JP2006104397A - Polyester film for transfer type image protecting film base material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film for a transfer type image protecting film base material which excels in the balance between surface smoothness and handling properties and can maintain high surface glossiness after transfer of a protecting layer. <P>SOLUTION: The film has a thickness of ≤6 μm, an arithmetic mean roughness (Ra) of at least one film surface of 0.031-0.045 μm, a rate of change in length in the longer direction of the film at the point of time of reaching 200°C of -1.5% to +1.0%, and a surface orientation of the film of ≥0.165. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polyester film, and more particularly to a polyester film for a substrate of a transfer type image protection film that provides a high gloss image.

  Biaxially oriented polyester film has various properties such as mechanical properties, heat resistance, electrical properties, chemical resistance, etc. in a highly balanced manner and is excellent in cost performance. It is widely used as industrial materials such as industrial use. In recent years, in particular, the demand for materials for various printing media has increased.

  For example, as represented by the use of the sublimation type thermal transfer system, it is possible to realize a high quality image by transferring a dye from a ribbon-shaped film to an image receiving paper. In addition, in order to provide long-term image quality maintenance (for example, weather resistance, light resistance, etc.) comparable to conventional silver salt photographs, a protective layer is provided on the transferred image. In general, a protective layer is provided on the ribbon-like film in parallel with the dye layers of the respective colors, and the protective layer is transferred to the image side by heating from the back surface of the substrate.

However, if the base material of the ribbon for transferring the protective layer is roughened, the protective layer at the interface becomes rough when the base material and the protective layer before transfer are laminated. Becomes the surface of the protective layer after transfer, and the unevenness of the surface causes irregular reflection of light, so that the glossiness is lowered and the image quality is impaired. It is easy to imagine that the surface of the base material is smoothed to increase the glossiness. However, when the surface is smoothed in a thin film, the winding characteristics are drastically reduced due to the handling of the process. Inappropriate.
JP-A-11-321130 JP 2003-341239 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is a transfer type image that has an excellent balance between smoothing of the surface and handling properties and can maintain high glossiness of the surface after transfer of the protective layer. It is providing the polyester film for base materials of a protective film.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by a film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is that the film thickness is 6 μm or less, the arithmetic average roughness (Ra) of at least one side of the film is 0.031 to 0.045 μm, and the film has a longitudinal direction at the time of reaching 200 ° C. The length change rate is -1.5% to + 1.0%, and the plane orientation degree of the film is 0.165 or more.

Hereinafter, the present invention will be described in detail.
The polyester constituting the film of the present invention refers to a polyester having 80% or more of repeating units having an ethylene terephthalate unit or an ethylene-2,6-naphthalate unit. Such a polyester is usually a method in which a polycondensation reaction is carried out via a transesterification reaction using a lower alkyl ester of an aromatic dicarboxylic acid and a glycol as main starting materials, or a main starting material of an aromatic dicarboxylic acid and a glycol. The raw material can be obtained by a method of performing a polycondensation reaction via an esterification reaction. In order to perform these reactions, a method of adding a metal compound as a catalyst is usually used. For example, compounds such as Ca, Mg, Mn, and Li are generally used as transesterification catalysts, and compounds such as Sb, Ti, Ge, Sn, and Co are commonly used as polycondensation reaction catalysts. Further, the polyester of the present invention may contain other third component without departing from the scope of the present invention. As the aromatic dicarboxylic acid component, for example, in addition to terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxyethoxybenzoic acid, etc.) ) Etc. can be used. As the glycol component, in addition to ethylene glycol, for example, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like can be used.

  The intrinsic viscosity of the polyester used in the present invention is usually 0.45 or more, preferably 0.50 to 1.0, more preferably 0.52 to 0.80. If the intrinsic viscosity is less than 0.45, there may be a problem that productivity at the time of film production is lowered or the mechanical strength of the film is lowered. On the other hand, it is preferable that the intrinsic viscosity does not exceed 1.0 from the viewpoint of the melt extrusion stability of the polymer.

