JP4200031B2 - Reversible thermosensitive recording medium - Google Patents

Description

【００８３】
＜評価＞
折り目の頂角が９０°以上である各実施例では５００回以上のリライトが可能であった。
比較例１、４からポリエチレンテレフタレートを単体で支持体としたものは１００〜２００回のリライトでシートに変形が発生し印字不良を起こし、寿命となることがわかった。
比較例２から発泡ポリエチレンテレフタレートの有するボイドによるクッション性では通常のＰＥＴに比べて寿命が殆ど改善されないことがわかった。
比較例３、６から、熱可塑性樹脂であっても、特定のゴム弾性を有する熱可塑性エラストマーを含まないポリプロピレン合成紙やＰＥＴ−Ｇ樹脂では寿命が改善されないことがわかった。
比較例５では、熱可塑性エラストマーでなく、シリコンゴムを支持体に使用したため、折り目の頂角が１８０°となり、折り返した部分に直線的な折り癖が永久変形として残らない。つまり、目視できる折り目が確認できないということが見出された。このようにエラスティックな可逆的感熱記録媒体では、実用的な薄さの範囲では使用に耐える腰（剛性）がなく、ストッカからの送り出しやプリンタ内での搬送が上手く行かないなどの理由から実際には使用できないことがわかった。
実施例４と比較例７の比較により、特定のゴム弾性を有する熱可塑性エラストマーの構成率が２０％程度の支持体ではリライト寿命に大きく寄与できないことがわかった。２５％以上あれば十分である。
【００８４】
【発明の効果】
本発明で規定する折り目試験を満足する可逆的感熱記録媒体であれば、リライト回数の増加に伴って媒体に発生するワカメ状の波打ち変形の発生を抑制でき、最終的に折れや波打ちシワ部に発生する印字・消去抜けがを防ぐことが可能となり、従来のＰＥＴベースの可逆的感熱記録媒体に比べてリライト寿命を大幅に改善できることが明らとなった。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reversible thermosensitive recording medium capable of repeatedly displaying a colored state and a decolored state reversibly by heat.
[0002]
[Prior art]
In recent years, there has been an active movement to suppress the use of paper to protect forests due to growing awareness of environmental issues. Display media that can replace paper include cathode ray tube monitors such as personal computers and liquid crystal panels. In recent years, electronic devices such as electronic paper using liquid crystal systems and electrophoresis have been proposed.
In addition, various reversible thermosensitive recording media capable of recording and erasing by heat have been put into practical use as promising candidates because of their listability, flexibility and texture close to paper.
[0003]
Conventionally, such a reversible thermosensitive recording medium has been mounted on a magnetic card and used for displaying a store point in a chain store. Also, it is mounted on reuse-type non-contact IC cards for commuter passes, ski lift tickets, etc., and used for displaying expiration dates. However, these are relatively hard media limited to the shape of a card, and it has been considered that the number of reuses should be several tens of times at most. When used as an alternative display medium for paper, it is generally required to have a larger size than A6, which is more flexible. Folding, deformation, etc., which hardly caused problems with card size Has emerged as a practical durability problem.
[0004]
In fact, reversible thermosensitive recording media have been put into practical use for office applications such as medical records, field instructions in factories and logistics, and kanban. Although it is assumed that there are about 100 times, the actual situation is that it can be used only about tens of times due to dirt, deformation, breakage, etc. that occur during actual use.
[0005]
Dirt, deformation or breakage occurs when a person handles it, and it also flutters due to airflow when used for posting, and is caused by placing heavy objects on the surface or hitting foreign objects. Furthermore, it also occurs due to jamming in a printer used for reversible thermal recording and erasing.
[0006]
In particular, dirt is generated not only by rubbing with foreign matter, but also by adhesion of water or oil to the surface of the medium or dust due to static electricity. In the case of dirt, the amount of heat from the thermal head inside the printer is not properly applied to the medium, which may cause printing defects and erasure defects, and the dirt transferred to the thermal head and transport roller in the printer is retransferred to the next medium surface. As a result, the contamination will spread to other clean media.
[0007]
In order to reduce these risks, it is considered effective to periodically clean the medium, but this cleaning process itself is one of the causes of the deformation of the medium, and an effective method for extending the life of the medium was awaited. It was.
[0008]
There are few inconveniences because it is used in a relatively clean and mild environment for office applications such as medical records, but there is a high risk of physical deformation such as bending / bending when used on the factory floor. Further, in principle, in order to reuse, it is necessary to go through a cleaning process to remove grease stains, and the life of the medium is particularly short, which has been a major obstacle in introducing a reversible thermosensitive recording medium as a substitute for paper.
[0009]
Conventionally proposed reversible thermosensitive recording media have used paper, non-woven fabric, woven fabric, synthetic resin film, synthetic paper, metal foil, glass, or a composite material thereof as a support. In practice, a flexible plastic film with relatively excellent dimensional stability, such as PET (polyethylene terephthalate), is often used as a support.
[0010]
However, when these materials are subjected to physical deformation such as creases and stretches, they remain permanently, causing poor contact with the thermal head and heat roll when reused, and there is a problem that the portions cannot be printed or erased. It was.
[0011]
As conventional techniques for improving the reusability of a reversible thermosensitive recording medium, the following has been proposed.
