JP2001062960A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a film sealed with an oligomer to be separated from a polymer onto a film surface by the heat treatment or the like even for a film of large oligomer content. SOLUTION: A coated layer containing a silane coupling agent containing an amino is formed at least on one face of a polyester film of 0.5 wt.% or more oligomer (cyclic trimer) content, and the oligomer amount on the surface of the coated layer after being treated at 180 deg.C for 10 minutes is 2.80 mg/m2 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film provided with a coating layer for sealing off the precipitation of oligomers, and more particularly, to a film having a high oligomer content by providing a coating layer having a specific composition. And a polyester film capable of sealing the deposition of oligomers at a high temperature with a coating layer.

[0002]

2. Description of the Related Art Polyester films represented by polyethylene terephthalate or polyethylene naphthalate have excellent properties such as mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and are cost-effective. It is used in various applications because of its excellent properties. However, as the uses are diversified, the processing and use conditions of the films are also diversified. For example, if a polyester film is left at a high temperature of 100 ° C. or higher, oligomers that have leached from the inside will precipitate on the film surface. Therefore, in particular, in a film containing a large amount of oligomer, precipitation of the oligomer on the film surface becomes severe, and various problems are caused by processing or using the film under such conditions. Further, various coating films have been proposed for the purpose of modifying the surface of the polyester film, but there is a problem that the precipitation of oligomers is accelerated depending on the composition to be applied.

Conventionally, methods for preventing the precipitation of oligomers include reducing the amount of oligomers contained in the raw material by solid-phase polymerization and improving the hydrolysis resistance of the polyester film by using a terminal blocking agent. And so on.

[0004]

However, in the case of solid-phase polymerization, the degree of polymerization of the polymer increases at the same time as the reduction of oligomers, so that the load on the extruder during film production increases and the number of production steps increases. , Which leads to an increase in manufacturing costs. In addition, the effect has not been seen depending on the production conditions of the film, and the prevention of oligomer precipitation on the film surface has not yet been achieved.

[0005] When an end-capping agent is used, there is a possibility that foreign matters are generated due to the end-capping agent, the polymer is colored, and the solid phase polymerizability is deteriorated. The present invention has been made in view of the above-mentioned conventional problems, and has as its object the presence of a large amount of oligomers, so that oligomers are likely to precipitate on the film surface. It is an object of the present invention to provide a polyester film capable of sealing a resulting oligomer.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above-mentioned circumstances, and as a result, even in a film having a high oligomer content, by forming a coating layer having a specific composition, a very The inventors have found that a polyester film with less oligomer precipitation can be obtained, and have completed the present invention.

[0007] In order to achieve the above object, according to the first aspect of the present invention, the content of the oligomer (cyclic trimer) is 0.1.
In a film in which a coating layer containing a silane coupling agent having an amino group is provided on at least one surface of a polyester film of 5% by weight or more, 180
The amount of oligomer on the surface of the coating layer after treatment at 10 ° C. for 10 minutes is 2.80 mg / m ² or less.

[0008] In the invention of claim 2 is the invention according to claim 1, silane coupling agent, the general formula _{Y- (CH 2) 3 -Si- (} X) 3 ( wherein, X is It indicates -OCH ₃ or -OCH ₂ CH _3,
Y represents an -NH ₂ or -NHCH ₂ CH ₂ NH _2. ).

According to the third aspect of the present invention, the first aspect of the present invention is provided.
In the above-mentioned invention, the silane coupling agent has the general formula Z- (CH_Two)_Three-Si- (X)_Three (Wherein X is -OCH_ThreeOr -OCH_TwoCH_ThreeIndicates that
Z is -NHCH_TwoCH _TwoNH_TwoIs shown. )
It is a compound.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
As the polyester in the present invention, typically, for example, polyethylene terephthalate in which 80% by mole or more of the structural unit is ethylene terephthalate, and 8% of the structural unit
Polyethylene-2,6-naphthalate in which 0 mol% or more is ethylene-2,6-naphthalate;
Poly-1,4-cyclohexane dimethylene terephthalate in which at least mol% is 1,4-cyclohexane dimethylene terephthalate is exemplified. Other examples include polyethylene isophthalate and poly-1,4-butylene terephthalate.

