JP2008023856A - Base material film for rewritable recording medium and rewritable recording medium employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base material film for a rewritable recording medium, which is excellent in balance between color developing properties and color erasing properties by thermal energy and in visibility of color developed print when employed as the base material of the rewritable recording medium and further in adhesion between the base material film and the rewritable print layer. <P>SOLUTION: The base material film for the rewritable recording medium includes a coating layer for improving the adhesion with the rewritable print layer which is formed at least on one side of a plastic film, the plastic film has its light transmittance of ≤15% and its thermal conductivity of 0.037-0.080 W/mK. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a base film for a rewrite recording medium capable of forming and erasing an image by controlling thermal energy, and a rewrite recording medium using the same. More specifically, when used as a base material for a rewritable recording medium, it has a good balance between color developability and decolorability due to thermal energy, and has excellent visibility of colored prints. Furthermore, a base film and a rewritable print layer The present invention relates to a base film for a rewritable recording medium having good adhesion to the rewritable recording medium and a rewritable recording medium using the same.

  In recent years, reversible thermosensitive recording media (hereinafter referred to as rewrite recording media) capable of recording and erasing images have attracted attention. A typical example is a rewritable recording medium composed of a reversible developer which usually develops a colorless or light leuco dye and heats the leuco dye to develop a color and then re-heats it to erase the color.

As a base material for such a rewritable recording material, paper, non-woven fabric, woven fabric, synthetic resin film, synthetic resin laminated paper, synthetic paper, metal foil, glass and the like can be used according to the purpose. For use in a thermal printer or word processor that is widely used and has a thermal head, paper, synthetic resin film, synthetic resin laminated paper, synthetic paper, and the like are preferable. Above all, the polyethylene terephthalate film used in prepaid cards such as telephone cards and orange cards not only has high mechanical strength, but also has high smoothness, making it easy to make the reversible thermosensitive recording layer a uniform layer. The image can be sharpened. For example, a transparent polyester film or a white polyester film is used as a base material for a rewritable recording material (see, for example, Patent Documents 1 and 2).
JP 2000-263934 A JP 2003-11504 A

On the other hand, as a heat-sensitive recording medium using a leuco dye as a color former, means for interspersing a minute air layer in a heat-sensitive color developing layer, or a heat insulating layer containing an air layer, for example, between a substrate and a heat-sensitive color developing layer A method for imparting heat insulation to a heat-sensitive recording medium and improving heat-sensitive color development using a means for forming a film is disclosed (for example, see Patent Documents 3 and 4).
JP 2002-301871 A JP 2002-258754 A

In addition, a technique for improving color developability by using a heat-insulating film or synthetic paper having an apparent density of 0.6 to 0.9 g / cm ³ as a base film of a thermal recording medium is disclosed. (For example, see Patent Document 5).
JP 2005-81626 A

  In the case of the heat-sensitive recording medium disclosed in the above-mentioned patent document, it is only necessary to develop a color. Therefore, it is preferable to impart heat insulating properties from the viewpoint of improving the color developability. On the other hand, in the case of a rewritable recording medium, reversibility of coloring and decoloring is required. In the case of the rewritable recording medium, unlike the heat-sensitive recording medium, it is necessary to heat it to a colored state and then rapidly cool it to room temperature to fix the colored state.

  That is, the leuco dye and the developer are heated to a temperature higher than their melting, and both are mixed in the molten state to cause color development, and then rapidly cooled from this color development state to fix the color development state. Therefore, the fixation of the colored state is affected by the temperature drop rate from the molten state. For example, in the cooling, decoloring occurs in the process of lowering the temperature, and the density is relatively lower than the decolored state before the temperature increase or the colored state fixed by rapid cooling.

  On the other hand, the provision of heat insulation acts in the negative direction with respect to rapid cooling. Therefore, regarding the color developability in the rewritable recording medium, the provision of heat insulation does not lead to the manifestation of a unique effect on the color developability, and there is an optimum value. For example, in the methods disclosed in Patent Documents 3 and 4, the heat insulation is insufficient. On the contrary, the method disclosed in Patent Document 5 has a problem that the heat developability is excessive and acts as a negative factor for rapid cooling, so that it cannot be said that the color developability is the best unlike the thermal recording medium. have.

  On the other hand, with regard to decoloring, when the temperature of the colored state fixed by cooling by the above method is raised again, decoloring starts at a temperature lower than the color developing temperature. Therefore, in general, decoloring is performed by heating at a temperature lower than the color development temperature to remove the cooling. Therefore, imparting heat insulation is preferable from the viewpoint of improving decolorization as in the case of color development on a heat-sensitive recording medium.

  In addition, in the method in which a minute air layer is scattered in the heat-sensitive color developing layer, light scattering is caused by the minute air layer contained in the heat-sensitive color developing layer, so that the sharpness of the printed image is deteriorated. There is a case. Moreover, the method of forming a heat insulation layer between a base material and a thermosensitive coloring layer is economically disadvantageous because the cost for forming the heat insulation layer is added. Furthermore, the method of forming a heat insulating layer between the base material layer and the thermosensitive coloring layer is because the surface of the heat insulating layer formed on the base material has irregularities, so that after the heat insulating layer is formed, the surface is smoothed by calendering. The necessity of this is described, and it has the problem that it becomes further disadvantageous in terms of economy.

  In addition, the plastic film often lacks the adhesion of ink to various inks, and the same problem occurs in the reversible thermosensitive recording medium.

  The object of the present invention is to solve the above-mentioned problems in the prior art, and when used as a base material for a rewritable recording medium, it has an excellent balance between color developability and decolorability due to thermal energy, and is colored. An object of the present invention is to provide a base film for a rewritable recording medium that is excellent in printing visibility and has excellent adhesion between the base film and the rewritable printing layer.

  The rewritable recording medium substrate film of the present invention that can solve the above-mentioned problems is a rewritable recording medium substrate in which a coating layer that improves adhesion to the rewritable printing layer is formed on at least one surface of a plastic film. The plastic film is characterized by having a light transmittance of 15% or less and a thermal conductivity of 0.037 to 0.080 W / mK.

  The light transmittance of the film is more preferably 13% or less, and further preferably 10% or less. When the light transmittance exceeds 15%, the concealing property of the base film for rewritable recording medium is lowered, and the color of the printed layer provided on the film surface is reduced, and the sharpness of the printed image when printed is lowered. . Although the lower limit of the light transmittance is not limited, it is preferably 1% or more, more preferably 3% or more from the viewpoint of suppressing the deterioration of the mechanical properties of the film due to the inclusion of a large amount of an additive that decreases the light transmittance described later. preferable.

  The upper limit of the thermal conductivity of the base film for a rewritable recording medium of the present invention is more preferably 0.077 W / mK, and further preferably 0.074 W / mK. On the other hand, the lower limit is more preferably 0.039 W / mK and even more preferably 0.041 W / mK. When the thermal conductivity of the film satisfies the above range, the color development and decoloring properties are improved and the balance between the two is improved when printing is performed using the base material of the rewritable recording medium.

  When the thermal conductivity exceeds 0.8 W / mK, the heat insulating property is insufficient, so that the loss of heat energy given for coloring and decoloring of the dye contained in the printing layer becomes large. In addition, due to insufficient heat insulation, it is necessary to increase energy such as when the color developability and decolorability are lowered, or when the temperature of the print head is increased to give a certain color developability and decolorization. Therefore, it is not preferable.

  On the other hand, when the thermal conductivity of the film is less than 0.037 W / mK, the heat insulation effect becomes too large, and it becomes difficult to fix the colored state by rapid cooling. For example, since heat applied for color development during color development is difficult to escape, a part of the dye is decolored by the heat and color developability deteriorates. Moreover, the operability at the time of manufacture of a film, such as deterioration of film quality such as the mechanical properties of the film due to imparting such characteristics, and frequent breakage during film production, which makes stable production impossible at an industrial level, decreases.

