JP2006028523A - Pore-containing polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film having both excellent characteristics (light weight, cushionability and the like) originating from a pore-containing structure and good handleability (conveyability). <P>SOLUTION: The pore-containing polyester film comprises many pores originating from a thermoplastic resin non-compartible with a polyester resin, wherein the film which is stored under the condition of the following (a) or (b) is cut out and a curl value after heat treating at a (Tg+30)°C for 30 minutes in a no load state of the cut film is 1.0 mm or less. The film is (a) cut on 500 mm in four directions and stored 6 months at a room temperature, and the film (b) which winds 1,000 m in a rolled form around tube 6 inch in diameter is stored 3 months at a room temperature. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a void-containing polyester-based film with less curling, and more particularly to a void-containing polyester-based film that is excellent in handling properties during post-processing and paper supply / discharge properties and is suitable for various printing and card films.

  Synthetic papers mainly made of synthetic resins have been developed in various applications because they are excellent in water resistance, surface gloss, printability due to a smooth surface, and the like. In particular, polyester resins typified by polyethylene terephthalate have characteristics of high heat resistance and high rigidity among synthetic paper raw materials, and are expanding the range of use.

Moreover, the cushioning property expressed by the cavity-containing structure is widely used as various printing films including thermal transfer printing applications (see, for example, Patent Document 1).
JP-A 63-280687

  Examples of the void-containing polyester film used for such applications include those in which voids are formed around the particles by mixing and stretching inorganic fine particles in the polyester, thermoplastic resins that are incompatible with the polyester resin, and the like. A method of mixing and dispersing in polyester and using it as a nucleus for forming cavities is known. In particular, the latter is widely used because it can reduce the weight of the film.

As the cavity forming agent used for the cavity formation, polyolefin resins typified by polypropylene resin and polymethylpentene resin, polystyrene resins and the like have been proposed (for example, see Patent Documents 2 to 4). .
JP 49-34755 A Japanese Patent Publication No.49-2016 Japanese Patent Publication No.54-2955

  In particular, the use of a base film for an IC card or various cards requires a relatively thick film having a thickness of 50 μm or more, preferably 100 μm or more, because it requires waist strength and high concealment. The film used for such applications is desired to have excellent flatness and little curl.

  This is because, when a curled film is used during high-speed handling in various printing methods or the like, problems such as poor printing due to poor feedability or poor transportability such as paper jams occur.

  Usually, the film is stored in the form of a roll, but if the film is stored for a long time, curling gradually becomes tighter on the inner side of the winding, so-called curled curl. The curl curl can be removed by heat treatment while keeping it flat, but it is desirable to use it without heat treatment in terms of cost.

  In white polyester films that contain white pigments such as titanium oxide and calcium carbonate and that do not contain cavities due to thermoplastic resins that are incompatible with polyester resins, and normal transparent polyester films, curl curls are very likely to occur. It is very gradual and very rare.

  On the other hand, with a void-containing polyester film containing a large number of voids derived from a thermoplastic resin incompatible with the polyester resin inside the film, it is very difficult to obtain a film with little curl by the conventional technology. .

  Because, in the production of a thick biaxially stretched film, the unstretched film becomes very thick first, so the cooling on the cooling roll is clearly different between the cooling surface and the opposite side. The resulting structure will be different on the front and back of the film.

  Furthermore, since it is a void-containing polyester film containing fine cavities inside, the size, shape and volume fraction of the cavities easily change over the thickness direction of the film, so the physical properties and structure of the film front and back are the same. Such films are extremely difficult to manufacture.

  As mentioned above, the difference in structure between the front and back of the film is likely to occur, and because of the structure containing voids inside, curl easily develops due to the subtle difference in the structure between the front and back of the film, and the curl is also at a high speed. Since it increases, the passability in a printing process will deteriorate remarkably. Such a thick void-containing polyester-based film is likely to curl, and it has been very difficult to stably produce at a low curl value.

  The object of the present invention is to provide a film that eliminates the above-mentioned drawbacks of the prior art and has both excellent properties (light weight, cushioning properties, etc.) derived from the cavity-containing structure and good handling properties (transportability). is there.

  This invention was made | formed in view of the above situations, Comprising: The cavity containing polyester-type film which could solve said subject is as follows.

