JP2005238622A - White laminated polyester film for thermal transfer recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white laminated polyester film having enough whiteness and cushioning properties as a substrate of a receiving sheet for thermal transfer recording, and providing excellent printing sensitivity and folding resistance and wrinkle resistance during processing and printing. <P>SOLUTION: The laminated polyester film is provided with an inorganic particle-containing polyester layer (A) on the thermal transfer side of a polyester layer (B) with fine voids, and a polyester layer (C) on the opposite side. (1) The void of the polyester layer (B) is 15-50 volume%, and the voids of the polyester layers (A) and (C) are ≤15 volume%, and the specific gravity of the whole laminated polyester is 0.8-1.3. (2) The sum of the thickness of the polyester layer (A) and the thickness of the polyester layer (B) is ≥10% of the whole thickness, and the thickness of the polyester layer (C) is larger than the thickness of the polyester layer (A). (3) The whiteness of the polyester layer (A) side is 80-140%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a white laminated polyester film for thermal transfer recording. More specifically, the present invention relates to a thermal transfer recording sheet exhibiting sufficient whiteness and cushioning properties as a receiving sheet substrate for thermal transfer recording and having excellent crease resistance.

  As one of the recording methods in the hard copy technology, a thermal transfer recording method having features such as non-impact, easy operation and maintenance, low cost, miniaturization, and high speed has attracted attention. With this thermal transfer recording method, a transfer sheet (ink ribbon) having an ink layer, which is a colorant-containing layer, is superposed on a receiving sheet, and then transferred by melting or sublimating from the ink ribbon side according to the heating of the thermal head. The color material-containing component or the color material to be transferred is transferred onto a receiving sheet in the form of fine dots (dots) and printed. Conventionally, a receiving sheet used in such a thermal transfer recording system is based on natural paper or a thick polyolefin film, and a white polyester film containing polypropylene synthetic paper, titanium oxide, calcium carbonate or the like on the surface layer. In addition, a laminate containing a void-containing polyester film impregnated with inorganic fine particles such as barium sulfate or polyester and a resin incompatible with polyester, and having a receiving layer on the outermost layer for further enhancing the printing function is widely used. .

The reason why these plastic films are used on the printing surface side is that they have both surface smoothness and moderate cushioning, so that the head, ribbon, and substrate surface during transfer can be evenly contacted. This is because good printability that cannot be obtained is obtained.
However, when a plastic film is used as a receiving sheet base material, there is a problem that folds are likely to be formed. For example, when a seal-like printed material is peeled off from a release paper, there is a problem that the quality of the printed material is significantly impaired due to the crease. . Polypropylene-based synthetic paper has a problem that it is easy to bend and wrinkle particularly in a sublimation printing method because it is weak against heat and poor in flexibility. On the other hand, the polyester film has better heat resistance than the polypropylene film, but has high rigidity and insufficient cushioning properties. Therefore, when using a polyester film, the cushioning property is secured by containing a large number of cavities inside, but the inclusion of these cavities makes the inside of the polyester film easy to break when folded and breaks. There is a problem of wrinkles. If there are many cavities in the interior, the cushioning and heat insulation properties are excellent, so there are advantages such as higher sensitivity in the sublimation printing method, better appearance of the printed matter, and higher printing speed. By raising the value, the inside of the polyester film tends to be bent and broken, and the problem that the crease property deteriorates becomes remarkable. Thus, printability, print sensitivity, and crease resistance are contradictory, and it has been difficult to achieve both.

  On the other hand, a device that defines the size of the internal cavity (see Patent Document 1) has been proposed, but it is insufficient in terms of compatibility with printing sensitivity. In addition, a structure having a two-layer structure in which a large number of cavities of inorganic particles are formed in the image receiving layer (see Patent Document 2) has been proposed, but surface smoothness is impaired by the large number of inorganic particles. Therefore, the glossiness of the receiving sheet is inferior, a thick receiving layer is necessary to cover a rough surface, and the sensitivity is not always sufficient.

Furthermore, in recent years, performance required for printing base materials is becoming more severe in response to demands for downsizing the apparatus, processing speed, and printing speed. Against this background, white films applied to the substrate satisfy whiteness, while maintaining printing characteristics and antistatic properties (receptor sheets stick to each other due to static electricity, and dust or dust adheres to the surface of the receptor sheet. There is a strong demand to improve a wide variety of properties, such as difficult to bend) and processing suitability such as folding resistance. In particular, it is required to apply a high amount of heat to the base film in a short time against the background of speeding up and downsizing of processing and printing. However, curling occurs and the heat insulating effect is low on the base film. For this reason, there is a problem that the processing and printing cannot be performed at high speed due to creases or wrinkles, and there is a need for a thermal transfer film that can solve these problems.
JP-A-6-1871 JP 2003-48292 A

  In light of the background of the prior art, the present invention exhibits excellent whiteness and cushioning properties as a receiving sheet base material for thermal transfer recording, and has excellent printing sensitivity during processing and printing with a film alone and a receiving sheet. An object of the present invention is to provide a white laminated polyester film capable of achieving both crease resistance and crease resistance.

The present invention has been intensively studied to solve such problems, and as a result, by defining the laminated structure of the void-containing polyester film, it is possible to achieve both crease resistance and printing sensitivity at an unprecedented high level. The present inventors have found that the printing sensitivity can be increased while maintaining the crease property, and have led to the present invention. That is, the present invention provides a polyester layer (A) containing inorganic particles on the thermal transfer surface side of the polyester layer (B) containing many fine cavities, and a polyester on the opposite side of the thermal transfer surface of the polyester layer (B). The laminated polyester film provided with the layer (C) is a white laminated polyester film for thermal transfer recording characterized by satisfying the following requirements.
(1) The porosity of the polyester layer (B) is 15 to 50% by volume, the porosity of the polyester (A) layer and the (C) layer is 15% by volume or less, and the specific gravity of the entire laminated polyester is 0.8. (2) The sum of the thickness of the polyester layer (A) and the thickness of the polyester layer (B) is 10% or more of the total thickness, and the thickness of the polyester layer (B) is polyester. It is larger than the thickness of the layer (A). (3) The whiteness on the polyester layer (A) side is 80 to 140%.

  According to the present invention, it is possible to obtain a heat-sensitive transfer recording receiving sheet having both sufficient crease resistance and high printing sensitivity and excellent whiteness. Moreover, since the film of the present invention and the obtained receiving sheet exhibit excellent curl resistance during processing and printing, they are excellent in flatness after printing, processability to the receiving sheet, and handleability.

