JPH09175041A - Repeated print recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a repeated print recording medium which is thermally rewritable and enables a clear contrast image to be formed and securely erased despite its frequent rewriting process, and can be fabricated into a curl-free card with superior surface scratch resistance and non-generation of surface cracks or separation. SOLUTION: This repeated print recording medium is composed of a smoothing layer 2, a photo-reflective layer 3, a primer layer 4, a thermal recording layer 5 consisting of an organic low molecular substance dispersed in a synthetic resin, and a protecting layer 6 with high heat resistance and high stretchability provided sequentially, at least, on one of the faces of a base sheet 1. The organic low molecular substance to be used is saturated straight- line fatty acid, and the protecting layer 6 to be used is an ultraviolet cationic polymerizable epoxy resin with an elongation percentage of 5-100%, and is formed so that its thickness ranges is 2 to 10μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable rewritable recording medium which is rewritable by heat, and more specifically, it improves a rewriting durability by improving a protective layer provided on a heat-sensitive recording layer on a substrate sheet. The repetitive print recording medium.

[0002]

2. Description of the Related Art Conventionally, various proposals have been made regarding the constitution and materials of a rewritable print recording medium which is rewritable by heat. For example, regarding the constitution, a heat-sensitive recording layer whose transparency-opacity reversibly changes depending on temperature is provided on a support made of various plastics, glass, metal, etc., and a heat-sensitive recording layer is further formed thereon as needed. There is one provided with a protective layer for protecting the. And
The heat-sensitive recording layer includes a layer in which various organic low molecular weight substances are dispersed in a resin, and the protective layer is provided with heat resistance against repeated rewriting, scratch resistance, etc.
For example, an ultraviolet curable resin is often used.

However, even when such a UV-curable resin is used for the protective layer, the thermal recording layer deteriorates and the color density gradually decreases during repeated rewriting by a thermal head printer or the like. There was a problem that the image became unclear. The cause of this deterioration is that heat and pressure are applied to the recording medium at the same time during printing and conveyance by a thermal head printer, etc., and by repeating this, structural changes occur in the thermal recording layer and the light scattering efficiency decreases. it is conceivable that.

Such deterioration of the heat-sensitive recording layer is caused by dipentaerythritol hexaacrylate (DP) especially in the protective layer.
Although it has heat resistance such as HA), it was remarkably observed when a hard ultraviolet curable resin having an elongation rate of less than 5% was used.
In the case of such a resin, there is a problem that, in many cases, the card is curled when processed into a card or the like due to shrinkage that occurs during curing. When the surface of the thermosensitive recording layer is bleeding with an organic low molecular weight substance (such as a fatty acid), the protective layer and the thermosensitive recording layer are not sufficiently adhered to each other and the coating is applied by a physical load caused by rewriting many times. Cracked into
There was also a problem such as peeling. In order to prevent this, it was necessary to take measures such as providing a primer coat layer between the heat-sensitive recording layer and the protective layer.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems and has a structure in which a heat-sensitive recording layer and a protective layer are sequentially laminated on one surface of a base sheet,
In a repetitive print recording medium that is rewritable by heat, the thermal recording layer does not deteriorate even when repeatedly rewritten by a thermal head printer, etc., and clear image formation and reliable erasing can be performed many times, and the protective layer is Good adhesion to the lower thermal recording layer, no curling due to shrinkage of the coating film even when processed into a card, etc. Furthermore, even if rewritten many times, the surface is less likely to be scratched and cracked or peeled off. It is an object of the present invention to provide a repetitive print recording medium excellent in performance that it does not occur.

[0006]

In order to solve the above-mentioned problems, the inventors of the present invention have conducted extensive studies focusing on the relationship between the heat-sensitive recording layer and the protective layer, particularly the material and physical properties of the protective layer. The invention has achieved the object. That is, the invention according to claim 1 has a heat-sensitive recording layer obtained by dispersing an organic low-molecular substance in a synthetic resin on at least one surface of a base sheet, and a heat-resistant recording layer is formed on the heat-sensitive recording layer. Of a repeating print recording medium having a protective layer having high elasticity and high elasticity, wherein the protective layer is formed using an ultraviolet cationic polymerization type epoxy resin having an elongation of 5 to 100%. It is a repetitive print recording medium.

