JPH11268435A - Polyester film for thermal-transfer image receiving sheet, and thermal-transfer image receiving sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal-transferred image of a high density, which is excellent in a surface smoothness and a folded wrinkle resistance. SOLUTION: This polyester film has numerous cavities deriving from a thermoplastic resin which is incompatible with polyester, in the film. In this case, the apparent specific gravity is made 1.3 or lower, the cohesive failure index of at least either one of the surfaces is made 3 or lower, and the glossiness of the surface is made 20% or higher. By this method, the polyester film having cavities which is excellent in a surface smoothness, by which a sufficient image density can be obtained, and also, which is excellent in a folded wrinkle resistance, and is useful for an image receiving sheet, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyester film for a thermal transfer image receiving sheet and a thermal transfer image receiving sheet.

[0002]

2. Description of the Related Art As a conventional thermal transfer image receiving sheet, there is known a natural paper or a sheet having a recording layer formed on the surface of natural paper. However, in this method, only those having insufficient surface smoothness can be obtained. On the other hand, in order to improve the smoothness of the image receiving sheet, a thin polypropylene synthetic paper and a natural paper were bonded together, or a thick polypropylene synthetic paper was used as a base material, and a recording layer was provided on these surfaces. Things are widely used. This is because polypropylene synthetic paper has surface smoothness that cannot be obtained with natural paper, and also has appropriate cushioning properties. By having an appropriate cushioning property, uniform and sufficient contact can be made between the heating head / transfer ribbon / image receiving sheet during thermal transfer, and a uniform and high-density printed matter can be obtained. . However, when polypropylene synthetic paper is used as a base material, polypropylene synthetic paper is extremely easily plastically deformed and has poor flexibility. There is a serious disadvantage that the quality of the printed matter is significantly impaired.

On the other hand, a method using a void-containing polyester film instead of polypropylene synthetic paper has also been proposed. However, void-containing polyester films are generally more rigid than polypropylene synthetic paper,
Insufficient cushioning properties. Therefore, in order to obtain the same image density as when using polypropylene synthetic paper using a void-containing polyester film, the void content must be higher than the void content of the polypropylene synthetic paper in order to secure cushioning properties. . As a result, the size of the cavity becomes extremely large, and the smoothness of the surface is impaired, or the surface is easily broken and wrinkles are easily generated. Further, when the void content is increased, the production stability becomes extremely poor,
It is extremely difficult to produce it stably on an industrial scale.

[0004]

SUMMARY OF THE INVENTION The present invention has the drawbacks of the prior art, namely, a problem that an image receiving sheet having excellent surface smoothness, sufficient image density, and excellent folding wrinkle resistance cannot be obtained. Is to be resolved.

[0005]

SUMMARY OF THE INVENTION The present invention provides a synthetic resin film for use as a thermal transfer image-receiving sheet having a thermal transfer recording layer formed on a composite substrate in which a synthetic resin film is bonded to one or both sides of a natural paper support. And a polyester film containing a large number of cavities derived from a thermoplastic resin incompatible with the polyester inside the film, having an apparent specific gravity of 1.3 or less, and a cohesive failure index of at least one of the surfaces thereof. Is 3 or less, and the glossiness of the surface is 20% or more.

[0006] The polyester in the present invention is obtained by polymerizing an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid or an ester thereof with a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol or neopentyl glycol. It is a polyester produced by condensation. These polyesters may be prepared by directly reacting an aromatic dicarboxylic acid and a glycol, or by subjecting an alkyl ester of the aromatic dicarboxylic acid to a transesterification reaction with a glycol followed by polycondensation, or a diglycol ester of an aromatic dicarboxylic acid. Can be produced by a method such as polycondensation. Representative examples of such polyesters include polyethylene terephthalate, polyethylene butylene terephthalate, and polyethylene-2,6-naphthalate. This polyester may be a homopolymer or a copolymer of the third component. In any case, in the present invention, a polyester having an ethylene terephthalate unit, a butylene 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 thermoplastic resin that is incompatible with the polyester used in the present invention is optional, and is not particularly limited as long as it is incompatible with the polyester. Specific examples include polystyrene-based resins, polyolefin-based resins, polyacryl-based resins, polycarbonate resins, polysulfone-based resins, and cellulose-based resins. In particular, polystyrene resins or polyolefin resins such as polymethylpentene and polypropylene are preferably used.

