examples of the "aryl group having 6 to 12 carbon atoms and having a substituent" include aryl groups having a substituent such as a p-tolyl group, a m-tolyl group, an o-tolyl group, a 2,5-dimethylphenyl group, a 2,4-dimethylphenyl group, a 3,5-dimethylphenyl group, a 2,3-dimethylphenyl group, a 3,4-dimethylphenyl group, a mesitylene group, a p-ethylphenyl group, a p-i-propylphenyl group, a p-t-butylphenyl group, a p-methoxyphenyl group, a 3,4-dimethoxyphenyl group, a p-ethoxyphenyl group, a p-chlorophenyl group, and a t-butylated naphthyl group.

[0070] The "substituent" is not particularly limited. Among the "hydrocarbon groups having 1 to 12 carbon atoms which may have a substituent," when the "hydrocarbon group having 1 to 12 carbon atoms" is a "linear alkyl group having 1 to 12 carbon atoms, or a branched alkyl group having 1 to 12 carbon atoms," examples of the substituent include a halogen atom, an alkoxy group, and the like. Furthermore, among the "hydrocarbon groups having 1 to 12 carbon atoms which may have a substituent," when the "hydrocarbon group having 1 to 12 carbon atoms" is an "alicyclic alkyl group having 3 to 12 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms," examples of the substituent include a halogen atom, an alkyl group, an alkoxy group, an aryl group, and the like. Of these, alkyl groups and alkoxy groups are preferred as the substituent. Here, the number of carbon atoms of the alkyl groups and alkoxy groups as the substituents is not particularly limited, but preferably has 1 to 6 carbon atoms, and more preferably has 1 to 4 carbon atoms. The "substituents" may be present in plural or none. Furthermore, the substitution positions of the multiple "substituents" may be the same or different. The substitution position of the above-mentioned "substituent" is preferably any one of the 2-position, 3-position, or 4-position of the aralkyl group or aryl group, and more preferably the 4-position.

[0071] In the formula (1) and the formula (2), the R 1 is preferably an unsubstituted or substituted aryl group having 6 to 12 carbon atoms. 1 is preferably a phenyl group, a p-tolyl group, a m-tolyl group, an o-tolyl group, a 2,5-dimethylphenyl group, a 2,4-dimethylphenyl group, a 3,5-dimethylphenyl group, a 2,3-dimethylphenyl group, or a 3,4-dimethylphenyl group, and among these, a p-tolyl group is more preferred. 1 If so, the sensitivity is better.

[0072] In the formula (1) and the formula (2), the A 1 is a carbon atom constituting a benzene ring, and the R 1 -SO3- can be bonded to a carbon atom that is not bonded. 1 The substitution positions of the above A may be the same or different. 1The substitution position is preferably the 2-, 3- or 4-position.

[0073] In the formulas (1) and (2), m is preferably an integer of 0 to 2, more preferably an integer of 0 to 1, and even more preferably 0.

[0074] Above A 1 Examples of the hydrocarbon group having 1 to 4 carbon atoms include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and t-butyl.

[0075] Specific examples of the compound represented by the above formula (1) include the following compounds, but the compound is not limited to these compounds.

[0076] That is, as the compound represented by the above formula (1), N,N'-di-[3-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-toluenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[3-(p-xylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-xylenesulfonyloxy)phenyl]urea, nyl]urea, N,N'-di-[3-(mesitylenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-ethyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-5-methyl-phenyl]urea, N,N'-di-[3-(benzenesulfonyloxy)-4-propyl-phenyl]urea,

[0077] N,N'-di-[3-(p-ethylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-propylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-isopropylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-t-butylbenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(p-methoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(m-methoxybenzenesulfonyloxy)phenyl]urea, N,N'-di-[3-(o-methoxybenzenesulfonyloxy)phenyl]urea,

[0078] N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(p-toluenesulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(m-toluenesulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(o-toluenesulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(p-xylenesulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(mesitylenesulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(1-naphthalenesulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(2-naphthalenesulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(p-ethylbenzenesulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(p-methoxy N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(benzylsulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(ethanesulfonyloxy)phenyl]urea, N-[3-(benzenesulfonyloxy)phenyl]-N'-[3-(benzenesulfonyloxy)-4-methylphenyl]urea, N-[3-(p-toluenesulfonyloxy)phenyl]-N'-[3-(m-toluenesulfonyloxy)phenyl]urea , N-[3-(p-toluenesulfonyloxy)phenyl]-N'-[3-(o-toluenesulfonyloxy)phenyl]urea, N-[3-(p-toluenesulfonyloxy)phenyl]-N'-[3-(p-toluenesulfonyloxy)-4-methylphenyl]urea, N-[3-(p-toluenesulfonyloxy)phenyl]-N'-[3-(p-ethylbenzenesulfonyloxy)phenyl]urea, N-[3-(p-toluenesulfonyloxy)phenyl]-N'-[3-(p-methoxybenzenesulfonyloxy)phenyl]urea,

[0079] N-[3-(p-toluenesulfonyloxy)phenyl]-N'-[3-(benzylsulfonyloxy)phenyl]urea, N-[3-(p-toluenesulfonyloxy)phenyl]-N'-[3-(p-methylbenzylsulfonyloxy)phenyl]urea, N-[3-(p-toluenesulfonyloxy)phenyl]-N'-[3-(p-methoxybenzylsulfonyloxy)phenyl]urea,

[0080] N,N'-di-[4-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[4-(benzenesulfonyloxy)-3-methyl-phenyl]urea, N,N'-di-[4-(benzenesulfonyloxy)-3-ethyl-phenyl]urea, N,N'-di-[4-(benzenesulfonyloxy)-3-propyl-phenyl]urea, N,N'-di-[4-(benzenesulfonyloxy)-3-t-butyl-phenyl]urea,

[0081] N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(p-toluenesulfonyloxy)phenyl]urea, N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(m-toluenesulfonyloxy)phenyl]urea, N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(o-toluenesulfonyloxy)phenyl]urea, N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(p-xylenesulfonyloxy)phenyl]urea, N-[4-(benzenesulfonyloxy) phenyl]-N'-[4-(mesitylenesulfonyloxy)phenyl]urea, N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(1-naphthalenesulfonyloxy)phenyl]urea, N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(2-naphthalenesulfonyloxy)phenyl]urea, N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(p-ethylbenzenesulfonyloxy)phenyl]urea, N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(p- N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(benzylsulfonyloxy)phenyl]urea, N-[4-(benzenesulfonyloxy)phenyl]-N'-[4-(ethanesulfonyloxy)phenyl]urea, N-[4-(p-toluenesulfonyloxy)phenyl]-N'-[4-(m-toluenesulfonyloxy)phenyl]urea, N-[4-(p-toluenesulfonyloxy)phenyl]-N'-[4-(o-toluenesulfonyloxy)phenyl N-[4-(p-toluenesulfonyloxy)phenyl]-N'-[4-(p-ethylbenzenesulfonyloxy)phenyl]urea, N-[4-(p-toluenesulfonyloxy)phenyl]-N'-[4-(p-methoxybenzenesulfonyloxy)phenyl]urea, N-[4-(p-toluenesulfonyloxy)phenyl]-N'-[4-(2-naphthalenesulfonyloxy)phenyl]urea, N-[4-(p-toluenesulfonyloxy)phenyl]-N'-[4-(benzylsulfonyloxy)phenyl]urea,N-[4-(p-toluenesulfonyloxy)phenyl]-N'-[4-(p-methylbenzylsulfonyloxy)phenyl]urea, N-[4-(p-toluenesulfonyloxy)phenyl]-N'-[4-(p-methoxybenzylsulfonyloxy)phenyl]urea,

