JP2017014392A - Polyester film prevented from oligomer precipitation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film which has excellent transparency after thermal processing and shows extremely little oligomer precipitation.SOLUTION: The polyester film prevented from oligomer precipitation is a laminated polyester film formed by arranging a coating layer having a thickness of 20 nm or more on at least one surface of a polyester substrate, where a coefficient of static friction μs of a contact surface, when one surface of the film and an opposite surface are piled so that they contact each other, is 0.1 to 0.6, Δhaze which is an increment in haze before and after a heat treatment at 150°C for 60 minutes is 0.3% or less, and haze before the heat treatment is 1.5% or less. Also provided is the polyester film prevented from oligomer precipitation, where the coating layer contains particles, the particles having an average particle diameter of 50 to 200 nm, which is larger than the coating layer.SELECTED DRAWING: None

Description

  The present invention relates to a polyester film used for industrial and packaging purposes. More specifically, the present invention relates to a polyester film having excellent post-heating oligomer precipitation preventing property.

  Polyester films represented by polyethylene terephthalate film have excellent properties such as mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc. Has been.

  Polyester is a linear polymer usually produced from a dicarboxylic acid component and a glycol component by a polycondensation reaction. However, conventionally known polyesters contain several percent of oligomers such as cyclic trimers. Such an oligomer such as a cyclic trimer has a problem that when the polyester film is heat-treated, the oligomer is precipitated on the film surface and the film is whitened. In particular, as the use of polyethylene terephthalate film diversifies, the processing conditions and use conditions of the film also diversify. For example, oligomer precipitation on the film surface requires high transparency such as optical use. It has become a big problem. From the viewpoint of productivity, the precipitation of oligomers by heat treatment is becoming more serious as the heat treatment temperature for post-processing increases.

  In order to reduce oligomers in the polyester film as a method for suppressing oligomer precipitation due to heating, it has been proposed to reduce the amount of cyclic oligomers in the polyester raw material by solid phase polymerization (see Patent Documents 1 and 2). Although this method can reduce the number of cyclic oligomers, the polycondensation reaction of the polyester proceeds at the same time, resulting in a problem that the degree of polymerization of the obtained polyester is increased and the load is increased when extrusion molding is performed.

  Moreover, the proposal which suppresses oligomer precipitation after a heating by giving a specific coating layer to a general polyester film and carrying out surface modification is made. (See Patent Document 3)

JP-A-9-99530 JP 2000-141570 A JP 2005-336394 A

  However, when the heating condition of the polyester film is higher and the requirement for transparency is high, the effect of preventing oligomer precipitation may be insufficient only by surface modification with a known coating layer. Specifically, when the polyester film is wound into a roll, stored and transported, the oligomer precipitation preventing function may be deteriorated as compared with the polyester film before winding.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a polyester film that is excellent in transparency after heat processing and has very little oligomer precipitation.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the following polyester film remarkably exhibits an oligomer precipitation preventing effect. That is, the present invention has the following configuration.

1. A laminated polyester film in which a coating layer having a thickness of 20 nm or more is provided on at least one surface of a polyester film base material, and the static friction coefficient of the contact surface when the one surface of the film and the opposite surface are in contact with each other μs is 0.1 or more and 0.6 or less, and Δhaze, which is an increase in haze before and after the heat treatment at 150 ° C. for 60 minutes, is 0.3% or less, and the haze before the heat treatment is 1. An oligomer precipitation preventing polyester film characterized by being 5% or less.
2. 2. The oligomer precipitation-preventing polyester film as described in the above item 1, wherein the coating layer contains particles, the average particle size of the particles is 50 nm or more and 200 nm or less, and is larger than the thickness of the coating layer.

  The oligomer precipitation-preventing polyester film of the present invention is excellent in transparency after heat processing and has almost no oligomer precipitation. Therefore, since it can be post-processed at a high temperature, it is a film suitably used in industrial applications including optical applications that require high quality.

