JP5573183B2 - Reversible thermosensitive recording medium and coloring method thereof - Google Patents

Description

  The present invention relates to a colored reversible thermosensitive recording medium having a gas barrier layer and a coloring method thereof.

It is known that a reversible thermosensitive recording medium using a leuco dye deteriorates when irradiated with sunlight, and the background portion turns brownish brown. Further, when sunlight is irradiated on the printing part, a phenomenon that the printing part is difficult to erase during erasing occurs. For this reason, there is a problem in that the density difference between the background portion becomes large between the sample not irradiated with sunlight and the sample irradiated, and the erasability of the printing portion deteriorates and remains unerased.
This will be described with reference to FIG. FIG. 1 is a diagram showing the discoloration of the background part due to the irradiation of sunlight and the remaining state of the printed part. In the figure, the discoloration of the background part becomes stronger due to the irradiation of sunlight from the left side to the right side. In addition, it is shown that the density of the remaining portion that disappears increases depending on the degree of irradiation.
As will be understood from FIG. 1, when the degree of discoloration of the background portion increases, the color tone differs greatly from the initial state, and the unerased residue when the printed portion is erased also becomes stronger. As a reversible thermosensitive recording medium, There is a problem that the function of the system is greatly degraded.

In order to solve such a problem, it has been proposed to reduce the visibility of the erased portion due to exposure to sunlight by arranging a colored layer on the reversible thermosensitive recording medium (see, for example, Patent Document 1 and Patent Document 2). ).
However, according to this proposal, there is a problem that the deterioration itself of the reversible thermosensitive recording medium cannot be suppressed, and the unerased problem cannot be solved.

As another proposal for improving the unerased problem, the present applicant has proposed to suppress deterioration of the reversible thermosensitive recording medium by providing a gas barrier layer so far (for example, Patent Document 3). ).
However, when the reversible thermosensitive recording medium having a gas barrier layer is exposed to sunlight, it has been confirmed by the present inventors that the reversible thermosensitive recording medium has a phenomenon of changing to a yellowish color. It was.
Although such discoloration is not based on the deterioration of the reversible thermosensitive recording medium, it is assumed that the color of the reversible thermosensitive recording medium is visually impaired, and inconvenience is caused in the use of the user in the logistics use process. Is done.

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, an object of the present invention is to provide a reversible thermosensitive recording medium having no color change before and after irradiation with sunlight, and a coloring method thereof.

In order to solve the above-mentioned problems, the present inventors have intensively studied and obtained the following knowledge.
That is, when the present inventors have exposed a reversible thermosensitive recording medium having a newly discovered gas barrier layer to sunlight, the problem that the reversible thermosensitive recording medium changes to a yellowish color, By coloring the reversible thermosensitive recording medium according to the discoloration after sunlight irradiation, it is possible to suppress the color change of the color before and after the sunlight irradiation, and the reversible feeling without any color change in the physical distribution process. The knowledge that the operation of the thermal recording medium becomes possible was obtained.

The above findings are based on the following examination results of the present inventors.
When the inventors of the present invention were exposed to sunlight for one day for each of the three reversible thermosensitive recording medium samples in which the characteristics of the gas barrier layer were changed, the discoloration shown in FIG. 2 was confirmed. In FIG. 2, the sample exposed to sunlight shows a yellowish discoloration compared to the sample not exposed to sunlight.
This yellowish discoloration has little discoloration if the gas barrier function of the gas barrier layer in the reversible thermosensitive recording medium is low, and when it is separated from sunlight, it returns to its original white state over time.
However, as the gas barrier function of the gas barrier layer is improved, the yellowish discoloration becomes stronger and the discolored state is maintained even when separated from sunlight.
Therefore, the reversible thermosensitive recording medium is visually recognized as deteriorated, and the visibility of the reversible thermosensitive recording medium is impaired.
Further, when the discoloration in a number of samples of the reversible thermosensitive recording medium in which the gas barrier characteristics of the gas barrier layer are changed, the color represented by the color space L ^* a ^* b ^* is approximately yellow in the a ^* b ^* plane. It was confirmed to be a red color mixture and discolored in a strong yellowish direction (b ^* direction).
Therefore, when samples of reversible thermosensitive recording media that were colored in anticipation of discoloration in the b ^* direction in advance were prepared and the color change before and after the sunlight irradiation was analyzed, the color before and after the sunlight irradiation was observed in some samples. It was confirmed that the taste change could be greatly suppressed.

That is, samples 1 to 13 of a reversible thermosensitive recording medium were prepared, and these samples were irradiated with sunlight before being irradiated with sunlight for a day (10: 00 to 16:30 time zone. Irradiation amount). Was about 100,000 Lux, and the change in hue after 30 ° C., 75% temperature and humidity conditions was measured and examined. The examination results are shown in FIGS. Here, FIG. 7 is a table showing the color change of Samples 1 to 13 measured with X-Rite 939 (reflective color colorimeter, manufactured by X-Rite). Moreover, FIG. 8 is a graph which shows the color change measured by X-Rite939 with respect to the samples 1-13.
The used samples 1 to 13 are as follows.
That is, Samples 1 to 3 are conventional uncolored reversible thermosensitive recording media. Samples 4 to 13 are reversible thermosensitive recording media colored in advance in anticipation of discoloration in the b ^* direction.

In addition, when coloring a reversible thermosensitive recording medium, it is also conceivable to color a color such as gray, blue, and green. However, with these colors, the change in color cannot be suppressed because the color change of the medium after irradiation with sunlight is a yellowish color. Further, when the color such as blue or green is colored, light having a wavelength of 620 nm to 660 nm which is a barcode reading wavelength is absorbed, which adversely affects the readability of the barcode.
For this reason, the color change of the medium after the sunlight irradiation needs to be colored corresponding to a yellowish tint.

The present invention is based on the above knowledge, and means for solving the above problems are as follows. That is,
<1> A reversible thermosensitive recording medium obtained by coloring an uncolored reversible thermosensitive recording medium having at least a gas barrier layer and a reversible thermosensitive recording layer. the value of ^{b *} of the ground tint which is represented by ^L * ^a * ^{b *} after sunlight continuous irradiation and ^b _{* s1} at dose of Lux · Hr, reversible thermosensitive recording medium after the coloring wherein ^{when b *} of the values was ^b _{* s2,} characterized in that the difference between the ^b _{* s2} and the ^b _{* ^s1, b} * s2 ^-b _{* s1} has been colored so as to -2～110 of A reversible thermosensitive recording medium.
<2> The reversible thermosensitive recording medium according to <1>, further including a colored layer that imparts a color tone that is b ^* _s2 .
<3> The reversible thermosensitive recording medium according to any one of <1> to <2>, wherein b ^* _s2− b ^* _s1 is colored so as to be 10 to 100.
<4> respect uncolored reversible thermosensitive recording medium, when the value of ^{a *} when the continuous irradiation with irradiation dose of sunlight 16 million Lux · Hr was ^a _{* L1,} the ^a _{* L1} The reversible thermosensitive recording medium according to any one of <1> to <3>, wherein the reversible thermosensitive recording medium is colored by color correction according to the above.
<5> When the a value in colored reversible thermosensitive recording medium was a ^* _s2, so that the difference between the a ^* _s2 and _{^{a * L1, a * s2 -a}} * L1 becomes the -2～70 The reversible thermosensitive recording medium according to <4>, wherein color correction is performed.
<6> against uncolored reversible thermosensitive recording medium, when the value of ^{b *} upon continuous irradiation with irradiation dose of sunlight 16 million Lux · Hr was ^b _{* L1,} and b ^* _s2 The reversible thermosensitive recording medium according to any one of <4> to <5>, wherein the color correction is performed so that the difference from b ^* _L1 and b ^* _s2− b ^* _L1 is 10 to 110. is there.
<7> The reversible thermosensitive recording medium according to any one of <1> to <6>, wherein the gas barrier layer has an oxygen permeability of 50 cc / (m ² · day · atm) or less.
<8> The reversible thermosensitive recording medium according to any one of <2> to <7>, wherein the color layer has a reflectance of 70% or more with respect to light having a wavelength of 660 nm.
<9> A coloring method of a reversible thermosensitive recording medium for coloring an uncolored reversible thermosensitive recording medium having at least a gas barrier layer and a reversible thermosensitive recording layer. in contrast, 600,000 the value of ^{b *} of the ground tint which is represented by ^L * ^a * ^{b *} after sunlight was irradiated continuously with an irradiation amount of Lux · Hr and ^b _{* s1,} after the colored when the ^{b *} value of the reversible thermosensitive recording medium was ^b _{* s2,} a difference between the ^b _{* s2} and the ^b _{* ^s1, b} * s2 ^-b _{* s1} is colored so that -2～110 And a coloring method for a reversible thermosensitive recording medium.
<10> respect uncolored reversible thermosensitive recording medium, when the value of ^{a *} when the continuous irradiation with irradiation dose of sunlight 16 million Lux · Hr was ^a _{* L1,} the ^a _{* L1} The method for coloring a reversible thermosensitive recording medium according to <9>, wherein the coloring is performed with color correction according to the above.

  According to the present invention, the conventional problems can be solved, the object can be achieved, and a reversible thermosensitive recording medium having no color change before and after sunlight irradiation and a coloring method thereof can be provided. .

FIG. 1 is a diagram showing discoloration of a background portion and disappearance change of an erasure portion when a conventional reversible thermosensitive recording medium is irradiated with sunlight. FIG. 2 is a diagram showing a discoloration state when sunlight is irradiated on a conventional reversible thermosensitive recording medium. FIG. 3 is a schematic sectional view showing an embodiment of the reversible thermosensitive recording medium of the present invention. FIG. 4 is a schematic sectional view showing another embodiment of the reversible thermosensitive recording medium of the present invention. FIG. 5 is a schematic sectional view showing still another embodiment of the reversible thermosensitive recording medium of the present invention. FIG. 6 is a graph showing reflectance characteristics with respect to light having a wavelength of 400 nm to 700 nm. FIG. 7 is a graph showing the color change measured with X-Rite 939 for Samples 1-13. FIG. 8 is a table showing the color change of Samples 1 to 13 measured with X-Rite 939 (reflective color colorimeter, manufactured by X-Rite).

(Reversible thermosensitive recording medium)
The reversible thermosensitive recording medium of the present invention is a colored reversible thermosensitive recording medium having at least a gas barrier layer and a reversible thermosensitive recording layer.
In particular, the reversible thermosensitive recording medium is a reversible thermosensitive recording medium obtained by coloring an uncolored reversible thermosensitive recording medium, and the uncolored reversible thermosensitive recording medium is irradiated with 600,000 Lux · Hr. the value of b ^* of the ground tint expressed sunlight consecutive irradiated after L ^* a ^* b ^* in an amount and b ^* _s1, the b ^* of the reversible thermosensitive recording medium after the coloring When the value is b ^* _s2 , the difference between b ^* _s2 and b ^* _s1, that is, b ^* _s2− b ^* _s1, is colored so as to be −2 to 110.
If the b ^* _s2− b ^* _s1 is less than −2, color change before and after sunlight irradiation cannot be suppressed, and ΔE that is a color difference before and after sunlight irradiation becomes large. From such a viewpoint, the lower limit of the b ^* _s2− b ^* _s1 is preferably 0 and more preferably 10.
On the other hand, if the b ^* _s2− b ^* _s1 exceeds 110, the color tone becomes too strong, the contrast of the image recorded on the medium is lowered, and in particular, the visibility of the printed image is lowered. . From such a viewpoint, the upper limit of the b ^* _s2- b ^* _s1 is preferably 100 and more preferably 90.
In addition, the irradiation amount of the sunlight assumes that the illuminance of sunlight outdoors is about 100,000 Lux, and the reversible thermosensitive recording medium is exposed to sunlight for about 6 hours a day. It is. In this specification, the irradiation amount of this sunlight is defined as equivalent to the daily irradiation of sunlight.
Further, as a technique equivalent to sunlight, a technique using artificial sunlight can be defined in the same manner.

The uncolored reversible thermosensitive recording medium is not particularly limited and may be appropriately selected depending on the purpose, and is a known reversible thermosensitive recording medium. Or, in order to enable printing display in blue, it is usually white. Such an uncolored reversible thermosensitive recording medium preferably has the following L ^* a ^* b ^* . That is, L ^* is preferably 80 or more, more preferably 85 or more, and particularly preferably 90 or more. As a ^* , -2 or more and 2 or less are preferred, -1.5 or more and 1.5 or less are more preferred, and -1 or more and 1 or less are especially preferred. b ^* is preferably −3 or more and 3 or less, more preferably −2.5 or more and 2.5 or less, and particularly preferably −2 or more and 2 or less.
Specific examples of commercially available uncolored reversible thermosensitive recording media include Ricoh's RECO-View Sheet 630BF (L ^* a ^* b ^* : 93, 0.2, 2.1), manufactured by Mitsubishi Paper Industries, Ltd. Examples include reversible thermosensitive recording media generally used in the field of reversible thermosensitive recording media such as thermolite card original sheet TRCG99SH (L ^* a ^* b ^* : 94, -0.2, -1.0). it can.
The uncolored reversible thermosensitive recording medium exhibits yellowish discoloration when irradiated with sunlight, and b ^* ₀ immediately after continuously irradiating sunlight with an irradiation amount of 600,000 Lux · Hr is sunlight. It changes in the direction which becomes larger in the positive direction (the direction in which yellowishness becomes stronger) than the b ^* value in the color before the irradiation.

The reason for causing such discoloration is not clear, but is considered as follows.
That is, it is generally considered that a dye that is excited by light and an active oxygen in which oxygen around the dye is activated by light cause a radical reaction to cause poor erasure and background discoloration. . Therefore, when a gas barrier layer is provided on the reversible thermosensitive recording medium so as to reduce the oxygen around the dye, it is considered that the result of reduction in erasure failure and background discoloration is obtained.
On the other hand, the excited dye returns to the ground state immediately after the light irradiation, but in the state where the gas barrier layer is disposed, the dye in the excited state maintains the excited state even after the light irradiation because there is less oxygen. As a result, it seems that the colored state was maintained.
This phenomenon varies greatly depending on the oxygen permeability (OTR) of the gas barrier layer. When this is larger than 100 cc / (m ² · day · atm), the colored state is not maintained, but it is 100 cc / (m ² · day · atm) or less. In the case of coloring, the coloring is maintained especially at 50 cc / (m ² · day · atm) or less. Further, at 1 cc / (m ² · day · atm) or less, the colored state is maintained, and if no external stimulus (for example, heat) is applied, it cannot return to the ground state, and the colored state is maintained. .
This suggests that the rate of change from the excited state to the ground state differs depending on the intervening state of oxygen, and it is inferred that the colored state is closely related to the oxygen permeability.