A first invention of the present invention is a void-containing polyester-based film containing a large number of voids derived from a thermoplastic resin incompatible with a polyester resin inside the film, under the following conditions (a) or (b) A void-containing polyester film characterized by having a curl value of 1.0 mm or less after heat-treating the cut film for 30 minutes at (Tg + 30) ° C. in an unloaded state. is there.
(A) Cut to 500 mm square and stored for 6 months at room temperature (b) Stored 1000 m in a roll on a 6 inch diameter tube for 3 months at room temperature

  A second invention is the void-containing polyester film according to the first invention, wherein the void-containing polyester film has a thickness of 50 to 500 μm.

  As described above, the void-containing polyester film of the present invention reduces the difference in physical properties due to the difference in structure between the front and back of the film, and has a curl value of 1 mm or less after heat treatment at no load (Tg + 30 ° C.) for 5 minutes. Therefore, naturally, before storing the film, even if the film is stored in a roll shape for a long time, there is a feature that curl curl is small.

  The polyester in the present invention is an esterification reaction between an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid or an ester thereof and a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol or neopentyl glycol. Alternatively, it is a polyester produced by polycondensation after a transesterification reaction. These polyesters may be subjected to a direct esterification reaction between an aromatic dicarboxylic acid and a glycol, followed by polycondensation, or an ester exchange reaction between an alkyl ester of an aromatic dicarboxylic acid and a glycol, followed by polycondensation, or It can be produced by a method such as polycondensation of diglycol ester of aromatic dicarboxylic acid.

  Typical examples of the polyester include polyethylene terephthalate, polyethylene butylene terephthalate, and polyethylene-2,6-naphthalate. This polyester may be a homopolymer or a copolymer of a 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. preferable.

  The voids in the void-containing polyester film of the present invention are obtained by mixing and dispersing a polyester resin and an incompatible thermoplastic resin or the like in the polyester and stretching the unstretched film obtained by extrusion into a sheet at least in a uniaxial direction. Can be formed.

  When a polyester resin and an incompatible thermoplastic resin are used as the core for forming a cavity, examples of the thermoplastic resin incompatible with the polyester resin include polystyrene resins, polyphenylene ether resins, and polyolefin resins. However, it is not limited to these.

  Polystyrene resin refers to a thermoplastic resin containing a polystyrene structure as a basic structural unit. In addition to homopolymers such as atactic polystyrene, syndiotactic polystyrene, and isotactic polystyrene, other components are grafted or block copolymerized. Modified resins, such as impact-resistant polystyrene resins and modified polyphenylene ether resins, and mixtures of thermoplastic resins having compatibility with these polystyrene resins, such as polyphenylene ether, are included.

  The polymethylpentene resin is a polymer having units derived from 4-methylpentene-1 at 80 mol% or more, preferably 90 mol% or more, and other components include ethylene units, propylene units, butene- Examples are 1 unit, units derived from 3-methylbutene-1, and the like. The melt flow rate of such polymethylpentene is preferably 200 g / 10 min or less, particularly preferably 30 g / 10 min or less. This is because when the melt flow rate exceeds 200 g / 10 min, it is difficult to obtain the effect of reducing the weight of the film.

  In addition to the homopolymers such as isotactic polypropylene and syndiotactic polypropylene, the polypropylene resins include modified resins obtained by grafting or block copolymerizing other components.

  As the presence state of the polypropylene resin, the above polypropylene resin may be used separately from the polymethylpentene, or a propylene unit introduced into the polymethylpentene resin as a copolymerization component is used. It doesn't matter.

  The mixing amount of these cavitation agents, that is, a thermoplastic resin incompatible with the polyester resin, with respect to the polyester varies depending on the desired amount of cavities, but is in the range of 3 to 20% by weight with respect to the entire film. Preferably, 5 to 18% by weight is preferable. And if it is less than 3 weight%, there exists a limit in increasing the production amount of a cavity. On the other hand, if it is 20% by weight or more, the stretchability of the film is remarkably impaired, and the heat resistance, strength, and waist strength are impaired.