The invention according to claim 2 is the repetitive print recording medium according to claim 1, wherein the organic low molecular weight substance is a saturated linear fatty acid. And
The invention according to claim 3 is such that the thickness of the protective layer is 2 to 1
The repetitive print recording medium according to claim 1 or 2, wherein the repetitive print recording medium is 0 μm. In the present invention, the numerical value of the elongation is based on the tensile breaking elongation (test speed F) of the tensile test method for JIS K-7127 plastic film and sheet.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the structure of one embodiment of the repetitive print recording medium of the present invention. However, the present invention is not limited to the above configuration. FIG.
The repetitive print recording medium 10 shown in FIG. 2 has a smoothing layer 2, a light reflecting layer 3 made of a metal vapor deposition film, etc.
The primer layer 4, the thermosensitive recording layer 5, and the protective layer 6 are laminated in this order.

The substrate sheet 1 is not particularly limited,
In addition to individual sheets or laminated sheets of various plastics,
Materials such as glass plates and metal plates can also be used. In addition, when the surface of the base material sheet 1 is not sufficiently smooth and the metal gloss is not obtained even if the light reflection layer 3 formed by a metal vapor deposition film or the like is directly provided on the base material sheet, the base material sheet 1 The smoothing layer 2 is provided on the top.

The smoothing layer 2 eliminates irregularities on the surface of the base material,
In order to improve the reflection efficiency of the light reflection layer 3 provided next,
It is provided in order to firmly fix the vapor deposition film to the surface of the base material. Therefore, various resins, for example, various thermosetting resins, ionizing radiation curing resins, and the like, which have heat resistance, can be preferably used. Such a smoothing layer 2 is formed by coating a solution of the above resin whose viscosity has been adjusted with a solvent or the like with a reverse roll coater or the like, drying the solvent components, and then heating, irradiating with ultraviolet rays, or applying necessary electrons. It can be formed by curing by means such as irradiation with rays. The thickness of the smoothing layer 2 is sufficient if the surface of the base material sheet 1 can be made smooth, and when an ordinary plastic sheet is used for the base material sheet 1, about 1 to 3 μm is suitable.

Next, the light reflecting layer 3 is provided under the thermosensitive recording layer 5 to improve its visibility during image recording. Therefore, the light reflection layer 3 is not particularly limited as long as it has high light reflection efficiency, and for example, a metal vapor deposition film of aluminum, tin, nickel or the like can be preferably used. In the case of aluminum vapor deposition film, its thickness is 3
It is sufficient if it is about 00 to 600Å.

The primer layer 4 provided on the light-reflecting layer 3 improves the adhesiveness of the heat-sensitive recording layer 5 provided on the light-reflecting layer 3 and prevents the light-reflecting layer 3 from deteriorating so that its gloss, that is, reflection. Good efficiency is maintained, for example, polyester or vinyl chloride / vinyl acetate copolymer,
Alternatively, a mixed resin of these can be used. The primer layer 4 can be formed by applying the resin solution as described above with a reverse roll coater or the like and drying it, and the thickness thereof may be thin, and may be about 0.3 to 1 μm.

