JP2020032649A - Heat-sensitive coating material and laser marking method using the same - Google Patents

Abstract

To provide a heat-sensitive coating material which can be color-developed with laser and has a high color-developing speed.SOLUTION: In order to solve the above subject, a heat-sensitive coating material according to the present invention includes amorphous first particles containing leuco dye, color developer and decolorant. When heated at a heating rate of 30°C/min from a temperature below the glass transition point of the first particles to the melting point, the heat-sensitive coating material develops a color at a temperature equal to or higher than the glass transition point of the first particles and lower than the melting point and decolorized at the melting point.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a heat-sensitive paint and a laser marking method using the same.

  Non-contact industrial inkjet printers and laser markers capable of high-speed printing are used in a wide range of fields such as foods, cosmetics, and electronic components. However, many of these marking devices print in a single color, and it is difficult to print in multiple colors. In order to perform multicolor printing in an ink jet printer, a plurality of inks, ink tanks, and nozzles for ejecting ink are required. Laser marking is a method of irradiating a target with a laser beam to melt, scorch, peel, oxidize, scrape, and discolor the surface for printing. In order to perform multicolor printing with a laser marker, it is necessary to apply a coating material that develops multiple colors depending on the laser wavelength to a printing surface in advance. Examples of the paint that develops multiple colors include a paint containing a substance that causes a structural change of a material at a specific wavelength to cause a color change. Therefore, it is necessary to irradiate laser beams of various wavelengths in order to develop a multicolor. In addition, in order to cause a structural change of a material, a high-output laser device is often required.

  On the other hand, in a thermal printer equipped with a thermal head, a technique for printing in multiple colors using a multicolor heat-sensitive recording material is known.

  Patent Document 1 discloses that at least an electron-donating compound, an electron-accepting compound, a reversible crystalline-amorphous transition of a part or all of a composition system or two phase-separated states or a phase-separated state-non- A thermoelectric material containing a reversible material that causes a change in the phase separation state and a thermoelectric characteristic control material is disclosed. The temperature-controlling agent is solid at room temperature, and at least a part of the temperature-controlling agent is compatible with the electron-accepting compound or the reversible material or the electron-accepting compound and the reversible material, and its crystalline-amorphous transition occurs. Or the phase-separated state-the phase change of the crystalline system-amorphous transition or the phase-separated state-non-phase-separated state by changing the non-phase-separated state, after the phase separation, the electron-donating compound and the electron-accepting compound Do not inhibit the interaction of

JP 2001-348568 A

  The thermoelectric material disclosed in Patent Document 1 is in a fluid state when heated from a color-developed state to its melting point or higher, weakens the interaction between the electron-donating compound and the electron-accepting compound, and causes the electron-accepting compound or the reversible material. Alternatively, at least a part of the temperature-reception characteristic controlling agent is compatible with the electron-accepting compound and the reversible material, and the interaction between the temperature-reducing characteristic controlling agent, the developer, and the reversible material becomes strong, and the color is erased. When quenched from that state, the solidification in an amorphous state is maintained while the interaction among the three components of the reversible material, the electron-accepting compound and the temperature-controlling agent is strengthened, and the decolored state is maintained.

  In the amorphous temperature indicating material, the reversible material and the temperature indicating property controlling agent crystallize at a rate corresponding to the heating temperature, and the color is developed. By mixing the amorphous temperature-indicating material into fine particles and mixing into the paint, it is possible to produce a paint that develops color by heating with a laser.

  In laser marking, a high printing speed is required. In order to increase the printing speed, it is desirable to use a temperature indicating material having a high developing speed.

  However, a high color developing speed means that it is easy to crystallize, and it is difficult to solidify in an amorphous state in a decolored state. The amorphous thermoelectric material is formed by rapidly cooling from a state in which the material is heated and melted to a temperature equal to or higher than the melting point to a temperature equal to or lower than the glass transition point. At this time, it passes through a temperature that is easy to be crystallized, which is between the melting point and the glass transition point. In the step of rapidly cooling the temperature indicating material, if the temperature indicating material is crystallized at the temperature at which the temperature indicating material easily crystallizes, the temperature indicating material will not be in an amorphous state but will crystallize and develop color. Therefore, it cannot be used as a paint that develops color when heated by a laser.

  Therefore, an object of the present invention is to provide a heat-sensitive paint which can be developed with a laser and has a high developing speed.

  In order to solve the above-mentioned problems, the heat-sensitive paint according to the present invention contains a leuco dye, a color developer and a decolorant, comprises amorphous first particles, and has a melting point from a temperature below the glass transition point of the first particles. Up to a glass transition point of the first particles and a temperature lower than the melting point when heated at a heating rate of 30 ° C./min.

  According to the present invention, it is possible to provide a heat-sensitive paint which can be developed with a laser and has a high developing speed.

5 is a graph showing the relationship between the temperature and the color density of the temperature-sensitive material used in the first embodiment. 4 is a DSC curve of a temperature-sensitive material having a high crystallization rate. 4 is a DSC curve of a temperature-sensitive material having a low crystallization rate. It is a graph which shows the relationship between the temperature of the temperature-sensitive material used in 2nd Embodiment, and color density. It is a mimetic diagram showing the color change of the paint concerning a 2nd embodiment. It is a graph which shows the relationship between the temperature of the temperature-sensitive material used in 3rd Embodiment, and color density. It is a graph which shows the relationship between the temperature of the temperature-sensitive material used in 3rd Embodiment, and color density. It is a mimetic diagram showing the color change of the paint concerning a 3rd embodiment. 9 is a photograph showing the temperature dependency of the paint according to Example 3. 9 is a photograph showing a result of laser printing of a paint according to Example 3.

Hereinafter, embodiments for carrying out the present invention (hereinafter, referred to as “embodiments”) will be described in detail with reference to the drawings as appropriate. In each of the drawings, common portions are denoted by the same reference numerals, and redundant description will be omitted.

[First Embodiment]
The heat-sensitive paint according to the first embodiment relates to a laser marking paint that forms a marking by irradiating the paint with a laser beam to locally heat the paint and discolor the paint.

  The heat-sensitive paint contains a temperature-sensitive material that changes color by heat due to irradiation with laser light, and a solvent. A resin, a viscosity modifier, a surface tension modifier, and the like may be added to the heat-sensitive paint in order to adjust the viscosity and the strength of the coating film (the paint after the solvent is dried).

<Solvent>
The coating material for laser marking is applied to a printing surface in advance in order to print with a laser beam. A solvent (coating solution) is required to apply it to the printing surface. The solvent can be selected according to the properties of the material forming the printing surface. In the case of a hydrophilic printing surface such as paper, it is preferable to use a hydrophilic solvent.

<Temperature-sensitive material>
The temperature-sensitive material is a particle containing a leuco dye, a color developer, and a decolorant, and is a material that changes color due to an amorphous-crystalline phase transition. Further, the temperature-sensitive material shows a hysteresis characteristic in a color density-temperature curve and has reversibility.

  The temperature-sensitive material according to the first embodiment is characterized in that when the temperature is raised from an amorphous and decolored state, the color is developed by crystallization. FIG. 1 shows the relationship between the color density and the temperature of the temperature-sensitive material according to the first embodiment. The broken line indicates the relationship between the color density and the temperature when the cooling rate is low. In FIG. 1, the vertical axis represents the color density, the horizontal axis represents the temperature, Ta represents the developing temperature of the thermosensitive material, Td represents the decoloring temperature, and the hatched portion represents the use temperature of the marking target. In the temperature-sensitive material according to the first embodiment, color development starts at Ta in the temperature rising process, and decoloration starts when the temperature reaches Td. If the cooling rate is high when the temperature is lowered from the decolored state, the solidified state remains in the decolored state. When the cooling rate is low, color development starts at Ta 'as shown by the broken line, and solidifies in the color developed state.