  In addition, in the film, inorganic or organic particles may be included in the polyester resin or incompatible resin as necessary in order to improve the concealability and the like. Examples of the particles include silica, kaolinite, talc, calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, titanium oxide, zinc sulfide, and organic white pigment, but are not particularly limited. Absent.

  The void-containing polyester film of the present invention has an apparent specific gravity of 1.30 or less, more preferably 1.20 or less, and most preferably 1.15 or less. When the apparent specific gravity exceeds 1.30, the amount of voids inherent in the film is too small, so that excellent properties (for example, light weight, cushioning properties, etc.) obtained by the void-containing structure are insufficient.

  On the other hand, the lower limit of the apparent specific gravity is not particularly limited. However, an apparent specific gravity of less than 0.80 is not preferable because the handling properties of the film are remarkably lowered.

  As a more preferable film material for making the apparent specific gravity of the film 1.30 or less, for example, polyethylene terephthalate resin is 80.0 to 98.0% by weight, polystyrene resin is 0.5 to 10.0% by weight, polypropylene Examples thereof include a composition comprising 0.5 to 10.0% by weight of resin, 0.5 to 10.0% by weight of polymethylpentene resin, and 0.5 to 20.0% by weight of titanium oxide particles.

  The void-containing polyester film of the present invention may be a single layer or a multilayer structure in which the same or different synthetic resin film layers are combined. The synthetic resin film layer used for the composite is obtained by, for example, a co-extrusion method, but can also be formed by a lamination method through a coating method, an adhesive layer, or the like.

  As the synthetic resin film, for example, a film mainly composed of one or more of polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polyarylate or polyimide can be used, but is not limited thereto. .

  Further, the synthetic resin film layer may contain a colorant, a light fastness agent, a fluorescent agent, an antistatic agent, and the like as necessary.

    The method for producing the void-containing polyester film of the present invention is arbitrary and is not particularly limited. For example, after forming a mixture of the above composition into a film shape to obtain an unstretched film, A general method of stretching in at least a uniaxial direction can be used.

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

  First, in the first-stage longitudinal stretching step, stretching is performed between two or many rolls having different peripheral speeds. As a heating means at this time, a method using a heating roll or a method using a non-contact heating method may be used, or they may be used in combination. However, in order to develop a large number of cavities at the incompatible resin interface, the stretching temperature is stretched 3 to 5 times at the secondary transition temperature Tg to (Tg + 50 ° C.) of the polyester. Next, the uniaxially stretched film is introduced into a tenter, and is stretched 2.5 to 5 times in the width direction at a temperature of the secondary transition temperature Tg to (melting point Tm-10 ° C. or lower) of the polyester.

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

  The fine void-containing polyester film of the present invention may have a coating layer on at least one surface thereof. By providing the coating layer, it is possible to improve the paintability and adhesion of ink and coating agent.

  The compound constituting the coating layer is preferably a copolyester resin, but in addition to this, it is disclosed as a means for improving the adhesion of a normal polyester film, such as a polyurethane resin, a polyester urethane resin, or an acrylic resin. The compound etc. which are present are applicable.

  As a method for providing the coating layer, conventionally used methods 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, and a reverse roll coating method can be applied.

  As a step of applying, any method such as a method of applying before stretching of the film, a method of applying after longitudinal stretching, and a method of applying to the film surface after the orientation treatment is possible.

  The fine void-containing polyester film thus obtained has excellent characteristics (light weight, cushioning properties, etc.) derived from the void-containing structure and good handling properties (transportability).

  In addition, it does not require a surfactant or polyether resin as a dispersant for polyolefin resins, so it has excellent heat resistance, small change in color tone even when reused self-recovery materials, and stable film production. Also excellent in properties. A preferable use ratio when reusing the self-collecting raw material is 5 to 50% by weight of the whole film.

  The void-containing polyester film that contains many voids derived from a thermoplastic resin that is incompatible with the polyester resin inside the film makes it easy to curl due to subtle structural differences between the front and back surfaces due to the structure containing voids inside. In addition, since the curl is also increased at a high speed, the passability in the printing process which is the subject of the present invention is remarkably deteriorated.

  However, since the curl value of the film of the present invention after heat treatment at (Tg + 30) ° C. for 30 minutes in an unloaded state is 1 mm or less, curl before storage naturally suppresses curl curl due to roll storage. it can. In other words, the subsequent increase in curling can be suppressed by producing the void-containing polyester film by strictly controlling it in a state of essentially zero curl.

