JP2000202972A - Void-containing polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a void-containing polyester film suitable as a base material of an image receiving sheet of thermal transfer, sublimation transfer or ink jet printer. SOLUTION: A void-containing polyester film containing many voids therein is constituted by bonding a void-containing polyester film (core layer) having an apparent specific gravity of 1.3 or more and containing many voids therein and a fine void-containing polyester film (skin layer) containing many fine voids originating from inorg. fine particles with an average particle size of below 1 μm. In this case, the void content in the skin layer is 20 vol.% or more and the thickness of the skin layer is l-20 μm and below 30% of the total thickness of the film and the apparent specific gravity of the whole of the film is below 1.3 and the average light moving distance thereof is 0.15 mm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a void-containing polyester film. More preferably, the present invention relates to a void-containing polyester film suitable as a base material of an image receiving sheet such as a thermal transfer, a sublimation transfer, and an ink jet printer.

[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 natural paper are bonded together or a thick polypropylene synthetic paper is used as a base material, and a recording layer is formed on these surfaces. Those provided are widely used. This is because polypropylene-based synthetic paper has a surface smoothness that cannot be obtained with natural paper, and also has an appropriate cushioning property. 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-based synthetic paper is used as the base material, the polypropylene-based synthetic paper is extremely easily plastically deformed and has poor flexibility. And there is a serious disadvantage that the quality of the printed matter is significantly impaired. On the other hand, a method using a polyester-based void-containing film instead of the polypropylene-based synthetic paper has been proposed. However, a polyester-based void-containing film generally has higher rigidity than a polypropylene-based synthetic paper and has insufficient cushioning properties.
Therefore, in order to obtain the same image density as in the case of using a polypropylene-based synthetic paper using a polyester-based void-containing film, the void content should be higher than that of the polypropylene-based synthetic paper in order to secure cushioning properties. There must be. 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. Furthermore, when the void content is increased, the production stability becomes extremely poor, so that it is extremely difficult to produce this stably on an industrial scale.

[0003]

The object of the present invention is to provide an image-receiving sheet which has the disadvantages of the prior art, namely, excellent surface smoothness, sufficient image density and sharpness, and excellent folding wrinkle resistance. It does not solve the problem of not being there.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a void-containing polyester film having a large number of voids therein, wherein the polyester film has an apparent specific gravity of 1.3 or less and contains a large number of voids inside the film. -Based film (core layer) and a polyester film (skin layer) containing fine voids containing a large number of fine voids derived from inorganic fine particles having an average particle diameter of less than 1 μm inside the film are joined, and the void content in layer B is contained. 20% by volume or more, the thickness of the B layer is 1 to 20 μm and less than 30% of the entire film thickness,
The present invention relates to a void-containing polyester film having an apparent specific gravity of less than 1.3 and an average light moving distance of 0.15 mm or less.

[0005] The polyester in the present invention is obtained by mixing an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid or an ester thereof with a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol and 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 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. The cavity derived from the thermoplastic resin incompatible with the polyester means that a cavity exists around the thermoplastic resin, and can be confirmed by, for example, a cross-sectional photograph of the film by an electron microscope. 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.

[0008] 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.

[0009] 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 such polymethylpentene is preferably 200 g / 10 min or less, more preferably 30 g / 10 min 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.

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, that is, the thermoplastic resin incompatible with the polyester, to the polyester varies depending on the desired amount of 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, in order to improve the concealing property and the like, inorganic or organic particles may be added to the film in the polyester or in the incompatible resin, if necessary. 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 void-containing polyester film of the present invention has an apparent specific gravity of 1.3 or less, preferably 1.2 or less.
More preferably, it must be 1.1 or less. And
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.

In order to significantly improve the image density during thermal transfer printing and achieve the object of the present invention, it is necessary to form cavities derived from inorganic fine particles in an amount of at least 20% by volume based on the B layer. Conversely, if the void content in the B layer is less than 20% by volume, the desired effect of improving the image density cannot be obtained.

The average particle diameter of the inorganic fine particles added to the layer B needs to be less than 1 μm, and the particularly preferable average particle diameter is 0.1 to 0.5 μm. Then, by forming cavities derived from inorganic fine particles having an average particle diameter in this range, it becomes possible to obtain a thermal transfer image excellent in gloss and image uniformity. Conversely, when inorganic fine particles having an average particle size of more than 1 μm are added to the B layer, it is relatively easy to form cavities of 20% by volume or more, but they are excellent in gloss and image uniformity. Thermal transfer images cannot be obtained.

The resulting image density is preferably 95 or more.