  In the white laminated polyester film of the present invention, the polyester layer (A) containing inorganic particles on the thermal transfer surface side of the polyester layer (B) containing many fine cavities is opposite to the thermal transfer surface of the polyester layer (B). The structure which provided the polyester layer (C) of the side is required. The polyester layer (B) alone has a problem of impairing the smoothness of the surface, and in production, the film is easily broken and the film formation is unstable, resulting in an increase in cost. In addition, when an incompatible resin is added to a single layer film so as to contain fine bubbles, depending on the type, the dispersed particulate incompatible resin may fall off and be produced for a long time. During film formation, a portion (drum, roll, coater, etc.) in contact with the film forming apparatus may be contaminated. Such contamination easily causes problems such as unfavorable influence on the film characteristics, and periodic cleaning as a countermeasure, resulting in a decrease in productivity and an increase in cost.

  Therefore, a layered structure of three or more layers, a polyester layer (A) containing inorganic particles as a layer that develops whiteness and smoothness or gloss, and a polyester layer (B) having a large number of fine cavities as cushioning properties, In order to satisfy all of the necessary characteristics of the entire film, such as a layer that expresses heat insulation and the like, and the polyester layer (C) is a layer that expresses crease resistance, etc. It is a success.

  The kind of polyester used for each layer of the polyester layer (A), polyester layer (B) and polyester layer (C) may be the same or different. In particular, as a combination of different polyesters, for example, when the polyester layers (A) and (C) are polyethylene naphthalate and the polyester layer (B) is polyethylene terephthalate, an effect of improving rigidity and the like can be obtained. Further, when the polyester layer (A) is a copolyester and the polyester layers (B) and (C) are homopolyesters, an effect of improving adhesion to the receiving layer or the coating layer can be obtained. The polyester layer (A) and the polyester layer (C) may have the same composition. In the case of the same composition, the polyester layer (A) and the polyester layer (C) can be melt-extruded from one extruder and separated and laminated on both sides of the polyester layer (B) in a T-die composite die. Cost is advantageous. In addition, the lamination thickness of the polyester layer (A) and the polyester layer (C) is obtained by adding a cross-sectional area difference between the respective channels of the polyester (A) layer and the polyester (C) layer in the T-die composite die. It can be set arbitrarily.

  As a method of laminating the polyester layer (A), the polyester layer (B), and the polyester (C), a method of compounding by co-extrusion during melt film formation, or a method of laminating after forming the films separately, respectively. However, the former method is more preferable in terms of cost and the like.

  In addition, when the white laminated polyester film of the present invention is used as a receiving sheet base material for thermal transfer recording, it may be used alone or may be used in combination with other materials, but the polyester layer (C) side. Is preferably used in combination with paper or a plastic film. For example, plain paper, fine paper, medium paper, coated paper, art paper, cast coated paper, resin impregnated paper, emulsion impregnated paper, latex impregnated paper, synthetic resin internal paper, glassine paper, laminate Paper such as paper, synthetic paper, non-woven fabric, or other types of film can be used.

  In the present invention, the polyester layer (B) needs to contain many fine cavities. As a method of incorporating fine bubbles in the polyester layer (B), (1) a foaming agent is incorporated into polyester, and bubbles are formed by foaming by heating during extrusion or film formation, or by foaming by chemical decomposition. Method, (2) A method of adding a gas or a vaporizable substance at the time of extrusion of a polyester, (3) A polyester resin that is incompatible with the polyester (incompatible resin) is added to the polyester, and it is uniaxial or biaxial A method of generating fine bubbles by stretching, (4) a method of adding a large amount of bubble-forming inorganic fine particles in place of the incompatible resin, and the like are preferably used. Any method may be used as long as it is within the scope of the object of the present invention, but the film-forming property, the ease of adjusting the amount of bubbles contained therein, and formation of finer and uniform size bubbles are formed. The use of the incompatible resin (3) is particularly preferably used from the comprehensive viewpoints of easiness and light weight. The incompatible resin referred to here is a thermoplastic resin other than polyester and is incompatible with the polyester. In the polyester, the resin is dispersed in the form of particles and stretched in the film. A resin having a large effect of forming bubbles in the resin is preferred. More specifically, the incompatible resin refers to a system in which polyester and the incompatible resin are melted by a known method, preferably a differential scanning calorimeter (DSC), dynamic viscoelasticity measurement or the like. When measured, it is a resin in which Tg corresponding to the incompatible resin is observed in addition to the glass transition temperature corresponding to polyester (hereinafter abbreviated as Tg).

  The melting point of such an incompatible resin is particularly preferably lower than the melting point of the polyester and higher than the temperature (heat treatment temperature) when the film is heat-fixed and oriented during film formation. From this point of view, among the incompatible resins, polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, polystyrene resins, polyacrylate resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins, and fluorine resins are preferably used. It is done. These incompatible resins may be homopolymers or copolymers, and two or more incompatible resins may be used in combination. Among these, polyolefin resins such as polypropylene and polymethylpentene having a small critical surface tension are preferable, and polymethylpentene is most preferable. Since the polymethylpentene has a relatively large difference in surface tension from the polyester and a high melting point, it has a feature that the effect of forming bubbles per added amount is large, and is particularly preferable as an incompatible resin.

The fine cavities in the present invention can contribute to imparting heat insulation and cushioning properties to the film itself to improve sensitivity, and are produced using the incompatible resin contained in the polyester as a core. Most preferably it is. Furthermore, when the cross section (thickness direction) of the polyester layer (B) is observed with a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like, the cross-sectional area of the bubble portion (however, the non-core that becomes the core of bubble generation) preferably has an average value of the compatible resin portion is excluded) is 1 to 25 m ^2, more preferably 1.5~20μm ^2, more preferably from 2 to 15 [mu] m ^2.

  The content of the incompatible resin in the polyester layer (B) is preferably 1 to 35% by weight, more preferably 2 to 25% by weight, and most preferably 3 to 15% by weight. If the addition amount is less than the above range, it is difficult to improve the whiteness and concealment of the film, and conversely, if the addition amount is more than the above range, film breakage or the like tends to occur during stretching, Productivity may be reduced.