  The reason why the polyester film of the present invention exhibits an oligomer precipitation preventing effect is considered as follows. That is, oligomer precipitation that cannot be prevented by surface modification by the conventional film coating layer is deposited on the surface through defects in the very small coating layer, and the cause of such defects is the surface of the film. This is thought to be due to the local frictional force applied to the surface.

  In the present invention, by reducing the static friction coefficient between one side of the film and the opposite side to a certain value or less, the frictional force to the coating layer is reduced, and the film is wound into a roll shape by keeping it at a certain value or more. It is considered that the local pressure load due to the winding slippage was eased, the transparency after heat processing was suitably excellent, and the precipitation of the cyclic oligomer was prevented.

Hereinafter, the present invention will be described in detail.
The oligomer precipitation preventing polyester film of the present invention is a laminated polyester film having a coating layer on at least one side of a polyester film substrate. The polyester film substrate is a film obtained by melt-extrusion of a polyester resin using a known method, and a film having a thickness of 10 to 250 μm is preferably used. Moreover, the polyester film base material may contain various stabilizers, ultraviolet light inhibitors, antistatic agents, lubricants, pigments, antioxidants, plasticizers, and the like.

  The polyester resin may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic diol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid. Examples of the aliphatic glycol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1, 4-cyclohexanedimethanol etc. are mentioned. Representative homopolyesters include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT) and the like, and polyethylene terephthalate is particularly preferable. On the other hand, examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (for example, P-oxybenzoic acid). 1 type or 2 types or more selected, and the diol component is selected from ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like. Or 2 or more types are mentioned. In any case, the polyester referred to in the present invention is preferably a polyester having 60% by mole or more, and preferably 80% by mole or more, having ethylene terephthalate as a repeating unit.

  The lower limit of the amount of oligomer contained in the polyester film substrate is preferably 0.25% by mass, more preferably 0.3% by mass, and still more preferably 0.35% by mass. If the amount of oligomer contained in the polyester film substrate is 0.25% by mass or more, the treatment for reducing the amount of oligomer does not require a particularly long time, which is preferable in terms of productivity.

  The upper limit of the amount of oligomer contained in the polyester film substrate is preferably 1% by mass, more preferably 0.95% by mass, and still more preferably 0.9% by mass. When the amount of oligomer contained in the polyester film substrate is 1% by mass or less, the effect of suppressing oligomer precipitation by the coating layer is particularly easily exhibited, which is preferable.

  When the oligomer precipitation-preventing polyester film of the present invention is rolled up, the oligomer precipitation-preventing effect is remarkably exhibited. In the film roll by the oligomer precipitation preventing polyester film of the present invention, the width of the film roll is not particularly limited, but from the viewpoint of ease of handling, the lower limit of the width of the film roll is 0.7 m or more. Preferably, it is 1.0 m or more. On the other hand, the upper limit of the width of the film roll is determined by the size of the customer's device to be post-processed. At present, 2.2 m is considered the maximum width, and it is more preferably 2.0 m or less. More preferably, it is 5 m or less. In addition, the winding length of the film roll is not particularly limited, but from the viewpoint of ease of winding and handling, when the film has a thickness of about 10 μm, it is preferably 10,000 m or less and more preferably 8000 m or less. preferable. When the film has a thickness of about 250 μm, it is preferably 2000 m or less, and more preferably 1800 m or less. Accordingly, when the thickness of the film is in the middle of 10 to 250 μm, it is preferable to set the winding length to be 500 m or more and 10,000 m or less. The lower limit of the winding length is preferably 100 m. When the winding length is 100 m or more, the effect of optimizing the front and back slipperiness in the present invention is more clearly exhibited.

  As the take-up core, usually, paper of 3 inches, 6 inches, 8 inches, etc., a plastic core or a metal core can be used.

  The kind of resin used for the coating layer of the polyester film of the present invention is not particularly limited, and preferably includes PMMA resin, aminoacrylic resin, cycloolefin polymer and the like.