The plastic film preferably includes a void-containing layer. Further, the main component of the plastic film is preferably a polyester resin. The apparent density of the plastic film is preferably 0.91 to 1.2 g / cm ³ .

When the main component of the film is a polyester resin, the apparent density of the film is preferably 0.91 to 1.20 g / cm ³ . The upper limit of the apparent density of the film is more preferably 1.18 g / cm ^3, further preferably 1.17 g / cm ^3. On the other hand, the lower limit of the apparent density of the film is more preferably 0.92 g / cm ³ and even more preferably 0.94 g / cm ³ . When the apparent density of the film exceeds 1.20 g / cm ³ , the thermal conductivity is not sufficiently lowered, which is not preferable. On the other hand, when the apparent density is less than 0.91 g / cm ³ , since the void content is too high, the heat insulating property becomes too large, the strength of the film is lowered, the waist is weakened, and the handleability is deteriorated. The characteristics as a polyester film tend to be impaired.

  Moreover, it is preferable that the said plastic film consists of laminated structures, and the outermost layer of the at least single side | surface is the layer B which does not contain a cavity substantially. Furthermore, it is preferable that the three-dimensional center plane average surface roughness (SRa) on the surface of the layer B which does not substantially contain the cavity of the plastic film is 0.07 to 0.30 μm.

  The upper limit of the three-dimensional center plane average surface roughness (SRa) of the surface of the B layer is preferably 0.30 μm, more preferably 0.28 μm, and further preferably 0.25 μm. On the other hand, the lower limit is preferably 0.07 μm, more preferably 0.08 μm, still more preferably 0.09 μm. When the three-dimensional center plane average surface roughness (SRa) of the surface exceeds 0.30 μm, when the rewrite printing layer is laminated on the surface, the surface of the printing layer becomes rough and the fineness of the printed image decreases. May occur. On the other hand, if SRa is less than 0.07 μm, the slipperiness of the base film for rewritable recording medium is lowered and the handling property of the film tends to deteriorate.

  The coating layer that improves the adhesion to the rewritable printing layer is preferably formed on the surface of a layer that does not substantially contain a plastic film cavity.

  In the rewritable recording medium of the present invention, the rewritable printing layer is laminated on the surface of the coating layer of the base film for the rewritable recording medium. Among them, the plastic film has a laminated structure, the outermost layer on at least one side thereof does not substantially contain a cavity, and the three-dimensional center plane average surface roughness (SRa) is 0.07 to 0.30 μm. The most preferred embodiment is a rewritable recording medium comprising a rewritable recording medium substrate film having a coating layer formed thereon and a rewritable printing layer laminated on the surface of the coating layer of the film.

  The base film for rewritable recording medium of the present invention has excellent heat developability and decoloring property when used as the base material of the rewritable recording medium because the thermal conductivity of the film is in a specific range. Further, since the adhesion between the coating layer and the rewritable printing layer is also excellent, when used as a base material for the rewritable recording medium, there is an advantage that the durability of the rewritable printing layer is improved.

  Furthermore, since the balance between color developability and decolorization by thermal energy is excellent, it is not necessary to interspers with the fine air layers for imparting heat insulation to the print layer. In addition, since the minute air layer contained in the printing layer does not cause light scattering, there is an advantage that the sharpness of the printed image does not deteriorate.

  Further, there is no need for calendering used to improve the surface roughness caused by the heat insulation layer lamination or the heat insulation layer required by a conventionally known method, which is advantageous in terms of economy, and a substrate for a rewritable recording medium. Suitable as a film.

  Furthermore, since the plastic film has a void-containing layer, light shielding properties can be imparted, so that the sharpness of the printed image when the rewritable printing layer is provided is improved.

In addition, by using a void-containing polyester film having an apparent density of 0.91 to 1.2 g / cm ³ as a plastic film, an appropriate cushioning property can be imparted to the substrate film. In this case, there is an advantage that the fineness of printing is improved.

  Furthermore, the plastic film has a laminated structure, and a layer that does not substantially contain voids is placed on the side where the rewrite printing layer is laminated, and the surface roughness of the layer that does not substantially contain voids is specified. By setting it as this range, the surface roughness of the printing layer laminated | stacked can be suppressed. As a result, the fineness of the printed image is improved. Moreover, by setting it as this laminated structure, it becomes difficult to cleave the film surface at the side which laminates a rewrite printing layer. Therefore, when used as a base material for a rewritable recording medium, there is an advantage that the durability of the rewritable printing layer is further improved.

  The base film for a rewrite recording medium of the present invention is a base film for a rewrite recording medium in which a coating layer that improves adhesion to the rewrite printing layer is formed on at least one surface of the plastic film, The light transmittance is 15% or less, and the thermal conductivity is 0.037 to 0.080 W / mK.

  Examples of the resin constituting the plastic film used for the base film for the rewritable recording medium of the present invention include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyolefin resins such as polypropylene, polyethylene and cyclic polyolefin, and cellulose triacetate. Cellulose derivative resins, styrene resins such as syndiotactic polystyrene, and engineering plastic resins such as polyphenylene sulfide and polyimide. Among these, the use of a polyester resin is preferable.

  As the plastic film, a stretched polyester film formed by stretching at least in a uniaxial direction and heat treatment is preferable, and a biaxially stretched polyester film is particularly preferable.

  The polyester includes aromatic dicarboxylic acids or esters thereof such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and glycols such as ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, and neopentyl glycol. Is a polyester produced by polycondensation. In addition to the direct weight method in which an aromatic dicarboxylic acid and a glycol are directly reacted, these polyesters can be transesterified by an alkyl ester of an aromatic dicarboxylic acid and a glycol and then subjected to a polycondensation, or an aromatic method. It can be produced by a method such as polycondensation of diglycol ester of dicarboxylic acid.

  Typical examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. The polyester may be a homopolymer or a copolymer of a third component. Among these polyesters, a polyester having an ethylene terephthalate unit, a trimethylene terephthalate unit, or an ethylene-2,6-naphthalate unit of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more is preferable. The polyester constituting each layer may be the same type or different types, but the same type is preferable from the viewpoint of curling suppression and economy.

  The film made of polyester is preferably a biaxially oriented polyester film from the viewpoint of mechanical strength and thermal dimensional stability.

  As a method of making the light transmittance of the plastic film 13% or less, a method of blending a pigment having a concealing property with a resin constituting the film is preferable. In the present invention, since the purpose of reducing the light transmittance of the film is to improve the sharpness of the printed image, it is preferably white. Therefore, the substrate film for a rewritable recording medium of the present invention preferably has a whiteness measured in accordance with JIS Z-8722 of 75 or more, more preferably 80 or more. In order to set the whiteness of the film to 75 or more, it is preferable to contain white pigments such as titanium oxide, calcium carbonate, zinc oxide, or barium sulfate, polymer beads blended with these, and the like in the film. A method using a fluorescent whitening agent in combination is also effective.

  It is preferable to contain 1-25 mass% of said white pigment with respect to the resin composition which comprises a film. If the content of the white pigment is excessively increased in order to further improve the light-shielding property, breakage occurs frequently during film production, making it difficult to perform stable production at an industrial level.

  Moreover, as a method of setting the thermal conductivity of the film of the present invention to 0.037 to 0.080 W / mK, a method of incorporating a cavity in the film and utilizing a heat insulating effect of air contained in the cavity is preferable. . For example, in order to increase the amount of cavities in the film, the method of increasing the number of cavities in the film and the method of increasing the cavities are used alone or in combination so that the thermal conductivity of the film falls within the above range. The conditions are set as appropriate within the range that does not deteriorate.

  For example, in the case of a void-containing polyester film, a mixture of a polyester resin and a thermoplastic resin that is incompatible with the polyester resin is melted and then extruded into a sheet to form an unstretched film. Is at least uniaxially stretched and then heat treated.