[0011] Examples of copolymerization components other than the above-mentioned superior constituents include propylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, neopentyl glycol, trimethylene glycol, tetramethylene glycol, and hexamethylene glycol. Diol components such as diethylene glycol, triethylene glycol, polyethylene glycol, polytetramethylene glycol, polyalkylene glycol, isophthalic acid,
Uses ester-forming derivatives such as 2,7-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, diphenyl ether dicarboxylic acid and oxymonocarboxylic acid. be able to.

As the polyester, besides a homopolymer or a copolymer, a blend of a small proportion with another resin can be used. Examples of resins to be blended with polyethylene terephthalate include, for example, various copolymerized polyethylene terephthalates such as isophthalic acid copolymer, cyclohexane dimethylene terephthalate copolymer, polyethylene glycol copolymer, polyethylene naphthalate and copolymerized polyethylene naphthalate, and poly (ethylene naphthalate). Butylene terephthalate and the like.

The intrinsic viscosity of the polyester film of the present invention is usually 0.40 to 0.90, preferably 0.45 to 0.95.
0.80, more preferably in the range of 0.50 to 0.70. When the intrinsic viscosity is less than 0.40, the mechanical strength of the film tends to be weak, and when the intrinsic viscosity is more than 0.90, the melt viscosity becomes high, and a load is applied to the extruder or the production cost is increased. Etc. may occur.

Conventionally, as a method for reducing oligomers in a film, a method has been used in which the amount of oligomers in the polymer is reduced in advance by solid phase polymerization to reduce the oligomers in the final film. In the case of (1), there is a problem that the intrinsic viscosity is increased and the cost is increased due to an increase in the number of steps. When the melting temperature is high or the residence time is long in the extruder in the film production process, the effect of reducing the oligomer cannot be obtained.

The polyester film of the present invention may contain additive particles, precipitated particles, other catalyst residues, etc. as a film surface projection forming agent in order to impart lubrication. The type, size and blending amount of these projection forming agents are
It is appropriately selected according to the desired slipperiness and transparency.

Further, the polyester film contains an antistatic agent, a stabilizer, a lubricant, a crosslinking agent, an antiblocking agent, an antioxidant, an ultraviolet absorber, a light blocking agent, a coloring agent, and the like, as required. Is also good.

Further, the polyester film of the present invention comprises:
It may have a multilayer structure, in which case some of the layers may be formed of a polymer other than polyester. That is, a laminated film may be used.

The present invention is characterized in that it is applied to a film having an oligomer (cyclic trimer) content of 0.5% by weight, preferably 0.6% by weight, more preferably 0.7% by weight or more. I do. When the oligomer (cyclic trimer) in the film is less than 0.5% by weight, the precipitation of the oligomer on the film surface due to the heat treatment is small, and the precipitation of the oligomer composed of the water-soluble organic silane compound used in the present invention is sealed. There is no need to provide a layer. However, in order to reduce the amount of oligomers in the film to less than 0.5% by weight, it is necessary to reduce the amount of oligomers contained in the raw material polymer. An increase in the intrinsic viscosity of the polymer is not preferable because the load on the extruder during the production of the film increases, and the productivity decreases.

The polyester film of the present invention is provided with a coating layer on at least one surface, and the amount of oligomer on the surface of the coating layer after heat treatment at 180 ° C. for 10 minutes is 2.8 mg / m 2.
² or less, preferably 1.60 mg / m ² or less, more preferably 1.00 mg / m ² or less. When the amount of the surface oligomer exceeds 2.80 mg / m ² , the use of the polyester film is limited, or a large amount of the oligomer is generated at a high temperature to become a foreign substance, which is not preferable.

In order to achieve the above object, the present invention is characterized in that a coating layer containing a silane coupling agent having an amino group is provided on a surface for preventing precipitation of an oligomer. When there is no coating layer containing a silane coupling agent having an amino group, a large amount of oligomers precipitate on the film surface due to heat treatment, and thus the deposited oligomers are undesirably coarse or haze value is increased. .