  The Tg of the resin used for the coating layer is preferably 90 ° C. or higher and 200 ° C. or lower, more preferably 95 ° C. or higher and 170 ° C. or lower, and further preferably 100 ° C. or higher and 150 ° C. or lower. A Tg of 90 ° C. or higher is preferred because the oligoblock property does not deteriorate. A resin having a Tg of over 200 ° C. is not particularly likely to be used as a transparent resin.

  As a means for expressing the slipperiness of the front and back of the film while maintaining the transparency of the film itself, a method of adding particles in the coating layer for preventing the precipitation of the oligomer, and the opposite surface to the coating layer for preventing the precipitation of the oligomer And a method of coating an easy-slip layer, and a method of providing a layer in which particles are dispersed only on the surface layer of a film as a substrate.

  When adding particles to the coating layer, the lower limit of the average particle size of the particles contained in the coating layer is preferably 50 nm, more preferably 60 nm, and even more preferably 70 nm. When the average particle size is 50 nm or more, the slipperiness does not become insufficient, and scratches are hardly scratched.

  The upper limit of the average particle size of the particles contained in the coating layer is preferably 200 nm, more preferably 180 nm, and even more preferably 160 nm. When the average particle size of the particles is 200 nm or less, the haze is low and the transparency is maintained, which is preferable. And it is preferable that the average particle diameter of particle | grains is larger than the thickness of an application layer. When the average particle diameter of the particles is larger than the thickness of the coating layer, moderate slipperiness is effectively obtained, and as a result, an oligomer precipitation suppressing effect is obtained. More preferably, the average particle diameter of the particles is more preferably 15 nm or more, and particularly preferably 20 nm or more, greater than the thickness of the coating layer. However, if the average particle size of the particles is too large with respect to the thickness of the coating layer, the particles are likely to fall off due to rubbing, so the average particle size of the particles may be larger in the range of 100 nm or less than the thickness of the coating layer. preferable.

  The average particle size of the particles was measured by observing the cross-sectional particles of the processed laminated film with a scanning electron microscope, observing 100 particles, and setting the average value to the average particle size.

  The shape of the particle is not particularly limited as long as it satisfies the object of the present invention, and spherical particles and non-spherical particles can be used. The particle size of the amorphous particles can be calculated as the equivalent circle diameter. The equivalent circle diameter is a value obtained by dividing the observed area of the particle by π and calculating the square root to double.

  Although it does not specifically limit as a kind of particle | grains contained in a coating layer, For example, a siloxane copolymerization acrylic resin, a crosslinked polystyrene, a polystyrene- divinylbenzene, a polymethylmethacrylate, a methylmethacrylate copolymer, a methylmethacrylate copolymer crosslinked body, poly Organic particles such as tetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, benzoguanamine resin, silicone resin, acrylic resin, silica, alumina, titanium dioxide, kaolin, talc, graphite, calcium carbonate, feldspar, molybdenum disulfide, carbon black Any of inorganic particles such as barium sulfate can be used. Moreover, you may use the core-shell type | mold particle | grains of the multilayer structure comprised with the substance from which each property inside and outside differs. Preferably, silica is used.

  The lower limit of the particle content contained in the coating layer is preferably 4 mass (%, relative to resin), more preferably 5 mass (%, relative to resin). When the content is 4% by mass or more, slipperiness is maintained and scratches are hardly scratched.

  The upper limit of the content of particles contained in the coating layer is preferably 20 mass (%, resin), more preferably 17 mass (%, resin), and even more preferably 15 mass (%, resin). It is. When it is 20% by mass or less, the haze is not too high and the transparency is maintained, which is preferable. The particle content is expressed in mass% of the particle content with respect to the resin solid content of the coating layer.

  The lower limit of the thickness of the coating layer is preferably 20 nm, more preferably 30 nm, and even more preferably 40 nm. When the thickness of the coating layer is 20 nm or more, it is preferable because the effect of suppressing oligomer precipitation becomes clear.