  The polyester film of the present invention has a thickness of 6 μm or less. 5 μm or less is preferable from the viewpoint of capacity as a final product, and 3 μm or more is preferable from the viewpoint of winding yield during film production.

  For the purpose of smoothness, the polyester film of the present invention needs to have an arithmetic average roughness (Ra) of at least one side of 0.031 to 0.045 μm, preferably 0.033 to 0.038 μm. The arithmetic average roughness (Ra) will be described in detail in the section of the best mode for carrying out the invention. When the arithmetic average roughness (Ra) exceeds 0.045 μm, the glossiness of the image after the transfer of the protective layer is inferior, which is inappropriate. Moreover, if arithmetic mean roughness (Ra) is less than 0.031 micrometer, the winding characteristic of a base material base will deteriorate and it is unpreferable.

  Of course, the surface opposite to the smooth surface may be roughened from the viewpoint of improving the winding characteristics. In this case, it is proposed to take a laminated structure having a smooth layer and a roughened layer when the polyester is melt extruded.

  One of the features of the present invention is to provide specific characteristics in the process of forming a polyester film for the purpose of improving thermal characteristics. That is, the rate of change of the film length in the longitudinal direction when reaching 200 ° C. needs to be −1.5% to + 1.0%, and the degree of plane orientation needs to be 0.165 or more. The rate of change of the film length in the longitudinal direction and the degree of plane orientation when reaching 200 ° C. will be described in detail in the section of the best mode for carrying out the invention. When the rate of change of the film length in the longitudinal direction at the time of reaching 200 ° C. is outside the range of −1.5% to + 1.0% or the plane orientation degree is less than 0.165, when the substrate is heated When the film stretches or shrinks, the ribbon is deformed when the protective layer is transferred, the peeling at the interface between the protective layer and the substrate becomes uneven, the unevenness is increased, the gloss of the final image is lowered, and the Is appropriate. The rate of change of the film length in the longitudinal direction when reaching 200 ° C. is preferably −0.5% to + 0.5%. The degree of plane orientation is preferably 0.167 or more, more preferably 0.170 or more.

  In the present invention, as a suitable application, for example, a substrate film to be held before transferring a protective layer of a printing screen in various methods typified by a sublimation type thermal transfer method and an ink jet method, Applications that require smoothness, applications that require optical properties, such as CRT protective films, and the like.

  Examples of particles present in the polyester for imparting winding properties to the film of the present invention include calcium carbonate, silica, talc, kaolin, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, Inorganic particles such as molybdenum sulfide, cross-linked polymer particles, organic particles such as calcium oxalate, and precipitated particles formed during polymerization of the polyester, preferably precipitated particles containing calcium carbonate, silica and calcium and phosphorus It is.

  For calcium carbonate, the particle size distribution is sharpened, coarse particles (particles significantly larger than the average particle size) can be easily cut, slipperiness and wear resistance are easily obtained after film formation, and a film that does not become a product is unnecessary. When the part is remelted and extruded, the particles are not easily broken, and the particle size is easily maintained. On the other hand, silica has advantages such as being available relatively inexpensively than other particles. Precipitated particles containing calcium and phosphorus are inexpensive because there is no need to add particles again, the deformation of the particles during stretching during film formation is small, the protrusion height can be maintained, and good winding characteristics are exhibited. There are advantages such as being able to.

  In order to express the effect of the present invention, it is of course possible to employ a plurality of types of particles represented above. In particular, in order to further improve the slipperiness of the film surface and the winding workability, in addition to the above-exemplified particles, small particles having an average particle size of less than 0.50 μm are used in a range not impairing the gist of the present invention. You can also Preferred as small particles are silica, crosslinked polymer particles, calcium carbonate, and precipitated particles formed during polymerization of the polyester.

  In the production of the polyester containing the additive particles, the particles may be added during the polyester synthesis reaction or directly to the polyester. When added during the synthesis reaction, a method in which the particles are dispersed in ethylene glycol or the like as a slurry and added at any stage of the polyester synthesis is preferable. On the other hand, when added directly to the polyester, a method of adding and mixing to the polyester using a twin-screw kneading extruder as dry particles or as a slurry dispersed in water or an organic solvent having a boiling point of 200 ° C. or less is preferable. . The particles to be added may be subjected to a treatment such as crushing, dispersing, classification, and filtration in advance as necessary.