  Therefore, by applying thermal energy corresponding to the temperature Ta to the temperature-sensitive material that has been erased in the amorphous state by a laser, the paint can be developed only in the laser-irradiated portion. After the color development, the color development state can be maintained by cooling without raising the temperature to Td or higher. Further, by setting Ta to a temperature higher than the range of the use temperature of the marking target (a temperature not assumed in the use process), new color development can be suppressed. For example, when the marking target is stored and used at room temperature, it is preferable to use a material that develops color at 60 ° C. or higher.

  2 and 3 are DSC curves obtained by differential scanning calorimetry (DSC) of the temperature-sensitive material. FIG. 2 is a DSC curve of a temperature-sensitive material having a high crystallization rate, and is a schematic diagram when measured at a temperature increase rate of 30 ° C./min and a temperature decrease rate of 20 ° C./min. FIG. 3 is a DSC curve of a temperature-sensitive material having a low crystallization rate, and is a schematic diagram when measured at a temperature rising rate of 5 ° C./min and a temperature decreasing rate of 20 ° C./min. The vertical axis is the heat flux (W), the horizontal axis is the temperature, Tg is the glass transition point, Ta is the starting temperature of the exothermic peak due to crystallization in the heating process (hereinafter, referred to as the crystallization starting temperature in the heating process), Td. Is the melting point. The melting point Td and the crystallization start temperature Ta in the temperature raising process in FIGS. 2 and 3 correspond to the decoloring temperature Td and the developing color temperature Ta in FIG. 1, respectively.

  2 and 3, when the temperature is increased, the baseline decreases at the glass transition point Tg accompanying the glass transition. Crystallization starts at the crystallization start temperature Ta in the temperature rising process, and an exothermic peak is observed. The leuco dye dissociated by the start of crystallization and the color developer are combined, and color development starts. An endothermic peak is observed at the melting point Td. The temperature-sensitive material that has reached the melting point is melted and discolored by the dissociation of the bond between the leuco dye and the developer. When the heating rate is slow, the crystallization start temperature Ta in the heating process appears at a lower temperature. When the heating speed is fast, the crystallization starting temperature Ta in the heating process appears at a higher temperature, or the crystallization starts. It melts at the melting point Td without the onset temperature Ta appearing.

  As shown in FIG. 2, when the temperature-sensitive material having a high crystallization rate is cooled from a temperature higher than the melting point Td, crystallization occurs and an exothermic peak is observed. As a result, the dissociated leuco dye and the color developer are combined to start color development. When heated again in this state, since the crystal has already been crystallized, a decrease in the baseline due to the glass transition and an exothermic peak due to the crystallization are not observed.

  As shown in FIG. 3, when the temperature-sensitive material having a low crystallization rate is cooled from a temperature equal to or higher than the melting point Td, no crystallization occurs and no exothermic peak due to crystallization is observed. Since the thermosensitive material is solidified while the leuco dye and the developer are dissociated, the decolored state is maintained. Although not shown in FIG. 3, when the cooling rate is low, the leuco dye and the color developer are combined and solidified in a colored state. The coloration state differs depending on the cooling rate. In the case of a material that is easily crystallized, the material easily crystallizes at a temperature equal to or higher than the glass transition temperature.

  As described above, laser marking requires a high printing speed. In order to increase the printing speed in laser marking, it is desirable to use a material having a high crystallization speed as the temperature-sensitive material.

  However, in laser marking, the temperature-sensitive material needs to be in a decolored state before laser irradiation. This is because the temperature-sensitive material in the decolored state is irradiated with a laser beam so that the temperature becomes equal to or higher than Ta and equal to or lower than Td, so that the temperature-sensitive material is developed. As can be seen from FIGS. 2 and 3, in the case of a temperature-sensitive material that is difficult to crystallize, the temperature-sensitive material can be kept in a decolored state before laser irradiation by rapidly cooling after melting the temperature-sensitive material. . On the other hand, in the case of a temperature-sensitive material that easily crystallizes, it crystallizes in the cooling process and develops color, so that it cannot be kept in a decolored state.

  As the quenching method, various cooling methods are supposed. However, due to the heat capacity of the temperature-sensitive material, the crystallization rate is so high that a crystallization peak is observed in the DSC measurement at a heating rate of 30 ° C./min or more. It is difficult to produce a temperature sensitive material that is fast. Furthermore, it is difficult to produce a heat-sensitive material that crystallizes and develops color when heated at a heating rate of 1000 ° C./min or more, such as spot heating by laser irradiation.

  As a result of intensive studies by the inventors, a solvent rapid evaporation method in which a temperature-sensitive material containing a leuco dye, a developer, and a decolorant is dissolved in a volatile solvent, and the solvent is dried below the glass transition point Tg of the temperature-sensitive material. It has been found that the use of a compound can produce a material which has a high crystallization rate and is decolorized in an amorphous state.

  As the solvent rapid evaporation method, for example, a freeze-drying method, a spray drying method, a vacuum drying method, a cold air drying method for a solution of a temperature-sensitive material comprising a leuco dye, a developer and a decolorant dissolved in a volatile solvent. May be applied. In either method, the volatile solvent can be volatilized rapidly. Although it depends on the drying speed, if the temperature is equal to or lower than the glass transition point, the temperature-sensitive material does not crystallize, so that an amorphous material can be produced even with a material that is easily crystallized. As the volatile solvent, a solvent having high volatility and capable of dissolving the leuco dye, the developer, and the decoloring agent can be used. Specifically, ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate, methyl acetate, ethyl propionate, and methyl propionate; ethers such as dimethyl ether and tetrahydrofuran; non-polar solvents such as hexane, benzene, and toluene; Etc. can be used.

  When the coating material containing the temperature-sensitive material prepared by the above method is heated from the temperature below the glass transition point of the temperature-sensitive material to the melting point at a heating rate of 30 ° C./min, the temperature is higher than the glass transition point of the temperature-sensitive material, and Color develops at temperatures below and disappears at the melting point of the thermosensitive material. Materials having a high crystallization rate (color developing rate) develop color at a temperature equal to or higher than the glass transition point and lower than the melting point, regardless of whether the heating rate is low or high. On the other hand, a material having a low crystallization rate (color developing rate) develops at a temperature higher than the glass transition point and lower than the melting point when the heating rate is low, but does not develop at a melting point without a color when the heating rate is high. Thaw. Therefore, when heated from a temperature below the glass transition point of the temperature-sensitive material to a melting point at a heating rate of 30 ° C./min, the color develops at a temperature above the glass transition point of the temperature-sensitive material and below the melting point, and It can be said that a material that loses color at the melting point has a high crystallization rate (color developing rate). By using a material having a high crystallization speed, the printing speed in laser marking can be improved.

  In the DSC measurement, when the material was heated at a heating rate of 30 ° C./min from a temperature lower than the glass transition point of the temperature-sensitive material to a melting point, the temperature was higher than the glass transition point of the temperature-sensitive material and lower than the melting point. Preferably, an exothermic peak due to crystallization of the warm material is observed.

  As described above, in a material having a high crystallization rate, an exothermic peak derived from crystallization is observed in a temperature range of a glass transition point or higher and lower than the melting point, even if the temperature rise rate is low or high in DSC measurement. . On the other hand, in the case of a material having a low crystallization rate, an exothermic peak due to crystallization is observed when the heating rate is low in the DSC measurement, but an exothermic peak due to crystallization is observed when the heating rate is high. Melts at melting point without appearance. Therefore, when heated at a heating rate of 30 ° C./min, at a temperature higher than or equal to the glass transition point of the temperature-sensitive material and lower than the melting point, a material in which an exothermic peak due to crystallization of the temperature-sensitive material is observed is a crystal. It can be said that the material has a high conversion rate.