[0012]
Patent Document 1 proposes a reversible thermosensitive recording medium in which one or two or more elastic layers, each of which has a rubber-elastic polymer as a main component, are provided separately from the support. This is intended to improve the reproducibility failure based on the poor adhesion between the heat-sensitive recording layer and the heating body for heat application, and to obtain a clear image and sufficient decolored state over a long period of time with good reproducibility. is there. In the embodiment, an elastic layer having a thickness of 5 to 20 μm is laminated on a 100 μm polyester film. This combination is used for the purpose of the present invention to be described later. It is not supposed to be a countermeasure against creases and deformations.
[0013]
As a proposal for improving printing defects by folding, wrinkling, or deformation of the entire reversible thermosensitive recording medium, Patent Document 2 discloses a low crystalline thermoplastic resin sheet having a crystallinity of 5% or less, or an amorphous resin. There is a double-sided amorphous sheet made by coextrusion of and a crystalline resin. The actually proposed support resin is a copolymer (PET-G) of terephthalic acid, cyclohexanedimethanol and ethylene glycol, or an alloy of the copolymer and polycarbonate (heat-resistant PET-G). Amorphous such as acid or copolymer of isophthalic acid and ethylene glycol (PET), polyester resin, ABS resin, AS resin, polystyrene, polyacrylonitrile, polymethyl acrylate, polymethyl methacrylate, vinyl acetate, polyvinyl alcohol, polycarbonate It becomes a simple substance or a mixture of a thermoplastic resin. These resins will be described later.Specific rubber elasticityIt is a thermoplastic resin having strong plastic flowability and no mold. Compared to what is intended to have elastic properties focusing on the rebound resilience of the present invention, the reversible thermosensitive recording medium has insufficient improvement in printing defects due to bending, wrinkling, and deformation of the whole, and several tens of times. Only the reuse of can be achieved.
[0014]
Further, there is Patent Document 3 as a proposal for improving wrinkles and deformation of the entire reversible thermosensitive recording medium. This is a support having one or more constituent layers and a thickness of 800 μm or less, and is the maximum measured by a microhardness meter when a load of 4.9 mN is held for 1 second using a triangular pyramid indenter. A card recording material comprising a support having a variation of 1.1 μm or more, a void content of 25% or less, and a rigidity of 4 mN or more. From the standpoint of rigidity and workability, a film of polyethylene terephthalate and vinyl chloride is raised as a support, and it can be seen that this is different from the idea of the present invention focusing on support rubber elasticity. Moreover, the composition ratio of the void-containing polyethylene terephthalate film and the white polyethylene terephthalate / thermoplastic polyurethane film assembly presented as examples are different from the scope of the present invention.
[0015]
This tooIn the present invention, tensile setPay attention to,What has elastic propertiesWhen usedIn comparison, the improvement of printing defects due to bending, wrinkling, and deformation of the entire reversible thermosensitive recording medium is inadequate, and only several tens of reuses can be achieved.
[0016]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-211152 (Claim 1, pages 12-13)
[Patent Document 2]
JP 2000-137782 A (Claim 1, page 3-4)
[Patent Document 3]
JP 2002-275286 A (Claim 1, pages 2-3)
[0017]
[Problems to be solved by the invention]
The present invention meets the potential lifetime of a reversible thermosensitive recording layer that is said to potentially withstand 500 reuses.Another object of the present invention is to provide a reversible thermosensitive recording material that can be used with good durability.
[0018]
In the present invention, a reversible thermosensitive recording medium having a reversible thermosensitive recording layer on a support satisfies the following bending test, and has physical properties of a tensile strength of 140 MPa or less and an elongation of 150% or more. And the support is composed of one or more layers, at least one layer of which is JIS K It is made of a polyester-based thermoplastic elastomer having a tensile permanent strain of 5% or less when a tensile strain of 25% is given in the tensile permanent strain test specified in 6262 (1997), and the heat in the entire support is described above. The desired purpose was achieved by setting the content of the plastic elastomer to 25% by mass or more..
Bending test:
When cut into a strip-like sample with a width of 20 mm and a length of 150 mm, it can be visually checked by folding it in the middle and reciprocating it 20 times with the roller specified in the crimping device in Section 8.2.3 of JIS Z 0237 (1991) Then, after leaving for 24 hours in an environment with a temperature of 25 ± 2 ° C. and a humidity of 60 ± 5%, the angle at the fold apex angle is 90 degrees or more and less than 180 degrees.
This roller has a spring hardness of 80 ± 5 Hs, a width of about 45 mm covered with a rubber layer of 6 mm, a diameter (including the rubber layer) of about 95 mm, and a mass of 2000 ± 50 g as defined in JIS. It is.
[0019]
[0020]
The above-mentioned pullThe tension set is calculated by the following formula.
Ts = {(L2-L0) / (L1-L0)} * 100
here
Ts: Tensile set (%)
L0: Distance between marked lines before tension (mm)
L1: Distance between marked lines during tension (mm)
L2: Distance between marked lines after contraction (mm)
[0021]
Moreover, the said support body is comprised from a multilayer, As the whole support body,A polyester-based thermoplastic elastomer whose tensile set is the above conditionIt is also preferable to contain 25% by mass or more.
It is also preferable to further provide one or more layers between the support and the reversible thermosensitive recording layer, at least at one location on the support-free side of the support and on the surface side of the thermosensitive recording layer.