Next, the heat-sensitive recording layer 5 provided on the primer layer 4 is formed of a layer in which an organic low molecular weight substance is dispersed in a synthetic resin. The heat-sensitive recording layer 5 is heated to a predetermined temperature with a thermal head or the like, so that the crystal structure of the dispersed organic low-molecular substance is changed to be transparent or opaque, and this is reversibly repeated. Therefore, printing and erasing can be repeated. As the synthetic resin used for the heat-sensitive recording layer, those having transparency, good film-forming properties, and capable of uniformly dispersing and holding an organic low-molecular substance are preferable. Examples of such synthetic resins include polyvinyl chloride, vinyl chloride-vinyl acetate copolymers and partially saponified products thereof, vinyl chloride-vinyl acetate-maleic acid copolymers, vinyl chloride-acrylic acid ester copolymers, and the like. Vinyl chloride resin. Vinylidene chloride
Vinylidene chloride resins such as vinyl chloride copolymers, vinylidene chloride-acrylic acid ester copolymers, vinylidene chloride-acrylonitrile copolymers. In addition, acrylic resins such as various polyacrylic acid esters and polymethacrylic acid esters, and various polyester resins can be used.

Various fatty acids and their derivatives can be used as the organic low-molecular substance dispersed in the synthetic resin of the heat-sensitive recording layer. Among them, saturated straight chain fatty acids are preferable,
Particularly, those having a carbon number C of 10 to 30 and a melting point of 30 to 160 ° C. are preferable. These organic low-molecular substances can be dispersed in the synthetic resin as one kind or a mixture of two or more kinds, and in particular, organic low-molecular substances having different melting points, for example, monocarboxylic acid and dicarboxylic acid of saturated linear fatty acid The use of a mixture of the above is preferred in that the temperature range for making the film transparent is broadened.

Examples of such fatty acids include capric acid, lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, arachidic acid, heneicosanoic acid and behenic acid. , Tricosanoic acid, lignoceric acid, pentacosanoic acid, and the like. Among the dicarboxylic acids, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecane diacid, dodecane diacid, tridecane diacid,
Tetradecane diacid, pentadecane diacid, hexadecane 2
Acid, heptadecane diacid, octadecane diacid, nonadecane diacid, eicosane diacid, heneicosane diacid, docosan diacid, and the like. Further, the mixing amount of the organic low molecular weight substance with respect to the synthetic resin is about 1% by weight to 60% by weight, and the range of 20% by weight to 50% by weight is more preferable as the content of the organic low molecular weight substance with respect to the whole. When the content of the organic low-molecular substance is 1% by weight or less, the print density is low and the sharpness becomes insufficient. On the other hand, when the content is 60% by weight or more, it becomes difficult to form a uniform coating film, which is not preferable.

Further, a small amount of a high boiling point solvent, a surfactant or the like can be added to the heat-sensitive recording layer 5 in order to improve film-forming property and processability. Specific examples of such additives include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, butylbenzyl phthalate, dioctyl phthalate, diisooctyl phthalate, dicapryl phthalate, and adipine as high boiling point solvents (plasticizers). Diisobutyl acid, dioctyl adipate, dibenzyl sebacate, dioctyl sebacate, triphenyl phosphate, tricresyl phosphate, trioctyl phosphate, octyl diphenyl phosphate, triacetin and the like.

As the surfactant, higher fatty acid alkali salt, polyethylene glycol alkyl ether, polyethylene glycol fatty acid ester, sorbitan fatty acid ester, fatty acid monoglyceride, polyhydric alcohol higher fatty acid ester, polyhydric alcohol higher alkyl ether, higher fatty acid alkyl sulfone. Examples thereof include acid salts, higher fatty acid alkylaryl sulfonates, and higher amine halogen acid salts.

The heat-sensitive recording layer 5 containing the above-mentioned synthetic resin and organic low-molecular substance as main components is made into a solution with an organic solvent, and the viscosity-adjusted coating liquid is applied onto the primer layer 4 in various rolls. It can be formed by coating and drying by means such as coating or printing. This thermal recording layer 5
The thickness of 2 to 25 μm is suitable.