From such a viewpoint, when the oxygen permeability of the gas barrier layer is 50 cc / (m ² · day · atm) or less, deterioration of the reversible thermosensitive recording medium can be suppressed and the effect of the coloring can be obtained. It will be demonstrated remarkably.
The oxygen permeability of the gas barrier layer can be measured, for example, by the following method.
That is, a gas barrier layer is provided on an arbitrary base material, and oxygen permeability (OTR value) is measured using an oxygen permeability measuring device (manufactured by Mocon; OX-TRAN100, trade name) according to JIS K7126 B method. . The measurement is performed under a predetermined temperature and humidity environment. For example, the atmosphere is 25 ° C. and 80% RH (relative humidity).

The color L ^* a ^* b ^* before and after the sunlight irradiation can be measured by a reflective color colorimeter such as X-Rite 939 (manufactured by X-Rite).

In the reversible thermosensitive recording medium having the gas barrier layer, as described above, it is possible to reduce erasure defects and background discoloration.
However, it is assumed that the reversible thermosensitive recording medium is exposed to sunlight for a long period of time in the course of physical distribution use, and further life extension is required by suppressing color change.
As the discoloration of the background, it has been confirmed that the brown discoloration as shown in FIG. 1 occurs. From the viewpoint of extending the life of the reversible thermosensitive recording medium against such discoloration, the sun In addition to the color determined by b ^* _s1 corresponding to the b ^* value after light irradiation, it is preferable to further correct the color in the red direction (the direction in which the a ^* value increases).
That is, when the relative uncolored reversible thermosensitive recording medium, the value of ^{a *} when the continuous irradiation with irradiation dose of 16 million Lux · Hr sunlight was ^a _{* L1,} the ^a _{* L1} It is preferable that color correction is performed according to the color. Here, the a ^* _L1 has a value that fluctuates in a direction in which the a ^* value becomes larger than the a ^* _L0 that is the value of a ^* before sunlight irradiation in the uncolored reversible thermosensitive recording medium. The discoloration of the background is shown.

More specifically, when the a value in colored reversible thermosensitive recording medium was a ^* _s2, the difference between the and the _{^{a * s2 a * L1, a}} * s2 -a * L1 is, -2 The color correction is preferably performed so as to be 70, more preferably 0 to 60, and particularly preferably 2 to 50.
When the a ^* _s2- a ^* _L1 is less than -2, yellow becomes too dark or green becomes strong. When yellow becomes too dark, it becomes impossible to suppress a change in color due to deterioration of the background portion due to sunlight irradiation for a long time, and there is a problem that ΔE becomes large. Further, when the green color becomes strong, the reflectance at a wavelength of 660 nm is lowered, so that the contrast due to the barcode is lowered and the barcode readability may be lowered. When the a ^* _s2− a ^* _L1 exceeds 70, redness becomes too strong, so that there is a problem that the contrast between the printing portion and the background at the time of printing is greatly lowered and visibility is lowered.

At this time, when the uncolored reversible thermosensitive recording medium is continuously irradiated with sunlight at a dose of 16 million Lux · Hr, the b ^* value is b ^* _L1. ^{* The} color correction is preferably performed so that the difference between _s2 and b ^* _L1 , b ^* _s2- b ^* _L1 is 10 to 110, preferably 15 to 90, more preferably 20 to 80. preferable.
When the b ^* _s2- b ^* _L1 is less than 10, the color change before and after the sunlight irradiation cannot be suppressed with respect to the long-term sunlight irradiation, which is the color difference before and after the sunlight irradiation. ΔE may increase.
When the b ^* _s2− b ^* _L1 exceeds 110, there is a problem that the color tone becomes too strong, the contrast of the image recorded on the medium is lowered, and particularly the visibility of the printed image is lowered.
When the color correction is performed so as to have the above a ^* _s2 and b ^* _s2 , in addition to the color change due to sunlight exposure, it is effective in anticipation of the color change due to long-term sunlight exposure. It is possible to provide a reversible thermosensitive recording medium that can be colored and has no color change due to long-term sunlight exposure.
Note that the amount of sunlight irradiated is about 160 hours (equivalent to 27 days) exposed to 100,000 Lux of sunlight considering that the reversible thermosensitive recording medium is actually used for a long period of time. Is assumed. In this specification, the amount of sunlight irradiation is defined as equivalent to the 27-day irradiation of sunlight. Further, as a technique equivalent to sunlight, a technique using artificial sunlight can be defined in the same manner.

The coloring species used for the coloring is not particularly limited as long as the color can be imparted, and a known coloring species can be selected according to the coloring color (L ^* a ^* b ^* ). it can.

  The yellow coloring species is not particularly limited, and examples thereof include pigment yellow 1 and C.I. I. Pigment yellow 2, C.I. I. Pigment yellow 3, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 16, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 73, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 75, C.I. I. Pigment yellow 83, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 95, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 98, C.I. I. Pigment yellow 114, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 129, C.I. I. Pigment yellow 151, C.I. I. Pigment yellow 154, and the like.

The red coloring species is not particularly limited. For example, pigment red 9, pigment red 48, pigment red 49, pigment red 52, pigment red 53, pigment red 57, pigment red 97, and pigment red 122 are color index names. Pigment Red 123, Pigment Red 144, Pigment Red 146, Pigment Red 149, Pigment Red 166, Pigment Red 168, Pigment Red 177, Pigment Red 178, Pigment Red 179, Pigment Red 180, Pigment Red 185, Pigment Red 192, Pigment Red 202, Pigment Red 206, Pigment Red 207, Pigment Red 209, Pigment Red 215, Pigment Red 216, Pigment Red 217, Pigment Red 220, Pigment Red 221, Pigment Red 223, Pigment Red 224, Pigment Red 226, Pigment Red 227, Pigment Red 228, Pigment Red 238, Pigment Red 240, Pigment Red 242 and Pigment Red 254 Or CI Pigment Red 255.
There is no restriction | limiting in particular as said coloring seed | species (coloring material), Although both a dye and a pigment can be used, a pigment is more preferable when heat resistance and light resistance are considered.
There are inorganic and organic pigments, and any of them can be used. Examples of the organic pigment include azo, phthalocyanine, indigo, anthraquinone, perylene, quinacridone, methine / azomethine, and isoindolinone.

As a specific example, as the coloring species that imparts yellowish coloring, the coloring species that impart redness coloring for correction, such as Bell Color Transparent Yellow 261 (manufactured by Sakata Inx Corporation), are bell colors. Examples thereof include gold red 337 (manufactured by Sakata Inx Corporation).
These can be diluted in a solvent to adjust the color as appropriate, and the color can be adjusted as appropriate by changing the mixing ratio of a plurality of coloring species. In the case of forming, the color can be appropriately adjusted depending on the thickness of the colored layer.

The aspect of the reversible thermosensitive recording medium is not particularly limited as long as it has the gas barrier layer and the reversible thermosensitive recording layer, and can be appropriately selected according to the purpose.
For example, a reversible thermosensitive recording medium in which the reversible thermosensitive recording layer and the gas barrier layer are arranged in this order on a support. In addition, various layers such as a protective layer, an intermediate layer, and an undercoat layer described later may be appropriately disposed. In these embodiments, the reversible thermosensitive recording layer, protective layer and the like can be colored by containing a coloring species that imparts the color (L ^* a ^* b ^* ).
The reversible thermosensitive recording medium may further include a colored layer imparting the color (L ^* a ^* b ^* ).

Although there is no restriction | limiting in particular as said colored layer, It is preferable to distribute | arrange on the sunlight irradiation surface side with respect to the said reversible thermosensitive recording layer.
In this case, it can be expected that the colored species contained in the colored layer absorb sunlight and suppress deterioration of the reversible thermosensitive recording medium due to exposure to sunlight.
The colored layer is not particularly limited, but it is preferable that the reflectance with respect to light having a wavelength of 660 nm is 70% or more.
One of the uses of the reversible heat-sensitive medium is to print and operate a bar code, and the bar code reader has a reading wavelength of 660 nm, and the reflectance of the colored layer (background portion) with respect to this wavelength. If the reflectance is 70% or more, the contrast with the printed barcode becomes high, and the barcode readability is not affected. On the other hand, if it is less than 70%, the contrast between the printed barcode and the background portion is lowered, which may cause the barcode readability to be greatly reduced.

There is no restriction | limiting in particular as a formation method of the said colored layer, According to the objective, it can select suitably, The method etc. which apply | coat and dry the coloring liquid containing the said colored seed | species are mentioned.
The coloring liquid is not particularly limited. For example, when the above-mentioned bell color transparent yellow 261 and bell color gold red 337 are used as the coloring species, the polybutyral resin is dissolved in a 1: 1 mixed solvent of isopropanol and methyl ethyl ketone. These colored species can be added to and mixed with the butyral resin thus prepared.
The method for applying the coloring liquid is not particularly limited, and examples thereof include printing with a gravure proofing machine and application with a spin coater.
Further, the method for adding the colored species to the layer constituting the reversible thermosensitive recording medium is not particularly limited, and examples thereof include a method of adding and mixing the colored species to the composition liquid for forming these layers. .

-Gas barrier layer-
The gas barrier layer forming material is not particularly limited and may be appropriately selected depending on the intended purpose. It is preferable to include a gas barrier resin. The gas permeability can be lowered by the hydrogen bonding force of the hydroxyl group contained in such a gas barrier resin.

There is no restriction | limiting in particular as said polyvinyl alcohol-type polymer, According to the objective, it can select suitably, For example, any of polyvinyl alcohol, its derivative (s), and modified substance may be sufficient. These may be used alone or in combination of two or more.
There is no restriction | limiting in particular as a polymerization degree of the said polyvinyl alcohol-type polymer, Although it can select suitably according to the objective, 100-5,000 are preferable and 500-3,000 are more preferable.
Moreover, there is no restriction | limiting in particular as a saponification degree of the said polyvinyl alcohol-type polymer, Although it can select suitably according to the objective, 60 mol% or more is preferable and 75 mol% or more is more preferable.
There is no restriction | limiting in particular as a polyvinyl alcohol derivative which comprises the said polyvinyl alcohol polymer, For example, the polyvinyl alcohol derivative etc. by which about 40 mol% of a hydroxyl group is acetalized etc. can be mentioned.
There is no restriction | limiting in particular as a modified product of the said polyvinyl alcohol, For example, the polyvinyl alcohol modified material obtained by copolymerizing a carboxyl group-containing monomer, an amino group-containing monomer, etc. can be mentioned.

  The polyvinyl alcohol-based polymer has an advantage that the gas barrier property in a dry state is very high, but the degree of decrease in the gas barrier property under high humidity is larger than the ethylene-vinyl alcohol-based copolymer. When used under high humidity, it is preferable to increase the content of the inorganic layered compound described later in the gas barrier coating composition.

Next, the ethylene-vinyl alcohol copolymer is not particularly limited and can be appropriately selected according to the purpose. For example, a copolymer obtained by saponifying an ethylene-vinyl acetate copolymer is used. it can.
Specific examples of those obtained by saponifying the ethylene-vinyl acetate copolymer include, for example, those obtained by saponifying an ethylene-vinyl acetate copolymer obtained by copolymerizing ethylene and vinyl acetate, and Examples thereof include those obtained by saponifying an ethylene-vinyl acetate copolymer obtained by copolymerizing other monomers together with ethylene and vinyl acetate.
Although there is no restriction | limiting in particular as an ethylene ratio in the monomer before the copolymerization of the said ethylene-vinyl acetate type copolymer, It is preferable that it is 20 mol%-60 mol%. When the ethylene ratio is less than 20 mol%, the gas barrier property under high humidity may be lowered. On the other hand, when the ethylene ratio exceeds 60 mol%, the gas barrier property tends to be lowered over the whole. .

The ethylene-vinyl acetate copolymer is not particularly limited, but preferably has a vinyl acetate component having a saponification degree of 95 mol% or more. Tend.
In addition, the ethylene-vinyl acetate copolymer is not particularly limited, but it has a lower molecular weight by treatment with a peroxide or the like in that the dissolution stability in a solvent is improved. preferable.

  There is no restriction | limiting in particular as a method of forming the said gas barrier layer, The method of apply | coating the gas barrier coating agent composition containing the said gas barrier resin is mentioned.

  The solvent that can be used in the gas barrier coating composition is not particularly limited as long as it dissolves either the polyvinyl alcohol polymer or the ethylene-vinyl alcohol copolymer. Either non-aqueous solvent can be used, but water with low toxicity is preferred.

Further, when the ethylene-vinyl alcohol copolymer is used as a gas barrier resin, a terminal-modified ethylene-vinyl alcohol copolymer that has been reduced in molecular weight by treatment with the peroxide, water, lower alcohol, It is particularly preferable that the gas barrier coating composition is formed using the mixed solvent.
In this case, 50% by mass to 85% by mass of water and lower alcohols such as ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, etc. Use of a mixed solvent containing at least one of 15% by mass to 50% by mass improves the solubility of the ethylene-vinyl alcohol copolymer and is suitable for maintaining an appropriate solid content.
If the content of the lower alcohol in the mixed solvent exceeds 50% by mass, cleavage will be insufficient when an inorganic layered compound described later is dispersed. Among the lower alcohols having 2 to 4 carbon atoms, n-propyl alcohol and iso-propyl alcohol are preferably used.

  Since the gas barrier resin contains a hydroxyl group in the molecule, it has a large water absorption, and the gas barrier property under high-humidity conditions may be lowered. Therefore, an inorganic layered compound is added to the gas barrier coating agent composition. It is preferable to prevent the oxidative decomposition of the electron donating color-forming compound in the reversible thermosensitive recording layer by adding and expanding the gas passage path length in the gas barrier layer to be formed and preventing gas intrusion. .