However, more preferred thermoplastic resins incompatible with polyester include, for example, the following. That is, the thermoplastic resin incompatible with the polyester contains at least a polystyrene resin, a polymethylpentene resin, and a polypropylene resin, and contains a polystyrene resin content (a weight%) and a polymethylpentene resin. The amount (b weight%) and the content of the polypropylene resin (c weight%) are as follows: 0.01 ≦ a / (b + c) ≦ 1, c / b ≦ 1, 3 ≦
It is most preferable to satisfy a + b + c ≦ 20, which is suitable for increasing the void ratio and improving the folding wrinkle resistance.

[0009] Here, the polystyrene resin refers to a thermoplastic resin having a polystyrene structure as a basic component, and includes other components in addition to homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene. Modified resins graft- or block-copolymerized, such as impact-resistant polystyrene resins and modified polyphenylene ether resins, and mixtures of these polystyrene-based resins with thermoplastic resins, such as polyphenylene ether, are also included.

[0010] The polymethylpentene resin is 8
0 mol% or more, preferably 90 mol% or more, is a polymer having units derived from 4-methylpentene-1, and other components include ethylene units, propylene units,
Derived units derived from butene-1 unit, 3-methylbutene-1 and the like are exemplified.

The melt flow rate of the polymethylpentene is preferably 200 g / 10 minutes or less,
More preferably, it is 30 g / 10 minutes or less. This is because if the melt flow rate exceeds 200 g / 10 minutes, it is difficult to obtain the effect of reducing the weight of the film.

Further, the polypropylene resin in the present invention also includes modified resins obtained by grafting or block copolymerizing other components in addition to homopolymers such as isotactic polypropylene and syndiotactic polypropylene. Further, as the presence state of the polypropylene resin in the present invention, the above polypropylene resin may be used separately from the polymethylpentene, or a propylene unit may be used as a copolymer component in the polymethylpentene resin. The introduced one may be used.

The mixing amount of these void-forming agents, ie, the thermoplastic resin incompatible with the polyester, to the polyester varies depending on the amount of the target voids, but is in the range of 3 to 20% by weight based on the whole film. And more preferably 5 to 18% by weight. And 3
If the amount is less than the weight percentage, there is a limit to increasing the amount of cavities generated. Conversely, if the content is 20% by weight or more, the stretchability of the film is significantly impaired, and the heat resistance, strength, and stiffness are impaired.

Further, inorganic or organic particles may be added to the film, if necessary, in the polyester or in the incompatible resin in order to improve the concealing property and the like. Particles that can be added include silica, kaolinite, talc,
Examples thereof include, but are not particularly limited to, calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, titanium oxide, zinc sulfide, and organic white pigment.

The polyester film for a thermal transfer image-receiving sheet of the present invention must have an apparent specific gravity of 1.3 or less, more preferably 1.1 or less. If the apparent specific gravity is larger than 1.3, the amount of cavities existing in the film is too small, and a sufficient image density cannot be obtained during thermal transfer printing. On the other hand, the lower limit of the apparent specific gravity is not limited, but is preferably 0.7 or more, and more preferably 0.8 or more, in order to secure the breaking wrinkle resistance.

The polyester film for a thermal transfer image-receiving sheet of the present invention needs to have a cohesive failure index of at least one surface of 3 or less, more preferably 2 or less, and most preferably 1. This requirement is the most important component of the present invention, and by satisfying this requirement, it is possible to dramatically improve the image density during thermal transfer printing. Conversely, when the cohesive failure index of the film surface exceeds 3, only an image density equivalent to that of a conventionally known void-containing polyester film can be obtained.

Here, the surface cohesive failure index is an index indicating the cohesive strength of the polyester constituting the film surface, and the larger the value, the higher the cohesive strength. The cohesive failure index on the surface is determined by the state of the cavities inherent in the polyester constituting the vicinity of the film surface. That is, to reduce the cohesive failure index,
This means that more fine cavities are formed in the vicinity of the film surface, and a remarkable improvement in image density can be obtained by this effect.