  From the viewpoint of improving the laser marking speed, when heated from a temperature below the glass transition point of the temperature-sensitive material to a melting point at a heating rate of 100 ° C./min, the temperature rises above the glass transition point of the temperature-sensitive material but below the melting point. It is more preferred to color and decolor at the melting point of the temperature sensitive material.

The speed of spot heating by the laser varies depending on the laser output and the spot area. For example, when a laser with a diameter of 14 mm is heated with a high-power laser (500 W), the speed becomes about 6000 ° C./min. However, the speed of spot heating actually applied to the base material coated with the thermal paint, the thickness of the paint, the thickness of the base material, the spot area, taking into account the thermal conductivity of the paint and the material constituting the base material, It is necessary to consider the heating rate and the thermal relaxation rate. In consideration of the above, for example, when a 10 W CO ₂ laser is irradiated to a diameter of 1 mm on a base material obtained by applying a thermal coating of about 10 μm to a PET film having a thickness of 100 μm, the heating rate of spot heating by the laser becomes about 1000 ° C./min. It is presumed to be. Therefore, when spot-heated with a laser at a heating rate of 1000 ° C./min from a temperature below the glass transition point of the thermosensitive material to the melting point, the color develops at a temperature above the glass transition point of the thermosensitive material but below the melting point. More preferably,

(Leuco dye)
The leuco dye is an electron-donating compound, and any of those conventionally known as dyes for pressure-sensitive copying paper and dyes for heat-sensitive recording paper can be used. For example, triphenylmethanephthalide type, fluoran type, phenothiazine type, indolylphthalide type, leuco auramine type, spiropyran type, rhodamine lactam type, triphenylmethane type, triazene type, spirophthalan xanthene type, naphtholactam type, An azomethine type is exemplified. Specific examples of leuco dyes include 9- (N-ethyl-N-isopentylamino) spiro [benzo [a] xanthene-12,3′-phthalide], 2-methyl-6- (Np-tolyl-N- Ethylamino) -fluoran 6- (diethylamino) -2-[(3-trifluoromethyl) anilino] xanthen-9-spiro-3′-phthalide, 3,3-bis (p-diethylaminophenyl) -6-dimethylamino Phthalide, 2'-anilino-6 '-(dibutylamino) -3'-methylspiro [phthalide-3,9'-xanthene], 3- (4-diethylamino-2-methylphenyl) -3- (1-ethyl -2-methylindol-3-yl) -4-azaphthalide, 1-ethyl-8- [N-ethyl-N- (4-methylphenyl) amino] -2,2,4-trimethyl-1, - dihydrospiro [11H-chromeno [2,3-g] quinoline -11,3'- phthalide and the like.

  One thermosensitive material may be used in combination with one or more leuco dyes.

(Developer)
The developer changes the structure of the leuco dye to come in contact with the electron-donating leuco dye to give a color. As the color developer, those known as color developers used for thermosensitive recording paper, pressure-sensitive copying paper, and the like can be used. Specific examples of such a developer include benzyl 4-hydroxybenzoate, 2,2'-biphenol, 1,1-bis (3-cyclohexyl-4-hydroxyphenyl) cyclohexane, 2,2-bis (3 Phenols such as -cyclohexyl-4-hydroxyphenyl) propane, bisphenol A, bisphenol F, bis (4-hydroxyphenyl) sulfide, paraoxybenzoate, and gallic ester. The developer is not limited to these, but may be any compound that is an electron acceptor and can change the color of the leuco dye. In addition, metal salts of carboxylic acid derivatives, salicylic acid and salicylic acid metal salts, sulfonic acids, sulfonates, phosphoric acids, metal phosphates, acid phosphates, acid phosphate metal salts, phosphorous acid, phosphorous acid Metal salts or the like may be used. In particular, those having high compatibility with a leuco dye and a decoloring agent described later are preferable, and organic developers such as 2,2'-bisphenol, bisphenol A, and gallic esters are preferable.

  Two or more types of color developers may be combined for one thermosensitive material. By combining a color developer, the color density of the leuco dye at the time of coloring can be adjusted. The amount of the developer used is selected according to the desired color density. For example, the amount may be selected within the range of about 0.1 to 100 parts by weight with respect to 1 part by weight of the leuco dye.