The inorganic layered compound is not particularly limited and may be appropriately selected depending on the intended purpose. However, an inorganic layered compound that swells and cleaves in the dispersion medium is preferable. For example, a kaolin having a 1: 1 structure of phyllosilicate is used. Nite group, antigolite group belonging to jamonite group, smectite group, vermiculite group which is hydrous silicate mineral, mica group and the like are preferable depending on the number of interlayer cations.
Specifically, kaolinite, nacrite, dickite, halloysite, hydrous halloysite, antigolite, chrysotile, pyrophyllite, montmorillonite, beidellite, saponite, hectorite, soconite, stevensite, tetrasilic mica, sodium teniolite, Examples include muscovite, margarite, talc, vermiculite, phlogopite, xanthophyllite, chlorite, and the like, which may be natural or synthetic. Also, scaly silica can be used. These may be used alone or in combination of two or more.
Among these, use of montmorillonite is preferable from the viewpoint of gas barrier performance when used in a gas barrier coating composition.

When the inorganic layered compound is a natural product, since the size after being dispersed in the gas barrier resin is relatively large, it is easy to ensure the gas barrier function. On the other hand, inorganic metal ions contained in a trace amount as impurities are recorded in the present invention. When an image of a material is formed, there may be a problem that a color component is formed due to oxidative degradation due to application of heat energy.
This phenomenon may be visually recognized as unerased when the image formed on the reversible thermosensitive recording medium is erased, and the image quality may be deteriorated. It is preferable to prevent oxidative deterioration of impurity inorganic metal ions by adding an alkali metal or an alkaline earth metal during mixing of the layered compound and the gas barrier resin.
On the other hand, when the inorganic layered compound is a synthetic product, since no impurities are mixed, there is no inconvenience in image quality, but the particle size may be reduced during the synthetic processing of the inorganic layered compound. As a result, the gas passage length is short, and there is a possibility that desired gas barrier properties cannot be expressed.
As the inorganic layered compound, both natural and synthetic inorganic layered compounds can be used, but as described above, the gas barrier resin / inorganic layered compound mixing ratio is adjusted while accurately grasping the characteristics of the substance used. By determining, suitable gas barrier characteristics can be obtained.

  The mass ratio (solid content mass ratio) between the gas barrier resin and the inorganic layered compound in the gas barrier coating composition is not particularly limited and may be appropriately selected depending on the intended purpose. The resin / inorganic layered compound is preferably in the range of 30/70 to 99/1, more preferably in the range of 30/70 to 50/50. If the mass ratio of the inorganic layered compound is reduced, sufficient gas barrier properties may not be obtained. On the other hand, if the amount is too large, the coating strength and adhesion to other layers may be insufficient or the transparency may be impaired. In some cases, the thermal recording image may be concealed.

  When the gas barrier layer contains the inorganic layered compound, it is preferable to improve the adhesion with the adjacent layer. In order to ensure the durability against formation and erasure of a recorded image over many times, which is a basic characteristic of the reversible thermosensitive recording medium, a silane coupling agent, a titanium coupling agent, an isocyanate compound, an aziridine compound, One or more modifiers such as carbodiimide compounds can be added.

The silane coupling agent is not particularly limited, and examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, vinyltriacetoxysilane. , Alkoxysilane having a vinyl group such as 3-propyltrimethoxysilane methacrylate, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltri Alkoxysilane having epoxy group such as methoxysilane, 3-aminopropyltriethoxysilane, 3-N- (2-aminoethyl) aminopropyltrimethoxysilane, 3-N- (2-aminoethyl) aminopropylmethyldimethoxysilane Amino such as A ureido group such as an alkoxysilane having a group and / or an imino group, an isocyanate alkoxysilane such as triethoxysilylpropyl isocyanate, an alkoxysilane having a mercapto group such as γ-mercaptopropyltrimethoxysilane, and a γ-ureidopropyltriethoxysilane. The alkoxysilane which has can be mentioned.
Among these specific exemplary compounds, a trialkoxysilane compound having an amino group or a mercapto group rapidly reacts with an organic residue adjacent to the gas barrier layer, and the trialkoxysilyl group alkyl group is a methyl group. It is preferable because the chemical reaction with the inorganic layered compound in the gas barrier layer reacts quickly.

  The aziridine compound is not particularly limited, and examples thereof include trimethylolpropane tris (3-aziridinylpropionate), trimethylolpropane tris [3- (2-methyl-aziridinyl) -propionate], trimethylolpropane tris. (2-aziridinyl butyrate), tris (1-aziridinyl) phosphine oxide, pentaerythritol tris-3- (1-aziridinylpropionate), pentaerythritol tetrakis-3- (1-aziridinylpropio) Nate), 1,6-bis (1-aziridinocarbamoyl) hexamethylenediamine and the like.

There is no restriction | limiting in particular as said isocyanate compound, According to the objective, it can select suitably, For example, the following are mentioned.
That is, hydrogenated TDI, hydrogenated XDI, hydrogenated MDI, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), xylylene diisocyanate (XDI) and other aliphatic or alicyclic diisocyanates, and burettes that are derivatives thereof. Type, isocyanurate type, adduct type, etc., polyisocyanate having 3 or more functional groups, isocyanate-containing oligomers, aliphatic isocyanate compounds such as polymers, phenylene diisocyanate (PDI), toluene diisocyanate (TDI), naphthalene diisocyanate ( NDI), aromatic diisocyanates such as 4,4'-diisocyanate diphenylmethane (MDI), and derivatives thereof, such as burette type, isocyanurate type, adduct type or more. Other polyisocyanates include various oligomers containing isocyanate, aromatic isocyanate compounds such as polymers.
In order to form the gas barrier layer, since the gas barrier coating composition basically contains water as a solvent for use with a water-soluble polymer, the reaction with water is suppressed and the film is formed after film formation. It is preferred that curing proceeds.
Therefore, a self-emulsifying type polyisocyanate compound that is present in a water-dispersed state by introducing a hydrophilic group into the skeleton of the isocyanate compound is more preferable. Furthermore, it is more preferable to introduce a hydrophobic group because the reaction with water before film formation can be further suppressed.

  The carbodiimide compound is not particularly limited, but is preferably a water dispersion type emulsion type. As the hydrophilic modification of the carbodiimide compound, a substance obtained by extending the chain by a urethanization reaction between an isocyanate-terminated carbodiimide compound and a polyol compound, and further hydrophilizing and modifying the molecular terminal with a hydrophilic oligomer is a balance between stability and crosslinkability. Is good.

  The method for producing the gas barrier coating agent is not particularly limited. For example, (1) a solution obtained by dissolving a gas barrier resin in the solvent is preliminarily swollen and cleaved in a dispersion medium such as water. (2) The inorganic layered compound is dispersed using a stirrer or a dispersing device. (2) The inorganic layered compound is swollen and cleaved in a dispersion medium such as water and then stirred. Examples thereof include a method of using an apparatus or a dispersion apparatus, and further adding and mixing a solution obtained by dissolving a gas barrier resin in the solvent into a dispersion liquid (dispersion solution) obtained by cleaving and dispersing the inorganic layered compound. When the inorganic layered compound is a natural product, it is preferable to add a compound containing an alkali (earth) metal ion such as magnesium hydroxide or calcium hydroxide to the mixed solution.

The stirring device and the dispersion device are not particularly limited, and known stirring devices and dispersion devices can be used. From the viewpoint of obtaining a transparent and stable inorganic layered compound dispersion, a high-pressure dispersion device, an ultrasonic dispersion device, and the like. It is preferable to use a machine or the like.
Examples of the high-pressure disperser include a nanomizer (trade name, manufactured by Nanomizer), a microfluidizer (trade name, manufactured by Microfridex), an optimizer (trade name, manufactured by Sugino Machine), and DeBee (trade name, Bee), Niro Soabi homogenizer (trade name, Niro Soabi), and the like. It is preferable to perform the dispersion treatment at 100 MPa or less as the pressure condition of these high-pressure dispersers. When the pressure condition exceeds 100 MPa, the inorganic layered compound is likely to be crushed and the gas passage length is shortened, so that the target gas barrier property may be lowered. Conversely, if the pressure condition is less than 1 MPa, there may be a problem that the dispersion of the inorganic layered compound does not proceed or that a huge amount of time is required for the dispersion.

  The silane coupling agent, isocyanate compound, aziridine compound and carbodiimide compound added to improve the adhesion between the gas barrier layer and the adjacent layer are preferably added after the dispersion adjustment of the gas barrier resin and the inorganic layered compound.

In order to improve the adhesion between the gas barrier layer and the adjacent layer, it is preferable to bond using an adhesive layer made of either an adhesive or an anchor coat agent.
The adhesive is not particularly limited and may include isocyanate, urethane, and acrylic laminating adhesives, and the anchor coating agent includes titanium, isocyanate, imine, and polybutadiene. And various other anchor coating agents for laminating. Note that these adhesives and anchor coat agents may contain an adhesion modifying material such as a crosslinking agent.

A method of providing the gas barrier layer and, if necessary, an anchor coat layer using the above materials will be described.
When a gas barrier layer is provided on the reversible thermosensitive recording layer, an adhesive or an anchor coating agent is applied as necessary, and then a gas barrier coating composition for forming the gas barrier layer is applied. And heat to dry. The coating method of the gas barrier coating composition is a conventional coating method such as a roll coating method using a gravure cylinder, a doctor knife method, an air knife / nozzle coating method, a bar coating method, a spray coating method or a dip coating method. A construction method can be used, and these methods may be combined.

  Although there is no restriction | limiting in particular as the thickness of the said gas barrier layer to apply | coat, 0.1 micrometer-5 micrometers are preferable, and 0.1 micrometer-0.5 micrometer are more preferable at the point that a highly transparent gas barrier layer can be formed. If the thickness is less than 0.1 μm, the target gas barrier property and the organic solvent shielding effect cannot be obtained. On the other hand, if the thickness exceeds 5 μm, the gas barrier property is not improved, and sufficient transparency is obtained. It may be difficult.

-Reversible thermosensitive recording layer-
The reversible thermosensitive recording layer contains an electron accepting compound (color former) and an electron donating color developing compound (developer), and the color tone reversibly changes depending on the temperature.

  The electron-donating color-forming compound (color former) is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include a colorless or light-colored dye precursor (leuco dye). Examples thereof include fluoran compounds, triphenylmethane phthalide compounds, azaphthalide compounds, phenothiazine compounds, leuco oxirane compounds, indolinophthalide compounds, and the like. These may be used alone or in combination of two or more.

  Specific examples of such a color former include, for example, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-di (n-) as the fluorane compound and azaphthalide compound. Butylamino) fluorane, 2-anilino-3-methyl-6- (Nn-propyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-isopropyl-N-methylamino) fluorane 2-anilino-3-methyl-6- (N-isobutyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluorane, 2-anilino -3-methyl-6- (N-sec-butyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-ethyl) Ruamino) fluoran, 2-anilino-3-methyl-6- (N-iso-amyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (Nn-propyl-N-isopropylamino) Fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-ethyl-p-toluidino) fluorane, 2-anilino-3 -Methyl-6- (N-methyl-p-toluidino) fluorane, 2- (m-trichloromethylanilino) -3-methyl-6-diethylaminofluorane, 2- (m-trifluoromethylanilino) -3 -Methyl-6-diethylaminofluorane, 2- (m-trichloromethylanilino) -3-methyl-6- (N-cyclohexyl-N-methyl) Mino) fluorane, 2- (2,4-dimethylanilino) -3-methyl-6-diethylaminofluorane, 2- (N-ethyl-p-toluidino) -3-methyl-6- (N-ethylanilino) fluorane 2- (N-ethyl-p-toluidino) -3-methyl-6- (N-propyl-p-toluidino) fluorane, 2-anilino-6- (Nn-hexyl-N-ethylamino) fluorane, 2- (o-chloroanilino) -6-diethylaminofluorane, 2- (o-chloroanilino) -6-dibutylaminofluorane, 2- (m-trifluoromethylanilino) -6-diethylaminofluorane, 2,3 -Dimethyl-6-dimethylaminofluorane, 3-methyl-6- (N-ethyl-p-toluidino) fluorane, 2-chloro-6-diethylaminophenyl Luolan, 2-bromo-6-diethylaminofluorane, 2-chloro-6-dipropylaminofluorane, 3-chloro-6-cyclohexylaminofluorane, 3-bromo-6-cyclohexylaminofluorane, 2-chloro- 6- (N-ethyl-N-isoamylamino) fluorane, 2-chloro-3-methyl-6-diethylaminofluorane, 2-anilino-3-chloro-6-diethylaminofluorane, 2- (o-chloroanilino)- 3-chloro-6-cyclohexylaminofluorane, 2- (m-trifluoromethylanilino) -3-chloro-6-diethylaminofluorane, 2- (2,3-dichloroanilino) -3-chloro-6 -Diethylaminofluorane, 1,2-benzo-6-diethylaminofluorane, 3-diethylamino-6 (M-trifluoromethylanilino) fluorane, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1- Ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide, 3- (1-octyl-2-methylindol-3-yl) -3- (2 -Ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-methyl-4-diethylaminophenyl) -4-azaphthalide, 3- ( 1-ethyl-2-methylindol-3-yl) -3- (2-methyl-4-diethylaminophenyl) -7-azaphthalide, 3- (1-ethyl-2- Tylindole-3-yl) -3- (4-diethylaminophenyl) -4-azaphthalide, 3- (1-ethyl-2-methylindol-3-yl) -3- (4-Nn-amyl-N -Methylaminophenyl) -4-azaphthalide, 3- (1-methyl-2-methylindol-3-yl) -3- (2-hexyloxy-4-diethylaminophenyl) -4-azaphthalide, 3,3-bis (2-Ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3,3-bis (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide and the like.