The polyester film for a thermal transfer image-receiving sheet of the present invention has a cohesive failure index of 3 or less at the surface and a gloss of 20% or more, more preferably at the same time.
Must be at least 30%. This is because the surface gloss
If it is less than 20%, the smoothness of the film surface and, in turn, the surface smoothness of the thermal transfer image-receiving sheet will be impaired, and it will be difficult to obtain uniform adhesion between the ink ribbon and the image-receiving paper during thermal transfer printing. It is because it falls to.
In addition, the thermal transfer image becomes rough, and the print quality is greatly reduced.

The method for obtaining the above cohesive failure index and glossiness is arbitrary and is not limited at all.
The axially oriented film will be described in detail by exemplifying means for achieving the cohesive failure index and gloss. First, the aforementioned cohesive failure index and glossiness can be achieved by bonding a polyester layer (skin layer) containing fine voids derived from fine particles having an average particle size of 0.1 to 1 μm to the film surface. The void content in the skin layer is not limited at all, but it is preferable to form voids of 20% by volume or more.

When the average particle diameter of the particles added to the skin layer is less than 0.1 μm, the ability to form cavities in the film stretching step described later is significantly reduced, and the cleavage strength of the film surface is reduced to 3 or less. And it is not possible to obtain the expected effect of improving the thermal transfer sensitivity characteristics. On the other hand, when particles having an average diameter of more than 1 μm are used, although the ability to form cavities is excellent, the smoothness of the film surface is significantly reduced, making it difficult to achieve a glossiness of 20% or more. Instead, it lowers it.

The particles that can be added to the skin layer may be inorganic particles or organic particles, and are not limited at all. For example, titanium dioxide, calcium carbonate, barium sulfate, zinc sulfide, Examples include silicon dioxide, aluminum oxide, talc, and kaolin.
These particles may be subjected to a surface treatment as necessary. Examples of the treating agent include, but are not limited to, aluminum oxide, silicon dioxide, zinc oxide, silicon-based resin, siloxane-based resin, fluorine-based resin, silane coupling agent and titanate coupling agent, polyol and polyvinylpyridine. Not something

Among them, particularly preferred particles include titanium oxide fine particles and zinc sulfide fine particles. Further, titanium oxide fine particles are most preferably used from the viewpoint that the film can be effectively provided with a hiding property. The titanium oxide fine particles may be either anatase type or rutile type.
Further, the particle surface may be subjected to an inorganic treatment such as alumina or silica, or may be subjected to a silicon-based or alcohol-based organic treatment.

The concentration of the fine particles added to the skin layer is arbitrary, but is preferably 20 to 50% by weight. If the addition amount is less than 20%, the ability to form cavities becomes insufficient, and it becomes difficult to reduce the cohesive failure index of the film surface to 3 or less. On the other hand, if it exceeds 50%, the smoothness of the film surface is rapidly deteriorated, and it is difficult to reduce the glossiness of the film surface to 20% or less.

Further, a coloring agent, a light-fast agent, a fluorescent agent, an antistatic agent and the like can be added to the skin layer as needed.

The thickness of the skin layer is preferably 1 to 20 μm and less than 30% of the total thickness of the film. When the thickness of the skin layer is less than 1 μm, the dispersion of the fine particle concentration per film surface area becomes large, so that the image density becomes uneven and the printed matter tends to give a rough impression. On the other hand, even if the skin layer is formed with a thickness exceeding 20 μm, the effect of improving the image density cannot be obtained and is meaningless. Furthermore, the skin layer thickness is 30 times
%, The stretchability of the whole film tends to be remarkably reduced, which is not preferable for securing stable industrial productivity.

The method for producing the polyester film for a thermal transfer image-receiving sheet of the present invention is optional and is not particularly limited. For example, it can be produced as follows.

First, as a method for joining the skin layer to the film surface, a co-extrusion method is used in which the resins of the layer A and the layer B are supplied to separate extruders, then laminated in a molten state and extruded from the same die. Is most preferred.

The unstretched film thus obtained is further stretched between rolls having different speeds (roll stretching), stretched by gripping and expanding with clips (tenter stretching), or stretched by air pressure. (Inflation stretching) and the like are subjected to biaxial orientation treatment. By performing the orientation treatment, interfacial separation occurs between the polyester / incompatible resin and between the polyester / fine particles, and many fine cavities are developed.

Therefore, the conditions for stretching and orienting the unstretched film are closely related to the formation of cavities. Below,
The stretching / orientation conditions will be described by taking as an example a sequential biaxial stretching method most preferably used, particularly a method of stretching an unstretched film in the longitudinal direction and then in the width direction.