  In addition, in the polyester layer (B) of the present invention, bubbles generated by stretching can be made finer by reducing the dispersion diameter of the incompatible resin, and as a result, the whiteness and film-forming property of the film can be improved. Therefore, it is more preferable to add a dispersant in addition to the above-described polyester and incompatible resin. Examples of the dispersant exhibiting the above-described effects include olefin polymers or copolymers having polar groups such as carboxyl groups and epoxy groups, and functional groups reactive with polyester, diethylene glycol, polyalkylene glycol, and surfactants. Thermal adhesive resin or the like can be used. Of course, these may be used alone or in combination of two or more. Such a dispersant may be used as a polyester obtained by copolymerizing a dispersant in a polymerization reaction in advance, or may be used directly as it is.

  The average dispersion diameter of the incompatible resin of the polyester layer (B) in the present invention is preferably 1 to 7 μm, more preferably 1 to 5 μm. When the average dispersion diameter of the incompatible resin exceeds 7 μm, the portion becomes a defective defect at the time of thermal transfer or the film is easily broken at the time of film formation, which is not preferable.

  The addition amount of the dispersant in the present invention is preferably 0.05 to 10% by weight, more preferably 0.1 to 7% by weight, and still more preferably 0.2 to 5% by weight. When the amount added is less than 0.05% by weight, the effect of refining the bubbles may be reduced. On the other hand, when the addition amount is more than 10% by weight, the effect of adding the incompatible resin is reduced, and problems such as a decrease in whiteness and an increase in cost are likely to occur.

  Further, in the present invention, the polyester layer (B) preferably contains 0.05 to 1.0% by weight, more preferably 0.1 to 0.5% by weight of an antioxidant, thereby further stabilizing the polymer extrusion. Thus, film formation can be performed. As the antioxidant, a hindered phenol-based antioxidant is particularly preferable from the viewpoint of dispersibility.

  The porosity of the polyester layer (B) containing fine cavities thus obtained is required to be 15 to 50% by volume. When the porosity is less than 15% by volume, sufficient cushioning properties cannot be obtained, so that transfer sensitivity is deteriorated and image uniformity is impaired. On the other hand, when the porosity is larger than 50%, problems such as deterioration of the crease resistance and the tendency to break during film formation occur. The porosity can be controlled by the type and amount of the incompatible resin and inorganic particles, the draw ratio during film formation, and the heat setting temperature. For example, the porosity can be increased by increasing the amount of incompatible resin added, increasing the draw ratio, and decreasing the heat setting temperature, and vice versa. In addition, the method based on the stretching ratio has a problem that the fracture at the time of film formation increases when the ratio is increased too much, and the heat setting temperature is too large to adjust the porosity. A preferable method is to appropriately select the amount and type of the incompatible resin or inorganic particles contained therein.

  In the present invention, the polyester layer (A) needs to contain inorganic particles in order to facilitate moderate whiteness and handleability. One kind of inorganic particles may be used, or two or more kinds may be used. For example, when the inorganic particles a that mainly adjust whiteness and the inorganic particles b that mainly adjust porosity are combined, the whiteness obtained from the (A) layer side of this patent is achieved and the printability is also improved. It is more preferable because it can be made.

  Examples of the inorganic particles contained in the polyester (A) layer include wet and dry silica, colloidal silica, calcium carbonate, aluminum silicate, calcium phosphate, alumina, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide (zinc white), and antimony oxide. , Cerium oxide, zirconium oxide, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, zinc carbonate, basic lead carbonate (lead white), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica, mica titanium, talc, Clay, kaolin, lithium fluoride, calcium fluoride, and the like can be used. In the polyester layer (A), it is preferable to use a combination of two or more kinds of inorganic particles, and a more preferable combination is a combination of titanium oxide and calcium carbonate or barium sulfate. When the porosity of the (A) layer is adjusted by the amount of calcium carbonate or barium sulfate, the desired whiteness, the porosity of the (A) layer, and the printability can be easily achieved.

  Such inorganic fine particles preferably have an average particle size in the polyester of 0.05 to 10 μm, more preferably 0.1 to 3 μm. When the average particle diameter is outside the above range, the inorganic fine particles may not be uniformly dispersed due to aggregation or the like, or the gloss or smoothness of the film surface may be deteriorated by the particles themselves.

  The total amount of inorganic particles added is preferably 20% by weight or less, and more preferably 17% by weight or less. When the addition amount is larger than the above range, not only the smoothness is extremely lowered, but also inconvenience such as film breakage may be caused at the time of stretching.

  Organic particles can also be used as the particles to be added to the layer (A). Crosslinked polymer particles, calcium oxalate, acrylic particles, imide particles and the like can be mentioned.

  Furthermore, in order to give the polyester film containing a white pigment a clearer and more bluish whiteness and to have a high-grade image, it is desirable that at least the polyester layer (A) contains a fluorescent whitening agent. . The fluorescent brightener to be contained here absorbs ultraviolet rays in sunlight or artificial light, maintains the function of radiating it into purple to blue visible light, and radiates the lightness of the polymer substance by its fluorescence action. It is a compound that promotes whiteness and blueness without lowering. Examples of fluorescent brighteners include “Ubitec” (Ciba-Geigy), “OB-1” (Eastman), “TBO” (Sumitomo Seika Co., Ltd.), and “Kaycoal” (Nippon Soda Co., Ltd.). "Kayalite" (Nippon Kayaku Co., Ltd.), "Lyukopua" EGM (Client Japan Co., Ltd.), etc. can be used. The optical brightener is not particularly limited and may be used alone or in combination of two or more in some cases. However, in the present invention, it is particularly excellent in heat resistance and has good compatibility with the above-described polyester. It is desirable to select one that can be uniformly dispersed, has little coloration, and does not adversely affect the resin.

  The content of the fluorescent brightening agent in the white polyester layer is preferably 0.005 to 1% by weight, and more preferably 0.01 to 0.5% by weight. If the content is less than the above range, it is difficult to obtain a sufficient whitening effect. If the content exceeds the above range, the uniform dispersibility decreases, the whitening effect called “density quenching” decreases, or the whiteness decreases due to coloring. It is easy to invite.

  The porosity of the polyester layer (A) and the polyester layer (C) is 15% by volume or less. When the porosity exceeds 15% by volume, the crease resistance deteriorates. With respect to the polyester layer (A), the porosity is more preferably 3 to 10% by volume. It is preferable to include a cavity in the polyester layer (A) because printability is improved.