  Examples of color formers other than the above fluorane compounds and azaphthalide compounds include 2- (p-acetylanilino) -6- (Nn-amyl-Nn-butylamino) fluorane, 2-benzylamino-6 -(N-ethyl-p-toluidino) fluorane, 2-benzylamino-6- (N-methyl-2,4-dimethylanilino) fluorane, 2-benzylamino-6- (N-ethyl-2,4- Dimethylanilino) fluorane, 2-benzylamino-6- (N-methyl-p-toluidino) fluorane, 2-benzylamino-6- (N-ethyl-p-toluidino) fluorane, 2- (di-p-methyl) Benzylamino) -6- (N-ethyl-p-toluidino) fluorane, 2- (α-phenylethylamino) -6- (N-ethyl-p-toluidino) fluorane 2-methylamino-6- (N-methylanilino) fluorane, 2-methylamino-6- (N-ethylanilino) fluorane, 2-methylamino-6- (N-propylanilino) fluorane, 2-ethylamino-6 -(N-methyl-p-toluidino) fluorane, 2-methylamino-6- (N-methyl-2,4-dimethylanilino) fluorane, 2-ethylamino-6- (N-ethyl-2,4- Dimethylanilino) fluorane, 2-dimethylamino-6- (N-methylanilino) fluorane, 2-dimethylamino-6- (N-ethylanilino) fluorane, 2-diethylamino-6- (N-methyl-p-toluidino) fluorane 2-diethylamino-6- (N-ethyl-p-toluidino) fluorane, 2-dipropylamino-6- (N-methyl) Ruanilino) fluorane, 2-dipropylamino-6- (N-ethylanilino) fluorane, 2-amino-6- (N-methylanilino) fluorane, 2-amino-6- (N-ethylanilino) fluorane, 2-amino-6 -(N-propylanilino) fluorane, 2-amino-6- (N-methyl-p-toluidino) fluorane, 2-amino-6- (N-ethyl-p-toluidino) fluorane, 2-amino-6- (N-propyl-p-toluidino) fluorane, 2-amino-6- (N-methyl-p-ethylanilino) fluorane, 2-amino-6- (N-ethyl-p-ethylanilino) fluorane, 2-amino-6 -(N-propyl-p-ethylanilino) fluorane, 2-amino-6- (N-methyl-2,4-dimethylanilino) fluorane 2-amino-6- (N-ethyl-2,4-dimethylanilino) fluorane, 2-amino-6- (N-propyl-2,4-dimethylanilino) fluorane, 2-amino-6- (N -Methyl-p-chloroanilino) fluorane, 2-amino-6- (N-ethyl-p-chloroanilino) fluorane, 2-amino-6- (N-propyl-p-chloroanilino) fluorane, 1,2-benzo-6 -(N-ethyl-N-isoamylamino) fluorane, 1,2-benzo-6-dibutylaminofluorane, 1,2-benzo-6- (N-methyl-N-cyclohexylamino) fluorane, 1,2- And benzo-6- (N-ethyl-N-toluidino) fluorane.

  The electron-accepting compound (developer) used in the reversible thermosensitive recording layer is not particularly limited as long as it has an action of developing the color former, and can be appropriately selected according to the purpose. However, a compound represented by the general formula (1) is preferable from the viewpoint of color density and erasing properties.

(In the general formula (1), l represents an integer of 0 to 2, m represents an integer of 0 or 1, n represents an integer of 1 to 3, and X and Y represent N. R ₁ represents a divalent group containing an atom or an O atom, R ₁ represents an optionally substituted aliphatic hydrocarbon group having 2 or more carbon atoms, and R ₂ represents 1 or more carbon atoms. Represents an aliphatic hydrocarbon group.)

In the general formula (1), the aliphatic hydrocarbon group may be linear or branched and may have an unsaturated bond. Examples of the substituent attached to the hydrocarbon group include a hydroxyl group, a halogen atom, and an alkoxy group. When the sum of the carbons of R ₁ and R ₂ is 7 or less, the stability of color development and the decoloring property are lowered. Therefore, the carbon number is preferably 8 or more, and more preferably 11 or more.
Preferable examples of R ₁ include the following.

Among them - _(CH 2) q- are particularly preferred.
In the formula, q, q ′, q ″, and q ′ ″ each represent an integer that satisfies the carbon number of R ¹ and R ² .
Preferred examples of R ₂ include those shown below.

Among them _{- (CH 2) q-CH} 3 are particularly preferred. In the formula, q, q ′, q ″, and q ′ ″ are the same as described above.
X and Y represent a divalent group containing an N atom or an O atom, preferably

Represents a divalent group containing at least one group represented by the formula: The following are mentioned as the example.

Of these, particularly preferred groups are as follows.

Furthermore, the following are mentioned as a specific phenol compound. However, the present invention is not limited to these.

(In the above formula, r represents an integer of 2 or more, and s represents an integer of 1 or more.)

  As the control agent used in the reversible thermosensitive recording layer, a compound containing an amide group, a urethane group, a urea group, a ketone group, a diacyl hydrazide group or the like as a partial structure is preferable from the viewpoint of color density and erasability. Among these, compounds having an amide group, a secondary amide group, and a urethane group are particularly preferable, and specific examples include the following.

(In the above formula, n, n ′, n ″, n ′ ″, n ″ ″ represent integers from 0 to 21. However, all are not 5 or less.)

_{C 11 H 23 CONHC 12 H 25} , C 15 H 31 CONHC 16 H 33, C 17 H 35 CONHC 18 H 37, C 17 H 35 CONHC 18 H 35, C 21 H 41 CONHC 18 H 37, C 15 H 31 CONHC ₁₈ H ₃₇ , C ₁₇ H ₃₅ CONHCH ₂ HNOCC ₁₇ H ₃₅ , C ₁₁ H ₂₃ CONHCH ₂ HNOCC ₁₁ H ₂₃ , C ₇ H ₁₅ CONHC ₂ H ₄ HNOCC ₁₇ H ₃₅ , C ₉ H ₁₉ CONHC ₂ H ₄ HNOCC ₉ H ₁₉ , C ₁₁ H ₂₃ CONHC ₂ H ₄ HNOCC ₁₁ H ₂₃ , C ₁₇ H ₃₅ CONHC ₂ H ₄ HNOCC ₁₇ H ₃₅ , (CH ₃ ) ₂ CHC ₁₄ H ₃₅ CONHC ₂ H ₄ HNOCC ₁₄ H ₃₅ (CH ₃ ) ₂ , C _{1 H 43 CONHC 2 H 4 HNOCC} 21 H 43, C 17 H 35 CONHC 6 H 12 HNOCC 17 H 35, C 21 H 43 CONHC 6 H 12 HNOCC 21 H 43, C 17 H 33 CONHCH 2 HNOCC 17 H 33, C ₁₇ H ₃₃ CONHC ₂ H ₄ HNOCC ₁₇ H ₃₃ , C ₂₁ H ₄₁ CONHC ₂ H ₄ HNOCC ₂₁ H ₄₁ , C ₁₇ H ₃₃ CONHC ₆ H ₁₂ HNOCC ₁₇ H ₃₃ , C ₈ H ₁₇ NHCOC ₂ H ₄ CONHC ₁₈ H _{37 , C 10 H 21 NHCOC 2 H} 4 CONHC 10 H 21, C 12 H 25 NHCOC 2 H 4 CONHC 12 H 25, C 18 H 37 NHCOC 2 H 4 CONHC 18 H 37, C 21 H 43 NHOCC 2 H _{CONHC 21 H 43, C 18 H} 37 NHOCC 6 H 12 CONHC 18 H 37, C 18 H 35 NHCOC 4 H 8 CONHC 18 H 35, C 18 H 35 NHCOC 8 H 16 CONHC 18 H 35, C 12 H 25 OCONHC 18 H ₃₇ , C ₁₃ H ₂₇ OCONHC ₁₈ H ₃₇ , C ₁₆ H ₃₃ OCONHC ₁₈ H ₃₇ , C ₁₈ H ₃₇ OCONHC ₁₈ H ₃₇ , C ₂₁ H ₄₃ OCONHC ₁₈ H ₃₇ , C ₁₂ H ₂₅ OCONHC ₁₆ H ₃₃ , C _{13 H 27 OCONHC 16 H 33, C} 16 H 33 OCONHC 16 H 33, C 18 H 37 OCONHC 16 H 33, C 21 H 43 OCONHC 16 H 33, C 12 H 25 OCONHC 14 H 29, C 13 _{27 OCONHC 14 H 29, C 16} H 33 OCONHC 14 H 29, C 18 H 37 OCONHC 14 H 29, C 22 H 45 OCONHC 14 H 29, C 12 H 25 OCONHC 12 H 37, C 13 H 27 OCONHC 12 H 37 C ₁₆ H ₃₃ OCONHC ₁₂ H ₃₇ , C ₁₈ H ₃₇ OCONHC ₁₂ H ₃₇ , C ₂₁ H ₄₃ OCONHC ₁₂ H ₃₇ , C ₂₂ H ₄₅ OCONHC ₁₈ H ₃₇ , C ₁₈ H ₃₇ NHCOOC ₂ H ₄ OCONHC ₁₈ H ₃₇ , _{C 18 H 37 NHCOOC 3 H 6} OCONHC 18 H 37, C 18 H 37 NHCOOC 4 H 8 OCONHC 18 H 37, C 18 H 37 NHCOOC 6 H 12 OCONHC 18 H 37, C 18 H _{7 NHCOOC 8 H 16 OCONHC 18 H} 37, C 18 H 37 NHCOOC 2 H 4 OC 2 H 4 OCONHC 18 H 37, C 18 H 37 NHCOOC 3 H 6 OC 3 H 6 OCONHC 18 H 37, C 18 H 37 NHCOOC 12 H ₂₄ OCONHC ₁₈ H ₃₇ , C ₁₈ H ₃₇ NHCOOC ₂ H ₄ OC ₂ H ₄ OC ₂ H ₄ OCONHC ₁₈ H ₃₇ , C ₁₆ H ₃₃ NHCOOC ₂ H ₄ OCONHC ₁₆ H ₃₃ , C ₁₆ H ₃₃ NHCOOC ₃ H ₆ OCN ₁₆ H ₃₃ , C ₁₆ H ₃₃ NHCOOC ₄ H ₈ OCONHC ₁₆ H ₃₃ , C ₁₆ H ₃₃ NHCOOC ₆ H ₁₂ OCONHC ₁₆ H ₃₃ , C ₁₆ H ₃₃ NHCOOC ₈ H ₁₆ OCONHC ₁₆ H _{33 , C 18 H 37 OCOHNC 6 H} 12 NHCOOC 18 H 37, C 16 H 33 OCOHNC 6 H 12 NHCOOC 16 H 33, C 14 H 29 OCOHNC 6 H 12 NHCOOC 14 H 29, C 12 H 25 OCOHNC 6 H 12 NHCOOC 12 H ₂₅ , C ₁₀ H ₂₁ OCOHNC ₆ H ₁₂ NHCOOC ₁₀ H ₂₁ , C ₈ H ₁₇ OCOHNC ₆ H ₁₂ NHCOOC ₈ H ₁₇

Etc.

  As a ratio of the color former and the color developer, an appropriate range varies depending on the combination of the compounds to be used. 10 is more preferable. If the amount of developer is less or more than this range, the density of the colored state may be lowered.

Hereinafter, the reversible thermosensitive recording medium will be described in more detail.
Examples of the binder resin used for forming the reversible thermosensitive recording layer include polyvinyl chloride, polyvinyl acetate, vinyl chloride vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, phenoxy resin, polyester, and aromatic. Examples include polyester, polyurethane, polycarbonate, polyacrylic acid ester, polymethacrylic acid ester, acrylic acid copolymer, maleic acid copolymer, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, and starches.
The role of these binder resins is to keep the materials of the composition uniformly dispersed without being displaced by the application of heat for recording and erasing.
Therefore, it is preferable to use a resin having high heat resistance as the binder resin. For example, the binder resin may be crosslinked with heat, ultraviolet light, electron beam, or the like.

  Specific examples of the resin in a crosslinked state include groups that react with a crosslinking agent such as acrylic polyol resin, polyester polyol resin, polyurethane polyol resin, phenoxy resin, polyvinyl butyral resin, cellulose acetate propionate, and cellulose acetate butyrate. Or a resin obtained by copolymerizing a monomer having a group that reacts with a crosslinking agent and another monomer.

  In addition, the acrylic polyol resin has different characteristics depending on the structure, and the hydroxyl monomer is hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl. Methacrylate (HPMA), 2-hydroxybutyl monoacrylate (2-HBA), 1,4-hydroxybutyl monoacrylate (1-HBA), and the like are used, but it is particularly preferable to use a monomer having a primary hydroxyl group. 2-Hydroxyethyl methacrylate is preferably used because the film has good crack resistance and durability.

There is no restriction | limiting in particular as a hardening | curing agent used for formation of the said reversible thermosensitive recording layer, Well-known isocyanates, amines, phenols, an epoxy compound, etc. are mentioned. Of these, isocyanate curing agents are preferably used.
The isocyanate-based compound used here is selected from known modified monomers such as urethane-modified products, allophanate-modified products, isocyanurate-modified products, burette-modified products, carbodiimide-modified products, and blocked isocyanates. The isocyanate monomer that forms the modified product includes tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), naphthylene diisocyanate (NDI), paraphenylene diisocyanate ( PPDI), tetramethylxylylene diisocyanate (TMXDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (HMDI), isophorone diisocyanate (IPDI), lysine diisocyanate (LDI), isopropylidenebis (4-cyclohexylisocyanate) (IPC) Cyclohexyl diisocyanate (CHDI), tolidine diisocyanate (TODI), and the like.

Furthermore, you may use the catalyst used for this kind of reaction as a crosslinking accelerator.
The crosslinking accelerator is not particularly limited, and examples thereof include tertiary amines such as 1,4-diaza-bicyclo [2,2,2] octane, and metal compounds such as organic tin compounds. Further, the total amount of the curing agent may or may not undergo a crosslinking reaction. That is, an unreacted curing agent may be present. Since this type of crosslinking reaction proceeds over time, the presence of an unreacted curing agent does not indicate that the crosslinking reaction has progressed at all, but an unreacted curing agent is detected. However, this does not mean that there is no resin in a crosslinked state. Further, as a method for distinguishing whether the polymer in the present invention is in a crosslinked state or in a non-crosslinked state, it can be distinguished by immersing the coating film in a highly soluble solvent.
That is, the polymer in the non-crosslinked state dissolves in the solvent and does not remain in the solute, so the presence or absence of the polymer structure of the solute may be analyzed. Therefore, if the presence of a polymer structure in the solute cannot be confirmed, it can be said that the polymer is in a non-crosslinked state, and can be distinguished from a crosslinked polymer. Here, this can be expressed as a gel fraction.

  The gel fraction refers to the ratio of gel formation when a resin solute in a solvent loses its independent motility due to interaction and assembles into a separate state (gel). The resin preferably has a gel fraction of 30% or more, more preferably 50% or more, still more preferably 70% or more, and particularly preferably 80% or more. If the gel fraction is small, the durability will be reduced repeatedly. Therefore, in order to improve the gel fraction, a curable resin that is cured by heat, UV, EB or the like may be mixed in the resin, or the resin itself may be crosslinked. .