  In order to increase the number of cavities in the film, a method of increasing the amount of the thermoplastic resin incompatible with the polyester, a method of reducing the size of the dispersion of the incompatible resin by physical or chemical means Is preferred. The physical means includes, for example, a method in which an incompatible resin is dispersed using a static mixer during melt extrusion, and the chemical means includes a method in which PEG or polystyrene is used in combination. Further, the incompatible resin will be described later.

  Moreover, as a method of increasing the size of the cavity, a method of increasing the stretching stress at the time of stretching the film (for example, lowering the stretching temperature or increasing the stretching ratio) is suitable.

  In the present invention, it is important to form a coating layer on at least one surface of the plastic film for improving the adhesion with the rewritable printing layer. In the present specification, the coating layer may be described as an adhesion improving layer of the rewritable printing layer.

  Thereby, the adhesiveness of the base film for rewrite recording media of this invention and a rewrite printing layer improves, and when it uses as a support body of a rewrite recording medium, durability of a rewrite printing layer improves.

  The adhesion improving layer of the rewritable printing layer is preferably formed on the surface of the outermost layer of the plastic film substantially free of voids.

  In the present invention, as the resin constituting the coating layer (adhesion improving layer of the rewritable printing layer), polyester, acrylic, polyurethane, or a copolymer of these is preferable, and these are used alone or in combination. Moreover, you may use together curable resins, such as a melamine type resin.

  For example, in the case of a polyester resin, the dicarboxylic acid component includes terephthalic acid, isophthalic acid, phthalic acid, 2,5-dimethylterephthalic acid, 1,4-naphthalenedicarboxylic acid, biphenyldicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,2-bis (phenoxy) ethane-p, p'-dicarboxylic acid, adipic acid, sebacic acid, dodecanedioic acid and the like, and ester-forming derivatives thereof.

  Examples of the glycol component of the polyester resin include ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, trimethylolpropane, and the like.

  In addition, when performing in-line coating using an aqueous coating solution, it is preferable to copolymerize a compound containing a carboxylate group or a compound containing a sulfonate group in order to impart water solubility or water dispersibility to the polyester resin. .

  Examples of the compound containing a carboxylate group include trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, 4-methylcyclohexene-1,2,3-tricarboxylic acid, trimesic acid, 1,2,3 , 4-butanetetracarboxylic acid, 1,2,3,4-pentanetetracarboxylic acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid, 5- (2,5-dioxotetrahydrofurfuryl)- 3-methyl-3-cyclohexene-1,2-dicarboxylic acid, 5- (2,5-dioxotetrahydrofurfuryl) -3-cyclohexene-1,2-dicarboxylic acid, cyclopentanetetracarboxylic acid, 2,3, 6,7-naphthalene tetracarboxylic acid, 1,2,5,6-naphthalene tetracarboxylic acid, ethylene glycol bistrimellitate, , 2 ', 3,3'-diphenyl tetracarboxylic acid, ethylene tetracarboxylic acid or alkali metal salts thereof, alkaline earth metal salts, ammonium salts.

  Examples of the compound containing a sulfonate group include sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, sulfo-p-xylylene glycol, 2-sulfo- Examples thereof include 1,4-bis (hydroxyethoxy) benzene and alkali metal salts, alkaline earth metal salts, and ammonium salts thereof.

  In addition, as the polyester resin, a modified polyester copolymer such as a block copolymer modified with acrylic, urethane, epoxy, or the like, a graft copolymer, or the like can also be used.

  Preferred polyester resins include terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid as acid components, ethylene glycol, 1,4-butanediol, neopentyl glycol, and diethylene glycol as glycol components. What uses the compound containing carboxylate groups, such as an acid and pyromellitic acid, as the structural component is mentioned.

  The polyester resin constituting the coating layer can be produced by a conventionally known production technique. For example, a polyester resin composed of terephthalic acid, isophthalic acid, trimellitic acid as an acid component, and ethylene glycol and neopentyl glycol as a glycol component will be described. Terephthalic acid, isophthalic acid, trimellitic acid and ethylene glycol, neopentyl glycol The first stage in which the esterification reaction is carried out directly or the ester exchange reaction of terephthalic acid, isophthalic acid, trimellitic acid and ethylene glycol or neopentyl glycol is carried out, and the second stage in which the reaction product of this first stage is subjected to a polycondensation reaction And a production method.

  At this time, conventionally known alkali metals, alkaline earth metals, manganese, cobalt, zinc, antimony, germanium, titanium compounds, and the like are used as reaction catalysts.

  The intrinsic viscosity of the polyester resin constituting the coating layer is preferably 0.3 dl / g or more, more preferably 0.35 dl / g or more, particularly preferably 0.4 dl / g from the viewpoint of adhesiveness. That's it.

  When using polyurethane as the resin constituting the coating layer, a heat-reactive water-soluble urethane containing a blocked isocyanate group in which a terminal isocyanate group is blocked with a hydrophilic group is suitable.

  Examples of the isocyanate group blocking agent include bisulfites and sulfone group-containing phenols, alcohols, lactams, oximes, and active methylene compounds. The blocked isocyanate group makes the urethane prepolymer hydrophilic or water-soluble. When heat energy is applied to the resin in the process of drying or heat setting during film production, the blocking agent deviates from the isocyanate group, so the resin is mixed with a water-dispersible copolyester resin mixed in a self-crosslinked network. While fixing, it also reacts with the terminal groups of the polyester resin. The water-soluble urethane resin at the time of preparing the coating solution is poor in water resistance because it is hydrophilic. However, when the thermal reaction is completed by coating, drying and heat setting, the hydrophilic group of the urethane resin, that is, the blocking agent is released, so A good coating film is obtained. Of the above blocking agents, bisulfites are most preferred as those having a suitable heat treatment temperature and heat treatment time and widely used industrially.

  The chemical composition of the urethane prepolymer used in the urethane resin includes a compound having two or more active hydrogen atoms in the molecule and a molecular weight of 200 to 20,000, and two or more isocyanate groups in the molecule. Or an organic polyisocyanate or a compound having a terminal isocyanate group obtained by reacting a chain extender having at least two active hydrogen atoms in the molecule.

  The obtained urethane polymer is preferably blocked using bisulfite. Mix with aqueous bisulfite solution and allow reaction to proceed with good agitation for about 5 minutes to 1 hour. The reaction temperature is preferably 60 ° C. or lower. Thereafter, it is diluted with water to an appropriate concentration to obtain a heat-reactive water-soluble urethane composition. The composition is adjusted to an appropriate concentration and viscosity when used. Usually, when heated to about 80 to 200 ° C., the bisulfite of the blocking agent is dissociated and the active isocyanate group is regenerated, so that the prepolymer A polyurethane polymer is produced by a polyaddition reaction that takes place within or between the molecules of the polymer, or has the property of causing addition to other functional groups.

  In this invention, you may use together the crosslinking agent which can bridge | crosslink this resin with the said resin. By using the crosslinking agent in combination, durability such as water resistance of the adhesion improving layer of the rewritable printing layer can be improved.

  In the case of using a crosslinking agent in combination, as a crosslinking agent, a phenol formaldehyde resin of a condensation product with formaldehyde such as alkylated phenols and cresols; an addition product of urea, melamine, benzoguanamine, etc. with formaldehyde, this addition product and a carbon atom An amino resin such as an alkyl ether compound composed of an alcohol having 1 to 6 alcohols; a polyfunctional epoxy compound; a polyfunctional isocyanate compound; a blocked isocyanate compound; a polyfunctional aziridine compound; an oxazoline compound and the like can be used. Examples of the phenol formaldehyde resin include alkylated (methyl, ethyl, propyl, isopropyl or butyl) phenol, p-tert-amylphenol, 4,4′-sec-butylidenephenol, p-tert-butylphenol, o-, m-, p-cresol, p-cyclohexylphenol, 4,4'-isopropylidenephenol, p-nonylphenol, p-octylphenol, 3-pentadecylphenol, phenol, phenyl o-cresol, p-phenylphenol, xylenol, etc. Mention may be made of condensates of phenols and formaldehyde.