It is also preferable that the thickness of the support is in the range of 75 μm to 2000 μm.
[0022]
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The present invention reduces plastic flow so that when a reversible thermosensitive recording medium is bent, bent, or deformed, the deformation is not made permanent. Focusing on the importance of giving specific elastic properties to the entire reversible thermosensitive recording medium, it was found that the properties satisfy the bending test described above.
[0024]
Furthermore, in order to have such a specific property, it has been found that it is preferable to use a material that satisfies the above-described properties mainly as a support in order to easily obtain such a property. It is.
[0025]
Conventional supports such as PET and PET-G are explained in the present invention even if the amount of deformation is a crease or wrinkle due to plastic deformation.TheContains elastic ingredientsThermoplastic elastomerOn the supportUseAs a result, the medium can be permanently deformed by plastic flow, and the risk of causing display defects due to poor contact between the thermal head or the erasing heat roll and the medium can be greatly reduced.
[0026]
Even if the crease actually enters, the apex angle of the crease is easy to open due to the rebound resilience of the medium itself, and the thermal head and heat roll can contact up to the vicinity of the valley of the crease. The degree of can be greatly reduced.
[0027]
Due to these effects, even when the medium is soiled, it can be safely washed and reused, and the medium can be actually used to near the potential life of the reversible thermosensitive recording layer.
[0028]
The reversible thermosensitive recording layer used in the present invention is preferably of a type that develops color at a high density by heating and decolors by reheating, and has a high image contrast and allows easy image recognition. As this type, a reversible thermosensitive recording layer comprising, as a main component, usually a colorless or light-colored dye precursor and a reversible developer that causes a reversible color change in the dye precursor due to a difference in cooling rate after heating. Are preferably used.
The reversible developer used in the present invention is not particularly limited as long as it is a compound that causes a reversible color change in the dye precursor by heating. For example, the carbon number disclosed in JP-A-6-210594 An electron accepting compound having 6 or more aliphatic hydrocarbon groups is preferable, and a phenolic compound having at least one aliphatic hydrocarbon group having 6 or more carbon atoms can be used.
[0029]
Examples of the colorless or light dye precursor used in the present invention include electron donating compounds generally used for pressure-sensitive recording paper, heat-sensitive recording paper, energized heat-sensitive recording paper, heat-sensitive transfer paper and the like. Examples thereof include triarylmethane compounds, diphenylmethane compounds, xanthene compounds, spiro compounds, and the like.
[0030]
Various binders are blended for the purpose of increasing the strength of the reversible thermosensitive recording layer. For example, starches, celluloses such as hydroxyethyl cellulose, modified polyvinyl alcohols, gelatin, casein, acrylate resins, water-soluble polymers including maleic anhydride, polyvinyl acetate, polyurethane, styrene-butadiene copolymers, etc. Latexes are raised.
[0031]
In addition, as an additive for adjusting the color development sensitivity and decoloring temperature, a heat-fusible substance having a melting point of 80 to 180 ° C. and a sensitizer used for general thermal paper are used as a reversible thermosensitive recording layer. It is also preferable to add.
[0032]
As the support used in the present invention, paper, synthetic paper, various non-woven fabrics, woven fabrics, resin films, metal foils, nets, sheets combining these, and the like that can satisfy the conditions defined in the present invention can be used.
[0033]
There is no particular limitation on the method for forming the reversible thermosensitive recording layer on the above-mentioned support, but there are coating methods such as air knife coating, blade coating, bar coating, curtain coating, gravure, offset, screen, flexographic. It is possible to adopt a printing method such as
[0034]
The reversible thermosensitive recording medium according to the present invention needs to satisfy predetermined characteristics in the bending test as described above as the entire recording medium. The fold here means that a linear crease remains as a permanent deformation only in the folded portion. In a reversible thermosensitive recording medium that is so elastic that this phenomenon is not seen at all, there is no stiffness (stiffness) that can withstand use in the range of practical thinness, and the feeding from the stocker and the conveyance in the printer do not work well. It is thought that it cannot actually be used for such reasons. Further, it is considered that such a medium in which no creases remain is completely returned to 180 degrees in the above folding test.
[0035]
A reversible thermosensitive recording medium that satisfies this condition has a very low degree of permanent deformation even when bent or bent temporarily during use or cleaning. Even if a crease is formed, the crease part opens due to its own resilience, so the printer's thermal head can properly touch the crease part when reused, resulting in unerased or missing prints. Hard to do. Further, the angle of the crease when it is left for 24 hours in an environment of temperature 25 ± 2 ° C. and humidity 60 ± 5% is more preferably 100 degrees or more and less than 180 degrees.
[0036]
Generally, polyethylene terephthalate used as a support for a reversible thermosensitive recording medium has a tensile strength of about 170 to 220 MPa, an elongation of 120%, and a specific gravity of 1.4 g / cm.²Even with foamed polyethylene terephthalate, the tensile strength is about 120 to 150 MPa, the elongation is 60 to 90%, and the specific gravity is 1.1 g / cm.²Degree. If the tensile strength of the medium exceeds 140 MPa or the elongation percentage is less than 150%, it will eventually be sufficientRubber elasticityIs not obtained, and permanent deformation due to bending or bending tends to remain. Regarding the specific gravity, in order to ensure the physical properties of a medium with practical rigidity on transportation, it is generally desirable to mix an appropriate filler such as a filler with the support, and these contributions 0.95g / cm compared to general rubber² It tends to have a relatively large specific gravity. As a medium using this type of support, 1.1 g / cm² The above is more preferable.