  As a method for adjusting the content of particles, a master raw material containing particles at a high concentration is prepared by the above-described method, and at the time of film formation, it is diluted with a raw material that does not substantially contain particles, and the particle content is reduced. It is effective to adjust this.

  Further, as additives other than the above-described protrusion forming agent, an antistatic agent, a stabilizer, a lubricant, a crosslinking agent, an antiblocking agent, an antioxidant, a colorant, a light blocking agent, an ultraviolet absorber, etc. May be contained within a range not impairing the effects of the present invention.

Next, the manufacturing method of the film of this invention is demonstrated concretely.
First, a polyester raw material is supplied to an extrusion apparatus. That is, it extrudes as a molten sheet from a slit-shaped die. Next, the molten sheet is rapidly cooled and solidified on the rotary cooling drum so as to have a temperature equal to or lower than the glass transition temperature to obtain a substantially amorphous non-oriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed.

  In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the biaxial stretching conditions, the unstretched sheet is stretched in the first axial direction. The stretching temperature range is usually 70 to 150 ° C., the stretching ratio is usually 2.5 to 6 times, and the stretching can be performed in one step or two or more steps. Next, in the second axis direction, that is, in the direction perpendicular to the first axis direction, the uniaxially oriented film is once cooled below the glass transition point, or pre-heated to a temperature range of, for example, 80 to 150 ° C. without cooling, Further, the film is stretched 2.5 to 5 times, preferably 3.0 to 4.7 times under substantially the same temperature, to obtain a biaxially oriented film.

  In addition, it is preferable to perform the stretching in the first axial direction in two or more stages because good thickness uniformity can be achieved. In addition, a method of re-stretching in the longitudinal direction after lateral stretching is also possible, but in any case, the product of the total stretching ratio in the longitudinal direction and the stretching ratio in the width direction should be 16 times or more. Preferred to achieve a film with a degree of 0.165 or higher. Also, so-called simultaneous biaxial stretching, in which stretching in the first axial direction and the direction perpendicular thereto, is simultaneously possible.

  The film thus obtained is heat-treated for 1 second to 5 minutes under elongation, limited shrinkage or constant length within 30%. At this time, restretching may be performed in the longitudinal direction, the transverse direction, or both directions in or after the heat treatment step.

  In addition to the optimum stretching conditions described above, the heat treatment condition is such that the maximum temperature applied to the film is 215 ° C. or higher, and various conditions of the process are appropriately selected, so that the film in the longitudinal direction when reaching 200 ° C. is selected. A film having a length change rate in the range of -1.5% to + 1.0% can be obtained.

  In addition, in the range which does not inhibit the effect of this invention, according to various end uses, in order to provide adhesiveness with the layer which contacts, a coating layer can be provided in the film surface. In order to impart this adhesion, a polymer (binder polymer) comprising at least one selected from the group consisting of an aqueous polyester polymer and an aqueous acrylic polymer is particularly useful.

  Also, urea, melamine, guanamine, and acrylamide that have been methylolated or alkylolized as a crosslinkable polymer to improve adhesion resistance (blocking resistance), water resistance, solvent resistance, and mechanical strength of the coating layer Compounds, polyamide compounds, epoxy compounds, aziridine compounds, block polyisocyanates, silane coupling agents, titanium coupling agents, zircoaluminate coupling agents, peroxides, thermal and photoreactive vinyl compounds Or a photosensitive resin. Further, if necessary, it may contain an antifoaming agent, a coating property improver, a thickener, an antistatic agent, an organic lubricant, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like. .

  As a method of applying the above-mentioned coating solution to a polyester film, Yuji Harasaki, Tsuji Shoten, published in 1979, reverse roll coater, gravure coater, rod coater, air doctor coater or other coating apparatus shown in "Coating system" Can be used.