  Further, even if the curl immediately after stretching is large, it can be wound in the reverse direction and stored, and the curl can be apparently made zero by applying a curl in the reverse direction. However, even if the apparent curl is made zero by this method, the curl component may disappear due to the heat of the printing process, and the initial large curl may cause printing failure. From this point, the initial curl value is strictly limited. It is important to keep control.

  In order to produce the film of the present invention, a special production method is required in addition to the production methods described above.

  As a technique for suppressing curling immediately after film production, (1) a method for suppressing the occurrence of curling by resisting internal strain by reducing the volume fraction of the cavities and suppressing the size of each cavity, (2) A method of providing a distribution of cavities in the film thickness direction, (3) Curling due to structural differences between the front and back of the film that are imparted in each step starting from a difference in crystallinity in the film thickness direction due to a cooling difference during extrusion. In order to control the film, a method in which a structural difference between the front and back surfaces of the film is positively generated and complemented with an inevitable structural difference to bring the curl value close to zero is suitable.

  Specifically, the degree of orientation of the film front and back is controlled independently by setting the temperature or heat quantity of the film front and back to different values in the stretching process and heat setting process such as longitudinal stretching and lateral stretching, and the structure of the film front and back By adopting conditions that balance the physical properties, zero curl film formation is realized.

  In addition, as a basic requirement for stable production in a state where the curl is low over the entire width, it is also important to form cavities with little change in the film thickness direction by a stretching formulation with little thickness unevenness.

  More specifically, for the longitudinal curl immediately after film formation, the structural difference between the front and back of the film during longitudinal stretching is controlled, and the lateral curl is controlled by controlling the structural difference between the front and back of the film during lateral stretching and heat setting. Creates internal distortion in the opposite direction, balances with the internal distortion caused by the structural difference between the front and back of the film, and suppresses curling.

  If it is a film of this invention, even if it rolls and preserve | saves, since the progression of curl curl can be suppressed, the outstanding characteristic derived from a cavity containing structure and favorable handling property are obtained.

  Next, the manufacturing method of the film of this invention is demonstrated in detail using an Example and a comparative example. Moreover, the evaluation method of the characteristic used by this invention is shown below.

(1) Glass transition temperature (Tg)
The sample (10 mg) is heated at a rate of temperature increase of 10 ° C./min using DSC (manufactured by DuPont, V4.OB2000 type), and the glass transition temperature is measured.

(2) Curl value The film was cut to 100 mm in the longitudinal direction and 50 mm in the width direction, conditioned for 1 day at a temperature of 23 ° C. and a humidity of 55 RH%, and then on a horizontal glass plate with the convex part of the film facing down. The vertical distance between the glass plate and the lower end of the four corners of the rising film was measured with a ruler in units of a minimum graduation of 0.5 mm, and the average value of the measured values at these four locations was taken as the curl value. Three samples were prepared and repeatedly measured, and the average value was taken as the curl value.

(3) Film handling (sheet-fed film transportability)
Prepare a mixture of water and isopropyl alcohol (70/30; weight ratio)
(A) Copolyester resin (Toyobo Co., Ltd., Vylonal MD1200) 92 parts by weight (B) Antistatic agent (Matsumoto Yushi Co., Efcol 214) 2 parts by weight (C) Organic particles (Nippon Shokubai Co., Ltd., Epostor S6 ) Disperse 5 parts by weight sufficiently in the mixed solution using a homogenizer, and adjust the total solid concentration of (A), (B), (C) to 3% by weight with respect to the total amount of the coating solution. The prepared coating solution was prepared.

This coating solution was applied to the film surface by a bar coating method to 8 g / m ² , then dried at 160 ° C. for 2 minutes, and 100 pieces of A4 size cut were prepared. This sample was subjected to a laser beam printer (Canon LBP430) and a conveyance test was performed. The handling property was evaluated according to the following three criteria based on the frequency of occurrence of conveyance failures such as creases, wrinkles, and paper jams caused by this test.