Next, the protective layer 6 provided on the thermal recording layer 5
As the above, a resin layer having both heat resistance and high elasticity is preferable, and a resin having an elongation rate of 5 to 100% is preferable. With a hard resin having an elongation of less than 5%, the cushioning property is lost, and the physical load on the heat-sensitive recording layer cannot be absorbed or mitigated. Therefore, the heat-sensitive recording layer is deteriorated due to repeated rewriting, resulting in image recording. The color density decreases. In addition, a resin having an elongation percentage of more than 100% is not preferable because the scratch resistance is insufficient and the surface is easily scratched, and at the same time, the heat resistance is insufficient. Examples of such a resin include, for example, an ultraviolet cationic polymerization type epoxy resin, a polyene / thiol type ionizing radiation curable resin, and a flexible urethane acrylate type ionizing radiation curable resin having two or less functional groups. In particular, the ultraviolet cationic polymerization type epoxy resin has almost no shrinkage during curing of the coating film and has excellent adhesiveness to the coating substrate, and the cured coating film formed is excellent in elasticity, heat resistance and scratch resistance. It is preferable in that

That is, the ultraviolet cation polymerization type epoxy resin forms a polymer by the formation of a cation catalyst by light irradiation and a polymerization reaction with a cation polymerization epoxy oligomer, and the cured coating film is heat resistant. And excellent scratch resistance, and elongation of 5 to 1 depending on the choice of oligomer.
A cured coating film having a stretchability of 00% can be prepared. Examples of such cationically polymerizable epoxy-based oligomers include bisphenol A epoxy, cycloaliphatic epoxy, monomer type glycidyl ether, and polyglycidyl ether of polyol, and their chemical formulas are as shown in the following chemical formula 1. A compound (compounds 1-5) is mentioned.

[0021]

Embedded image Then, as the photocation catalyst, an aryldiazonium salt, an aryliodonium salt, an arylsulfonium salt, a sulfonylacetophenone, an allene-ion complex or the like can be used.

An ultraviolet cationic polymerization type epoxy resin using the above cationically polymerizable epoxy type oligomer and a photocationic catalyst does not have a curing inhibitory effect by oxygen at the time of curing and is a cured coating excellent in surface curability. A film can be formed. In addition, since the volumetric shrinkage rate during curing is small and the adhesiveness to the coating substrate is also very excellent, it shows good adhesiveness also to the thermosensitive recording layer, especially on the surface of the thermosensitive recording layer. Even if there is bleeding of a low molecular weight substance (fatty acid), it is possible to satisfactorily laminate without the need to provide a primer coat layer or the like. Therefore, even when rewriting is performed many times, peeling of the protective layer does not occur, the initial state can be maintained, and the effect of improving durability can be obtained. Further, in processing a card or the like, even if a thick protective layer is laminated, deformation such as warpage or curling hardly occurs, and it is particularly effective when a thin base sheet is used.

If desired, a lubricant such as various waxes, a surfactant, an antistatic agent, an ultraviolet absorber or the like may be added to the protective layer as described above. Then, as a means for forming the protective layer, various roll coating methods or printing methods can be used, and the coating solution adjusted to have a viscosity suitable for each method is applied to a predetermined thickness and dried. After removing the solvent component, the protective layer can be formed by curing the coating film through an ultraviolet irradiation device. The thickness of the protective layer to be formed is 2 to 10 μm.
m is suitable, and 4 to 8 μm is more preferable. If the thickness of the protective layer is less than 2 μm, the scratch resistance is insufficient, the cushioning effect cannot be obtained, and the thermal recording layer is deteriorated by repeated rewriting, which is not preferable. On the other hand, if the thickness exceeds 10 μm, the thermal sensitivity at the time of printing and erasing decreases, which is not preferable.

[0024]

EXAMPLES The present invention will be described in more detail with reference to specific examples and comparative examples. [Example 1] A polyethylene terephthalate film [Lumirror E-22 (double-sided treatment) manufactured by Toray Industries, Inc.] having a thickness of 188 [mu] m was provided with an epoxy acrylate resin layer having a thickness of 2 [mu] m as a smoothing layer on one surface thereof. , A 600 Å-thick aluminum vapor-deposited layer was provided thereon as a light-reflecting layer, and then a primer layer having a thickness of 0.
A 5 μm polyester-vinyl vinyl acetate (copolymer) resin layer was provided. The above-mentioned smoothing layer was formed by coating the coating liquid with a reverse roll coater and then curing the coating film through an ultraviolet irradiation device, and the primer layer was formed by coating the coating liquid with a reverse roll coater and drying.