Further, the film containing voids of the present invention must have an average light moving distance inside the film of 0.15 mm or less, preferably 0.13 mm or less, more preferably 0.10 mm or less. If the average light moving distance exceeds 0.15 mm, the printed image will be inferior in sharpness and the image will be blurred, which is not preferable.

This average light moving distance can be usually obtained from MTF which is an index indicating the high resolution of the photographic material. A Probability Description of the Yule-Niel
senEffect II: The Impact of Halftone Geometry (Jou
rnal of Imaging Science and Technology pp637, vol
ume 41, 1997) experimentally states that the MTF and the average light travel distance have a relationship of Equation 1.

[0019]

(Equation 1) In other words, if the MTF of each frequency is found, this kp will be found. However, the MTF is usually calculated from the reflected light density of screens with different line widths and intervals (spatial frequency) placed on paper or recording film or printed directly, or the spatial frequency changes continuously. From the light having a sinusoidal function distribution using the reflection density. However, this method only requires relatively low frequencies. In particular, when kp is obtained from paper or a recording film, the error becomes very large.Therefore, the kp obtained from the method of the embodiment described later and the sharpness of the printed matter on the paper or the recording film are relatively small. Think of it as a good match.

A uniform biaxially oriented film will be described in detail by exemplifying means for achieving the dynamic hardness, gloss, and average light moving distance. First, the above-mentioned dynamic hardness 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 particularly limited, but may be 20% by volume.
It is preferable to form the above cavity. Note that the fine cavities derived from the fine particles mean that cavities exist at least partially around the fine particles, and can be confirmed by, for example, a cross-sectional photograph of the film by an electron microscope.

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 dynamic hardness of the film surface is reduced to 5. It is difficult to reduce the thermal transfer sensitivity to 0 or less, and the desired effect of improving the thermal transfer sensitivity characteristics cannot be obtained.
Conversely, when particles having an average diameter of more than 5 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.
The thermal transfer sensitivity characteristic is rather lowered. Preferably it is 0.1 to 3 μm, more preferably 0.1 to 2 μm and most preferably 0.1 to 1 μm.

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 dynamic hardness of the film surface to 5.0 or less. On the other hand, if it exceeds 50%, the smoothness of the film surface is rapidly impaired, and it is difficult to make the glossiness of the film surface 20% or more.

Further, a coloring agent, a light-proofing 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. If the thickness of the skin layer is less than 1 μm, the variation in the concentration of fine particles per surface area of the film 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 average light travel distance can be controlled by the amount and type of particles in the skin layer and the core layer, the amount of cavities, and the thickness ratio. Considering other parameters and productivity, as an example, when titanium oxide is used for the skin layer, the added amount is 20 to 40% by weight, the thickness of the skin layer is 5 to 25% of the entire thickness, Specific gravity is 0.75
A value of about 1.05 seems to be good. However, in the present invention, the raw materials can be changed without being limited to this method.

The method of producing the void-containing polyester film of the present invention is arbitrary, and is not particularly limited. For example, it can be produced as follows. First, as a method of joining the skin layer to the film surface,
It is most preferable to adopt a co-extrusion method in which the resins of the layer A and the layer B are supplied to different extruders, then laminated in a molten state and extruded from the same die.

The unstretched sheet 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 sheet are closely related to the formation of cavities. Hereinafter, the stretching / orienting conditions will be described by taking as an example a sequential biaxial stretching method most preferably used, particularly a method of stretching an unstretched sheet 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 50 ° C. to a temperature equal to or lower than the glass transition point of the polyester using a heating roll, and then the front and back sides 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 only 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 2 ° C.
00 ° C. The biaxially stretched film thus obtained is subjected to a heat treatment as necessary. The heat treatment is preferably performed in a tenter, and the melting point of the polyester is Tm-50.
It is preferable to carry out in the range of ° C. to Tm.

The void-containing film of the present invention obtained by the above-described production method contains sufficient fine voids in the skin layer and has excellent production stability. The void-containing polyester film 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 generally 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 get. To prepare a thermal transfer image-receiving sheet using the void-containing polyester film of the present invention, a recording layer for receiving ink or a diffusible (sublimable) dye migrating from the thermal transfer ink sheet is formed on the film surface. do it. 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 void-containing polyester film of the present invention may be used alone as a substrate, or may be used in combination with another substrate. Other substrates that can be combined include
Examples include, but are not limited to, natural paper, various synthetic resin films, woven fabrics, and nonwoven fabrics. Alternatively, the surface opposite to the surface on which the receiving layer is formed may be subjected to adhesive processing to be used as a heat transfer printable adhesive label.