(Decoloring agent)
The decoloring agent is a compound capable of dissociating the bond between the leuco dye and the developer, and a compound capable of controlling the coloration temperature of the leuco dye and the developer. Generally, in the temperature range in which the leuco dye is colored, the decoloring agent is solidified in a phase-separated state. Further, in the temperature range where the leuco dye is in the decolored state, the decolorant is in a molten state, and the function of dissociating the bond between the leuco dye and the color developer is exhibited. As the material for the decoloring agent, a material capable of dissociating the bond between the leuco dye and the color developing agent can be widely used. As long as the polarity is low and the color does not show color development with respect to the leuco dye and the polarity is high enough to dissolve the leuco dye and the color developer, various materials can be used as the decolorizer. Among them, when used as a decoloring agent in a coating for laser marking, a material that easily crystallizes is preferable as the decoloring agent. Representatively, hydroxy compounds, ester compounds, peroxy compounds, carbonyl compounds, aromatic compounds, aliphatic compounds, halogen compounds, amino compounds, imino compounds, N-oxide compounds, hydroxyamine compounds, nitro compounds, azo compounds, diazo compounds Various organic compounds such as compounds, horse mackerel compounds, ether compounds, fat compounds, sugar compounds, peptide compounds, nucleic acid compounds, alkaloid compounds, and steroid compounds can be used. Specifically, tricaprin, isopropyl myristate, m-tolyl acetate, diethyl sebacate, dimethyl adipate, 1,4-diacetoxybutane, decyl decanoate, diethyl phenylmalonate, diisobutyl phthalate, triethyl citrate, phthalate Benzyl butylate, butyl phthalyl butyl glycolate, methyl N-methylanthranilate, ethyl anthranilate, 2-hydroxyethyl salicylate, methyl nicotinate, butyl 4-aminobenzoate, methyl p-toluate, 4-nitrobenzoic acid Ethyl, 2-phenylethyl phenylacetate, benzyl cinnamate, methyl acetoacetate, geranyl acetate, dimethyl succinate, dimethyl sebacate, diethyl oxalate, monoolein, butyl palmitate, ethyl stearate, methyl palmitate Tyl, methyl stearate, linalyl acetate, di-n-octyl phthalate, benzyl benzoate, diethylene glycol dibenzoate, methyl p-anisate, m-tolyl acetate, cinnamyl cinnamate, 2-phenylethyl propionate, stearic acid Butyl, ethyl myristate, methyl myristate, methyl anthranilate, neryl acetate, isopropyl palmitate, ethyl 4-fluorobenzoate, cyclandate (mixture of isomers), butopyronoxyl, ethyl 2-bromopropionate, tricaprylin, ethyl levulinate Hexadecyl palmitate, tert-butyl acetate, 1,1-ethanediol diacetate, dimethyl oxalate, tristearin, methyl acetylsalicylate, benzal diacetate, methyl 2-benzoylbenzoate Ethyl 2,3-dibromobutyrate, ethyl 2-furancarboxylate, ethyl acetopyruvate, ethyl vanillate, dimethyl itaconate, methyl 3-bromobenzoate, monoethyl adipate, dimethyl adipate, 1,4-diethyl Acetoxybutane, diethylene glycol diacetate, ethyl palmitate, diethyl terephthalate, phenyl propionate, phenyl stearate, 1-naphthyl acetate, methyl behenate, methyl arachidate, methyl 4-chlorobenzoate, methyl sorbate, isonicotine Ethyl acid, dimethyl dodecandioate, methyl heptadecanoate, ethyl α-cyanocinnamate, ethyl N-phenylglycine, diethyl itaconate, methyl picolinate, methyl isonicotinate, methyl DL-mandelate, 3-aminobenzoic acid Methyl, -Methyl methyl salicylate, diethyl benzylidene malonate, isoamyl DL-mandelic acid, triethyl methanetricarboxylate, diethyl formaminomalonate, 1,2-bis (chloroacetoxy) ethane, methyl pentadecanoate, ethyl arachidinate, 6-bromohexane Ethyl acid, monoethyl pimerate, hexadecyl lactate, ethyl benzylate, mefenpyr-diethyl, procaine, dicyclohexyl phthalate, 4-tert-butylphenyl salicylate, isobutyl 4-aminobenzoate, butyl 4-hydroxybenzoate, tripalmitin, 1 , 2-diacetoxybenzene, dimethyl isophthalate, monoethyl fumarate, methyl vanillate, methyl 3-amino-2-thiophenecarboxylate, etomidate, cloquintocet-mexyl , Methyl benzylate, diphenyl phthalate, phenyl benzoate, propyl 4-aminobenzoate, ethylene glycol dibenzoate, triacetin, ethyl pentafluoropropionate, methyl 3-nitrobenzoate, 4-nitrophenyl acetate, 3-hydroxy- Methyl 2-naphthoate, trimethyl citrate, ethyl 3-hydroxybenzoate, methyl 3-hydroxybenzoate, trimebutine, 4-methoxybenzyl acetate, pentaerythritol tetraacetate, methyl 4-bromobenzoate, ethyl 1-naphthalene acetate , 5-nitro-2-furaldehyde diacetate, ethyl 4-aminobenzoate, propylparaben, 1,2,4-triacetoxybenzene, methyl 4-nitrobenzoate, diethyl acetamidomalonate, valetamate bromide 2-naphthyl benzoate, dimethyl fumarate, adiphenine hydrochloride, benzyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, vinyl butyrate, vitamin K4, methyl 4-iodobenzoate, methyl 3,3-dimethylacrylate, Propyl gallate, 1,4-diacetoxybenzene, diethyl mesooxalate, dimethyl 1,4-cyclohexanedicarboxylate (cis-, trans-mixture), triethyl 1,1,2-ethanetricarboxylate, dimethyl hexafluoroglutarate Amyl benzoate, ethyl 3-bromobenzoate, ethyl 5-bromo-2-chlorobenzoate, bis (2-ethylhexyl) phthalate, diethyl allylmalonate, diethyl bromomalonate, diethyl ethoxymethylenemalonate, diethyl ethylmalonate , Difumarate Chill, diethyl maleate, diethyl malonate, diethyl phthalate, dimethyl 1,3-acetone dicarboxylate, dimethyl phthalate, ethyl 3-aminobenzoate, ethyl benzoate, ethyl 4- (dimethylamino) benzoate, nicotinic acid Ethyl, ethyl phenylpropiolate, ethyl pyridine-2-carboxylate, ethyl 2-pyridyl acetate, ethyl 3-pyridyl acetate, methyl benzoate, ethyl phenyl acetate, amyl 4-hydroxybenzoate, 2,5-diacetoxytoluene, Ethyl 4-oxazolecarboxylate, 1,3,5-cyclohexanetrimethyl tricarboxylate (cis-, trans-mixture), methyl 3- (chlorosulfonyl) -2-thiophenecarboxylate, pentaerythritol distearate, benzyl laurate, Acetylene range Diethyl rubonate, phenyl methacrylate, benzyl acetate, dimethyl glutarate, ethyl 2-oxocyclohexanecarboxylate, ethyl phenylcyanoacetate, ethyl 1-piperazinecarboxylate, methyl benzoylformate, methyl phenylacetate, phenylacetate, diethylsuccinate , Tributyrin, diethyl methylmalonate, dimethyl oxalate, diethyl 1,1-cyclopropanedicarboxylate, dibenzyl malonate, methyl 4-tert-butylbenzoate, ethyl 2-oxocyclopentanecarboxylate, methyl cyclohexanecarboxylate, -Ethyl methoxyphenylacetate, methyl 4-fluorobenzoylacetate, dimethyl maleate, methyl terephthalaldehyde, ethyl 4-bromobenzoate, methyl 2-bromobenzoate, methyl 2-iodobenzoate Chill, ethyl 3-iodobenzoate, ethyl 3-furancarboxylate, diallyl phthalate, benzyl bromoacetate, dimethyl bromomalonate, methyl m-toluate, diethyl 1,3-acetonedicarboxylate, methyl phenylpropiolate, butyric acid 1 -Naphthyl, ethyl o-toluate, methyl 2-oxocyclopentanecarboxylate, isobutyl benzoate, ethyl 3-phenylpropionate, di-tert-butyl malonate, dibutyl sebacate, diethyl adipate, diethyl terephthalate, phthalate Dipropyl acetate, 1,1-ethanediol diacetate, diisopropyl adipate, diisopropyl fumarate, ethyl cinnamate, 2-ethylhexyl 2-cyano-3,3-diphenylacrylate, neopentyl glycol diacrylate, trioley Ethyl benzoyl acetate, ethyl p-anisate, diethyl suberate, sorbitan tristearate, sorbitan monostearate, stearamide, glycerol monostearate, glycerol distearate, 3- (tert-butoxycarbonyl) phenylboronic acid, Racecadotril, 4-[(6-acryloyloxy) hexyloxy] -4′-cyanobiphenyl, 2- (dimethylamino) vinyl 3-pyridyl ketone, stearyl acrylate, ethyl 4-bromophenylacetate, dibenzyl phthalate, 3, Methyl 5-dimethoxybenzoate, eugenol acetate, didodecyl 3,3'-thiodipropionate, vanillin acetate, diphenyl carbonate, ethyl oxanilate, methyl terephthalaldehyde, methyl 4-nitrophthalate, (4- Nitrobenzoyl) ethyl acetate, dimethyl nitroterephthalate, methyl 2-methoxy-5- (methylsulfonyl) benzoate, methyl 3-methyl-4-nitrobenzoate, dimethyl 2,3-naphthalenedicarboxylate, bis (2,4-adipate) -Ethylhexyl), 4'-acetoxyacetophenone, trans-3-benzoyl acrylate, coumarin-3-carboxylate, BAPTA tetraethyl ester, methyl 2,6-dimethoxybenzoate, di-tert-butyl iminodicarboxylate, p -Benzyl benzyloxybenzoate, methyl 3,4,5-trimethoxybenzoate, methyl 3-amino-4-methoxybenzoate, diethylene glycol distearate, ditetradecyl 3,3'-thiodipropionate, ethyl 4-nitrophenylacetate , Methyl-chloro-3-nitrobenzoate, 1,4-dipropionyloxybenzene, dimethyl terephthalate, ethyl 4-nitrocinnamate, dimethyl 5-nitroisophthalate, triethyl 1,3,5-benzenetricarboxylate, N -(4-Aminobenzoyl) -diethyl L-glutamate, 2-methyl-1-naphthyl acetate, 7-acetoxy-4-methylcoumarin, methyl 4-amino-2-methoxybenzoate, 4,4'-diacetoxybiphenyl Dimethyl 5-aminoisophthalate, 1,4-dihydro-2,6-dimethyl-3, diethyl 5-pyridinedicarboxylate, and ester compounds such as dimethyl dimethyl 4,4′-biphenyldicarboxylate, cholesterol, cholesteryl bromide, β -Estradiol, methylandrostenediol, pregnenolo Cholesterol benzoate, cholesterol acetate, cholesterol linoleate, cholesterol palmitate, cholesterol stearate, cholesterol n-octanoate, cholesterol oleate, 3-chlorocholestene, trans-cholesterol cinnamate, cholesterol decanoate, hydrocinnamic Cholesterol acid, cholesterol laurate, cholesterol butyrate, cholesterol formate, cholesterol heptanoate, cholesterol hexanoate, cholesterol hydrogen succinate, cholesterol myristate, cholesterol propionate, cholesterol valerate, cholesterol hydrogen phthalate, cholesterol hydrogen phthalate, cholesterol phenylacetate Acid cholesterol, cholesterol 2,4-dichlorobenzoate, cholesterol pelargonate Cholesterol nonyl carbonate, cholesterol heptyl carbonate, cholesterol oleyl carbonate, cholesterol methyl carbonate, cholesterol ethyl carbonate, cholesterol isopropyl carbonate, cholesterol butyl carbonate, cholesterol isobutyl carbonate, cholesterol amyl carbonate, cholesterol n- Octyl carbonate, cholesterol hexyl carbonate, allyl estrenol, altrenogest,
9 (10) -dehydronandrolone, estrone, ethinyl estradiol, estriol, estradiol benzoate, β-estradiol 17-cypionate, 17-β-estradiol valerate, α-estradiol, β-estradiol 17-heptanoate, gestrinone, Mestranol, 2-methoxy-β-estradiol, nandrolone, (−)-norgestrel, quinestrol, trenbolone, tibolone, stanolone, androsterone, abiraterone, abiraterone acetate, dehydroepiandrosterone acetate, dehydroepiandrosterone acetate, ethisterone, episterone Androsterone, 17β-hydroxy-17-methylandrosta-1,4-dien-3-one, methylandrostenediol, methylte Tosterone, Δ9 (11) -methyltestosterone, 1α-methylandrostan-17β-ol-3-one, 17α-methylandrostan-17β-ol-3-one, stanozolol, testosterone, testosterone propionate, altrenogest, 16-dehydropregnenolone acetate, 16,17-epoxypregnenolone acetate, 11α-hydroxyprogesterone, 17α-hydroxyprogesterone caproate, 17α-hydroxyprogesterone, pregnenolone acetate, 17α-hydroxyprogesterone acetate, megestrol acetate, medole acetate Roxyprogesterone, pregnenolone acetate, 5β-pregnane-3α, 20α-diol, budesonide, corticosterone, cortisone acetate, cortisone, cortex Ron, deoxycorticosterone acetate, deflazacort, hydrocortisone acetate, hydrocortisone, hydrocortisone 17-butyrate, 6α-methylprednisolone, prednisolone, prednisone, prednisolone acetate, sodium deoxycholate, sodium cholate, methyl cholate, hyodeoxycholic acid Steroid compounds such as methyl, β-cholestanol, cholesterol-5α, 6α-epoxide, diosgenin, ergosterol, β-sitosterol, stigmasterol, and β-sitosterol acetate. It is preferable to include these compounds from the viewpoint of compatibility with the leuco dye and the developer. Further, two or more of these decoloring agents may be combined. By combining the decoloring agent, the freezing point and the melting point can be adjusted.