As a gel fraction measurement method, the membrane is peeled off from the support and the initial weight of the membrane is measured, and then the membrane is placed in a 400 mesh wire net and immersed in a solvent in which the resin before crosslinking is soluble for 24 hours. Then vacuum dry and measure the weight after drying.
The gel fraction calculation is performed according to the following formula.
Gel fraction (%) = [weight after drying (g) / initial weight (g)] × 100
When calculating the gel fraction by this calculation, the calculation is performed excluding the weight of organic low-molecular substance particles other than the resin component in the reversible thermosensitive recording layer. At this time, when the weight of the organic low molecular weight substance is not known in advance, the weight ratio is obtained from the area ratio per unit area and the specific gravity of the resin and the low molecular weight organic substance by cross-sectional observation such as TEM and SEM. The gel fraction value may be calculated by calculating the molecular substance weight.

  In the case of the measurement, a reversible thermosensitive recording layer is provided on the support, and another layer such as a protective layer is laminated thereon, and the support and the reversible thermosensitive recording layer. If there is another layer in between, the film thickness of the reversible thermosensitive recording layer and other layers is examined by cross-sectional observation of the TEM, SEM, etc., and the surface for the film thickness of the other layers is shaved, The reversible thermosensitive recording layer surface may be exposed and the reversible thermosensitive recording layer may be peeled off and gel fraction measurement may be performed in the same manner as in the measurement method.

  In this method, when there is a protective layer made of an ultraviolet curable resin or the like in the upper layer of the reversible thermosensitive recording layer, the thickness of the protective layer is reduced and the reversible feeling is prevented in order to prevent this layer from being mixed as much as possible. The surface of the thermal recording layer must also be shaved slightly to prevent the influence on the gel fraction value.

As the reversible thermosensitive recording medium, an additive for improving and controlling the recording layer coating characteristics and coloring / decoloring characteristics can be used as necessary.
Examples of these additives include surfactants, conductive agents, fillers, antioxidants, light stabilizers, color stabilizers, and the like.

In forming the reversible thermosensitive recording layer, a coating prepared by uniformly mixing and dispersing the mixture of the developer, color former, various additives, curing agent, crosslinked resin and coating solvent is used. Use liquid.
Specific examples of the solvent used for preparing the coating liquid include, for example, water; alcohols such as methanol, ethanol, isopropanol, n-butanol, methyl isocarbinol; acetone, 2-butanone, ethyl amyl ketone, diacetone alcohol, Ketones such as isophorone and cyclohexanone; Amides such as N, N-dimethylformamide and N, N-dimethylacetamide; Diethyl ether, isopropyl ether, tetrahydrofuran, 1,4-dioxane, 3,4-dihydro-2H-pyran and the like Ethers; glycol ethers such as 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, ethylene glycol dimethyl ether; 2-methoxyethyl acetate, 2-ethoxyethyl acetate, 2-butyl ether Glycol ether acetates such as xylethyl acetate; esters such as methyl acetate, ethyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, and ethylene carbonate; aromatic hydrocarbons such as benzene, toluene, xylene; hexane, heptane, iso -Aliphatic hydrocarbons such as octane and cyclohexane; halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane, dichloropropane and chlorobenzene; sulfoxides such as dimethyl sulfoxide; N-methyl-2-pyrrolidone, N -Pyrrolidones such as octyl-2-pyrrolidone and the like can be mentioned.

The coating liquid can be prepared, for example, using a known coating liquid dispersing apparatus such as a paint shaker, a ball mill, an attritor, a three-roll mill, a keddy mill, a sand mill, a dyno mill, or a colloid mill.
In addition, each material may be dispersed in a solvent by using the coating liquid dispersing apparatus, or may be dispersed and mixed in a solvent alone. Further, it may be dissolved by heating and precipitated by rapid cooling or cooling.

  The coating method for providing the reversible thermosensitive recording layer is not particularly limited, and blade coating, wire bar coating, spray coating, air knife coating, bead coating, curtain coating, gravure coating, kiss coating. Known methods such as coating, reverse roll coating, dip coating, and die coating can be used.

There is no restriction | limiting in particular as said support body, According to the objective, it can select suitably, For example, paper, a resin film, PET film, a synthetic paper, metal foil, glass, or these composites etc. are mentioned. These can be used alone or in combination, with a thickness as required.
There is no restriction | limiting in particular as thickness of the said support body, Arbitrary thickness can be selected from about several micrometers to about several mm.
The support may have a magnetic recording layer on the same surface and / or the opposite surface to the reversible thermosensitive recording layer.
The reversible thermosensitive recording medium may be attached to another medium via an adhesive layer or the like.
Also, a back coat layer is provided on one side of a support such as a PET film, a release layer used for a thermal transfer ribbon on the opposite side of the back coat layer, a reversible thermosensitive recording layer on the release layer, and paper or resin on the surface. A resin layer that can be transferred to a film, a PET film, or the like may be provided and transferred using a thermal transfer printer.
The reversible thermosensitive recording medium may be processed into a sheet shape or a card shape, and the shape thereof can be processed into an arbitrary shape, and printing on the surface of the medium can be performed.
The reversible thermosensitive recording medium may be used in combination with an irreversible thermosensitive recording layer. At this time, the color tone of each recording layer may be the same or different.

Examples of the drying / curing method for the reversible thermosensitive recording layer include a method of performing a curing treatment as necessary after coating and drying.
For example, the heat treatment may be performed at a relatively high temperature for a short time using a high-temperature bath or the like, or may be heat-treated at a relatively low temperature for a long time.
As specific conditions for the crosslinking reaction at the time of curing, it is preferable to heat for about 1 minute to 150 hours under a temperature condition of about 30 ° C. to 130 ° C. from the viewpoint of reactivity, and a temperature condition of 40 ° C. to 100 ° C. It is more preferable to heat for about 2 minutes to 120 hours.
In addition, since productivity is emphasized in production, it is difficult to take time until the crosslinking is sufficiently completed.
Therefore, a crosslinking step may be provided separately from the drying step. As a condition for the crosslinking step, it is preferable to heat at a temperature of 40 ° C. to 100 ° C. for about 2 minutes to 120 hours.
The thickness of the reversible thermosensitive recording layer is preferably 1 μm to 20 μm, and more preferably 3 μm to 15 μm.

Improvement of adhesion of the reversible thermosensitive recording layer to the protective layer, prevention of alteration of the recording layer by application of the protective layer, prevention of migration of the additive contained in the protective layer to the recording layer, and addition of the additive contained in the recording layer For the purpose of preventing the transition to the protective layer, an intermediate layer may be provided between them.
The thickness of the intermediate layer is preferably in the range of 0.1 μm to 20 μm, and more preferably 0.3 μm to 10 μm.
As a solvent, a coating liquid dispersing device, a binder, a coating method, and a drying / curing method used for the intermediate layer coating solution, a method used for forming the reversible thermosensitive recording layer can be used.

The thickness of the protective layer is preferably 0.1 μm to 20 μm, more preferably 0.3 μm to 10 μm.
As a solvent, a coating liquid dispersing device, a binder, a coating method, and a drying / curing method used for the coating liquid for the protective layer, the methods used for forming the reversible thermosensitive recording layer can be used.

As the reversible thermosensitive recording layer, the intermediate layer, and the protective layer, other fillers that do not have ultraviolet absorption performance or ultraviolet shielding performance may be added.
The filler can be divided into an inorganic filler and an organic filler. Inorganic fillers include calcium carbonate, magnesium carbonate, anhydrous silicic acid, hydrous silicic acid, hydrous aluminum silicate, hydrous calcium silicate, alumina, iron oxide, calcium oxide, magnesium oxide, chromium oxide, manganese oxide, silica, talc, Mica, etc. Examples of organic fillers include silicone resin, cellulose resin, epoxy resin, nylon resin, phenol resin, polyurethane resin, urea resin, melamine resin, polyester resin, polycarbonate resin, styrene, polystyrene, polystyrene / isoprene, styrene vinylbenzene, and other styrene series Examples thereof include resins, acrylic resins such as vinylidene chloride acrylic, acrylic urethane, and ethylene acrylic, polyethylene resins, formaldehyde resins such as benzoguanamine formaldehyde, melamine formaldehyde, polymethyl methacrylate resins, and vinyl chloride resins.
The said filler may be used individually by 1 type, and may use 2 or more types together. When using 2 or more types together, there is no restriction | limiting in particular about how to combine the said inorganic filler and the said organic filler.
Moreover, there is no restriction | limiting in particular as a shape of the said filler, For example, spherical shape, a granular form, plate shape, needle shape, etc. are mentioned.
There is no restriction | limiting in particular as content of the filler in the said protective layer, 5 volume%-50 volume% are preferable by a volume fraction.

A lubricant may be added as the reversible thermosensitive recording layer, the intermediate layer, and the protective layer.
Specific examples of the lubricant include synthetic waxes such as ester wax, paraffin wax, and polyethylene wax: vegetable waxes such as hardened castor oil: animal waxes such as beef tallow hardened oil: higher alcohols such as stearyl alcohol and behenyl alcohol : Higher fatty acids such as margaric acid, lauric acid, mystynoic acid, palmitic acid, stearic acid, behenic acid, and fumenic acid: higher fatty acid esters such as fatty acid ester of sorbitan: stearic acid amide, oleic acid amide, lauric acid amide, Examples thereof include amides such as ethylene bis stearamide, methylene bis stearamide, and methylol stearamide.
Although there is no restriction | limiting in particular as content of the lubricant in each said layer, 0.1%-95% are preferable at a volume fraction, and 1%-75% are more preferable.

As the reversible thermosensitive recording medium, in addition to the reversible thermosensitive recording layer, intermediate layer and protective layer, an undercoat layer may be provided between the reversible thermosensitive recording layer and the support.
In this case, as the undercoat layer, it is preferable to use hollow particles for the purpose of improving the coloring sensitivity and decoloring sensitivity.
As the hollow particles, known hollow particles can be used, but those having a hollow ratio of 70% or more are preferable. However, as the hollow particles, it is necessary to reduce the thickness of the wall material together with a high hollow ratio. When the wall material is thinned, the strength against pressure or the like is weakened and the wall material is easily broken. On the other hand, if the wall material is simply hardened to give strength, it tends to become brittle and is easily broken by bending. Therefore, a balance between hardness and flexibility is necessary for the wall material, and acrylonitrile and methacrylonitrile are mentioned as preferable wall materials having both hardness and flexibility. Specific examples of the hollow particles include those described in JP-A-2005-199704.

Embodiments of the reversible thermosensitive recording medium will be described with reference to the drawings. FIG. 3 is a schematic sectional view showing an embodiment of the reversible thermosensitive recording medium of the present invention.
The reversible thermosensitive recording medium 10 shown in FIG. 3 includes an undercoat layer 2, a thermoreversible recording layer 3, an intermediate layer 4, a gas barrier layer 5, a colored layer 6, and a protective layer 7 in this order on a support 1. It depends on what was arranged.
In the reversible thermosensitive recording medium 10, the reversible thermosensitive recording medium 10 is colored by the colored layer 6 in anticipation of the discoloration of the uncolored reversible thermosensitive recording medium after irradiation with sunlight. It is possible to suppress the change in color.

FIG. 4 is a schematic cross-sectional view showing another embodiment of the reversible thermosensitive recording medium of the present invention.
In the reversible thermosensitive recording medium 20 shown in FIG. 4, an undercoat layer 2, a thermoreversible recording layer 3, an intermediate layer 4, a gas barrier layer 5, and a protective layer 7 are arranged in this order on a support 1, and are protected. It relates to the layer 7 that has been colored.
In the reversible thermosensitive recording medium 20, the reversible thermosensitive recording medium 20 is colored in anticipation of the discoloration of the uncolored reversible thermosensitive recording medium after irradiation with sunlight by the protective layer 7 to which color is imparted. Therefore, it can suppress that a color changes before and after sunlight irradiation.

FIG. 5 is a schematic cross-sectional view showing another embodiment of the reversible thermosensitive recording medium of the present invention.
The reversible thermosensitive recording medium 30 shown in FIG. 5 includes an undercoat layer 2, a thermoreversible recording layer 3, an intermediate layer 4, a gas barrier layer 5, a protective layer 7, and a colored layer 6 in this order on a support 1. It depends on what was arranged.
In the reversible thermosensitive recording medium 30, the reversible thermosensitive recording medium 30 is colored by the colored layer 6 in anticipation of discoloration of the uncolored reversible thermosensitive recording medium after irradiation with sunlight. It is possible to suppress the change in color.
The layer structure of the reversible thermosensitive recording medium can be selected as appropriate according to the purpose, and is not limited to the layer structure of the embodiment.

(Coloring method of reversible thermosensitive recording medium)
The coloring method of the reversible thermosensitive recording medium of the present invention is a coloring method for an uncolored reversible thermosensitive recording medium having at least a gas barrier layer and a reversible thermosensitive recording layer. in contrast, 600,000 the value of ^{b *} of the ground tint which is represented by ^L * ^a * ^{b *} after sunlight was irradiated continuously with an irradiation amount of Lux · Hr and ^b _{* s1,} after the colored when the ^{b *} value of the reversible thermosensitive recording medium was ^b _{* s2,} a difference between the ^b _{* s2} and the ^b _{* ^s1, b} * s2 ^-b _{* s1} is colored so that -2～110 It is characterized by doing.
If the b ^* _s2− b ^* _s1 is less than −2, color change before and after sunlight irradiation cannot be suppressed, and ΔE that is a color difference before and after sunlight irradiation becomes large. From such a viewpoint, the lower limit of the b ^* _s2− b ^* _s1 is preferably 0 and more preferably 10.
On the other hand, if the b ^* _s2− b ^* _s1 exceeds 110, the color tone becomes too strong, the contrast of the image recorded on the medium is lowered, and in particular, the visibility of the printed image is lowered. . From such a viewpoint, the upper limit of the b ^* _s2- b ^* _s1 is preferably 100 and more preferably 90.
In addition, the irradiation amount of the sunlight assumes that the illuminance of sunlight outdoors is about 100,000 Lux, and the reversible thermosensitive recording medium is exposed to sunlight for about 6 hours a day. It is.

Further, the coloring method of the reversible thermosensitive recording medium is not particularly limited, but the uncolored reversible thermosensitive recording medium was continuously irradiated with sunlight at an irradiation amount of 16 million Lux · Hr. ^{when a *} of the values was ^a _{* L1} of time, it is preferable to color by the color correction in response to the ^a _{* L1.} Here, the a ^* _L1 has a value that fluctuates in a direction in which the a ^* value becomes larger than the a ^* _L0 that is the value of a ^* before sunlight irradiation in the uncolored reversible thermosensitive recording medium. The discoloration of the background is shown.