  In the present invention, from the viewpoint of cost, in order to provide a coating layer, a so-called in-line coating method in which coating is performed in the film manufacturing process is recommended. As a method of coating within the film production process, a coating solution is applied to an unstretched polyester film, and a method of biaxially stretching sequentially or simultaneously, coating to a uniaxially stretched polyester film, and further perpendicular to the previous uniaxially stretched direction. There is a method of stretching in the direction of the above, or a method of applying to a biaxially stretched polyester film and then stretching in the transverse and / or longitudinal direction.

  According to the film of the present invention, there is provided a polyester film for a substrate of a transfer type image protection film that has an excellent balance between smoothing of the surface and handling properties and can maintain high glossiness of the surface after transfer of the protective layer. And its industrial value is high.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited by a following example, unless the summary is exceeded. In addition, the evaluation method in an Example is as follows. In Examples and Comparative Examples, “part” means “part by weight”, “%” means “wt%”, and “ppm” means “weight ppm”.

(1) Intrinsic viscosity of polymer [η] (dl / g)
1 g of the polymer was dissolved in 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) and measured at 30 ° C.

(2) Average particle diameter of added particles (d50) (μm)
In the equivalent spherical distribution measured with a centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type) manufactured by Shimadzu Corporation, the particle size with an integrated volume fraction of 50% integrated from the large particle side is the average particle size (d50) of the added particles. did.

(3) Average particle size of precipitated particles (d50) (μm)
A polyester film containing precipitated particles is sandwiched between a preparation and melted, cooled, then observed with a microscope, and the image is measured by processing with an image processing apparatus (“Quantime 500+” manufactured by Leica). In its equivalent spherical distribution The particle size with an integrated volume fraction of 50% integrated from the large particle side was defined as the average particle size (d50) of the precipitated particles.

(4) Measurement of the amount of precipitated particles 1.0 liter of o-chlorophenol was added to 100 g of polyester, heated at 120 ° C. for 3 hours, and then centrifuged for 40 minutes using an ultracentrifuge (product of Hitachi Koki “55P-72”). Separation is performed and the resulting particles are vacuum dried at 100 ° C. When the above particles are processed with a scanning differential calorimeter and a melting peak corresponding to the polymer is observed, o-chlorophenol is added to the particles, and after heating and cooling, the centrifugation operation is performed again. And the particle | grains from which the melting peak was no longer recognized are set as precipitation particle | grains. Centrifugation is usually performed twice.

(5) Arithmetic mean roughness Ra (μm)
A test piece was cut out from the center in the width direction of the master roll, and Ra was measured and calculated by the following method to obtain arithmetic average roughness Ra (μm). That is, it calculated | required as follows using "SE3500" by Kosaka Laboratory. Using a stylus with a tip radius of 5 μm and a load of 30 mg, the film surface was measured for an evaluation length of 2.5 mm. Arithmetic mean roughness (Ra) was in accordance with JIS B 0601-1994. That is, a reference length L is extracted from the roughness curve in the direction of the average line, the x-axis is taken in the direction of the average line of the extracted portion, the y-axis is taken in the direction of the vertical magnification, and the roughness curve is expressed as y = f ( When expressed by x), the value obtained by the following formula is expressed in micrometers (μm). The longitudinal magnification was 200,000 times, the cut-off value was 0.08 mm, 10 roughness curves were measured for each surface, and an average of 10 points for each Ra was taken.
Ra = (1 / L) ∫ 0 L | f (x) | dx

(6) Rate of change in film length in the longitudinal direction when reaching 200 ° C. (%)
About the test piece cut out from the center in the width direction of the master roll, the temperature rise curve was collected under the following conditions using TMA manufactured by Seiko Instruments Inc. When the original length was 100%, the rate of change of the film length in the longitudinal direction when reaching 200 ° C. was expressed as elongation (plus) and shrinkage (minus). The measurement conditions are as follows.
Sample width (width direction) = 4mm
Sample chucking length (longitudinal direction) = 10 mm
Initial load = 10g
Temperature increase rate = 10 ° C./min Temperature increase range = 23 ° C. to 230 ° C.

