JP2007069441A - Substrate film for rewrite recording medium and rewrite recording medium using the film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate film for a rewrite recording medium which is superior in color developing properties by a thermal energy of the rewrite recording medium and discoloring properties, has a good balance in both properties, and is excellent in fine precise nature and clarity of a color-developed printed image when it is used as the substrate for the rewrite recording medium. <P>SOLUTION: The substrate film for the rewrite recording medium comprises a plastic film characterized by a light transmission of ≤15% and a thermal conductivity of 0.037-0.080 W/mK. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a base film for a rewrite recording medium capable of forming and erasing an image by controlling thermal energy, and a rewrite recording medium using the same. More specifically, the rewrite recording medium is excellent in color development and decoloration by thermal energy, and has a good balance between the two, and has excellent visibility of the printed color and the like. The present invention relates to a rewritable recording medium.

  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 the base material of 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. In the case of using in a thermal printer or word processor that has a thermal head that is widely used, 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 including an air layer, for example, between a substrate and a heat-sensitive color developing layer There has been disclosed a method of imparting heat insulation to a heat-sensitive recording medium and improving heat-sensitive color development using a means for forming (see, for example, 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 heat-sensitive 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.

  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 base film for a rewritable recording medium which has a good balance and is excellent in the fineness and sharpness of a color printed image.

  The base film for a rewritable recording medium of the present invention capable of solving the above problems is characterized in that the light transmittance is less than 15% and the thermal conductivity is 0.037 to 0.080 W / mK. A base film for a rewritable recording medium, characterized by comprising a plastic film.

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

  The upper limit of the thermal conductivity of the base film for a rewritable recording medium of the present invention is more preferably 0.077 W / mK, and further preferably 0.074 W / mK. On the other hand, the lower limit is more preferably 0.039 W / mK and even more preferably 0.041 W / mK. When the thermal conductivity of the film satisfies the above range, 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 0.8 W / mK, the heat insulating property is insufficient, so that the loss of heat energy given for coloring and decoloring of the dye contained in the printing layer becomes large. In addition, due to insufficient heat insulation, it is necessary to increase energy such as when the color developability and decolorability are lowered, or when the temperature of the print head is increased to give a certain color developability and decolorization. Therefore, it is not preferable.

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

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

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

  Moreover, it is preferable that the said plastic film consists of laminated structures, and a cavity is not contained substantially in the outermost layer of at least one side. Furthermore, it is preferable that the three-dimensional center plane average surface roughness (SRa) on the surface of the layer of the plastic film substantially free of voids is 0.07 to 0.30 μm.

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

  The rewritable recording medium of the present invention uses a base film for a rewritable recording medium in which the plastic film has a laminated structure, and at least the outermost layer on one side does not substantially contain cavities. This is a rewritable recording medium in which a rewritable printing layer is laminated on the surface side of a layer that is not contained.

  The base film for rewritable recording medium of the present invention is specified for the thermal conductivity of the film. Therefore, when used as the base material of the rewritable recording medium, it has excellent color developability and decoloring property due to thermal energy, and There is a balance between the two. In addition, since the base film for a rewritable recording medium of the present invention is excellent in light shielding properties, it is excellent in the sharpness of a printed image.

  Further, the base film for rewritable recording medium of the present invention has an appropriate cushioning property because the void-containing layer is formed and the apparent density of the film is specified. For example, a thermal head When printing is performed by this method, there is an advantage that the fineness of printing is improved.

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

  Furthermore, as described above, since the coloring and decoloring properties by heat energy are excellent and the balance between the two is taken, there is no need to interpose a fine air layer for imparting heat insulation to the printing 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, it is unnecessary for the heat treatment layer lamination and the calender treatment for improving the surface roughness caused by the heat insulation layer, which is necessary in a conventionally known method, and it is advantageous in terms of economy. It has many advantages as a film and can be suitably used for a rewrite recording medium.

  The base film for a rewritable recording medium of the present invention is composed of a plastic film having a light transmittance of less than 15% and a thermal conductivity of 0.037 to 0.080 W / mK.

  The material of the base film for a rewritable recording medium of the present invention is not limited. For example, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyolefin resins such as polypropylene, polyethylene and cyclic polyolefin, cellulose derivative resins such as cellulose triacetate, styrene resins such as syndiotactic polystyrene, and engineering plastics such as polyphenylene sulfide and polyimide. Based resins and the like. Among these, the use of a polyester resin is preferable.

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

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

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

  The method for setting the light transmittance to 13% or less is not limited, but it is preferable to add a pigment having a concealing property to the resin constituting the film. In the present invention, the purpose of reducing the light transmittance is to improve the sharpness of a printed image. Therefore, it is preferable to impart white light shielding properties. Therefore, the substrate film for a rewritable recording medium of the present invention preferably has a whiteness measured in accordance with JIS Z-8722 of 75 or more, more preferably 80 or more. In order to set the whiteness of the film to 75 or more, it is preferable to contain white pigments such as titanium oxide, calcium carbonate, zinc oxide, or barium sulfate, polymer beads blended with these, and the like in the film. A method using a fluorescent whitening agent in combination is also effective.

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

  Moreover, although the method to make the thermal conductivity of the film of this invention 0.037-0.080 W / mK is not limited, The method of making the film contain a cavity and utilizing the heat insulation effect of the air contained in the cavity Is a preferred embodiment.