The silane coupling agent has at least two kinds of functional groups having different reactivities in one molecule, and is generally a compound represented by YRSIX ₃ . Where Y
Is an organic functional group such as a vinyl group, an epoxy group or an amino group; R is an alkylene group such as methylene, ethylene, propylene, etc .; In the silane coupling agent to be provided, it is essential that Y is an amino group. When Y is a vinyl group or an epoxy group, there is no sealing effect of the oligomer, which is not preferable. Specific compounds include, for example, N-β
(Aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, and the like.

Preferred silane coupling agents used in the present invention
The silane coupling agent has the general formula Y- (CH_Two)_Three-Si- (X)_Three (Wherein X is -OCH_ThreeOr -OCH_TwoCH_ThreeIndicates that
Y is -NH_TwoOr -NHCH_TwoCH_TwoNH_TwoIs shown. )so
A compound represented by the formula, which is more preferable as a specific compound.
The silane coupling agent is generally used for the run coupling agent.
Formula Z- (CH_Two)_Three-Si- (X)_Three (Wherein X is -OCH_ThreeOr -OCH_TwoCH_ThreeIndicates that
Z is -NHCH_TwoCH _TwoNH_TwoIs shown. )
It is a compound.

In the oligomer precipitation preventing layer in the present invention, a water-soluble or water-dispersible binder resin other than the above-mentioned silane coupling agent may be used in combination, if necessary. Examples of such a binder resin include polyvinyl alcohol, polyester, polyurethane, acrylic resin, vinyl resin, epoxy resin, amide resin and the like. Each of these skeleton structures may have a substantially composite structure by copolymerization or the like. Examples of the binder resin having a composite structure include acrylic resin-grafted polyester, acrylic resin-grafted polyurethane, vinyl resin-grafted polyester, and vinyl resin-grafted polyurethane.

For the purpose of preventing the oligomer from depositing on the film surface, which is the object of the present invention, it is preferable to use polyvinyl alcohol among the above binders. The amount of the binder component is preferably not more than 50 parts by weight, more preferably not more than 30 parts by weight based on the coating layer.

Further, in the coating layer of the film of the present invention,
If necessary, a crosslinking reactive compound may be contained. Examples of the crosslinking reactive compound include methylolated or alkylolated urea-based, melamine-based, guanamine-based, acrylamide-based, polyamide-based compounds, polyamines, epoxy compounds, oxazoline compounds, aziridine compounds, block isocyanate compounds, and silane cups. Ring agents, titanium coupling agents, zircon-aluminate coupling agents, metal chelates, organic acid anhydrides, organic peroxides, polyfunctional low molecular compounds such as heat or photoreactive vinyl compounds and photosensitive resins and It is selected from polymer compounds.

The crosslinking reactive compound mainly improves the cohesiveness, surface hardness, abrasion resistance, solvent resistance and water resistance of the coating layer by a crosslinking reaction with the functional group of the resin contained in the coating layer. be able to. For example, when the functional group is a hydroxyl group, the crosslinking reactive compound is preferably a melamine-based compound, a blocked isocyanate compound, an organic acid anhydride, or the like, and when the functional group is an organic acid and its anhydride, the crosslinking reactive compound Are preferably epoxy compounds, melamine compounds, oxazoline compounds, metal chelates, and the like. When the functional group is an amine, the crosslinking reactive compound is preferably an epoxy compound, and the resin contained in the coating layer has It is preferable to select and use those having high functional group and crosslinking reaction efficiency.

The crosslinking reactive compound may be a low molecular weight compound or a high molecular polymer having a reactive functional group as long as two or more reactive functional groups are contained in one molecule. .

The amount of the crosslinking reactive compound is preferably not more than 50 parts by weight, more preferably not more than 30 parts by weight, particularly preferably not more than 15 parts by weight based on the coating layer. Further, the coating layer of the present invention may contain inert particles as needed for improving the slipperiness of the coating layer.

