JP2008030369A - Base material film for rewritable recording medium and rewritable recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the base material film for a rewritable recording medium, which is excellent in color developing properties and decolorizing properties by heat energy, in addition, the balance of both of which is well, and further in transparency. <P>SOLUTION: In the rewritable base material film for the rewritable recording medium employed in the rewritable recording medium formed by laminating a rewritable print layer onto one side of the base material, the base material film is a plastic film having its light transmittance of >15% and its thermal conductance 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 particularly, the present invention relates to a base film for a rewrite recording medium which is excellent in color development and decoloring property by thermal energy of the rewrite recording medium, has a good balance between both, and further has excellent transparency, and a rewrite 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.

On the other hand, there is a market demand for a rewritable recording medium having transparency as a constituent material of various cards such as a membership card, a cash card, and a point card. As the support for the transparent rewritable recording medium, a transparent film or sheet such as a polyethylene terephthalate film or a vinyl chloride sheet is used (see, for example, Patent Documents 6 and 7).
JP 2000-263934 A JP 2002-59653 A

  However, in the methods disclosed in these patent documents, since the heat insulating property of the support is insufficient, the balance between the color developability and the color erasing property is insufficient, and improvement thereof is desired.

  On the other hand, even in the method of imparting heat insulation to the support, the above-mentioned problems have not been solved, and transparency is also insufficient.

  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 rewrite recording medium, the rewrite recording medium is excellent in color developability and decolorization by thermal energy, and both. It is another object of the present invention to provide a rewrite recording medium substrate film having a good balance and excellent transparency.

  The rewritable recording medium substrate film of the present invention capable of solving the above-mentioned problems is a rewritable recording medium substrate film used for a rewritable recording medium in which a rewritable printing layer is laminated on one side of the substrate film. The base film is made of a plastic film having a light transmittance of more than 15% and a thermal conductivity of 0.037 to 0.080 W / mK.

  The light transmittance of the film is preferably 17% or more, and more preferably 20% or more. When the light transmittance is 15% or less, the transparency of the base film for rewritable recording medium is lowered, and it becomes difficult to apply to the use utilizing the transparency as described above. The upper limit of the light transmittance is preferably 50%, more preferably 45%, particularly preferably 40%, from the viewpoint of the balance between the light transmittance and the heat insulating property.

  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, when used as a base material for a rewritable recording medium, the color development and decoloring properties of printed folds are improved and the balance between the two is improved.

  When the thermal conductivity exceeds 0.080 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 insulating properties, 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.

Further, as the plastic film, a void-containing polyester film having an apparent density of 0.91 to 1.2 g / cm ³ is preferable.

The upper limit of the apparent density of the void-containing polyester film, 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 , further preferably 0.94 g / cm ³ . When the apparent density of the film exceeds 1.20 g / cm ³ , the decrease in thermal conductivity is insufficient. On the other hand, when the apparent density is less than 0.91 g / cm ³ , the void content is increased and the heat insulation is increased. Furthermore, the characteristics of the polyester film tend to be impaired, for example, the strength of the film decreases, the waist becomes weak, and the handleability deteriorates.

  The void-containing polyester film has a laminated structure with B / A or B / A / B as a unit, the B layer is a polyester layer containing a polyester resin and particles, and the A layer is a polyester resin and the polyester resin. A void-containing polyester layer made of a composition in which an incompatible thermoplastic resin is mixed is preferable. The B layer is a layer on which a rewrite print layer is laminated when a rewrite recording medium is used. Furthermore, the B layer is a layer that does not substantially contain a cavity inside, and preferably has a three-dimensional center plane average surface roughness (SRa) of 0.07 to 0.30 μm.

  The upper limit of the three-dimensional center plane average surface roughness (SRa) 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.

  In the rewritable recording medium of the present invention, a rewritable printing layer is laminated on the surface opposite to the antistatic layer of the substrate film for rewritable recording medium. Among these, as a plastic film, it has a laminated structure with B / A or B / A / B as a unit, and the B layer does not substantially contain a cavity inside, and the three-dimensional center plane average surface roughness (SRa ) Is 0.07 to 0.30 μm, and the A layer is composed of a void-containing polyester layer, and a rewrite printing layer is laminated on the surface of the B layer of the base film for a rewrite recording medium using the void-containing laminated polyester film. The rewritable recording medium is the most preferred embodiment.

  Moreover, it is preferable to form the coating layer which consists of adhesive property modification resin which improves the adhesiveness with a rewritable printing layer in the surface at the side by which the rewritable printing layer of a plastic film is laminated | stacked. Further, the polyester-based graft copolymer obtained by graft-polymerizing a polymerizable unsaturated monomer containing at least one carboxyl group residue on a polyester-based resin containing at least one ethylene glycol residue on at least one surface of the adhesion modifying resin. More preferably, it is a coalescence.

Further, an antistatic layer comprising an antistatic agent and a binder resin as a constituent component is formed on the surface opposite to the side on which the rewritable printing layer of the plastic film is laminated, and the surface resistivity (25 ° C., 65% RH) is preferably 1 × 10 ¹³ Ω / □ or less. The surface specific resistance value (25 ° C., 65% RH) is preferably small, but if it is less than 1 × 10 ⁶ Ω / □, there is practically no difference in effect.

  Further, when the present inventors observed the surface of the film in detail, the low molecular weight product mainly composed of oligomers and monomers such as cyclic trimers deposited on the surface of the plastic film has a particulate form. I found out. Conventional quantification of low molecular weight substances uses a method in which the surface of a plastic film is washed or eluted with a solvent (for example, chloroform) that dissolves low molecular weight substances, and cyclic trimers dissolved in the solvent are quantified. (For example, the above-mentioned Patent Document 6). However, in this method, not only the surface of the film but also low molecular weight substances existing in the film are extracted, so that the correspondence with the practical characteristics is not good.

Therefore, the present inventors paid attention to the fact that surface precipitates exist as particles, and deposited them on the surface of the film during heat treatment using a method capable of quantifying the area occupied by these precipitated particles deposited on the surface with a microscope. It was found that low molecular weight products. That is, rewrite recording medium for the substrate film of the present invention, "when 20 minutes heat treatment at 170 ° C., the occupied area ratio 0.008μm ^{2 /} μm 2 of particles deposited on the surface of the side of stacking the rewrite printing layer Low molecular weight that deposits on the surface of the substrate film in the processing step of laminating the rewritable printing layer or when the obtained rewritable recording medium is heated for color development or decoloration. Problems caused by things can be prevented in advance.

The base film for a rewrite recording medium of the present invention has an occupation area ratio of particles deposited on the surface on which the rewrite printing layer is laminated at least 0.008 μm ² / μm when the film is heat-treated at 170 ° C. for 20 minutes. It is preferable to control to ² or less. Filling ratio of particles deposited on the surface of the film is more preferably at 0.007μm ² / μm ² or less, more preferably 0.006μm ² / μm ² or less, particularly preferably 0.005μm ² / μm ² or less It is. When the occupied area ratio of the particles deposited on the surface of the film exceeds 0.008 μm ² / μm ² , when the rewritable recording medium is used, the durability stability when coloring and erasing are repeated becomes insufficient. .

  The rewritable recording medium of the present invention has a configuration in which a rewritable printing layer is laminated on one side of the above-mentioned rewritable recording medium substrate 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. 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.

  Since the rewritable recording medium of the present invention has transparency, for example, rewritable display information can be viewed from both the front and back sides of the rewritable recording medium. Further, by laminating a metallic luster material such as a white film or an aluminum vapor deposition film, the sharpness of the rewritable display information image can be improved. Moreover, the design etc. of a rewrite recording medium can be improved by laminating | printing printed matter. Therefore, for example, by using the rewritable recording medium of the present invention as a material for the various cards described above, it is possible to increase the degree of freedom of expression regarding the design and information displayed on the card. Further, since the sense of cleanliness can be improved by the transparency, it can be suitably used as a card material used in the industry where the corporate image and the brand image are emphasized. Further, when used as a material for the card, rewritable display information can be viewed from both the front and back sides of the card, so that the convenience of the card user can be improved.

Furthermore, by using a void-containing polyester film with 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 base film, so that printing is performed by, for example, a thermal head method. In this case, 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, the rewritable layer also has an advantage that durability stability is further improved when coloring and erasing are repeated.

  Furthermore, by forming a coating layer made of an adhesion modifying resin that improves adhesion to the rewritable printing layer on the surface of the plastic film on which the rewritable printing layer is laminated, the coating layer and the rewritable printing layer Since it has excellent adhesion and excellent durability when repeated coloring and decoloring, the durability of the rewritable printing layer is highly excellent when used as a base material for a rewritable recording medium.

Furthermore, an antistatic layer comprising an antistatic agent and a binder resin as constituent components is formed on the surface of the plastic film opposite to the side on which the rewritable printing layer is laminated, and the surface resistivity of the antistatic layer (25 ° C., 65 % RH) value is controlled to 1 × 10 ¹³ Ω / □ or less, for example, when used as a support for a rewritable recording medium, for example, due to friction with a roll or thermal head during printing in a printer. Occurrence of static electricity failure such as poor running is suppressed.