Then, a coating solution for heat-sensitive recording layer having the following composition was coated on the primer layer by a reverse roll coater so that the thickness of the coating film after drying was 10 μm, and dried to form a heat-sensitive recording layer. After the formation, subsequently, a protective layer coating solution having the following composition is coated thereon by a reverse roll coater equipped with a hot air drying device and an ultraviolet irradiation device in the same manner as the smoothing layer, followed by drying to remove the solvent. An ultraviolet irradiation device (two high pressure mercury lamps with an output of 160 W / cm, distance of 10 cm) was continuously passed at a speed of 10 m / min to cure the coating film and form a protective layer having a thickness of 7 μm. 1
A repetitive print recording medium was obtained.

Composition of coating liquid for heat-sensitive recording layer Vinyl chloride-vinyl acetate copolymer (manufactured by VYHH UCC) 30 parts by weight Organic low molecular weight substance behenic acid 7 parts by weight Sebacic acid 3 parts by weight Diluting solvent (tetrahydrofuran / ethyl cellosolve weight Ratio 1: 1) 100 parts by weight

Composition of coating liquid for protective layer UV cationic polymerization type epoxy resin (flexible type) 50 parts by weight Diluting solvent (isopropyl alcohol / ethyl acetate weight ratio 1: 1) 30 parts by weight (hereinafter isopropyl alcohol is referred to as IPA) Yes.)

Comparative Example 1 In the constitution of the repetitive print recording medium of Example 1, the protective layer coating solution was changed to a coating solution having the following composition, and a protective layer coating film was formed to a thickness of 5 μm. Except for the above, all were processed in the same manner as in Example 1 to prepare a repetitive print recording medium of Comparative Example 1. Composition of coating liquid for protective layer UV cationic polymerization type epoxy resin (hard type) 50 parts by weight Diluting solvent (IPA / ethyl acetate weight ratio 1: 1) 50 parts by weight

[Comparative Example 2] In the constitution of the repetitive print recording medium of Example 1, the protective layer coating solution was changed to a coating solution having the following composition, and the protective layer coating film was formed to a thickness of 6 μm. Except for the above, all were processed in the same manner as in Example 1 to prepare a repeated print recording medium of Comparative Example 2. Composition of coating liquid for protective layer UV cationic polymerization type epoxy resin (flexible, highly stretchable type) 50 parts by weight Diluting solvent (IPA / ethyl acetate weight ratio 1: 1) 50 parts by weight

[Tests and Results] Repetition print recording media of Example 1 and Comparative Examples 1 and 2 prepared as described above were tested for rewriting durability by the following method, and the results are shown in Tables 1 and 2. It was shown to. In addition, the elongation percentage of the resin used for each protective layer was separately measured and is also shown in each table. (Rewriting durability test method) Printing method: 8 dots /
0.32 mJ / dot using mm line type thermal head
An image is formed with the applied energy of. Erasure method: 1.0kg of hot stamp with a set temperature of 90 ℃
The image is erased by pressing under a pressure of / cm ² for 1 second. Evaluation method: Printing and erasing were repeated by the above method, and the print densities at the initial stage, 50 times, 100 times, 500 times and 1000 times were measured by a Macbeth reflection densitometer (RD-918S,
It was measured by a visual filter (the numerical value of the print density is shown in Table 1). Further, the state and appearance of the protective layer after rewriting were visually evaluated. Judgment Criteria Good (good): Change in print density due to rewriting was less than 0.20 in reflection density value, and the state of the protective layer after rewriting was good. Poor (poor): Change in print density due to rewriting exceeds 0.20 in reflection density value, or the state of the protective layer after rewriting is poor.