The void-containing polyester film thus obtained is excellent in surface smoothness, sufficient image density and resolution, and excellent in folding wrinkle resistance as compared with those conventionally proposed. Labels, cards, packaging materials, maps, white boards, building materials, wallpapers, decorative boards, delivery slips, magnetic cards, electrical insulating materials, display reflectors, preferably image receiving sheets such as thermal transfer, sublimation transfer, laser beam printers, inkjet printers, etc. Optimum substrate for photographic paper.

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 cut out accurately 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 10000

2) Cavity content in layer B The thickness of layer B of the unstretched film is T1, the thickness of layer B of the biaxially stretched film is T2, and the total stretching ratio of the film = longitudinal stretching ratio × lateral stretching ratio (unstretched film) Was set as D), and was calculated by the following equation. Cavity content (%) = 100−100 × T1 / (T2 ×
D) The void content in the B layer can be measured by the above method, and can also be calculated from the B layer thickness change rate before and after heat pressing, cross-sectional observation using an electron microscope, and the like. When evaluating the void content by the heat press method, the void in the film is 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 determined by F.
(%), And the rate of weight change per unit area of the film before and after the heat press is G (%), which can be calculated by the following equation. Cavity content (%) = (F / G) × 100

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

4) Surface glossiness Using VGS-1001DP manufactured by Nippon Denshoku Industries Co., Ltd., 6
The reflectance at 0 degree was determined.

5) Thermal transfer sensitivity characteristics (relative image density) 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 crosslinking agent: 0 5.5 parts Water: 67.4 parts Isopropyl alcohol: 25 parts Surfactant: 0.1 parts After drying, apply to the film surface to a weight of 4 g / m ² , fix the size, and fix at 30 ° C at 30 ° C. The recording layer is formed by heat treatment for 2 seconds, and a thermal transfer image receiving sheet is prepared. A sample obtained by cutting the thermal transfer image-receiving sheet obtained in this way into A6 size was prepared using a commercially available ink ribbon (print set P-PS100 for a sublimation transfer printer manufactured by Caravelle Data System Co., Ltd.) and a commercially available thermal transfer printer (manufactured by Bon Electric Co., Ltd.). Thermal transfer type label printer BLP-32
Using 3), printing is performed at a printing speed of 100 mm / sec and a head voltage of 18 V. In the printing pattern, for each of the four colors of C (cyan), M (magenta), Y (yellow), and K (black) in which these are overprinted, seven square solid characters of 9 mm × 9 mm in each color (total). 28
A) A pattern arranged in the A6 sheet is used. After printing, CMY using a Macbeth densitometer (TR-927)
The reflection density of each color K is measured, and the average density of four colors (total 28 locations) is determined. Similarly, 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) in the same manner. The average density is determined, and the thermal transfer sensitivity characteristic is evaluated based on the ratio (%) of the density of the sample to the density of the commercially available image receiving paper.

6) 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

7) Cavity content in the 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, the total stretching ratio of the film = longitudinal stretching ratio × lateral stretching ratio (unstretched film) Was set as D), and was calculated by the following equation. 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 represented by F = (after heat press). B layer thickness) / (B layer thickness before heat press), and the rate of change in weight per unit area of the film before and after heat press is G = (weight per unit area after heat press) / (per unit area before heat press) Weight) can be calculated by the following equation. Cavity content (%) = 100− (F / G) × 100

8) Measurement of average light moving distance kp inside the film A dot screen is placed on the film, and the reflectance of the film portion at each dot area ratio is measured. The reflectance with respect to the area ratio is plotted, and the value of kp is determined by Equation 2 and the least squares method so that the minimum value is obtained. The value of kp at that time is defined as the average light moving distance. The measuring instrument, conditions, etc. are as follows. Screen: A in photographic emulsion on transparent polyester
M halftone created at 65 dpi. Dot area ratio should be at least every 10% from 0 to 100% and 95
Use%. Measuring device: Edmund Scientific Infiviver Video microscope to CCD camera (Sony XC-7
8) Capture the image. At this time, the magnification is set so that the width is 2 mm on a 14-inch television monitor. The image is decomposed into 512 × 384 pixels, and the reflectance distribution at each point (based on the aluminum oxide white plate) is obtained. The reflectance with the largest number of points is defined as the reflectance Rp of this sample, and plotted against each dot area ratio F. The image analysis software is IMAGELAB (Werner Frei As
sociates), but other software may be used as long as the function is satisfied.