  The upper limit of the thickness of the coating layer is preferably 150 nm, more preferably 130 nm, and still more preferably 120 nm. When the thickness of the coating layer is 150 nm or less, it is preferable that the blocking problem hardly occurs.

  The lower limit of the ratio of the thickness of the coating layer to the average particle size of the particles in the coating layer is preferably 0.1, more preferably 0.2, and even more preferably 0.3. It is preferable that the ratio of the thickness of the coating layer / the average particle size of the particles in the coating layer is 0.1 or more because the particles do not fall off, the film surface is not likely to be damaged, and the oligomer is difficult to precipitate.

  The upper limit of the ratio of the thickness of the coating layer / the average particle size of the particles in the coating layer is preferably 0.9, more preferably 0.85, and even more preferably 0.83. When the ratio of the thickness of the coating layer / the average particle size of the particles in the coating layer is 0.9 or less, the slipperiness will not be insufficient and the film surface will not be easily scratched.

  An undercoat layer may be provided on the surface of the polyester film substrate, but the resin of the undercoat layer is preferably a polyester resin. Naphthalene dicarboxylic acid is preferably included as the acid component of the polyester resin, and it is preferable to include naphthalenedicarboxylic acid because the refractive index increases and the iris color under a fluorescent lamp is easily suppressed. The adhesive improvement with an oligo block layer and the refractive index are adjusted by these, and the light transmittance improvement effect can also be anticipated. Further, a crosslinking agent may be contained in the undercoat layer. By containing a crosslinking agent, the solvent resistance at the time of applying the coating layer for suppressing oligomer precipitation can be enhanced. Examples of the crosslinking agent include urea, epoxy, melamine, isocyanate, and oxazoline. Among these, melamine-based, isocyanate-based, and oxazoline-based are more preferable in view of the stability over time of the coating liquid and the effect of improving adhesion under high-temperature and high-humidity treatment. Moreover, in order to promote a crosslinking reaction, it is also preferable to use a catalyst etc. suitably as needed.

  The lower limit of the thickness of the undercoat layer is preferably 5 nm, more preferably 10 nm. When the thickness of the undercoat layer is 5 nm or more, the adhesion with the oligo block layer is preferably increased.

  The upper limit of the thickness of the undercoat layer is preferably 100 nm, more preferably 80 nm. When the thickness of the undercoat layer is 100 nm or less, the haze is not excessively increased, and high transparency is not likely to be impaired, which is preferable.

  The lower limit of the refractive index of the undercoat layer is preferably 1.5, more preferably 1.53, and even more preferably 1.55. When the refractive index of the undercoat layer is 1.5 or more, the effect of improving the light transmittance becomes clear, which is preferable.

  The upper limit of the refractive index of the undercoat layer is preferably 1.7, more preferably 1.67, and even more preferably 1.65. When the refractive index of the undercoat layer is 1.7 or less, it is preferable that the haze does not become too high and high transparency is maintained.

In order to adjust the refractive index of the undercoat layer to be high, it is preferable to contain high refractive index particles in the undercoat layer. The high refractive index particles in the undercoat layer are not particularly limited, and specific examples include metal oxide particles having a refractive index of 1.7 or more and 3.0 or less. Examples of such metal oxide include TiO2 (refractive index 2.7), ZnO (refractive index 2.0), Sb2O3 (refractive index 1.9), SnO2 (refractive index 2.1), ZrO2 (refractive index 2). .4), Nb2O5 (refractive index 2.3), CeO2 (refractive index 2.2), Ta2O5 (refractive index 2.1), Y2O3 (refractive index 1.8), La2O3 (refractive index 1.9), In2O3 (Refractive index 2.0), Cr2O3 (refractive index 2.5), etc., and complex oxides containing these metal atoms.
Is mentioned.

  In the present invention, as a method of providing a coating layer having an oligomer precipitation inhibiting effect on a polyester film substrate, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these is used to produce a polyester film. A method of coating outside the process is preferred. Although it may be applied during the film manufacturing process, the former method is more preferable because it requires care not to cause minute defects in the coating layer due to stretching after application. is there.

