JP2006001237A - Thermal recording sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording sheet which can be easily bent, stretched and contracted without spoiling appearance. <P>SOLUTION: The thermal recording sheet 10 comprises a substrate sheet 1 formed of an olefin resin and with an elastic modulus of ≤600 MPa, and a thermal recording material layer 2 provided on this substrate sheet 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording sheet capable of recording characters and pictures by heating in a pattern.

  A thermal recording sheet is known as a recording sheet that can easily record (print) characters and patterns with a relatively simple apparatus. The heat-sensitive recording sheet is provided with a heat-sensitive recording material layer formed of a resin to which a leuco dye and a developer are added, for example, on a base sheet (see, for example, Patent Document 1). The base sheet is generally formed of paper or polyethylene terephthalate. In such a heat-sensitive recording sheet, a desired character or picture is printed by heating the heat-sensitive recording material layer in a pattern with a heat-sensitive recording printer (thermal printer) or the like.

  When a heat-sensitive recording sheet is used, printing can be performed in a short time and at low cost even when the lot is small, as compared with the case where letterpress printing is performed on a base sheet such as paper. In addition, when using a recording sheet (recording sheet that is printed using a transfer ribbon) using a heat-melt transfer method or a heat sublimation transfer method, printed information remains on the transfer ribbon that becomes waste after use. However, when a heat-sensitive recording sheet is used, there is no risk of information leaking from the waste even if personal information, trade secret information, or the like is printed.

The heat-sensitive recording sheet is used as a paper sheet for facsimile or a receipt printed on a register, or as a pressure-sensitive adhesive sheet or pressure-sensitive label attached to a product or the like with an adhesive layer provided on the back surface. Recently, there is a demand for use in a state where the sheet is bent or stretched, such as by attaching a heat-sensitive recording sheet to a curved surface portion or using it for a bracelet for identifying a patient in a hospital or the like.
Japanese Patent Publication No. 5-4913

  However, in the conventional thermal recording sheet, since the base sheet is formed of a material having poor flexibility such as paper or polyethylene terephthalate, it is difficult to bend into a desired shape if it is used in the bent state as described above. There are many things. In addition, when such a thermal recording sheet is forcibly bent, a high bending stress is generated in the entire thermal recording sheet, so that the thermal recording material layer is cracked or broken and the appearance of the thermal recording sheet is increased. There is a risk of damage.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a heat-sensitive recording sheet that can be easily bent and stretched without impairing the appearance.

  The heat-sensitive recording sheet of the present invention for solving the above-described problems has a base sheet having an elastic modulus of 600 MPa or less formed of an olefin resin and a heat-sensitive recording material layer provided on the base sheet. Features.

  According to this invention, since the base sheet has the above elastic modulus, a heat-sensitive recording sheet having high flexibility and stretchability can be easily obtained. Further, when the thermal recording sheet is bent or stretched, shear stress and compression (tensile) stress (hereinafter simply referred to as “stress”) applied to the entire thermal recording sheet are absorbed by the base sheet, and as a result. As described above, since the stress applied to the heat-sensitive recording material layer due to bending and expansion / contraction is reduced, the occurrence of cracks and breaks in the heat-sensitive recording material layer is suppressed. Therefore, it is possible to obtain a heat-sensitive recording sheet that can be easily bent and stretched without impairing the appearance.

  In the heat-sensitive recording sheet of the present invention, it is preferable that a surface protective layer is further provided on the heat-sensitive recording material layer in the heat-sensitive recording sheet.

  According to the present invention, desired characteristics can be added to the heat-sensitive recording sheet by the surface protective layer, so that it becomes easy to obtain a heat-sensitive recording sheet having various characteristics according to the application and required performance.

  In the heat-sensitive recording sheet of the present invention, in the heat-sensitive recording sheet, the surface protective layer is preferably formed from a cured product of an ionizing radiation curable resin.

  According to this invention, since it has a surface protective layer formed from a cured product of an ionizing radiation curable resin, weather resistance, solvent resistance, scratch resistance, etc. can be imparted to the thermal recording sheet, As a result, it is possible to expand the application of the thermal recording sheet.

  In addition, when a conventionally used heat-sensitive recording sheet is provided with an inflexible surface protective layer made of a cured product of an ionizing radiation curable resin, it becomes difficult to bend or stretch the heat-sensitive recording sheet. In addition, if the forcible bending or expansion is applied forcibly, the surface protective layer is cracked or broken and the appearance is easily impaired, but according to the present invention, the elastic modulus of the base sheet is within the above range. The base sheet can absorb the stress when bending or stretching is applied, and as a result, the thermal recording sheet can be bent or stretched while preventing the surface protective layer from cracking or breaking. It becomes easy.

  In the heat-sensitive recording sheet of the present invention, it is preferable that an intermediate layer is further provided between the heat-sensitive recording material layer and the surface protective layer.

  According to this invention, since the intermediate layer is provided between the heat-sensitive recording material layer and the surface protective layer, the adhesion between the heat-sensitive recording material layer and the surface protective layer can be improved.

  In the heat-sensitive recording sheet of the present invention, it is preferable that a pressure-sensitive adhesive layer is further provided on the back surface of the base sheet in the heat-sensitive recording sheet. The “back surface of the base material sheet” in the present invention means a surface on the side opposite to the surface on the side where the heat-sensitive recording material layer is provided, among the surfaces in the thickness direction of the base material sheet.

  According to this invention, since the pressure-sensitive adhesive layer is provided on the back surface of the base material sheet, this heat-sensitive recording sheet can be easily attached to various adherends.