[0082] N,N'-di-[4-(benzylsulfonyloxy)phenyl]urea, N,N'-di-[4-(benzylsulfonyloxy)-3-methyl-phenyl]urea, N,N'-di-[4-(phenylethanesulfonyloxy)phenyl]urea, N,N'-di-[4-(phenylpropanesulfonyloxy)phenyl]urea, N,N'-di-[4-(p-methoxybenzylsulfonyloxy)phenyl]urea,

[0083] N,N'-di-[2-(benzenesulfonyloxy)phenyl]urea, N,N'-di-[2-(benzenesulfonyloxy)-4-methyl-phenyl]urea, N,N'-di-[2-(benzenesulfonyloxy)-4-ethyl-phenyl]urea, N,N'-di-[2-(benzenesulfonyloxy)-5-methyl-phenyl]urea, N,N'-di-[2-(benzenesulfonyloxy)-4-propyl-phenyl]urea,

[0084] N,N'-di-[2-(o-toluenesulfonyloxy)phenyl]urea, N,N'-di-[2-(m-toluenesulfonyloxy)phenyl]urea, N,N'-di-[2-(p-toluenesulfonyloxy)phenyl]urea, N,N'-di-[2-(p-toluenesulfonyloxy)-4-methyl-phenyl]urea,

[0085] Examples of such compounds include N,N'-di-[2-(p-xylenesulfonyloxy)phenyl]urea, N,N'-di-[2-(m-xylenesulfonyloxy)phenyl]urea, and N,N'-di-[2-(mesitylenesulfonyloxy)phenyl]urea. Among these, N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea is particularly preferred as the compound represented by formula (1) above, from the viewpoints that good color development can be achieved with laser light and that excellent resistance to moist heat can also be achieved.

[0086] Specific examples of the compound represented by the formula (2) include, but are not limited to, the following compounds:

[0087] That is, as the compound represented by the above formula (2), 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate, 4-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate, 2-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate, 3-[(3-phenylureido)phenyl]-2-methylbenzenesulfonate, 4-[(3-phenylureido)phenyl]-2-methylbenzenesulfonate, 2-[(3-phenylureido)phenyl [(3-phenylureido)phenyl]-2-methylbenzenesulfonate, 3-[(3-phenylureido)phenyl]-3-methylbenzenesulfonate, 4-[(3-phenylureido)phenyl]-3-methylbenzenesulfonate, 2-[(3-phenylureido)phenyl]-3-methylbenzenesulfonate, 3-[(3-phenylureido)phenyl]-benzenesulfonate, 4-[(3-phenylureido)phenyl]-benzenesulfonate, 2-[(3-phenylureido)phenyl]-benzenesulfonate,

[0088] 3-[3-(4-methylphenylureido)]phenyl-4-methylbenzenesulfonate, 4-[3-(4-methylphenylureido)]phenyl-4-methylbenzenesulfonate, 2-[3-(4-methylphenylureido)]phenyl-4-methylbenzenesulfonate, 3-[3-(4-methylphenylureido)]phenyl-2-methylbenzenesulfonate, 4-[3-(4-methylphenylureido)]phenyl-2-methylbenzenesulfonate, 2-[3-(4-methylphenylureido)]phenyl-2-methylbenzenesulfonate benzenesulfonate, 3-[3-(4-methylphenylureido)]phenyl-3-methylbenzenesulfonate, 4-[3-(4-methylphenylureido)]phenyl-3-methylbenzenesulfonate, 2-[3-(4-methylphenylureido)]phenyl-3-methylbenzenesulfonate, 3-[3-(4-methylphenylureido)]phenyl-benzenesulfonate, 4-[3-(4-methylphenylureido)]phenyl-benzenesulfonate, 2-[3-(4-methylphenylureido)]phenyl-benzenesulfonate,

[0089] 3-[3-(2-methylphenylureido)]phenyl-4-methylbenzenesulfonate, 4-[3-(2-methylphenylureido)]phenyl-4-methylbenzenesulfonate, 2-[3-(2-methylphenylureido)]phenyl-4-methylbenzenesulfonate, 3-[3-(2-methylphenylureido)]phenyl-2-methylbenzenesulfonate, 4-[3-(2-methylphenylureido)]phenyl-2-methylbenzenesulfonate, 2-[3-(2-methylphenylureido)]phenyl-2-methylbenzenesulfonate benzenesulfonate, 3-[3-(2-methylphenylureido)]phenyl-3-methylbenzenesulfonate, 4-[3-(2-methylphenylureido)]phenyl-3-methylbenzenesulfonate, 2-[3-(2-methylphenylureido)]phenyl-3-methylbenzenesulfonate, 3-[3-(2-methylphenylureido)]phenyl-benzenesulfonate, 4-[3-(2-methylphenylureido)]phenyl-benzenesulfonate, 2-[3-(2-methylphenylureido)]phenyl-benzenesulfonate,

[0090] 3-[3-(3-methylphenylureido)]phenyl-4-methylbenzenesulfonate, 4-[3-(3-methylphenylureido)]phenyl-4-methylbenzenesulfonate, 2-[3-(3-methylphenylureido)]phenyl-4-methylbenzenesulfonate, 3-[3-(3-methylphenylureido)]phenyl-2-methylbenzenesulfonate, 4-[3-(3-methylphenylureido)]phenyl-2-methylbenzenesulfonate, 2-[3-(3-methylphenylureido)]phenyl-2-methylbenzenesulfonate benzenesulfonate, 3-[3-(3-methylphenylureido)]phenyl-3-methylbenzenesulfonate, 4-[3-(3-methylphenylureido)]phenyl-3-methylbenzenesulfonate, 2-[3-(3-methylphenylureido)]phenyl-3-methylbenzenesulfonate, 3-[3-(3-methylphenylureido)]phenyl-benzenesulfonate, 4-[3-(3-methylphenylureido)]phenyl-benzenesulfonate, 2-[3-(3-methylphenylureido)]phenyl-benzenesulfonate,

[0091] Examples of the compound represented by formula (2) include 3-(3-phenylureido)phenyl-4-propyloxybenzenesulfonate, 4-(3-phenylureido)phenyl-4-propyloxybenzenesulfonate, 2-(3-phenylureido)phenyl-4-propyloxybenzenesulfonate, 3-(3-phenylureido)phenyl-4-phenyloxybenzenesulfonate, 4-(3-phenylureido)phenyl-4-phenyloxybenzenesulfonate, and 2-(3-phenylureido)phenyl-4-phenyloxybenzenesulfonate. Among these, 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate is particularly preferred as the compound represented by formula (2) above, from the viewpoints that good color development with laser light can be achieved and that excellent resistance to moist heat can also be achieved.

[0092] The color developer may contain a compound represented by formula (1) alone or may contain two or more compounds represented by formula (1). Similarly, the color developer may contain a compound represented by formula (2) alone or may contain two or more compounds represented by formula (2). Furthermore, the color developer may contain both a compound represented by formula (1) and a compound represented by formula (2).

[0093] The color developer may contain a color developer other than the color developers exemplified above (other color developers) within a range that does not impair the effects of the present invention.

[0094] Examples of the other color developers include known non-phenol color developers such as N-3-[(p-toluenesulfonyl)oxy]phenyl-N'-(p-toluenesulfonyl)-urea (trade name: PF-201), N-[2-(3-phenylureido)phenyl]-benzenesulfonamide (trade name: NKK-1304), and 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone (trade name: UU); 4,4'-isopropylidenediphenol (BPA); and 4,4'-dihydroxydiphenyl Examples of known color developers include sulfone (BPS), 4-allyloxy-4'-hydroxydiphenyl sulfone (trade name: BPS-MAE), 4-allyloxy-4'-hydroxy-diphenyl sulfone (trade name: TGSA), 4-hydroxy-4'-propoxydiphenyl sulfone, 4-hydroxy-4'-isopropoxysulfone (trade name: D-8), N-(m-tolylaminocarbonyl)-methionine, N-(m-tolylaminocarbonyl)-phenylalanine, and N-(phenylaminocarbonyl)-phenylalanine.