[0045]

(Equation 2) The value of A is determined by Imaging Science (author JCDain).
ty et al., published in Academic Press), pp. 244, found the MTF of paper using a 100 μm-thick polyester film containing 5% titanium oxide (TA-300 manufactured by Fuji Titanium Co., Ltd.). Then, kp when it is most approximated to Equation 1 by the least squares method is obtained. Using this kp, the minimum value of A in the method using the screen is 0.810
And adopted it. Samples are stacked on each other so that Rp is not substantially affected by the pedestal.

9) Sharpness of image Ph with a printer (CAMEDIA P-300 manufactured by Olympus Optical)
Images from otoCD (manufactured by Kodak) were launched, and ◎ was given for clear images, ○ for virtually no problems, and × for blurred images.

Example 1 (Preparation of Cavity Forming Agent)
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) 50% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.64 and 50% by weight of anatase type titanium dioxide (TA-300 manufactured by Fuji Titanium Co., Ltd.) 50
% 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. Subsequently, 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 an intrinsic viscosity of 0.1% were used.
The polyethylene terephthalate resin of No. 62 was mixed with pellets in an amount of 85% by weight and vacuum-dried to obtain a raw material for the film constituting the layer A. On the other hand, 30% by weight of a polyethylene terephthalate resin having an intrinsic viscosity of 0.62 and 70% by weight of the above-mentioned master pellets containing fine particles (titanium oxide) were mixed and vacuum-dried to obtain a raw material for a film constituting the B layer.

(Preparation of Unstretched Film) Next, the raw materials of the films constituting the above layers 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 sheet having a thickness of about 600 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 sheet is uniformly heated to 65 ° C. using a heating roll,
The speed is regulated (2 m / min) by sandwiching the film between a metal roll whose temperature is controlled to 65 ° C. and a rubber roll whose temperature is not controlled,
Similarly, it was stretched 3.4 times with a high-speed roll (metal roll was controlled at a temperature of 30 ° C., and a rubber roll was not controlled) whose speed was regulated (6.8 m / min). 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 addition, an infrared heater having a gold reflection film at the center of the nip roll (rated 20
(W / cm) was placed opposite to both surfaces of the film (a distance of 1 cm from the film surface), the layer A surface was heated at 100% of the rated current, and the layer B surface was heated at 60% of the rated. The uniaxially stretched film thus obtained is guided to a tenter, heated to 140 ° C., stretched transversely 3.7 times, and fixed in width.
A heat treatment was performed at 220 ° C. for 5 seconds, and the film was relaxed by 4% in the width direction at 220 ° C. to obtain a 75 μm-thick void-containing polyester film (Example 1).

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.

Comparative Example 2 The procedure of Example B was repeated except that 84% by weight of a 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 layer B. A void-containing polyester film (Comparative Example 2) was obtained 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 were used. Flow rate 1.
A polystyrene resin (Comparative Example 3) was prepared in the same manner as in Example 1 except that 7% by weight of a polystyrene resin (TOPOREX 570-57U manufactured by Mitsui Toatsu Co., Ltd.) was used. Obtained.

Example 2 The hollow particles were hollowed out in the same manner as in Example 1 except that zinc sulfide fine particles having an average particle size 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 polyester-containing 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.

Example 3 The discharge ratio of the layer A and the layer B was changed to 85 to 15 by volume,
Layer B1 (non-drum surface) / layer A / layer B2 (drum surface) in the same manner as in Example 1 except that the discharge amount of layer B is equally divided into two to form layer B on both sides of layer A. An unstretched sheet having the structure was prepared. The subsequent stretching and heat treatment steps were carried out in exactly the same manner as in Example 1 to obtain a void-containing polyester film (Example 3).

Example 4 As raw materials for 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 whitening agent (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 sheet was uniformly heated to 83 ° C.
The speed is controlled (2 m / min) by sandwiching the film between a metal roll and a non-heated rubber roll whose temperature is controlled to ℃, and the speed is similarly controlled (6.8 m / min). Rubber roll temperature is not controlled)
Stretched 3.4 times. 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 is guided to a tenter, heated to 130 ° C., stretched 3.5 times in a transverse direction, fixed in width, subjected to a heat treatment at 220 ° C. for 5 seconds, and further heated at 220 ° C. in the width direction. It was relaxed by 4% to obtain a void-containing polyester film (Example 4).

