JP2013103486A - Reversible thermosensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible thermosensitive recording material that has a reversible thermal recording layer wherein the polymer resin used for a base material of the reversible thermal recording layer is useful from the point of protection of global environment where the raw material can be the carbon dioxide, improves the durability of the heat-sensitive recording layer, can control decrease of contrast of a transparent part and an opaque part caused when image forming and erasure are repeated by a heating element, and can continue to form excellent image.SOLUTION: The reversible thermosensitive recording material has, on the base material or at least one surface of the base material, a heat-sensitive recording layer formed with the resin composition that contains the organic low molecular substance dispersed in the polymer resin and the resin as a principal ingredient, and the heat-sensitive recording layer is a reversible thermal recording layer into which the transparency can change reversibly by the temperature. The polymer resin to form the recording layer is the selfcrosslinkable type polyhydroxy polyurethane resin that is induced from the reaction of the five-membered ring cyclic carbonate compound and the amine compound and has the isocyanate group that the masking is done in the structure.

Description

  The present invention makes it possible to repeat recording and erasing of an image by utilizing reversible change in transparency depending on the temperature of the heat-sensitive recording layer, particularly improving the durability of the heat-sensitive recording layer and rewriting the good recording. The present invention relates to a reversible thermosensitive recording material that can be repeatedly processed.

  Magnetic cards and IC cards that can record and store various kinds of information are used in commuter pass tickets for transportation, admission permits to event venues and buildings, and various prepaid cards. However, with these cards, the stored contents cannot be directly viewed, so the payment amount and balance cannot be easily checked, and there is a problem from the viewpoint of clarifying the guarantee of the contents of the stored information for the user. there were. Conventionally, in order to solve such problems, these cards are used as recording media, and visual recording is performed on the cards, the recording is erased, and the recording is rewritten as the stored information is changed. Have been proposed (Patent Documents 1 to 3). For example, in a heat-sensitive recording material, the heat-sensitive recording layer is composed of a reversible heat-sensitive recording paint, so that when the heat is applied from the outside by a thermal head or the like, the heat-sensitive recording layer is transparent according to the temperature. There is a method of changing the light transmittance in the range from the state to the cloudy state, while maintaining the state after cooling. By using such a thermal recording layer, it becomes possible to write characters and images. This technology is extremely useful as a method for making visible records on cards that are based on the premise that the content of stored information will be changed as described above, and displaying the changed content as needed. It is.

  As a typical reversible thermosensitive recording material used in this case, on a base sheet, for example, a polymer resin such as vinyl chloride-vinyl acetate copolymer is used as a base material. In addition, there is a structure having a reversible thermosensitive recording layer formed of a resin composition in which organic low molecular weight substances such as higher fatty acids are dispersed in the form of fine particles. In these reversible thermosensitive recording materials, image formation is performed by making the thermosensitive recording layer transparent or opaque by heating. For example, when a pressure is applied using a thermal head or the like, As the image formation and deletion are repeated, the following problems occur. That is, as the formation and erasure of the image is repeated, the polymer resin that is the base material of the reversible thermosensitive recording layer in which the organic low molecular weight material is dispersed in the form of fine particles is deformed, and the organic material finely dispersed in the layer is deformed. The low molecular substance particles gradually become particles having a larger diameter, and the effect of scattering light is reduced. Eventually, the image and the contrast are lowered, and it becomes impossible to rewrite the characters and the image in a good state. For this reason, the use of various polymer resins has been proposed for the purpose of improving the durability of the base material (see, for example, Patent Documents 4 to 6).

  Furthermore, recently, due to increasing environmental problems, many manufacturers are actively engaged in environmental measures, and there is a movement to construct products using materials with excellent environmental conservation. The above-mentioned reversible thermosensitive recording material is no exception, and it is possible to rewrite a disposable object as many times as possible, especially against the backdrop of garbage problems and forest destruction problems. Attention has been paid to helping to solve environmental problems (eco), and it has been actively studied and partly put into practical use. However, most of the conventional reversible thermosensitive recording materials are made of petroleum-derived materials, and from the original point of view, the current environmental conservation on a global scale is still insufficient.

  As can be seen in Non-Patent Documents 1 and 2, polyhydroxypolyurethane resins using carbon dioxide as a raw material, which are useful in the above-mentioned points, have been known for a long time, but the actual situation is that their application development has not progressed. is there. This is because the above-mentioned resins that have been conventionally known are clearly inferior in terms of characteristics as compared with conventional polyurethane-based resins that are the same type of high molecular compound (petrolithic plastic) (Patent Documents 7 and 8).

  On the other hand, the global warming phenomenon, which is thought to be caused by the ever-increasing carbon dioxide emissions, has become a global problem in recent years, and the reduction of carbon dioxide emissions is a globally important issue. There is a long-awaited technology that can use carbon dioxide as a raw material for production. Furthermore, from the viewpoint of exhaustible petrochemical resources (petroleum), the shift to renewable resources such as biomass and methane has become a global trend.

  Against the background as described above, the polyhydroxy polyurethane resin has been reviewed again. In other words, carbon dioxide, which is the raw material for this resin, is a readily available and sustainable carbon resource, and plastics that use carbon dioxide as a raw material solve problems such as global warming and resource depletion. It is because it can be said that it is an effective means.

JP-A 63-139784 Japanese Patent Publication No. 01-30638 Japanese Patent Application Laid-Open No. 07-25146 Japanese Patent Laid-Open No. 04-189176 JP 05-85047 A JP 07-125450 A U.S. Pat. No. 3,072,613 JP 2000-319504 A

N. Kihara, T. Endo, J. Org. Chem., 1993, 58, 6198 N. Kihara, T. Endo, J. Polymer Sci., Part A Polmer Chem., 1993, 31 (11), 2765

  Under the circumstances described above, the durability of the polymer resin used for the base material of the reversible thermosensitive recording layer constituting the reversible thermosensitive recording material is improved, and heat and pressure are applied by a heating element such as a thermal head. This is an environmentally friendly product that can form a good image with excellent contrast between the transparent and opaque areas of the image, even when the image is formed and erased many times. Development of a certain reversible thermosensitive recording material is desired.