First, the first-stage longitudinal stretching step is the most important process for forming many fine cavities inside the film. In longitudinal stretching, stretching is performed between two or many rolls having different peripheral speeds. As the heating means at this time,
A method using a heating roll or a method using a non-contact heating method may be used, or both may be used. Among these, the most preferred stretching method is a method using both roll heating and non-contact heating. In this case, the film is first preheated to a temperature of 50 ° C. to the glass transition point of the polyester by using a heating roll, and then the front and back of the film are heated by independent infrared heaters of a control system. At this time,
The skin layer surface is heated to a lower temperature, and the insufficient heat is compensated for by infrared heating from the opposite surface. Thus, it is extremely important to heat and stretch the film front and back to different temperatures. The method of providing a temperature difference with a non-contact heating device is merely one preferable example, and the same effect can be obtained by another method, for example, a method of sandwiching a film between rolls having different temperatures and heating. In any case, the heating of the entire film is mainly performed from the anti-skin layer side to supply a sufficient amount of heat enough to uniformly stretch the film, and the skin layer surface is stretched at a lower temperature. This is an important point for forming a large number of cavities derived from inorganic fine particles.

Next, the uniaxially stretched film thus obtained is introduced into a tenter and stretched 2.5 to 5 times in the width direction. The preferred stretching temperature at this time is 100 ° C to 20 ° C.
0 ° C.

The biaxially stretched film thus obtained is subjected to a heat treatment if necessary. The heat treatment is preferably performed in a tenter, and the melting point of the polyester is Tm-50 ° C.
It is preferably performed in the range of -Tm.

The polyester film for a thermal transfer image-receiving sheet of the present invention obtained by the above-mentioned production method has sufficient fine voids in the skin layer and also has excellent production stability.

The polyester film for a thermal transfer image-receiving sheet of the present invention may have a coating layer on at least one of the surfaces. By providing a coating layer, it is possible to improve the wettability and adhesion of ink, a coating agent, and the like. As the compound constituting the coating layer, a polyester resin is preferable, and in addition, a compound disclosed as a means for improving the adhesiveness of a normal polyester film, such as a polyurethane resin, a polyester urethane resin, and an acrylic resin. Etc. are applicable.

As a method of providing a coating layer, a method usually used such as a gravure coating method, a kiss coating method, a dip method, a spray coating method, a curtain coating method, an air knife coating method, a blade coating method, a reverse roll coating method, etc. Applicable. As the step of applying, any method such as a method of applying before stretching the film, a method of applying after longitudinal stretching, and a method of applying to the surface of the film after the orientation treatment is possible.

The void-containing polyester film thus obtained has a remarkable effect of improving image density while having excellent folding wrinkle resistance and surface smoothness as compared with the conventional void-containing film. Can be

The method for preparing a composite substrate with natural paper using the polyester film for a thermal transfer image-receiving sheet of the present invention is not limited at all, and is arbitrary.

In order to prepare a thermal transfer image-receiving sheet using the polyester film for a thermal transfer image-receiving sheet of the present invention, the film surface receives ink or a diffusible (sublimable) dye transferred from the thermal transfer ink sheet. It is necessary to form a thermal transfer recording layer for the purpose. In this case, the recording layer may be formed directly on the film, or may be formed via an undercoat layer such as an easy-adhesion layer, a whiteness improving layer, or an antistatic layer.

The thermal transfer recording layer may be formed after the formation of the thermal transfer recording layer, or may be formed after a base material laminated to the natural paper has been formed.

Examples Next, examples of the present invention and comparative examples will be described. The measurement / evaluation method used in the present invention will be described below.

1) Apparent Specific Gravity A film was accurately cut out into a square of 10 cm × 10 cm, and its thickness was measured at 50 points to obtain an average thickness t (unit: μm).
Ask for. Next, the weight of the sample is measured up to 0.1 mg and is referred to as w (unit: g). Then, the apparent specific gravity was calculated by the following equation. Apparent specific gravity (-) = (w / t) x 10
000

2) Cohesive failure index Two types of adhesive tapes, (1) KOKUYO Mending Tape T-
118 (18mm width), (2) Nichiban cellophane tape (24mm width)
Prepare Cut these tapes to 50 mm (turned back at the end), stick them to the film so that air bubbles do not enter them, and squeeze them with your fingers to make them adhere sufficiently. Then, the tape is peeled off at a stretch in the direction of 180 °, and evaluated in five steps according to the peeling state of the film surface.