  In the heat-sensitive recording sheet of the present invention, it is preferable that a release sheet is further provided on the outer surface of the pressure-sensitive adhesive layer in the heat-sensitive recording sheet. The “outer surface of the pressure-sensitive adhesive layer” in the present invention means a surface on the side opposite to the surface on the back surface side of the base material sheet among the surfaces in the thickness direction of the pressure-sensitive adhesive layer.

  According to the present invention, since the release sheet is provided on the pressure-sensitive adhesive layer, it is easy to handle and store the heat-sensitive recording sheet before use.

  According to the heat-sensitive recording sheet of the present invention, a sheet that can be easily bent and stretched without deteriorating the appearance can be obtained, so that it is used by being attached to a curved surface portion or deformed into a bracelet shape. It is possible to expand the application of the thermal recording sheet.

  Hereinafter, the thermal recording sheet of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing the basic structure of a thermal recording sheet 10 of the present invention. As shown in FIG. 1, the heat-sensitive recording sheet 10 of the present invention comprises a base sheet 1 and a heat-sensitive recording material layer 2 provided on the base sheet 1 as essential constituent members. Hereinafter, these indispensable constituent members (hereinafter referred to as “essential members”) will be described with reference to FIG. 1 and FIG. 2 to be described later, and then arbitrary constituent members (hereinafter referred to as “optional members”). This will be described with reference to the drawings as appropriate.

I. Essential components;
(Substrate sheet)
The base sheet 1 has an elastic modulus of 600 MPa or less. That is, the base sheet 1 is rich in flexibility. Therefore, the thermal recording sheet 10 can be easily bent or stretched, and even if the thermal recording sheet 10 is bent or stretched, the thermal recording material layer 2 is hardly cracked or broken.

  From the viewpoint of preventing the thermal recording material layer 2 from being cracked or broken when the thermal recording sheet 10 is bent or stretched, the elastic modulus of the base sheet 1 is more preferably 350 MPa or less. The lower limit of the elastic modulus of the base sheet 1 is determined in consideration of the ease of handling when the base sheet 1 is manufactured, and this value is usually about 200 MPa, although it depends on the composition of the material. A base material sheet having an elastic modulus of less than 200 MPa may be cut or deformed when produced by sheeting (sheeting) using a calendar roll machine or the like.

  Here, the elastic modulus is measured by a plastic tensile test method of JIS-K7113. Specifically, for the base sheet 1 processed into the shape of a No. 2 type test piece, data measured by performing a tensile test under the conditions of 25 ° C., a tensile speed of 50 mm / min, and a distance between grips of 80 mm are obtained. This is a value calculated based on the original.

  The base sheet 1 is made of, for example, olefin resin such as polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, ethylene-propylene-butene copolymer, ethylene-vinyl alcohol copolymer, and olefin thermoplastic elastomer. Can be formed. As long as the above-mentioned elastic modulus can be obtained, one kind of the above olefinic resins may be used alone, or a plurality of kinds may be mixed and used. When a plurality of types are mixed and used, it becomes easy to adjust the elastic modulus of the base sheet 1.

  From the viewpoint of forming the base sheet 1 having the above elastic modulus, it is particularly preferable to use an olefin-based thermoplastic elastomer as the material of the base sheet 1. As the olefin-based thermoplastic elastomer, an olefin-based thermoplastic elastomer that is a mixture of a hard segment composed of a crystalline olefin-based resin and a soft segment composed of an amorphous olefin-based resin can be used. For example, (A) an olefinic thermoplastic elastomer described in JP-A-5-77371, (B) an olefinic thermoplastic elastomer described in JP-A-7-316358, (C) Examples thereof include olefinic thermoplastic elastomers described in JP-A-6-23278. Further, (D) an olefinic thermoplastic elastomer that is a mixture of a hard segment made of a crystalline olefin resin and a soft segment made of a partially cross-linked olefin elastomer (rubber) can also be used. Specific examples of the (D) olefinic thermoplastic elastomer include (D-1) an olefinic thermoplastic elastomer described in JP-B-5321021, and (D-2) JP-B-53-34210. And (D-3) olefinic thermoplastic elastomers described in JP-B-56-15741.

  The olefinic thermoplastic elastomer (A) is a resin obtained by mixing crystalline polypropylene as a hard segment and amorphous polyolefin as a soft segment in which the mass ratio of the propylene component is 50% by mass or more. Preferred examples of the crystalline polypropylene include propylene-ethylene random copolymer and propylene-1 butene random copolymer. Preferred examples of the amorphous polyolefin include propylene-1 butene-ethylene terpolymer. When this olefinic thermoplastic elastomer is used, the base material sheet 1 which is rich in flexibility and excellent in transparency and mechanical strength can be formed.

  The olefin-based thermoplastic elastomer (B) is a composition in which a crystalline polyolefin as a hard segment is mixed with a low crystalline polyolefin as a soft segment having a propylene and / or 1-butene content of 50% by mass or more. It is a resin in which 0.5 parts by mass or more of an oil gelling agent such as N acylamino acid amine salt and N acylamino acid ester is added to 100 parts by mass. When this olefinic thermoplastic elastomer is used, the base material sheet 1 which is rich in flexibility and whose surface adhesiveness is suppressed can be formed.

  The olefinic thermoplastic elastomer (C) has a melt index of 0.1 to 4 g / 10 min, isotactic polypropylene as a hard segment insoluble in boiling heptane, a number average molecular weight Mn of 25,000 or more, and a weight average A soft polypropylene composed of atactic polypropylene as a soft segment soluble in boiling heptane in which the ratio of the molecular weight Mw to the number average molecular weight Mn is Mw / Mn ≦ 7. When this olefinic thermoplastic elastomer is used, the base material sheet 1 which is rich in flexibility and excellent in mechanical properties can be formed.