Furthermore, more desirable physical properties of the reversible thermosensitive recording medium according to the present invention are to simultaneously satisfy a tensile strength of 130 MPa or less and an elongation of 200% or more.
[0037]
Even if the support is typified by conventional PET or PET-G, even if the amount of deformation causes plastic deformation and creases and wrinkles, the medium undergoes permanent deformation due to plastic flow, and the thermal head, the erasing heat roll and the medium The risk of causing display defects due to poor contact can be greatly reduced, and even if the crease actually enters, the apex angle of the crease is easy to open due to the rebound resilience of the medium itself, and the thermal head and heat roll In order to greatly reduce the degree of missing prints and erasure defects.Specific thermoplastic elastomerIs preferably applied to at least one layer constituting the support. To that end, the layer isTensionPhysical properties within permanent strain range(Ie specific rubber elasticity)havePolyester thermoplastic elastomerIt is preferable that 25 mass% or more is included. More preferably, it is more practical to contain 30% by mass or more.
[0038]
Thus, at least one layer constituting the support isIf it consists of a polyester-based thermoplastic elastomer with the above specific rubber elasticityEven when the other layers have little or no such property, the above-mentioned conditions can be satisfied as a recording medium.
[0039]
Examples of this include materials such as polyethylene terephthalate that are relatively inexpensively distributed.Thermoplastic elastomer as aboveCan be used as a support for a reversible thermosensitive recording medium.
[0040]
[0041]
[0042]
[0043]
Also, on polyethylene terephthalate film that has been subjected to appropriate easy adhesion treatment such as corona treatment and primer coating.Rubber elasticity whose tensile set satisfies the above conditionsIt is also possible to produce the support of the present invention by extruding a thermoplastic elastomer having a T from a T-die or the like and joining.
[0044]
The above isThermoplastic elastomer as described aboveIn the preferred embodiment of the present invention, the support is composed of multiple layers, and the support as a whole is described.Thermoplastic elastomer as described aboveOne or more ofTheIt is preferable to contain 25 mass% or more. That is, it resists bending and deformation in a multi-layered support.Specific rubber elasticityIf the functions are assigned to each specific layer, the durability of the entire medium will be improved even if a material with bending / bending commonly used in other layers is used. It becomes possible. IeSpecific rubber elasticityHaveThermoplastic elastomerThere are multiple layers containing and they are as a whole supportThe thermoplastic elastomerNaturally, a case where the amount of the compound is contained in a specific amount or more is also included. In that case, it becomes a support having two or more layers containing the resin as mentioned above.
[0045]
As defined aboveSpecific rubber elasticityGeneral as a resin havingNaThermoplastic elastomer, generalNaAlloys of thermoplastic elastomers and various resins, etc., generalNaThermoplastic elastomer compositions can be used.
Examples that can be used in the present invention are given below, but the present invention is not limited thereto.Yes.
[0046]
heatPlastic elastomers include styrene / butadiene / styrene block copolymers, styrene / isoprene / styrene block copolymers, styrene / ethylene / butylene / styrene block copolymers, styrene / ethylene / propylene / styrene block copolymers, and hydrogenation. -Type styrene-butadiene random copolymer, polyolefin-based thermoplastic elastomer, dynamic vulcanization-type polyolefin-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, 1,2-polybutadiene-based heat Plastic elastomer, ethylene vinyl acetate thermoplastic elastomer, polyvinyl chloride thermoplastic elastomer, natural rubber thermoplastic elastomer, fluororubber thermoplastic elastomer, Lance polyisoprene thermoplastic elastomer, and chlorinated polyethylene-based thermoplastic elastomer and the like.
[0047]
Further, in an embodiment of the present invention, one or more layers are further provided between the support and the reversible thermosensitive recording layer, at least one side of the support without the thermosensitive recording layer and at the surface side of the thermosensitive recording layer. There are reversible thermosensitive recording media. Specifically, these layers are subbing layers that can be formed between the support and the reversible thermosensitive recording layer, or functions such as friction and charge control that can be formed on the side of the support that does not have the thermosensitive recording layer. Or a protective layer that can be formed on the surface side of the thermosensitive recording layer.
[0048]
In forming these layers, a coating method such as air knife coating, blade coating, bar coating, or curtain coating, or a printing method such as gravure, offset, screen, or flexo can be employed.
[0049]
Although the undercoat layer, the back layer, the protective layer, etc. can be imparted to the medium with the undercoat layer, the back layer, the protective layer, etc. by a technique such as joining a polyethylene terephthalate (PET) base material, etc., which has been previously formed, If the PET film is too thick, it will affect the physical properties of the entire media,Defined in the present inventionThe condition may not be satisfied, and the improvement of the durability against bending, bending, and deformation of the entire medium may be incomplete, and therefore sufficient consideration is required. In such a case, the above-mentioned base material used as an undercoat layer or the like is substantially regarded as the base material of the support, and a direction satisfying the conditions of the above claims is tried. Also good.