  The lower limit of the solid content concentration of the coating solution for forming the coating layer is preferably 0.1% by mass, more preferably 0.2% by mass. When the solid content of the coating solution is 0.1% by mass or more, the solvent resistance of the coating film is satisfied, and when it is formed into a roll, a problem that a part of the coating layer is transferred to the back side is preferable.

  The upper limit of the solid content concentration of the coating layer is preferably 10% by mass, more preferably 5% by mass. When the solid content concentration of the coating layer is 10% by mass or less, it is preferable that the viscosity does not become too high, the coating property is good, and the coating layer tends to be uniform.

  The lower limit of the drying temperature after coating is preferably 70 ° C, more preferably 80 ° C, and even more preferably 90 ° C. When the drying temperature is 70 ° C. or higher, the resin is hardly cured and the effect of suppressing oligomer precipitation is effectively exhibited.

  The upper limit of the drying temperature after coating is 180 ° C, preferably 170 ° C, more preferably 160 ° C. A drying temperature of 180 ° C. or lower is preferable because there is no fear of deformation of the substrate due to heat, and flatness is maintained.

  The lower limit of the drying time after coating is 10 seconds, preferably 15 seconds or more, and more preferably 20 seconds or more. When the drying time is 10 seconds or more, curing failure does not occur and the effect of suppressing oligomer precipitation is reliably obtained.

  The upper limit of the drying time after application is 120 seconds, preferably 90 seconds or less, and more preferably 60 seconds or less. It is preferable that the drying time after application is 120 seconds or less because there is no problem of deformation of the base material due to heat, and flatness is maintained.

  The lower limit of the static friction coefficient of the contact surface when the film is superposed so that one side of the film and the opposite side are in contact with each other is preferably 0.1. The static friction coefficient is about 0.1 as a range that can be industrially mass-produced.

  The upper limit of the static friction coefficient of the contact surface when the film is superposed so that one side of the film and the opposite side are in contact with each other is preferably 0.6, more preferably 0.5. When the coefficient of static friction is 0.6 or less, there is no fear of scratching, and an oligomer precipitation suppressing effect is remarkably obtained, which is preferable.

  The coefficient of static friction between the contact surfaces when the one surface of the polyester film substrate finally provided with the coating layer and the opposite surface are in contact with each other is more preferably 0.2 or more and 0.5 or less. Especially preferably, it is 0.3 or more and 0.4 or less. When the static friction coefficient is 0.6 or less, the frictional force applied to the coating layer does not increase excessively, and scratches and cracks do not occur in the coating layer, so that the oligomer precipitation preventing property is not impaired. On the other hand, if the coefficient of static friction is 0.1 or more, there is no problem of slipping too much after winding, and it is difficult to feed the winding slip, so there is no problem of applying local pressure, and there is a possibility that the coating layer may be scratched or cracked. Absent.

  After the production, the upper limit of the initial haze not particularly heat-treated is preferably 1.5%, more preferably 1.3%, still more preferably 1.2%, and particularly preferably 1.0%. An initial haze of 1.5% or less is preferable from the viewpoint of transparency.

  The upper limit of Δhaze, which is the amount of increase in haze before and after heat treatment at 150 ° C. for 60 minutes, is preferably 0.3%, more preferably 0.2%, and even more preferably 0.1%. When the Δhaze is 0.3% or less, the transparency of the film after heating is maintained, and the optical characteristics are maintained. Further, when the Δhaze is 0.3% or less, oligomer precipitation is suppressed when the film wound in a roll shape is wound after long-term storage, and transparency is maintained, which is preferable.

  Δhaze in the present invention is an index of easiness of whitening by heating, and is represented by Δhaze = (haze after heating) − (haze before heating). The range of Δhaze of 0.3 or less corresponds to the amount of increase in haze before and after heating when it is judged that there is no whitening due to heating when a strong light is applied to the film in a dark room and visually confirmed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to a following example. In the examples and comparative examples, “parts” means “parts by weight”.