3) Surface glossiness Using VGS-1001DP manufactured by Nippon Denshoku Industries Co., Ltd.
The reflectance at 0 degree was determined.

4) Thermal Transfer Sensitivity Characteristics (Relative Image Density) For a sample obtained by cutting a thermal transfer image receiving sheet into A6 size, a commercially available ink ribbon (Print set P- for a sublimation transfer printer manufactured by Caravelle Data System Co., Ltd.)
Printing is performed at a printing speed of 100 mm / sec and a head voltage of 18 V using a PS100) and a commercially available thermal transfer printer (BLP-323, a thermal transfer label printer manufactured by Bon Electric Co., Ltd.). The print pattern is 9 mm x 9 mm for each of the four colors C (cyan), M (magenta), Y (yellow), and K (black) obtained by superimposing them.
A pattern is used in which seven (7) total solid square characters (total 28) are arranged in an A6 sheet. After printing, the reflection density of each color of CMYK is measured using a Macbeth densitometer (TR-927), and the average density of four colors (total 28 locations) is obtained.

Similarly, the same applies to a commercially available image-receiving paper (print set P-PS100 for a sublimation transfer printer manufactured by Caravelle Data System Co., Ltd .: a sheet obtained by laminating a foamed polypropylene film on both sides of natural paper and forming a recording layer). The average density is determined by the above method, and the thermal transfer sensitivity characteristic is evaluated by the ratio (%) of the density of the sample to the density of the commercially available image receiving paper.

5) Folding wrinkle resistance The thermal transfer image-receiving sheet prepared by the above method is 5 cm long,
Cut into strips 1 cm wide, wrapped around a 5 mm diameter glass rod, and wrung. Thereafter, the sample was stretched again, and the state of wrinkles generated on the surface was observed using a stereoscopic microscope. Rank A: No wrinkles Rank B: Thin wrinkles on the entire surface Rank C: Thick wrinkles on the entire surface

6) Thickness of Skin Layer The cut surface of the film was observed and observed with an electron microscope.

7) Void Content in Skin Layer The thickness of the skin layer of the unstretched film is T1, the thickness of the skin layer of the biaxially stretched film is T2, and the total stretching ratio of the film =
The longitudinal stretching ratio × lateral stretching ratio (measured by writing a magnification marker on an unstretched film) was set to D, and calculated by the following formula.
Cavity content (%) = 100−100 × T1 / (T2
× D)

The void content in the skin layer can be measured by the above-described method, and can also be calculated from the skin layer thickness change rate before and after heat pressing, cross-sectional observation using an electron microscope, and the like. When the void content is evaluated by the heat press method, the voids in the film are completely crushed by a heat press machine, and the change rate of the B layer thickness (observed by an electron microscope) before and after the heat press is expressed as F = (after heat press). B layer thickness) /
(Thickness of B layer before heat press), and G = (weight per unit area after heat press) / (weight per unit area before heat press) before and after heat press , Can be calculated by the following equation. Cavity content (%) = 100− (F / G) × 100

Example 1 (Preparation of cavity forming agent) Melt flow rate as raw material
20% by weight of a 1.7 polystyrene resin (TOPOLEX 570-57U manufactured by Mitsui Toatsu Co., Ltd.) and a melt flow rate of 1.7
Polypropylene resin (Noblene manufactured by Mitsui Toatsu Co., Ltd.)
FO-50F) 20 wt% and melt flow rate 8 polymethylpentene resin (TPX, manufactured by Mitsui Petrochemical Co., Ltd.)
DX-845) 60% by weight of pellets were mixed, supplied to a twin-screw extruder, and sufficiently kneaded to prepare a cavity-forming agent.

(Preparation of Master Pellets Containing Fine Particles) Anatase-type titanium dioxide (TA-300 manufactured by Fuji Titanium Co., Ltd.) 50 having an average particle size of 0.3 μm (electron microscopic method) in 50% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.64 as a raw material
% By weight is supplied to a vent-type twin-screw extruder and preliminarily kneaded, and then the molten polymer is continuously supplied to a vent-type single-screw kneader and kneaded to contain fine particles (titanium oxide). The master pellet was prepared.