More specifically, when the a value in colored reversible thermosensitive recording medium was a ^* _s2, the difference between the and the _{^{a * s2 a * L1, a}} * s2 -a * L1 is, -2 The color correction is preferably performed so as to be 70, more preferably 0 to 60, and particularly preferably 2 to 50.
When the a ^* _s2- a ^* _L1 is less than -2, yellow becomes too dark or green becomes strong. If yellow becomes too dark, it becomes impossible to suppress a change in color due to deterioration of the background due to sunlight irradiation for a long time, and there is a problem that ΔE becomes large. Further, when the green color becomes strong, the reflectance at a wavelength of 660 nm is lowered, so that the contrast due to the barcode is lowered and the barcode readability may be lowered. When the a ^* _s2− a ^* _L1 exceeds 70, redness becomes too strong, so that there is a problem that the contrast between the printing portion and the background at the time of printing is greatly lowered and visibility is lowered.

At this time, relative to the uncolored reversible thermosensitive recording medium, when the b ^* value at the time of continuous irradiation with irradiation dose of sunlight 16 million Lux · Hr was b ^* _L1, the b ^{* The} color correction is preferably performed so that the difference between _s2 and b ^* _L1 , b ^* _s2- b ^* _L1 is 10 to 110, preferably 15 to 90, more preferably 20 to 80. preferable.
When the b ^* _s2- b ^* _L1 is less than 10, the color change before and after the sunlight irradiation cannot be suppressed with respect to the long-term sunlight irradiation, which is the color difference before and after the sunlight irradiation. ΔE may increase.
When the b ^* _s2− b ^* _L1 exceeds 110, there is a problem that the color tone becomes too strong, the contrast of the image recorded on the medium is lowered, and particularly the visibility of the printed image is lowered.
When the color correction is performed so as to have the above a ^* _s2 and b ^* _s2 , in addition to the color change due to sunlight exposure, it is effective in anticipation of the color change due to long-term sunlight exposure. It is possible to provide a reversible thermosensitive recording medium that can be colored and has no color change due to long-term sunlight exposure.
Note that the amount of sunlight irradiated is about 160 hours (equivalent to 27 days) exposed to 100,000 Lux of sunlight considering that the reversible thermosensitive recording medium is actually used for a long period of time. Is assumed.

  For the other matters, all the matters described in the reversible thermosensitive recording medium of the present invention can be applied.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, the thought of this invention is not limited to these Examples. In the examples, “parts” and “%” represent “parts by mass” and “mass%” unless otherwise specified.

[Preparation of gas barrier layer forming material]
<Preparation of ethylene-vinyl alcohol copolymer solution A>
To 60 parts of a mixed solvent containing 50% by mass of purified water and 50% by mass of iso-propyl alcohol (IPA), an ethylene-vinyl alcohol copolymer (trade name: Soarnol D-2908, manufactured by Nippon Synthetic Chemical Co., Ltd., hereinafter "EVOH 30 parts) and 10 parts of hydrogen peroxide having a concentration of 30% by mass were added, heated to 80 ° C. with stirring, and reacted for 2 hours. After cooling, catalase was added to 3,000 ppm to remove residual hydrogen peroxide, whereby a substantially transparent ethylene-vinyl alcohol copolymer solution A (EVOH solution A) having a solid content of 30% by mass was obtained. Got.

<Preparation of inorganic layered compound dispersion A>
5 parts of natural montmorillonite (trade name: Kunipia F, manufactured by Kunimine Kogyo Co., Ltd.), which is an inorganic layered compound, was added to 95 parts of purified water while stirring and sufficiently dispersed with a high-speed stirrer. Further, 1 part of magnesium hydroxide was added. Thereafter, the mixture was kept at 40 ° C. for 1 day to obtain an inorganic layered compound dispersion A having a solid content of 5%.

<Preparation of EVOH Gas Barrier Resin Mixture 1 (EV1)>
26.7 parts of EVOH solution A was added to 60 parts of a mixed solvent of 50% by weight of purified water and 50% by weight of IPA, and the mixture was sufficiently stirred and mixed. While this solution was stirred at high speed, 4 parts of the inorganic layered compound dispersion A was added.
3 parts of cation exchange resin is added to 100 parts of this mixed solution, and the mixture is stirred for 1 hour at a stirring speed that does not cause crushing of the cation exchange resin. Only the ion exchange resin was filtered off with a strainer.
The mixed solution obtained from the above operation was further subjected to a dispersion treatment with a high-pressure dispersion apparatus at a pressure of 50 MPa, then filtered through a 300 mesh filter, and a gas barrier resin mixed solution 1 (EVOH / Inorganic layered compound = 80/20, hereinafter referred to as “EV1”).

<Preparation of EVOH gas barrier resin mixed solution 2 (EV2)>
Except for changing the addition amount of EVOH solution A of EV1 from 26.7 parts to 20 parts and changing the addition amount of inorganic layered compound dispersion A from 4 parts to 8 parts, A gas barrier resin mixed solution 2 (hereinafter referred to as “EV2”) of EVOH / inorganic layered compound = 60/40 was obtained.

<Preparation of EVOH gas barrier resin mixed solution 3 (EV3)>
Except for changing the addition amount of EVOH solution A of EV1 from 26.7 parts to 30 parts and changing the addition amount of inorganic layered compound dispersion A from 4 parts to 2 parts, A gas barrier resin mixed solution 3 (hereinafter referred to as “EV3”) of EVOH / inorganic layered compound = 90/10 was obtained.

<Preparation of EVOH Gas Barrier Resin Mixture 4 (EV4)>
Except for changing the addition amount of EVOH solution A of EV1 from 26.7 parts to 31.7 parts and changing the addition amount of inorganic layered compound dispersion A from 4 parts to 1 part, it was the same as the preparation of EV1. As a result, EVOH / inorganic layered compound = 95/5 gas barrier resin mixed solution 4 (hereinafter referred to as “EV4”) was obtained.

[Coloring species 1]
<Preparation of Colored Liquid 1 (CI1)>
Polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., BL-1) is dissolved in a mixed solvent of IPA and methyl ethyl ketone (MEK) having a mixing ratio of 1: 1 (IPA: MEK), and a butyral resin liquid having a solid content of 10% by mass. Got.
To 32 parts of this butyral resin liquid, 2 parts of Bell Color Transparent Yellow 261 (manufactured by Sakata Inx) were mixed and sufficiently stirred to prepare Colored Liquid 1 (hereinafter referred to as “CI1”).

<Preparation of Colored Liquid 2 (CI2)>
Except for changing the amount of butyral resin liquid added from 32 parts to 24 parts and changing the amount of added bell color transparent yellow 261 from 2 parts to 6 parts, coloring liquid 2 (hereinafter “ CI2 ") was prepared.

<Preparation of Colored Liquid 3 (CI3)>
Except for changing the addition amount of the butyral resin liquid from 32 parts to 24 parts and changing the addition amount of the bell color transparent yellow 261 from 2 parts to 12 parts, the coloring liquid 3 (hereinafter “ CI3 ") was prepared.

<Preparation of Colored Liquid 4 (CI4)>
Colored liquid 4 (hereinafter referred to as “Liquid”) was prepared in the same manner as CI 1 except that the amount of butyral resin liquid added was changed from 32 parts to 24 parts and the amount of bell color transparent yellow 261 was changed from 2 parts to 24 parts. CI4 ") was prepared.

[Coloring species 2]
<Preparation of Colored Liquid 5 (CI5)>
A mixed ink 1 was prepared by mixing bell color transparent yellow 261 (manufactured by Sakata Inx) and bell color gold red 337 (manufactured by Sakata Inx) so that the mixing ratio was 72: 2 (transparent yellow: gold red).
A colored liquid 5 (hereinafter referred to as “CI5”) was prepared in the same manner as CI2, except that the mixed ink 1 was used instead of the bell-color transparent yellow 261.

<Preparation of Colored Liquid 6 (CI6)>
A colored liquid 6 (hereinafter referred to as “CI6”) was prepared in the same manner as CI3 except that the mixed ink 1 was used instead of the bell-color transparent yellow 261.

<Preparation of Colored Liquid 7 (CI7)>
A colored liquid 7 (hereinafter referred to as “CI7”) was prepared in the same manner as CI4 except that the mixed ink 1 was used in place of the bell-color transparent yellow 261.

[Coloring seed 3]
<Preparation of Colored Liquid 8 (CI8)>
A mixed ink 2 was prepared by mixing bell color transparent yellow 261 (manufactured by Sakata Inx) and bell color gold red 337 (manufactured by Sakata Inx) so that the mixing ratio was 50: 5 (transparent yellow: gold red).
A colored liquid 8 (hereinafter referred to as “CI8”) was prepared in the same manner as CI2, except that the mixed ink 2 was used in place of the bell-color transparent yellow 261.

<Preparation of Colored Liquid 9 (CI9)>
A colored liquid 9 (hereinafter referred to as “CI9”) was prepared in the same manner as CI3 except that the mixed ink 2 was used instead of the bell-color transparent yellow 261.

<Preparation of Colored Liquid 10 (CI10)>
A colored liquid 10 (hereinafter referred to as “CI10”) was prepared in the same manner as CI4 except that the mixed ink 2 was used in place of the bell-color transparent yellow 261.

[Coloring seed 4]
<Preparation of Colored Liquid 11 (CI11)>
A mixed ink 3 was prepared by mixing bell color transparent yellow 261 (manufactured by Sakata Inx) and bell color gold red 337 (manufactured by Sakata Inx) so that the mixing ratio was 50:50 (transparent yellow: gold red).
A colored liquid 11 (hereinafter referred to as “CI11”) was prepared in the same manner as CI4 except that the mixed ink 3 was used instead of the bell-color transparent yellow 261.

Example 1
As a support, a 125 μm thick white turbid polyester film (manufactured by Teijin DuPont Co., Ltd., Tetron film U2L98W) was used.

<Formation of undercoat layer>
30 parts by mass of styrene-butadiene copolymer (manufactured by Nippon A & L Co., Ltd., PA-9159), 12 parts by mass of polyvinyl alcohol resin (manufactured by Kuraray Co., Ltd., Poval PVA103), hollow particles (manufactured by Matsumoto Yushi Co., Ltd., Microsphere) R-300) 20 parts by mass and water 40 parts by mass were added and stirred for about 1 hour until a uniform state was obtained to prepare an undercoat layer coating solution. The obtained undercoat layer coating solution was applied onto the support with a wire bar and dried by heating at 80 ° C. for 2 minutes to form an undercoat layer having a thickness of 20 μm.

<Formation of reversible thermosensitive recording layer>
The developer represented by the following structural formula: 3.5 parts by mass, 1.5 parts by mass of dialkylurea (manufactured by Nippon Kasei Co., Ltd., Haclean SB), 50% by mass solution of acrylic polyol (manufactured by Mitsubishi Rayon Co., hydroxyl value: 69) , Molecular weight: 30,000, glass transition temperature: 80 ° C.) 12 parts by mass and methyl ethyl ketone 150 parts by mass were pulverized and dispersed using a ball mill so that the average particle size was about 1 μm.

Next, 1.5 parts by mass of 2-anilino-3-methyl-6dibutylaminofluorane and an isocyanate curing agent (Nihon Polyurethane Co., Ltd., Coronate HX) were added to the dispersion obtained by pulverizing and dispersing the developer. 1.5 parts by mass was added, and the mixture was sufficiently stirred to prepare a thermosensitive layer coating solution.
Next, the obtained heat-sensitive layer coating solution was applied onto the undercoat layer using a wire bar, dried at 100 ° C. for 2 minutes, and then cured at 60 ° C. for 24 hours to a thickness of about 11 μm. A reversible thermosensitive recording layer was formed.

<Formation of intermediate layer>
Acrylic polyol resin 50 mass% solution (Mitsubishi Rayon Co., Ltd., hydroxyl value: 108, molecular weight: 65,000, glass transition temperature: 80 ° C.) 3 mass parts, zinc oxide fine particle 30 mass% dispersion (Sumitomo Cement Co., Ltd.) , ZS303) 7 parts by mass, isocyanate-based curing agent (manufactured by Nippon Polyurethane Co., Ltd., Coronate HL) 1.5 parts by mass, and 7 parts by mass of methyl ethyl ketone were added and stirred sufficiently to prepare an intermediate layer coating solution.
Next, the intermediate layer coating solution is applied onto the reversible thermosensitive recording layer with a wire bar, heated and dried at 90 ° C. for 1 minute, and then heated at 60 ° C. for 2 hours to form an intermediate layer having a thickness of about 2 μm. Formed.

<Formation of gas barrier layer 1 (GBL1)>
To 10 parts of EV1, 0.3 part of a silane coupling agent (trade name: SH-6062, manufactured by Toray Dow Corning Co., Ltd.) was added, followed by stirring and mixing. Next, a wire bar was applied onto the intermediate layer, dried at 100 ° C. for 1 minute, and then heated at 50 ° C. for 24 hours to provide a gas barrier layer having a thickness of 1.2 μm (hereinafter referred to as “GBL1”). .
Note that the oxygen permeability GBL1 (referred to as cc / m ² / 24hr / atm or less "OTR"), oxygen sample was applied using the conditions EV1 to OPP film (manufactured by Toyobo Co., Ltd. PYLEN film -OT P2261 50μm) When the measurement was performed under the conditions of a temperature of 25 ° C. and a humidity of 80% RH using a transmittance measuring device (“OX-TRN100 type oxygen permeability measuring device” manufactured by Modern Controls), the OTR was 20.

<Formation of colored layer>
CI1 was printed on GBL1 using a gravure proofing machine (manufactured by Gravure Service Equipment Co., Ltd.) at a printing speed of 25 m / min and then dried at 60 ° C. to form a colored layer having a thickness of 0.5 μm.

<Formation of protective layer>
3 parts by mass of pentaerythritol hexaacrylate (manufactured by Nippon Kayaku Co., Ltd., KAYARAD DPHA), 3 parts by mass of urethane acrylate oligomer (manufactured by Negami Kogyo Co., Ltd., Art Resin UN-3320HA), acrylic ester of dipentaerythritol caprolactone ( Nippon Kayaku Co., Ltd., KAYARAD DPCA-120) 3 parts by mass, silica (Mizusawa Chemical Co., Ltd., P-526) 1 part by mass, photopolymerization initiator (Nippon Ciba Geigy Co., Ltd., Irgacure 184) 0.5 Part by mass and 11 parts by mass of isopropyl alcohol were added, and the mixture was well stirred by a ball mill and dispersed so that the average particle size was about 3 μm to prepare a coating solution for a protective layer.
The protective layer coating solution was applied onto the colored layer with a wire bar, heated and dried at 90 ° C. for 1 minute, and then crosslinked with an 80 W / cm ultraviolet lamp to form a protective layer having a thickness of 4 μm. Next, curing was performed at 60 ° C. for 24 hours.
From the above, the reversible thermosensitive recording medium in Example 1 was produced.