  As a method for containing a cavity, (1) a method in which a foaming agent is contained and foamed by heat at the time of extrusion or film formation, or foamed by chemical decomposition, (2) a gas such as carbon dioxide gas at the time of extrusion or after extrusion, or A method in which a vaporizable substance is added and foamed; (3) a method in which hollow fine particles are blended; and (4) a thermoplastic resin B incompatible with the thermoplastic resin A in the thermoplastic resin A constituting the film. (5) A method of stretching uniaxially or biaxially after melt extrusion, (5) A method of incorporating organic or inorganic fine particles into the thermoplastic resin A, and stretching uniaxially or biaxially after melt extrusion Can be mentioned. Moreover, you may implement combining these methods.

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

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

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

  In the present invention, in the case of using a method of adding heat insulation by incorporating cavities in the film, the film is made into a laminated structure, and substantially no cavities are contained on the surface of the void-containing layer. It is preferable to laminate the layers. By adopting this laminated structure, it is possible to suppress the cleavage of the film surface due to the destruction of the interface of the cavity. That is, it is preferable that the resin composition constituting the surface layer (hereinafter referred to as the surface forming layer) is stopped from blending the foaming agent and the cavity forming agent as described above. It is a preferable embodiment that an additive for concealing is added to the surface forming layer from the viewpoint of concealing and controlling the surface roughness described later.

  2-30 micrometers is preferable and, as for the thickness of the said surface formation layer, 3-25 micrometers is more preferable. When the thickness of the surface forming 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 the surface forming layer exceeds 30 μm, it is disadvantageous in terms of imparting heat insulation. In addition, it is preferable that the thickness of the said surface formation layer shall be 5-25% with respect to the film total thickness.

  In the case where the rewritable printing layer is laminated only on one side of the base film, the above-mentioned surface forming layer may be laminated on only one side in order to achieve the object of the present invention. In addition, it is a more preferable embodiment to laminate | stack this surface formation layer on both surfaces of a film from the point which suppresses the curling of a laminated | multilayer film.

  The method for laminating the surface forming layer is not limited. For example, the surface forming layer and the cavity-containing film layer may be formed by individually bonding two films obtained with an adhesive or the like, or the surface-forming layer and the cavity-containing film layer may be laminated by a coextrusion method. You may use the method of extending | stretching the heat-treated film at least to one direction, and heat-processing. The latter method is more economical and is a preferred embodiment.

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

  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 (A) and the other surface layer (B) of the laminated polyester film the same.

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

  The rewritable recording medium of the present invention has a structure in which a rewritable printing layer is laminated on the surface forming layer (a layer in which no void is substantially contained in the film).

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

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

  The type of dye or binder resin that constitutes the rewrite printing layer of the rewrite recording medium is not limited. What is necessary is just to select and determine suitably according to the performance and market demand of a rewrite recording medium.

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

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

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

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

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

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

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

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

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

(9) Color developability of rewrite printing layer The rewrite 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.

(10) 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.

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

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

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

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

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

  The obtained unstretched film is uniformly heated to 65 ° C. using a heating roll, and 3.4 between two pairs of nip rolls (low speed roll: 1 m / min, high speed roll: 3.4 m / min) having different peripheral speeds. Stretched 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. Subsequently, the edge of the film was gripped with a clip, guided to a hot air zone heated to 130 ° C. and dried, and then stretched 4.0 times in the width direction. Subsequently, the film was heated with an infrared heater at 250 ° C. for 0.6 seconds with the film width fixed, to obtain a base film for a rewritable recording medium having a thickness of 188 μm. Table 1 shows the characteristic values of the obtained base film for a rewritable recording medium. In addition, the whiteness of the obtained base film for rewritable recording media was 84.

[Manufacture of rewrite recording media]
20 parts 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 mass of octadecanohydrazide and 80 parts by mass of polyvinyl butyral (BX-1) manufactured by Sekisui Chemical Co., Ltd. as a binder resin are pulverized and dissolved in a ball mill for 24 hours to form a 10% by mass methyl ethyl ketone solution. A forming solution was prepared.

The printing layer solution is applied to the surface forming layer surface of the base film for rewritable recording medium so as to have a thickness of 3 μm after drying by the wire bar method, dried at 80 ° C. for 2 minutes, and the printing layer is laminated. A rewrite recording medium was obtained.
The rewrite printing characteristics of the obtained rewrite recording medium were evaluated. The results are shown in Table 1.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  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 a rewritable recording medium of the present invention is specified for the thermal conductivity of the film, and therefore has excellent color developability and decoloring property due to thermal energy when used as a base material for the rewritable recording medium, and Since both are balanced and excellent in light shielding properties, the printed image is excellent in sharpness. Therefore, since it can be suitably used as a base film for a rewritable recording medium, the contribution to the industry is great.

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 (7)

  A base film for a rewritable recording medium, comprising a plastic film having a light transmittance of 15% or less and a thermal conductivity of 0.037 to 0.08 W / mK.   The base film for a rewritable recording medium according to claim 1, wherein the plastic film includes a void-containing layer.   The base film for a rewritable recording medium according to claim 1 or 2, wherein a main component of the plastic film is a polyester resin. 4. The base film for a rewrite recording medium according to claim 3, wherein an apparent density of the plastic film is 0.91 to 1.2 g / cm < ³ >.   The base film for a rewritable recording medium according to any one of claims 1 to 4, wherein the plastic film has a laminated structure, and at least one outermost layer is substantially free of voids. .   The three-dimensional center plane average surface roughness (SRa) on the surface of the layer substantially free of voids of the plastic film is 0.07 to 0.30 μm. Base film for rewritable recording media.   A rewritable recording medium comprising a rewritable printing layer laminated on a surface side of a layer substantially free of voids of the substrate film for a rewritable recording medium according to claim 5 or 6.