  The temperature-sensitive material contains at least the above-mentioned leuco dye, developer, and decolorant. However, when a material having a color developing action and a color erasing action in one molecule is used, the color developing agent and the color erasing agent may be omitted. Further, if the ability to change color by crystallization is maintained, materials other than leuco dyes, developers, and decolorants can be included. For example, by including a pigment, it is possible to change the color at the time of decoloration and at the time of color development.

(Particulate)
In the coating material according to the first embodiment, amorphous particles containing at least a leuco dye, a color developer, and a decoloring agent constituting the temperature-sensitive material need to be independently present in the coating material.

  As a technique for preparing a paint that satisfies the above conditions, there are a technique of directly dispersing amorphous particles in a paint, and a technique of microcapsulating amorphous particles and dispersing microcapsules in the paint.

  For example, an amorphous material containing a leuco dye, a color developing agent and a decoloring agent is formed by a solvent rapid evaporation method, and then the temperature-sensitive material can be made into fine particles by grinding. The method of micronization is not particularly limited, and various pulverization methods such as a mortar, a ball mill, a rod mill, a bead mill, and a homogenizer can be used. When the spray drying method is used in the solvent rapid evaporation method, it can be used as it is as particles.

  The particle size of the amorphous particles is not particularly limited, but is preferably equal to or less than the resolution of visual observation and a camera, and is preferably equal to or less than 20 μm from the viewpoint of visibility. On the other hand, it has been experimentally shown that if the particle size is too small, the coloring property is impaired, and it is preferable that the particle size be 100 nm or more.

  Further, the leuco dye, the color developer and the decoloring agent may be dispersed in the paint by enclosing them in microcapsules. Microencapsulation improves the environmental resistance of the composition to humidity and the like, and enables storage stability, stabilization of discoloration characteristics, and the like. Further, when a paint is prepared, it is possible to suppress the influence of the leuco dye, the color developing agent, and the decoloring agent from other compounds such as a resin agent and an additive. In this specification, microencapsulation means that the inclusions are protected by a resin wall film.

  The resin coating used for the microcapsules is a urea resin coating composed of a polyvalent amine and a carbonyl compound, a melamine resin coating composed of a melamine / formalin prepolymer, a methylol melamine prepolymer, a methylated melamine prepolymer, and a polyvalent isocyanate and a polyol compound. Urethane resin film, amide resin film composed of polybasic acid chloride and polyvalent amine, and vinyl resin film composed of various monomers such as vinyl acetate, styrene, (meth) acrylate, acrylonitrile, and vinyl chloride. However, the present invention is not limited to these. Furthermore, by performing surface treatment of the formed resin film and adjusting the surface energy at the time of forming an ink or a paint, it is possible to perform additional treatment such as improving the dispersion stability of the microcapsules.

  From the viewpoint of storage stability, the diameter of the microcapsules is preferably in the range of about 0.1 to 100 μm, and more preferably in the range of 0.1 to 1 μm.

<Additives>
Additives may be added to the temperature-sensitive material and the coating material to such an extent that the temperature-sensitive function is not affected. As the additive, for example, a resin, a dye, a pigment, a heat storage material, a high heat conductive material, and a light absorbing material can be used. By adding a dye or a pigment to the temperature-sensitive material, the color tone at the time of color development and / or the color erasure can be adjusted. By adding a heat storage material such as a heat storage capsule or a high thermal conductive material to the temperature-sensitive material or paint, the outside of the temperature-sensitive material reaches the developing or decoloring temperature, and the temperature-sensitive material itself changes color. It is possible to adjust the required heat energy.

  By adding the light absorbing material to the temperature-sensitive material or paint, it becomes possible to increase the thermal energy applied to the temperature-sensitive material at a specific wavelength, and to reduce the required laser output.

<Laser marking method>
When performing laser marking using the paint according to the first embodiment, the wavelength, output, and irradiation time of the laser beam are determined by the temperature-sensitive material (combination of leuco dye, color developer, and decolorant), additives, and microcapsules. It is appropriately adjusted depending on the type of the resin film used for the above.

  In the present embodiment, printing is performed by utilizing the heat generated by the paint due to the irradiation of the laser beam. Therefore, the wavelength of the laser beam may be selected to be a wavelength that is absorbed by the temperature-sensitive material and the paint. Since organic materials are often used for paints, it is preferable that the laser beam is infrared light, which has a large absorption of the organic materials. The output of the laser beam is not particularly limited. By selecting a wavelength at which the temperature-sensitive material and the paint have a large absorption, the paint can be discolored and a marking can be formed even with a low power laser beam.

[Second embodiment]
<Thermal paint>
The paint according to the second embodiment includes two kinds of temperature-sensitive materials (hereinafter, referred to as a first temperature-sensitive material and a second temperature-sensitive material) having different color tones at the time of color development in order to make the marking multicolored. . In the following embodiments, description of the same configuration as the first embodiment will be omitted.