(Example 2)
A reversible thermosensitive recording medium in Example 2 was produced in the same manner as in Example 1 except that CI2 was used instead of CI1 in the formation of the colored layer in Example 1.

(Example 3)
A reversible thermosensitive recording medium in Example 3 was produced in the same manner as in Example 1 except that CI3 was used instead of CI1 in the formation of the colored layer in Example 1.

(Example 4)
A reversible thermosensitive recording medium in Example 4 was produced in the same manner as in Example 1 except that CI4 was used instead of CI1 in forming the colored layer in Example 1.

(Example 5)
In the formation of the colored layer in Example 1, CI4 was printed on GBL1 using a gravure proofing machine, dried at 60 ° C., and printed by overlapping three layers to form a 1.5 μm colored layer Produced a reversible thermosensitive recording medium in Example 5 in the same manner as in Example 1.

(Example 6)
In Example 3, a reversible thermosensitive recording medium in Example 6 was produced in the same manner as in Example 3 except that the gas barrier layer 2 (GBL2) was formed as follows instead of GBL1.

<Formation of gas barrier layer 2 (GBL2)>
A gas barrier layer 2 having a thickness of 2 μm (hereinafter referred to as “GBL2”) was provided on the intermediate layer in the same manner as the formation of GBL1 in Example 1 except that 10 parts of EV2 was added instead of 10 parts of EV1. .
When the OTR of GBL2 was measured in the same manner as GBL1, the OTR of GBL2 was 5.

(Example 7)
In Example 6, a reversible thermosensitive recording medium in Example 7 was produced in the same manner as in Example 6 except that the gas barrier layer 3 (GBL3) was formed as follows instead of GBL2.

<Formation of gas barrier layer 3 (GBL3)>
A gas barrier layer 3 having a thickness of 0.6 μm (hereinafter referred to as “GBL3”) is formed on the intermediate layer in the same manner as in the formation of GBL1 in Example 1, except that 10 parts of EV3 is added instead of 10 parts of EV1. Provided.
When the OTR of GBL3 was measured in the same manner as GBL1, the OTR of GBL3 was 50.

(Example 8)
A reversible thermosensitive recording medium in Example 8 was produced in the same manner as in Example 2 except that CI5 was used instead of CI2 in the formation of the colored layer in Example 2.

Example 9
A reversible thermosensitive recording medium in Example 9 was produced in the same manner as in Example 3 except that CI6 was used instead of CI3 in the formation of the colored layer in Example 3.

(Example 10)
A reversible thermosensitive recording medium in Example 10 was produced in the same manner as in Example 4 except that CI7 was used instead of CI4 in forming the colored layer in Example 4.

(Example 11)
A reversible thermosensitive recording medium in Example 11 was produced in the same manner as in Example 2 except that CI8 was used instead of CI2 in the formation of the colored layer in Example 2.

(Example 12)
A reversible thermosensitive recording medium in Example 12 was produced in the same manner as in Example 3 except that CI9 was used instead of CI3 in forming the colored layer in Example 3.

(Example 13)
A reversible thermosensitive recording medium in Example 13 was produced in the same manner as in Example 4 except that CI10 was used in place of CI4 in forming the colored layer in Example 4.

(Example 14)
A reversible thermosensitive recording medium in Example 14 was produced in the same manner as in Example 5 except that CI10 was used instead of CI4 in the formation of the colored layer in Example 5.

(Example 15)
A reversible thermosensitive recording medium in Example 15 was produced in the same manner as in Example 4 except that CI11 was used instead of CI4 in the formation of the colored layer in Example 4.

(Comparative Example 1)
In Example 1, a reversible thermosensitive recording medium in Comparative Example 1 was produced in the same manner as in Example 1 except that a protective layer was formed on GBL1 without forming a colored layer.

(Comparative Example 2)
In Example 7, a reversible thermosensitive recording medium in Comparative Example 2 was produced in the same manner as in Example 7 except that a protective layer was formed on GBL3 without forming a colored layer.

(Comparative Example 3)
In Example 6, a reversible thermosensitive recording medium in Comparative Example 3 was produced in the same manner as in Example 6 except that a protective layer was formed on GBL2 without forming a colored layer.

(Comparative Example 4)
In Example 1, instead of GBL1, after forming the gas barrier layer 4 (GBL4) as follows, a protective layer was formed on the gas barrier layer 4 (GBL4) without forming a colored layer. In the same manner as in Example 1, a reversible thermosensitive recording medium in Comparative Example 4 was produced.

<Formation of gas barrier layer 4 (GBL4)>
On the intermediate layer, silicon oxide (SiO) is vapor-deposited by a high-frequency heating method under a vacuum of 1 × 10 ⁻⁵ Torr using a vacuum vapor deposition apparatus, and a silicon oxide vapor deposition layer having a vapor deposition layer SiOx thickness of 30 nm ( A gas barrier layer 4 (hereinafter referred to as “GBL4”) made of SiOx was formed.
As for the OTR of GBL4, a sample obtained by depositing silicon oxide (SiO) on an OPP film (pyrene film—OT P2261 50 μm manufactured by Toyobo Co., Ltd.) under the above-described conditions was used as an oxygen transmission rate measuring device (“OX” manufactured by Modern Controls Co., Ltd.). -TRN100 type oxygen transmission rate measuring apparatus ") was measured under the conditions of a temperature of 25 ° C and a humidity of 80% RH, and the OTR of GBL4 was 0.5.

(Comparative Example 5)
In Example 1, instead of GBL1, after forming the gas barrier layer 5 (GBL5) as follows, the protective layer was formed on the gas barrier layer 5 (GBL5) without forming the colored layer. In the same manner as in Example 1, a reversible thermosensitive recording medium in Comparative Example 5 was produced.

<Production of gas barrier layer 5 (GBL5)>
A gas barrier layer 5 (hereinafter referred to as “GBL5”) having a thickness of 0.5 μm was provided on the intermediate layer in the same manner as in the production of GBL1, except that 10 parts of EV4 was added instead of 10 parts of EV1.
When the OTR of GBL5 was measured in the same manner as GBL1, the OTR of GBL5 was 100.

(Comparative Example 6)
In Example 1, the reversible thermosensitive recording medium in Comparative Example 6 was produced in the same manner as in Example 1 except that the protective layer was formed on the intermediate layer without forming GBL1 and the colored layer.

(Measurement method and evaluation results)
<Measurement method of oxygen permeability (OTR)>
Measurement of ^{OTR (cc / m 2 / 24hr} / atm) in the reversible thermosensitive recording medium of Example 15 and Comparative Examples 1 to 6 were performed by the following methods. The results are shown in Table 1 below.
That is, a gas barrier layer was provided on each OPP film (Toyobo Pyrene Film—OT P2261 50 μm), and the temperature was set to 25 ° C. with an oxygen permeability measuring device (“OX-TRN100 type oxygen permeability measuring device” manufactured by Modern Controls). The measurement was performed under the condition of humidity 80% RH.

<Evaluation of color change: Daylight equivalent test>
Thermal printing simulator using end face type thermal head KSB320AA (resistance value 1,206 ohm) manufactured by Kyocera Corporation and ceramic heater (4 mm width) for the reversible thermosensitive recording media in Examples 1-15 and Comparative Examples 1-6. Each sample was printed with a solid image printed at a printing speed of 2 inches / sec.
Next, in these samples, the density and color (L ^* a ^* b ^* ) of the background portion where printing is not performed are measured with X-Rite 939 (reflective color colorimeter, manufactured by X-Rite). It was measured.
Next, an artificial solar testing machine (SEL-25KP30 type, manufactured by Celic) is used for the sample after the measurement, and the illuminance is 100,000 Lux (measured by Lux HiTester 3423, manufactured by HIOKI), irradiation time. Was irradiated with artificial sunlight under the conditions of 6 hours, a total illuminance of 600,000 Lux · Hr, a temperature of 35 ° C., and a humidity of 80% RH. Considering the time during which the reversible thermosensitive recording medium is exposed to the sun in actual use, this test was defined as equivalent to one day of sunlight in the daytime, and was regarded as a daylight equivalent to sunlight test.
Immediately after the test, a sample was taken out and the density and color (L ^* a ^* b ^* ) of the background portion were measured under the same conditions as before artificial sunlight irradiation. Manufactured).
By the above, regarding the reversible thermosensitive recording media in Examples 1 to 15 and Comparative Examples 1 to 6, the difference in the density of the background portion before and after artificial sunlight irradiation, and before and after artificial sunlight irradiation ΔE indicating the difference in color of the background after solar irradiation was obtained, and ΔE was evaluated according to the following criteria. The results are shown in Tables 2 and 3 below.

-Evaluation criteria for color change △ E-
◎: Less than 2.0 ○: 2.0 or more and less than 3.0 Δ: 3.0 or more and less than 4.5 ×: 4.5 or more and less than 8.0 XX: 8.0 or more

<About changes in color relating to sunlight equivalent test for 1 day>
As shown in Table 2 above, it was confirmed that the samples relating to the reversible thermosensitive recording media of Comparative Examples 1 to 5 provided with a gas barrier layer colored the background when irradiated with sunlight.
Moreover, it was confirmed that there is a difference in the degree of coloring of the background depending on the value of OTR indicating the oxygen permeability of the gas barrier layer.
It was confirmed that the color change greatly fluctuated especially in the direction of b ^* after sunlight irradiation and changed color in the yellow direction. On the other hand, Comparative Example 6 having no gas barrier layer fluctuated in both a ^* and b ^* , but a strong discoloration in the yellow direction could not be confirmed.
From this, in the reversible thermosensitive recording medium having a gas barrier layer, it was confirmed that the yellow color corresponding to the OTR value indicating the oxygen permeability of the gas barrier layer was strongly discolored (b ^* fluctuated to the + side). .

Among the comparative examples 1 to 5, the reversible thermosensitive recording media in the examples 1 to 15 having the colored layer corresponding to the color change in the yellow direction confirmed in the comparative examples 1 to 3 having good gas barrier properties. Formed.
That is, each of the reversible thermosensitive recording media of Examples 1 to 5 and Examples 8 to 15 is different from the reversible thermosensitive recording medium having a gas barrier layer of OTR = 20 in Comparative Example 1 in the coloring liquid and the colored layer. While changing the color scheme according to the thickness, a colored layer colored in a yellow color is arranged.
The reversible thermosensitive recording medium in Example 6 is a reversible thermosensitive recording medium having a gas barrier layer of OTR = 5 in Comparative Example 3 with a colored layer colored in a yellow color. .
The reversible thermosensitive recording medium in Example 7 is a reversible thermosensitive recording medium having a gas barrier layer of OTR = 50 in Comparative Example 2 with a colored layer colored in a yellowish color. .

Here, in the colored layers in Examples 1 to 15, the color of the background of the reversible thermosensitive recording medium is the color after irradiation of sunlight corresponding to the reversible thermosensitive recording medium in the corresponding non-colored comparative example for one day. It is colored with a predetermined coloring amount with respect to the b ^* value in the taste (L ^* a ^* b ^* ). The relationship of the coloring amount is shown in Table 3 below.
In Table 3, b ^* _s0 , b ^* _s1 , b ^* _s2 , and b ^* _s3 indicate the following matters.
That is, b ^* _s0 represents the b ^* value on the background of the uncolored reversible thermosensitive recording medium before irradiation with sunlight.
b ^* _s1 represents the b ^* value on the background of the uncolored reversible thermosensitive recording medium after irradiation with sunlight for 1 day.
b ^* _s2 represents the b ^* value on the background of the colored reversible thermosensitive recording medium before irradiation with sunlight.
b ^* _s3 represents the b ^* value of the background of the colored reversible thermosensitive recording medium after irradiation with sunlight for 1 day.

<Measurement method and evaluation of contrast>
When printing on a reversible thermosensitive recording medium, the density difference between the printed image and the background portion can be expressed by an index of ease of visual recognition of the printed image. Is defined as contrast. The contrast is expressed by a value obtained by subtracting the reflection density of the background portion where printing is not performed from the reflection density of the printed image portion.
Here, X-Rite 939 (reflective color calorimeter, manufactured by X-Rite) is used for the reflection density measurement, and V (visual filter) is used among the V, C, M, and Y filters in the reflection density measurement mode. Judgment is made based on the result of measurement in the mode.
The measurement was performed by printing a 1 cm square solid image so that the concentration can be easily measured. Regarding the background portion, an area where printing is not performed is measured.
Contrast evaluation criteria were in the following ranges. The results are shown in Table 3 below.
-Evaluation criteria for contrast-
A: 1.30 or more
○: 1.15 or more and less than 1.30
Δ: 1.00 or more and less than 1.15
×: Less than 1.0

In the reversible thermosensitive recording media in Examples 1 to 15 that are colored in this way, the color change can be suppressed compared to the reversible thermosensitive recording media in Comparative Examples 1 to 3 (see Tables 2 and 3 above). ).
For example, the reversible thermosensitive recording medium in Example 1 changes in color until the color difference ΔE indicating the color difference before and after sunlight irradiation is half or less compared to the reversible thermosensitive recording medium in Comparative Example 1. Can be suppressed.
Further, also in the reversible thermosensitive recording medium in Example 7 corresponding to Comparative Example 2 and Example 6 corresponding to Comparative Example 3, the color difference ΔE can be reduced and the color change can be suppressed.
Further, as shown in Tables 2 and 3, it can be seen that ΔE tends to decrease as the difference from b ^* _s2− b ^* _s1 increases.
However, when the difference from b ^* _s2− b ^* _s1 is increased, coloring becomes stronger, and when information such as characters is printed on a reversible thermosensitive recording medium, the appearance of the printed portion and the unprinted background portion is apparent. Contrast will be lowered. There is also a problem that the tint of the color becomes too strong, making it difficult to recognize the intended print image. In Examples 1 to 7, coloring is performed only in the b * direction. At this time, the difference from b ^* _s2− b ^* _s1 needs to be 110 or less, and preferably 100 or less.