  The porosity of the polyester layer (A) is preferably larger than the porosity of the polyester layer (C). The polyester layer (A) is on the receiving layer side and preferably contains voids in order to increase printing sensitivity. However, the polyester layer (C) is a layer responsible for curling resistance, and it is not preferred that there are voids. Thus, by controlling the porosity of the polyester layer (A) and the polyester layer (C), it is possible to efficiently achieve sensitivity and crease property. Thus, the method for controlling the porosity of the polyester layer (A) and the polyester layer (C) is not particularly limited, but it can be achieved by appropriately selecting the type, amount and size of the inorganic particles contained in each layer. Is possible.

In the white laminated polyester film of the present invention, the sum of the thicknesses of the polyester layer (A) and the polyester layer (C) is 10% or more, preferably 13% or more, more preferably 15% or more. More preferably, it is 20% or more. When the sum of the thickness is less than 10%, the crease resistance deteriorates. In the white laminated polyester film of the present invention, the thickness of the polyester layer (C) needs to be larger than the thickness of the polyester layer (A), and preferably the thickness of the polyester layer (C) is the polyester layer. (A) It is desirable that it is 0.5 μm or more larger than the thickness, more preferably 1 μm or more, further preferably 2 μm or more, particularly preferably 3 μm or more. The method for controlling the thicknesses of the polyester layers (A), (B) and (C) is not particularly limited. For example, in the case of lamination by coextrusion, the amount of resin supplied from each extruder is adjusted. When the polyester layer (A) and the polyester layer (C) are supplied from the same extruder, the flow path cross-sectional areas of the polyester layer (A) and the polyester layer (C) in the T-die composite die are respectively set. By making a difference, it is possible to adjust arbitrarily.
Since the polyester layer (A) is a heat-sensitive transfer surface, if the laminated thickness is thick, the printability such as sensitivity reduction is impaired. On the other hand, the polyester layer (C) is on the reverse side of the thermal transfer, and has the effect of improving the folding property of the entire film due to the rigidity of the (C) layer. Therefore, when the polyester layer (C) becomes thinner than the polyester layer (A), the crease resistance deteriorates. For the polyester layer (A), the layer thickness is preferably 0.1 to 6.0 μm and more preferably 0.3 to 3.0 μm in order to increase the printability with higher sensitivity. If the lamination thickness of the polyester layer (A) is less than 0.1, the smoothness of the surface cannot be maintained or sufficient whiteness cannot be obtained, which is not preferable. On the other hand, if the laminated thickness exceeds 6.0 μm, the printing sensitivity is deteriorated, which is not preferable.

  Moreover, the thickness of the whole white laminated polyester film is not particularly defined, but it is preferably 20 to 150 μm from the viewpoint of the balance of workability such as crease resistance, whiteness, heat insulation, and printing characteristics, and more preferably. Is 25-100 μm.

  The specific gravity of the white laminated polyester film for thermal transfer in this patent is 0.8 to 1.3, more preferably 0.9 to 1.1. When the specific gravity is less than 0.8, the sharpness of the image is improved, but the film strength may be lowered, the wrinkle resistance may be deteriorated, and the image reproducibility may be deteriorated. On the other hand, when the specific gravity exceeds 1.3, the cushioning property and the heat insulating property are lowered and the printing property is lowered, or the whiteness of the film is insufficient, and the printed image tends to be dark.

  As for the whiteness of the white laminated polyester film for thermal transfer recording of the present invention, the whiteness measured from the polyester layer (A) side is 80% to 140%, more preferably 100% to 130%. When the whiteness is less than 80%, the printed image has a dark impression due to insufficient whiteness. In addition, when a receiving layer is provided, a layer to which a white pigment is newly added must be laminated to adjust the whiteness, which is not preferable from the viewpoint of cost. Examples of methods for increasing whiteness include increasing the amount of inorganic particles represented by titanium dioxide and barium sulfate, increasing the amount of fluorescent whitening agent, and lowering the stretching temperature during longitudinal stretching. It can be achieved by doing. Further, when the whiteness exceeds 140%, a large amount of inorganic particles or fluorescence is present in the polyester (A) layer, the polyester (B) layer, the polyester (C) layer, or in the plurality of layers from the polyester (A) to the (C) layer. It is necessary to add a brightening agent, and film forming properties such as film breakage deteriorate. Further, it is not preferable from the viewpoint of cost.

  The heat shrinkage stress value in the longitudinal direction (film forming direction) at 190 ° C. of the entire laminated polyester film is preferably 20 gf / 5 mm or more, more preferably 30 gf / 5 mm or more, and further preferably 40 gf / 5 mm or more. is there. Moreover, although an upper limit in particular is not prescribed | regulated, Usually, it is 100 gf / 5mm or less from balance, such as film forming property and heat gain. When the value of the heat shrinkage stress in the longitudinal direction at 190 ° C. is smaller than 20 gf / 5 mm, curling occurs after processing or printing, which is not preferable. In recent years, with the downsizing and speeding up of processing and printing apparatuses, curling is likely to occur due to the large tension applied in the longitudinal direction of the receiving sheet. Therefore, the value of the heat shrinkage stress in the longitudinal direction at 190 ° C. is 20 gf / 5 mm or more is preferable from the viewpoint of curling resistance. In order to increase the value of the heat shrinkage stress, the stretching ratio is increased, the stretching temperature is lowered, the temperature of heat setting is lowered, the time is shortened, and the thickness of the polyester layers (A) and (C) is summed. However, it is necessary to adjust to the optimum conditions in consideration of the influence of other factors such as porosity, heat shrinkage, and film forming property. For example, the stretching ratio in the longitudinal direction is 3 to 4 times, the stretching temperature is 80 to 110 ° C., the heat setting temperature is 200 to 230 ° C., the heat setting time is 15 seconds or less, and the thicknesses of the polyester layers (A) and (C) It is preferably achieved by making the sum of 10% or more.

  It is preferable that the displacement value of the thermo-mechanical testing machine measurement of the width direction in 190 degreeC of the whole laminated polyester film is 0 to 2%, More preferably, it is 0.5 to 2%, More preferably, it is 0.5 to 1 .5%. If it is less than 0% or more than 2%, curling tends to occur after printing, which is not preferable. The displacement value in the width direction can be controlled by the transverse draw ratio, temperature, heat setting temperature, time, and relaxation rate, but a more preferable method is in the zone of 190 ° C in the latter half of the heat setting process. A method of performing relaxation treatment in the width direction can be mentioned. In addition, in order to accurately control the displacement value measured by the thermomechanical testing machine within the above range, the film temperature at the oven outlet is changed to a glass transition by sufficiently cooling in the oven continuously after the heat setting process. It is important to control below this point.