  Furthermore, by reducing the amount of low molecular weight components that precipitate on the film surface when heated, low molecular weight materials that migrate from the base film to the rewritable printing layer when used as a support for a rewritable recording medium can be reduced. Therefore, the rewrite printing layer has excellent durability stability when coloring and erasing are repeated, and troubles due to smearing can be reduced when printing with a processing step or printer for forming the rewrite printing layer.

  The base film for a rewritable recording medium of the present invention is composed of a plastic film having a light transmittance of more than 15% and a thermal conductivity of 0.037 to 0.080 W / mK. The material used for the base film for a rewrite recording medium of the present invention and the method for producing the film will be described in detail below.

(1) Plastic film Examples of the material of 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. Examples thereof include cellulose derivative resins, styrene resins such as syndiotactic polystyrene, and engineering plastic resins such as polyphenylene sulfide and polyimide. Of these, polyester resins are preferred.

  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.

  In order to make the light transmittance of the base film exceed 15%, it is preferable that the resin constituting the film does not contain as much particles as possible to inhibit transparency. In the present invention, for the purpose of increasing the light transmittance of the film, the printed image is given visibility from both the front and back sides of the rewrite recording medium, the design is given, and the print image is sharp. The purpose is to develop advantages such as improvement.

  The base film for a rewritable recording medium of the present invention preferably has a whiteness measured in accordance with JIS Z-8722 of less than 25, more preferably 20 or less. In order to make the whiteness of the film less than 25, white pigments such as titanium oxide, calcium carbonate, zinc oxide, or barium sulfate, polymer beads blended with these, or the like should be reduced or the content thereof should be reduced. It is preferable. It is preferable that the said white pigment is less than 1 mass% with respect to the resin composition which comprises a film.

  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. As for the specific conditions, the appropriate range varies depending on the material used and the equipment capacity, so it is not possible to set a numerical range in general. Therefore, first, a preliminary experiment with large conditions is performed, the thermal conductivity of the obtained film is evaluated, and the conditions under which the thermal conductivity can stably satisfy the range of 0.037 to 0.080 W / mK should be selected. That's fine. The condition setting is not performed by trial and error, but is performed according to the following technical guidelines.

  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 biaxially 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.

  As a method for containing voids in a plastic film, (1) a method in which a foaming agent is contained and foamed by heat during extrusion or film formation, or foamed by chemical decomposition, (2) carbon dioxide gas at the time of extrusion or after extrusion, etc. (3) A method of blending hollow fine particles, (4) Heat incompatible with the thermoplastic resin A in the thermoplastic resin A constituting the film Examples include a method in which the plastic resin B is contained and the polymer extrusion is uniaxially or biaxially stretched, and (5) a method in which the thermoplastic resin A contains organic or inorganic fine particles and the melt extrusion is biaxially stretched. be able to. 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 a thermoplastic resin incompatible with the polyester resin, for example, a polyolefin resin typified by polypropylene or polymethylpentene, various modified resins. Examples include polyolefin resins, polystyrene resins, polyacrylic resins, polycarbonate resins, polysulfone resins, cellulose resins, polyphenylene ether resins, and phenoxy resins. Moreover, you may use together white pigments, such as a titanium oxide, barium sulfate, zinc sulfide, a calcium carbonate.

  When a void-containing polyester film is used as the base film, a thermoplastic resin that is incompatible with the polyester resin and the polyester resin is used as a material for forming the film. As the thermoplastic resin incompatible with the polyester resin, a single thermoplastic resin may be used, 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 void-containing polyester film in the range of 0.91 to 1.2 g / cm ³ , for example, the inclusion of a thermoplastic resin incompatible with the polyester resin shown below. Examples thereof include a method for adjusting the amount to an appropriate value and a method for adjusting the stretching temperature and the stretching ratio of the film.

  The void-containing polyester film has a laminated structure with B / A or B / A / B as a unit, the B layer is a polyester layer containing a polyester resin and particles, and the A layer is non-phased with the polyester resin and the polyester resin. It is preferably a laminated film which is a void-containing polyester layer made of a composition in which a soluble thermoplastic resin is mixed. Note that the B layer is a layer on which a rewrite print layer is laminated when a rewrite recording medium is used. Furthermore, it is preferable that the B layer contains substantially no cavity.

  Here, the layer substantially free of voids (B layer) means a layer having a void lamination number density of less than 0.0 pieces / μm. Note that the cavity stacking number density is obtained by dividing the number of layers of cavities existing in the thickness direction of the B layer by the thickness of the B layer.

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. Next, a straight line is drawn perpendicularly to the film surface at any location on the photographic image, and the number of cavities that intersect the straight line in the B layer is counted. The number of cavities is defined as the number of cavities in the thickness direction of the B layer (the number of stacked layers). Further, the thickness (μm) of the B layer is measured along this straight line, and the number of cavities stacked in the B layer is divided by the thickness of the B layer to obtain the cavity stack number density (pieces / μm). In addition, measurement is performed at five places per photograph, and an average value of a total of 25 places is obtained to obtain a cavity layer number density of the B layer.

  In the present invention, when the void-containing polyester film having the above-described laminated structure is used as the plastic film, cleavage of the film surface can be suppressed. For example, when a foaming agent or a cavity-expressing material (a thermoplastic resin incompatible with polyester) is contained in the surface layer B, a reduction in surface strength due to void destruction tends to occur during processing.

  2-30 micrometers is preferable and, as for the thickness of 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 addition, the thickness of the base film for rewritable recording media of the present invention may be appropriately determined depending on the application and standard when used in the market within a total thickness of 25 to 300 μm.

  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.

  As a method for laminating the B layer, for example, a method of laminating two films obtained by individually forming the B layer and the A layer with an adhesive or the like may be used. You may use the method of biaxially stretching the film which laminated | stacked A layer, and then heat-processing. The latter coextrusion method is more economical and is a preferred embodiment.

  In order to control the three-dimensional center plane average surface roughness (SRa) of the B layer to 0.07 to 0.30 μm, the average particle diameter of inorganic and / or organic fine particles contained in the polyester resin constituting the B layer, The content and the thickness of the B layer are adjusted as appropriate. The particles to be contained in the layer B are preferably white pigments having a function of imparting concealability to the film, and examples include titanium oxide (anatase type, rutile type), barium sulfate, calcium carbonate, silica, and zinc sulfide. These particles may be used alone or in combination of two or more.

  In this invention, when using a void containing polyester film as a biaxially stretched polyester film, it is preferable to manufacture using 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. When a laminated film having a layer structure of B / A or B / A / B is used, at least two extruders are used, the polyester resin is melted in one extruder, and the polyester is used in the other extruder. A mixture of a resin and a thermoplastic resin that is incompatible with the polyester resin is melted, joined by a feed block, and coextruded into a sheet to produce an unstretched film. The thickness of each layer can be adjusted by the amount of molten resin discharged from the B layer and the A layer.

  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.

Moreover, plastic film used for the base film in the present invention, the occupied area ratio of particles deposited on the surface of the side to be laminated at least rewrite the print layer is 0.008μm ^{2 /} μm 2 or less when heated for 20 minutes at 170 ° C. It is.

  In the present invention, as a method of setting the occupied area ratio of particles deposited on the surface of the plastic film after the heat treatment in the above range, for example, when using a polyester resin as a raw material for forming the plastic film, the content of the cyclic trimer It is preferable to use a polyester resin that has been subjected to a so-called low-oligomerization treatment in which the amount is reduced.

  When forming into a film using the polyester resin which carried out said low oligomerization process, you may reduce the amount of cyclic trimers contained in the polyester resin of all the layers which form a polyester film. However, by using a laminated polyester film having a laminated structure of B / A or B / A / B, only the polyester resin used for any one of the B layers on which the rewritable printing layer is laminated is reduced by a method of reducing the amount of cyclic trimer. Moreover, the occupied area ratio of the particles deposited on the film surface can be reduced to the above range. This method is economically advantageous because it can reduce the amount of the polyester resin subjected to the low oligomerization treatment, and is recommended as a more preferred embodiment. Most preferred is a laminated polyester film having a laminated structure of B / A / B. In this case, the low molecular weight material deposited on the opposite surface of the rewritable printing layer is prevented from adhering to the surface of the rewritable printing layer when the rewritable recording medium is rolled up or stacked on a sheet. can do.

  In the case of reducing only the amount of cyclic trimer contained in the polyester resin used for the surface layer (B layer), it is important to optimize the thickness of the surface layer. The thickness of the surface layer (B layer) is preferably 5 to 20%, more preferably 7 to 15% with respect to the total thickness. If it is less than 5%, the cyclic trimer contained in the A layer may pass through the B layer and precipitate on the surface of the B layer. On the other hand, when the thickness of the surface layer (B layer) exceeds 20% with respect to the total thickness, the movement of the cyclic trimer from the A layer is stopped inside the B layer, and the cyclic trim to the surface of the B layer is stopped. Since the effect of suppressing the precipitation of the monomer is saturated, it is economically disadvantageous. Furthermore, it is more preferable to set the thickness of the B layer in consideration of the effect of controlling the surface roughness by the B layer.

  The content of the cyclic trimer in the low oligomerization polyester resin is preferably 6000 ppm or less, more preferably 5000 ppm or less, and particularly preferably 4000 ppm or less. When the content of the cyclic trimer in the polyester resin exceeds 6000 ppm, the ratio of the occupied area of the particles due to the cyclic trimer deposited on the surface of the base film increases.