<Evaluation of prolonging service life: Sunlight 27 days equivalent test>
Thermal printing simulator using end face type thermal head KSB320AA (resistance value 1,206 ohm) manufactured by Kyocera Corporation and ceramic heater (4 mm width) for the reversible thermosensitive recording media in Examples 1-15 and Comparative Examples 1-6. Each sample was printed with a solid image printed at a printing speed of 2 inches / sec.
Next, in these samples, the density and color (L ^* a ^* b ^* ) of the background portion where printing is not performed are measured with X-Rite 939 (reflective color colorimeter, manufactured by X-Rite). It was measured.
Next, an artificial solar testing machine (SEL-25KP30 type, manufactured by Celic) is used for the sample after the measurement, and the illuminance is 100,000 Lux (measured by Lux HiTester 3423, manufactured by HIOKI), irradiation time. For 160 hours, total illumination was 16 million Lux.Hr, temperature was 35 ° C., and humidity was 80% RH. Considering the time during which the reversible thermosensitive recording medium is exposed to the sun in actual use, this test was defined as equivalent to 27 days of sunlight in the daytime, and was regarded as a test equivalent to irradiation with sunlight 27 days.
Immediately after the test, a sample was taken out and the density and color (L ^* a ^* b ^* ) of the background portion were measured under the same conditions as before artificial sunlight irradiation. X-Rite 939 (reflective color colorimeter, X-Rite Co., Ltd.) Manufactured).
By the above, regarding the reversible thermosensitive recording media in Examples 1 to 15 and Comparative Examples 1 to 6, the difference in the density of the background portion before and after artificial sunlight irradiation, and before and after artificial sunlight irradiation ΔE indicating the difference in color of the background after solar irradiation was obtained, and ΔE was evaluated according to the following criteria.
In addition, the contrast measurement method and evaluation were performed in the same manner as in the case of sunlight daily irradiation. The results are shown in Table 4, Table 5-1, and Table 5-2.

-Evaluation criteria for color change △ E-
◎: Less than 3.5 ○: 3.5 or more and less than 5.0 Δ: 5.0 or more and less than 7.0 ×: 7.0 or more and less than 12.0 ××: 12.0 or more

<About changes in color relating to sunlight 27-day irradiation equivalent test>
As shown in Table 4 above, it was confirmed that the samples relating to the reversible thermosensitive recording media in Comparative Examples 1 to 6 had higher b ^* values on the + side, as in the sunlight equivalent to 1-day irradiation test. Furthermore, the a ^* value of the background portion is higher on the + side (approximately equivalent to the red color side) than in the sunlight equivalent to one day irradiation test. A brownish discoloration was observed.
This indicates that the background portion is colored by the irradiation of sunlight. The state of this coloring varies depending on the OTR value, and the change becomes larger as the OTR is higher. This is considered to be due to the deterioration of the electron donating color-forming compound of the thermoreversible recording material due to the entry of oxygen or the like.
In particular, the reversible thermosensitive recording medium in Comparative Example 5, which is inferior in gas barrier properties, and the reversible thermosensitive recording medium in Comparative Example 6, which does not have a gas barrier layer, are greatly deteriorated by long-time sunlight irradiation in this test. The color change ΔE at is increased.
On the other hand, the lower the OTR, the smaller the change in the color change a ^* in the background, but the yellow discoloration in the b ^* direction becomes stronger. As a result, the value of ΔE is 11 or more. I'm stuck.
However, in the reversible thermosensitive recording medium in Comparative Example 4 having a low OTR, as shown in Table 1-2 above, yellowish coloring after irradiation with sunlight appears strongly, and the color change becomes large. This is presumed that when the amount of oxygen penetration by the gas barrier layer is low, the dye contained in the reversible thermosensitive recording layer continues to be excited even after irradiation with sunlight and exhibits a colored state.
Further, the reversible thermosensitive recording medium in Comparative Examples 1 to 4 suppresses a change in color in comparison with the reversible thermosensitive recording medium in Comparative Example 5 that is inferior in gas barrier properties and Comparative Example 6 that does not have a gas barrier layer. However, as described above, the color change on the b ^* value side cannot be suppressed, and in addition, the color change on the a ^* value side is suppressed when used for a long period of time. I can't. Here, as described above, the color change on the a ^* value side is considered to be due to the deterioration of the thermoreversible recording material due to the intrusion of oxygen or the like. Did not return to the color.

As shown in Table 4 above, the reversible thermosensitive recording media in Examples 1 to 7 in which the colored layers are arranged on the reversible thermosensitive recording media in Comparative Examples 1 to 3 have a color difference ΔE more than that of Comparative Examples 1 to 3. Both are small and can suppress the color change.
However, in Examples 1 to 7, the color change on the a ^* value side is larger than the color change on the b ^* value side, and the deterioration of the reversible thermosensitive recording medium is assumed when long-term use is assumed. It is considered that the color change on the a ^* value side is influenced by the color change as a whole.
Therefore, from the viewpoint of further extending the life of the reversible thermosensitive recording medium, the reversible feeling in Examples 8 to 15 in which the color is corrected in accordance with the color change on the a ^* side in addition to the color change on the b ^* side. A thermal recording medium was manufactured and the color change was examined.
That is, the reversible thermosensitive recording media in Examples 8 to 10 and 14 are different from the reversible thermosensitive recording media in Examples 2 to 5 in that the colored species 2 is used instead of the colored species 1 and the a ^* value side. It is the 1st color correction example which performed the color correction, and replaces the reversible thermosensitive recording medium in Examples 11-13 with the coloring seed | species 1 with respect to the reversible thermosensitive recording medium in Examples 2-4. It is the 2nd color correction example which performed the color correction of a ^* value side using the coloring seed | species 3, and the reversible thermosensitive recording medium in Example 15 is a reversible thermosensitive recording medium in Example 4. This is a third color correction example in which the color correction on the a ^* value side is performed using the color seed 4 instead of the color seed 1.

Here, the tint correction in Examples 8 to 15 is to correct the a ^* to the + side with respect to the reversible thermosensitive recording media in Examples 1 to 7, and specifically, the corresponding uncorrected The reversible thermosensitive recording medium in the coloring comparative example is corrected for the a ^* value in the color after irradiation with sunlight equivalent to 27 days.
Further, regarding the b ^* value that varies depending on the change of the coloring species that increases a ^* to the + side, sunlight is irradiated to the reversible thermosensitive recording medium in the corresponding uncolored comparative example at the same time for 27 days. The relationship between the b ^* value and the color tone is adjusted. The results are shown in Tables 5-1 and 5-2 below.
In Tables 5-1 and 5-2, a ^* _L0 , a ^* _L1 , a ^* _L2 , a ^* _L3 , b ^* _s0 , b ^* _L1 , b ^* _s2 , and b ^* _L3 indicate the following items. .
That is, a ^* _L0 indicates the a ^* value on the background of the uncolored reversible thermosensitive recording medium before irradiation with sunlight.
a ^* _L1 represents the a ^* value on the background of the uncolored reversible thermosensitive recording medium after irradiation with sunlight for 27 days.
a ^* _L2 indicates the a ^* value on the background of the colored reversible thermosensitive recording medium before irradiation with sunlight.
a ^* _L3 indicates the a ^* value of the background of the colored reversible thermosensitive recording medium after irradiation with sunlight for the 27th day.
b ^* _s0 represents the b ^* value of the background of the uncolored reversible thermosensitive recording medium before irradiation with sunlight.
b ^* _L1 indicates the b ^* value of the background of the uncolored reversible thermosensitive recording medium after irradiation with sunlight for 27 days.
b ^* _s2 represents the b ^* value on the background of the colored reversible thermosensitive recording medium before irradiation with sunlight.
b ^* _L3 indicates the b ^* value of the background of the colored reversible thermosensitive recording medium after irradiation with sunlight for the 27th day.

  Further, in the same manner as the contrast measurement method and evaluation in the sunlight equivalent test, the contrast in the sunlight equivalent test was evaluated. The results are shown in Tables 5-1 and 5-2 below.

As understood from Tables 5-1 and 5-2, the reversible thermosensitive recording media in Examples 8 to 15 subjected to color correction were reversible thermosensitive in Comparative Example 1 having a gas barrier property of OTR = 20. The color change can be further suppressed with respect to the recording medium, and the light resistance of the reversible thermosensitive recording medium in which the color change is a problem can be improved and the life can be further extended. Yes.
Moreover, the extension of the life of the reversible thermosensitive recording media in Examples 8 to 15 showed unexpectedly remarkable results. The reason why such a result was obtained is not necessarily clear, but it is presumed that the colored species used in the colored layer absorbed sunlight and suppressed deterioration in the reversible thermosensitive recording layer. Is done.
In particular, in Examples 8 to 12 in which a ^* _L2− a ^* _L1 is −2 to 16 and b ^* _s2− b ^* _L1 is 18 to 70, the color is good even when used for a long time. The change can be suppressed low, and a high-contrast image can be formed.

From the above results, in a reversible thermosensitive recording medium having a gas barrier layer, by suppressing the coloring change before and after sunlight irradiation by providing effective coloring for the background color development phenomenon caused by sunlight irradiation for one day. Therefore, it is possible to operate a reversible thermosensitive recording medium that does not change color in the process of physical distribution.
Furthermore, after the sunlight is irradiated for a long time, the brown color of the background progresses. By coloring the reversible thermosensitive recording medium in anticipation of the color change and the color development phenomenon of the background caused by the sunlight irradiation for 1 day. It is possible to suppress not only the color change due to the background color development phenomenon but also the color change due to sunlight irradiation for a long time. This makes it possible to operate a reversible thermosensitive recording medium that does not change its color even in the course of physical distribution usage in which sunlight is irradiated for a long time.

(Measurement method of reflectance)
About the reversible thermosensitive recording medium in Examples 1-15 and Comparative Examples 1-6, the reflectance with respect to the light of the wavelength of 660 nm used as a reading wavelength of a barcode reader was measured as follows. The results are shown in Table 6 below.
The reflectance was measured using an X-Rite 939 (reflective color colorimeter, manufactured by X-Rite), displayed in a reflectance mode in which the reflectance for each wavelength can be measured, and the reflectance for a predetermined wavelength was read. .

  As shown in Table 6 above, the reversible thermosensitive recording media in Examples 1 to 15 have a reflectivity with respect to light having a wavelength of 660 nm of more than 80%, so that the barcode can be read when a barcode is printed. An excellent reversible thermosensitive recording medium can be provided.

  FIG. 6 shows the reflectivity of the reversible thermosensitive recording media in Examples 10 and 13 and Comparative Example 1 with respect to light having a wavelength of 400 nm to 700 nm. As shown in FIG. 6, the reversible thermosensitive recording media in Examples 10 and 13 have a reflectance of 600 nm to 700 nm exceeding 80%, and barcode reading using light with a wavelength of 600 nm to 700 nm. Can be carried out effectively.

  The reversible thermosensitive recording medium of the present invention can suppress color change before and after sunlight irradiation. Therefore, the reversible thermosensitive recording medium is particularly suitable for the operation of reversible thermosensitive recording media exposed to sunlight in the process of physical distribution use. It can be used as a recording medium.

DESCRIPTION OF SYMBOLS 1 Support body 2 Undercoat layer 3 Reversible thermosensitive recording layer 4 Intermediate layer 5 Gas barrier layer 6 Colored layer 7 Protective layer 10, 20, 30 Reversible thermosensitive recording medium

JP-A-8-183253 JP-A-8-238844 JP 2009-28911 A

Claims (9)

A reversible thermosensitive recording medium colored with an uncolored reversible thermosensitive recording medium having at least a gas barrier layer and a reversible thermosensitive recording layer,
The gas barrier layer has an oxygen permeability of 50 cc / (m ² · day · atm) or less,
The value of b ^* of the color of the background expressed by L ^* a ^* b ^* after continuously irradiating sunlight with an irradiation amount of 600,000 Lux · Hr to the uncolored reversible thermosensitive recording medium. _Is b ^* _s1 ,
When the b ^* value of the reversible thermosensitive recording medium after the coloring was b ^* _s2,
A reversible thermosensitive recording medium, wherein the difference between b ^* _s2 and b ^* _s1 , b ^* _s2− b ^* _s1, is −2 to 110. The reversible thermosensitive recording medium according to claim 1 having a colored layer which imparts the tint to be b ^* _s2. b ^* _s2 -b ^* _s1 is reversible thermosensitive recording medium according to any one of claims 1 to 2 which is colored so that 10 to 100. Against uncolored reversible thermosensitive recording medium, when the value of ^{a *} when the continuous irradiation with irradiation dose of sunlight 16 million Lux · Hr was ^a _{* L1,} corresponding to the ^a _{* L1} The reversible thermosensitive recording medium according to any one of claims 1 to 3, which is colored with color correction. When the a value in colored reversible thermosensitive recording medium was a ^* _s2, tint as the difference between the a ^* _s2 and _{^{a * L1, a * s2 -a}} * L1 becomes the -2～70 The reversible thermosensitive recording medium according to claim 4, wherein correction is performed. The relative uncolored reversible thermosensitive recording medium, when the value of ^{b *} in the case where the solar light irradiated continuously at dose of 16 million Lux · Hr was ^b _{* L1,} and b ^* _s2 b ^* The reversible thermosensitive recording medium according to any one of claims 4 to 5, wherein the color correction is performed so that a difference from _L1 , b ^* _s2- b ^* _L1, is 10 to 110. The reversible thermosensitive recording medium according to any one of claims 2 to 6, wherein the colored layer has a reflectance of 70% or more with respect to light having a wavelength of 660 nm. A coloring method of a reversible thermosensitive recording medium for coloring an uncolored reversible thermosensitive recording medium having at least a gas barrier layer and a reversible thermosensitive recording layer,
The gas barrier layer has an oxygen permeability of 50 cc / (m ² (Day / atm) or less,
L after continuously irradiating the uncolored reversible thermosensitive recording medium with sunlight at a dose of 600,000 Lux · Hr. ^* a ^* b ^* B of the background color represented by ^* The value of b ^* _s1 age,
B of the reversible thermosensitive recording medium after coloring. ^* The value of b ^* _s2 When
Said b ^* _s2 And b ^* _s1 Difference from b ^* _s2 -B ^* _s1 Is colored so as to be −2 to 110, a coloring method for a reversible thermosensitive recording medium. A when the uncolored reversible thermosensitive recording medium is continuously irradiated with sunlight at a dose of 16 million Lux · Hr. ^* The value of a ^* _L1 When said a ^* _L1 The coloring method for a reversible thermosensitive recording medium according to claim 8, wherein the coloring is performed by correcting the color according to the color.