  As the first temperature-sensitive material and the second temperature-sensitive material, the temperature-sensitive materials used in the first embodiment can be used. The first temperature-sensitive material and the second temperature-sensitive material have different glass transition points or developing temperatures. In the DSC measurement, when the temperature rise rate increases, the glass transition point and the temperature of the crystallization start temperature Ta become closer.

Hereinafter, a color change of a paint using two kinds of temperature-sensitive materials will be described with reference to FIGS. 4 and 5. FIG. 4 is a graph showing the relationship between the temperature and the color density of two kinds of temperature-sensitive materials used for the paint according to the second embodiment. In FIG. 4, the vertical axis represents color density and the horizontal axis represents temperature. _Ta1 is the _developing temperature of the first thermosensitive material, _Ta2 is the _developing temperature of the second thermosensitive material, and _Td1 is the first thermosensitive temperature. decoloring temperature of the material (melting point), T _d2 decoloring temperature of the second temperature sensitive material (melting point), the hatched portion is the operating temperature range of the marking object.

As shown in FIG. 4, the first temperature-sensitive material and the second temperature-sensitive material have different developing temperatures and different heat energies required for discoloration. The first temperature sensitive material begins to developer temperature _{T a1,} decoloring starts at temperature _{T d1.} The second temperature sensitive material begins to developer at the temperature T _a1, decoloring starts at temperature T _d2. Also, having a first, color erasing temperature of the second temperature sensitive material, color developing temperature relationship _{T a1 <T a2 <T d1} <T d2. In _addition, it may be a relationship of _{T a1 <T a2 <T d2} <T d1.

  FIG. 5 is a schematic diagram showing a color change state of the paint containing the first temperature-sensitive material and the second temperature-sensitive material. Before the laser light irradiation, both the first temperature-sensitive material and the second temperature-sensitive material are in a decolored state (FIG. 5A).

The heat energy of not less than the heat energy of heat (T _a1 ) required for the first temperature-sensitive material to develop and less than the heat energy of heat _Ta2 required for the second temperature-sensitive material to develop color. When applied to the paint by a laser beam, the first temperature-sensitive material develops color, but the second temperature-sensitive material remains decolorized. Therefore, only the first temperature-sensitive material exhibits a developed color (FIG. 5B).

When the thermal energy of the heat (T _a2 ) required for the second temperature-sensitive material to develop color is equal to or more than the heat energy and less than T _d1 and T _d2 is applied to the paint by a laser beam, the first temperature-sensitive material and the second 2. Both thermosensitive materials develop color. Therefore, both the first temperature-sensitive material and the second temperature-sensitive material exhibit a developed color (FIG. 5C).

Thus, by mixing a plurality of temperature-sensitive materials, it is possible to make the marking multi-colored. Even if the paint once developed is decolorized at a temperature higher than T _d1 and T _d2 , if a material with a high crystallization rate is used, it will be crystallized in the cooling process, so the decolored state must be maintained. It is difficult. Therefore, irreversible printing is possible.

The heat-sensitive paint is used to determine the melting point T _d1 of the first temperature-sensitive material and the second temperature-sensitive material from the lower temperature T _g of the glass transition point T _g1 of the first temperature-sensitive material and the glass transition point T _g2 of the second temperature-sensitive material. when heated at a heating rate of 30 ° C. / min to a low temperature T _m of the melting point T _d2 of, develop for the two stages in the temperature range below the temperature T _m a the temperature T _g or more. Further, in the differential scanning calorimetry (DSC), when heated at a heating rate of 30 ° C. / min from the temperature T _g to a temperature T _m, the temperature range below the temperature Tm be the temperature T _g above, derived from crystallization Preferably, two exothermic peaks are observed. For example, when the characteristic temperature of the first temperature-sensitive material and the characteristic temperature of the second temperature-sensitive material have a relationship of T _g1 <T _g2 <T _d1 <T _d2 , the crystallization is performed in a temperature range of T _g1 or more and less than T _g2. observed exothermic peak first one from which it is derived is, T _g2 or more second exothermic peak derived from crystallization temperature range of less than T _d1 that is observed preferable.

Further, the temperature T _g to a temperature T _m, with a heating rate of 1000 ° C. / min, when heated spot laser, to color developing in two stages in a temperature range below the temperature T _m A the temperature T _g or more More preferably, it is a feature.

  In the present embodiment, a paint containing two kinds of temperature-sensitive materials has been described. However, the heat-sensitive paint may contain two or more kinds of temperature-sensitive materials.

<Laser marking method>
As the laser marking method, the same method as in the first embodiment can be used.

  In the case of the second embodiment in which the paint contains a plurality of temperature-sensitive materials, the color tone of the heat-sensitive paint is controlled by changing the output or irradiation time of the laser light without changing the wavelength of the laser light. Is preferred. When temperature-sensitive materials have absorption in the same wavelength region, the color tone of the coating film can be obtained by changing the output or irradiation time with only one wavelength laser by using a laser with a wavelength that all temperature-sensitive materials have absorption. Can be controlled.

  Therefore, it is preferable that the first temperature-sensitive material and the second temperature-sensitive material are colored by a laser beam having the same wavelength.

[Third embodiment]
<Thermal paint>
The coating material for laser marking according to the third embodiment has the same configuration as that of the second embodiment except that the color developing time of the temperature-sensitive material is changed. In the third embodiment, the crystallization rates of the first temperature-sensitive material and the second temperature-sensitive material, that is, the color development time are different. For example, a first temperature sensitive material, in less than heating rate _{R A} (e.g. heating rate 100 ° C. / min), although developer by crystallization, heating rate _{R A} (e.g. heating rate 100 ° C. / min) In the above, a material which reaches the melting point without crystallization and does not develop color is used. As the second temperature-sensitive material, a material that crystallizes and develops at a temperature rising rate _RA (for example, 100 ° C./min) or more is used.

The color change of the paint will be described with reference to FIGS. FIG. 6 is a graph showing the relationship between the temperature and the color density of the first temperature-sensitive material and the second temperature-sensitive material contained in the paint at a temperature rising rate R _A (for example, a temperature rising rate of 100 ° C./min). FIG. 7 is a graph showing the relationship between the temperature and the color density of the first temperature-sensitive material and the second temperature-sensitive material included in the paint at a temperature rising rate R _A (for example, a temperature rising rate of 100 ° C./min). 6 and 7, the vertical axis represents color density, the horizontal axis is the temperature, T _a1 is developing color temperature of the first temperature sensitive material, T _a2 is developing color temperature of the second temperature sensitive material, the T _d1 first decoloring temperature of 1 temperature sensitive material (melting point), T _d2 decoloring temperature of the second temperature sensitive material (melting point), the hatched portion is the operating temperature range of the marking object.

As shown in FIG. 6, when the heating rate is lower than R _A (for example, at a heating rate of 100 ° C./min), the first and second thermosensitive materials have different developing temperatures, and are required for discoloration. Heat energy is different. The first temperature sensitive material begins to developer temperature _{T a1,} decoloring starts at temperature _{T d1.} The second temperature sensitive material begins to developer at the temperature T _a1, decoloring starts at temperature T _d2. Also, having a first, color erasing temperature of the second temperature sensitive material, color developing temperature relationship _{T a1 <T a2 <T d1} <T d2. In _addition, it may be a relationship of _{T a1 <T a2 <T d2} <T d1. This configuration is the same as in the first embodiment.

On the other hand, when the temperature is higher than the heating rate _RA (for example, at a heating rate of 100 ° C./min), as shown in FIG. The color _develops at _Ta2 or more.

  FIG. 8 is a schematic diagram illustrating a color change state of the paint according to the third embodiment. The first thermosensitive material and the second thermosensitive material are materials that change from a decolored state to a developed color state by applying thermal energy. Before the laser beam irradiation, both the first and second thermosensitive materials are used. The color is erased (FIG. 8A).