[Evaluation method]
(1) Haze Measured according to JIS K 7105 “Testing method for optical properties of plastic” haze (cloudiness value). NDH-300A type turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd. was used for the measuring instrument.

(2) Evaluation of increase in haze before and after heat treatment (Δhaze) Film was cut into 50 mm × 75 mm square and before heat treatment according to JIS K 7105 “Testing method for optical properties of plastic” haze (cloudiness value) The initial haze was measured. NDH-300A type turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd. was used for the measuring instrument. In order to measure haze after heating, a protective film (PC-T073 manufactured by Fujimori Kogyo Co., Ltd.) is brought into close contact with a surface on which the haze evaluation has not been performed before the heat treatment of the sample film piece so that bubbles do not enter. With the protective film attached, the film is set in an oven heated to 150 ° C., and the film is taken out after 60 minutes. Thereafter, the protective film is peeled off, the haze of the film is measured by the same method as above, and the haze is obtained after heating. The haze difference before and after heating is defined as Δhaze.
ΔHaze (%) = (Haze after heating) − (Haze before heating)

(3) Measurement of static friction coefficient Static friction coefficient of the contact surface when it was stacked using a universal testing machine (AGS-1kNG, manufactured by Shimadzu Corporation) so that one side of the film and the opposite side were in contact with each other. (Μs) was measured in accordance with JIS K-7125 under the following conditions.
Test piece: width 50 mm x length 60 mm
Load: 4.4kg
Test speed: 200 mm / min

Example 1
2.5 parts of melamine cross-linked alkyl-modified alkyd resin (manufactured by Hitachi Chemical Co., Ltd .: Tesfine 322: solid content 40%), 0.025 part of P-toluenesulfonic acid (manufactured by Hitachi Chemical Co., Ltd .: dryer 900) as an acid catalyst, Solid content 1 prepared by dissolving 0.3 part of silica sol methyl ethyl ketone dispersion (manufactured by Nissan Chemical Industries, Ltd .: MEK-ST-L: solid content 30%) as a lubricant in a mixed solution of 50 parts of toluene and 47.2 parts of methyl ethyl ketone. A coating solution of wt% was applied to the non-smooth surface of a 125 μm-thick biaxially stretched polyethylene terephthalate film (Toyobo Co., Ltd .: A4100) and dried at 150 ° C. for 1 minute, so that the thickness of the coating layer was 75 nm.

(Example 2)
A film was prepared in the same manner as in Example 1 except that the coating liquid of Example 1 was coated such that the coating thickness after drying was 25 nm.

(Example 3)
3.0 parts of polyester resin (Toyobo Co., Ltd .: Byron 20SS: solid content 30%), 0.13 parts of isocyanate (manufactured by Nippon Polyurethane Co., Ltd .: Coronate L: solid content 75%), and silica sol methyl ethyl ketone dispersion (as a lubricant) Nissan Co., Ltd .: MEK-ST-L: solid content 30%) 0.3 parts of toluene in a mixed solution of 50 parts of toluene and 46.8 parts of methyl ethyl ketone, a coating solution having a solid content of 1% by weight, It apply | coated to the non-smooth surface of the 125-micrometer-thick biaxially-stretched polyethylene terephthalate film (Toyobo Co., Ltd. product: A4100), it dried at 150 degreeC for 1 minute, and the thickness of the coating layer was 75 nm.

Example 4
1.0 parts of polymethyl methacrylate (Mitsubishi Rayon Co., Ltd .: BR-80: solid content 100%), silica sol methyl ethyl ketone dispersion as a lubricant (Nissan Chemical Industry Co., Ltd .: MEK-ST-L: solid content 30%) 3 parts of 50 parts of toluene and 48.7 parts of methyl ethyl ketone were mixed to prepare a coating solution having a solid content of 1% by weight. A 125 μm thick biaxially stretched polyethylene terephthalate film (manufactured by Toyobo Co., Ltd .: A4100) It apply | coated to the smooth surface and dried at 150 degreeC for 1 minute, and the thickness of the application layer was 75 nm.