  As a method for producing a polyester resin in which the content of the cyclic trimer is reduced (in this specification, it may be abbreviated as a low oligomerization-treated polyester resin), for example, the intrinsic viscosity is 0.40 to 0.60 dl / and a method of subjecting a polyester having a predetermined intrinsic viscosity to a heat treatment under a condition in which the intrinsic viscosity does not substantially change in an inert gas atmosphere or under reduced pressure. Further, there is a method of extracting with a solvent that dissolves the cyclic trimer.

  In addition, since the cyclic trimer is produced in the melt extrusion process of the polyester resin in the production process of the polyester film, the increase amount of the cyclic trimer when the polyester resin is melted at a temperature of 290 ° C. for 30 minutes is 5000 ppm or less. It is also preferable to use a technique for lowering. The increase amount of the cyclic trimer is preferably 3000 ppm or less, more preferably 2000 ppm or less, and particularly preferably 1000 ppm.

  Moreover, the method of reducing the increase amount of the cyclic trimer to 5000 ppm or less when the polyester resin is melted at a temperature of 290 ° C. for 30 minutes is shown below. In order to suppress the regeneration of the cyclic trimer in the molten state at the time of molding, it is important to reduce the amount of the active polymerization catalyst remaining in the polyester as much as possible. As a typical means for reducing the amount of such an active polymerization catalyst, the following method may be mentioned.

  As a first means, a polymerization catalyst is inactivated by contacting polyester with water.

  Examples of the method for deactivating the polyester polycondensation catalyst include a method in which the polyester chip is contacted with water, water vapor or water vapor-containing gas after melt polycondensation or after solid phase polymerization.

  Examples of the water treatment method include a method of immersing in water and a method of applying water on the chip with a shower. The treatment time is 5 minutes to 2 days, preferably 10 minutes to 1 day, more preferably 30 minutes to 10 hours, and the water temperature is 20 to 180 ° C., preferably 40 to 150 ° C., more preferably 50 to 120 ° C.

  Below, the method of performing water treatment industrially is illustrated. The treatment method may be either a continuous method or a batch method, but the continuous method is preferred for industrial use.

  A silo-type treatment tank is used when water-treating polyester chips in a batch system. In other words, the polyester chip is received in a silo and treated with water in a batch system. In the case where the polyester chips are water-treated in a continuous manner, the polyester chips can be continuously or intermittently received in the tower-type treatment tank from the upper part and water-treated.

  When the polyester chip and water vapor or water vapor-containing gas are contacted, the water vapor or water vapor containing gas or water vapor containing air at a temperature of 50 to 150 ° C., preferably 50 to 110 ° C., is preferably granular polyethylene terephthalate. -0.5 g or more of water vapor is supplied per 1 kg of tort or brought into contact with granular polyethylene terephthalate and water vapor.

  The contact between the polyester chip and water vapor is usually performed for 10 minutes to 2 days, preferably 20 minutes to 10 hours.

  Hereinafter, a method for industrially performing contact treatment between granular polyethylene terephthalate and water vapor or a gas containing water vapor is exemplified, but the method is not limited thereto. The processing method may be either a continuous method or a batch method.

  When a polyester chip is contact-treated with water vapor in a batch system, a silo type processing apparatus can be used. That is, a polyester chip is received in a silo, and contact processing is performed by supplying steam or a steam-containing gas in a batch manner.

  When the polyester chips are continuously contacted with water vapor, the column-type processing device continuously receives the granular polyethylene terephthalate from the top and continuously supplies the water vapor in a cocurrent or countercurrent manner to contact the water vapor. be able to.

  As described above, when treated with water or steam, the granular polyethylene terephthalate is drained with a draining device such as a vibrating sieve or a Simon Carter as necessary, and transferred to the next drying step by a conveyor. .

  The polyester chip that has been contact-treated with water or water vapor can be dried by a commonly used polyester drying process. As a continuous drying method, a hopper-type ventilation dryer is generally used in which a polyester chip is supplied from the upper part and a drying gas is supplied from the lower part.

  As a dryer for drying in a batch mode, drying may be performed while aeration gas is passed under atmospheric pressure.

  As the dry gas, atmospheric air may be used, but dry nitrogen and dehumidified air are preferable from the viewpoint of preventing molecular weight reduction due to hydrolysis or thermal oxidative decomposition of polyester.

The second means is a method based on catalyst deactivation by a phosphorus compound.
In particular, when an aluminum or titanium-based polycondensation catalyst is used, the effect is small in the inactivation (first means) of the polymerization catalyst by the contact treatment with water. Therefore, a method in which a phosphorus compound is added to a polyester melt after melt polycondensation or solid phase polymerization to inactivate the polymerization catalyst can be mentioned.

  In the case of melt-polymerized polyester, a method of inactivating the aluminum catalyst by mixing the polyester after the completion of the melt-polymerization reaction and the polyester resin blended with the phosphorus compound in an apparatus such as a line mixer that can be mixed in a molten state. Is mentioned.

  In addition, as a method of blending the phosphorus compound with the solid phase polymerized polyester, a method of dry blending the phosphorus compound with the solid phase polymerized polyester, a polyester master batch chip in which the phosphorus compound is melt kneaded and mixed with the solid phase polymerized polyester chip are mixed. And a method in which a predetermined amount of a phosphorus compound is blended with polyester and melted in an extruder or molding machine to inactivate the catalyst.

  The amount of the phosphorus compound required to completely deactivate the catalyst is at least 5 moles in terms of the residual amount with respect to the catalyst metal content remaining in the polyester.

  Examples of the phosphorus compound used include phosphoric acid, phosphorous acid, phosphonic acid, and derivatives thereof. Specific examples include phosphoric acid, phosphoric acid trimethyl ester, phosphoric acid triethyl ester, phosphoric acid tributyl ester, phosphoric acid triphenyl ester, phosphoric acid monomethyl ester, phosphoric acid dimethyl ester, phosphoric acid monobutyl ester, phosphoric acid dibutyl ester, Phosphoric acid, phosphorous acid trimethyl ester, phosphorous acid triethyl ester, phosphorous acid tributyl ester, methylphosphonic acid, methylphosphonic acid dimethyl ester, ethylphosphonic acid dimethyl ester, phenylphosphonic acid dimethyl ester, phenylphosphonic acid diethyl ester, phenyl -Luphosphonic acid diphenyl ester, etc., and these may be used alone or in combination of two or more.

The third means is a method for suppressing the reprecipitation of the cyclic trimer in the melt extrusion process during film production.
In the polyester film manufacturing process, as a method for suppressing the formation of cyclic trimer, a method of melt-extruding a polyester resin, lowering the melting temperature when manufacturing the sheet, and shortening the residence time thereof Is preferred. The melting temperature can be adjusted by controlling the temperature of the flow path through which the molten resin passes, and is preferably controlled in the range from the melting point of the polyester resin to + 30 ° C., and in the range up to + 15 ° C. More preferably, it is controlled. In addition, since the polyester resin has a slow crystallization rate, it flows without being solidified substantially in the manufacturing process in the range up to the melting point of −10 ° C. Therefore, in order to reduce the formation of the cyclic trimer, the resin temperature is set to be low. It is also preferable to control the temperature range.

  In the present invention, the occupied area ratio of the surface precipitated particles can be set within the range of the present invention by the above method.

  Further, as another means for achieving a ratio of the occupied area of particles deposited on the surface of the base film after the heat treatment within the above range, a coating layer made of a resin having a crosslinked structure is used, and at least the rewritable printing phase of the plastic film is provided. The method of apply | coating to the surface of the side to laminate | stack, and utilizing the barrier effect which suppresses the surface migration of a low molecular weight component by this application layer is mentioned. Of course, the method of applying to both sides and sandwiching the plastic film is most suitable. As the resin, the above-mentioned polyester-based graft copolymer is suitable. This method may be performed alone or in combination with at least one of the above three means.

(2) Functionality imparted by coating layer (2-1) Adhesion improving layer In the present invention, the adhesiveness for improving the adhesion with the rewritable printing layer on the surface of the plastic film on which the rewritable printing layer is laminated. It is a preferred embodiment to form a coating layer made of a modified resin.

  Examples of the adhesion modifying resin include polyester, polyurethane, acrylic resin, vinyl resin, epoxy resin, amide resin, polyvinyl alcohol, or a copolymer of each resin. These resins may be resins grafted by introducing a copolymer component into the main chain of each resin. Examples of the graft resin include acrylic resin graft polyester, acrylic resin graft polyurethane, vinyl resin graft polyester, and vinyl resin graft polyurethane.

  In the present invention, among these graft resins, a polyester graft polymer obtained by graft polymerization of a polymerizable unsaturated monomer containing at least one carboxyl group residue on a polyester resin containing an ethylene glycol residue, It is particularly preferable as a binder resin constituting the antistatic layer.

  In this specification, the “polyester-based graft polymer” means that all the polyester-based resin molecules are graft-polymerized with the above acid anhydride, or the polyester-based resin has the above-mentioned acid. It means a mixture of graft polymer molecules grafted with anhydride and unreacted polyester resin molecules not grafted with acid anhydride as described above.