  The olefinic thermoplastic elastomer (D-1) is produced by uniformly blending and mixing a crystalline olefin polymer as a hard segment and a partially cross-linked monoolefin copolymer rubber as a soft segment. Resin. Examples of the crystalline olefin polymer that is a hard segment include polyethylene, polypropylene, and polymethylpentene. Examples of the monoolefin copolymer rubber that is a soft segment include ethylene-propylene copolymer rubber, ethylene-propylene-non-polymer. Examples thereof include conjugated terpolymer diene rubber.

  The olefinic thermoplastic elastomer (D-2) is prepared by mixing an olefinic polymer as a hard segment and an uncrosslinked monoolefin copolymer rubber as a soft segment with the addition of a crosslinking agent, and melt kneading. This is a resin produced by partially crosslinking the soft segment.

  The olefinic thermoplastic elastomer (D-3) comprises a peroxide-decomposable olefinic polymer as a hard segment, a peroxide-crosslinked olefinic copolymer rubber and a peroxide non-crosslinked hydrocarbon rubber as a soft segment, It is a resin produced by adding a mineral oil softener such as a paraffinic or naphthenic softener and mixing them, and then melt-kneading them in the presence of an organic peroxide to partially crosslink soft segments. The peroxide-decomposable olefin polymer as a hard segment has the property that the molecular weight decreases and the fluidity increases when mixed and heated with a peroxide. As such a polymer, for example, isotactic polypropylene is used. , Propylene-ethylene copolymer, propylene-butene-1 copolymer and the like. Peroxide-crosslinked olefin copolymer rubber as a soft segment has the property of cross-linking and reducing fluidity when mixed with peroxide and heated, and examples of such copolymer rubber include ethylene- Examples include propylene copolymer rubber and ethylene-propylene-nonconjugated terpolymer diene rubber. Peroxide non-crosslinked hydrocarbon rubber as a soft segment has the property that it does not crosslink even when heated with a peroxide and does not change in fluidity. Examples of such hydrocarbon rubber include polyisobutylene and butyl rubber. Is mentioned.

  The mass ratio of the hard segment to the soft segment (hard segment: soft segment) in the olefin-based thermoplastic elastomer is usually 10:90 to 90:10, and the elastic modulus of the base sheet 1 is within this range. The pressure is adjusted to 600 MPa or less. For example, when the blending ratio of the soft segment is increased within this range, the elastic modulus of the base sheet 1 can be decreased.

  Additives such as a colorant, a filler, a heat stabilizer, a flame retardant, an ultraviolet absorber, and a radical scavenger are added to the base sheet 1 as long as the base sheet 1 can have the above elastic modulus. can do. Examples of the colorant include organic pigments such as isoindolinone yellow, quinacridone red, and phthalocyanine blue, and inorganic pigments such as petals, yellow lead, ultramarine blue, carbon black, titanium white, antimony white, and lead white. As a heat-sensitive recording sheet, since there is generally a great demand for a white type in order to ensure sufficient concealing property, a sheet mainly composed of a white pigment such as titanium white is usually used most often. It is preferable that the addition amount of a coloring agent is about 0-20 mass% from a viewpoint which makes the elasticity modulus of the base material sheet 1 in said range. As the filler, powder having an average particle size of about 0.1 to 10 μm, such as calcium carbonate, barium sulfate, clay, and talc, is used. It is preferable that the addition amount of an inorganic filler is about 0-20 mass% from a viewpoint which makes the elasticity modulus of the base material sheet 1 in said range.

  The base sheet 1 is obtained, for example, by melt-kneading the above forming material and molding the sheet into a sheet or film by an extrusion molding method, a calendar method, or the like. At this time, whether or not the film is stretched can be appropriately selected. In the case of stretching, for example, uniaxial stretching or biaxial stretching is appropriately applied.

  The thickness of the base sheet 1 is preferably 30 to 120 μm. When the thickness of the base sheet 1 is larger than 120 μm, the thermal recording sheet 10 becomes too thick and it becomes difficult to bend or stretch the thermal recording sheet 10. Further, when the thickness of the base sheet 1 is smaller than 30 μm, it is difficult to form the base sheet 1 or when the thermosensitive recording sheet 10 is bent or stretched within a normal use range. The base sheet 1 may be easily broken.

  The base sheet 1 may have a single-layer structure or a laminated structure composed of a plurality of layers. From the viewpoint of flattening the surface of the base sheet 1, as in the base sheet 1 </ b> A shown in FIG. 2, an upper layer 1 a to which no additive is added, a middle layer 1 b to which an additive is added, and a lower layer to which no additive is added. A three-layer structure composed of 1c is preferable. For example, in the case of forming a single-layer base sheet, when the molten resin to which the additive has been added is extruded from the extruder, the molten resin and the extrusion port of the extruder come into contact with each other on the sheet surface. In the case of forming the base sheet 1A having the three-layer structure as described above, the molten resin not containing the additive is not the molten resin containing the additive. Since it comes into contact with the mouth, the sheet surface tends to be flat.

  One or both surfaces of the base sheet 1, 1A are preferably subjected to easy adhesion treatment such as application of an easy adhesion primer layer, corona discharge treatment, plasma treatment, ozone treatment, flame treatment and the like. When easy adhesion treatment is performed on the surface of the base sheet 1, 1A, the adhesiveness with the heat-sensitive recording material layer 2 and the pressure-sensitive adhesive layer 5 described later is improved. As a material for the easy adhesion primer layer (also referred to as anchor coat), polyester resin, polycarbonate resin, polyamide resin, acrylic resin, epoxy resin, urethane resin, chlorinated polypropylene, polyethyleneimine, alkyl titanate, and the like can be used. .