(Example 5)
2.5 parts of melamine cross-linked alkyl-modified alkyd resin (manufactured by Hitachi Chemical Co., Ltd .: Tesfine 322: solid content 40%), 0.025 part of P-toluenesulfonic acid (manufactured by Hitachi Chemical Co., Ltd .: dryer 900) as an acid catalyst, Solid content 1 prepared by dissolving 0.18 part of silica sol methyl ethyl ketone dispersion (manufactured by Nissan Chemical Industries, Ltd .: MEK-ST-L: solid content 30%) as a lubricant in a mixed solution of 50 parts of toluene and 47.3 parts of methyl ethyl ketone. A coating solution of wt% was applied to the non-smooth surface of a 125 μm thick biaxially stretched polyethylene terephthalate film (Toyobo Co., Ltd .: A4100) and dried at 150 ° C. for 1 minute to make the coating layer thickness 25 nm.

(Comparative Example 1)
A solution obtained by mixing 50 parts of ethyl silicate (manufactured by Colcoat: Colcoat N-103X), 25 parts of water and 25 parts of isopropyl alcohol was applied to the non-smooth surface of wire bar # 5 (Toyobo Co., Ltd .: A4100) at 150 ° C. Dried for 1 minute. The thickness of the coating layer was 75 nm.

(Comparative Example 2)
2.5 parts of melamine cross-linked alkyl-modified alkyd resin (manufactured by Hitachi Chemical Co., Ltd .: Tesfine 322: solid content 40%), 0.025 part of P-toluenesulfonic acid (manufactured by Hitachi Chemical Co., Ltd .: dryer 900) as an acid catalyst, Solid content 1 prepared by dissolving 0.1 part of silica sol methyl ethyl ketone dispersion (manufactured by Nissan Chemical Industries, Ltd .: MEK-ST-L: solid content 30%) as a lubricant in a mixed solution of 50 parts of toluene and 47.4 parts of methyl ethyl ketone. A coating solution of wt% was applied to a non-smooth surface of a 125 μm-thick biaxially stretched polyethylene terephthalate film (Toyobo Co., Ltd .: A4100) and dried at 150 ° C. for 1 minute, so that the thickness of the coating layer was 7.5 nm. .

(Comparative Example 3)
2.5 parts of melamine cross-linked alkyl-modified alkyd resin (manufactured by Hitachi Chemical Co., Ltd .: Tesfine 322: solid content 40%), 0.025 part of P-toluenesulfonic acid (manufactured by Hitachi Chemical Co., Ltd .: dryer 900) as an acid catalyst A coating solution having a solid content of 1% by weight dissolved in a mixed solution of 50 parts of toluene and 47.5 parts of methyl ethyl ketone was applied to a non-smooth surface of a 125 μm thick biaxially stretched polyethylene terephthalate film (Toyobo Co., Ltd .: A4100). And dried at 150 ° C. for 1 minute to set the thickness of the coating layer to 75 nm.

  The oligomer precipitation-preventing polyester film of the present invention is excellent in transparency after heat processing and has almost no oligomer precipitation, so that it can be post-processed at a high temperature, including optical applications that require high quality. The film is also preferably used in industrial applications and general packaging applications.

Claims (2)

  A laminated polyester film in which a coating layer having a thickness of 20 nm or more is provided on at least one surface of a polyester film base material, and the static friction coefficient of the contact surface when the one surface of the film and the opposite surface are in contact with each other μs is 0.1 or more and 0.6 or less, and Δhaze, which is an increase in haze before and after the heat treatment at 150 ° C. for 60 minutes, is 0.3% or less, and the haze before the heat treatment is 1. An oligomer precipitation preventing polyester film characterized by being 5% or less.   The oligomer precipitation-preventing polyester film according to claim 1, wherein the coating layer contains particles, and the average particle size of the particles is 50 nm or more and 200 nm or less, and is larger than the thickness of the coating layer.