[0095] Further, other color developers include, for example, 1,1-bis(p-hydroxyphenyl)cyclohexane, 1,1-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 2,2'-methylenebis(4-chlorophenol), 2,2-bis(4-hydroxyphenyl)-4-methylpentane, poly(4-hydroxybenzoic acid), benzyl 4-hydroxybenzoate, 2,4-bis(phenylsulfonyl)phenol, α-{4-[(4-hydroxyphenyl)sulfonyl]phenyl}-ω-hydroxypoly(polymerization degree n=1 to 7)(oxyethyleneoxyethyleneoxy)

[0033] Examples of suitable hydroxybenzoates include 4-hydroxybenzoates, ...

[0096] The content of the developer is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, relative to 100% by mass of the total solid content of the color-forming layer 4. A content of 10% by mass or more can further improve sensitivity. Furthermore, the content of the developer is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, relative to 100% by mass of the total solid content of the color-forming layer 4.

[0097] When the color-forming layer 4 contains a non-phenolic color developer, the content of the non-phenolic color developer is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to 100% by mass of the total amount of color developers in the color-forming layer 4. It may also be 100% by mass. When the content is within the above range, the environmental load can be further reduced. Furthermore, the total content of the compound represented by formula (1) and / or the compound represented by formula (2) is preferably within the above range, relative to 100% by mass of the total amount of color developers in the color-forming layer 4.

[0098] The melting point of the developer is not particularly limited, but is preferably 130°C or higher, more preferably 140°C or higher, and even more preferably 150°C or higher. The melting point of the developer is preferably 195°C or lower, more preferably 185°C or lower. The melting point of the non-phenolic developer is preferably within the above range. When the melting point is within the above range, the sensitivity to laser light can be adjusted to a more appropriate range, which can further improve the suitability for laser marking, and the heat resistance and moist heat resistance can also be excellent.

[0099] The leuco dye is not particularly limited, and examples thereof include 2'-bromo-6'-(dibutylamino)-3'-methylspiro[isobenzofuran-1(3H),9'-[9H]xanthene]-3-one, 3-(1-ethyl-2-methylindol-3-yl)-3-(4-diethylamino-2-methylphenyl)-4-azaphthalide, 6-(dimethylamino)-3,3-bis[4-(dimethylamino)phenyl]-1(3H)-isobenzofuranone, 1,2-dihydro-1-ethyl-8-[N-(4-methylphenyl)-N-ethylamino]-2,2,4-trimethylspiro[11H]-chromeno(2,3-g)quinoline-11,3'-phthalide, 2'-[bis(phenylmethyl)amino]-6'-(diethylamino)-spiro[isobenzofuran-1(3H),9'-(9H)xanthene]-3-one, 3-(N-isobutyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-isopentyl-N-ethyl)amino-6-methyl-7-o-chloroanilinofluoran, 3-(N-methyl-N-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-p-toluidino)-6-methyl-7-anilinofluoran oran, 3-(N-ethyl-N-isopentyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethoxypropyl-N-ethyl)amino-6-methyl-7-anilinofluoran, 3-(N-cyclohexyl-N-methyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-n-propyl)amino-6-methyl-7-anilinofluoran, 3-dibutylamino fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-p-toluidinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-8-methylfluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-chlorofluoran, 3-dibutylamino-6-methyl-7-bromofluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-dipentylamino-6-methyl-7-anilinofluoran, 3-dimethylamino-5-methyl-7-methylfluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, crystal violet lactone, etc. These leuco dyes can be used alone or in combination of two or more. ,

[0100] The average particle size of the leuco dye is not particularly limited, but is preferably 0.1 μm to 1.0 μm. Generally, leuco dyes react by melting, and as the average particle size increases, the reaction slows down, resulting in lower sensitivity characteristics. On the other hand, as the average particle size decreases, the risk of unexpected color development increases due to heat during drying of the coating liquid. By setting the average particle size of the leuco dye within the above range, the sensitivity characteristics and color development temperature of the leuco dye can be appropriately adjusted. In this specification, the average particle size refers to the particle size at 50% of the integrated value in the particle size distribution measured by laser diffraction / scattering (D50, median diameter). The average particle size measured by laser diffraction / scattering can be measured using a laser diffraction / scattering particle size distribution analyzer (e.g., Microtrac-Bell, device name: MT3300EX-II).

[0101] The content of the leuco dye is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on 100% by mass of the total solid content of the color-forming layer 4. A content of 5% by mass or more can further improve sensitivity. Furthermore, the content of the leuco dye is preferably 40% by mass or less, more preferably 30% by mass or less, based on 100% by mass of the total solid content of the color-forming layer 4.

[0102] Examples of the binder include acrylic resins such as acrylic resin, styrene-acrylic resin, acrylic-urethane resin, acrylic-amide resin, and vinyl acetate-acrylic resin; maleic acid resins such as maleic acid resin, styrene-maleic acid resin, and olefin-maleic acid resin; and styrene-butadiene latex (SBR) resin. These resins may be modified by known methods. Other examples include starch, casein, gelatin, polyamide, polyacrylamide, modified polyacrylamide, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl acetate, isobutylene-maleic anhydride copolymer, diisobutylene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, methyl vinyl-maleic anhydride copolymer, isopropylene-maleic anhydride copolymer, styrene-butadiene copolymer, polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinyl acetate copolymer, polyurethane, polystyrene, polyvinylpyrrolidone, acrylonitrile, and methyl vinyl ether. These binders can be used alone or in combination of two or more.

[0103] The content of the binder is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 25% by mass or more, relative to 100% by mass of the total solid content of the color-forming layer 4. The content of the binder is preferably 60% by mass or less, more preferably 50% by mass or less, relative to 100% by mass of the total solid content of the color-forming layer 4.

[0104] Examples of the lubricant include hydrocarbon waxes such as paraffin, polyethylene, polystyrene, etc., ester waxes such as carnauba wax, oils such as silicone oil, whale oil, etc., fatty acids such as oleic acid, metal soaps such as zinc stearate, etc. These lubricants can be used alone or in combination of two or more.

[0105] The content of the lubricant is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, relative to 100% by mass of the total solid content of the color-forming layer 4. The content of the lubricant is preferably 10% by mass or less, more preferably 5% by mass or less, relative to 100% by mass of the total solid content of the color-forming layer 4.

[0106] Examples of the dispersant include anionic surfactants such as sodium dialkyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, and alkyl ether sulfate salts; nonionic surfactants such as acetylene glycol and alkylene oxide adducts of acetylene glycol; polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and sulfonic acid-modified polyvinyl alcohol; and polymer dispersants such as styrene-acrylic copolymers and acrylic resins. These dispersants can be used alone or in combination of two or more.

[0107] The content of the dispersant is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more, relative to 100% by mass of the total solid content of the color-forming layer 4. The content of the dispersant is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, relative to 100% by mass of the total solid content of the color-forming layer 4.

[0108] Examples of the filler include inorganic fillers such as aluminum hydroxide, magnesium hydroxide, aluminum oxide, magnesium oxide, aluminum silicate, calcium carbonate, magnesium carbonate, barium sulfate, silica gel, activated clay, talc, clay, kaolin, calcined kaolin, diatomaceous earth, white carbon, silicon oxide, silica, colloidal silica, and titanium oxide; and organic fillers such as styrene-acrylic resin particles, polystyrene resin particles, urea-formalin resin particles, and polyolefin resin particles. These fillers can be used alone or in combination of two or more.