  As the polyester-based resin constituting the polyester film of the present invention, those having ethylene terephthalate and / or ethylene naphthalate units as main components are preferred from the viewpoint of ester bonds. The polyester layer (B) preferably has a polyester melting point of 245 ° C. or higher and 280 ° C. or lower from the viewpoints of heat resistance and film formability. For the polyester layers (A) and (C), the polyester layer (B) is more preferable than the polyester layer (B) for the purpose of imparting adhesiveness to a base material such as paper or plastic or a receiving layer, or printing properties when direct printing is performed. The melting point may be low, and is preferably 200 ° C. or higher and 280 ° C. or lower. The polyester of the present invention may contain other copolymerization components as long as the properties are not impaired. Examples of such copolymer components include diphenyl dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, 5-sodium sulfoisophthalic acid, phthalic acid, isophthalic acid and other aromatic dicarboxylic acids, Acid, succinic acid, eicoic acid, adipic acid, sebacic acid, dimer acid, dodecanedioic acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, cyclohexyne dicarboxylic acid and other alicyclic dicarboxylic acids, p-oxybenzoic acid Oxycarboxylic acids such as acids, polyfunctional acids such as trimellitic acid and pyromellitic acid can be used. On the other hand, examples of the glycol component include propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, triethylene glycol and other aliphatic glycols, and cyclohexanedimethanol. And the like, aromatic glycols such as bisphenol A and bisphenol S, diethylene glycol, polyalkylene glycol, and the like can be used. Furthermore, polyethers such as polyethylene glycol and polytetramethylene glycol may be copolymerized. In particular, by adding an appropriate amount of a polyester copolymerized with diethylene glycol, polyethylene glycol, or polytetramethylene glycol as a glycol component, a fine dispersion effect is exhibited when the polyester contains an incompatible thermoplastic resin. When providing a coating layer for imparting antistatic properties and image durability, it is preferable because the effect is improved and the processing suitability such as crease resistance is improved.

  These dicarboxylic acid components and glycol components may be used in combination of two or more, or two or more polyesters may be blended and used. Furthermore, in this polyester, if necessary, as long as the effects of the present invention are not impaired, appropriate additives such as heat stabilizers, oxidation stabilizers, organic lubricants, organic fine particles, Inorganic particles, fillers, nucleating agents, dyes, dispersants, coupling agents and the like may be blended.

  The intrinsic viscosity of the polyester resin as described above (measured in an orthochlorophenol at 25 ° C.) is preferably 0.40 to 1.20 dl / g, more preferably 0.50 to 0.80 dl / g, 0.55-0.75 dl / g is still more preferable. Furthermore, the amount of carboxyl terminal groups of the polyester film serving as the substrate is preferably 25 to 60 equivalent / ton, more preferably 35 to 55 equivalent / ton from the viewpoint of adhesiveness with the deposited film. When the carboxyl end group amount is less than 25 equivalents / ton, the adhesion with the deposited film is lowered, which is not preferable. On the other hand, when the carboxyl end group amount exceeds 60 equivalents / t, it is not preferable because it is colored or the film forming property of the polyester film is deteriorated.

  Regarding the concealability of the white laminated polyester film for thermal transfer recording of the present invention, the optical density is preferably 0.5 or more, more preferably 0.55 or more. By controlling the optical density within this range, it is preferable that the surface of the adhesive layer of the paper or base film when the paper or base film is laminated can be concealed by the polyester film layer. The color tone b value measured from the polyester layer (A) side is preferably 2 or less, more preferably 1 or less, and most preferably 0 or less. When the color tone b value is larger than 2, the film itself is a yellowish color even if the light resistance is satisfied, and the printed image tends to have an old impression, which is not preferable.

In addition, the white laminated film of the present invention is subjected to surface modification by low-temperature plasma treatment, corona discharge treatment, coating, etc., in order to enhance adhesion when laminated with a receiving layer formed on the surface or other materials. Among them, the coating is particularly preferable because it can exhibit excellent adhesion and can impart an antistatic effect. The imparting of the antistatic effect is preferable in terms of improving the transportability of the receiving paper and preventing adhesion of dust, etc. The surface specific resistance measured from the coated surface side is 10 ¹³ Ω / □ or less, and the PH is 4 to 10. Preferably there is. Here, the surface resistivity measured from the coated surface is preferably 10 ¹² Ω / □ or less, particularly preferably 10 ¹¹ Ω / □ or less, and particularly preferably 10 ¹⁰ Ω / □ or less. The smaller the surface specific resistance, the lower the charging during processing, transporting in the printing press, or passing through the thermal head (adding antistatic properties), and improving the paper feeding properties. Sex is expressed. In addition, when imparting antistatic properties, either a layer of an antistatic agent alone or a layer in combination with a binder resin can be adopted, but in particular, the layer in combination with the latter binder resin is a receiving layer or other layer. It is more preferable in that the effect of improving the adhesion at the time of bonding to the material can be expected.

  In the present invention, when the coating layer is provided on the polyester (A) layer side, the surface PH of the coating layer is preferably 4 to 10, particularly preferably 4.5 to 9.5, and particularly preferably 5 to 9. . When the receiving layer is disposed on the coating layer surface, if the surface PH is less than 4 or more than 10, the characteristics at the time of printing may deteriorate. In particular, when the surface pH becomes acidic with a pH of less than 4, depending on the dye, a phenomenon such as discoloration occurs, which causes a problem in practical use, and the printing characteristics are greatly deteriorated, making it difficult to produce a blurred image or a desired color tone. Because.

  The method for forming the coating layer in the present invention is preferably a method in which the coating liquid is applied to the polyester layer (A) or (C) layer of the white laminated polyester film and dried. For example, reverse coating (roll) coating, gravure coating, knife coating, air knife coating, roll coating, blade coating, bead coating, rotating screen coating, slot orifice coating, rod coating, bar coating, and die coating. , Spray coat, curtain coat, die slot coat, champlex coat, brush coat, two coat, metering blade size press coat, bill blade coat, short dwell coat, gate roll coat, gravure reverse coat, extrusion coat, extrusion A method such as coating can be used.

  Moreover, as a coating process, either the method of apply | coating in the film forming process of a white laminated polyester film (in-line coating), and the method of apply | coating and drying on the film after film forming (offline coating) may be sufficient. In-line coating is a more excellent method in terms of uniform coating, thin film coating, and economic efficiency. In addition, the surface before coating may be subjected to pretreatment such as corona discharge treatment or plasma treatment on the surface in advance for the purpose of improving coatability.