  In addition, when the base sheet 1, 1A is formed of an olefin resin, generation of chlorine compound gas such as dioxin is suppressed when the thermal recording sheet 10 is incinerated.

(Thermal recording material layer)
The heat-sensitive recording material layer 2 is formed using various known heat-sensitive recording materials. As the heat-sensitive recording material, for example, a material obtained by adding a leuco dye and a developer to a binder resin can be used.

  Examples of leuco dyes include (A) 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-diethylaminophenyl)- Blue coloring dyes such as 6-dimethylaminophthalide, (B) green coloring dyes such as 3- (N-ethyl-Np-tolyl) amino-7-N-methylanilinofluorane, (C) Red chromogenic dyes such as 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, (D) 3- (N-ethyl-N-isoamyl) amino-6-methyl Black coloring dyes such as -7-anilinofluorane and 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluorane can be used. Each leuco dye mentioned above may be used individually by 1 type, and may mix and use multiple types. The content of the leuco dye in the heat-sensitive recording material layer 2 is usually about 5 to 35% by mass.

Developers include (I) phenolic compounds such as 4,4′-isopropylidenediphenol, 4,4′-cyclohexylidenediphenol, (II) N- (p-tolylsulfonyl) carbamoyl acid-p - cumyl phenyl ester, N-(p-tolyl sulfonyl) having a _-SO 2 NH- bond in the molecule, such as a carbamoyl acid -p- benzyloxyphenyl ester, (III) p-chlorobenzoic acid zinc, 4- And zinc salts of aromatic carboxylic acids such as [2- (p-methoxyphenoxy) ethyloxy] zinc salicylate. The content of the developer is not particularly limited, and is usually about 1 to 10 parts by mass and preferably about 1 to 5 parts by mass with respect to 1 part by mass of the leuco dye.

  Examples of the binder resin containing a leuco dye or a developer include oxidized starch and hydroxyethyl cellulose.

  If necessary, the heat-sensitive recording material layer 2 may contain a storability improving agent for further improving the storage stability of the recorded characters and pictures and a sensitizer for further increasing the recording sensitivity. Examples of the storage stabilizer include (i) hindered products such as 2,2′-methylenebis (4-methyl-6-tert-butylphenol) and 4,4′-thiobis (2-methyl-6-tert-butylphenol). Examples thereof include epoxy compounds such as phenol compounds, (ii) 4,4′-diglycidyloxydiphenylsulfone, 4-benzyloxy-4 ′-(2-methylglycidyloxy) diphenylsulfone. Specific examples of the sensitizer include stearamide, dibenzyl terephthalate and the like. Content of a storage stabilizer and a sensitizer is not specifically limited, It adjusts suitably in 4 mass parts or less of each with respect to 1 mass part of leuco dyes.

  The heat-sensitive recording material layer 2 preferably contains an auxiliary agent as necessary. Examples of the assistant include pigments such as kaolin, light (heavy) calcium carbonate, and titanium oxide, and surfactants such as sodium dioctylsulfosuccinate and sodium dodecylbenzenesulfonate.

The heat-sensitive recording material layer 2 is composed of, for example, water as a dispersion medium, a leuco dye finely pulverized to an average particle size of 2 μm or less, a developer, a binder resin, and a storage stabilizer added as necessary. It is formed by adding a sensitizer and an auxiliary agent and mixing them by stirring to prepare a coating solution for the heat-sensitive recording material layer, coating the coating solution on the substrate sheet 1 and drying it. The coating amount of the coating liquid for heat-sensitive recording material layer has a weight after drying was 2~12g / ^{m 2} approximately, and preferably from 3 to 10 g / ^{m 2} approximately.

II. Optional components;
In the thermosensitive recording sheet 10 having the basic structure shown in FIG. 1, optional members such as a surface protective layer, an intermediate layer, a pressure-sensitive adhesive layer, and a release sheet can be appropriately provided according to required performance and use. Hereinafter, each arbitrary member will be described.

(A) a surface protective layer;
FIG. 3 is a cross-sectional view showing an example of a thermal recording sheet 10 </ b> A provided with the surface protective layer 3. As shown in FIG. 3, the surface protective layer 3 is provided on the heat-sensitive recording material layer 2, and imparts solvent resistance, scratch resistance, and weather resistance to the heat-sensitive recording sheet 10A. 2 is a layer for retaining the characters and designs recorded in 2 for a long period of time. Further, by providing the surface protective layer 3, it is possible to give gloss to the surface of the thermal recording sheet 10A.

  Here, the heat-sensitive recording material layer 2 is generally easily colored, discolored or faded by heating or application of an organic solvent. Therefore, it is preferable to use a coating liquid for forming the surface protective layer 3 that does not require heating or use of an organic solvent in the process of forming the surface protective layer 3.

  From the viewpoint of suppressing color development or the like of the heat-sensitive recording material layer 2, as a coating liquid for forming the surface protective layer 3, an aqueous solution or aqueous dispersion of an aqueous resin (resin that can be dissolved or dispersed in water), or It is preferable to use an ionizing radiation curable resin that does not use a solvent. From the viewpoint of forming the surface protective layer 3 in a short time and enhancing the durability of the surface protective layer 3, it is more preferable to use an ionizing radiation curable resin.