[0109] The content of the filler is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more, relative to 100% by mass of the total solid content of the color-forming layer 4. The content of the filler is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, relative to 100% by mass of the total solid content of the color-forming layer 4.

[0110] Examples of the crosslinking agent include organic crosslinking agents such as cationic crosslinking agents and non-cationic crosslinking agents; and inorganic crosslinking agents such as zirconium carbonate. Examples of the cationic crosslinking agent include epichlorohydrin-based resins such as polyamide epichlorohydrin resins, polyamine epichlorohydrin resins, and polyamide polyamine epichlorohydrin resins. Examples of the non-cationic crosslinking agent include oxazoline-based compounds such as oxazoline group-containing polymers and oxazoline group-containing low molecular weight compounds. These crosslinking agents can be used alone or in combination of two or more.

[0111] The content of the crosslinking agent is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, relative to 100% by mass of the total solid content of the color-forming layer 4. The content of the crosslinking agent is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, relative to 100% by mass of the total solid content of the color-forming layer 4.

[0112] The color-forming layer 4 may further contain a laser sensitizer. Examples of the laser sensitizer include heavy metal compounds. Specific examples include copper compounds such as copper phosphonate; molybdenum compounds such as amine molybdate; zinc compounds such as zinc oxide and zinc borate; cerium compounds such as cerium oxide; and nickel compounds such as nickel oxide. In this specification, the term "heavy metal" refers to a metal having a specific gravity of 5.0 g / cm or more. 3 The above metal elements are used. The color-forming layer 4 does not necessarily contain the above laser sensitizer. The laser-marking information recording medium 1 of this embodiment can exhibit vivid color development without using a laser sensitizer, which can further reduce the environmental impact.

[0113] The content of the laser sensitizer may be 20% by mass or less, 15% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, or 0.1% by mass or less, relative to 100% by mass of the total solid content of the color-forming layer 4.

[0114] The coating amount (dry mass) of the color-forming layer 4 is, for example, 0.3 g / m 2 ~10g / m 2 is preferred, and more preferably 2.5 g / m 2 ~6.5g / m 2 When the coating amount is within the above range, the color development of the laser marking information recording medium 1 obtained can be made more appropriate.

[0115] (Intermediate Layer) The intermediate layer 5 is a layer intended to suppress the adverse effects of external factors such as chemicals migrating to the color-forming layer 4 and reducing the color density, thereby further improving the print storage stability (moisture and heat resistance, etc.) of the laser-markable information recording medium 1. In particular, when the laser-markable information recording medium 1 of this embodiment includes a second substrate 7 or a laminate layer 6, oil-soluble components in the second substrate 7 or laminate layer 6 may migrate to the color-forming layer 4, resulting in a decrease in color density during storage, particularly when stored in a high-temperature, high-humidity environment, which can cause a moisture and heat resistance problem. In such cases, by providing the intermediate layer 5 between the color-forming layer 4 and the second substrate 7 or laminate layer 6, the migration of oil-soluble components in the second substrate 7 or laminate layer 6 to the color-forming layer 4 can be suppressed, thereby improving the moisture and heat resistance.

[0116] The laser-markable information recording medium 1 according to the second embodiment of the present invention essentially includes an intermediate layer 5 containing a resin having a water-soluble portion and / or a crosslinking agent. In the second embodiment of the present invention, the inclusion of such an intermediate layer 5 can further inhibit the migration of external factors, such as chemicals, into the color-forming layer 4. In particular, when the intermediate layer 5 contains a resin having a water-soluble portion, the water-soluble portion can more effectively inhibit the migration of oil-soluble components, etc., in the second substrate 7 or the laminate layer 6. Furthermore, when the intermediate layer 5 contains a crosslinking agent, a dense crosslinked structure can be formed within the intermediate layer 5, and the crosslinked structure can more effectively inhibit the migration of oil-soluble components, etc., in the second substrate 7 or the laminate layer 6. The intermediate layer 5 may further include other components as necessary. Examples of such other components include resins, surfactants, and preservatives.

[0117] Furthermore, the laser-markable information recording medium 1 of the first and third aspects of the present invention may or may not include an intermediate layer 5. From the viewpoint of further improving print preservation properties such as moist heat resistance, it is preferable to include the intermediate layer 5. In the first and third aspects of the present invention, the intermediate layer 5 can be formed mainly from a resin. The resin is not particularly limited, but, as in the second aspect, it is preferable to include a resin having a water-soluble portion. The intermediate layer 5 may further include other components as necessary. Examples of such other components include a crosslinking agent, a surfactant, a preservative, an inorganic pigment, and an organic pigment. Among these, it is preferable to include a crosslinking agent, as in the second aspect.

[0118] Examples of the resin having a water-soluble portion include a hydroxy group-containing resin such as a polyvinyl alcohol (PVA) resin having a hydroxy group as the water-soluble portion; and a carboxy group-containing resin such as an acrylic resin having a carboxy group as the water-soluble portion. Among these, the resin having a water-soluble portion is preferably a carboxy group-containing resin. Because the carboxy group is a highly hydrophilic functional group, it is particularly effective in inhibiting the migration of oil-soluble components into the color-forming layer 4, and is also thought to be capable of forming a crosslinked structure with a crosslinking agent described below.

[0119] The resin having a water-soluble portion is preferably a core-shell resin. In this specification, the term "core-shell resin" refers to a resin having a structure in which a hydrophobic core particle is coated with a water-soluble shell polymer.

[0120] Among the core-shell resins, a core-shell resin having a carboxy group as the water-soluble portion (a core-shell carboxy group-containing resin) is preferred. Here, the core-shell carboxy group-containing resin is considered to contain a carboxy group at least in the structure of a water-soluble shell polymer.

[0121] Examples of the core-shell type carboxy group-containing resin include core-shell type acrylic resins such as core-shell type acrylic resins, core-shell type styrene-acrylic resins, core-shell type acrylic-urethane resins, core-shell type acrylic-amide resins, and core-shell type vinyl acetate-acrylic resins; and core-shell type maleic acid-based resins. The core-shell type carboxyl group-containing resin is preferably a core-shell type acrylic resin, and among these, at least one selected from the group consisting of core-shell type acrylic resins, core-shell type styrene-acrylic resins, and core-shell type acrylic-urethane resins is more preferred, and at least one selected from the group consisting of core-shell type acrylic resins and core-shell type styrene-acrylic resins is even more preferred. Examples of the core-shell type acrylic resin include resins commercially available under the name Bariastar (manufactured by Mitsui Chemicals, Inc.).

[0122] Other examples of the resin include SBR resin.

[0123] The content of the resin is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, relative to 100% by mass of the total solid content of the intermediate layer 5. The content of the resin may be 99% by mass or less, or may be 95% by mass or less, relative to 100% by mass of the total solid content of the intermediate layer 5.

[0124] The content of the resin having a water-soluble portion is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to 100% by mass of the total amount of resin in the intermediate layer 5. It may also be 100% by mass. When the content is within the above range, the barrier properties of the intermediate layer 5 can be further improved, and print preservability such as moist heat resistance can be further improved. Furthermore, the content of the core-shell resin is preferably within the above range, relative to 100% by mass of the total amount of resin in the intermediate layer 5.