The inert particles include inorganic inert particles and organic inert particles. Examples of the inorganic inert particles include silica sol, alumina sol, calcium carbonate, and titanium oxide. Examples of the organic inert particles include fine particles containing a homopolymer or a copolymer of a polystyrene resin, a polyacrylic resin, and a polyvinyl resin, or organic particles represented by crosslinked particles obtained by combining these with a crosslinkable component. These inert particles preferably have a softening temperature or a decomposition temperature of about 200 ° C. or more, more preferably 250 ° C. or more, and particularly preferably 300 ° C. or more.

The average particle size (d) of the inert particles is 1/3 ≦ d / L ≦ 3, more preferably 1/2 ≦ d / L ≦ 2, when the average film thickness of the coating layer is (L). Is preferably selected so as to satisfy the following relationship.

The coating layer of the present invention may contain, if necessary, a surfactant, an antifoaming agent, a coating improver, a thickener, a low-molecular antistatic agent, an organic lubricant, an antioxidant, an ultraviolet absorber, A small amount of additives such as a foaming agent, a dye and a pigment may be contained.
These additives may be used alone or in combination of two or more as needed.

The coating layer of the film of the present invention may be formed on only one side of the polyester film or on both sides. In the case of forming on one side only, another type of coating layer may be formed on the opposite side, if necessary, to further impart other characteristics. The film before application may be subjected to a chemical treatment, a discharge treatment or the like in order to improve the coating property and adhesion of the coating solution to the film.

The thickness of the coating layer is 0.01 to 2 μm, more preferably 0.03 to 0.5 μm, particularly 0.06 to 0.2 μm.
Is preferable. When the thickness of the coating layer is less than 0.01 μm, a sufficient effect of preventing oligomer precipitation may not be obtained, and when it exceeds 2 μm, the blocking resistance tends to be insufficient.

The film thickness of the present invention is usually 10 to 10
0 μm, preferably 20 to 75 μm, more preferably 20 to 50 μm. When the ratio exceeds this range, the handleability of the film may be deteriorated, and the production cost may be increased.

The film haze value after heat treatment at 180 ° C. for 10 minutes is usually 1.0 to 6.0%, preferably 1.5 to 6.0%.
It is 5.0%, more preferably in the range of 2.0 to 5.0%. For a film having a film haze of less than 1.0%, it is necessary to reduce the content of the added particles in order to reduce the film haze, and if this is the case, the slipperiness of the film deteriorates and the workability deteriorates. Film haze is 6.
If it exceeds 0%, the use may be limited.

The change in film haze by heat treatment at 180 ° C. for 10 minutes is 2.00%, preferably 1.5%.
0%, more preferably 1.00% or less. 180 ° C
Change in film haze by heat treatment for 10 minutes at 2.
If it exceeds 00%, the effect of the oligomer sealing layer used in the present invention is not obtained, and the oligomer is deposited on the film surface, and the deposited oligomer becomes undesirably coarse.

As a method for producing the biaxially stretched polyester film, a known method can be employed. For example, a pre-dried polyester chip and necessary additives are mixed and put into a hopper into an extruder.
It is melt-kneaded at a temperature of 300 ° C., extruded from a die into a sheet, and quenched on a casting drum (rotary cooling drum) of about 70 ° C. or less to obtain an unstretched sheet. It is possible to employ a method in which the film is stretched at an area magnification of 4 times or more, preferably 9 times or more, and further heat-set at a temperature of 120 to 200 ° C. The method of forming a coating layer on the surface of a biaxially stretched polyester film is as follows:
Although not particularly limited, a method of applying a coating solution during the process of producing a polyester film is preferably employed. Specifically, a method of applying and drying a coating solution on an unstretched sheet surface, a method of applying and drying a coating solution on a monoaxially stretched film surface, and a method of applying and drying a coating solution on a biaxially stretched film surface And the like. In these, after applying the coating solution to the surface of the unstretched film or the uniaxially stretched film,
It is economical to dry and cure the coating simultaneously with the heat treatment of the film.

Further, as a method of forming a coating layer, a method in which some of the above-described coating methods are used in combination may be employed, if necessary. Specifically, there is a method in which the first layer is applied to the surface of the unstretched sheet and dried, then stretched in a uniaxial direction, and then the second layer is applied and dried.