  The polyester-based graft polymer can form a cross-link between resin molecules by the action of the unit by introducing a unit derived from the above acid anhydride into the polyester-based resin. For example, when a coating solution containing a polyester-based graft polymer as a main component is prepared, the acid anhydride group in the resin molecule is changed to a carboxyl group by hydrolysis or the like in the coating solution. Thereafter, the coating solution is applied to a base film, and an acid anhydride group is formed between resin molecules or active hydrogen groups possessed by other molecules by a thermal history applied when forming a coating layer by drying or the like. A cross-linked structure is formed between resin molecules, for example, by pulling out and generating an ester group.

  The above “grafting” is to introduce a branched polymer composed of a polymer different from the main chain into the main chain of the main polymer.

  Graft polymerization is generally carried out by reacting at least one polymerizable unsaturated monomer using a radical initiator in a state where a hydrophobic copolymerizable polyester resin is dissolved in an organic solvent. . The reaction product after completion of the grafting reaction includes, in addition to a desired graft polymer of a hydrophobic copolymerizable polyester and a polymerizable unsaturated monomer, a hydrophobic copolymerizable polyester resin that has not undergone grafting, and It also contains a polymer of the above unsaturated monomer that has not been grafted to the hydrophobic copolymerizable polyester. The polyester-based graft polymer in the present invention includes not only the above-mentioned polyester-based graft polymer but also a reaction including an unreacted hydrophobic copolymerizable polyester, a polymer of an unsaturated monomer that has not been grafted, and the like. Also referred to as a mixture.

The acid value of the polyester-based graft polymer obtained by graft polymerization of at least one polymerizable unsaturated monomer to the hydrophobic copolymerizable polyester resin is preferably 600 eq / 10 ⁶ g or more. More preferably, it is 1200 eq / 10 ⁶ g or more. When the acid value of the graft polymer is less than 600 eq / 10 ⁶ g, it cannot be said that the adhesiveness with the layer coated with the graft polymer-containing layer which is the object of the present invention is sufficient.

  Moreover, the mass ratio of the hydrophobic copolymerizable polyester resin and the polymerizable unsaturated monomer to obtain a desired graft polymer is polyester / polymerizable unsaturated monomer = 40/60 to 95/5. The range is desirable, more desirably 55/45 to 93/7, and most desirably 60/40 to 90/10. When the mass ratio of the hydrophobic copolymerizable polyester resin is less than 40% by mass, the excellent adhesiveness of the polyester resin cannot be exhibited. On the other hand, when the mass ratio of the hydrophobic copolymerizable polyester resin is larger than 95% by mass, blocking, which is a defect of the polyester resin, easily occurs.

  The graft polymer is in the form of an organic solvent solution or dispersion, or an aqueous solvent solution or dispersion. In particular, a dispersion of an aqueous solvent, that is, a form of a water-dispersed resin is preferable from the viewpoint of working environment and applicability. Such a water-dispersed resin is usually obtained by graft polymerization of at least one hydrophilic polymerizable unsaturated monomer onto the hydrophobic copolymerizable polyester resin in an organic solvent, followed by water addition and organic It can be obtained by distilling off the solvent.

  The polyester-based graft polymer preferably exhibits a translucent or milky white appearance having an average particle diameter of 500 nm or less, particularly 10 to 500 nm, measured by a laser light scattering method. Graft polymers with various particle sizes can be obtained by adjusting the polymerization method. From the viewpoint of dispersion stability, the average particle size is preferably 400 nm or less, more preferably 300 nm or less. When it exceeds 500 nm, the gloss of the coating film surface is lowered and the transparency is lowered. On the other hand, if it is less than 10 nm, the water resistance, which is the object of the present invention, is lowered, which is not preferable.

  The polymerizable unsaturated monomer to be grafted to the hydrophobic copolymerizable polyester resin is a hydrophilic radical polymerizable monomer, and is a radical polymerization having a hydrophilic group or a group that can be changed to a hydrophilic group later. It is a possible monomer. Examples of the hydrophilic group include a carboxyl group, a hydroxyl group, a phosphoric acid group, a phosphorous acid group, a sulfonic acid group, an amide group, and a quaternary ammonium base. On the other hand, examples of the group that can be changed to a hydrophilic group include an acid anhydride group, a glycidyl group, and a chloro group. Among these groups, a carboxyl group is preferable from the viewpoint of increasing the water dispersibility and the acid value of the graft polymer. Therefore, a polymerizable unsaturated monomer having a carboxyl group or a group capable of becoming a carboxyl group is preferable.

  The glass transition temperature of the graft polymer is 30 ° C. or lower, preferably 10 ° C. or lower. By using a graft polymer having a glass transition temperature of 30 ° C. or lower for the graft polymer-containing layer, a laminated polyester film having excellent adhesion can be obtained. When the physical properties of the graft polymer are out of the above range, the effect of the graft polymer-containing layer containing the graft polymer is hardly exhibited.

  The above-mentioned hydrophobic copolymerizable polyester resin needs to be essentially water-insoluble which does not inherently disperse or dissolve in water. When a polyester resin that is dispersed or dissolved in water is used for graft polymerization, the adhesiveness and water resistance, which are the objects of the present invention, are deteriorated. The composition of the dicarboxylic acid component of this hydrophobic copolymerizable polyester resin is as follows: aromatic dicarboxylic acid 60 to 99.5 mol%, aliphatic dicarboxylic acid and / or alicyclic dicarboxylic acid 0 to 40 mol%, polymerizable unsaturated It is preferable that it is 0.5-10 mol% of dicarboxylic acid containing a double bond. When the aromatic dicarboxylic acid is less than 60 mol%, or when the aliphatic dicarboxylic acid and / or alicyclic dicarboxylic acid exceeds 40 mol%, the adhesive strength is lowered.

  Moreover, when the dicarboxylic acid containing a polymerizable unsaturated double bond is less than 0.5 mol%, it becomes difficult to efficiently graft the polymerizable unsaturated monomer to the hydrophobic copolymerizable polyester resin. On the other hand, if it exceeds 10 mol%, the viscosity increases too late in the grafting reaction, which is not preferable because it prevents the uniform progress of the reaction. More preferably, the aromatic dicarboxylic acid is 70 to 98 mol%, the aliphatic dicarboxylic acid and / or the alicyclic dicarboxylic acid is 0 to 30 mol%, and the dicarboxylic acid containing a polymerizable unsaturated double bond is 2 to 7 mol%. It is.

  Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid and the like. It is preferable not to use a hydrophilic group-containing dicarboxylic acid such as 5-sodium sulfoisophthalic acid because the water resistance, which is the object of the present invention, decreases. Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, and dimer acid. Examples of the alicyclic dicarboxylic acid include 1,4-cyclohexanedicarboxylic acid, 1, Examples include 3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid and its acid anhydride. Examples of dicarboxylic acids containing polymerizable unsaturated double bonds include α, β-unsaturated dicarboxylic acids, fumaric acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid, unsaturated double bonds Examples of the alicyclic dicarboxylic acid to be used include 2,5-norbornene dicarboxylic acid anhydride and tetrahydrophthalic anhydride. Of these, fumaric acid, maleic acid, and 2,5-norbornene dicarboxylic acid are preferred from the viewpoint of polymerizability.

  On the other hand, examples of the glycol component include aliphatic glycols having 2 to 10 carbon atoms and / or alicyclic glycols having 6 to 12 carbon atoms and / or ether bond-containing glycols. Examples of the aliphatic glycol having 2 to 10 carbon atoms include ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6 -Hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-ethyl-2-butylpropanediol, and the like. Examples of the alicyclic glycol having 6 to 12 carbon atoms include 1,4-cyclohexanedimethanol. In the present invention, the glycol component preferably comprises ethylene glycol. Satisfying this requirement is a preferred embodiment in terms of cost performance of the polyester resin.

  Examples of the ether bond-containing glycol include diethylene glycol, triethylene glycol, dipropylene glycol, and glycols obtained by adding ethylene oxide or propylene oxide to two phenolic hydroxyl groups of bisphenols, such as 2,2-bis (4 -Hydroxyethoxyphenyl) propane and the like. Polyethylene glycol, polypropylene glycol, and polytetramethylene glycol may be used as necessary.

  In the hydrophobic copolymerizable polyester resin, 0 to 5 mol% of a trifunctional or higher polycarboxylic acid and / or polyol can be copolymerized. As the trifunctional or higher polycarboxylic acid, (anhydrous) Trimellitic acid, (anhydrous) pyromellitic acid, (anhydrous) benzophenone tetracarboxylic acid, trimesic acid, ethylene glycol bis (anhydro trimellitate), glycerol tris (anhydro trimellitate) and the like are used. On the other hand, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol and the like are used as the trifunctional or higher functional polyol. The tri- or higher functional polycarboxylic acid and / or polyol is copolymerized in the range of 0 to 5 mol%, preferably 0 to 3 mol% with respect to the total acid component or the total glycol component. Gelation during polymerization tends to occur, which is not preferable. The weight average molecular weight of the hydrophobic copolymerizable polyester resin is preferably in the range of 5,000 to 50,000. When the weight average molecular weight is less than 5,000, the adhesive strength is lowered. On the other hand, when the weight average molecular weight exceeds 50,000, problems such as gelation at the time of polymerization occur.