  Therefore, the object of the present invention is to improve the durability of the polymer resin used for the base material of the reversible thermosensitive recording layer and to generate transparency when the image formation and erasure are repeated by a heating element such as a thermal head. It is an object of the present invention to provide a reversible thermosensitive recording material having a reversible thermosensitive recording layer that can suppress a decrease in contrast between a portion and an opaque portion and can continuously form a good image. Furthermore, an object of the present invention is to develop a technology that can provide a product that is environmentally friendly from the viewpoint of global environmental protection, in which the polymer resin that is the base material of the reversible thermosensitive recording layer can use carbon dioxide as a raw material. It is in.

  The above object is achieved by the present invention described below. That is, the present invention relates to a thermal recording formed by a resin composition comprising, as a main component, a polymer resin and an organic low-molecular substance dispersed in the polymer resin on at least one surface of the substrate. A thermosensitive recording material comprising a layer, wherein the thermosensitive recording layer is a reversible thermosensitive recording layer whose transparency can be reversibly changed with temperature, and a polymer resin for forming the recording layer comprises: Provided is a reversible thermosensitive recording material which is a self-crosslinking polyhydroxy polyurethane resin having an isocyanate group masked in its structure, which is derived from a reaction between a 5-membered cyclic carbonate compound and an amine compound. .

Preferred embodiments of the present invention include the following.
A reversible thermosensitive recording material, wherein the five-membered cyclic carbonate compound is a reaction product of an epoxy compound and carbon dioxide, and the structure contains carbon dioxide in the range of 1 to 25% by mass.
The masked isocyanate group is a reaction product of an organic polyisocyanate group and a masking agent, and the masked portion is dissociated by heat treatment to form an isocyanate group, which reacts with a hydroxyl group in the structure. Reversible thermosensitive recording material that self-crosslinks.
A reversible thermosensitive recording material, wherein the self-crosslinking polyhydroxypolyurethane resin is obtained by modifying a polyhydroxypolyurethane resin derived from a reaction between a 5-membered cyclic carbonate compound and an amine compound with a modifier.

  According to the present invention, by using a specific polymer resin as a base material of the reversible thermosensitive recording layer, durability when heating and pressure such as a thermal head or a thermal roll are repeatedly applied can be improved. Thus, even when image formation and erasure are repeated many times, there is provided a reversible thermosensitive recording material capable of good image formation in which a decrease in contrast between a transparent portion and an opaque portion is suppressed. In the reversible thermosensitive recording material provided by the present invention, since the resin used as the base material of the reversible thermosensitive recording layer is carbon dioxide as a raw material and carbon dioxide can be incorporated into the resin, From the viewpoint of maintenance, there is another effect that it is possible to provide a useful material and an environmentally-friendly product using the material.

Next, the present invention will be described in more detail with reference to preferred embodiments.
The reversible thermosensitive recording material of the present invention is provided with a thermosensitive recording layer whose transparency can be reversibly changed with temperature on at least one surface of a substrate. It is formed of a resin composition containing, as a main component, an organic low molecular weight substance dispersed in the polymer resin as a main component. In the present invention, a self-crosslinked polyhydroxypolyurethane resin having an isocyanate group masked in its structure, which is derived from a reaction between a 5-membered cyclic carbonate compound and an amine compound, is used as the base material. It is characterized by that. Hereinafter, these materials will be described.

  The self-crosslinking polyhydroxypolyurethane resin used for the base material of the heat-sensitive recording layer in the present invention is a reaction product of at least one unmasked free isocyanate group, which is a reaction product of an organic polyisocyanate compound and a masking agent. It can be easily obtained by reacting with a hydroxyl group in a polyhydroxypolyurethane resin derived from a reaction between a 5-membered cyclic carbonate compound and an amine compound.

  The masked isocyanate group of the self-crosslinking polyhydroxypolyurethane resin used in the present invention is the one in which the masking agent reacts with the isocyanate group of the organic polyisocyanate compound. As a result, an isocyanate group is formed. And this produced | generated isocyanate group will react with the hydroxyl group in the structure of a self-crosslinking type polyhydroxy polyurethane resin, and will self-crosslink. For this reason, in the reversible thermosensitive recording material of the present invention using the above-described resin as a base material of the thermosensitive recording layer, when heating and pressure are applied by a thermal head or a hot roll or the like for image formation and erasure. However, the durability of repetition is improved, and the reversible thermosensitive recording layer can form a good image in which a decrease in contrast between the transparent portion and the opaque portion is suppressed even after the durability.

  Furthermore, the self-crosslinking polyhydroxypolyurethane resin used in the present invention is a resin derived from a reaction between a 5-membered cyclic carbonate compound and an amine compound, and the 5-membered cyclic carbonate compound comprises an epoxy compound and carbon dioxide. Since it can be obtained by reacting, the material is excellent in environmental conservation.

[Base material of reversible thermosensitive recording layer]
In the present invention, as described above, the self-crosslinking polyhydroxypolyurethane resin used as the base material of the reversible thermosensitive recording layer uses a modifier having a free isocyanate group and a masked isocyanate group. It is obtained by reacting an isocyanate group with a hydroxyl group in the polyhydroxypolyurethane resin. What is necessary is just to use the reaction product of an organic polyisocyanate compound and a masking agent as a modifier used above. Below, each component is demonstrated.