As a method of applying a coating solution on the surface of the polyester film, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, etc., which is described in "Coating System", written by Yuji Harazaki, Maki Shoten, 1979, can be used. Can be used.

It is preferable that the coating liquid used in the present invention is usually prepared using water as a main medium from the viewpoint of safety and hygiene. As long as water is the main medium, a small amount of an organic solvent may be contained for the purpose of improving dispersion in water or improving film forming performance. When the organic solvent is used by mixing with water as a main medium, it is preferable to use the organic solvent within a range that dissolves in water, but if it is a stable emulsion that does not separate when left for a long time, It may be used without dissolving in water. The organic solvent may be used alone, but may be used in combination of two or more as needed.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In addition,
The measuring methods and definitions of various physical properties and characteristics in the present invention are as follows. In Examples and Comparative Examples,
“Parts” and “%” mean “parts by weight” and “% by weight”, respectively. (1) Oligomer (cyclic trimer) content in polyethylene terephthalate After a predetermined amount of polyethylene terephthalate is dissolved in o-chlorophenol, reprecipitated with tetrahydrofuran and filtered to remove linear polyethylene terephthalate.
Next, the obtained filtrate is subjected to liquid chromatography (Shimadzu L
C-7A), the amount of oligomer (cyclic trimer) contained in polyethylene terephthalate is determined, and this value is divided by the amount of polyethylene terephthalate used for measurement.
The amount of oligomer (cyclic trimer) contained in polyethylene terephthalate is defined as the amount.

The amount of the oligomer (cyclic trimer) determined by liquid chromatography was determined from the ratio of the peak area of the standard sample to the peak area of the measured sample (absolute calibration curve method). The standard sample was prepared by accurately weighing an oligomer (cyclic trimer) that had been previously collected and dissolving it in DMF (dimethylformamide) that was weighed accurately. The concentration of the standard sample is preferably in the range of 0.001 mg / ml to 0.50 mg / ml.

The conditions for liquid chromatography were as follows. Mobile phase A: acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: MCI GEL ODS manufactured by Mitsubishi Chemical Corporation
1HU Column temperature: 40 ° C. Flow rate: 1 ml / min Detection wavelength: 254 nm (2) Heat treatment of film A4 size Kent paper and polyester film to be heat treated are combined. At this time, the four corners are clipped with a gem clip or the like so that the surface with the coating layer is on the outside, and the Kent paper and the polyester film are stopped.

Under a nitrogen atmosphere, the polyester film is left in an oven at 180 ° C. for 10 minutes to perform a heat treatment. (3) Amount of oligomer on film surface The polyester film after heat treatment is folded to form a square box so that the top is open and the area of the bottom is 250 cm ² . When a coating layer is provided, the coating layer face is on the inside.

Next, in the box created by the above method,
Add 10 ml of DMF, leave for 3 minutes, and collect DMF.
The recovered DMF is subjected to liquid chromatography (Shimadzu LC-
7A) to determine the amount of oligomer in DMF, and divide this value by the area of the film in contact with DMF to obtain the amount of oligomer on the film surface (mg / m ² ).

The amount of oligomer in DMF was determined from the peak area ratio between the peak area of the standard sample and the peak area of the measurement sample (absolute calibration curve method). The standard sample was prepared by accurately weighing oligomers (cyclic trimers) that had been previously collected and dissolving them in accurately weighed DMF. The concentration of the standard sample is 0.
A range of 001 mg / ml to 0.01 mg / ml is preferred.

The conditions for liquid chromatography were as follows. Mobile phase A: acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: MCI GEL ODS manufactured by Mitsubishi Chemical Corporation
1HU Column temperature: 40 ° C. Flow rate: 1 ml / min Detection wavelength: 254 nm (4) Film haze According to JIS-K6714, the turbidity of the film was measured with a spectroscopic turbidimeter NDH-20D manufactured by Nippon Denshoku Industries Co., Ltd.

(5) Change in Haze Value Due to Heat Treatment The film haze of each of the film before heat treatment and the film after heat treatment was measured, and the change in haze value due to heat treatment was determined by the following equation.