[0125] Examples of the crosslinking agent include organic crosslinking agents such as cationic crosslinking agents and non-cationic crosslinking agents; and inorganic crosslinking agents such as zirconium carbonate. Examples of the cationic crosslinking agent include epichlorohydrin-based resins such as polyamide epichlorohydrin resins, polyamine epichlorohydrin resins, and polyamide polyamine epichlorohydrin resins. Examples of the non-cationic crosslinking agent include oxazoline-based compounds such as oxazoline group-containing polymers and oxazoline group-containing low molecular weight compounds. The crosslinking agent is preferably a cationic crosslinking agent, and polyamide epichlorohydrin resin is more preferred. These crosslinking agents can be used alone or in combination of two or more.

[0126] The content of the crosslinking agent is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, relative to 100% by mass of the total solids content of the intermediate layer 5. The content of the crosslinking agent is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, relative to 100% by mass of the total solids content of the intermediate layer 5. When the content is within the above range, an appropriate crosslinked structure can be formed, which can further improve the barrier properties of the intermediate layer 5 and further improve print storage stability such as moist heat resistance.

[0127] The coating amount (dry mass) of the intermediate layer 5 is, for example, 0.3 g / m 2 ~10g / m 2 is preferable, and more preferably 1.0 g / m 2 ~4.0g / m 2When the coating amount is within the above range, the barrier properties of the resulting laser-marking information recording medium 1 can be made more appropriate, and the print storage stability such as moist heat resistance can be further improved.

[0128] (Laminate Layer) The laminate layer 6 is intended to enhance adhesion between the intermediate layer 5 and the second substrate 7. Furthermore, if the laser-markable information recording medium 1 does not include the intermediate layer 5, it can also function as a layer that enhances adhesion between the color-forming layer 4 and the second substrate 7 (not shown). The laminate layer 6 may be omitted if not required. For example, if the first substrate 2 and / or the second substrate 7 are heat-sealable resin films, the laser-markable information recording medium can be obtained by heat sealing. Alternatively, the color-forming layer 4 may be applied to the first substrate 2, and then the second substrate 7 may be attached thereto before the color-forming layer 4 is completely dried, allowing the color-forming layer 4 to completely dry. The material for forming the laminate layer 6 is not particularly limited, and examples thereof include known or commonly used laminating adhesives, pressure-sensitive adhesives, thermoplastic resins, hot melt adhesives, and water-based adhesives. The laminate layer 6 may also contain other components.

[0129] Examples of the laminating adhesive include dry laminating adhesives such as urethane, ether, ester, and epoxy types; and non-solvent laminating adhesives such as urethane, ether, ester, epoxy, and isocyanate types. The laminating adhesives may be one-component or two-component. The laminating adhesives may be aliphatic or aromatic. Among these, from the viewpoint of excellent adhesive strength, urethane-type laminating adhesives are preferred, urethane-type dry laminating adhesives are more preferred, and two-component and urethane-type dry laminating adhesives are even more preferred. Furthermore, from the viewpoint of environmental friendliness, isocyanate-type non-solvent laminating adhesives are preferred. The two-component laminating adhesives are used by mixing a base agent and a curing agent, and the curing agent can be a known or commonly used curing agent such as an isocyanate-type curing agent. The laminating adhesives may be used alone or in combination of two or more types.

[0130] Examples of the pressure-sensitive adhesive include acrylic pressure-sensitive adhesives, rubber pressure-sensitive adhesives (natural rubber-based, synthetic rubber-based, and mixtures thereof), silicone pressure-sensitive adhesives, polyester pressure-sensitive adhesives, urethane pressure-sensitive adhesives, polyether pressure-sensitive adhesives, polyamide pressure-sensitive adhesives, and fluorine-containing pressure-sensitive adhesives. Among these, acrylic pressure-sensitive adhesives are preferred from the viewpoint of excellent adhesion and transparency. The pressure-sensitive adhesives can be used alone or in combination of two or more.

[0131] The coating amount (dry mass) of the laminate layer 6 is, for example, 0.3 g / m 2 ~50g / m 2 is preferred, and more preferably 0.5 g / m 2 ~40g / m 2 When the coating amount is within the above range, the adhesion between the layers becomes more appropriate, and peeling between the layers can be further suppressed.

[0132] (Other Layers) The printing layer can be provided at an appropriate position depending on the intended use of the laser-marking information recording medium of the present invention. For example, when the first substrate is a transparent or translucent layer and the printing is visible from the first substrate side, the printing layer can be provided on the surface opposite the first substrate side relative to the color-forming layer. The printing layer can be provided, for example, between the color-forming layer and the intermediate layer, between the intermediate layer and the laminate layer, between the laminate layer and the second substrate, or on the surface of the second substrate opposite the surface on which the laminate layer is provided. Furthermore, when the second substrate is a transparent or translucent layer and the printing is visible from the second substrate side, the printing layer can be provided on the surface opposite the second substrate side relative to the color-forming layer. The printing layer can be provided, for example, between the color-forming layer and the anchor layer, between the anchor layer and the first substrate, or on the surface of the first substrate opposite the surface on which the anchor layer is provided. By providing such a printing layer, the printed portion of the color-developing layer can be seen against the background of the printing layer, improving the contrast of the printed portion and improving visibility and aesthetics. The printing layer can be formed mainly from a known or commonly used white ink such as titanium oxide or a colored ink. The printing layer may further contain other components as necessary.

[0133] [Laser Marking Method] The laser marking information recording medium of the first and second aspects of the present invention can develop color by irradiation with laser light. The laser light is not particularly limited, and examples include infrared laser light such as carbon dioxide laser light, YAG laser light, and YVO laser light; visible light laser light such as green laser light; and ultraviolet laser light such as excimer laser light and THG laser light. Among these, the laser light is preferably ultraviolet laser light with a wavelength of more than 351 nm and not more than 400 nm, more preferably ultraviolet laser light with a wavelength of more than 353 nm and not more than 390 nm, even more preferably ultraviolet laser light with a wavelength of more than 353 nm and not more than 360 nm, and particularly preferably THG laser light. Using such laser light as a light source can result in better color development.

[0134] The laser-markable information recording medium of the third aspect of the present invention can develop color by irradiation with ultraviolet laser light having a wavelength of more than 351 nm and not more than 400 nm. Among these, the ultraviolet laser light is preferably ultraviolet laser light having a wavelength of more than 353 nm and not more than 390 nm, more preferably ultraviolet laser light having a wavelength of more than 353 nm and not more than 360 nm, and even more preferably THG laser light. When such laser light is used as a light source, better color development can be achieved.

[0135] The laser-markable information recording medium of the present invention develops color primarily through a reaction between the leuco dye contained in the color-developing layer and the color developer. This allows for clearer printing than conventional laser marking, which involves abrading, gasifying, or carbonizing the target object. Furthermore, the laminated structure of the present invention allows the first substrate and / or second substrate to protect the coating layers, such as the color-developing layer, thereby suppressing dust generation during laser irradiation and further reducing contamination of the working environment.

[0136] [Method for manufacturing a laser-markable information recording medium] The method for manufacturing the laser-markable information recording medium of the present invention is not particularly limited, and it can be manufactured by a known or conventional method. For example, a coating liquid for the color-forming layer is prepared by dispersing the materials contained in the color-forming layer 4 in a solvent such as water, and this is applied to the first substrate 2, and then the second substrate 7 is laminated thereon to obtain the laser-markable information recording medium 1 shown in Figure 1.

[0137] (Preparation Process) The method for preparing the color-forming layer coating liquid is not particularly limited. For example, it can be prepared by pre-dispersing all of the materials in the same solvent. Alternatively, the dye and developer, which react with each other, may be prepared as separate dispersions and then mixed to form the color-forming layer coating liquid. In this case, the other components may be added to either the dye-containing dispersion or the developer-containing dispersion, or to both. Examples of methods for preparing the color-forming layer coating liquid include stirring, ultrasonic treatment, and crushing using a ball mill, bead mill, sand mill, high-pressure homogenizer, etc. These methods can be used alone or in combination of two or more.