(Modifier)
<Organic polyisocyanate compound>
As a modifier used in the present invention, a reaction product of an organic polyisocyanate compound and a masking agent is used. First, components constituting the modifier will be described. The organic polyisocyanate compound that can be used in the present invention is an organic compound having at least two isocyanate groups in an aliphatic or aromatic compound, and is conventionally widely used as a raw material for the synthesis of polyurethane resins. . In the present invention, any of these known organic polyisocyanate compounds can be used. Particularly preferable organic polyisocyanate compounds are as follows.

  For example, 1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate), 4,4′- Examples include dicyclohexylmethane diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, tolidine diisocyanate, and xylylene diisocyanate. Furthermore, adducts of these organic polyisocyanate compounds and other compounds, for example, those having the following structural formula can be suitably used, but are not limited thereto.

<Masking agent>
The modifying agent used in the present invention is a reaction product of the organic polyisocyanate compound and the masking agent as described above. As the masking agent, alcohol-based, phenol-based, active methylene-based, acid amide-based, imidazole-based In the present invention, these may be used alone or in combination. Specific masking agents that can be used in the present invention include the following.

  Examples of alcohol-based modifiers include methanol, ethanol, propanol, butanol, 2-ethylhexanol, methyl cellosolve, and cyclohexanol. Examples of phenol-based modifiers include phenol, cresol, ethylphenol, and nonylphenol. . Active methylene-based modifiers include dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone and the like, and acid amide-based modifiers include acetanilide, acetate amide, caprolactam, γ-butyrolactam and the like. Examples of imidazole-based modifiers include imidazole and 2-methylimidazole. Urea-based modifiers include urea, thiourea, ethyleneurea, etc., oxime-based modifiers include formamide oxime, acetoxime, methyl ethyl ketoxime, cyclohexanone oxime, etc., and pyridine-based modifiers include Examples include 2-hydroxypyridine and 2-hydroxyquinoline.

<Synthesis of modifier>
By reacting an organic polyisocyanate compound and a masking agent as listed above, a modifier having at least one free isocyanate group and the other having a masked isocyanate group is synthesized in the present invention. To do. The specific synthesis method is not particularly limited. For example, the masking agent as described above and the organic polyisocyanate compound are present in an organic solvent and a catalyst at a functional group ratio in which one or more isocyanate groups are excessive in one molecule. The modifier used in the present invention can be easily obtained by reacting at a temperature of 0 to 150 ° C., preferably 20 to 80 ° C. for 30 minutes to 3 hours in the absence or absence.

(Polyhydroxy polyurethane resin)
In the present invention, a self-crosslinked polyhydroxypolyurethane resin obtained by modifying a polyhydroxypolyurethane resin with a specific modifier as described above is used. The polyhydroxypolyurethane resin used in this case is, for example, a 5-membered cyclic carbonate. It can be easily obtained by reacting a compound with an amine compound. Below, each component used in this case is demonstrated.

<5-membered cyclic carbonate compound>
The 5-membered cyclic carbonate compound used in the present invention can be produced by reacting an epoxy compound and carbon dioxide as shown by the following [Formula-A]. More specifically, the epoxy compound is reacted with carbon dioxide in the presence or absence of an organic solvent and in the presence of a catalyst at a temperature of 40 ° C. to 150 ° C. for 10 to 20 hours at normal pressure or slightly increased pressure. Can be obtained.

  As an epoxy compound used above, the following compounds are mentioned, for example.

  The epoxy compounds listed above are preferable compounds used in the present invention, and the present invention is not limited to these exemplified compounds. Accordingly, not only the compounds exemplified above, but also any other compounds that are currently commercially available and can be easily obtained from the market can be used in the present invention.

Examples of the catalyst used in the reaction of the epoxy compound and carbon dioxide as described above include a base catalyst and a Lewis acid catalyst.
Base catalysts include tertiary amines such as triethylamine and tributylamine, cyclic amines such as diazabicycloundecene, diazabicyclooctane and pyridine, alkali metals such as lithium chloride, lithium bromide, lithium fluoride and sodium chloride Salts, alkaline earth metal salts such as calcium chloride, quaternary ammonium salts such as tetrabutylammonium chloride, tetraethylammonium bromide, benzyltrimethylammonium chloride, carbonates such as potassium carbonate and sodium carbonate, zinc acetate, lead acetate, copper acetate And metal acetates such as iron acetate, metal oxides such as calcium oxide, magnesium oxide and zinc oxide, and phosphonium salts such as tetrabutylphosphonium chloride.

  Examples of the Lewis acid catalyst include tin compounds such as tetrabutyltin, dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin octoate.

  The amount of the catalyst may be 0.1 to 100 parts by mass, preferably 0.3 to 20 parts by mass, per 50 parts by mass of the epoxy compound. If the amount used is less than 0.1 parts by mass, the effect as a catalyst is small, and if it exceeds 100 parts by mass, various performances of the final resin may be deteriorated. However, in the case where the residual catalyst causes a serious performance deterioration, it may be configured to be removed by washing with pure water.

  Examples of the organic solvent that can be used in the reaction between the epoxy compound and carbon dioxide include dimethylformamide, dimethyl sulfoxide, dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, and tetrahydrofuran. These organic solvents and other poor solvents such as methyl ethyl ketone, xylene, toluene, tetrahydrofuran, diethyl ether, and cyclohexanone may be used in a mixed system.

In the present invention, the polyhydroxypolyurethane resin used is, as shown by the following [Formula-B], a 5-membered cyclic carbonate compound obtained as described above and an amine compound in the presence of an organic solvent. It can obtain by making it react at the temperature of 20 to 150 degreeC.