  The ionizing radiation curable resin is composed of a monomer (monomer) or a prepolymer (including oligomers) having an ionizing radiation polymerizable functional group such as a radical polymerizable unsaturated group or a cationic polymerizable functional group in the molecule. , Both monomers and prepolymers may be included. Each of the prepolymer and the monomer may be used alone, or a plurality of types may be mixed and used.

  Examples of the prepolymer having a radical polymerizable unsaturated group include polyester (meth) acrylate, urethane (meth) acrylate, epoxy (meth) acrylate, melamine (meth) acrylate, triazine (meth) acrylate, and silicone (meth) acrylate. Can be mentioned. In the present specification, “(meth) acrylate” refers to methacrylate or acrylate. Examples of the prepolymer having a cationic polymerizable functional group include prepolymers of epoxy resins such as bisphenol type epoxy resins and novolak type epoxy resins, and vinyl ether type resins such as fatty acid type vinyl ethers and aromatic vinyl ethers. The molecular weight of the prepolymer is usually about 250 to 100,000.

  Examples of the monomer having a radical polymerizable unsaturated group include monofunctional monomers such as acrylate compounds such as methyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and phenoxyethyl (meth) acrylate. In the polyfunctional monomer, for example, diethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylylpropane tri (meth) acrylate, trimethylylpropane ethylene oxide tri (meth) acrylate, pentaerythritol tetra (meth) ) Acrylate compounds such as acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane trithioglycolate, pentaerythritol In addition to the thiol-based compounds Lumpur tetrathioglycolate like, polyenes, etc. that is generated by adding the allyl alcohol to both ends of the polyurethane consisting of diol and diisocyanate.

  When the ionizing radiation curable resin is cured with ultraviolet rays, it is preferable to add a photopolymerization initiator to the ionizing radiation curable resin. Photoinitiators used for monomers or prepolymers having radically polymerizable unsaturated groups include benzoin, benzoin methyl ether, acetophenone, dimethylaminoacetophenone, benzophenone, p-phenylbenzophenone, 2-methylthioxanthone , 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone and the like. Photopolymerization initiators used for monomers or prepolymers having cationically polymerizable unsaturated groups include aromatic sulfonium salts, aromatic diazonium salts, aromatic iodonium salts, metallocene compounds, benzoin sulfonic acid esters, etc. Is mentioned. The photopolymerization initiator is usually added in an amount of about 0.1 to 5 parts by mass with respect to 100 parts by mass of the ionizing radiation curable resin.

  It is preferable to add a photosensitizer to the ionizing radiation curable resin. As the photosensitizer, for example, p-dimethylbenzoic acid ester, tertiary amines, thiol sensitizers and the like can be used. Moreover, you may add a filler, a lubricant, a ultraviolet absorber, an antibacterial agent, an antifungal agent, etc. to ionizing radiation curable resin as needed. As the filler, inorganic fillers such as calcium carbonate, kaolin, silica, and alumina, or resin beads such as polyethylene resin, polyamide resin, and urethane resin can be used. As the lubricant, fatty acid metal salts such as zinc stearate and calcium stearate, fatty acid, fatty acid amide, long chain alkyl alcohol, paraffin wax and the like can be used.

When an ionizing radiation curable resin is used as a coating liquid for forming the surface protective layer 3, the ionizing radiation curable resin is applied to the heat-sensitive recording material layer 2, and this ionizing radiation is irradiated to the ionizing radiation. The radiation curable resin is cured. The coating amount of the ionizing radiation curable resin is usually about 1 to 10 g / m ^{2 in} terms of the mass after curing. As a coating method, a roll coating method, a gravure roll coating method, a reverse roll coating method, an offset gravure coating method, or the like can be used.

  As the ionizing radiation, various kinds of radiation having energy capable of crosslinking or polymerizing the ionizing radiation curable resin can be used. As the ionizing radiation, ultraviolet rays or electron beams are usually used, and among these, electron beams are preferably used. When an electron beam is used as ionizing radiation, it is not necessary to add an initiator for photopolymerization to the ionizing radiation curable resin, and ionizing radiation curable even if an ultraviolet absorber is added to impart light resistance. Since the polymerization or crosslinking of the resin is not inhibited, the surface protective layer 3 having a high crosslinking density can be obtained stably.

  When the ionizing radiation curable resin is cured by an electron beam, the accelerating voltage of the electron beam is usually selected within the range of 70 to 300 kV depending on the type of ionizing radiation curable resin used and the thickness of the surface protective layer 3. Is done. Moreover, the irradiation amount of an electron beam is suitably selected in the range of 1-10 Mrad normally, Preferably it is 3-5 Mrad. The electron beam source is not particularly limited, and for example, various electron beam accelerators such as a cockroft Walton type, a bandegraft type, a resonant transformer type, an insulated core transformer type, a linear type, a dynamitron type, and a high frequency type should be used. Can do.

  When the ionizing radiation curable resin is cured by ultraviolet rays, radiation containing ultraviolet rays having a wavelength of 190 to 380 nm is used. The ultraviolet ray source is not particularly limited, and for example, a high pressure mercury lamp, a low pressure mercury lamp, a metal halide lamp, a carbon arc lamp, a black light (ultraviolet radiation type fluorescent lamp) or the like is used.

  As the above-mentioned aqueous resin, various resins can be used. Specific examples of the aqueous resin will be exemplified in the description of the intermediate layer described later. From the viewpoint of obtaining a durable, flexible or stretchable surface protective layer, a urethane-based, polyvinyl alcohol-based, or acrylic-based aqueous resin is preferable. When applying aqueous resin in the form of an emulsion, select an emulsion neutralizing agent that will not alter or degrade the thermal head of the printer for printing letters or designs on the thermal recording sheet as much as possible. There is a need to. From this viewpoint, it is preferable to use ammonia (water) or alkanolamines such as triethylamine and triisopropanolamine rather than using an inorganic metal salt as a neutralizing agent.