[0050]
First, an example of an undercoat layer that can be formed between the support and the reversible thermosensitive recording layer will be described. The reason for providing the undercoat layer is as follows. However, when it is difficult to combine a plurality of functions in a single undercoat layer, a plurality of layers having each function are provided and they are combined. It may be an undercoat layer. The coating of the undercoat layer is preferably one that does not undergo significant dissolution / swelling in the organic solvent used when an organic solvent-based reversible thermosensitive recording layer is subsequently laminated.
[0051]
The first reason for providing the undercoat layer is to obtain a heat insulating effect. In order to erase and print a reversible thermosensitive recording medium, the medium may be heated to about 200 ° C. with a thermal head. Even in such a case, a thermoplastic elastomer having a relatively low heat resistance can be used as a support. It is. Thermoplastic elastomers are advantageous in that they have thermoformability, and molded products have been put to practical use in shoe soles, tubes, hoses, sports equipment and medical supplies. Because of such characteristics, when a film or sheet of a reversible thermosensitive recording medium is used as a support, it can be considered that the film is deformed by the heat of a thermal head or a heat roll. The purpose of protecting the support from this heat is to provide a heat insulating effect.
[0052]
Further, this heat insulating effect is effective in giving a sufficient amount of heat to the reversible thermosensitive recording layer with a small amount of heating. If the reversible thermosensitive recording layer is exposed to temperature in the color development / erasing process for a short time, sufficient print density may not be obtained or erasing may not be performed completely, resulting in image residue. is there.
[0053]
In order to solve this problem, it is conceivable to increase the amount of heat applied from the thermal head to the reversible thermosensitive recording layer. However, excessive heat damages the reversible thermosensitive recording layer and the protective layer described later, and the coloring / erasing function is reduced. Repeated durability may decrease. If the heat insulating effect is obtained, it is possible to effectively keep a small amount of heat to the reversible heat-sensitive recording layer without letting it escape to the support side, and therefore, there is an effect of preventing a decrease in repeated durability of the coloring / erasing function.
The undercoat layer having a heat insulation effect may be formed by dispersing hollow fine particles made of plastic foam such as polyurethane, polystyrene and vinyl chloride containing voids sealed with air or gas, glass or ceramics in a binder. Moreover, you may laminate | stack and form the polyester film etc. which formed the void by extending | stretching etc. on a support body. It is also possible to apply a method in which organic and inorganic fillers are dispersed in various binders and to ensure voids in the gaps between the fillers.
[0054]
The second reason for providing the undercoat layer is to improve the adhesive strength between the reversible thermosensitive recording layer and the support. By applying an undercoat layer containing a polyester resin or a polyvinyl acetate resin, it may be possible to improve the adhesive strength between the reversible thermosensitive recording medium and the support.
[0055]
The third reason for providing the undercoat layer is to prevent the developer or dye of the reversible thermosensitive recording layer from diffusing to the support. When the developer or dye diffuses, defective print density or unerased residue occurs. In order to prevent this, a layer having a barrier effect may be added to the multilayer structure of the undercoat layer, and it is preferable that the undercoat layer itself has a barrier effect. In particular, the elastic material, which is a feature of the present invention, often has a relatively sparse molecular density space to provide rubber elasticity, and the developer and additive are often easily diffused and adsorbed. Therefore, the undercoat layer having such a barrier effect is effective.
[0056]
The fourth reason for providing the undercoat layer is that, contrary to the third reason, there is a barrier effect for preventing the support from being attacked by the coating liquid for forming the reversible thermosensitive recording layer. That is, the support can preferably have,Specific rubber elasticitySome materials satisfying the requirements have poor solvent resistance. For example, even when using an organic solvent-based reversible thermosensitive recording layer, a layer having a barrier effect having a function of blocking the organic solvent is provided.Specific rubber elasticityIt is also possible to protect the support containing the material having swell so as not to swell or dissolve.
[0057]
Examples of these layers having a barrier effect include a film obtained by applying and drying a hybrid resin of acrylic and urethane containing an alcohol having a relatively low solubility as a solvent, an aqueous UV curable ester acrylate resin and urethane. The cured film of acrylate resin is raised. Other hydrophobic polymer emulsions such as latex such as styrene / butadiene copolymer and ethylene / vinyl acetate copolymer, and water-resistant polyvinyl by adding melamine or polyamide resin to cause condensation reaction or cross-linking reaction Water-soluble polymers such as alcohols, cellulose derivatives, and copolymers containing acrylamide are exemplified. Such a layer having a barrier effect may be added as a constituent layer when a protective layer described later is used. The undercoat layer may be formed by techniques such as film lamination, vapor deposition, and sputtering in addition to coating and printing.
[0058]
It is preferable to provide a back layer that can be composed of one or more layers on the surface of the support opposite to the reversible thermosensitive recording layer. The back layer here is a layer mainly for the purpose of reducing frictional resistance and preventing charging. Has rebound resilienceThermoplastic elastomerIn many cases, the sliding support with the guide rail or the other reversible thermosensitive recording medium superimposed on the elastic support including is high. Therefore, for smooth feeding from the medium stocker and smooth conveyance within the printer, it is preferable to apply and cover a functional layer having good slippage on the back surface of the reversible thermosensitive recording medium as a back layer. This can be done by coating silicon resin particles, polytetrafluoroethylene resin particles, molybdenum disulfide particles, carbon black particles called thermal black, etc. dispersed in a binder, or inks, varnishes, paints, etc. containing silicon resin This can be realized by printing and coating.