[0138] (Coating Process) The method for applying the color-forming layer coating liquid is not particularly limited, and examples thereof include a method of directly applying the coating liquid to a substrate, and a method of applying the coating liquid to a release liner or the like and then transferring the coating liquid to a substrate. Examples of coating methods include air knife coating, barber blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, and gravure coating. Hand coating using a wire bar is also possible. These methods can be used alone or in combination of two or more.

[0139] (Drying Step) The method for drying the coating liquid for the color-forming layer is not particularly limited, and examples thereof include heat drying, room temperature drying, vacuum drying, etc. These methods can be used alone or in combination of two or more. The color-forming layer 4 can be formed by these methods.

[0140] When the laser-markable information recording medium of the present invention includes layers other than the first substrate, the color-developing layer, and the second substrate, the manufacturing method of the laser-markable information recording medium can be the same as that described above. When a laminate layer is included, the laminate layer can be formed by a known or commonly used method such as dry lamination, non-solvent lamination, extrusion lamination, or hot-melt lamination.

[0141] A method for producing a laser-markable information recording medium according to one embodiment of the present invention is illustrated below with reference to FIG. 2 . First, a coating liquid for an anchor layer is applied to a first substrate 2 and dried to form an anchor layer 3. Next, a coating liquid for a color-forming layer is applied to the anchor layer 3 and dried to form a color-forming layer 4. Next, a coating liquid for an intermediate layer is applied to the color-forming layer 4 and dried to form an intermediate layer 5, thereby producing a first laminate. Next, a laminate layer 6 is formed on a second substrate 7 to produce a second laminate. Next, the first laminate is laminated with the laminate layer 6 interposed therebetween so that the intermediate layer 5 of the first laminate is in contact with the laminate layer 6, thereby producing a laser-markable information recording medium 1. The anchor layer coating liquid and the intermediate layer coating liquid can be prepared by the same method as the color-forming layer coating liquid. The preparation, coating, and drying methods are not particularly limited, and the methods listed above can be used. The method of laminating the laminate layer 6 is not particularly limited, and known or conventional methods can be used depending on the material of the laminate layer 6. For example, bonding by dry lamination using a dry lamination adhesive, non-solvent lamination using a non-solvent lamination adhesive, hot melt lamination using a hot melt adhesive, or extrusion lamination using a thermoplastic resin can be used. When using the extrusion lamination method, a known or conventional anchor coating agent for extrusion lamination can also be used as an auxiliary agent. When a pressure-sensitive adhesive is used as the material of the laminate layer 6, the first laminate and the second laminate can be bonded together by applying pressure with or without heating.

[0142] In another embodiment, when the laser marking information recording medium 1 includes an intermediate layer 5, the laminate layer 6 may be formed on the intermediate layer 5 (not shown).

[0143] In another embodiment, when the laser marking information recording medium 1 does not include the intermediate layer 5, the laminate layer 6 may be formed on the color-developing layer 4 (not shown).

[0144] The method for forming each of the above layers is not particularly limited, and for example, multiple layers may be simultaneously coated using a curtain coater or the like, or the layers may be formed individually and sequentially. Alternatively, some layers may be simultaneously coated and some layers may be formed individually and sequentially.

[0145] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0146] A first laminate was prepared by laminating an anchor layer, a color-developing layer, and an intermediate layer in this order on a first substrate using the following process. Furthermore, a second laminate was prepared by laminating a laminate layer on a second substrate using the following process. The intermediate layer of the first laminate was laminated so that it was in contact with the laminate layer of the second laminate, thereby preparing an information recording medium for laser marking. This was then used in the tests described below to evaluate the recording medium.

[0147] Example 1 (Production of information recording medium for laser marking) <Anchor layer> A styrene acrylic resin having a solid content concentration of 38% by mass was applied to the surface of resin film A (material: polypropylene, thickness: 30 μm) as the first substrate by a conventional method using water as a solvent, and then dried to form an anchor layer with a coating amount of 0.9 g / m 2 An anchor layer of (dry mass) was formed.

[0148] <Color-forming layer> A coating liquid for the color-forming layer (solids concentration 21% by mass) was prepared by a conventional method, containing 17.4% by mass of 3-dibutylamino-6-methyl-7-anilinofluoran as a dye, 26.8% by mass of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea as a developer, 10.0% by mass of kaolin (water dispersion) as a filler, 33.1% by mass of styrene butadiene latex (SBR) as a binder, 1.5% by mass of polystyrene as a lubricant, 9.1% by mass of an acrylic resin as a dispersant, 2.0% by mass of polyamide epichlorohydrin resin as a crosslinking agent, and water as a solvent. The coating liquid for the color-forming layer was applied to the surface of the anchor layer by a conventional method and dried, resulting in a coating weight of 4.5 g / m. 2(dry mass) of color-forming layer A was formed. The numerical values ​​of each material above indicate the mass ratio of each material relative to 100% by mass of the color-forming layer (dry state).

[0149] <Intermediate layer> A coating liquid for an intermediate layer (solid content concentration 18.5% by mass) containing 85.0% by mass of a core-shell type acrylic resin as a resin, 15.0% by mass of a polyamide epichlorohydrin resin as a crosslinking agent, and water as a solvent was prepared by a conventional method. The coating liquid for an intermediate layer was applied to the surface of the color-developing layer by a conventional method and dried, resulting in a coating amount of 1.9 g / m 2 (dry mass) of intermediate layer A was formed to obtain a first laminate. The numerical values ​​of each material above indicate the mass ratio of each material relative to 100% by mass of the intermediate layer (dry state).

[0150] <Laminate layer> A urethane adhesive A for dry lamination (main agent: 93.7% by mass, curing agent: 6.3% by mass) containing ethyl acetate as a solvent and having a solid content of 22% by mass was applied to the surface of a resin film B (material: polyethylene terephthalate, thickness: 50 μm) as a second substrate by a conventional method to form a laminate layer A, thereby obtaining a second laminate. Note that the numerical values ​​of each material above indicate the mass ratio of each material to 100% by mass of the laminate layer (dry state).

[0151] Next, the laminate layer A of the second laminate was directly contacted with the intermediate layer of the first laminate by dry lamination (dry lamination method), and thus a laser marking information recording medium of Example 1 consisting of [resin film A / anchor layer / color-developing layer A / intermediate layer A / laminate layer A / resin film B] was produced.

[0152] Example 2 (Preparation of information recording medium for laser marking) An information recording medium for laser marking of Example 2 was prepared in the same manner as in Example 1, except that resin film C (material: polyethylene terephthalate, thickness: 12 μm) was used instead of resin film B as the second substrate.

[0153] Example 3 (Preparation of information recording medium for laser marking) An information recording medium for laser marking of Example 3 was prepared in the same manner as in Example 1, except that resin film C (material: polyethylene terephthalate, thickness: 12 μm) was used instead of resin film B as the second substrate, laminate layer B was used instead of laminate layer A, and lamination was performed by bonding instead of dry lamination. The laminate layer B was formed by applying acrylic adhesive B to the surface of the second substrate by a conventional method and drying by heating. In this case, because laminate layer B is adhesive, it can be laminated by bonding it so that it is in direct contact with intermediate layer A of the first information recording medium.

[0154] Example 4 (Preparation of information recording medium for laser marking) An information recording medium for laser marking of Example 4 was prepared in the same manner as in Example 1, except that resin film D (material: biaxially oriented polypropylene, thickness: 40 μm) was used instead of resin film B as the second substrate.