  In addition, the liquid medium of the coating layer forming coating liquid may be any of water, solvent, or a mixture of both. However, when the coating layer is provided by an in-line coating method, the handling property and safety such as explosion prevention are provided. In view of the above, an aqueous medium or a mixed liquid medium mainly composed of water is preferably used.

  The coating thickness is preferably 0.005 to 10 μm, more preferably 0.01 to 1 μm. When the thickness of the coating layer is less than 0.005 μm, the antistatic property tends to be insufficient. On the other hand, when the thickness of the coating layer is thicker than 10 μm, the coating property of the coating layer forming coating liquid may be lowered at the time of coating, or the cost may be reduced and the economy may be lowered.

  By providing a heat-sensitive receiving layer on the polyester layer (A) side surface of the present invention, it can be used as an ink-receiving part of a heat-sensitive receiving sheet. The heat-sensitive receiving layer is a layer for receiving dyes and pigments transferred from the thermal transfer sheet and maintaining the formed image. Preferred resins for forming the receiving layer include, for example, polyolefin resins such as polypropylene, halogenated polymers such as polyvinyl chloride and polyvinylidene chloride, vinyl resins such as polyvinyl acetate and polyacrylic esters, and polyester resins. , Polystyrene resins, polyamide resins, ionomers, cellulose acetates such as cellulose acetate, polycarbonate resins, polyvinyl acetal resins, polyvinyl alcohol resins, and vinyl chloride-vinyl acetate copolymers and ethylene vinyl acetate copolymers. As mentioned above, a copolymer resin of the above resin or its monomer can be mentioned.

  In addition, pigments and fillers such as titanium oxide, zinc oxide, kaolin clay, calcium carbonate, and fine powder silica can be added for the purpose of improving the whiteness of the receiving layer and further enhancing the clarity of the image. Moreover, an antistatic agent can also be kneaded and mixed with the receiving layer coating solution.

  Examples of the antistatic agent include fatty acid esters, sulfate esters, phosphate esters, amides, quaternary ammonium salts, betaines, amino acids, acrylic resins, and ethylene oxide adducts. The addition amount of the antistatic agent is preferably 0.1 to 2% by weight based on the resin. The above-mentioned receiving layer is obtained by dissolving a resin with additives necessary in an appropriate organic solvent, or by dispersing a dispersion in an organic solvent or water, for example, gravure printing, screen printing, gravure printing It is formed by applying and drying on the peeling member by means of a reverse roll coating method using

  The thickness of the receiving layer may be appropriately selected depending on the intended use of the thermal transfer receiving sheet and the material of the equipment used, but is usually 1 to 50 μm, preferably 1 to 10 μm when dried.

  In the present invention, the white laminated polyester film having a receiving layer can be used as it is as a heat-sensitive receiving sheet, or a plastic film such as paper or polypropylene is bonded to the polyester layer (C) side, or the paper or plastic film. Further, a polyester film layer or the like can be further provided on the opposite side of the sheet to form a heat-sensitive receiving sheet.

  Next, although an example is demonstrated about the manufacturing method of the white laminated polyester film of this invention, this invention is not limited only to this example.

  In a composite film forming apparatus having an extruder (A), an extruder (B), and an extruder (C), in order to form a polyester layer (B), a polyester chip containing inorganic particles vacuum-dried, and if necessary Extruder (B) in which the incompatible resin chips and the incompatible resin chips are mixed with the incompatible resin chips in an amount of 1 to 35% by weight, and heated to 260 to 300 ° C. After being melt-extruded and filtered through a 10 to 50 μm cut filter, it is introduced into a T-die composite die. You may add a 0.05-10 weight% of dispersing agent to this raw material as needed. In addition, the incompatible resin may be added by previously drying a master chip in a vacuum. On the other hand, in order to laminate the polyester layer (A), a polyester chip and a master chip of inorganic fine particles are mixed so that the inorganic fine particles are 1 to 35% by weight and sufficiently vacuum-dried. If necessary, a fluorescent whitening agent may be added to the raw material in an amount of 0.01 to 1.5% by weight. Next, this dry raw material is supplied to an extruder (A) heated to 260 to 300 ° C., melted and filtered in the same manner as in the case of the polyester (B) layer, and introduced into the T-die composite die. Furthermore, in order to laminate the polyester layer (C), a polyester chip to which inorganic fine particles and the like are added as needed is sufficiently vacuum-dried, and the dried raw material is extruded into an extruder (C ), Similarly melted and filtered, and introduced into the T-die composite die. In the T-die composite die, the polymer of the extruder (B) is in the center, the polymer of the extruder (A) is on the surface of the printing surface side, and the polymer of the extruder (C) is the opposite side of the polymer of the extruder (A). Laminate so as to be the surface layer on the side and co-extrusion into a sheet to obtain a melt-laminated sheet.

  This melt-laminated sheet is closely cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 to 60 ° C. to produce an unstretched laminated film. The unstretched laminated film is led to a roll group heated to 70 to 120 ° C., stretched 2 to 5 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film), and cooled with a roll group of 20 to 30 ° C.

  Subsequently, after the corona discharge treatment is performed on the polyester layer (A) side of the film stretched in the longitudinal direction, a coating layer forming coating solution is applied to the treated surface. The film coated with this coating layer forming coating liquid is guided to a tenter while holding both ends of the film with clips, and stretched 2 to 5 times in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 90 to 150 ° C. To do.

  The stretching ratio is 2 to 5 times in the longitudinal and lateral directions, but the area ratio (longitudinal stretching ratio x lateral stretching ratio) is preferably 6 to 20 times. If the area magnification is less than 6 times, the resulting film has insufficient whiteness and film strength. Conversely, if the area magnification exceeds 20 times, the film tends to be broken during stretching.

  In order to complete the crystal orientation of the biaxially stretched laminated film thus obtained and to impart flatness and dimensional stability, heat treatment is subsequently performed at 150 to 240 ° C. for 1 to 30 seconds in the tenter, The white laminated polyester film of the present invention can be obtained by uniformly cooling and then cooling to room temperature and winding. In addition, in the said heat processing process, you may perform a 3-12% relaxation process in a horizontal direction or a vertical direction as needed. Biaxial stretching may be either sequential stretching or simultaneous biaxial stretching, and may be re-stretched in either the longitudinal or transverse direction after biaxial stretching.