[0059]
In order to prevent sticking of media and adsorption of dust due to static electricity, the surface resistance of the media is set to 10¹³It is preferable to control to less than Ω / □. However, it has rebound resilience for realizing the reversible thermosensitive recording medium of claim 1.Thermoplastic elastomerElastic supports containing are often insulators. In order to satisfy the physical properties defined in the present invention, the amount of additive that can be added by blending or the like is limited.¹³A surface resistance of less than Ω / □ may not be realized. In such cases, the back layer has a multi-layer structure and has an anti-static effect such as conductive silica black or white carbon, which has a structural structure such as ketjen black, or quaternary ammonium salts. By forming a layer having an antistatic ability containing a certain additive or the like using a technique such as printing or coating, the surface resistance is reduced to 10¹³It is possible to make it less than Ω / □.
[0060]
It is also effective to make the back layer have a curl correction function. Has sufficient impact resilienceThermoplastic elastomerIn consideration of laminating a polyethylene terephthalate film in which a reversible thermosensitive recording layer is previously formed on an elastic support containing an adhesive, etc. by hot pressing through an adhesive or the like, the support being pressed is subjected to pressure and heat. Is contracted in the Z-axis direction and extended in the XY direction. On the other hand, since the polyethylene terephthalate film is relatively hard, it hardly undergoes deformation. For this reason, after the heat and pressure of the press are removed, the support containing the “support rubber elasticity” component may be elastically shrunk to generate a serious curl with the reversible heat-sensitive recording layer surface convex. In order to compensate and prevent this, a polyethylene terephthalate film can be laminated as a back layer on the surface opposite to the reversible thermosensitive recording layer. The polyethylene terephthalate film as such a back layer can be previously provided with a layer having the above-mentioned lubricating function and / or antistatic function by coating or printing.
[0061]
Next, it is also preferable to form a protective layer on the surface side of the reversible thermosensitive recording layer. Rather, more generally, a protective layer is usually formed on the surface of the reversible thermosensitive recording layer. The protective layer contains a dye / developer in a high ratio, so the heat-sensitive recording layer with a relatively low physical strength is used as an external environmental condition such as moisture, and the thermal head and heat roll used for printing erasure. Provided to protect against damage from sliding. Examples of the material for forming the protective layer include polyurethane resin, polyvinyl alcohol, nitrocellulose, and acrylic acid ester. It is also possible to add a crosslinking agent such as an epoxy compound or a vinyl compound as necessary in order to improve the film strength or improve the denseness. Moreover, it is also preferable to mix | blend a silicone resin particle, a silicone oil, a lubricant like wax, a head cleaning agent like an alumina, and an antistatic agent as needed.
[0062]
In the recording medium of the present invention, the thickness of the support is preferably in the range of 75 μm to 2000 μm. When considering a practical configuration, the undercoat layer is 5 μm or less, the thickness of the reversible thermosensitive recording layer is 10 μm or less, the protective layer is 5 μm or less, and the reversible thermosensitive recording layer and the support are sandwiched on the opposite side. The provided functional layer is often 5 μm or less, and if the support is 75 μm or more, the total thickness of these layers is relatively thin with respect to the support. This is because it can be said that the physical properties of the support.
[0063]
In order to impart resistance to folding and deformation to a reversible thermosensitive recording medium, the present inventionThermoplastic elastomer with specific rubber elasticityHowever, if the total thickness of the medium is less than 75 μm, a sufficient impact resilience effect cannot be obtained, so that it is difficult to sufficiently obtain the effect of preventing folding and deformation. Compared to materials such as polyethylene terephthalate that are often usedMade of thermoplastic elastomerSince the support tends to be inferior in tensile strength, a certain amount of thickness is still required. In addition, since such a support often has no stiffness when compared with the same thickness, there is a high possibility that handling and machine conveyance will be difficult with a medium thinner than 75 μm.
[0064]
On the other hand, if the thickness exceeds 2000 μm, there is a merit that it can be independent depending on the size, but it is not desirable from the convenience of mass transportation because the weight increases, and the number of sheets that can be stored in the stocker is limited This is not appropriate because the uneconomical side becomes large. A more preferable range of the thickness of the support is from 100 μm to 1500 μm.
[0065]
As is clear from the above description, there are cases where each layer other than the support, the undercoat layer, the back layer and the like are quite thick, or the layer includes a polyethylene terephthalate film as in the back layer described above. In such cases, the supportRubber elasticityAs a recording medium, each of the above layers may also contribute greatly to the properties such asSpecific rubber elasticityIt is not negligible that the resin having s is present in each layer other than the support. In such a case, that is, when the above layers include a resin layer as a base material, or when a resin having such properties is included in the binder of each layer and the layers are formed thick, In some cases, it may be practical to consider the amount as a substantially “support-containing” resin.
[0066]
Thermoplastic elastomer with specific rubber elasticityThe following are: thermoplastic polyolefin elastomers, dynamically vulcanized polyolefin thermoplastic elastomers, polyurethane thermoplastic elastomers, polyester thermoplastic elastomers, polyamide thermoplastic elastomers, 1,2-polybutadiene thermoplastic elastomers, ethylene acetate One or more thermoplastic elastomers selected from vinyl thermoplastic elastomers, polyvinyl chloride thermoplastic elastomers, natural rubber thermoplastic elastomers, fluororubber thermoplastic elastomers, and chlorinated polyethylene thermoplastic elastomers are selected. Is preferred. These thermoplastic elastomers can be produced by chemical synthesis, and it is relatively easy to control various physical properties. Further, if necessary, new characteristics can be imparted by blending or other methods, which is preferable as a support component of the reversible thermosensitive recording medium.