(B) an intermediate layer;
FIG. 4 is a cross-sectional view showing an example of a thermosensitive recording sheet 10 </ b> B provided with the intermediate layer 4. As shown in FIG. 4, the intermediate layer 4 is provided between the heat-sensitive recording material layer 2 and the surface protective layer 3 to improve the adhesion between the surface protective layer 3 and the heat-sensitive recording material layer 2, or to apply the intermediate layer 4. The surface protective layer 3 can be prevented from decreasing the glossiness of the surface protective layer 3 by permeating into the heat-sensitive recording material layer 2 or the surface of the heat-sensitive recording material layer 2 can be flattened. It is a layer for improving the coating suitability of the coating liquid for the protective layer.

  As described in the section of the surface protective layer 3, from the viewpoint of suppressing the color development of the heat-sensitive recording material layer 2, the coating liquid for forming the intermediate layer 4 is an aqueous resin solution or aqueous dispersion, or It is preferable to use an ionizing radiation curable resin. As the ionizing radiation curable resin, a material appropriately selected from the same materials as those exemplified in the section of the surface protective layer 3 can be used.

  Examples of water-based resins include cellulose (fibre) resins, acrylic resins, urethane resins, polyester resins, vinyl chloride-vinyl acetate copolymers, casein, starch, rosin resins, polyvinyl alcohol resins, epoxy resins, And polycarbonate resin. One of the above thermoplastic resins may be used alone, or a plurality of them may be used in combination.

  Examples of acrylic resins include polymethyl (meth) acrylate, polybutyl (meth) acrylate, methyl (meth) acrylate-ethyl (meth) acrylate copolymer, methyl (meth) acrylate-butyl (meth) acrylate copolymer, methyl ( Examples include a meth) acrylate-styrene copolymer, a methyl (meth) acrylate-2hydroxyethyl (meth) acrylate copolymer, and a methyl (meth) acrylate-2 hydroxyethyl (meth) acrylate-styrene copolymer.

  The urethane-based resin is mainly produced by reacting polyol (polyhydric alcohol) with polyisocyanate. As the polyol, for example, acrylic polyol, polyester polyol, polyether polyol and the like are used. Examples of the polyisocyanate include aromatic isocyanates such as 2,4-tolylene diisocyanate, xylene diisocyanate, and diphenylmethane diisocyanate, or 1,6-hexamethylene diisocyanate, hydrogenated tolylene diisocyanate, and isophorone diisocyanate. Aliphatic (or alicyclic) isocyanates are used. These polyisocyanates can also be used in the form of adducts, blocked isocyanates, or multimers such as trimers and pentamers.

  Various additives such as extender pigments, pigments, surfactants, ultraviolet absorbers, and heat stabilizers are added to the coating solution for forming the intermediate layer 4 as necessary. As extender pigments, particles of calcium carbonate, barium sulfate, silica, kaolinite, diatomaceous earth, white clay, aluminum hydroxide, zinc white and the like can be used.

The intermediate layer 4 is formed by applying a coating liquid for forming the intermediate layer 4 on the heat-sensitive recording material layer 2 and drying or curing the coating liquid. As a coating method, roll coating, bar coating, knife coating or the like can be used. The coating amount of the coating liquid is a weight after drying or curing is 2~12g / ^{m 2} approximately, and preferably from 3 to 10 g / ^{m 2} approximately.

(C) an adhesive layer;
FIG. 5 is a cross-sectional view showing an example of a thermal recording sheet 10 </ b> C provided with the pressure-sensitive adhesive layer 5. As shown in FIG. 5, the pressure-sensitive adhesive layer 5 is formed on the back surface of the base sheet 1 to bond the heat-sensitive recording sheet 10 </ b> C and a desired adherend. The pressure-sensitive adhesive layer 5 is formed as a uniform whole-surface solid layer or as a layer selectively formed at a desired location, depending on the application of the thermal recording sheet 10C. In addition, the code | symbol 6 in FIG. 5 shows the release sheet mentioned later.

  Examples of the pressure-sensitive adhesive used for forming the pressure-sensitive adhesive layer 5 include (meth) acrylic acid ester homopolymers, (meth) acrylic acid esters and copolymers of other monomers, acrylic pressure-sensitive adhesives, poly Synthetic rubber adhesives such as isoprene rubber, polybutadiene rubber, styrene-butadiene rubber, or natural rubber adhesives. A tackifier, a crosslinking agent, an antioxidant, an ultraviolet absorber, a silane coupling agent, and the like may be added to the pressure-sensitive adhesive as necessary.

  The pressure-sensitive adhesive layer 5 can be directly coated on the back surface of the base sheet 1, but is preferably formed by a transfer (coating) method. In the transfer method, a coating solution for the pressure-sensitive adhesive layer in which the above-mentioned pressure-sensitive adhesive is dissolved or dispersed in a solvent is applied to the release sheet, and the coated surface of the release sheet faces the back surface of the base sheet 1. The pressure-sensitive adhesive layer 5 is laminated on the base sheet 1. When the transfer method is employed, solvent drying and crosslinking are performed on the release sheet in a state separated from the heat-sensitive recording material layer 2. Therefore, the pressure-sensitive adhesive layer 5 can be dried and crosslinked by applying sufficient heat without causing unnecessary color development or the like in the heat-sensitive recording material layer 2. As a method for applying the coating liquid to the release sheet, a comma coating method, a roll coating method, or the like can be used, and the thickness of the pressure-sensitive adhesive layer 5 is preferably 5 to 30 μm. In addition, the release sheet used here is provided on the adhesive layer 5 as it is, and becomes a release sheet 6 described later.