[Measurement and evaluation method of characteristics]
The characteristic value of this invention is calculated | required with the following evaluation method and evaluation criteria.
(1) Fine bubbles inside the film and the thickness of the polyester layer After freezing the sample, the cross-section is cut out, and the cross-section is 500-5, using a scanning electron microscope S-2100A type (manufactured by Hitachi, Ltd.). The presence or absence of fine bubbles was examined from a cross-sectional photograph taken by magnifying the image at a magnification of 000 times. Determination of the presence or absence of the bubble-containing, if 1 [mu] m ² or more when calculated as an average value when converted to average cross-sectional area of the bubble portion of the cross-sectional photograph to a perfect circle "with bubbles", if less than 1 [mu] m ² "without bubbles" It was. However, when two or more adjacent bubbles were connected to each other, it was calculated as one bubble. Moreover, the length of the thickness direction of each polyester layer was measured from the cross-sectional photograph, and the thickness of each layer was calculated | required by calculating backward from magnification. In addition, when calculating | requiring the cross-sectional area of a bubble part and the thickness of each polyester layer, the cross-sectional photograph of five places selected arbitrarily from a mutually different measurement visual field was used, and it computed as the average value.
(2) Porosity of each layer From the cross-sectional photograph taken with a scanning electron microscope as in (1) above, only the void portion of the surface layer is traced on a transparent film, and an image analyzer (manufactured by Nireco Corporation: Luzex IID) is used. Used, the area ratio of voids was determined, and this value was taken as the volume% as it was.
(3) Specific gravity A sample sample obtained by cutting a film into a size of 50 mm × 60 mm was obtained using JIS K-7112 (1980) using a high-precision electronic hydrometer SD-120L (Mirage Trading Co., Ltd.). It measured according to the A method (substitution method in water). The measurement was performed under conditions of a temperature of 23 ° C. and a relative humidity of 65%.
(4) Thermal shrinkage stress in the longitudinal direction Using TM-9300 manufactured by ULVAC-RIKO, using a sample size of 5 mm wide x 20 mm long, with an initial load of 0 g at 30 ° C. and a temperature rising rate of 10 ° C./min The stress was measured while raising the temperature from 30 ° C., and the value at 190 ° C. was read.
(5) Displacement value of thermomechanical tester measurement (TMA) in the width direction Using TM-9300 manufactured by ULVAC-RIKO Inc., using a sample size width of 5 mm × length of 20 mm, a load of 5 g, and a heating rate of 10 ° C. The displacement was measured while raising the temperature from 30 ° C./min, and the value at 190 ° C. was read. Note that the extension direction of the sample length is expressed as + and the contraction direction as − compared to the initial value.
(6) Whiteness X value which is a tristimulus value of color under optical conditions according to JIS Z-8722 (2000) using a spectroscopic color difference meter SE-2000 (manufactured by Nippon Denshoku Industries Co., Ltd.) , Y value and Z value were measured, and the whiteness was calculated from the following formula.
Whiteness (%) = 4 × 0.847 × Z value−3 × Y value (7) Printability The following receiving layer-forming coating solution is applied to the coated surface of the white laminated polyester film of the present invention using a micro gravure coater. It was applied at ² g / m ² when dried to obtain a receiving sheet for thermal transfer recording.
[Receptive layer forming coating solution]
Polyester resin (Toyobo Co., Ltd., Byron 200) 20 parts Silicone oil (Shin-Etsu Chemical Co., Ltd., X-22-3000T) 2 parts Toluene 39 parts Methyl ethyl ketone 39 parts Next, weighed 125 g / m ² of paper Lamination is done so that the image-receiving layer is on the outside, and Canon's card photo printer “CP-300” (Canon) and a special ink ribbon (attached to color ink, paper set KL-36IP) Then, test printing was performed on the receiving layer forming surface of the receiving sheet, and the determination was made as follows. ○ and △ are acceptable.
○: Clean and good.
Δ: Slight “chip” is observed, but generally clean and good.
×: “Missing” and “Crushing” are seen in multiple places.
(8) Curl evaluation Test printing was performed in the same manner as in (7) above, and the printed material was placed on a flat table, and the four corners between the flat table and the printed material were measured and judged according to the following criteria. . ○ and △ are acceptable.
○: 0 to 1 mm
Δ: 1 to 5 mm
×: Greater than 5 mm (9) Image density (print sensitivity)
In the same manner as (7) above, solid prints of C (cyan), M (magenta), and Y (yellow) were obtained. The reflection density of the obtained print was measured using a Macbeth densitometer, and the average density of three colors (N = 5 times) was obtained. In the same manner, the average density of Lumirror E60 (50 μm) manufactured by Toray Industries, Inc. was determined in the same manner as described above, and the printing sensitivity was evaluated based on the average density ratio of each sample.
Δ, ○, and ◎ are acceptable.
◎: 103% or more ○: 101 to 103%
Δ: 100 to 101%
X: Less than 100% (10) Folding resistance wrinkle resistance The film was bonded to one side of a paper having a weight of 125 g / m ² and cut into a strip having a length of 300 mm and a width of 50 mm. One end of the strip-shaped film is fixed, and the film side is turned inside, and the film is wound around 180 ° around a cylindrical glass rod having a diameter of 6 mm. A weight of 50 g is attached to both ends of the glass rod, and the film is rubbed over the glass rod over a length of 100 mm by pulling the free end side once. The surface of the squeezed film was folded with a stereomicroscope (10 times) and the state of wrinkles was observed. ○ and △ are acceptable.
◎: No wrinkles / cm ²
○: 1 to 5 cm ²
Δ: Folding wrinkles 5-10 cm ²
X: Wrinkles at least 10 / cm ² (11) Productivity The productivity of a film was determined using the occurrence frequency of tears according to the following criteria.
○: Film can be stably formed without tearing. Δ: The film tears less than 1/12 hours. ×: Breaks more than once / 12 hours and production is difficult.

  The present invention will be described with reference to the following examples, but the present invention is not limited thereto.

(Example 1)
In a composite film-forming apparatus having an extruder (a) and an extruder (b), 7 weights of titanium oxide (surface untreated) having an average particle diameter of 0.2 μm is used to form the polyester layers (A) and (C). %, Calcium carbonate particles having an average particle diameter of 0.9 μm (surface treated with 6 parts by weight of trimethyl phosphate for 100 parts of calcium carbonate), 1% by weight of optical brightener “OB-1” (Eastman Kodak) Polyethylene terephthalate containing 0.15% by weight (melting point: 256 ° C .: hereinafter abbreviated as PET) is vacuum-dried at 180 ° C. for 3 hours, then supplied to the extruder (a) side and melted at 280 ° C. After extrusion, foreign matter was filtered through a 35 μm cut filter and then introduced into a T-die composite die.