Comparative Example 4 Vacuum-dried polyethylene terephthalate chips having an intrinsic viscosity of 0.62 and 88% by weight of polyethylene terephthalate chips, 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. 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, a master pellet containing fine particles (calcium carbonate) containing 30% by weight of calcium carbonate particles (Bihoku Powder Co., Ltd., Softon 3200) having an average particle diameter of 0.8 μm (electron microscopic method) was prepared. Then, 45% by weight of this 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 for a film constituting the B layer. The raw materials of the film constituting each layer are supplied to separate extruders,
Layer B was bonded to both sides of layer A using a feed block. In the subsequent steps, longitudinal stretching was performed 3.5 times at 98 ° C., 3.2 times transverse stretching at 125 ° C., and heat treatment was performed at 220 ° C. by a conventional method to obtain a void-containing polyester film (Comparative Example 4).

Example 5 The raw material composition ratio of the film constituting the layer A was as follows: cavity forming agent / fine pellet (titanium oxide) -containing master pellet / polyethylene terephthalate resin having an intrinsic viscosity of 0.62 = 7/5/8
A void-containing polyester film (Example 5) was obtained in exactly the same manner as in Example 1 except that the film was set to 8. Table 1
Can be considered as follows from the measurement results of The thermal transfer recording sheet using the films of Examples 1 to 5 as the base material satisfies the requirements defined in the present invention, and therefore has excellent surface smoothness and fold wrinkle resistance, and has a high-density thermal transfer image. It turns out that it can be obtained. On the other hand, Comparative Example 3 in which the apparent specific gravity exceeds the requirement specified in the present invention, Comparative Examples 1, 2, and 4, in which the surface void content satisfies the requirement specified in the present invention, the relative image density is small. It can be seen that a high-density thermal transfer image cannot be obtained. Further, the relationship between the average light moving distance and the sharpness of the actual image can be understood.

[0059]

According to the present invention, there is provided a void-containing polyester film having excellent surface smoothness and sufficient image density and resolution.

[0060]

[Table 1]

[0061]

[Table 2]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08J 9/00 CFD C08K 3/20 4J002 C08K 3/20 3/30 3/30 C08L 67/02 C08L 67 / 02 B29C 55/02 // B29C 55/02 B41M 5/26 H (C08L 67/02 25:04 23:10 23:00) B29K 67:00 105: 04 B29L 7:00 9:00 F term (reference) 2H111 AA01 AA26 AA27 CA13 CA14 CA25 CA31 CA33 CA41 CA43 CA45 4F071 AA20 AA21 AA22 AA45 AA46 AB18 AB21 AB23 AB26 AB30 AH16 BA01 BB06 BB08 BC01 4F074 AA24 AA26 AA32 AA65 AC17 AC29 CA01 DA21A01 DA23A01 DA23A23 AK12A AK12B AK41A AK41B BA02 BA25 DE01B DJ03A DJ06B EH20 EH202 EJ38 EJ382 GB90 JA13 JK15 YY00 YY00B 4F210 AA12 AA13 AA24 AB12 AG01 AG03 AG20 AH53 QA02 QA03 QC06 QG01 QG15 4J002 BB124 BB173 BC032 CF001 CF051 CF061 CF071 CF081 CH072 DE136 DE146 DE236 DG026 DG046 DJ016 DJ036 DJ046 FD016 GQ00 GS00

Claims (6)

[Claims] Claims: 1. A void-containing polyester film containing a large number of voids therein, which is derived from a void-containing polyester film (core layer) containing a large number of voids inside the film and inorganic fine particles having an average particle diameter of less than 1 μm. A polyester film (skin layer) containing fine cavities containing a large number of fine cavities inside the film is joined, the void content of the skin layer is 20% by volume or more, and the thickness of the skin layer is 1 to 20%.
μm and less than 30% of the total thickness of the film, the apparent specific gravity of the entire film is less than 1.3, and the average light moving distance is 0.3 mm.
A void-containing polyester film having a thickness of 15 mm or less. 2. A void-containing polyester film, wherein the fine particles added to the skin layer according to claim 1 are titanium oxide. 3. A void-containing polyester film, wherein the fine particles added to the skin layer according to claim 1 are zinc sulfide. 4. A thermoplastic resin incompatible with polyester containing at least a polystyrene resin, a polymethylpentene resin and a polypropylene resin, wherein the polystyrene resin content (a wt%) and the polymethylpentene resin The void-containing polyester film according to claim 1, 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 5. The film according to claim 1, wherein the film contains fine cavities by being oriented at least uniaxially. 6. A void-containing polyester film containing a large number of voids derived from a thermoplastic resin incompatible with polyester inside the film, wherein the relative image density specified in the text is greater than 95%, and The void-containing polyester film according to any one of claims 1 to 5, wherein the wrinkle resistance defined in the above is A.