Next, 10% by weight of the cavity-forming agent obtained by the above method, 5% by weight of master pellets containing fine particles (titanium oxide) and 85% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 are mixed in a pellet and dried under vacuum. And the raw material of the film constituting the A layer.

On the other hand, 30% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and the fine particles (titanium oxide)
70% by weight of the contained master pellets were pellet-mixed and vacuum-dried to obtain a raw material of a film constituting the layer B.

(Preparation of Unstretched Film) Then, the raw materials of the films constituting each layer were supplied to separate extruders, and the layer B was joined to one surface of the layer A in a molten state using a feed block. At this time, the discharge amount ratio of the A layer and the B layer was controlled to 93: 7 volume ratio using a gear pump.
Then, it was extruded onto a cooling drum adjusted to 30 ° C. by using a T-die to prepare an unstretched film having a thickness of about 300 μm. At this time, extrusion was performed so that the layer B side was a non-drum surface and the layer A side was a drum surface.

(Preparation of Biaxially Stretched Film) The obtained unstretched film was uniformly heated to 65 ° C. using a heating roll, and the film was sandwiched between a metal roll whose temperature was controlled to 65 ° C. and a rubber roll whose temperature was not controlled. Speed regulation (3m / min)
Similarly, it was stretched 3.4 times with a high-speed roll (the temperature of a metal roll was controlled at 30 ° C. and the temperature of a rubber roll was not controlled) whose speed was regulated (10.2 m / min). At this time, the two sets of rolls whose speed was regulated had a distance between the speed regulation points of 25 cm.
And placed so that the surface B (non-drum surface) side is in contact with the rubber roll surface. In addition, an infrared heater (rated at 20 W / cm) having a gold reflective film at the center of the nip roll was installed opposite to both surfaces of the film (a distance of 1 cm from the film surface), and the A layer surface was rated at 100 mm.
%, And the layer B surface was heated at 60% of the rated value.
The uniaxially stretched film thus obtained is guided to a tenter, heated to 150 ° C., stretched transversely by 3.7 times, fixed in width, subjected to a heat treatment at 220 ° C. for 5 seconds, and further heated at 210 ° C. in the width direction. By relaxing by 4%, a void-containing polyester film having a thickness of 38 μm (Example 1) was obtained.

(Preparation of Thermal Transfer Image-Receiving Sheet) On layer B (skin layer) of the obtained void-containing polyester film, a coating liquid having the following composition: water-dispersible copolymerized polyester resin: 2 parts water-dispersible acrylic-styrene copolymer Resin: 5 parts Water-dispersible isocyanate-based cross-linking agent: 0.5 parts Water: 67.4 parts Isopropyl alcohol: 25 parts Surfactant: 0.1 parts After drying, the film surface is adjusted to have a weight of 4 g / m ^2. And heat-treated at 160 ° C. for 30 seconds to form a thermal transfer recording layer.

Next, a film having the above heat transfer recording layer formed on one side of a natural paper core material having a basis weight of 150 g / m ² , and a void-containing polyester film having no heat transfer recording layer formed thereon (Example 1) were dry-laminated. After bonding with A
The sheet was cut into six sizes to form a thermal transfer image-receiving sheet.

Comparative Example 1 In longitudinal stretching of a film, both sides of the film were rated at 95
%, Except that infrared heating was performed at a current value of 1%.
A void-containing polyester film (Comparative Example 1) was obtained in exactly the same manner as described above. Further, according to the same method as in the first embodiment,
A thermal transfer image receiving sheet was prepared.

Comparative Example 2 The above-mentioned fine particles (titanium oxide) were used as a raw material for the layer B.
A void-containing polyester film (Comparative Example 2) was obtained in exactly the same manner as in Example 1, except that the content-containing master pellet was vacuum-dried alone. Further, a thermal transfer image-receiving sheet was prepared in the same manner as in Example 1.

Comparative Example 3 As raw materials of the film constituting the layer A, 10% by weight of a master pellet containing fine particles (titanium oxide) subjected to vacuum drying, 83% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 subjected to vacuum drying, and a melt Flow rate 1.
A void-containing polyester film (Comparative Example 3) was obtained in the same manner as in Example 1, except that 7% by weight of a polystyrene resin (TOPOLEX 570-57U manufactured by Mitsui Toatsu Co., Ltd.) was used as a pellet mixture. Was. Further, a thermal transfer image-receiving sheet was prepared in the same manner as in Example 1.