  Examples of amino resins include methoxylated methylol urea, methoxylated methylol N, N-ethylene urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine, and the like. Are preferably methoxylated methylol melamine, butoxylated methylol melamine, methylolated benzoguanamine, and the like.

  Examples of the polyfunctional epoxy compound include diglycidyl ether of bisphenol A and oligomer thereof, diglycidyl ether of hydrogenated bisphenol A and oligomer thereof, orthophthalic acid diglycidyl ester, isophthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, p-oxybenzoic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, succinic acid diglycidyl ester, adipic acid diglycidyl ester, sebacic acid diglycidyl ester, ethylene glycol diglycidyl ether, propylene Glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether and Polyalkylene glycol diglycidyl ethers, trimellitic acid triglycidyl ester, triglycidyl isocyanurate, 1,4-diglycidyloxybenzene, diglycidyl propylene urea, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol triglycidyl Examples include ether, triglycidyl ether of glycerol alkylene oxide adduct, and the like.

  As the polyfunctional isocyanate compound, a low-molecular or high-molecular aromatic or aliphatic diisocyanate or a trivalent or higher polyisocyanate can be used. Examples of the polyisocyanate include tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and trimers of these isocyanate compounds. Furthermore, an excess amount of these isocyanate compounds and low molecular active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine, or polyester polyols, poly The terminal isocyanate group containing compound obtained by making it react with polymer active hydrogen compounds, such as ether polyols and polyamides, can be mentioned.

  The blocked isocyanate can be prepared by subjecting the isocyanate compound and the blocking agent to an addition reaction by a conventionally known appropriate method. Examples of the isocyanate blocking agent include phenols such as phenol, cresol, xylenol, resorcinol, nitrophenol and chlorophenol; thiophenols such as thiophenol and methylthiophenol; oximes such as acetoxime, methyl etiketooxime and cyclohexanone oxime. Alcohols such as methanol, ethanol, propanol and butanol; halogen-substituted alcohols such as ethylene chlorohydrin and 1,3-dichloro-2-propanol; tertiary alcohols such as t-butanol and t-pentanol ; Lactams such as ε-caprolactam, δ-valerolactam, ν-butyrolactam, β-propyllactam; aromatic amines; imides; acetylacetone, acetoacetate, ethyl malonate Active methylene compounds such as esters, mercaptans, imines; ureas; diaryl compounds; include the sodium bisulfite and the like.

  These crosslinking agents may be used alone or in combination of two or more. As a compounding quantity of a crosslinking agent, when using a polyester-type graft copolymer as adhesiveness modification resin which comprises an application layer, 5 mass parts-40 mass parts are preferable with respect to 100 mass parts of resin, for example. As a blending method of the cross-linking agent, (1) when the cross-linking agent is water-soluble, it is directly dissolved or dispersed in an aqueous solvent solution or dispersion of the graft copolymer, or (2) the cross-linking agent is oil-soluble. In some cases, there is a method of adding to the reaction solution after completion of the grafting reaction. These methods can be appropriately selected depending on the type and properties of the crosslinking agent. Further, a curing agent or an accelerator can be used in combination with the crosslinking agent. The graft copolymer-containing layer may further contain additives such as an antistatic agent, an inorganic lubricant, and an organic lubricant within a range that does not impair the effects of the present invention. It is given to the material film surface.

  The preparation of the coating liquid in the present invention is preferably performed at 20 ° C. or higher and 30 ° C. or lower from the viscosity and the sedimentation rate of the particles. As a result, a stable mixed solution can be obtained, and entrainment of bubbles (amount of foaming) can be reduced.

  The coating solution can be applied by any known method. For example, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire barber coating method, pipe doctor method, impregnation / coating method and curtain coating method. These methods can be used alone or in combination.

  In the present invention, the formation of the coating layer (adhesion modification layer) on the plastic film is carried out in the plastic film manufacturing process, and a so-called in-line coating method using a heat treatment process in manufacturing the film. It is preferable to carry out. That is, it is preferable to carry out the method by applying the coating solution to an unstretched or uniaxially stretched polyester film substrate, then drying, and further performing uniaxial stretching or biaxial stretching, followed by heat setting.

  The drying temperature in the case of the in-line coating method is preferably 70 to 140 ° C., and the drying time is adjusted according to the solid content concentration and the coating amount of the coating solution, but the temperature (° C.) and time (second). The product of 3,000 is preferably 3,000 or less. When the product exceeds 3,000, the coating layer undergoes a crosslinking reaction before stretching, and cracks are likely to occur in the coating layer (adhesion modified layer).

  Moreover, after extending | stretching a coating layer, in the state which fixed the film so that film width length may not change, an infrared rays heater is used and a coating layer is heat-processed at 250-260 degreeC for 0.5 to 1 second for a short time. It is preferable for promoting the crosslinking reaction.

  Under the present circumstances, when 1-10 mass% of acid compounds are added with respect to resin in a coating liquid, a crosslinking reaction is further accelerated | stimulated and an application layer will become firmer. Therefore, the oligomer which precipitates on the film surface when the film is heated can be blocked by the coating layer, and oligomer deposition on the coating layer surface can be suppressed.

  The film after stretching is usually subjected to a relaxation treatment of about 2 to 10%, but in the present invention, the coating layer is coated with an infrared heater in a state where the coating layer is less distorted, i.e., fixed so that the film width does not change. It is preferable to heat. By adopting such a method, crosslinking in the coating layer is promoted and becomes stronger. If the heating temperature or time is greater than the above conditions, crystallization or dissolution of the film tends to occur. On the other hand, if the one condition is a heating temperature or time smaller than the above condition, crosslinking of the coating layer tends to be insufficient.

The coating amount after drying of the coating layer finally obtained (solid mass per unit area of the film) is preferably 0.01 to 0.50 g / m ² , more preferably 0.02 to 0.40 g / m. ² , particularly preferably 0.05 to 0.30 g / m ² . When the coating amount after drying is less than 0.01 g / m ² , the adhesion is insufficient. When the coating amount exceeds 0.50 g / m ² , it tends to be easily blocked, and the number of foreign matters in the coating layer is also likely to increase.

In addition, it is attached to the film surface that the cleanness in the air in the coating process (number of particles of 0.5 μm or more / ft ³ ) is controlled by a hepa filter so as to be class 100,000 after the unstretched film is created. It is effective in reducing foreign matter.

  In the present invention, the three-dimensional average roughness (SRa) of the coating layer surface is preferably 0.07 to 0.30 μm. It is more preferably 0.08 to 0.28 μm, and further preferably 0.09 to 0.25 μm. When the three-dimensional average roughness (SRa) of the surface exceeds 0.30, when a rewritable printing layer is laminated on the surface, the surface roughness of the surface causes the surface of the printing layer to be printed. This is not preferable because the fineness of the image may deteriorate. On the contrary, if it is less than 0.07 μm, the slipperiness of the base film for rewritable recording medium is lowered, and the handling property of the film is deteriorated.

  The surface roughness is preferably controlled by, for example, blending inorganic and / or organic fine particles in the coating layer. Moreover, you may carry out by mix | blending inorganic and / or organic microparticles | fine-particles with the said surface formation layer. Moreover, you may carry out combining these methods.