The heat energy of the heat energy (T _a1 ) required for the first thermosensitive material to develop color is equal to or more than the thermal energy of the heat (T _a2 ) necessary for the second thermosensitive material to develop color. When the coating is applied to the coating with a laser beam so as to have a heating rate of less than R _A (for example, a heating rate of 100 ° C./min), only the first temperature-sensitive material is developed, and the second temperature-sensitive material is colored. It remains erased. Therefore, only the first temperature-sensitive material exhibits a developed color (FIG. 8B).

The heat energy required for the second thermosensitive material to develop color is equal to or more than the heat energy of heat (T _a2 ) and less than T _d1 and T _d2 , at a temperature increase rate _RA (for example, a temperature increase rate of 100 ° C./min). When the paint is applied to the paint with a laser beam so as to be less than ()), the paint develops both the first temperature-sensitive material and the second temperature-sensitive material. Therefore, both the first temperature-sensitive material and the second temperature-sensitive material exhibit a developed color (FIG. 8C).

The heat energy required for the second thermosensitive material to develop color is equal to or more than the heat energy of heat (T _a2 ) and less than T _d1 and T _d2 , at a temperature increase rate _RA (for example, a temperature increase rate of 100 ° C./min). As described above, when applied to the paint with a laser beam, the first temperature-sensitive material does not appear and only the second temperature-sensitive material appears. Therefore, only the second temperature-sensitive material exhibits a developed color (FIG. 8D).

  As described above, by including temperature-sensitive materials having different crystallization speeds (developing speeds), it is possible to print three colors with two types of temperature-sensitive materials.

  Further, in order to control the crystallization rate, not only a temperature-sensitive material having a high crystallization rate as shown in FIG. 2 but also a temperature-sensitive material having a low crystallization rate as shown in FIG. 3 can be mixed.

<Laser marking method>
As the laser marking method, the same method as in the first embodiment can be used.

  In the case of the third embodiment in which the paint contains a plurality of temperature-sensitive materials, by irradiating the laser light by changing the output or irradiation time of the laser light without changing the wavelength of the laser light as in the second embodiment. It is preferable to control the color tone of the heat-sensitive paint.

  Further, in order to change the rate of temperature rise of the paint by the laser beam, the output of the laser beam may be controlled.

  Next, the present invention will be described more specifically with reference to examples. Note that the present invention is not limited to these examples.

<Production of heat-sensitive paint>
As a thermosensitive material, 2'-methyl-6 '-(Np-tolyl-N-ethylamino) spiro [isobenzofuran-1 (3H), 9'-[9H] xanthen] -3-one as a leuco dye (RED520 manufactured by Yamada Chemical Industry), 1 part by weight of octyl gallate manufactured by Tokyo Kasei Kogyo Co., Ltd. as a color developer, and 100 parts by weight of methylandrostenediol manufactured by Tokyo Chemical Industry Co., Ltd. as a decolorizer.

  A leuco dye constituting a temperature-sensitive material, a developer, a decoloring agent, and 1,000 parts by weight of tetrahydrofuran as a volatile solvent are mixed, and at 0 ° C. which is equal to or lower than a glass transition point of the temperature-sensitive material, tetrahydrofuran is vacuum-dried, A temperature-sensitive material in an amorphous and decolored state was produced. The prepared temperature-sensitive material was crushed in a mortar to prepare amorphous particles of the temperature-sensitive material. The temperature-sensitive material was colorless and transparent.

  Next, a heat-sensitive paint was prepared as follows using the prepared temperature-sensitive material. Pure water in a vessel provided with stirring blades, a copolymer of polyvinyl alcohol and polyvinyl acetate having a number average molecular weight (Mn) of 10,000 as a resin (repeating number of polyvinyl alcohol units: repeating number of polyvinyl acetate units ≒ 36: 64, the hydroxyl value was 285), and amorphous particles of a temperature-sensitive material were charged and mixed for about 1 hour to prepare a paint containing the temperature-sensitive material.

<DSC measurement>
The temperature of the prepared coating material was increased by differential scanning calorimetry (DSC) from 0 ° C., which is lower than the glass transition point of the temperature-sensitive material, to 220 ° C., which is higher than or equal to the melting point of the temperature-sensitive material, at a heating rate of 30 ° C./min. did. As a result, an exothermic peak derived from crystallization was observed around 80 ° C., and an endothermic peak derived from melting point was observed around 195 ° C.
Thereafter, the temperature of the prepared coating material was lowered at a temperature reduction rate of 20 ° C./min by differential scanning calorimetry (DSC). As a result, an exothermic peak due to crystallization was observed in the course of the temperature drop. From the above results, it was confirmed that the temperature-sensitive material used in Example 1 was a material that easily crystallized.

<Confirmation of color development function>
The prepared paint was heated at a heating rate of 30 ° C./min from 0 ° C., which is lower than the glass transition point of the temperature-sensitive material, to 220 ° C., which was higher than the melting point of the temperature-sensitive material. As a result, it was confirmed that the color developed red at 80 ° C. and disappeared at 195 ° C., which is the melting point.

(Comparative Example 1)
A temperature-sensitive material was produced in the same manner as in Example 1 except that the temperature-sensitive material was cooled by a liquid quenching method to produce amorphous particles.

  Specifically, the same leuco dye, developer and decoloring agent as in Example 1 were mixed, heated to 220 ° C., which is higher than the melting point of the temperature-sensitive material, and melted. Quenched by impregnation. After cooling, the temperature-sensitive material was colored red. It is considered that the crystals crystallized and developed during the cooling process. Therefore, it was not possible to obtain a temperature-sensitive material in an amorphous and decolored state.

  As described above, from Example 1 and Comparative Example 1, the leuco dye, the developer, and the decoloring agent constituting the temperature-sensitive material are dissolved in the highly volatile organic solvent, and the solvent is evaporated below the glass transition point. Thus, it was found that an amorphous temperature-sensitive material having a high crystallization rate can be obtained.

  1 part by weight of 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (CVL manufactured by Yamada Chemical Industries) as a thermosensitive material as a leuco dye, and octyl gallate manufactured by Tokyo Chemical Industry as a color developer Was used in the same manner as in Example 1 except that 1 part by weight of the compound was used and 100 parts by weight of 17α-hydroxyprogesterone acetate manufactured by Tokyo Kasei Kogyo Co., Ltd. as a decolorizing agent. The prepared paint was subjected to DSC measurement in the same manner as in Example 1 to confirm the color developing function.

  In the DSC measurement, an exothermic peak derived from crystallization was observed at around 110 ° C. and an endothermic peak derived from the melting point was observed around 215 ° C. in the course of the temperature rise. An exothermic peak due to crystallization was observed during the cooling process. From the above results, it was confirmed that the temperature-sensitive material used in Example 2 was a material that easily crystallized.

  Further, the prepared coating material was heated at a heating rate of 30 ° C./min from 0 ° C., which is lower than the glass transition point of the temperature-sensitive material, to 220 ° C., which was higher than the melting point of the temperature-sensitive material. As a result, it was confirmed that the color developed blue at 110 ° C. and disappeared at 215 ° C., which is the melting point.

(Comparative Example 2)
A temperature-sensitive material was produced in the same manner as in Example 2 except that the temperature-sensitive material was cooled by a liquid quenching method to produce amorphous particles.

  Specifically, the same leuco dye, developer, and decolorant as in Example 2 were mixed, heated to 220 ° C., which is higher than the melting point of the temperature-sensitive material, and allowed to melt. Quenched by impregnation. After cooling, the temperature-sensitive material was colored blue. It is considered that the crystals crystallized and developed during the cooling process. Therefore, it was not possible to obtain a temperature-sensitive material in an amorphous and decolored state.