The polymerizable unsaturated monomer includes, for example, fumaric acid, monoethyl fumarate, diethyl fumarate, diester of fumaric acid such as dibutyl fumarate; maleic acid and its anhydride, monoethyl maleate, maleic acid Monoester or diester of maleic acid such as diethyl and dibutyl maleate; Itaconic acid and its anhydride, monoester or diester of itaconic acid; maleimide such as phenylmaleimide; styrene, α-methylstyrene, t-butylstyrene, chloro Styrene derivatives such as methylstyrene; vinyltoluene, divinylbenzene and the like. Acrylic polymerizable monomers that are one of polymerizable unsaturated monomers include, for example, alkyl acrylate, alkyl methacrylate (the alkyl group is methyl, ethyl, n-propyl, isopropyl, n-butyl). Group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, phenyl group, benzyl group, phenylethyl group, etc.): 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2- Hydroxypropyl methacrylate-containing acrylic monomer: acrylamide, methacrylamide, N-methyl methacrylamide, N-methyl acrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylol acrylamide N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, amide group-containing acrylic monomer of N-phenylacrylamide: N, N-diethylaminoethyl acrylate, amino group-containing acrylic monomer of N, N-diethylaminoethyl methacrylate : Glycidyl acrylate, epoxy group-containing acrylic monomer of glycidyl methacrylate: Acrylic monomers containing carboxyl groups or salts thereof such as acrylic acid, methacrylic acid and their salts (sodium salt, potassium salt, ammonium salt) It is done. However, acrylic polymerizable monomers are less preferred for use in the present invention because they are less effective in reducing the surface energy hydrogen bond strength component term (γs ^h ) of the present invention. The said polymerizable unsaturated monomer can be copolymerized using 1 type, or 2 or more types. Among the above monomers, maleic anhydride and its ester, and a combination of maleic anhydride and styrene are preferable.

  As the graft polymerization initiator, organic peroxides and organic azo compounds known to those skilled in the art can be used. Benzoyl peroxide, t-butylperoxypivalate as organic peroxide, 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile) as organic azo compound Etc. The amount of the polymerization initiator used for the graft polymerization is at least 0.2% by mass, preferably 0.5% by mass or more, based on the polymerizable unsaturated monomer. In addition to the polymerization initiator, a chain transfer agent for adjusting the chain length of the branched polymer, for example, octyl mercaptan, mercaptoethanol, 3-t-butyl-4-hydroxyanisole and the like may be used as necessary. In this case, it is desirable to add in the range of 0 to 5% by mass with respect to the polymerizable unsaturated monomer.

(2-2) Antistatic layer In the present invention, an antistatic layer comprising an antistatic agent and a binder resin as a constituent component is formed on the surface of the plastic film opposite to the side on which the rewritable printing layer is laminated. It is also a preferred embodiment that the surface specific resistance (25 ° C., 65% RH) of the layer is controlled to 1 × 10 ¹³ Ω / □ or less.

(I) Antistatic agent In the present invention, the antistatic agent is an indispensable material for controlling the surface resistivity (25 ° C., 65 RH%) within the above range, and various antistatic agents are known. Yes. However, in the present invention, as the antistatic agent, (a) an anionic polymer compound having at least one sulfonate group or phosphate group in the molecule, and (b) a cationic polymer containing a quaternary ammonium base. It is preferable to use a polymer antistatic agent selected from a compound or (c) polythiophene or a derivative thereof.

  Because, when using a low molecular weight anionic antistatic agent that is widely used as an antistatic agent, when the long plastic film is wound into a roll, the antistatic agent is an antistatic layer of the plastic film. May transfer to the opposite side. For example, when a rewrite print layer is laminated on the surface to which the antistatic agent is transferred, the adhesion of the rewrite print layer is lowered. In order to prevent such transfer of the antistatic agent, it is preferable to use an anionic polymer compound, a cationic polymer compound, or a π-electron conjugated conductive polymer as the antistatic agent.

(Anionic polymer compound)
The anionic polymer compound is preferably a polymer antistatic agent having at least one sulfonate group or phosphate group in the molecule. This polymer antistatic agent is characterized by a structure having a large number of highly hydrophilic sulfonic acid components and phosphoric acid components. These polymer antistatic agents may be used alone or in combination of two or more.

  Resins containing a sulfonate group component in the molecule include polystyrene sulfonic acid sodium salts, potassium salts, lithium salts, ammonium salts, homopolymers such as phosphonium salts, and acrylic monomers such as acrylic acid esters or methacrylic acid esters. And a copolymer of styrene sulfonic acid monomer and a copolymer of acrylamidomethylpropane sulfonic acid and unsaturated monomer. In the present invention, the sulfonate can be a mixture of a metal salt and an amine salt.

  Examples of the resin containing a phosphate group in the molecule include resins obtained by polymerizing or copolymerizing various phosmers (manufactured by Unichemical) which are unsaturated monomers containing a phosphate group.

  The weight average molecular weight of the antistatic agent is preferably in the range of 1,000 to 1,000,000, more preferably 5,000 to 1,000,000. If the weight average molecular weight is less than 1,000, the transfer of the antistatic agent described above is increased. On the other hand, if it exceeds 1,000,000, it is preferable for suppressing the transition, but uniform mixing with the modified resin becomes difficult, and the uniformity of the coating film tends to be lowered.

(Cationic polymer compound)
As the cationic polymer compound, a polymer compound containing a quaternary ammonium base is preferable. This refers to a polymer compound having a component containing a quaternary ammonium base in the main chain or side chain in the molecule. Examples of such constituents include, for example, a pyrrolidinium ring, an alkylamine quaternized product, a copolymer of these with acrylic acid or methacrylic acid, an N-alkylaminoacrylamide quaternized product, a vinylbenzyltrimethylammonium salt, 2-hydroxy 3-methacryloxypropyl trimethyl ammonium salt etc. are mentioned. Further, these may be combined or copolymerized with other resins. In addition, examples of anions that serve as counter ions of these quaternary ammonium salts include ions such as halogen, alkyl sulfate, alkyl sulfonate, and nitric acid.

(Π-electron conjugated conductive polymer)
Examples of the π-electron conjugated conductive polymer include polyaniline or a derivative thereof, polypyrrole / or a derivative thereof, polyisothianaphthene or a derivative thereof, polyacetylene or a derivative thereof, and polythiophene or a derivative thereof. Among them, polythiophene or a derivative thereof is particularly preferable from the viewpoint of little coloring.

(Ii) Binder resin In the present invention, a binder resin is used in the antistatic layer for the purpose of holding an antistatic agent. As the binder resin, the resin used for the adhesion improving layer can be used.

(2-3) Crosslinking structure In addition, a high degree of heat and heat resistance adhesion is obtained by blending a crosslinking agent in the coating solution for the adhesion improving layer or the coating solution for the antistatic layer and causing a crosslinking reaction with the functional group of the binder resin. To suppress the transfer of low molecular weight materials from the plastic film to the rewritable printing layer, or to transfer the low molecular weight materials transferred from the antistatic agent or plastic film to the opposite surface of the antistatic layer. It becomes possible. In particular, when used in combination with the above graft polymer, these effects become more remarkable.

  As a cross-linking agent, phenol formaldehyde resins of condensates with formaldehyde such as alkylated phenols and cresols; adducts of urea, melamine, benzoguanamine and the like with formaldehyde, these adducts and alcohols having 1 to 6 carbon atoms An amino resin such as an alkyl ether compound comprising: a polyfunctional epoxy compound; a polyfunctional isocyanate compound; a blocked isocyanate compound; a polyfunctional aziridine compound; an oxazoline compound, and the like. 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 above isocyanate compound and 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; sodium bisulfite, and the like.

(2-4) Addition of other functionality In the adhesion improving layer and the antistatic layer, a surfactant, slipperiness and blocking property used for improving the leveling property within a range not impairing the effects of the present invention. Additives such as inorganic or organic particles that improve handling properties, waxes that control slipperiness and surface energy, and the like can be included. Further, in order to improve the blocking property of the antistatic layer, a polyolefin resin or a fluorine resin may be blended. These additives are contained in the coating solution.

(2-5) Method for Forming Coating Layer (Adhesion Improvement Layer, Antistatic Layer) In the present invention, the adhesion improvement layer is a coating solution containing an adhesion modifying resin, a solvent, and other additives as required. The antistatic agent layer is a coating solution containing a binder resin, an antistatic agent, a solvent, and other additives as required, and coated on one side of the surface of the plastic film, dried, and optionally heat treated. It is formed by doing.

  In particular, the plastic film has a laminated structure having B / A or B / A / B as a unit, and the B layer is a polyester layer containing a polyester resin and particles, and does not substantially contain a cavity. In the case of a void-containing laminated polyester film in which the layer is a void-containing polyester layer made of a composition in which a polyester resin and a thermoplastic resin incompatible with the polyester resin are mixed, the adhesion improving layer is the side on which the rewrite printing layer is laminated Preferably, the antistatic layer is formed on the other surface.

  The coating solution is preferably an aqueous solution or an aqueous dispersion because an organic solvent that causes a problem with the environment is not used. The solid content concentration in the coating solution is usually 1% by mass to 50% by mass, preferably 3% by mass to 30% by mass.