  As a method for adding a cavity to the plastic film, (1) a method in which a foaming agent is contained and foamed by heat at the time of extrusion or film formation, or foamed by chemical decomposition, (2) carbonic acid at the time of extrusion or after extrusion. A method of adding a gas such as a gas or a vaporizable substance and foaming; (3) a method of blending hollow fine particles; and (4) an incompatible with the thermoplastic resin A constituting the film. (5) A method of stretching uniaxially or biaxially after melt extrusion, and (5) adding organic or inorganic fine particles to the thermoplastic resin A, uniaxially or biaxially after melt extrusion Examples thereof include a stretching method. Moreover, you may implement combining these methods.

  Among the above methods, the methods other than the above (3) can simultaneously impart cushioning properties to the film by containing the cavities. When the cushioning property of the film is given, for example, when printing is performed by a thermal head method, an effect that the fineness of printing is improved is also added.

  Among the above-described void-containing methods, the method (4), that is, the thermoplastic resin A constituting the film contains the thermoplastic resin B incompatible with the thermoplastic resin A, and the film is stretched. One preferred embodiment is a method of generating cavities by peeling the interface between the two resins. As thermoplastic resin A which comprises a film, a polyester resin is preferable. When polyethylene terephthalate or polyethylene-2,6-naphthalate is used as the polyester resin, as the thermoplastic resin B incompatible with the polyester resin, for example, polyolefin resins typified by polypropylene and polymethylpentene, various types Examples thereof include modified polyolefin resins, polystyrene resins, polyacrylic resins, polycarbonate resins, polysulfone resins, cellulose resins, polyphenylene ether resins, and phenoxy resins. Moreover, you may use together the said white pigment.

  A thermoplastic resin incompatible with the above-mentioned polyester resin may be used alone, or a plurality of thermoplastic resins may be used in combination. The content of the thermoplastic resin that is incompatible with the polyester resin is preferably 3 to 20% by mass, more preferably 5 to 15% by mass with respect to the polyester resin. When the content of the thermoplastic resin incompatible with the polyester resin is less than 3% by mass with respect to the polyester resin forming the void-containing polyester layer, the void content formed inside the film is reduced. The decrease in conductivity tends to be insufficient. On the other hand, when the content of the incompatible thermoplastic resin exceeds 20% by mass with respect to the polyester resin, breakage tends to occur frequently in the film manufacturing process.

In the present invention, in order to set the apparent density of the film in the range of 0.91 to 1.2 g / cm ³ , for example, the content of the thermoplastic resin incompatible with the polyester resin shown below is appropriately set. Examples thereof include a method of adjusting to a proper value and a method of adjusting a stretching temperature and a stretching ratio of the film.

  In the present invention, in the case of using a method for adding heat insulation by incorporating cavities in the film, the film is formed into a laminated structure, and the cavities are substantially formed on the surface of the void-containing layer A. It is preferable to laminate the layer B which does not contain. By adopting this laminated structure, it is possible to suppress the cleavage of the film surface due to the destruction of the interface of the cavity. That is, it is preferable to stop the blending of the foaming agent and the cavity forming agent as described above into the resin composition constituting the layer B that does not substantially contain the cavity. It is a preferable embodiment that an additive for concealing is added to the surface forming layer from the viewpoint of concealing and controlling the surface roughness described later.

  2-30 micrometers is preferable and, as for the thickness of the said B layer, 3-25 micrometers is more preferable. When the thickness of the B layer is less than 2 μm, it becomes difficult to suppress cleavage on the surface of the film. On the other hand, when the thickness of B layer exceeds 30 micrometers, it becomes disadvantageous at the point of heat insulation provision. In addition, it is preferable that the thickness of the said B layer shall be 5-25% with respect to the film total thickness.

  In the case where the rewritable printing layer is laminated only on one side of the base film, in order to achieve the object of the present invention, the lamination of the B layer is sufficient on only one side. In addition, it is a more preferable embodiment that the B layer is laminated on both surfaces of the A layer from the viewpoint of suppressing curling of the laminated film.

  The method for laminating the B layer is not limited. For example, it may be a method in which two films obtained by individually forming the B layer and the A layer are bonded with an adhesive or the like, or a film in which the B layer and the A layer are laminated by a coextrusion method at least in one direction Alternatively, a method of stretching and heat treatment may be used. The latter method is more economical and is a preferred embodiment.

  The three-dimensional center plane average surface roughness (SRa) of the B layer is preferably controlled by adding inorganic and / or organic fine particles to the resin composition constituting the B layer. As the fine particles, a white pigment having a concealing property is more preferable.

  In the present invention, when a void-containing polyester film is used as the plastic film, it is preferably produced by the following method.

  As a method for producing a void-containing polyester film, a polyester resin and a mixture made of a thermoplastic resin incompatible with the polyester resin are melted and extruded into a sheet to obtain an unstretched film. A general method of stretching and then heat-treating can be used.

  The conditions for stretching and orienting an unstretched film are closely related to the physical properties of the film. Below, taking the most general sequential biaxial stretching method, particularly a method of stretching an unstretched film in the longitudinal direction and then in the width direction, the stretching and heat treatment conditions will be described.

  In the longitudinal stretching step, stretching is performed between two or many rolls having different peripheral speeds. As a heating means at this time, a method using a heating roll or a method using a non-contact heating method may be used, or they may be used in combination. Next, the uniaxially stretched film is introduced into a tenter and stretched 2.5 to 5 times in the width direction at a temperature of (Tm-10 ° C.) or lower. However, Tm means the melting point of polyester.

  Further, the biaxially stretched film is subjected to heat treatment as necessary. The heat treatment is preferably performed in a tenter, and is preferably performed in the range of (Tm-60 ° C.) to Tm.

  When the film for rewritable recording medium of the present invention is produced by a method of containing cavities, it has a problem that curl curl generation is larger than a white polyester film containing a white pigment or a transparent polyester film. In particular, when the film for rewritable recording medium of the present invention is thick, the occurrence of curling becomes remarkable.

  Because, in the production of a thick biaxially stretched film, the unstretched film becomes very thick first, so the cooling on the cooling roll is clearly different between the cooling surface and the opposite side. The resulting structure will be different on the front and back of the film. Furthermore, since it is a void-containing polyester film containing fine cavities inside, the size, shape and volume fraction of the cavities easily change over the thickness direction of the film, so the physical properties and structure of the film front and back are the same. Such films are extremely difficult to manufacture.

  Therefore, in the present invention, it is preferable that the curled value after heat-treating the laminated polyester film at 110 ° C. for 30 minutes in an unloaded state is 1 mm or less. The curl value after the heat treatment is more preferably 0.9 mm or less, and further preferably 0.8 mm or less. When the curl value exceeds 1 mm, the flatness as a rewrite recording medium is deteriorated, which is not preferable.

  As a technique for suppressing curling, (1) a method for suppressing the occurrence of curling by resisting internal strain by reducing the volume fraction of the cavities and suppressing the size of each cavity, and (2) film (3) In order to control the curl caused by the structural difference between the front and back of the film applied in each step starting from the difference in crystallinity in the film thickness direction due to the cooling difference during extrusion. In addition, a method of positively generating a structural difference between the front and back of the film and complementing the necessary structural difference to bring the curl value close to zero is preferable.

  Specifically, the degree of orientation of the film front and back is controlled independently by setting the temperature or heat quantity of the film front and back to different values in the stretching process and heat setting process such as longitudinal stretching and lateral stretching, and the structure of the film front and back By adopting conditions that balance the physical properties, zero curl film formation is realized. In particular, a method in which the temperature or the amount of heat on the front and back sides of the film is different at a stage where the film thickness during longitudinal stretching is thick is suitable.

  In addition, as a basic requirement for stable production in a state where the curl is low over the entire width, it is also important to form cavities with little change in the film thickness direction by a stretching formulation with little thickness unevenness.