Film haze value after heat treatment-film haze value before heat treatment = change in haze value (6) Productivity The following judgment was made based on the production costs in the polymerization step of the raw materials and the film forming step of the film.

：: There is no problem in the manufacturing process and manufacturing conditions, and the productivity is high. Δ: Manufacturing process, manufacturing conditions, etc. have some restrictions,
Productivity is slightly lower. X: Production process and film forming conditions are limited, and productivity is poor.

(7) Lab-off test 100 parts by weight of a curable silicone resin (KS-779 manufactured by Shin-Etsu Chemical Co., Ltd.) and 1 part by weight of a curing agent (CAT PL-8 manufactured by Shin-Etsu Chemical Co., Ltd.) Parts, methyl ethyl ketone / toluene / n-heptane mixed solvent 2
Using a coating solution consisting of 200 parts by weight, applying with a Meyer bar so that the applied thickness after curing is 0.1 μm,
A release film on which a cured silicone resin film was formed was obtained.

After coating, the sample was heated at 23 ° C./50% R
After leaving in the room of H for 30 days, the coated surface was rubbed several times with a fingertip, and the degree of detachment of the cured silicone resin film was judged according to the following evaluation criteria and used as a measure of adhesion.

◎: good adhesion without falling off. ：: Slightly falling off, but good adhesion. Δ: Slightly falling off, slightly inferior in adhesion, but at a level that is not problematic in practical use.

×: There is detachment, poor adhesion. In Examples and Comparative Examples, the binder resins and the like used for forming the oligomer precipitation preventing layer are as follows.

[Examples of Compounds] Silane Coupling Agent (A): N-β (aminoethyl) γ-aminopropyltrimethoxysilane In the preparation of the coating solution, pure water was used as the diluent for concentration adjustment.

Silane Coupling Agent (B): N-β (aminoethyl) γ-aminopropyltriethoxysilane In the preparation of the coating solution, pure water was used as the diluent for concentration adjustment.

Silane Coupling Agent (C): In adjusting the coating solution of γ-aminopropyltrimethoxysilane, pure water was used as a diluent for adjusting the concentration.

Silane Coupling Agent (D): N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane In adjusting the coating solution, pure water was used as a diluent for adjusting the concentration.

Silane Coupling Agent (E): N-Phenyl-γ-aminopropyltrimethoxysilane In the preparation of the coating solution, pure water was used as the diluent for the concentration adjustment.

Silane Coupling Agent (F): In preparing a coating solution of γ-glycidoxypropyltriethoxysilane, a 2% acetic acid aqueous solution was used as a diluent for concentration adjustment because it was difficult to dissolve in pure water.

PVA-based resin: polyvinyl alcohol having a degree of saponification of 88 mol% and a degree of polymerization of 500 [Production method of polyester (I)] 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol were used as starting materials, and a catalyst was used. Magnesium acetate tetrahydrate 0.
09 parts by weight were placed in a reactor, the reaction start temperature was set to 150 ° C., and the reaction temperature was gradually increased with the removal of methanol, and the temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 parts of ethyl acid phosphate to the reaction mixture, 0.05 parts of silica particles dispersed in ethylene glycol having an average particle diameter of 1.6 μm and 0.04 parts of antimony trioxide were added. A time polycondensation reaction was performed. That is, if the temperature is 2
The temperature was gradually raised from 30 ° C to 280 ° C. On the other hand, the pressure was gradually reduced from the normal pressure, and finally was 0.3 mmHg. After 4 hours from the start of the reaction, the reaction was stopped and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (I) was 0.65, and the content of the oligomer (cyclic trimer) was 1.01% by weight.

[Production Method of Polyester (II)] Polyester (I) was subjected to solid phase polymerization to obtain polyester (II).
The intrinsic viscosity of the obtained polyester (II) was 0.75, and the content of the oligomer (cyclic trimer) was 0.32% by weight.

[Production Method of Polyester (III)] The polyester (I) is subjected to solid phase polymerization for a longer time than the polymerization time at the time of production of the polyester (II), and the polyester (III) is produced.
I got The intrinsic viscosity of the obtained polyester (III) is 0.70, and the content of the oligomer (cyclic trimer) is 0.5.
It was 0% by weight.