○: No conveyance failure occurred in 100 sheets Δ: Occurrence of conveyance failure in 100 sheets 1 time or more and less than 5 times ×: Generation of conveyance defects in 100 sheets 5 times or more

(4) Apparent specific gravity According to JIS K-7112 floating and sinking method.

(5) Intrinsic viscosity of polyester The polyester was dissolved in a mixed solvent of 60% by weight of phenol and 40% by weight of 1,1,2,2-tetrachloroethane, and the solid content was substantially filtered, and then measured at 30 ° C. .

Example 1
(Manufacture of master pellets)
As raw materials, 70% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g and 6% by weight of polystyrene resin (Topolex 570-57U, manufactured by Mitsui Toatsu Co., Ltd.) with a melt flow rate of 2.0 g / 10 min, melt flow Polyethylene pentene resin (TPI, DX made by Mitsui Petrochemical Co., Ltd.) and 6% by weight of polypropylene resin (Mitsui Toatsu Co., Ltd., Nobrene FO-50F) with a rate of 1.7 g / 10 min and a melt flow rate of 8 g / 10 min. -845) 18 wt% of the pellets were mixed, supplied to a twin screw extruder and kneaded sufficiently, and the strand was cooled and cut to produce a master pellet (A) containing a cavity forming agent.

  In addition, 50 wt% of anatase-type titanium dioxide particles (TA-300, manufactured by Fuji Titanium Co., Ltd.) having an average particle size of 0.3 μm are added to 50 wt% of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g produced by a known method. The mixture was supplied to a vent type twin screw extruder and pre-kneaded. This molten resin was continuously supplied to a vent type single-screw kneader, kneaded and extruded. The obtained strand was cooled and cut to produce a titanium dioxide-containing master pellet (B).

  Next, 63% by weight of polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g, 25% by weight of the above-mentioned cavity forming agent-containing master pellet (A), and 12% by weight of master pellet (B) are mixed in a pellet and vacuum dried. Was used as a raw material for the film.

(Manufacture of unstretched film)
Next, the raw material of the above film is supplied to an extruder, and is extruded onto a cooling drum adjusted to 30 ° C. using an extrusion line provided with a static mixer immediately before the T die, and is about 1900 μm thick. A stretched film was prepared. The residence time after kneading was 5.3 minutes, and cooling was performed by blowing cold air adjusted to 20 ° C. on the opposite surface of the cooling drum.

(Manufacture of biaxially stretched film)
The obtained unstretched film is uniformly heated to 65 ° C. using a heating roll, and 3.4 between two pairs of nip rolls (low speed roll: 1 m / min, high speed roll: 3.4 m / min) having different peripheral speeds. Stretched twice. At this time, as an auxiliary heating device for the film, an infrared heater (rated: 40 W / cm) provided with a gold reflective film in the middle part of the nip roll was placed opposite to both sides of the film (a distance of 1 cm from the film surface). Was heated at 18 W / cm and the opposite surface was heated at 12 W / cm. After longitudinal stretching, the film was quenched rapidly in a water bath adjusted to 15 ° C. The uniaxially stretched film thus obtained was guided to a tenter, heated to 140 ° C. and transversely stretched 3.6 times, fixed in width, subjected to heat treatment at 230 ° C. for 5 seconds, and further at 210 ° C. in the width direction. To 5% to obtain a void-containing polyester film having a thickness of 188 μm. The temperature difference between the front and back of the film in the stretched part was controlled at 10 ° C., and the temperature difference between the front and back of the film in the heat setting section was controlled within 3 ° C. The Tg of the film was 78 ° C.
(Save)
The film was stored in a 500 mm square immediately after film formation and stored at room temperature for 6 months. The curl value and handleability after the heat treatment were investigated for those subjected to the above storage.

Comparative Example 1
During the production of the unstretched film, no air cooling was performed on the film surface on the opposite side of the cooling drum. During longitudinal stretching, the roll preheating temperature was 60 ° C., and infrared heating was performed at 21 W / cm on one side and 21 W / cm on the opposite side. The film after longitudinal stretching was alternately cooled on the front and back of the film with a cooling roll having a roll surface temperature of 45 ° C. The transverse stretching temperature was 130 ° C., and the heat treatment temperature after fixing the width was 210 ° C. The maximum temperature difference between the front and back of the film in the tenter was 10 ° C. Other than that, a void-containing polyester film was obtained in the same manner as in Example 1. The Tg of the film was 78 ° C. For storage, it was cut into a 500 mm square immediately after film formation and stored at room temperature for 6 months. The curl value and handling property of the film after the heat treatment were investigated for those subjected to the above storage.