(D) a release sheet;
The release sheet 6 is provided on the outer surface of the pressure-sensitive adhesive layer 5 as shown in FIG. 5, and when the pressure-sensitive adhesive layer 5 is inadvertently adhered to another object or the thermal recording sheet 10C is wound up. In other words, the adhesive layer 5 is temporarily bonded to the pressure-sensitive adhesive layer 5 until the heat-sensitive recording sheet 10C is used.

  As the release sheet 6, a release agent such as silicone resin is applied to the surface of paper such as high-quality paper, linter paper, sulfuric acid paper, glassine paper, craft paper, or resin sheets such as polyester resin and olefin resin. The machined one is used. The thickness of the release sheet 6 is usually 25 to 75 μm.

(E) other optional members;
In the heat-sensitive recording sheet of the present invention, optional members other than the optional members (a) to (d) described above can be appropriately provided. For example, in order to suppress heat conduction from the base sheet 1 (see FIG. 1) to the thermosensitive recording material layer 2 (see FIG. 2), a heat insulating material is provided between the base sheet and the thermosensitive recording material layer. A layer can be provided. Providing this heat insulating material layer suppresses the temperature rise of the heat sensitive recording material layer 2 even when the heat sensitive recording sheet 10 (see FIG. 1) is attached to an adherend that is at a relatively high temperature. It is possible to prevent color development, discoloration, or fading in the heat-sensitive recording material layer 2.

  Such a heat insulating material layer can be formed of, for example, a polyolefin-based resin or a urethane-based resin to which a foaming agent or a microballoon (hollow spherical particle) is added, According to heat dissipation etc., it selects suitably in the range of about 3-20 micrometers.

  The thermosensitive recording sheet of the present invention constituted by the members described above is printed on a container of chemicals, detergents, cosmetics, foods, beverages, etc. with desired characters or designs printed by a thermal recording printer (thermal printer). It can be used as various content display labels, price tag labels, etc., or as a bracelet used for patient identification in a hospital, and is particularly suitable for use in a bent state.

  In the heat-sensitive recording sheet of the present invention, since the elastic modulus of the base sheet is 600 MPa or less as described above, that is, since the base sheet is rich in flexibility, it is easy to obtain a sheet having high flexibility and stretchability. Can do.

  When the heat-sensitive recording sheet is bent, the stress applied to the entire heat-sensitive recording sheet is absorbed by the base material sheet, and as a result, the stress applied to the heat-sensitive recording material layer is reduced. For this reason, the occurrence of cracks and breaks in the heat-sensitive recording material layer is suppressed, and when the heat-sensitive recording sheet has a surface protective layer (see FIG. 3), the surface protective layer is cracked or broken. Is also suppressed. Therefore, it is possible to obtain a heat-sensitive recording sheet that can be easily bent and stretched without impairing the appearance, regardless of whether or not it has a surface protective layer.

  Furthermore, in the heat-sensitive recording sheet of the present invention, even when pulled in the in-plane direction, the tensile stress applied to the entire heat-sensitive recording sheet as it expands and contracts is absorbed by the base sheet, so that the heat-sensitive recording material layer is cracked. There is an advantage that breakage is difficult to occur. When a sheet made of resin is applied to the curved surface portion, the sheet may be applied while stretching the sheet in order to follow the shape of the curved surface portion. Since the heat-sensitive recording sheet of the present invention can absorb the tensile stress with the base sheet as described above, even when pasting in such a procedure, the pasting itself is easy and the deterioration of the appearance is suppressed. The

  In addition, when the thermal recording sheet of the present invention is pulled in the in-plane direction, since the tensile stress applied to the entire thermal recording sheet is absorbed by the base sheet, so-called necking hardly occurs in the base sheet. Also from this point, there is an advantage that the appearance is hardly impaired.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples.

Example 1
As a base material sheet, an olefin-based thermoplastic elastomer sheet (thickness 80 μm, width 15 cm) prepared by mixing a hard segment made of crystalline polypropylene and a soft segment made of styrene-butadiene rubber so as to have an elastic modulus of 600 MPa. ) Was used. The elastic modulus of the base sheet was measured by the plastic tensile test method of JIS-K7113 as described above in the description of the base sheet.

In producing the heat-sensitive recording sheet, first, corona discharge treatment was performed on both surfaces of the base sheet. Further, a black color-forming leuco dye, a developer and a sensitizer were added to methylcellulose resin, and this was dissolved in water to prepare a coating solution for a heat-sensitive recording material layer. And this coating liquid was apply | coated to the single side | surface of a base material sheet, it was made to dry, and the heat-sensitive recording material layer was formed. The coating amount of the coating solution at this time was 6 g / m ² (the amount after drying).

Next, 100 parts by mass of a 10% by mass aqueous solution of acetoacetyl-modified polyvinyl alcohol, 5 parts by mass of 10% by mass slurry (dispersion medium; water) of kaolin (average particle diameter; 1 μm), and aluminum hydroxide (average particle diameter; 1 μm) 50 mass% slurry (dispersion medium; water) 5 parts by mass and zinc stearate 30 mass% dispersion liquid (dispersion medium; water) 1 part by mass was prepared. Was coated on the heat-sensitive recording material layer so that the coating amount was 3 g / m ² (the amount after drying) and dried to form an intermediate layer.