[0155] Example 5 (Preparation of information recording medium for laser marking) An information recording medium for laser marking of Example 5 was prepared in the same manner as in Example 1, except that laminate layer C was used instead of laminate layer A and non-solvent lamination was used instead of dry lamination. The laminate layer C was formed by applying isocyanate-type adhesive C for non-solvent lamination to the surface of the second substrate.

[0156] Example 6 (Preparation of Laser Markable Information Recording Medium) An information recording medium for laser marking of Example 6 was prepared in the same manner as in Example 1, except that the intermediate layer A was not formed.

[0157] Example 7 (Preparation of information recording medium for laser marking) An information recording medium for laser marking of Example 7 was prepared in the same manner as in Example 1, except that color forming layer B was used instead of color forming layer A. The color forming layer B was the same as color forming layer A, except that 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate was used as the color developer instead of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0158] Example 8 (Preparation of information recording medium for laser marking) An information recording medium for laser marking of Example 8 was prepared in the same manner as in Example 1, except that color forming layer C was used instead of color forming layer A. The color forming layer C was the same as color forming layer A, except that 4-hydroxy-4'-propoxydiphenyl sulfone was used as the developer instead of N,N'-di-[3-(p-toluenesulfonyloxy)phenyl]urea.

[0159] Comparative Example 1 (Preparation of information recording medium for laser marking) An information recording medium for laser marking of Comparative Example 1 consisting of [resin film A / anchor layer / color-developing layer A / intermediate layer A] was prepared in the same manner as in Example 1, except that the laminate layer and second substrate were not laminated.

[0160] Comparative Example 2 (Preparation of information recording medium for laser marking) An information recording medium for laser marking of Comparative Example 2 was prepared in the same manner as in Example 1, except that color-forming layer B was used instead of color-forming layer A and the laminate layer and second substrate were not laminated.

[0161] Comparative Example 3 (Preparation of information recording medium for laser marking) An information recording medium for laser marking of Comparative Example 3 was prepared in the same manner as in Example 1, except that color-forming layer C was used instead of color-forming layer A and the laminate layer and second substrate were not laminated.

[0162] <Evaluation> The laser marking information recording media prepared in the Examples and Comparative Examples were evaluated as follows. The results are shown in Tables 1 and 2.

[0163] (1) Optical Density of Printed Area by THG Laser Printing was performed on a laser marking information recording medium using a UV laser printer manufactured by Keyence Corporation, with the operation speed set to either 1000 mm / sec, 1300 mm / sec, or 1600 mm / sec. The optical density (OD value) of the colored printed area was then measured using a spectrophotometer (manufactured by Videojet X-Rite Inc., device name: X-rite eXact). Furthermore, when printing was performed at an operation speed set to 1300 mm / sec, if dust generation was observed or damage was confirmed when the surface of the printed area after printing was visually inspected, the appearance was evaluated as "×." If no dust generation or surface damage was observed, the appearance was evaluated as "○." In this measurement, the frequency of the UV laser printer was 55 Hz, and the laser power was 50%. During printing, the laser light was irradiated onto the second substrate side, which is one end face, of the laser marking information recording medium of the example, and onto the intermediate layer side, which is one end face, of the laser marking information recording medium of the comparative example. The UV laser printer is a printing device that emits laser light with a wavelength of 355 nm and uses a THG laser as a light source.

[0164]

[0165] (2) Optical Density of Colored Portion Before and After Humid Heat Resistance Test A laser marking information recording medium was colored to the maximum color density using a thermal gradient plate set at 170°C with a 10°C gradient. The optical density of the colored portion was measured using a spectrophotometer (manufactured by Videojet X-Rite Inc., device name: X-rite eXact), and this optical density was recorded as the optical density before the humidity and heat resistance test. Next, the laser marking information recording medium was left standing for one day in an environment of 50°C and 100% humidity, and then the optical density of the colored portion was measured again in the same manner, and this optical density was recorded as the optical density after the humidity and heat resistance test. The optical density value after the test was divided by the optical density value before the test to determine the residual rate of the colored portion (optical density after humidity and heat resistance test / optical density before humidity and heat resistance test).

[0166]

[0167] As shown in Table 1, the laser marking information recording medium having the second substrate did not generate dust when irradiated with laser light, and no damage was observed on the second substrate after printing, confirming that it is suitable for printing with a UV laser printer (Examples 1 to 8). Furthermore, all of the optical densities exceeded 1, confirming that high contrast and good color development could be achieved (Examples 1 to 8).

[0168] Furthermore, the thickness and material of the second substrate and the material of the laminate layer were not limited and were widely applicable. In particular, comparing Example 1 and Example 2, when substrates made of the same resin were used, Example 1, which had a larger thickness, tended to exhibit a higher optical density. Specifically, in Example 1, printing was performed by irradiating resin film B (thickness: 50 μm) with laser light, and the optical density was 1.52. On the other hand, in Example 2, resin film C (thickness: 12 μm) was used, and the optical density was 1.46. The reason for this is unclear, but it is possible that, for example, increasing the thickness of the first substrate improves its physical strength, thereby improving protection for the color-forming layer 4, thereby suppressing damage to the printed area during laser light irradiation and improving color development.

[0169] On the other hand, in the case of information recording media for laser marking that did not have a second substrate, dust generation and damage to the surface on the intermediate layer side were observed when irradiated with laser light, and a decrease in optical density was also observed, confirming that they were not suitable for printing with a UV laser printer (Comparative Examples 1 to 3).

[0170] Here, the laser-markable information recording medium of the examples has a laminated structure in which the color-forming layer is sandwiched between a first substrate and a second substrate, which are resin films that transmit ultraviolet light. Therefore, as in the above examples, the laser light irradiated onto the second substrate passes through the second substrate and efficiently acts on the color-forming layer, which is believed to have absorbed the laser light and, due to its energy, exhibited good color development. Furthermore, because laser light is generally high-energy, when the color-forming layer absorbs the laser light, some kind of impact phenomenon, such as foaming or gasification, can occur. However, because the color-forming layer is protected by being sandwiched between the substrates, it is believed that laser marking was possible without damage. As a result, it is believed that all of the laser-markable information recording mediums of the examples were laser-markable and achieved good color development. On the other hand, the laser-markable information recording medium of the comparative example has a laminated structure without a second substrate, so the laser light is irradiated onto the intermediate layer, which is a coating layer. For example, since the intermediate layer, which is a coating layer, has a physical strength inferior to that of the substrate, it is possible that it could not withstand the impact when the color-developing layer absorbs the laser light and was damaged, or that the intermediate layer itself absorbed the laser light and was damaged by its energy.In addition, in the laser-marking information recording media of Examples 1 to 8, the first substrate, like the second substrate, is a resin film that transmits ultraviolet light, so printing was possible even when laser light was irradiated from the first substrate side.

[0171] Furthermore, as shown in Table 2, in the moist heat resistance test, the color-developing portion remained higher when the intermediate layer was included (Example 1) than when the intermediate layer was not included (Example 6), confirming that the inclusion of an intermediate layer further improved moist heat resistance. This is because the intermediate layer has a crosslinked structure derived from a resin having a water-soluble portion and a crosslinking agent, and the water-soluble portion and the crosslinked structure inhibit the migration of oil-soluble components, etc., in the second substrate and laminate layer to the color-developing layer, resulting in improved moist heat resistance. Furthermore, it was confirmed that the absolute value of the optical density before the moist heat resistance test was also higher when the intermediate layer was included (Example 1) than when the intermediate layer was not included (Example 6). This is thought to be because, when the intermediate layer was not included, as in Example 6, the color-developing portion was affected by the laminate layer, even between the time when the laser marking information recording medium was produced and the time when it was used in the moist heat resistance test, and the optical density of the color-developing portion decreased. In other words, even in a less stressful environment such as a moist heat resistance test, the optical density of the color-developing portion may decrease due to the influence of the laminate layer, but by providing the intermediate layer of the present invention, such a decrease in optical density can be further suppressed.