<Amine compound>
As an amine compound used for the said reaction, a diamine is preferable and what was conventionally used for manufacture of a polyurethane resin can be used, and it is not specifically limited. For example, aliphatic diamines such as methylenediamine, ethylenediamine, trimethylenediamine, 1,3-diaminopropane, hexamethylenediamine, octamethylenediamine; phenylenediamine, 3,3′-dichloro-4,4′-diaminodiphenylmethane, 4 , 4′-methylenebis (phenylamine), 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfone, metaxylylenediamine, paraxylylenediamine, and the like; 1,4-cyclohexanediamine, 4 Alicyclic diamines such as 1,4'-diaminocyclohexylmethane, 1,4'-diaminomethylcyclohexane and isophoronediamine; alkanol dimers such as monoethanoldiamine, ethylaminoethanolamine and hydroxyethylaminopropylamine Examples include amines. In addition, any amine compound that is currently commercially available and can be easily obtained from the market can be used in the present invention.

(Self-crosslinking type polyhydroxy polyurethane resin)
<Synthesis method>
The self-crosslinking polyhydroxypolyurethane resin used in the present invention can be obtained by reacting the modifier and the polyhydroxypolyurethane resin as described above. Specifically, it is obtained by reacting a hydroxyl group in the polyhydroxy polyurethane resin with at least one free isocyanate group in the modifier.

The modification rate of the self-crosslinking polyhydroxypolyurethane resin used in the present invention with the modifier is preferably 2 to 60%. If the modification rate is less than 2%, durability or contrast due to sufficient crosslinking may be deteriorated, which is not preferable. On the other hand, if it exceeds 60%, the possibility that the dissociated isocyanate group remains without reacting is not preferable. The modification rate is calculated as follows.
Modification rate (%) = {1− (hydroxyl group of resin after modification ÷ hydroxyl group of resin before modification)} × 100

  The reaction between the modifier and the polyhydroxypolyurethane resin is preferably carried out in the presence or absence of an organic solvent and a catalyst at a temperature of 0 to 150 ° C., preferably 20 to 80 ° C., for 30 minutes to 3 hours. Thus, a self-crosslinking type polyhydroxy polyurethane resin suitable for the present invention can be easily obtained. However, it should be noted that the reaction is carried out at a temperature lower than the dissociation temperature of the masking agent during the reaction, and the synthesized self-crosslinking polyhydroxypolyurethane resin must have an isocyanate group masked in its structure. Don't be.

<Physical properties>
The self-crosslinking polyhydroxypolyurethane resin used in the present invention that can be obtained as described above has a number average molecular weight (standard polystyrene equivalent value measured by GPC) of about 2,000 to 100,000. Is preferred. More preferably, it is 5,000-70,000.

  The hydroxyl group content of the self-crosslinking polyhydroxy polyurethane resin used in the present invention is preferably a hydroxyl value of 20 to 300 mgKOH / g. When the hydroxyl group content is less than the above range, the effect of reducing carbon dioxide is insufficient. On the other hand, when the hydroxyl group content exceeds the above range, various physical properties as a polymer compound are insufficient.

(Other binder resins)
In forming the reversible thermosensitive recording layer characterizing the present invention, it is necessary to use the above-mentioned self-crosslinking polyhydroxypolyurethane resin as a base material. As the resin composition used in the formation, In addition to these, other binder resins may be used. That is, in the resin composition for forming the heat-sensitive recording layer for the purpose of coating appropriateness to the base material for forming the heat-sensitive recording layer, improvement in film formability, and adjustment of contrast, various conventionally known binder resins are used. May be used in combination. The other resin used for mixing is preferably one that can chemically react with the polyisocyanate group formed by dissociation of the masking agent in the self-crosslinking polyhydroxypolyurethane resin essential in the present invention. However, the present invention is not limited to this, and even a resin having no reactivity can be used in combination with the above-described self-crosslinking polyhydroxypolyurethane resin as appropriate according to the purpose.

  As other binder resins that can be used in combination with the self-crosslinking type polyhydroxypolyurethane resin, various conventionally used resins can be used and are not particularly limited. For example, chlorination of polyvinyl chloride, polyvinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer, etc. Vinyl copolymers, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride copolymers such as vinylidene chloride-acrylonitrile copolymers, polyesters, polyamides, polyacrylates or polymethacrylates or acrylate-methacrylate copolymers Examples include coalescence. These may be used alone or in combination of two or more.

[Low molecular weight organic substance dispersed in the base material of the reversible thermosensitive recording layer]
The reversible thermosensitive recording layer characterizing the reversible thermosensitive recording material of the present invention comprises a polymer resin containing the above-mentioned self-crosslinking polyhydroxypolyurethane resin as a base material, and an organic low molecular weight substance is dispersed in the base material. Become. That is, the organic low molecular weight substance exists in a state of being dispersed in the form of particles in a base material mainly composed of a self-crosslinking type polyhydroxypolyurethane resin, and the particle size thereof is in the range of about 0.1 to 2 μm. It is preferable that they are distributed. The organic low molecular weight substance used in the present invention is generally called a wax or wax, and is a compound containing a long chain alkyl group having about 10 to 60 carbon atoms that is solid at room temperature, Fatty acids composed of chain alkyl groups, alcohols, esters, amides, ketones, ethers, thioethers or amines are preferred.

  More specifically, lauric acid, dodecanoic acid, myristic acid, palmitic acid, pentadecanoic acid, stearic acid, arachidic acid, behenic acid, heneicosanoic acid, tricosanoic acid, glinoceric acid, pentacosanoic acid, serotic acid, heptacosanoic acid, montanic acid Higher fatty acid compounds such as mellicic acid, nonadecanoic acid and oleic acid; higher alcohol compounds such as stearyl alcohol, behenyl alcohol and C30 alcohol; octadecyl laurate, tetradecyl palmitate, dodecyl behenate, methyl stearate, tetradecyl stearate, Octadecyl stearate, stearyl stearate, behenyl stearate, behenyl behenate, behenyl montanate, stearic acid C30 alcohol ester, behenic acid C30 alcohol ester Higher fatty acid ester compounds such as telluric acid amide; stearic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, N-stearyl stearic acid amide, N-oleyl palmitic acid amide, N-stearyl erucic acid amide, N-stearyl olein Amide compounds such as acid amides; ketone compounds such as distearyl ketone and dibehenyl ketone can be used, and these can be used.