(7) Degree of plane orientation About the test piece cut out from the central portion in the width direction of the master roll, the maximum refractive index nγ in the film plane using an Abbe refractometer manufactured by Atago Optical Co., Ltd. The refractive index nα and the refractive index nα in the thickness direction were measured, and the plane orientation degree Δp was calculated from the following equation. The refractive index was measured at 23 ° C. using sodium D line as a light source.
Δp = ((nγ + nβ) / 2) −nα

(8) Winding characteristics The following is the non-defective product ratio (ratio of rolls that could be wound without defects such as wrinkles) from a master roll produced by the method described in the examples to a roll of 500 mm width and 35000 m length. Judged by the criteria of.
◎: Good product rate is high and economic efficiency is good ○: Slightly good product rate is lowered, but is economically satisfactory level, good ×: Good product rate is low, economically harmful level, poor

(9) Production of transfer-type image protective film A non-defective roll produced by the method described in (8) above was unwound, and a coating for the backcoat layer was applied to the entire surface by a gravure coating method. Thereafter, it was stored in an oven at 55 ° C. for 5 days and cured to form a backcoat layer. The coating material for the backcoat layer is 5.0 parts by weight of Denkabutyral # 3000K (manufactured by Denki Kagaku Kogyo Co., Ltd.) as the polyvinyl acetal resin and 0.5 of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) as the isocyanate. Parts by weight, 20 parts by weight of phosphanol GB520 (manufactured by Toho Chemical Co., Ltd.) as the phosphate ester, 0.5 parts by weight of Nipsil E-200A (manufactured by Nippon Silica Industry Co., Ltd.) as the silica, and methyl ethyl ketone It was prepared by mixing 37 parts by weight and 37 parts by weight of toluene. Subsequently, the roll-shaped film after the backcoat layer was cured was rewound again, and the coating for the screen protective layer was applied to the opposite surface of the backcoat layer by bar coating so as to have a thickness of about 2.0 μm. It dried in oven and produced the transfer type image protection film. The coating material for the image protective layer is 20.0 parts by weight of CAB500-0.5 (manufactured by Eastman Chemical Co.) as cellulose acetate butyrate resin, 40.0 parts by weight of methyl ethyl ketone, and 40.0 parts by weight of toluene. And were prepared.

(10) Glossiness Using the transfer type image protection film prepared by the method described in the above (9), the image protective layer is transferred onto the non-protected image, and the glossiness of the surface is measured by Gloss Meter VG2000 (NIPPON 20 ° Gloss was measured using a DENSHOKU product, and judged according to the following criteria.
◎: Gloss is sufficient and excellent ○: Gloss is slightly lowered, but it is a level that is not a problem in practical use, Good ×: Gloss is insufficient, cannot be used practically, and is poor

  Regarding the above-mentioned transfer-type image protective film that prints and heat-transfers to the dye-receiving layer of photographic paper, the thermal transfer film of SVM-25LS ink ribbon, a sublimation type Digital Photo Printer DPP-SV series genuine media manufactured by Sony Corporation. It was used by replacing the part and pasting it with a ribbon. A Sony Digital Photo Printer was used as a print for evaluation. Specifically, first, using Adobe Photoshop software made by Adobe, create a solid white image, transfer the data to the printer DPP-SVM77, to the thermal transfer film portion of the SVM-25LS ink ribbon, Using the ink ribbon in which the thermal transfer film of the present invention was replaced, each image protection film was transferred onto a white solid image. A white solid image was transferred and printed on the photographic paper by the thermal transfer head of the printer.

The polyester raw material used in the following examples is prepared by the following method.
(Polyester raw material a)
86 parts of terephthalic acid and 70 parts of ethylene glycol were placed in a reactor, and an esterification reaction was carried out at about 250 ° C. under a pressure of 0.5 kg / mm ² for 4 hours. Next, 0.015 part of antimony trioxide, silica particles having an average particle diameter of 2.2 μm, and 0.01 part of phosphoric acid were added. While gradually raising the temperature from 250 ° C. to 285 ° C., the pressure was gradually reduced from normal pressure to 0.5 mmHg. After 4 hours, the polycondensation reaction was stopped to obtain a polyester (a) having an intrinsic viscosity of 0.66. This polyester (a) contained 0.50% by weight of silica particles.