  More specifically, for the longitudinal curl immediately after film formation, the structural difference between the front and back of the film during longitudinal stretching is controlled, and the lateral curl is controlled by controlling the structural difference between the front and back of the film during lateral stretching and heat setting. It is preferable to create an internal strain in the opposite direction and balance the internal strain due to the structural difference between the front and back of the film, which is inevitably generated, and suppress curling.

  Moreover, as a curling generation suppression method, it is also effective to make the thickness of the surface layer (B) and the other surface layer (B ′) of the laminated polyester film the same.

  The total thickness of the film for rewrite recording medium of the present invention is preferably 25 to 300 μm. What is necessary is just to determine suitably by the use at the time of using in a market, and a specification.

  The rewritable recording medium of the present invention has a structure in which a rewritable printing layer is laminated on the B layer (a layer containing substantially no cavities in the film) via a coating layer.

  Here, the film substantially free of voids means a film having a void lamination number density of less than 0.0 pieces / μm. The cavity lamination number density is obtained by dividing the number of cavity laminations existing in the thickness direction of the film by the thickness of the film.

The cavity stacking number density can be measured using the following method.
A scanning electron microscope is used for observing the cavity of the film cross section, and a split cross section that is parallel to the longitudinal stretching direction of the film and perpendicular to the film surface is observed at five different portions of the sample. The observation is performed at an appropriate magnification of 300 to 3000 times, and a photograph is taken so that the dispersion state of the cavities in the entire thickness of the film can be confirmed. Then, at any location on the photographic image, a straight line is drawn perpendicularly to the film surface, and the number of cavities that intersect the straight line is counted. The number of cavities is defined as the number of cavities (number of layers) in the thickness direction of the film. Further, the total thickness (μm) of the film is measured along this straight line, and the number of cavities stacked is divided by the total thickness of the film to obtain the number of cavities stacked (number / μm). In addition, measurement is performed at five locations for each photograph, and the average value of a total of 25 locations is obtained as the density of the number of stacked cavities in the sample.

  As the leuco dye, the reversible developer dye, and the binder resin constituting the rewritable printing layer of the rewritable recording medium, known commercially available products can be used and may be appropriately selected and determined according to the performance of the rewritable recording medium and the market demand.

  Hereinafter, the present invention will be described in detail by way of examples. The characteristics of the film-writable recording medium obtained in each example were measured and evaluated by the following methods.

(1) Intrinsic viscosity 0.1 g of the chip sample was precisely weighed and dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane = 6/4 (mass ratio), and measured at 30 ° C. using an Ostwald viscometer. In addition, the measurement was performed 3 times and the average value was calculated | required.

(2) Three-dimensional center plane average surface roughness (SRa)
Using a stylus type three-dimensional surface roughness meter (SE-3AK, manufactured by Kosaka Laboratory Ltd.), the surface of the film was subjected to the conditions of a needle radius of 2 μm, a load of 30 mg, and a needle speed of 0.1 mm / sec. In the longitudinal direction of the film, the cut-off value is 0.25 mm, the measurement length is 1 mm, and it is divided into 500 points at a 2 μm pitch, and the height of each point is determined by a three-dimensional roughness analyzer (Kosaka Laboratory Co., Ltd.) Manufactured by TDA-21). The same operation was performed 150 times continuously at intervals of 2 μm in the width direction of the film, that is, over 0.3 mm in the width direction of the film, and the data was taken into the analyzer. Next, the three-dimensional average surface roughness SRa was determined using the analyzer. The unit of SRa is μm. In addition, the measurement was performed 3 times and those average values were employ | adopted.

(3) Film thickness Using a Millitron thickness meter, a total of 15 points were measured, with 5 points per film, and the average value was determined.

(4) Layer thickness of film The film was cut using a microtome to obtain a cross section perpendicular to the film surface. A sample obtained by coating the cross section with a platinum / palladium alloy by sputtering was used as an observation sample. The cross section of the film was observed using a scanning electron microscope (manufactured by Hitachi, Ltd., model S-510), and a photograph was taken at an appropriate magnification at which the total thickness of the film became one field of view. From this image, the thickness of each layer was measured using a scale. Measurement was performed on three independently prepared cross-sectional samples, and the average value was taken as the layer thickness of the laminated film.

(5) Light transmittance of laminated film According to JIS-B0601-1982, Poic integrating sphere type H.264 is used. T.A. Measurement was performed using an R meter (manufactured by Nippon Seimitsu Optics). The smaller this value, the higher the light shielding property.

(6) Apparent density of film Four films were cut into 5.0 cm squares and used as samples. Four samples were stacked, and the total thickness was measured at 10 points using a micrometer with four significant figures, and the total value of the stacked thickness was determined. The average value was divided by 4 and rounded to 3 significant figures to obtain an average thickness per sheet (t: μm). The mass (w: g) of the four samples was measured using an automatic upper pan balance with four significant digits, and the apparent density was determined from the following equation. The apparent density was rounded to 3 significant figures.
Apparent density (g / cm ³ ) = (w / (5.0 × 5.0 × 4 × t)) × 10 ⁴

(7) Thermal conductivity Measured by a steady comparison method in accordance with ASTM E1530. UNITHERM2010 (manufactured by ANTER) was used as a measuring instrument. As a sample, a film laminated with a total thickness of about 1 mm was used, and the thermal conductivity in the thickness direction was measured at 120 ° C.

(8) Surface Cleavage Resistance of Film A cross cut of 100 grids is made at 1 mm intervals on the film surface on the side where the rewritable printing layer of the film sample is laminated, and 24 mm wide × 40 mm centering on the cross cut portion. Adhesive tape (manufactured by Nichiban Co., Ltd., CT405AP-24) is attached so as to have a long area. Next, after applying a load of 1 kgf / cm ^{2 to} the affixed portion for 10 seconds, when the adhesive tape was peeled off in the vertical direction of the film, the number peeled off to the adhesive tape side was counted, and the following criteria were used. Judged.
○: 0 to 20 pieces / 100 pieces △: 21 to 50 pieces / 100 pieces ×: 51 to 100 pieces / 100 pieces

(9) Adhesiveness with the rewritable printing layer A cross cut of a grid of 1 mm intervals is put on the surface of the rewritable printing layer, and an adhesive tape (Nichiban) is formed so as to have an area of 24 mm wide × 40 mm long around the cross cut portion. CT405AP-24) was applied, and a load of 1 kg / cm ² was applied to the applied portion for 10 seconds, and then the cellophane tape was peeled off to the cellophane tape side when peeled off in the vertical direction of the film. The number for 100 areas was counted and judged according to the following criteria.
○: 0 to 20 pieces / 100 pieces △: 21 to 50 pieces / 100 pieces ×: 51 to 100 pieces / 100 pieces

(10) Color developability of rewritable printing layer The rewritable recording medium was colored with an applied energy of 0.7 mJ / dot using a commercially available thermal card printer. After color development, it was rapidly cooled to room temperature, and the color developability was judged. The color development was determined by classifying 1 to 5 grades by visual observation. Grade 1 was the best and Grade 5 was the worst.

(11) Decoloring property of rewrite printing layer Printing was performed by the method described above, and then decoloring was performed with an applied energy of 0.56 mJ / dot. The decoloring property was determined by classifying it into 1 to 5 grades by visual observation. Grade 1 was the best and Grade 5 was the worst.

(12) Fineness of rewrite print image The dot shape of the print image of the print sample was determined by observing with a microscope. The closer the dot shape is to a square, the better the definition. Judgment was made according to the following criteria.
◎: Roughly square ○: Slightly rounded △: Slightly distorted due to white spots etc. ×: Shrimp

(13) Sharpness of rewrite print image The print image developed by the above method was determined by visual observation.
◯: Good sharpness ×: Poor sharpness

Example 1
[Preparation of Cavity Forming Agent-Containing Master Pellet (I)]
As one of the raw materials for the intermediate layer (M), a 20% by mass polystyrene resin having a melt flow rate of 1.5 (G797N, manufactured by Nippon Polystyrene Co., Ltd.) and a gas phase polymerization polypropylene resin having a melt flow rate of 3.0 (Idemitsu Petrochemical) 20% by mass (F300SP, manufactured by the company) and 60% by mass of polymethylpentene resin (Mitsui Chemicals Co., Ltd .: TPX DX-820) having a melt flow rate of 180 are mixed with pellets and supplied to a twin screw extruder and kneaded sufficiently. The strand was cooled and cut to prepare a cavity-forming agent-containing master pellet (I).