Furthermore, the following higher aliphatic ethers, higher aliphatic thioethers, higher aliphatic amines, and the like are exemplified, but the present invention is not limited thereto.
For example, C ₁₆ H ₃₃ —O—C ₁₆ H ₃₃ ,
_{C 16 H 33 -S-C 16} H 33, C 18 H 37 -S-C 18 H 37, C 12 H 25 -S-C 12 H 25, C 19 H 39 -S-C 19 H 39,
_{C 12 H 25 -S-S-} C 12 H 25,
_{C 11 H 23 -OCO-CH 2} CH 2 -O-CH 2 CH 2 -OCO-C 11 H 23,
_{C 17 H 35 -OCO-CH 2} CH 2 -O-CH 2 CH 2 -OCO-C 17 H 35,
_{C 12 H 25 -OCO-CH 2} CH 2 -S-CH 2 CH 2 -OCO-C 12 H 25,
_{C 18 H 37 -OCO-CH 2} CH 2 -S-CH 2 CH 2 -OCO-C 18 H 37,
_{C 18 H 37 -OCO-CH 2} CH 2 -NH-CH 2 CH 2 -OCO-C 18 H 37 and the like. These long-chain alkyl group-containing compounds may be used singly or in combination of two or more.

  In addition, organic low-molecular substances (hereinafter referred to as low-melting-point organic low-molecular substances) as mentioned above, organic low-molecular substances with higher melting points (hereinafter referred to as high-melting-point organic low-molecular substances) It is also effective to add a substance). That is, in this way, the temperature range for transparency can be expanded. As the high melting point organic low molecular weight substance used in this case, a substance having a melting point of 80 ° C. to 180 ° C. is preferable, and saturated aliphatic bisamide and saturated aliphatic dicarboxylic acid having a melting point in the range of 90 ° C. to 160 ° C. are particularly preferable. . Specific examples include those listed below.

  For example, saturated aliphatic bisamides include ethylene bis stearamide, ethylene bis behenamide, hexamethylene bis behenamide, hexamethylene bis behenamide, N, N-distearyl adipate amide, N, N-diamide. Examples include stearyl eicosane diamide, N, N-distearyl sebacic diamide, N, N-dilauryl decanedioic acid amide, N, N-distearyl dodecanedioic acid amide, and the like.

  Examples of saturated aliphatic dicarboxylic acids include adipic acid, pyrophosphoric acid, suberic acid, azelaic acid, sebacic acid, undecanediic acid, dodecanediic acid, tridecanediic acid, tetradecanediic acid, pentadecanediic acid, hexadecanediic acid, peptadecanediic acid, octadecane Examples include diacid, nonadecanedioic acid, and eicosandioic acid.

  However, the present invention is not limited to these, and other high-melting-point organic low-molecular substances such as bisamides, dicarboxylic acids, saturated fatty acid monoamides, methylolic acid amides, unsaturated fatty acid bisamides, and aromatic bisamides other than those described above can also be used. . Further, these high melting point organic low molecular weight substances may be used alone or in combination of two or more.

  When the low melting point organic low molecular weight substance and the high melting point organic low molecular weight substance are used as the organic low molecular weight substance, the blending ratio is preferably in the range of 99: 1 to 45:55 by mass ratio. Outside this range, not only the effect of expanding the transparent temperature range is not obtained, but also the contrast between the transparent state and the white turbid state may be insufficient, which is not preferable.

  Further, the ratio of the organic low molecular weight substance and the polymer resin in the heat-sensitive recording layer is preferably 1: 1 to 1:10 by mass ratio. If the ratio of the polymer resin is less than this, it becomes difficult to form a film as a heat-sensitive recording layer, and if it is more than this, the contrast when opaque (white turbid state) is reduced due to the small amount of organic low-molecular substances. This is not preferable.

[Other additives]
Furthermore, the reversible thermosensitive recording layer made of the materials as described above is blended with a lubricant, an antistatic agent, a plasticizer, a dispersant, a stabilizer, a surfactant, an inorganic or organic filler, if necessary. May be.

[Thickness of reversible thermosensitive recording layer]
The film thickness of the reversible thermosensitive recording layer is usually 1 to 40 μm, preferably 2 to 20 μm. If the heat-sensitive recording layer is too thick, heat distribution in the layer occurs, which is not preferable. On the other hand, if the thermosensitive recording layer is thinner than this, the white turbidity is lowered and the contrast is lowered, which is not preferable.

[Middle layer]
The reversible thermosensitive recording material of the present invention can be provided with various intermediate layers as required. The intermediate layer may be a single layer or a combination of multiple layers, and can be appropriately provided as necessary within the scope of the effect of the present invention. Various functional layers such as a printed layer, a colored layer, and a heat-resistant protective layer can be provided. Conventionally known materials can be used for the printing layer and the colored layer in this case, and as a material used for the heat-resistant protective layer, silicone resin, acrylic resin, alkyd resin, UV curable resin, and EB curable resin are used. .

[Other layers]
Furthermore, if it is within the range of the effect of the present invention, the magnetic recording layer for recording information and the contrast between the transparent state and the white turbid state of the thermal recording layer are improved between the substrate and the thermal recording layer. Therefore, a reflective layer such as metal vapor deposition can be provided on the substrate. Furthermore, an adhesive layer that enhances the adhesion of the substrate, the heat-sensitive recording layer, and various intermediate layers can be provided. The uppermost layer is preferably provided with a slipping protective layer for the purpose of preventing surface scratches and head wrinkle adhesion due to the thermal head.