(Polyester raw material b)
In polyester raw material a, instead of using silica particles, polyester (b) having an intrinsic viscosity of 0.66 was obtained in the same manner as polyester a, except that crosslinked polymer particles having an average particle size of 0.3 μm were added. This polyester b contained 0.20% by weight of crosslinked polymer particles.

(Polyester raw material c)
A polyester (c) for dilution having an intrinsic viscosity of 0.66 was obtained in the same manner as the polyester a except that the polyester raw material a was not added with silica particles.

(Polyester raw material d)
A polyester (d) having an intrinsic viscosity of 0.66 was obtained in the same manner as for the polyester a except that calcium carbonate particles having an average particle diameter of 1.8 μm were added in place of the silica particles in the polyester raw material a. This polyester d contained 0.50% by weight of calcium carbonate particles.

(Polyester raw material e)
100 parts of dimethyl terephthalate, 70 parts of ethylene glycol and 0.11 part of calcium acetate monohydrate are placed in a reactor and heated for heating and distilled off to conduct transesterification, which takes 4 hours from the start of the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, a solution obtained by uniformly dissolving 0.124 part of triethyl phosphite and 0.54 part of triethyl phosphate in ethylene glycol is added to the reaction mixture, and then 0.04 part of antimony trioxide is added, and then 10 minutes are added. In short, it reached 236 ° C. From this point, the pressure in the system is gradually reduced, and the temperature in the system is 265 ° C. and the pressure is 300 mmHg 80 minutes after the addition of antimony trioxide. Thereafter, the temperature is gradually raised and reduced and finally 285 ° C. and 1 mmHg or less. did. After 4 hours, the inside of the system was returned to normal pressure and the polymer was discharged to form a chip to obtain a polyester (e) having an intrinsic viscosity of 0.66. In this polyester (e), a large number of uniform and fine precipitated particles were observed, and the average particle size was 1.8 μm. When the amount of the precipitated particles was measured according to the method described, it was 0.4% by weight based on the polyester.

  Polyester (a), polyester (b) and polyester (c) are mixed and contain 0.05% silica particles having an average particle size of 2.2 μm and 0.02% crosslinked polymer particles having an average particle size of 0.3 μm. The raw material to be used. The mixed raw material was dried by a conventional method, supplied to an extruder, melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.75 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.65 times at 75 ° C. Thereafter, the film was guided to a tenter and stretched 4.35 times at 110 ° C. in the transverse direction and heat-treated at 230 ° C. to obtain a biaxially stretched polyester film having a thickness of 4.5 μm. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

  The polyester (c) and the polyester (d) are mixed to obtain a raw material containing 0.07% calcium carbonate particles having an average particle diameter of 1.8 μm, and this is used in the same manner as in Example 1 to obtain a thickness of 4 A biaxially stretched polyester film having a thickness of 5 μm was obtained. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

  Polyester (c) and polyester (e) are mixed to form a raw material containing 0.12% of precipitated particles. The mixed raw material is dried by a conventional method and supplied to an extruder, and melted at 290 ° C. to obtain a sheet. And then rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.75 times at 90 ° C. in the longitudinal direction by using a roll stretching method, and further stretched 1.45 times at 75 ° C. Thereafter, the film was guided to a tenter and stretched 4.05 times at 110 ° C. in the transverse direction and heat-treated at 220 ° C. to obtain a biaxially stretched polyester film having a thickness of 4.5 μm. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

  Polyester (c) and polyester (d) are mixed to obtain a raw material containing 0.15% of calcium carbonate particles having an average particle diameter of 1.8 μm. The mixed raw material is dried by a conventional method and supplied to an extruder. It was melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.75 times at 90 ° C. in the longitudinal direction by using a roll stretching method, and further stretched 1.45 times at 75 ° C. Then, it led to the tenter, stretched 4.05 times at 110 ° C. in the transverse direction, and heat treated at 215 ° C. to obtain a biaxially stretched polyester film having a thickness of 4.5 μm. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