[0067]
【Example】
Examples will be described below. The present invention is not limited to this embodiment. Unless otherwise specified, “parts” and “%” represent “parts by mass” and “mass%”, respectively.
[0068]
Example 1
<Reversible thermosensitive recording layer>
25 parts of 3-di-n-butylamino-6-methyl-7-anilinofluorane was dispersed in a ball mill for 24 hours together with 80 parts of a 2.5% aqueous polyvinyl alcohol solution to obtain a dye precursor dispersion. Next, 63 parts of 4'-hydroxy-n-heptaneanilide was dispersed in a ball mill for 24 hours together with 200 parts of an aqueous 2.5% polyvinyl alcohol solution to obtain a reversible developer dispersion. The two selected dispersions were mixed, 130 parts of 10% polyvinyl alcohol aqueous solution was added, and stirred to obtain a reversible thermosensitive recording layer coating material.
[0069]
The obtained paint was coated on a Hirerel 4057 manufactured by Toray DuPont Co., Ltd. as a support so as to have a dry thickness of 5 μm with a Mayer bar, and then supercalendered to form a reversible thermosensitive recording layer. . This Hytrel support is composed of a block copolymer of polybutylene terephthalate as a hard segment and polyether as a soft segment.Specific rubber elasticityHaveThermoplastic elastomerIt is itself.
[0070]
<Protective layer>
Initiator Irgacure 184 (5% solids) and polyflow 425 (0.15% solids) as a leveling agent were added to Arakawa Chemical Industries' urethane acrylate UV curable resin beam set EM92, and 3 μm of Meyer bar was added. It was coated to a thickness and UV cured.
<Back layer>
In order to reduce the frictional resistance on the back side of the support, a back layer was formed by offset printing at a thickness of 0.05 g / m 2 UV cured varnish PPC-D9 manufactured by Dainichi Seika Co., Ltd., to obtain a sample.
[0071]
Example 2
A sample was prepared by preparing a sample in the same manner as in Example 1 except that the support was changed to a polyester elastomer nouvellean P4110AN manufactured by Teijin Chemicals Ltd .; thickness of 300 μm.
This nouvelle support isSpecific rubber elasticityHaveThermoplastic elastomerIt is made of a polyester elastomer resin that is itself.
[0072]
Example 3
Teijin DuPont polyethylene terephthalate (PET) film Melinex S type; Toray DuPont thermoplastic elastomer Hytrel 4057; The sample was prepared in the same manner as in Example 1 except that the reversible thermosensitive recording layer and the protective layer were coated on the PET side.
[0073]
Example 4
The support was changed to Teijin DuPont's milk white PET film U298W; 188 μm, Toray DuPont's Hytrel 6347; A sample was prepared and a sample was obtained in the same manner as in Example 1 except that the protective layer was coated on the PET side.
[0074]
Example 5
Transesterification of dimethyl isophthalate, dimethyl sebacate, and hexamethylene glycol with a dibutyltin diacetate catalyst followed by an amorphous polyester synthesized by a condensation reaction and polybutylene terephthalate, a separate condensation reaction product, are heated. The polyester block copolymer obtained by melting was melted at 250 ° C., extruded from a T-die, and cast on a PET film having a thickness of 300 μm on a 75 μm thickness as a support. This PET film is a polyethylene terephthalate (PET) film Melinex S type manufactured by Teijin DuPont, which is 75 μm thick. In advance, an acrylic urethane hybrid resin hybridurde HY560 manufactured by Air Products is used with a Meyer bar so that the thickness is 1 μm. Coated and dried. In addition, it casted so that the surface which coated this hybrid resin of PET film beforehand came to the cast side. Thereafter, a sample was prepared in the same manner as in Example 1 except that a reversible thermosensitive recording layer was formed on the PET film side to obtain a sample.
[0075]
Comparative Example 1
A sample was prepared in the same manner as in Example 1 except that the support was changed to Teijin DuPont milk white PETU298W; 250 μm thick.
Comparative Example 2
A sample was prepared in the same manner as in Example 1 except that the support was changed to Toyobo Co., Ltd. Crisper G1212; 250 μm thick.
[0076]
Comparative Example 3
A sample was prepared in the same manner as in Example 1 except that the support was changed to a polypropylene synthetic paper FGS130 manufactured by YUPO Corporation, having a thickness of 130 μm.
Comparative Example 4
Commercially available PET-based relite sheet 430-BD (black) manufactured by Ricoh Co .; 135 μm thickness was used as it was.
[0077]
Comparative Example 5
A sample was prepared in the same manner as in Example 1 except that the support was changed to a silicon rubber sheet (thickness 0.5 mm).
Comparative Example 6
A sample was prepared in the same manner as in Example 1 except that the support was changed to a PET-G EPC410 manufactured by Tsutsunaka Plastic Industry Co., Ltd .;
Comparative Example 7
The support was changed to Teijin DuPont Milk White PETU298W; 188 μm thick, Toray DuPont Hytrel 6347; 50 μm thick bonded to 5 μm thick Cemedine Co. A sample was prepared in the same manner as in Example 1 except that the protective layer was coated on the PET side.