[Base material]
As the base material constituting the reversible thermosensitive recording material of the present invention, plastic films, glass plates, metal plates, paper, and the like can be used, and various thicknesses are possible. Further, those provided with a colored coating layer on the front or back surface thereof, a plastic film kneaded with a colored pigment, or the like can be used. Further, a plastic film provided with a reflective layer such as metal vapor deposition can be used.

  The reversible thermosensitive recording material of the present invention uses a specific self-crosslinking polyhydroxypolyurethane resin as a polymer resin that serves as a base material for a reversible thermosensitive recording layer provided on at least one surface of a substrate. Its durability has been improved, and the decrease in contrast between the transparent part and the opaque part, which has occurred when image formation and erasure are repeated by applying heat with a heating element such as a thermal head, etc., has been continuously improved. Formation is possible. Moreover, since the 5-membered cyclic carbonate compound constituting the resin used in the present invention can use carbon dioxide as a production raw material, carbon dioxide can be incorporated into the resin. For this reason, the reversible thermosensitive recording material of the present invention can contribute to the reduction of carbon dioxide, and it is possible to provide an environmentally friendly product that is useful from the viewpoint of global environmental conservation.

  Next, the present invention will be described in more detail with reference to specific production examples, examples and comparative examples, but the present invention is not limited to these examples. In the following examples, “part” and “%” are based on mass unless otherwise specified. The infrared absorption spectrum was measured with an infrared spectroscopic analyzer FT-720 (manufactured by Horiba Seisakusho).

<Production Example 1> (Production of modifier)
Trimethylolpropane and hexamethylene diisocyanate trimer adduct [Coronate HL (trade name), manufactured by Nippon Polyurethane Co., Ltd., NCO = 12.9%, solid content 75%] 100 parts, 24.5 parts of ethyl acetate at 100 ° C. While stirring well, 25.5 parts of ε-caprolactam was added and allowed to react for 5 hours. According to the infrared absorption spectrum of the obtained modifier, absorption due to free isocyanate groups remained at 2,270 cm ⁻¹ . Further, when this free isocyanate group was quantified, the theoretical value was 2.1% at a solid content of 50%, whereas the measured value was 1.8%.

The main structure of the modifier synthesized above is presumed as follows.

<Production Example 2> (Production of modifier)
Hexamethylene diisocyanate and water adduct [Duranate 24A-100 (trade name), manufactured by Asahi Kasei Co., Ltd., NCO = 23.0%] 100 parts and 132 parts of ethyl acetate were stirred well at 80 ° C., and 32 parts of methyl ethyl ketoxime was added. Added and allowed to react for 5 hours. According to the infrared absorption spectrum of the resulting modifier, absorption due to free isocyanate groups remained at 2,270 cm ⁻¹ . When this free isocyanate group was quantified, the theoretical value was 2.9% at a solid content of 50%, whereas the measured value was 2.6%.

The main structure of the modifier synthesized above is presumed as follows.

<Production Example 3> (Production of modifier)
Trimethylolpropane and tolylene diisocyanate trimer adduct [Coronate L (trade name), manufactured by Nippon Polyurethane Co., Ltd., NCO = 12.5%, solid content 75%] 100 parts, ethyl acetate 67.3 parts at 80 ° C. While stirring well, 17.3 parts of methyl ethyl ketoxime was added and allowed to react for 5 hours. According to the infrared absorption spectrum of the resulting modifier, absorption due to free isocyanate groups remained at 2,270 cm ⁻¹ . When this free isocyanate group was quantified, the theoretical value was 2.3% at a solid content of 50%, whereas the measured value was 2.0%.

The main structure of the modifier synthesized above is presumed as follows.

<Production Example 4> (Production of 5-membered cyclic carbonate compound)
In a reaction vessel equipped with a stirrer, a thermometer, a gas introduction tube and a reflux condenser, a divalent epoxy compound represented by the following formula A [Epicoat 828 (trade name), manufactured by Japan Epoxy Resins Co., Ltd., epoxy equivalent 187 g / mol], 100 parts, 100 parts of N-methylpyrrolidone and 1.5 parts of sodium iodide were added and dissolved uniformly.

  Thereafter, the mixture was heated and stirred at 80 ° C. for 30 hours while bubbling carbon dioxide at a rate of 0.5 liter / min. After completion of the reaction, the obtained solution was gradually added to 300 parts of n-hexane with high-speed stirring at 300 rpm, and the resulting powdery product was filtered with a filter, further washed with methanol, N-methylpyrrolidone and Sodium iodide was removed. The powder was dried in a drier to obtain 118 parts (yield 95%) of a white powder 5-membered cyclic carbonate compound (1-A).

In the infrared absorption spectrum of the obtained product (1-A), a peak derived from an epoxy group in the vicinity of 910 cm ⁻¹ almost disappears in the product, and the cyclic carbonate does not exist in the raw material in the vicinity of 1,800 cm ^−1. Absorption of the carbonyl group of the group was confirmed. Moreover, the number average molecular weight of the product was 414 (polystyrene conversion, Tosoh; GPC-8220). In the obtained 5-membered cyclic carbonate compound (1-A), 19% of carbon dioxide was immobilized.

<Production Example 5> (Production of 5-membered cyclic carbonate compound)
Instead of the divalent epoxy compound A used in Production Example 4, a divalent epoxy compound represented by the following formula B [YDF-170 (trade name), manufactured by Toto Kasei Co., Ltd., epoxy equivalent 172 g / mol] The reaction was carried out in the same manner as in Production Example 4 to obtain 121 parts (yield 96%) of a 5-membered cyclic carbonate compound (1-B) as a white powder.

生成物は、製造例４と同様に、赤外吸収スペクトル、ＧＰＣ、ＮＭＲで確認した。得られた５員環環状カーボネート化合物（１−Ｂ）中には、２０．３％の二酸化炭素が固定化されていた。

The product was confirmed by infrared absorption spectrum, GPC and NMR as in Production Example 4. In the obtained 5-membered cyclic carbonate compound (1-B), 20.3% of carbon dioxide was immobilized.