[Preparation of titanium oxide-containing master pellets (b)]
As one of the raw materials for the intermediate layer (M), anatase type titanium dioxide (manufactured by Fuji Titanium Co., Ltd.) having an average particle size of 0.3 μm (electron microscopic method) on 49.5% by mass of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g TA-300) 50% by mass and fluorescent whitening agent (manufactured by Eastman Chemical Co., Ltd., OB-1) 0.05% by mass were mixed into a vented twin screw extruder, pre-kneaded, and then melted. The polymer was continuously supplied to a bent type single-screw kneader and kneaded to prepare titanium oxide-containing master pellets (b).

[Preparation of coating solution for coating layer formation]
Copolymerized polyester resin (Toyobo Co., Ltd., Vylonal MD1100) / Block type isocyanate group-containing resin (Daiichi Kogyo Seiyaku Co., Ltd., Elastron BN11) / Organic in a mixed solvent of water / isopropyl alcohol = 60/40% by mass Particles (manufactured by Nippon Shokubai Co., Ltd., poster S12: average particle size 1.2 μm) / fluorine surfactant (manufactured by Dainippon Ink Co., Ltd., F1405) in solid content of 3.5 / 6.5 / 10.0 / 0, respectively. 0.07% by mass was added and dissolved and dispersed with a stirrer.

[Manufacture of base film for rewrite recording medium]
A mixture of 7% by mass of the above-mentioned cavity forming agent-containing master pellets (A), 7% by mass of titanium oxide-containing master pellets (B) and 86% by mass of PET resin having an intrinsic viscosity of 0.62 dl / g was used as a raw material for the intermediate layer. Further, a mixture of 30% by mass of titanium oxide-containing master pellets (b) and 70% by mass of PET resin having an intrinsic viscosity of 0.62 dl / g is supplied to two extruders so as to be laminated on both surfaces of the intermediate layer, It joined with the feed block so that the thickness ratio of surface layer / intermediate layer / surface layer might be 8/84/8. Subsequently, it was extruded from a three-layer die onto a cooling drum adjusted to 20 ° C. to produce a three-layer unstretched film having a thickness of 1.6 mm. At the time of extrusion, the polyester resin and the mixture of the polyester resin and the master pellet were previously dried in vacuum and then supplied to the extruder. The cooling drum was cooled by blowing cold air adjusted to 20 ° C. on the opposite surface of the cooling drum.

  The obtained unstretched film is uniformly heated to 65 ° C. using a heating roll, and 3.4 between two pairs of nip rolls (low speed roll: 1 m / min, high speed roll: 3.4 m / min) having different peripheral speeds. The uniaxially stretched PET film containing voids was obtained by stretching it twice. At this time, as an auxiliary heating device for the film, an infrared heater (rated: 40 W / cm) provided with a gold reflective film in the middle part of the nip roll was placed opposite to both sides of the film (a distance of 1 cm from the film surface). Was heated at 18 W / cm and the opposite surface was heated at 12 W / cm.

On one side of the above-mentioned void-containing uniaxially stretched PET film, the coating layer forming coating solution is finely filtered with a felt type polypropylene filter medium having a filterable particle size of 10 μm (initial filtration efficiency of 95%), and applied by a reverse roll method. , Dried. The coating amount at this time was 0.1 g / m ² .

  Subsequently, after coating the coating layer forming coating solution, the edge of the film was gripped with a clip, guided to a hot air zone heated to 130 ° C. and dried, and then stretched 4.0 times in the width direction. Subsequently, with the film width fixed, the film was heated with an infrared heater at 250 ° C. for 0.6 seconds to produce a 188 μm-thick void-containing biaxially stretched polyester film laminated with a coating layer. A material film was used.

  Table 1 shows the characteristic values of the obtained base film for a rewritable recording medium. In addition, the whiteness of the obtained base film for rewritable recording media was 84.

[Manufacture of rewrite recording media]
20 parts 3-di-n-butylamino-6-methyl-7-anilinofluorane as leuco dye and N- [3- (p-hydroxyphenyl) propiono] -N'-n- as reversible developer 100 parts of octadecanohydrazide and 80 parts of polyvinyl butyral (BX-1 manufactured by Sekisui Chemical Co., Ltd.) as a binder resin are pulverized and dissolved in a ball mill for 24 hours to form a 10% by mass methyl ethyl ketone solution to obtain a printing layer forming solution. Prepared.
The obtained printing layer forming solution was applied to the surface of the coating layer of the base film for rewritable recording medium so that the thickness after drying was 3 μm by the wire bar method, and dried at 80 ° C. for 2 minutes. And a rewritable recording medium was obtained.
The rewritable printing characteristics of the obtained rewritable recording medium and the adhesion between the rewritable printing layer and the substrate film for the rewritable recording medium were evaluated. The results are shown in Table 1.

  The base film for rewritable recording medium obtained in Example 1 is optimized for heat insulation, and therefore has an excellent balance between color development and decoloring, which are rewritable printing characteristics. Moreover, since it was excellent in light-shielding property, it was excellent in the sharpness of the printed image at the time of printing. In addition, since the surface roughness of the surface on which the rewritable printing layer is laminated is specified, the surface roughness of the printing layer is suppressed, so that the fineness of the printed image does not deteriorate. In addition, the surface of the film on the side where the rewritable printing layer is laminated has excellent surface cleavage resistance, and a coating layer that improves adhesion with the rewritable printing layer is formed, so the adhesion with the printing layer is good. It was high quality as a base film for a rewrite recording medium.

Example 2
In Example 1, the rewrite of Example 2 was performed in the same manner as in Example 1 except that the compounding amounts of the void forming agent-containing master pellets (A) and the PET resin in the intermediate layer were changed to 9 and 84% by mass, respectively. A base film for recording medium and a rewritable recording medium were obtained. Table 1 shows the properties of the obtained base film for a rewrite recording medium and the rewrite recording medium.

  The base film for rewritable recording medium and the rewritable recording medium obtained in Example 2 have the same characteristics as the base film for rewritable recording medium and the rewritable recording medium obtained in Example 1, and have high quality. Met.

Example 3
In Example 1, as a polyester resin composition for forming an intermediate layer, 7% by mass of titanium oxide-containing master pellets (b) and hollow glass beads having an average particle diameter of 5 μm (prepared by classifying commercially available glass beads) 5% by mass The base film for rewritable recording medium and the rewritable recording medium of Example 3 were obtained in the same manner as in Example 1 except that the mixture was changed to a kneaded product of 88% by mass of PET resin having an intrinsic viscosity of 0.62 dl / g. Obtained. Table 1 shows the properties of the obtained base film for a rewrite recording medium and the rewrite recording medium.

  The base film for rewritable recording medium and the rewritable recording medium obtained in Example 3 have the same characteristics as the base film for rewritable recording medium and the rewritable recording medium obtained in Example 1, and have high quality. Met.

Comparative Example 1
In the method of Example 1, the base material for the rewritable recording medium of Comparative Example 1 was used in the same manner as in Example 1 except that the compounding of the cavity forming agent-containing master pellets (A) into the polyester resin composition for forming the intermediate layer was stopped. Films and rewritable recording media were obtained. Table 1 shows the properties of the obtained base film for a rewrite recording medium and the rewrite recording medium.