Example 2 The hollow particles were prepared in the same manner as in Example 1 except that zinc sulfide fine particles having an average particle diameter of 0.3 μm (electron microscopic method) were used as the fine particle-containing master pellets used in the layer B instead of the titanium oxide particles. A containing polyester film (Example 2) was obtained. In addition, the same raw material as that of Example 1 was used for the material of the layer A. Further, a thermal transfer image-receiving sheet was prepared in the same manner as in Example 1.

Example 3 The same raw material as in Example 1 was used, and the discharge amount of the B layer was divided equally into two to form the B layer on both sides of the A layer. At this time, the discharge amount of each layer was adjusted so that the discharge amount ratio of the A layer and the B layer was 85:15 by volume, and the thickness of the unstretched film was about 200 μm. The subsequent stretching and heat treatment steps were performed in the same manner as in Example 1 to obtain a 25 μm-thick void-containing polyester film (Example 3). Example 1
In the same manner as in the above, a thermal transfer image-receiving sheet was prepared.

Example 4 As raw materials for the layer B, 40% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62, 50% by weight of master pellets containing fine particles (titanium oxide) used in Example 1, and master pellets containing a fluorescent brightener (Eastman OB in polyethylene terephthalate resin with intrinsic viscosity of 0.62
-1 (2% by weight) was mixed with pellets and vacuum-dried. Except for this, an unstretched film was prepared in exactly the same manner as in Example 1.

The obtained unstretched film was uniformly heated to 83 ° C. using a heating roll, and the speed was regulated (3 m / min) by sandwiching the film between a metal roll whose temperature was controlled to 93 ° C. and a non-heated rubber roll. And speed regulation (10.2m /
Min), and stretched 3.4 times with the high-speed roll (metal roll was controlled at 30 ° C., rubber roll temperature was not controlled).
At this time, the two sets of rolls whose speeds were regulated were installed in parallel so that the interval between the speed regulation points was 25 cm, and they were arranged so that the B surface (non-drum surface) side was in contact with the rubber roll surface.
In this example, the film was heated only by the roll heating without using the auxiliary heating device.

The uniaxially stretched film thus obtained was guided to a tenter, heated to 120 ° C., stretched 3.5 times in a transverse direction, fixed in width, and subjected to a heat treatment at 220 ° C. for 5 seconds.
The film was relaxed by 4% in the width direction at 10 ° C. to obtain a void-containing polyester film (Example 4). Further, a thermal transfer image-receiving sheet was prepared in the same manner as in Example 1.

Comparative Example 4 Vacuum dried 88% by weight of polyethylene terephthalate chips having an intrinsic viscosity of 0.62, 2% by weight of polyethylene glycol flakes having a molecular weight of 4000 and polymethylpentene pellets having a melt flow rate of 180 (TPX, manufactured by Mitsui Petrochemical Co., Ltd.) DX-820) 10 wt% was added and mixed to obtain a raw material for a film constituting the layer A.

On the other hand, in the same manner as in Example 1, fine particles (calcium carbonate) containing 30% by weight of calcium carbonate particles having an average particle size of 0.8 μm (electron microscopic method) (Softon 3200, manufactured by Bihoku Powder Co., Ltd.) A master pellet was prepared, and 45% by weight of the master pellet and 55% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 were mixed and vacuum-dried to obtain a raw material of a film constituting the B layer.

The raw materials of the film constituting each layer were supplied to separate extruders, and the B layer was joined to both sides of the A layer using a feed block. In the subsequent steps, the film was stretched 3.5 times at 98 ° C., stretched 3.2 times at 125 ° C., and then heat-treated at 220 ° C. to obtain a 50 μm-thick void-containing polyester film (Comparative Example 4). Was. Also,
A thermal transfer image-receiving sheet was prepared in the same manner as in Example 1.

Comparative Example 5 The procedure of Example B was repeated except that 84% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 16% by weight of master pellets containing fine particles (titanium oxide) were mixed and vacuum-dried as a raw material for the B layer. A void-containing polyester film (Comparative Example 5) was obtained in the same manner as in Example 1. Further, a thermal transfer image-receiving sheet was prepared in the same manner as in Example 1.