  Examples of the method for applying this coating solution to a plastic film include reverse roll coating, gravure coating, kiss coating, roll brushing, spray coating, air knife coating, wire barber coating, and pipe doctor method. , Impregnation / coating method, curtain coating method and the like, and these methods can be carried out alone or in combination.

  In the present invention, the formation of the antistatic layer on the plastic film is preferably carried out by a so-called in-line coating method which is carried out in the plastic film production process. That is, it may be carried out by a method in which the above-mentioned coating solution is applied to an unstretched or uniaxially stretched plastic film, dried, further uniaxially stretched or biaxially stretched, and then heat-set.

  When the above-mentioned polyester-based graft polymer is used as the adhesion-modifying resin used for the adhesion-improving layer or the binder resin of the antistatic layer, when the coating layer is formed by the in-line coating method, the drying temperature is 70 to 140 ° C. Preferably, the drying time is adjusted according to the solid content concentration and the coating amount of the coating solution, but the product of temperature (° C.) and time (seconds) 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.

  Moreover, after extending | stretching a coating layer, in the state which fixed the film so that film width length may not change, it is bridge | crosslinking by heat-processing a coating layer with an infrared heater at 250-260 degreeC for 0.5 to 1 second for a short time. It is preferable for promoting the 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 surface of the coating layer 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 finally obtained coating layer (solid content mass per unit film area) is preferably 0.01 to 0.50 g / m ² , more preferably 0.02 to 0.40 g / m 2. 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 , adhesion and durability tend to be insufficient. On the other hand, 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.

(3) Rewrite recording medium The rewrite recording medium includes a base film and a rewrite printing layer laminated on one side of the base film. Further, in practice, the rewritable recording medium is often used in a configuration in which a protective layer is provided on the surface of the rewritable print layer and an adhesive layer is provided on the uppermost layer.

  As the leuco dye, the reversible developer, and the binder resin constituting the rewritable printing layer of the rewritable recording medium, known commercially available products can be used. Further, as a means for recording / erasing the rewritable recording medium in a non-contact manner, a laser having a specific wavelength such as a semiconductor laser, a carbon dioxide gas laser, or a YAG laser, a lamp having a width in wavelength, or the like can be used.

  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 (manufactured by Kosaka Laboratory, SE-3AK), 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. The film was measured in the longitudinal direction of the film with a cut-off value of 0.25 mm, measured over a measurement length of 1 mm, and divided into 500 points at a pitch of 2 μm. 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 Δ: 21 to 50 pieces / 100 pieces ×: 51 to 100 pieces / 100 pieces (9) Surface resistivity value After leaving the film in an atmosphere of 23 ° C. and 65% RH for 24 hours Then, the surface resistivity value (Ω / □) of the surface of the antistatic agent layer was measured at an applied voltage of 500 V using a surface resistance measuring device (manufactured by Mitsubishi Oil Chemical Co., Ltd., Hiresta IP).

(10) Transparency A film for rewrite recording medium was brought into close contact with the NBS 1963A resolving power target, and was visually observed under a fluorescent lamp from the rewrite recording medium film side, and judged according to the following criteria.
○: A pattern with a spatial frequency of 1 / mm can be visually recognized, and the spatial pattern can be identified. X: A pattern with a spatial frequency of 1 / mm cannot be visually recognized.

(11) Infrared absorption analysis method The film to be measured is sampled to about 2 cm × 2 cm, the measurement target surface is brought into close contact with the ATR crystal and set in an IR measuring apparatus, and the IR spectrum is measured by the following method. The baseline was a line connecting the hems on both sides of each maximum absorption peak.
Apparatus: FT-IR FTS-60A / 896 (manufactured by Varian Technologies Japan Limited)
Single reflection ATR attachment: silver gate (manufactured by SPECAC)
ATR crystal: Ge
Incident angle: 45 °
Resolution: 4cm ^-1
Integration count: 128 times

The absorbance ratio T1 (= B / A) of the absorbance B having an absorption maximum at 1781 ± 10 cm ⁻¹ and the absorbance A having an absorption maximum at 1341 ± 10 cm ⁻¹ was determined. Here, the absorption having an absorption maximum at 1781 ± 10 cm ⁻¹ is attributed to an acid anhydride residue, and the absorption having an absorption maximum at 1341 ± 10 cm ⁻¹ is attributed to an ethylene glycol residue.

(12) Occupied area ratio of surface-deposited particles by heat treatment (a) Heat treatment A small piece is cut out from any 5 points of the film to be measured, the end is gripped with a snake eye clip and heated in hot air at 170 ° C. for 20 minutes. did. At this time, the film was held so as not to come into contact with other films and instruments, and handled so as not to cause scratches. After heating, it was taken out to room temperature and sufficiently cooled naturally, and then the following observation was performed.

(B) Ratio of Occupied Area of Precipitated Particles on Film Surface First, dust and the like were carefully removed from a film piece to be measured by a static elimination blower. This surface was measured with a non-contact type three-dimensional shape measuring device (manufactured by Micromap; Micromap 557). The optical system used was a mirro-type two-beam interference objective lens (50 ×) and a zoom lens (Body Tube, 0.5 ×), and received light with a 2/3 inch CCD camera using a light source of 5600 Å. The measurement was performed in the WAVE mode, and a field of view of 245 μm square was processed as a digital image of 480 pixels. For analysis of the image, surface shape data was obtained by using an analysis software (Micromap 123, version 4.0) and performing detrending in the quartic function mode. Particle analysis was performed from the shape data using analysis software (SX-Viewer, version 3.4.2). After performing planar correction and interpolation using the correction function of the software, protrusions having a longest diameter of 0.01 to 2000 μm and a height of 0.1 μm to 1000 μm were analyzed. As projection analysis parameters, a binarization threshold value 0.01, a rebinarization threshold value 50, and a block size 4 were given, and the projections were binarized and extracted. The area occupied by the protrusions was determined from the obtained analysis results, and the ratio of the area occupied by the protrusions and the area of the visual field (6.0 × 10 ⁴ μm ² ) increased before and after the heat treatment was defined as the occupied area ratio. The measurement was performed on five pieces of film, each at any three locations avoiding clear scratches and foreign matters, and the average value in a total of 15 fields was obtained and used.

(13) Color development 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.

(14) 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.

(15) Fineness of rewrite print image The shape of the dot 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

(16) Sharpness of rewrite print image The print image developed by the above method was visually observed and judged.
◯: Good sharpness ×: Poor sharpness

(17) Adhesiveness of rewritable printing layer A cross cut of grids at intervals of 1 mm is put on the surface of the rewritable printing layer, and adhesive tape (Nichiban Co., Ltd.) is formed so that the area of 24 mm width × 40 mm length is centered on the crosscut portion Manufactured by CT405AP-24), a load of 1 kg / cm ² was applied to the affixed portion for 10 seconds, and then the cellophane tape was peeled off to the cellophane tape side when the cellophane tape was peeled off in the vertical direction of the film. The number for each area 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

(18) Durability and stability of rewrite printing characteristics Color development and color erasure were determined by visual observation when color development and color erasure were repeated 200 times by the above method.
◯: When the characteristics do not change due to repetition with respect to the first color development or decoloring property, or the change is slight X: The characteristics clearly change with repetition for the first color development or decoloration Case

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

[Preparation of coating solution for forming an adhesion improving layer for a rewrite printing layer]
Copolymerized polyester resin (Toyobo Co., Ltd., Vylonal MD1100) / block type isocyanate group-containing resin (Daiichi Kogyo Seiyaku Co., Ltd., Elastron) in a mixed solvent of water / isopropyl alcohol (= 60/40; mass%) BN11) / organic particles (manufactured by Nippon Shokubai Co., Ltd., poster S12: average particle size 1.2 μm) / fluorine-based surfactant (manufactured by Dainippon Ink Co., Ltd., F1405) in solid content of 3.5 / 6.5 / It added under stirring so that it might become 10.0 / 0.07 (mass%), and the aqueous dispersion was prepared. In the preparation of the coating solution, the temperature was controlled at 20 ° C. or higher and 30 ° C. or lower from the viscosity and the sedimentation rate of the particles. By this temperature control, it was possible to stably prepare an aqueous dispersion and to reduce entrainment (bubble generation amount) of bubbles.

[Preparation of coating solution for forming antistatic layer]
40 parts by mass of the aqueous dispersion prepared by the above method, 4.3 parts by mass of polystyrene sulfonate ammonium salt (manufactured by NSC Japan, molecular weight 70,000), 24 parts by mass of water and 36 parts by mass of isopropyl alcohol, Colloidal silica particles (Nissan Chemical Industry Co., Ltd., Snow Chemical Co., Ltd.) mixed with each other and further dispersed with 10% by weight aqueous solution of an anionic surfactant, 0.6 parts by weight, 1 part by weight of propionic acid, and homogenizer in ion-exchanged water. Tex OL, mean particle size 40 nm) (particle a) 20% by weight aqueous dispersion of 1.8 parts by mass, dry-process silica particles dispersed by ionizing water with a homogenizer (Nippon Aerosil Co., Ltd., Aerosil OX50, average) 1.1 parts by mass of a 4% by mass aqueous dispersion of an aggregated particle size of 200 nm and an average primary particle size of 40 nm (particle b) was added and coated. And the. The mass ratio of the particles a and the particles b is 8, and the content of the particles b is 0.42% by mass with respect to the resin composition of the antistatic layer.