  The rewritable recording medium substrate film obtained in Comparative Example 1 is inferior in heat insulation to the rewritable recording medium substrate film obtained in Example 1. Therefore, the erasability was inferior to the rewritable recording medium obtained in Example 1.

Comparative Example 2
In the method of Example 1, for the rewritable recording medium of Comparative Example 2 in the same manner as in Example 1 except that the compounding of the titanium oxide masterbatch (B) into the polyester resin composition is stopped as the raw material used in the intermediate layer. A base film and a rewritable recording medium were obtained. Table 1 shows the properties of the obtained base film for a rewrite recording medium and the rewrite recording medium.

  The base film for rewritable recording medium obtained in Comparative Example 2 is inferior in light-shielding property to the base film for rewritable recording medium obtained in Example 1, and the printed printed image is sharp. It was inferior.

Comparative Example 3
One side of a commercially available white PET film is 13% by mass of 92% hollow particles made of a copolymer resin mainly composed of vinylidene chloride-acrylonitrile having an average particle size of 5 μm, and 3% by mass of styrene / butadiene copolymer latex. A base film for a rewritable recording medium was obtained by applying a heat-insulating coat coating solution comprising a dispersion composed of (solid content equivalent amount) and 84% by mass of water to a thickness of 10 μm after drying and drying. In addition, the calendar process of this film was not implemented. Moreover, the printing layer was laminated | stacked on the said heat insulation coating layer side.
Table 1 shows the characteristics of the obtained rewritable recording medium and the rewritable recording medium obtained by laminating the rewritable printing layer in the same manner as in Example 1.

  The base film for rewritable recording medium obtained in Comparative Example 3 is inferior in heat insulation to the base film for rewritable recording medium obtained in Example 1. Therefore, the erasability was inferior to the rewritable recording medium obtained in Example 1. Moreover, the surface roughness of the heat insulation coating layer surface of the base film for rewritable recording media obtained in this Comparative Example was rough, and the fineness of the printed image was inferior. Further, the surface cleavage resistance of the film surface on the side where the rewrite printing layer was laminated was slightly inferior.

Comparative Example 4
In Example 1, the rewrite of Comparative Example 4 was performed in the same manner as in Example 1 except that the compounding amounts of the void forming agent-containing master pellets (A) and the PET resin in the intermediate layer were changed to 15 and 78% by mass, respectively. A base film for recording medium and a rewritable recording medium were obtained. Table 1 shows the properties of the obtained base film for a rewrite recording medium and the rewrite recording medium.

  The rewritable recording medium substrate film obtained in Comparative Example 4 has a lower apparent density and a higher cavity content than the rewritable recording medium substrate film obtained in Example 1. Therefore, since the heat insulating property was too good, the color development was inferior to the rewritable recording medium obtained in Example 1. Further, the surface cleavage resistance of the film surface on the side where the rewrite printing layer was laminated was slightly inferior.

Comparative Example 5
In the method of Comparative Example 2, the base for the rewritable recording medium of Comparative Example 4 was prepared in the same manner as in Example 1 except that the surface forming layer was not laminated at the time of forming the polyester film, and only the intermediate layer was formed. A material film and a rewritable recording medium were obtained. Table 1 shows the properties of the obtained base film for a rewrite recording medium and the rewrite recording medium.

  The base film for rewritable recording medium obtained in Comparative Example 5 is not laminated with a surface forming layer in addition to the problems of the base film for rewritable recording medium obtained in Comparative Example 2. Moreover, since the surface cleavage resistance of the film surface on the side where the rewritable printing layer is laminated is poor, the adhesion of the rewritable printing layer is also poor.

Comparative Example 6
A substrate film for rewrite recording medium and a rewrite recording medium of Comparative Example 6 were obtained in the same manner as in Example 1 except that the coating layer was not formed in the method of Example 1. Table 1 shows the properties of the obtained base film for a rewrite recording medium and the rewrite recording medium.
The base film for a rewrite recording medium obtained in this comparative example was inferior in the adhesion of the rewrite print layer.

Examples 4 and 5
In the method of Example 1, Examples 4 and 5 were carried out in the same manner as in Example 1 except that the coating layer forming coating solution for improving the adhesion to the rewritable printing layer was changed to the one prepared by the following method. A base film for a rewrite recording medium and a rewrite recording medium were obtained. Table 1 shows the properties of the obtained base film for a rewrite recording medium and the rewrite recording medium.
The base film for rewrite recording medium and the rewrite recording medium obtained in Examples 4 and 5 have the same characteristics as the base film for rewrite recording medium and the rewrite recording medium obtained in Example 1. High quality.

[Preparation of coating solution for coating layer formation in Example 4]
In a mixed solvent of water / isopropyl alcohol = 60/40% by mass, a copolymer polyester resin (Toyobo Co., Ltd., Vylonal MD1100) / melamine resin (Sumitomo Chemical Industries, Ltd., SMITEX M-3) / amorphous silica particles ( Fuji Silysia Co., Ltd., Silicia 310) / Fluorosurfactant (Dainippon Ink Co., Ltd., F1405) was added to a solid content of 4.0 / 0.8 / 0.3 / 0.035% by mass, respectively. Then, it was prepared by dissolving and dispersing with a stirrer.

[Preparation of coating solution for coating layer formation in Example 5]
Copolymerized polyester resin (Toyobo Co., Ltd., Vylonal MD1100) / acrylic resin (manufactured by Nippon Shokubai Co., Ltd., Acryset 270E) / amorphous silica particles (Fuji Silysia Co., Ltd.) Manufactured by Cylicia 310) / fluorine-based surfactant (F1405, manufactured by Dainippon Ink and Co., Ltd.) was added so as to be 1.0 / 3.0 / 0.3 / 0.060% by mass, respectively, and dissolved by a stirrer. And dispersed and prepared.

  FIG. 1 shows the relationship between the thermal conductivity of the base film for a rewrite recording medium and the color developability and decolorability of the rewrite recording medium using the data of Examples and Comparative Examples. From FIG. 1, it can be understood that the limited range of the present invention is a critical range.

  The substrate film for rewritable recording medium of the present invention, when used as a substrate for a rewritable recording medium, is excellent in the balance between color development and decoloring by heat energy, and is excellent in the visibility of the printed color, Since it has excellent adhesion to the rewritable printing layer, it is suitable as a base film for a rewritable recording medium and greatly contributes to the industry.

It is explanatory drawing which shows the relationship between the heat conductivity of the base film for rewrite recording media, and the coloring property and decoloring property of a rewrite recording medium using the data of an Example and a comparative example.

Claims (8)

  A base film for a rewrite recording medium in which a coating layer for improving adhesion to a rewrite printing layer is formed on at least one surface of a plastic film, the plastic film having a light transmittance of 15% or less and a heat A base film for a rewrite recording medium, wherein the conductivity is 0.037 to 0.080 W / mK.   The base film for a rewritable recording medium according to claim 1, wherein the plastic film includes a void-containing layer.   The base film for a rewritable recording medium according to claim 1 or 2, wherein a main component of the plastic film is a polyester resin. The base film for a rewrite recording medium according to claim ³ , wherein the apparent density of the plastic film is 0.91 to 1.2 g / cm ³ .   The base film for a rewritable recording medium according to any one of claims 1 to 4, wherein the plastic film has a laminated structure, and at least one outermost layer thereof is a layer that does not substantially contain a cavity.   6. The rewritable recording medium according to claim 5, wherein the three-dimensional center plane average surface roughness (SRa) on the surface of the layer substantially free of voids of the plastic film is 0.07 to 0.30 [mu] m. Substrate film.   The base film for a rewritable recording medium according to claim 6, wherein a coating layer is formed on the surface of a layer that does not substantially contain a cavity of the plastic film. A rewritable recording medium comprising a rewritable printing layer laminated on the surface of the coating layer of the substrate film for a rewritable recording medium according to claim 1.

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