  On the other hand, in order to form the polyester layer (B), 5% by weight of polymethylpentene (manufactured by Mitsui Chemicals, TPX, DX820: hereinafter abbreviated as PMP) is added to PET, and polyethylene having a molecular weight of 4,000 as a dispersant. Copolymerized PET containing 10% by weight of glycol (hereinafter abbreviated as PEG) was added so that PEG would be 1% by weight with respect to the entire resin constituting the polyester (B) layer, and a hindered phenol system was further added. After 0.05% by weight of antioxidant was vacuum dried at 180 ° C for 3 hours, supplied to the extruder (b) side, melted at 280 ° C and filtered with a 35 µm cut filter. And introduced into a T-die composite base.

Next, the polyester layers (A) and (C) were joined so as to be laminated on both surface layers of the polyester layer (B) in the die, and then co-extruded into a sheet shape to obtain a melt-laminated sheet. However, at this time, the thicknesses of the polyester layers (A) and (C) are controlled by the shape (cross-sectional area) of the joining portion of the composite die, and the polyester layer (A) is more than the polyester layer (C) as shown in Table 1. It was adjusted to be thin. Then, the molten laminated sheet was closely cooled and solidified by an electrostatic charge method on a drum maintained at a surface temperature of 25 ° C. to obtain an unstretched laminated film. Subsequently, the unstretched laminated film was preheated with a group of rolls heated to 85 ° C. according to a conventional method, and then slightly stretched 1.1 times in the longitudinal direction (longitudinal direction) using a 90 ° C. heated roll. The film was stretched 1 time and cooled with a roll group at 25 ° C. to obtain a uniaxially stretched film. Subsequently, the drum contact side of the unstretched laminated film is subjected to corona discharge treatment in the air, and the following coating layer forming coating solution is applied to the treated surface on the polyester layer (A) by a bar coating method using a metalling bar. It was applied to. While holding both ends of the uniaxially stretched film coated with this coating layer forming coating solution with clips, it is guided to a 130 ° C preheating zone in the tenter, and continuously in a 110 ° C heating zone in a direction perpendicular to the longitudinal direction (lateral Direction) was stretched 3.3 times. Subsequently, a heat treatment at 220 ° C. was performed in the heat treatment zone in the tenter, and after 4% transverse treatment at 180 ° C., 1% relaxation treatment was further conducted at 140 ° C. A coating layer having a thickness of 0.08 μm is provided on a polyester film having a thickness of 50 μm which is wound up and has a structure in which the polyester layer (A) is 2 μm on one side, the polyester layer (B) is 40 μm, and the polyester layer (C) is 8 μm. A white laminated polyester film was obtained. Moreover, it confirmed that the micro bubble was contained in the inside of the polyester layer (B) by magnifying and observing the cross section of this white laminated polyester film by SEM. These fine bubbles are formed around PMP dispersed in the form of particles, and the circumference is an ellipse whose major axis is the stretching direction and whose minor axis is the film thickness direction, and the average value of the cross-sectional area is It was 4.5 μm ² .

  The characteristics of the white laminated polyester film thus obtained are as shown in Table 5 and are found to be excellent as a receiving sheet substrate for thermal transfer recording.

(Examples 2-9)
According to the composition of Tables 1 and 2, a white laminated polyester film was obtained in the same manner as in Example 1. However, the polyester layers (C) of Examples 4 to 9 were supplied from another independent extruder (c) to obtain melt-laminated sheets having a three-layer configuration of A / B / C in the composite die. Further, calcium carbonate having a surface treated with trimethyl phosphate (6 parts by weight with respect to 100 parts by weight of calcium carbonate) was used. As shown in Table 5, the properties of the obtained white laminated polyester film are excellent in printing sensitivity, crease resistance, curling property, whiteness and the like, and are found to be good as a receiving sheet substrate for thermal transfer recording. .

(Comparative Examples 1-9)
According to the composition of Tables 3 and 4, a white laminated polyester film was obtained in the same manner as in Example 1. However, the polyester layers (C) of Comparative Examples 7 to 9 were supplied from another independent extruder (c) to obtain a melt-laminated sheet having a three-layer structure of A / B / C in the composite die. The characteristics of the obtained white laminated polyester film are as shown in Table 6. For example, in Comparative Examples 1, 3, 4, and 9, printing sensitivity is low, and in Comparative Examples 2, 5, and 6, folding resistance is inferior. It can be seen that none of the standards has been achieved in terms of printing sensitivity, crease resistance, whiteness, printability, or film formability as a receiving sheet substrate for thermal transfer recording.

Claims (7)

A polyester layer (A) containing inorganic particles is provided on the thermal transfer surface side of the polyester layer (B) containing many fine cavities, and a polyester layer (C) is provided on the opposite side of the thermal transfer surface of the polyester layer (B). A white laminated polyester film for thermal transfer recording, wherein the laminated polyester film satisfies the following requirements.
(1) The porosity of the polyester layer (B) is 15 to 50% by volume, the porosity of the polyester (A) layer and the (C) layer is 15% by volume or less, and the specific gravity of the entire laminated polyester is 0.8. (2) The sum of the thickness of the polyester layer (A) and the thickness of the polyester layer (B) is 10% or more of the total thickness of the film, and the thickness of the polyester layer (C) Is larger than the thickness of the polyester layer (A) (3) The whiteness on the polyester layer (A) side is 80 to 140% The white polyester film for thermal transfer recording according to claim 1, wherein the thickness of the polyester layer (A) is 0.1 to 6.0 µm. The white polyester film for thermal transfer recording according to claim 1 or 2, wherein the porosity of the polyester layer (A) layer is larger than the porosity of the polyester layer (C). The white polyester film for thermal transfer according to any one of claims 1 to 3, wherein the polyester layer (A) contains at least two kinds of inorganic particles. The value of heat shrinkage stress in the longitudinal direction at 190 ° C of the entire laminated polyester film is 20 gf / 5 mm or more, and the displacement value of thermomechanical tester in the width direction at 190 ° C is 0 to 2%. The white polyester film for thermal transfer according to any one of 1 to 4. The polyester layer for thermal transfer according to any one of claims 1 to 5, wherein the polyester layer (B) contains a thermoplastic resin incompatible with the polyester. The polyester film according to any one of claims 1 to 6, which has a structure in which a thermal transfer receiving layer is provided on the polyester layer (A) side.