  Next, a coating solution for a surface protective layer composed of urethane acrylate prepolymer and dipentaerythritol hexaacrylate is applied on the intermediate layer, and an electron beam with an acceleration voltage of 165 keV is applied to this coating solution at a dose of 3 Mrad. The surface protective layer was formed by irradiation to obtain a heat-sensitive recording sheet of Example 1.

(Example 2)
A heat-sensitive recording sheet of Example 2 was obtained in the same manner as in Example 1 except that a polypropylene-based thermoplastic elastomer sheet (thickness: 80 μm) adjusted to have an elastic modulus of 500 MPa was used as the base sheet.

Example 3
A thermosensitive recording sheet of Example 3 was obtained in the same manner as in Example 1 except that a polypropylene-based thermoplastic elastomer sheet (thickness: 80 μm) adjusted to have an elastic modulus of 300 MPa was used as the base sheet.

(Comparative Example 1)
A thermosensitive recording sheet of Comparative Example 1 was obtained in the same manner as in Example 1 except that a polypropylene-based thermoplastic elastomer sheet (thickness: 80 μm) adjusted to have an elastic modulus of 700 MPa was used as the base sheet.

(Evaluation)
(A) Bending test I;
Each heat-sensitive recording sheet obtained in Examples 1 to 3 and Comparative Example 1 was bent at 180 ° at room temperature (about 25 ° C.) with the surface protective layer on the outside, and the bent portions were visually observed. Then, the presence or absence of cracks was evaluated. In addition, a thermal printer (Sato, model number: MR410e) is used at the bent position of the thermal recording sheet, the printing speed is set to 6 inches (15 cm) / second, the printing density level is printed at the highest level, and printing is performed appropriately. Evaluated what was done. Further, each obtained thermal recording sheet was bent at 180 ° at a low temperature (0 ° C.), and in the same manner as described above, the presence or absence of cracks and the evaluation of whether or not printing was properly performed were performed. These results are shown in Table 1.

  In Table 1, the case where no crack was observed on the thermal recording sheet was indicated by ○, the case where a crack was observed was indicated by ×, the case where the thermal recording sheet was properly printed was indicated by ○, and the printed portion was colored. The case where there was no is represented by x.

(B) Bending test II;
Each of the heat-sensitive recording sheets obtained in Examples 1 to 3 and Comparative Example 1 was bent under the same conditions as in the bending test I, except that the surface protective layer was folded inside, and the cracks at the bent portions were observed. The presence / absence evaluation and the suitability of printing on the folded portion were evaluated. These results are also shown in Table 1.

  In Table 1, the case where no crack was observed on the thermal recording sheet was indicated by ○, the case where a crack was observed was indicated by ×, the case where the thermal recording sheet was properly printed was indicated by ○, and the printed portion was colored. The case where there was no is represented by x.

(C) tensile test;
Each thermal recording sheet obtained in Examples 1 to 3 and Comparative Example 1 was processed into a rectangular shape of 10 cm × 2.54 cm (1 inch), and the thermal recording sheet was 10% in the longitudinal direction by a tensile tester at room temperature. After stretching (1 cm), the surface of the thermosensitive recording sheet (surface of the surface protective layer) was visually observed to evaluate the presence or absence of cracks. Further, printing was performed on the stretched thermal recording sheet in the same manner as in the above bending test, and it was evaluated whether the printing was properly performed. These results are also shown in Table 1.

  In Table 1, the case where no crack was observed on the thermal recording sheet was indicated by ○, the case where a crack was observed was indicated by ×, the case where the thermal recording sheet was properly printed was indicated by ○, and the printed portion was colored. The case where there was no is represented by x.

(Evaluation results)
In each of the heat-sensitive recording sheets of Examples 1 to 3, no crack was observed in any of the bending test and the tensile test at normal temperature and low temperature, and printing was properly performed after each test. On the other hand, the thermal recording sheet of Comparative Example 1 shows cracks in both the bending test and the tensile test at normal temperature and low temperature, and the printed part does not develop color after each test and is not printed properly. It was.

It is sectional drawing which shows the basic structure of the thermosensitive recording sheet of this invention. It is sectional drawing which shows the other example of the structure of the base material sheet in the thermosensitive recording sheet of this invention. It is sectional drawing which shows the other example of the thermosensitive recording sheet of this invention. It is sectional drawing which shows the further another example of the thermosensitive recording sheet of this invention. It is sectional drawing which shows the further another example of the thermosensitive recording sheet of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A base material sheet 2 Thermal recording material layer 3 Surface protective layer 4 Intermediate layer 5 Adhesive layer 6 Release sheet 10, 10A, 10B, 10C Thermal recording sheet

Claims (6)

  A heat-sensitive recording sheet comprising: a base material sheet having an elastic modulus of 600 MPa or less formed of an olefin resin; and a heat-sensitive recording material layer provided on the base material sheet.   The heat-sensitive recording sheet according to claim 1, further comprising a surface protective layer provided on the heat-sensitive recording material layer.   The heat-sensitive recording sheet according to claim 2, wherein the surface protective layer is formed from a cured product of an ionizing radiation curable resin.   The heat-sensitive recording sheet according to claim 2, wherein an intermediate layer is further provided between the heat-sensitive recording material layer and the surface protective layer.   The heat-sensitive recording sheet according to any one of claims 1 to 4, wherein an adhesive layer is further provided on the back surface of the base sheet. The heat-sensitive recording sheet according to claim 5, further comprising a release sheet on the outer surface of the pressure-sensitive adhesive layer.

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