[Manufacture of base film for rewrite recording medium]
A mixture composed of 7% by mass of the above-mentioned void forming agent-containing master pellets (A) 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. In addition, a PET resin having an intrinsic viscosity of 1000 ppm containing an amorphous silica particle having an average particle diameter of 2 μm and having an intrinsic viscosity of 0.62 dl / g was supplied to two extruders so as to be laminated on both surfaces of the intermediate layer, and the surface layer / intermediate It joined with the feed block so that the thickness ratio of layer / surface layer might be 8/84/8. Subsequently, it was extruded from a die onto a rotary cooling roll adjusted to 20 ° C. to produce a three-layer unstretched film having a thickness of 1.6 mm. At the time of extrusion, the raw material resin was vacuum dried in advance and then supplied to the extruder.

In addition, the polyester resin used for the surface layer used the polyester resin by which the low oligomerization process was carried out with the following method.
That is, PET was dried at 160 ° C. under reduced pressure, and then nitrogen gas containing 400 ppm of ethylene glycol was circulated at 40 liters per 1 kg of crude PET at a rate of 1.2 kg / cm ^2. And subjected to a heat treatment at 215 ° C. for 20 hours to perform a low oligomerization treatment. The obtained PET had an intrinsic viscosity of 0.612 dl / g and a cyclic trimer content of 3,400 ppm. The amount of cyclic trimer in PET before the oligomerization was 9,600 ppm. The PET used for the intermediate layer was not subjected to a low oligomerization treatment. The amount of cyclic trimer in this PET was 9,600 ppm. 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.

The coating solution for forming an adhesion improving layer and the coating solution for forming an antistatic layer are each finely filtered with a felt type polypropylene filter medium having a particle size of 10 μm (initial filtration efficiency of 95%), and the above-mentioned cavity is formed by a reverse roll method. Each of the containing uniaxially stretched PET films was coated on one side and the other side and dried. The coating amount after drying was 0.1 g / m ² on both sides.

  Subsequently, the end 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. In addition, the film is heated at 250 ° C. for 0.6 seconds with an infrared heater in a state where the width of the film is fixed, and an adhesion improving layer for improving adhesion to the rewritable printing layer is provided on one side, and an antistatic layer is provided on the other side. A void-containing biaxially stretched polyester film having a thickness of 188 μm was produced as a base film for a rewritable recording medium. Table 1 shows the characteristic values of the obtained base film for a rewritable recording medium.

[Manufacture of rewrite recording media]
20 parts by mass of 3-di-n-butylamino-6-methyl-7-anilinofluorane as the leuco dye and N- [3- (p-hydroxyphenyl) propiono] -N′-n as the reversible developer -100 parts by weight of octadecanohydrazide and 80 parts by weight of polyvinyl butyral (BX-1) as a binder resin were ground and dissolved in a ball mill for 24 hours so as to be a 10% by weight methyl ethyl ketone solution, A coating solution for a rewritable printing layer was prepared.

The rewritable coating layer coating solution is applied to the surface of the adhesion improving layer of the rewritable recording medium base film so that the thickness after drying is 3 μm by the wire bar method, and dried at 80 ° C. for 2 minutes. A rewritable recording medium in which a printing layer was laminated was obtained.
Rewrite printing characteristics of the obtained rewritable recording medium, adhesion between the rewritable printing layer and the substrate film for the rewritable recording medium, durability stability when the coloring and erasing are repeated in the rewritable printing layer (simply durability of the rewritable printing characteristics) (Sometimes abbreviated as stability). The results are shown in Table 1.

  The base film for rewritable recording medium and the rewritable recording medium obtained in Example 1 were excellent in all characteristics and high quality.

  The base film for rewritable recording medium obtained in Example 1 and the rewritable recording medium manufactured using the same were excellent in all characteristics and high quality.

Example 2
In Example 1, Example 2 was carried out in the same manner as in Example 1 except that the compounding amounts of the void forming agent-containing master pellet (ii) and the PET resin in the intermediate layer were changed to 9% by mass and 84% by mass, respectively. 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 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, a PET resin 88 having 5% by mass of hollow glass beads having an average particle diameter of 5 μm (prepared by classifying commercially available glass beads) and an intrinsic viscosity of 0.62 dl / g A base film for rewrite recording medium and a rewrite 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 a mixture consisting of mass%. 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.

Example 4
In Example 1, the coating solution for forming the adhesion improving layer and the coating solution for forming the antistatic layer were each changed to the coating solution prepared by the following method, and the low oligomerization treatment of the polyester resin used for the surface layer was canceled, A base film for a rewrite recording medium and a rewrite recording medium of Example 4 were obtained in the same manner as in Example 1, except that the polyester resin having a cyclic trimer content of 9,600 ppm was used. . 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 4 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.

[Preparation of coating solution for forming an adhesion improving layer]
(Preparation of copolyester resin)
In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, 345 parts by weight of dimethyl terephthalate, 211 parts by weight of 1,4-butanediol, 270 parts by weight of ethylene glycol, and tetra-n-butyl titanate 0.5 part by mass was charged, and a transesterification reaction was performed from 160 ° C. to 220 ° C. over 4 hours. Next, 14 parts by mass of fumaric acid and 160 parts by mass of sebacic acid were added, and the temperature was raised from 200 ° C. to 220 ° C. over 1 hour to carry out an esterification reaction. Next, the temperature was raised to 255 ° C., the pressure of the reaction system was gradually reduced, and the mixture was reacted for 1 hour 30 minutes under a reduced pressure of 29.3 Pa to obtain a copolyester. The obtained copolyester was light yellow and transparent and had a weight average molecular weight of 20,000. Moreover, the ratio of the aromatic component by NMR analysis was 70 mol%.

(Preparation of water-dispersible graft resin)
A reactor equipped with a stirrer, a thermometer, a reflux device and a quantitative dropping device was charged with 75 parts by mass of copolyester, 56 parts by mass of methyl ethyl ketone and 19 parts by mass of isopropyl alcohol, and heated and stirred at 65 ° C. to dissolve the resin. . After the resin was completely dissolved, 15 parts by weight of maleic anhydride was added to the polyester solution.
Next, a solution prepared by dissolving 10 parts by mass of styrene and 1.5 parts by mass of azobisdimethylvaleronitrile in 12 parts by mass of methyl ethyl ketone was dropped into the polyester solution at 0.1 ml / min, and stirring was further continued for 2 hours. After sampling for analysis from the reaction solution, 5 parts by mass of methanol was added. Next, 300 parts by mass of water and 15 parts by mass of triethylamine were added to the reaction solution and stirred for 1 hour. Thereafter, the reactor internal temperature was raised to 100 ° C., and methyl ethyl ketone, isopropyl alcohol and excess triethylamine were distilled off to obtain a water-dispersible graft resin. This water-dispersible graft resin) was light yellow and transparent. The acid value of this resin was 1,400 eq / t.

(Coating solution adjustment)
40 parts by mass of a 25% by mass aqueous dispersion of the above water-dispersible graft resin, 24 parts by mass of water and 36 parts by mass of isopropyl alcohol were mixed, and a 10% by mass aqueous solution of 10% by mass of an anionic surfactant was added. 6 parts by mass, 1 part by mass of propionic acid, 20% by mass dispersion of colloidal silica particles (Nissan Chemical Industry Co., Ltd., Snowtex OL, average particle size 40 nm) (particles a) dispersed with a homogenizer in ion-exchanged water 4 parts by mass of a dry-process silica particle (Nippon Aerosil Co., Ltd., Aerosil OX50, average agglomerated particle size 200 nm, average primary particle size 40 nm) (particle b) obtained by dispersing 1.8 parts by mass of the liquid in ion-exchanged water using a homogenizer 1.1 parts by mass of a% aqueous dispersion was added to obtain a coating solution. The mass ratio of the particles a and the particles b is 8, and the content of the particles b is 0.42% by mass with respect to the resin composition of the coating layer.

[Preparation of coating solution for forming antistatic layer]
40 parts by weight of a 25% by weight aqueous dispersion of the water-dispersible graft resin, 4.3 parts by weight of polystyrene sulfonate ammonium salt (manufactured by NSC Japan, molecular weight 70,000), 24 parts by weight of water and isopropyl alcohol 36 parts by mass of each, and further colloidal silica particles (Nissan Chemical Co., Ltd.) dispersed by a homogenizer in ion-exchanged water and 0.6 parts by mass of a 10% by mass aqueous solution of an anionic surfactant and 1 part by mass of propionic acid. Dry silica particles (manufactured by Nippon Aerosil Co., Ltd.) obtained by dispersing a 20 mass% aqueous dispersion of Snowtex OL, average particle size 40 nm (particle a), manufactured by Kogyo Co., Ltd., with 1.8 parts by mass of homogenizer in ion-exchanged water. (Aerosil OX50, average aggregate particle size 200 nm, average primary particle size 40 nm) (particle b) Parts was added, and the coating solution. The mass ratio of the particles a and the particles b is 8, and the content of the particles b is 0.42% by mass with respect to the resin composition of the coating layer.