Example 2
The roll preheating temperature for longitudinal stretching was set to 70 ° C., and the film was immediately stretched 3.4 times. Infrared heating was performed at 15 W / cm on one side and 10 W / cm on the opposite side. After longitudinal stretching, the film was quenched rapidly in a water bath adjusted to 15 ° C. Other than that, a void-containing polyester film was obtained in the same manner as in Example 1. The Tg of the film was 78 ° C. Immediately after the film formation, a roll of 1000 m in a 6-inch diameter tube was stored at room temperature for 3 months. The curl value and handleability after the heat treatment were investigated for those subjected to the above storage.

Reference example 1
During the production of the unstretched film, no air cooling was performed on the film surface on the opposite side of the cooling drum. During longitudinal stretching, the roll preheating temperature was 62 ° C., and infrared heating was performed at 19 W / cm on both sides. The film after the longitudinal stretching was alternately cooled on the front and back of the film with a cooling roll having a roll surface temperature of 48 ° C. The transverse stretching temperature was 125 ° C., and the heat treatment temperature after fixing the width was 215 ° C. The maximum temperature difference between the front and back of the film in the tenter was 10 ° C. Other than that, a void-containing polyester film was obtained in the same manner as in Example 1. The Tg of the film was 78 ° C. Immediately after film formation, a roll of 1000 m in a 6-inch diameter tube was stored at room temperature for 6 months. The curl value and handleability after the heat treatment were investigated for those subjected to the above storage.

Comparative Example 2
During the production of the unstretched film, no air cooling was performed on the film surface on the opposite side of the cooling drum. During longitudinal stretching, the roll preheating temperature was 75 ° C., and infrared heating was performed at 17 W / cm on both sides. The film after the longitudinal stretching was alternately cooled on the front and back of the film with a cooling roll having a roll surface temperature of 48 ° C. The transverse stretching temperature was 150 ° C., and the heat treatment temperature after fixing the width was 230 ° C. The maximum temperature difference between the front and back of the film in the tenter was 15 ° C. Other than that, a void-containing polyester film was obtained in the same manner as in Example 1. The Tg of the film was 78 ° C. Immediately after the film formation, a roll of 1000 m in a 6-inch diameter tube was stored at room temperature for 3 months. The curl value and handleability after the heat treatment were investigated for those subjected to the above storage.

  Table 1 shows the measurement results of the void-containing polyester film obtained by the above method.

  From the measurement results in Table 1, it can be considered as follows. It can be seen that the films of Example 1 and Example 2 satisfying the requirements defined in the present invention can provide good handling properties while maintaining excellent properties (light weight: apparent specific gravity) due to the void-containing structure. In contrast, the films of Comparative Examples 1, 2, and 3 having a curl value of 1 mm or more after heat treatment at (Tg + 30) ° C. for 30 minutes under no load frequently caused poor conveyance during a conveyance test using a printing press. .

  The void-containing polyester film of the present invention has excellent properties derived from the void-containing structure (lightweight, cushioning property) because the curl curl is small even when the film is stored in a roll shape for a long period of time before storing the film. In addition, it is possible to obtain good handling properties (transportability) while maintaining printing suitability, etc., and in particular use for using a hollow-containing polyester film having a thickness of 50 to 500 μm (for various printing, for cards, etc. Suitable as a base film).

Claims (2)

A void-containing polyester-based film containing a large number of voids derived from a thermoplastic resin incompatible with the polyester resin inside the film, and the film stored under the conditions (a) or (b) below is cut out, A void-containing polyester film, wherein the cut film has a curl value of 1.0 mm or less after being heat-treated at (Tg + 30) ° C. for 30 minutes under no load.
(A) Cut to 500 mm square and stored for 6 months at room temperature (b) Stored 1000 m in a roll on a 6 inch diameter tube for 3 months at room temperature   The void-containing polyester film according to claim 1, wherein the void-containing polyester film has a thickness of 50 to 500 µm.