<Polymerization Example 1> (Production of self-crosslinking type polyhydroxy polyurethane resin)
A reaction vessel equipped with a stirrer, a thermometer, a gas introduction tube and a reflux condenser was replaced with nitrogen, and 100 parts of the 5-membered cyclic carbonate compound (1-A) obtained in Production Example 4 was added to the reactor. N-methylpyrrolidone was added to a concentration of 35% and dissolved uniformly. Next, 27.1 parts of hexamethylenediamine was added, and the mixture was stirred at a temperature of 90 ° C. for 10 hours, and reacted until no hexamethylenediamine could be confirmed. Next, 20 parts of the modifier (solid content 50%) obtained in Production Example 1 was added and reacted at 90 ° C. for 3 hours. After confirming that the absorption of the isocyanate group by the infrared absorption spectrum disappeared, a self-crosslinking polyhydroxy polyurethane resin solution was obtained.

<Polymerization Examples 2 to 4> (Production of self-crosslinking type polyhydroxy polyurethane resin)
Hereinafter, as described in Table 1, a 5-membered cyclic carbonate compound, a polyamine compound, and a modifier are combined and reacted in the same manner as in Polymerization Example 1, and then self-crosslinking polyhydroxypolyurethane resins of Polymerization Examples 2 to 4 are used. A solution was obtained. Table 1 shows the physical properties of the obtained resin.

<Comparative resin example 1> (Production of polyester polyurethane resin)
The polyester polyurethane resin used in the comparative example was synthesized as follows. A reaction vessel equipped with a stirrer, a thermometer, a gas introduction tube and a reflux condenser was replaced with nitrogen, and 150 parts of polybutylene adipate having an average molecular weight of about 2,000 and 15 parts of 1,4-butanediol were 200 parts. In a mixed organic solvent consisting of 50 parts of dimethylformamide. Thereafter, 62 parts of water-added MDI (methylenebis (1,4-cyclohexane) -diisocyanate) dissolved in 171 parts of dimethylformamide was gradually added dropwise while stirring well at 60 ° C. For 6 hours. This solution had a solid content of 35% and a viscosity of 3.2 MPa · s (25 ° C.).

<Comparative resin example 2>
35 parts of vinyl chloride-vinyl acetate copolymer (manufactured by Nissin Chemical) was dissolved in 65 parts of tetrahydrofuran to obtain a resin solution having a solid content of 35%.

<Comparative resin example 3>
35 parts of chlorinated polyolefin resin (manufactured by Nippon Paper Chemicals) was dissolved in 70 parts of tetrahydrofuran to obtain a resin solution having a solid content of 35%.

<Example 1>
Using each of the resins obtained in the above polymerization examples, a heat-sensitive recording layer, a heat-resistant protective layer (intermediate layer), and a slippery protective layer were formed in this order on the substrate by the following method. An example reversible thermosensitive recording material was prepared. In addition, as a base material, the metal reflective base material which formed the 0.1 micrometer-thick aluminum layer by the vacuum evaporation method on the 188 micrometer polyethylene terephthalate film was used.

[Formation of thermal recording layer]
A solution having the following composition was prepared using the self-crosslinking polyhydroxy polyurethane resin obtained in Polymerization Example 1 as a base material. Then, the prepared solution was applied onto the above-described metal reflective substrate using a wire bar, and then heated and dried at 140 ° C. for 4 minutes to form a thermosensitive recording layer having a thickness of 12 μm. The heat-sensitive recording layer could reversibly change the transparency that became transparent in the temperature range of 75 to 108 ° C.

(Thermosensitive recording layer coating composition; clearing temperature range 75 to 108 ° C.)
Resin obtained in Polymerization Example 1 (solid content 35%) 100 parts Stearic acid 10 parts Eicosane diacid 4 parts Di-2-ethylhexyl phthalate 2 parts Tetrahydrofuran 170 parts

<Example 2>
A thermosensitive recording layer was formed on a metal reflective substrate in the same manner as in Example 1 except that a solution having the following composition was prepared and used. The transparent temperature range of the thermosensitive recording layer is the same as in Example 1.
Resin obtained in Polymerization Example 2 (solid content 35%) 100 parts Stearic acid 10 parts Eicosane diacid 4 parts Di-2-ethylhexyl phthalate 2 parts Tetrahydrofuran 170 parts

<Example 3>
A thermosensitive recording layer was formed on a metal reflective substrate in the same manner as in Example 1 except that a solution having the following composition was prepared and used. The transparent temperature range of the thermosensitive recording layer is the same as in Example 1.
Resin obtained in Polymerization Example 3 (solid content 35%) 100 parts Stearic acid 10 parts Eicosane diacid 4 parts Di-2-ethylhexyl phthalate 2 parts Tetrahydrofuran 170 parts

<Example 4>
A thermosensitive recording layer was formed on a metal reflective substrate in the same manner as in Example 1 except that a solution having the following composition was prepared and used. The transparent temperature range of the thermosensitive recording layer is the same as in Example 1.
Resin obtained in Polymerization Example 4 (solid content 35%) 100 parts Stearic acid 10 parts Eicosane diacid 4 parts Di-2-ethylhexyl phthalate 2 parts Tetrahydrofuran 170 parts

<Comparative Example 1>
A thermosensitive recording layer was formed on a metal reflective substrate in the same manner as in Example 1 except that a solution having the following composition was prepared and used.
Resin obtained in Comparative Resin Example 1 (solid content 35%) 100 parts Stearic acid 10 parts Eicosane diacid 4 parts Di-2-ethylhexyl phthalate 2 parts Polyisocyanate (Nippon Polyurethane, Coronate HL) 5 parts Tetrahydrofuran 180 parts