Example 5 The raw material composition ratio of the film constituting the layer A was as follows: cavity forming agent / master pellet containing fine particles (titanium oxide) / polyethylene terephthalate resin having an intrinsic viscosity of 0.62 = 7/5/8
8 and the film thickness after biaxial stretching is 50
A void-containing polyester film (Example 5) was obtained in the same manner as in Example 1 except that the discharge amount of the layer B was adjusted to be μm. Further, a thermal transfer image-receiving sheet was prepared in the same manner as in Example 1.

Using a synthetic polypropylene paper (manufactured by Toyobo) having an apparent specific gravity of 0.60, a thermal transfer image-receiving sheet was prepared in the same manner as in Example 1.

[0072]

[Table 1]

From the measurement results in Table 1, the following can be considered. Since the thermal transfer image-receiving sheets using the films of Examples 1 to 5 satisfy the requirements specified in the present invention, the thermal transfer image-receiving sheets using the conventionally used polypropylene synthetic paper (Comparative Example 6) It can be seen that the thermal transfer image has excellent folding wrinkle resistance and high density. In contrast, Comparative Example 3 in which the apparent specific gravity exceeds the requirement specified in the present invention, Comparative Examples 1, 4, and 5 in which the surface cohesive failure index exceeds the requirement specified in the present invention, and the glossiness of the surface in the present invention In Comparative Example 2, which does not satisfy the requirements defined in (1), the relative image density is small, and a high-density thermal transfer image cannot be obtained.

[0074]

As described above, the present invention is to provide a void-containing polyester film having excellent surface smoothness, sufficient image density, and excellent fold wrinkle resistance and useful for an image receiving sheet. Recognize.

Claims (9)

[Claims] 1. A synthetic resin film for use in a thermal transfer image-receiving sheet having a thermal transfer recording layer formed on a composite substrate in which a synthetic resin film is bonded to one or both sides of a natural paper support, wherein the synthetic resin film is used. Consists of a polyester film containing a large number of cavities derived from a thermoplastic resin incompatible with the polyester inside the film, the apparent specific gravity is 1.3 or less, and the cohesive failure index of at least one of the surfaces is 3 or less. And a glossiness of the surface of the polyester film is 20% or more. 2. The polyester film for a thermal transfer image-receiving sheet according to claim 1, wherein the film contains a large number of cavities derived from a thermoplastic resin incompatible with polyester and has an average particle size of 0.1 to 1 μm. A polyester layer (skin layer) containing a large number of cavities derived from a polyester film bonded to the film surface, having an apparent specific gravity of 1.3 or less, and a cohesive failure index of at least one of the surfaces. Is 3 or less, and the glossiness of the surface is 20% or more. 3. The polyester film for a thermal transfer image-receiving sheet according to claim 2, wherein the void content in the skin layer is 20% by volume or more. 4. A polyester film for a thermal transfer image receiving sheet according to claim 2, wherein the skin layer has a thickness of 1 to 20 μm and less than 30% of the total thickness of the film. 5. A polyester film for a thermal transfer image-receiving sheet, wherein the fine particles added to the skin layer according to claim 2 are titanium oxide. 6. The polyester film for a thermal transfer image-receiving sheet according to claim 2, wherein the fine particles added to the skin layer according to any one of claims 2 to 4 are zinc sulfide. 7. A thermoplastic resin which is incompatible with polyester and contains at least a polystyrene resin, a polymethylpentene resin and a polypropylene resin, and the content (a weight%) of the polystyrene resin and the polymethylpentene resin. The polyester film for a thermal transfer image-receiving sheet according to any one of claims 1 to 6, wherein the content of the resin (b wt%) and the content of the polypropylene resin (c wt%) satisfy the following relationship. 0.01 ≦ a / (b + c) ≦ 1 c / b ≦ 13 3 ≦ a + b + c ≦ 20 8. A thermal transfer image-receiving sheet having a thermal transfer recording layer formed on a composite substrate in which a synthetic resin film is bonded to one or both sides of a natural paper support, wherein the synthetic resin film is used. A heat transfer image-receiving sheet using any one of the above polyester films for a heat transfer image-receiving sheet. 9. A thermal transfer image-receiving sheet having a thermal transfer recording layer formed on a composite substrate having a synthetic resin coating layer formed on one or both sides of a natural paper support, wherein the relative image density specified in the text is 95%. A thermal transfer image-receiving sheet, which is larger and has a fold wrinkle resistance defined in the text of A.