(Comparative Example 1)
Polyester (a) and polyester (c) were mixed to obtain a raw material containing 0.30% silica particles having an average particle size of 2.2 μm. The mixed raw material was dried by a conventional method, supplied to an extruder, melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.75 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.35 times at 75 ° C. Then, it led to the tenter, stretched 3.90 times at 110 ° C. in the transverse direction, and heat treated at 210 ° C. to obtain a 4.5 μm thick biaxially stretched polyester film. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

(Comparative Example 2)
A polyester (c) and a polyester (d) are mixed to obtain a raw material containing 0.03% calcium carbonate particles having an average particle diameter of 1.8 μm. Using this raw material, a thickness 4 A biaxially stretched polyester film having a thickness of 5 μm was obtained. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

(Comparative Example 3)
The polyester (a) and the polyester (c) are mixed and used as a raw material containing 0.30% silica particles having an average particle size of 2.2 μm. The mixed raw material is dried by a conventional method and supplied to an extruder. It was melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.75 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.65 times at 75 ° C. Thereafter, the film was guided to a tenter and stretched 4.35 times at 110 ° C. in the transverse direction and heat-treated at 230 ° C. to obtain a biaxially stretched polyester film having a thickness of 4.5 μm. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

(Comparative Example 4)
Polyester (c) and polyester (d) are mixed to obtain a raw material containing 0.03% calcium carbonate particles having an average particle size of 1.8 μm, and the mixed raw material is dried by a conventional method and supplied to an extruder. It was melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.75 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.65 times at 75 ° C. Thereafter, the film was guided to a tenter and stretched 4.35 times at 110 ° C. in the transverse direction and heat-treated at 230 ° C. to obtain a 4.5 μm thick biaxially stretched polyester film. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

(Comparative Example 5)
Polyester (c) and polyester (e) are mixed together to form a raw material containing 0.12% of precipitated particles. The mixed raw material is dried by a conventional method and supplied to an extruder, and melted at 290 ° C. to obtain a sheet. And then rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.75 times at 90 ° C. in the longitudinal direction by using a roll stretching method, and further stretched 1.45 times at 75 ° C. Thereafter, the film was guided to a tenter, stretched 4.05 times at 110 ° C. in the transverse direction, and heat treated at 230 ° C. to obtain a biaxially stretched polyester film having a thickness of 4.5 μm. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

(Comparative Example 6)
Polyester (c) and polyester (e) are mixed to form a raw material containing 0.12% of precipitated particles. The mixed raw material is dried by a conventional method and supplied to an extruder, and melted at 290 ° C. to obtain a sheet. And then rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.75 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.50 times at 75 ° C. Then, it led to the tenter, stretched 3.90 times at 110 ° C. in the transverse direction, and heat treated at 210 ° C. to obtain a 4.5 μm thick biaxially stretched polyester film. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

(Comparative Example 7)
Polyester (c) and polyester (d) are mixed to obtain a raw material containing 0.15% of calcium carbonate particles having an average particle diameter of 1.8 μm. The mixed raw material is dried by a conventional method and supplied to an extruder. It was melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.40 times at 83 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.20 times at 93 ° C. Then, it led to a tenter and stretched 4.00 times at 125 ° C. in the transverse direction and heat-treated at 208 ° C. to obtain a biaxially stretched polyester film having a thickness of 4.5 μm. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.
The results obtained for Examples 1 to 4 and Comparative Examples 1 to 7 are summarized in Table 1 below.

  The film of the present invention can be suitably used, for example, as a substrate for a transfer type image protection film that provides a high gloss image.

Claims (1)

The film thickness is 6 μm or less, the arithmetic average roughness (Ra) of at least one side of the film is 0.031 to 0.045 μm, and the rate of change in the length of the film in the longitudinal direction when reaching 200 ° C. is −1. A polyester film for a base material of a transfer type image protective film, characterized in that the film has a surface orientation degree of 0.165 or more, and is from 5% to + 1.0%.