[0031]

[Table 1] (Test results) *: Printing is possible, but the protective layer is deteriorated.

[0032]

[Table 2] (Continued test results) *: In Comparative Example 2, the protective layer lacked heat resistance and the printed (heated) portion deteriorated.

As is clear from the test results of Tables 1 and 2, the repetitive print recording medium of Example 1 showed little decrease in print density even after 1000 rewritings (printing / erasing), and The state of the protective layer was also good. On the other hand, in the repetitive print recording medium of Comparative Example 1, the print density was lowered by 500 times of rewriting, and it became defective. Further, the repetitive print recording medium of Comparative Example 2 lacked heat resistance, and the protective layer was deteriorated in the initial printing, and rewriting was not possible.

[0034]

As described in detail above, the present invention
The invention described in, on at least one surface of the substrate sheet,
A repetitive print recording medium comprising a thermosensitive recording layer in which an organic low molecular weight substance is dispersed in a synthetic resin, and a protective layer having heat resistance and high elasticity is provided on the thermosensitive recording layer. The protective layer is an ultraviolet cationic polymerization type epoxy resin having an elongation of 5 to 100%.
By adopting such a constitution, since the ultraviolet cationic polymerization type epoxy resin having an elongation of 5 to 100% used for the protective layer has excellent adhesiveness to the heat-sensitive recording layer, the bleeding of fatty acid Even in the case where the above occurs, the protective layer can be provided on the heat-sensitive recording layer without performing the primer treatment. Then, the resin of the protective layer hardly shrinks during curing, and the cured coating film of the formed protective layer has high elasticity, cushioning property, scratch resistance, and heat resistance, so that the thermal recording layer at the time of rewriting. The stress applied to is absorbed and relieved, the initial state can be maintained even after a large number of rewritings, the surface of the protective layer does not crack or peel off, and the scratch resistance is excellent, so the rewriting durability is significantly improved. Even when processed into a card or the like, there is an effect that curls are hardly generated. As described above, according to the first aspect of the invention, there is an effect that a repetitive print recording medium excellent in performance and durability can be provided with high productivity.

The invention according to claim 2 is the repetitive print recording medium according to claim 1, wherein a saturated linear fatty acid is used as the organic low molecular weight substance in the heat-sensitive recording layer. . By adopting such a constitution, the change of the crystalline state of the organic low molecular weight substance, that is, the saturated straight chain fatty acid by heating during printing and erasing, specifically, the transparency and the opacity becomes clear, and Printing and erasing become possible.

According to a third aspect of the present invention, in the repetitive print recording medium according to the first or second aspect of the invention, the protective layer has a film thickness of 2 to 10 μm. By adopting such a configuration, excellent properties such as adhesiveness, high elasticity, cushioning property, scratch resistance, and heat resistance of the protective layer can be sufficiently exerted, and rewriting durability, printing and erasing can be performed. The effect that a repetitive print recording medium excellent in performance such as good thermal sensitivity in the above can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the configuration of an embodiment of a repetitive print recording medium of the present invention.

[Explanation of symbols]

1 Base Material Sheet 2 Smoothing Layer 3 Light Reflecting Layer 4 Primer Layer 5 Thermal Recording Layer 6 Protective Layer 10 Repeated Printing Recording Medium

Claims (3)

[Claims] 1. A heat-sensitive recording layer obtained by dispersing an organic low-molecular substance in a synthetic resin is provided on at least one surface of a substrate sheet, and heat resistance and high elasticity are provided on the heat-sensitive recording layer. A repetitive print recording medium provided with a protective layer having
A repetitive print recording medium, wherein the protective layer is an ultraviolet cationic polymerization type epoxy resin having an elongation of 5 to 100%. 2. The repeated print recording medium according to claim 1, wherein the organic low molecular weight substance is a saturated linear fatty acid. 3. The repeated print recording medium according to claim 1, wherein the protective layer has a film thickness of 2 to 10 μm.