Comparative Example 1
In Example 1, the base film for a 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 an intermediate layer was stopped. A rewrite recording medium was obtained. Table 2 shows the characteristics 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, the raw material used for the intermediate layer is the same as that of Example 1 except that 7% by mass of the titanium oxide-containing master pellet (B) prepared by the following method is added. The base film for rewrite recording media and the rewrite recording medium of Comparative Example 2 were obtained. Table 2 shows the characteristics of the obtained base film for a rewrite recording medium and the rewrite recording medium.

[Preparation of titanium oxide-containing master pellets (b)]
As one of the raw materials for the intermediate layer, anatase type titanium dioxide (TA-300, manufactured by Fuji Titanium Co., Ltd.) having an average viscosity of 49.5% by mass of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g and an average particle size of 0.3 μm (electron microscopic method). ) A mixture of 50% by mass and 0.5% by mass of optical brightener (manufactured by Eastman Chemical Co., OB-1) was supplied to a vented twin-screw extruder and pre-kneaded, and then the molten polymer was continuously used. Then, the mixture was supplied to a vent type single-screw kneader and kneaded to prepare titanium oxide-containing master pellets (b).

  The base film for rewritable recording medium obtained in Comparative Example 2 was inferior in transparency to the base film for rewritable recording medium obtained in Example 1.

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 2 shows the properties 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. Moreover, transparency was also inferior. Further, the antistatic property was inferior, and the surface cleavage resistance of the film surface on the side where the rewritable printing layer was laminated was slightly inferior. Furthermore, the suppression of precipitation of low molecular weight components in the polyester on the film surface was insufficient.

Comparative Example 4
In Example 1, Comparative Example 4 was carried out in the same manner as in Example 1, except that the blending amounts of the void forming agent-containing master pellets (A) and the PET resin in the intermediate layer were changed to 15% by mass and 78% by mass, respectively. A base film for a rewrite recording medium and a rewrite recording medium were obtained. Table 2 shows the characteristics of the obtained base film for a rewrite recording medium and the rewrite recording medium.

  The rewritable recording medium base film obtained in Comparative Example 4 has a lower apparent density and a higher cavity content than the rewritable recording medium base 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, when forming the void-containing polyester film, the same method as in Example 1 except that only the intermediate layer A is formed as a single layer without laminating the surface layer B that does not substantially contain voids. By the method, the base film for rewrite recording medium and the rewrite recording medium of Comparative Example 5 were obtained. Table 2 shows the characteristics 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 has a surface forming layer laminated in addition to the deterioration of the quality of the base film for rewritable recording medium obtained in Comparative Example 2. Therefore, the surface cleavage resistance of the film surface on the side where the rewritable printing layer was laminated was inferior. Furthermore, the suppression of precipitation of low molecular weight components in the polyester on the film surface was insufficient.

Comparative Example 6
In Comparative Example 2, the polyester resin used in the surface layer was the same as Comparative Example 2 except that a polyester resin having a cyclic trimer amount of 9,600 ppm before the oligomerization was used. A base film for a rewrite recording medium and a rewrite recording medium were obtained. Table 2 shows the characteristics 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 6 has a low quality in the polyester on the film surface in addition to the deterioration of the quality of the base film for rewritable recording medium obtained in Comparative Example 2. Suppression of precipitation of molecular weight components was also insufficient.

Comparative Example 7
In Comparative Example 2, the base film for rewrite recording medium and the rewrite recording medium of Comparative Example 7 were obtained in the same manner as in Comparative Example 2, except that the adhesion improving layer was not formed during film formation. Table 2 shows the characteristics 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 7 is not only deteriorated in the quality of the base film for rewritable recording medium obtained in Comparative Example 2, but also has good adhesion to the rewritable printing layer. It was inferior.

Comparative Example 8
In the method of Comparative Example 2, the base film for rewrite recording medium and the rewrite recording medium of Comparative Example 8 were obtained in the same manner as in Comparative Example 2, except that the antistatic layer was not formed during film formation. Table 2 shows the characteristics 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 8 was inferior in antistatic property in addition to the quality deterioration of the base film for rewritable recording medium obtained in Comparative Example 2. .

Comparative Example 9
In the method of Comparative Example 2, the base film for a rewritable recording medium of Comparative Example 9 was prepared in the same manner as in Comparative Example 2 except that neither the adhesion improving layer nor the antistatic layer was formed during film formation. A rewrite recording medium was obtained. Table 2 shows the characteristics 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 9 is not only the quality deterioration of the base film for rewritable recording medium obtained in Comparative Example 2, but also the adhesion to the rewritable printing layer and The antistatic property was inferior.

Comparative Example 10
In Comparative Example 6, a biaxially stretched polyester film was obtained in the same manner as in Comparative Example 6, except that the adhesion improving layer and the antistatic layer were not formed during film formation. Next, the biaxially stretched polyester film is coated with the coating solution for forming the adhesion improving layer and the antistatic layer used in Example 4 and dried. An antistatic layer was formed. Except for these, a rewrite recording medium substrate film and a rewrite recording medium of Comparative Example 10 were obtained in the same manner as in Comparative Example 6. Table 2 shows the characteristics 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 10 is inferior in quality of the rewritable recording medium base film obtained in Comparative Example 6 and has poor adhesion to the rewritable printing layer. It was. In addition, the low molecular weight component in the polyester expressed in Example 4 had little effect of suppressing precipitation on the surface of the rewrite printing layer adhesion improving layer and the antistatic layer, and the occupied area ratio of particles deposited on both surfaces was high. . Note that, on the surface of the adhesion improving layer and the antistatic layer of the base film for rewritable recording medium obtained in Comparative Example 10, the absorbance ratio T1 evaluated by infrared absorption analysis was as small as 0.03, and the acid anhydride The concentration of the product was low.

  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 base film for rewritable recording medium of the present invention, when used as the base material of the rewritable recording medium, is excellent in color development and decoloring by heat energy, and has a good balance between them, and further has excellent transparency. For example, rewritable display information can be viewed from both the front and back sides of the rewritable recording medium. Moreover, the visibility of the display information which can be rewritten can be improved by laminating | stacking metallic luster materials, such as a white film and an aluminum vapor deposition film. Moreover, the design etc. of a rewrite recording medium can be improved by laminating | printing printed matter. Therefore, for example, by using the rewritable recording medium of the present invention as a material for the various cards described above, it is possible to increase the degree of freedom of expression regarding the design and information displayed on the card. Further, since the sense of cleanliness can be improved by the transparency, it can be suitably used as a card material used in the industry where the corporate image and the brand image are emphasized. Further, when used as a material for the card, rewritable display information can be viewed from both the front and back sides of the card, so that the convenience of the card user can be improved. Therefore, since the base film for rewrite recording medium of the present invention has such advantages, it can be suitably used as a support for the rewrite 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 (9)

  A substrate film for a rewritable recording medium used for a rewritable recording medium in which a rewritable printing layer is laminated on one side of a substrate film, wherein the substrate film has a light transmittance of more than 15% and a thermal conductivity of 0. A base film for a rewritable recording medium, comprising a plastic film having a thickness of 0.037 to 0.080 W / mK. The base film for a rewritable recording medium according to claim 1, wherein the plastic film is a void-containing polyester film having an apparent density of 0.91 to 1.2 g / cm ³ .   The void-containing polyester film has a laminated structure in units of B / A or B / A / B. The B layer is a polyester layer containing a polyester resin and particles, and a rewritable printing layer is laminated when used as a rewritable recording medium. 3. The rewritable recording medium according to claim 2, wherein the layer A is a void-containing polyester layer comprising a composition in which a polyester resin and a thermoplastic resin incompatible with the polyester resin are mixed. Base film.   The rewrite recording according to claim 3, wherein the B layer is a layer that does not substantially contain a cavity therein, and has a three-dimensional center plane average surface roughness (SRa) of 0.07 to 0.30 μm. Base film for media.   5. A coating layer made of an adhesion modifying resin for improving adhesion to the rewritable printing layer is formed on the surface of the plastic film on which the rewritable printing layer is laminated. The base film for rewritable recording media according to any one of the above.   The adhesion modifying resin is a polyester graft copolymer obtained by graft polymerization of a polymerizable unsaturated monomer containing at least one carboxyl group residue on a polyester resin containing at least one ethylene glycol residue on at least one side. The substrate film for a rewritable recording medium according to claim 1, wherein the substrate film is a rewritable recording medium. An antistatic layer composed of an antistatic agent and a binder resin is formed on the surface of the plastic film opposite to the side on which the rewritable printing layer is laminated, and the surface resistivity (25 ° C., 65% RH) of the antistatic layer is formed. The substrate film for a rewrite recording medium according to any one of claims 1 to 6, wherein the value is 1 × 10 ¹³ Ω / □ or less. The plastic film when heated at 170 ° C. 20 min, claim 1 occupied area ratio of particles deposited on the surface of the side to be laminated at least rewrite the print layer is characterized in that at 0.008μm ^{2 /} μm 2 or less The base film for rewrite recording media in any one of -7.   A rewritable recording medium obtained by laminating a rewritable printing layer on the rewritable recording medium substrate film according to claim 1.

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