Example 1 (Preparation of Coating Solution-1) A silane coupling agent (A) was added to 9
A coating solution containing 0% by weight and 10% by weight of a PVA-based resin was prepared. The solid content of the coating solution was 2% by weight. (Production of film) After drying the polyester (I), 28
Extruded at a temperature of 0 to 300 ° C., cast on a cooling drum while using the electrostatic adhesion method, and has a thickness of about 550 μm.
m was obtained. This film was stretched 3.7 times in the machine direction at 85 ° C., and one side of the film was coated with the coating solution-1.
Was applied to a thickness of 0.06 μm, stretched 3.9 times in the transverse direction at 100 ° C., and heat-treated at 210 ° C. to give a thickness of 38 μm.
Was obtained.

(Examples 2 to 5, Comparative Examples 1-2) In the same manner as in Example 1, except that the silane coupling agent (A) was changed as shown in Table 1 below. To obtain a film.

[0066]

[Table 1] Comparative Example 3 A biaxially stretched polyester film was obtained in the same manner as in Comparative Example 2, except that the polyester (I) was changed to the polyester (II).

Comparative Example 4 A biaxially stretched polyester film was obtained in the same manner as in Comparative Example 2, except that the polyester (I) was changed to the polyester (III).

The evaluation results of the films obtained in the respective Examples and Comparative Examples are shown in Tables 2 and 3 below.

[0069]

[Table 2]

[0070]

[Table 3] As is clear from Tables 2 and 3, in Examples 1 to 5 satisfying the requirements of the present invention, the productivity is good, the change in the haze value after the heat treatment is small, and the result of the rub-off test is practical. It is higher than a level without problems. On the other hand, in Comparative Examples 1 to 4 that do not satisfy the requirements of the present invention, any of the items cannot be satisfied.

The inventions (technical ideas) other than those described in the claims which can be grasped from the above embodiments will be described below together with their effects. (1) In the invention described in claim 1, the thickness of the coating layer is 0.01 to 2 μm. In this case, a sufficient effect of preventing the precipitation of oligomers can be obtained, and the blocking resistance can be sufficiently ensured.

(2) In the first aspect of the present invention,
The film has a thickness of 10 to 100 μm. In this case, the handleability of the film is good and the production cost does not increase. (3) At least one surface of the uniaxially stretched polyester film is coated with a coating solution containing a silane coupling agent having an amino group, then stretched in the lateral direction and heat-treated, and simultaneously coated in a process of heat-treating the film. A method for producing a polyester film in which the layer is dried and cured. in this case,
Compared to the case where the coating solution containing the silane coupling agent is applied to the biaxially stretched film, there is no need to provide a drying step dedicated to the coating layer, which is economical.

[0073]

As described in detail above, according to the polyester films of the first to third aspects of the present invention, oligomers that precipitate on the film surface even at high temperatures can be suppressed, and useful polyester films can be obtained. Can be provided at low cost, and its industrial value is high.

Claims (3)

[Claims] An oligomer (cyclic trimer) content of 0.1.
In a film in which a coating layer containing a silane coupling agent having an amino group is provided on at least one surface of a polyester film of 5% by weight or more, 180
A polyester film, wherein the amount of the oligomer on the surface of the coating layer after treatment at 10 ° C. for 10 minutes is 2.80 mg / m ² or less. 2. A silane coupling agent represented by the general formula: Y- (CH ₂ ) ₃ —Si— (X) ₃ (where X represents —OCH ₃ or —OCH ₂ CH ₃ ,
Y represents an -NH ₂ or -NHCH ₂ CH ₂ NH _2. The polyester film according to claim 1, which is a compound represented by the formula: 3. A silane coupling agent represented by the general formula Z- (CH_Two)_Three-Si- (X)_Three (Wherein X is -OCH_ThreeOr -OCH_TwoCH_ThreeIndicates that
Z is -NHCH_TwoCH _TwoNH_TwoIs shown. )
The polyether according to claim 1, which is a compound.
Steal film.