<Comparative example 2>
A thermosensitive recording layer was formed on a metal reflective substrate in the same manner as in Example 1 except that a solution having the following composition was prepared and used.
Resin obtained in Comparative Resin Example 2 (solid content 35%) 100 parts Stearic acid 10 parts Eicosane diacid 4 parts Di-2-ethylhexyl phthalate 2 parts Polyisocyanate (Nippon Polyurethane, Coronate HL) 5 parts Tetrahydrofuran 180 parts

<Comparative Example 3>
A thermosensitive recording layer was formed on a metal reflective substrate in the same manner as in Example 1 except that a solution having the following composition was prepared and used.
Resin obtained in Comparative Resin Example 3 (solid content 35%) 100 parts Stearic acid 10 parts Eicosane diacid 4 parts Di-2-ethylhexyl phthalate 2 parts Polyisocyanate (Nippon Polyurethane, Coronate HL) 5 parts Tetrahydrofuran 180 parts

[Formation of heat-resistant protective layer]
Next, a heat-resistant protective layer as an intermediate layer was further formed on the heat-sensitive recording layers formed in the above-described examples and comparative examples, respectively, as described below. Specifically, an acrylic ultraviolet curable resin (manufactured by Dainichi Seika Kogyo Co., Ltd.) was applied so that the thickness after drying was 5 μm, and then irradiated with ultraviolet rays at 500 mJ / cm ² to form a heat-resistant protective layer.

[Formation of slippery protective layer]
Further, on the heat-resistant protective layer, a slippery protective layer as the uppermost layer was formed as follows to obtain reversible thermosensitive recording materials of Examples and Comparative Examples. The slipping protective layer was formed by applying a polysiloxane-modified polyurethane resin (manufactured by Dainichi Seika Kogyo Co., Ltd.) so that the thickness after drying would be 1.0 μm.

<Evaluation>
For each of the reversible thermosensitive recording materials of Examples 1 to 4 and Comparative Examples 1 to 3 obtained as described above, image formation was performed using a line-type thermal head (8 dots / mm), and a hot plate pressure bonding method ( The initial printing and erasing characteristics were evaluated at a hot plate temperature (100 to 105 ° C.). Then, the operation of erasing this image was repeated 100 times, and the durability was evaluated by the following methods and criteria.

(durability)
Contrast; (background density−printing density) of 1.0 or less was evaluated as x. The measurement was performed with a Macbeth reflection densitometer (RD-914).

(Environmental compliance)
A determination was made based on whether or not carbon dioxide was immobilized in each resin of the forming material of the “thermosensitive recording layer” of the reversible thermosensitive recording materials of Examples and Comparative Examples.

  In the case of the material of Comparative Example 1 in which the polyester polyurethane resin is used as the base material of the heat-sensitive recording layer, the resin is compatible with the organic low-molecular substance constituting the heat-sensitive recording layer. Not expressed. In the case of the materials of Comparative Examples 2 and 3, the durability was inferior as shown in Table 1, because the resin used for the base material of the heat-sensitive recording layer was added with polyisocyanate. However, since there is no reactive group in the resin used, it is considered that the crosslinking effect cannot be obtained and the durability is lowered. In contrast, the self-crosslinking polyhydroxypolyurethane resin used in the base material of the heat-sensitive recording layer in each example has a hydroxyl group in its structure, so that it is different from the isocyanate group generated by dissociation of the masking agent. As a result, a durability was improved as shown in Table 2.

  According to the present invention described above, by using a specific polymer resin as the base material of the reversible thermosensitive recording layer, it is possible to improve durability when heating and pressure are repeatedly applied by a heating element such as a thermal head. Thus, even when image formation and erasure are repeated many times, there is provided a reversible thermosensitive recording material capable of good image formation in which a decrease in contrast between the transparent portion and the opaque portion is suppressed. Then, by using this material having excellent durability, it becomes possible to continue rewriting characters and images satisfactorily, so that the material can be used, for example, an IC card in which stored information is changed. When it is applied to a class, etc., it is possible to continuously perform display for content assurance in a good state at any time. In addition, since the self-crosslinking polyhydroxy polyurethane resin used as a base material of the reversible thermosensitive recording layer in the present invention can use carbon dioxide as a production raw material, according to the present invention, it is regarded as a global warming gas. It is possible to provide a reversible thermosensitive recording material as a product for the global environment that can contribute to the reduction of carbon dioxide.

Claims (4)

A base material and at least one surface of the base material have a thermosensitive recording layer formed of a polymer composition and a resin composition containing as a main component an organic low molecular weight substance dispersed in the polymer resin. A thermal recording material,
The thermosensitive recording layer is a reversible thermosensitive recording layer whose transparency can reversibly change depending on temperature, and the polymer resin for forming the recording layer is obtained from a reaction between a 5-membered cyclic carbonate compound and an amine compound. A reversible thermosensitive recording material, which is a self-crosslinking polyhydroxypolyurethane resin having an isocyanate group masked in its structure.   The reversible feeling according to claim 1, wherein the 5-membered cyclic carbonate compound is a reaction product of an epoxy compound and carbon dioxide, and carbon dioxide is contained in the structure in an amount of 1 to 25% by mass. Thermal recording material.   The masked isocyanate group is a reaction product of an organic polyisocyanate group and a masking agent, and the masked portion is dissociated by heat treatment to form an isocyanate group, which reacts with a hydroxyl group in the structure. The reversible thermosensitive recording material according to claim 1 or 2, which is self-crosslinking.   The reversible of any one of claims 1 to 3, wherein the self-crosslinking polyhydroxypolyurethane resin is obtained by modifying a polyhydroxypolyurethane resin derived from a reaction between a 5-membered cyclic carbonate compound and an amine compound with a modifier. Sensitive thermal recording material.