[0172] Furthermore, as shown in Table 2, in a test using the non-phenolic color developer 3-[(3-phenylureido)phenyl]-4-methylbenzenesulfonate as the color developer, it was confirmed that the moist heat resistance was significantly improved when a second substrate and a laminate layer were provided (Example 7) compared to when a second substrate and a laminate layer were not provided (Comparative Example 2). These results demonstrate that even for color developers that are relatively susceptible to the effects of high-temperature, high-humidity environments, the laminate structure of the present invention improves moist heat resistance. This is thought to be because the color-forming layer is protected by the second substrate and the laminate layer, making it difficult for water (moisture) in the environment to reach the color developer contained in the color-forming layer, thereby further suppressing the decolorization reaction caused by the water.

[0173] Variations of the invention according to the present disclosure are described below. [Appendix 1] An information recording medium for laser marking, comprising a first substrate, a color-developing layer, and a second substrate laminated in this order, wherein the first substrate is a layer that transmits ultraviolet light, the color-developing layer contains a leuco dye and a color developer, and the color developer contains a non-phenolic color developer. [Appendix 2] The information recording medium for laser marking according to Appendix 1, wherein the non-phenolic color developer contains at least a compound represented by formula (1) above and / or a compound represented by formula (2). [Appendix 3] The information recording medium for laser marking according to Appendix 1 or 2, wherein the non-phenolic color developer contains at least a compound represented by formula (1). [Appendix 4] The information recording medium for laser marking according to any one of Appendices 1 to 3, wherein a laminate layer is further provided between the color-developing layer and the second substrate. [Appendix 5] The laser-markable information recording medium according to any one of Appendices 1 to 3, which is a thermosensitive recording medium further comprising an intermediate layer between the color-developing layer and the second substrate, the intermediate layer containing a resin having a water-soluble portion and / or a crosslinking agent. [Appendix 6] The laser-markable information recording medium according to Appendices 5 and 6, which is further comprising a resin having a water-soluble portion and a crosslinking agent. [Appendix 7] The laser-markable information recording medium according to Appendices 5 or 6, which is further comprising a core-shell resin having at least a carboxy group as the water-soluble portion. [Appendix 8] The laser-markable information recording medium according to any one of Appendices 5 to 7, which is further comprising a laminate layer between the intermediate layer and the second substrate. [Appendix 9] An information recording medium for laser marking, comprising a first substrate, a color-developing layer, an intermediate layer, and a second substrate laminated in this order, wherein the first substrate is a layer that transmits ultraviolet light, the color-developing layer contains a leuco dye and a color developer, and the intermediate layer contains a resin having a water-soluble portion and / or a crosslinking agent. [Appendix 10] The information recording medium for laser marking according to Appendix 9, wherein the intermediate layer contains a resin having a water-soluble portion and a crosslinking agent. [Appendix 11] The information recording medium for laser marking according to Appendix 10, wherein the resin having a water-soluble portion is a core-shell type resin having at least a carboxy group as the water-soluble portion.[Appendix 12] The laser-markable information recording medium according to any one of Appendices 9 to 11, further comprising a laminate layer between the intermediate layer and the second substrate. [Appendix 13] The ultraviolet laser-markable information recording medium is an information recording medium comprising a first substrate, a color-developing layer, and a second substrate laminated in this order, wherein the first substrate is a layer that transmits ultraviolet light, and the color-developing layer contains a leuco dye and a color developer, and is capable of developing color upon irradiation with ultraviolet laser light having a wavelength of more than 351 nm and not more than 400 nm. [Appendix 14] The laser-markable information recording medium according to Appendices 13 and 14, wherein the ultraviolet laser light is THG laser light. [Appendix 15] The laser-markable information recording medium according to Appendices 13 or 14, further comprising a laminate layer between the color-developing layer and the second substrate. [Appendix 16] The laser-markable information recording medium according to any one of Appendices 1 to 15, further comprising an anchor layer between the first substrate and the color-developing layer. [Appendix 17] The laser-markable information recording body according to any one of Appendices 1 to 16, wherein the second substrate is a layer that transmits ultraviolet light. [Appendix 18] The laser-markable information recording body according to any one of Appendices 1 to 17, wherein the first substrate is a resin film. [Appendix 19] The laser-markable information recording body according to any one of Appendices 1 to 18, wherein the thickness of the first substrate is 15 μm or more. [Appendix 20] The laser-markable information recording body according to any one of Appendices 1 to 19, wherein the second substrate is a resin film. [Appendix 21] The laser-markable information recording body according to any one of Appendices 1 to 20, wherein the thickness of the second substrate is 15 μm or more. [Appendix 22] The laser-markable information recording body according to any one of Appendices 1 to 21, wherein the first substrate is located on one end surface of the laser-markable information recording body, and the second substrate is located on the other end surface of the laser-markable information recording body.

[0174] REFERENCE SIGNS LIST 1 Laser marking information recording medium 2 First substrate 3 Anchor layer 4 Color-developing layer 5 Intermediate layer 6 Laminate layer 7 Second substrate

Claims

1. An information recording medium for laser marking, comprising a first substrate, a color-developing layer, and a second substrate laminated in this order, the first substrate being a layer that transmits ultraviolet light, the color-developing layer containing a leuco dye and a color developer, and the color developer containing a non-phenolic color developer.

2. The laser marking information recording medium according to claim 1, wherein the non-phenolic color developer contains at least a compound represented by the following formula (1) and / or a compound represented by the following formula (2): (In formula (1), R 1 is a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and a plurality of R 1 may be the same or different. 1 is a hydrocarbon group having 1 to 4 carbon atoms, and a plurality of A 1 may be the same or different. m represents an integer of 0 to 4, and multiple m's may be the same or different. (The symbols in formula (2) are the same as those in formula (1) above.) 3. The laser markable information recording medium according to claim 2, further comprising a laminate layer provided between the color-developing layer and the second substrate.

4. An information recording medium for laser marking, comprising a first substrate, a color-developing layer, an intermediate layer, and a second substrate laminated in this order, wherein the first substrate is a layer that transmits ultraviolet light, the color-developing layer contains a leuco dye and a color developer, and the intermediate layer contains a resin having a water-soluble portion and / or a crosslinking agent.

5. The laser markable information recording medium according to claim 4, wherein the intermediate layer contains a resin having a water-soluble portion and a crosslinking agent.

6. The laser markable information recording medium according to claim 5, wherein the resin having a water-soluble portion is a core-shell type resin having at least a carboxy group as the water-soluble portion.

7. The laser markable information recording medium according to claim 6, further comprising a laminate layer provided between the intermediate layer and the second substrate.

8. An information recording medium for ultraviolet laser marking, which is an information recording medium having a first substrate, a color-developing layer, and a second substrate laminated in this order, wherein the first substrate is a layer that transmits ultraviolet light, the color-developing layer contains a leuco dye and a color developer, and which can develop color when irradiated with ultraviolet laser light having a wavelength of more than 351 nm and not more than 400 nm.

9. The laser marking information recording medium according to claim 8, wherein the ultraviolet laser beam is a THG laser beam.

10. The laser markable information recording medium according to claim 9, further comprising a laminate layer provided between the color-developing layer and the second substrate.

11. The laser markable information recording medium according to any one of claims 1 to 10, further comprising an anchor layer provided between the first substrate and the color-developing layer.

12. The laser markable information recording medium according to any one of claims 1 to 10, wherein the second substrate is a layer that transmits ultraviolet light.

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