[0078]
Evaluation
<Vertical angle of fold>
Bending test:
When cut into a strip-shaped sample with a width of 20 mm and a length of 150 mm, the reversible thermosensitive recording layer surface is folded inward at the center, and conforms to the provisions of JIS Z 0237 (1991), section 8.2.3. Wrapped with a rubber layer with a spring hardness of 80 Hs, a thickness of 6 mm, a width of 45 mm, a diameter (including the rubber layer) of about 95 mm, and a mass of 2000 g. Thereafter, after standing for 24 hours in an environment of a temperature of 25 ± 2 ° C. and a humidity of 60 ± 5%, the angle with the fold as the apex angle was measured with a protractor.
[0079]
<Physical properties>
The tensile strength and elongation were measured according to JIS C 2318 (1997).
[0080]
<Number of rewrites>
The sample size was standardized to A5 size, and rewrite durability evaluation (printing → erasing / times) was performed with Oji Paper Prototype Rewrite Printer (thermal head writing and erasing were performed with a heat roll). Assuming soiling in practical use, each time 10 rewrites were completed, it was washed for 3 minutes with a washing machine (NA-FD6001 manufactured by Matsushita Electric Industrial Co., Ltd.) in an aqueous solution of 0.1% by weight of detergent (attack manufactured by Kao Corporation). . After rinsing with running water, it was drained and dried in an oven at 40 ° C. for 20 minutes to resume the rewrite durability evaluation.
[0081]
Usually, as the number of rewrites increases, wakame-shaped wavy deformation occurs on the medium parallel to the medium feeding direction in the printer. In addition, before and after each washing, there was a tendency of bending or deformation that seems to be caused by stirring and collision. These eventually become creases and wrinkles, and printing / erasing omission occurs. The number of rewrites until this occurred was counted.
The evaluation test results are summarized in Table 1.
[0082]
[Table 1]

[0083]
<Evaluation>
In each of the examples where the apex angle of the fold was 90 ° or more, rewrite was possible 500 times or more.
From Comparative Examples 1 and 4, it was found that when polyethylene terephthalate was used alone as a support, the sheet was deformed after 100 to 200 rewrites, resulting in poor printing and a long life.
From Comparative Example 2, it was found that the life of the foamed polyethylene terephthalate was hardly improved in the cushioning property by the voids as compared with ordinary PET.
From Comparative Examples 3 and 6, even if it is a thermoplastic resin, Thermoplastic elastomer with specific rubber elasticityIt was found that the polypropylene synthetic paper and PET-G resin that do not contain styrene do not improve the service life.
In Comparative Example 5,Because silicon rubber is used for the support instead of thermoplastic elastomer,The apex angle of the fold is 180 °, and no linear crease remains as a permanent deformation in the folded portion. That is, it was found that a visible fold could not be confirmed. Such an elastic reversible thermosensitive recording medium does not have sufficient rigidity (stiffness) to withstand use in the range of practical thinness, and it is actually because it cannot be sent out from the stocker or transported in the printer. It was found that it cannot be used.
By comparing Example 4 and Comparative Example 7,Thermoplastic elastomer with specific rubber elasticityIt was found that a support having a composition ratio of about 20% cannot greatly contribute to the rewrite life. 25% or more is sufficient.
[0084]
【The invention's effect】
If the reversible thermosensitive recording medium satisfies the crease test defined in the present invention, the occurrence of wakame-like wavy deformation that occurs in the medium with an increase in the number of rewrites can be suppressed. It has become possible to prevent printing / erasing omissions that occur, and to greatly improve the rewrite life compared to conventional PET-based reversible thermosensitive recording media.

Claims (3)

A reversible thermosensitive recording medium comprising a reversible thermosensitive recording layer on a support, the reversible thermosensitive recording medium satisfying a bending test under the following conditions, and has a tensile strength of 140 MPa or less and an elongation of 150% or more. The support is composed of one or more layers, at least one layer of which is JIS K It consists of a polyester-based thermoplastic elastomer having a tensile permanent strain of 5% or less when a tensile strain of 25% is given in the tensile permanent strain test specified in 6262 (1997), and the thermoplastic as the support. A reversible thermosensitive recording medium comprising 25% by mass or more of an elastomer .
Bending test:
When cut into a strip-shaped sample with a width of 20 mm and a length of 150 mm, it can be visually checked by folding it in the middle and reciprocating it 20 times with a roller specified in the crimping device in Section 8.2.3 of JIS Z 0237 (1991). After a crease is formed, and then left for 24 hours in an environment with a temperature of 25 ± 2 ° C. and a humidity of 60 ± 5%, the angle with the crease apex angle is 90 degrees or more and less than 180 degrees. 2. The reversible thermosensitive recording medium according to claim 1, wherein the support is composed of multiple layers, and the support as a whole contains 25% by mass or more of the thermoplastic elastomer . Wherein between the support and the thermosensitive recording layer, the side without the thermosensitive recording layer of the support, the thermosensitive recording layer further include one or more layers on at least one place on the surface side of the, according to claim 1 or 2 comprising a Reversible thermosensitive recording medium.