(Comparative Example 3)
1 part by weight of 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (CVL manufactured by Yamada Chemical Industry) as a thermosensitive material as a leuco dye, and octyl gallate manufactured by Tokyo Chemical Industry as a developer Was used in the same manner as in Example 1 except that 1 part by weight of the compound was used and 100 parts by weight of vitamin K4 manufactured by Tokyo Chemical Industry Co., Ltd. as a decolorizing agent. The prepared paint was subjected to DSC measurement in the same manner as in Example 1 to confirm the color developing function.

  The temperature-sensitive material of Comparative Example 3 could be made amorphous and decolored by the liquid quenching method. The leuco dye, the developer, and the decoloring agent constituting each of the temperature-sensitive materials were mixed, and the sample was rapidly cooled by impregnating the sample container with liquid nitrogen from 220 ° C., which is higher than the melting point of the temperature-sensitive material. The temperature-sensitive material was crushed in a mortar to obtain amorphous particles. The produced amorphous particles were colorless and transparent.

  In the DSC measurement, only an endothermic peak derived from the melting point was observed in the temperature rising process. No exothermic peak was observed during the cooling process. From this result, it was confirmed that the third temperature-sensitive paint was a material that was difficult to crystallize.

  Further, the prepared coating material was heated at a heating rate of 30 ° C./min from 0 ° C., which is lower than the glass transition point of the temperature-sensitive material, to 220 ° C., which was higher than the melting point of the temperature-sensitive material. As a result, the temperature reached 120 ° C., which is the melting point, without developing color. It is considered that, because the crystallization speed was low, no crystallization occurred at the heating rate of 30 ° C./min, and no color was developed.

<Preparation of temperature-sensitive paint>
Paints containing both the temperature-sensitive materials produced in Example 1 and Example 2 were produced by the following method.

  Pure water in a vessel provided with stirring blades, a copolymer of polyvinyl alcohol and polyvinyl acetate having a number average molecular weight (Mn) of 10,000 as a resin (repeating number of polyvinyl alcohol units: repeating number of polyvinyl acetate units ≒ 36: 64, the hydroxyl value is 285), the amorphous temperature-sensitive material particles prepared in Example 1 and the amorphous temperature-sensitive material particles prepared in Example 2 are charged, and mixed for about 1 hour. A temperature-sensitive paint containing two types of temperature-sensitive materials was prepared.

  By impregnating the base material (paper) in the prepared coating material for 10 minutes, the coating material was absorbed on the surface of the base material. Thereafter, the substrate was taken out of the paint, and pure water was volatilized to produce a substrate in which the paint was absorbed.

<Confirmation of color development function>
Thermal energy was applied to the prepared substrate using a hot plate. FIG. 9 shows a state of color change due to heat energy of the paint according to the example. The temperature was increased at 30 ° C./min, and when the surface temperature of the base material reached 80 ° C., which is the _developing temperature _Ta1 of the first temperature-sensitive material, the heated portion of the base material turned red. On the other hand, when the heating rate is increased to 100 ° C./min and thermal energy is added at a high speed, when the surface temperature of the substrate reaches 110 ° C., which is the _developing temperature _Ta2 of the second temperature-sensitive material, The heated portion of the substrate turned blue. Further, when the base material once discolored was placed in an environment of 20 ° C., it was confirmed that the discolored state was maintained.

  Next, with respect to the produced base material, the discoloration function of the paint was confirmed when the laser was irradiated at a low output and when the laser was irradiated at a high output.

First, thermal energy was applied by irradiating the produced base material with a CO ₂ laser having an output of 0.5 W. When the surface temperature of the base material that absorbed the coating material reached 80 ° C., which is the color development temperature _Ta1 of the first temperature-sensitive material, the laser irradiation part of the base material turned red.

Next, with respect to the produced base material, the laser output was increased to 1.5 W, and heat energy was applied at a high speed. When the surface temperature of the base material that absorbed the paint reached 110 ° C., which is the _developing temperature _Ta2 of the second temperature-sensitive material, it was confirmed that the laser-irradiated portion of the base material turned blue. FIG. 10 shows how the color of the paint according to the example changes when the laser output is increased and heated to 110 ° C. The rate of temperature rise up to 110 ° C. was 100 ° C./min.

  In addition, when the irradiation of the laser was stopped and the substrate once discolored was placed in an environment of 20 ° C., it was confirmed that the discolored state was maintained.

  From the above, it was confirmed that the use of the coating material according to the present example enabled discoloration in multiple colors by laser irradiation.

Claims (14)

Leuco dye, including a developer and a decoloring agent, comprising amorphous first particles,
Heating at a heating rate of 30 ° C./minute from the temperature below the glass transition point of the first particles to the melting point, the color develops at a temperature above the glass transition point of the first particles but below the melting point. paint. The heat-sensitive paint according to claim 1,
In differential scanning calorimetry (DSC), when heating is performed at a heating rate of 30 ° C./min from a temperature below the glass transition point of the first particles to a melting point, a temperature above the glass transition point of the first particles but below the melting point is obtained. Wherein the exothermic peak due to crystallization of the first particles is observed. The heat-sensitive paint according to claim 1 or 2,
From the temperature below the glass transition point of the first particles to the melting point, spot heating with a laser at a heating rate of 1000 ° C./min, the color development at a temperature above the glass transition point of the first particles but below the melting point. Characterized thermal paint. The heat-sensitive paint according to any one of claims 1 to 3,
The heat-sensitive paint according to claim 1, wherein the first particles comprise only a leuco dye, a developer, and a decolorant. The heat-sensitive paint according to any one of claims 1 to 4,
The heat-sensitive paint is characterized in that the temperature-sensitive particles are microencapsulated. A heat-sensitive paint according to any one of claims 1 to 5,
Leuco dye, comprising a developer and a decoloring agent, further comprising amorphous second particles,
The first particles and the second particles have different glass transition points or developing temperatures,
A heating rate of 30 ° C./min from a low temperature Tg of the glass transition point of the first particles and the glass transition point of the second particles to a low temperature Tm of the melting points of the first particles and the second particles. A heat-sensitive paint which develops in two stages in a temperature range between the temperature Tg and the temperature below the temperature Tm. The heat-sensitive paint according to claim 6,
The first particles and the second particles have different crystallization rates from each other. The heat-sensitive paint according to claim 6 or 7,
In differential scanning calorimetry (DSC), when heating is performed from the temperature Tg to the temperature Tm at a heating rate of 30 ° C./min, an exothermic peak due to crystallization falls within a temperature range of the temperature Tg or more and less than the temperature Tm. A heat-sensitive paint characterized in that two are observed. A heat-sensitive paint according to any one of claims 6 to 8,
A heat-sensitive paint characterized in that when a spot is heated by a laser from the temperature Tg to the temperature Tm at a heating rate of 1000 ° C./min with a laser, the color develops in two stages in a temperature range from the temperature Tg to the temperature Tm. It is a heat-sensitive paint according to any one of claims 6 to 9,
The first particles and the second particles are colored by a laser beam having the same wavelength. The heat-sensitive paint according to any one of claims 6 to 10, wherein
The heat-sensitive paint, wherein the second particles comprise only a leuco dye, a developer, and a decolorant. It is a heat-sensitive paint according to any one of claims 6 to 12, wherein
A heat-sensitive paint, wherein the second particles are microencapsulated. The heat-sensitive paint according to claim 3, 9, or 10,
The heat-sensitive paint, wherein the laser beam is an infrared laser. A laser marking method using the heat-sensitive paint according to any one of claims 1 to 13,
A laser marking method comprising controlling the color tone of the heat-sensitive paint by irradiating the laser while changing the output or irradiation time of the laser without changing the wavelength of the laser.

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