JP2002170222A - Polyester film for magnetic recording medium and identifying method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for a magnetic recording medium wherein it can be easily identified that the polyester film for the magnetic recording medium is formed by using a recycled resin and which has the same quality as the polyester film consisting of dimethyl terephthalate produced from para- xylene and to provide an identifying method therefor. SOLUTION: A magnetic material coating surface of the poly ester film has <=10 nm central plane average roughness and the polyester film contains 1-500 wt.ppm inorganic compound to dimethyl phthalate as an identification compound. The identifying method of the polyester film is also provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a magnetic recording medium comprising a dimethyl terephthalate composition containing an inorganic compound as a discriminating compound and a method for discriminating the same. More specifically, the present invention relates to a method for decomposing a polyalkylene terephthalate. Polyester film composed of dimethyl terephthalate composition (hereinafter abbreviated as “raw material recycled DMT”) obtained by adding an inorganic compound as an identification compound to dimethyl terephthalate polymerized and esterified with methanol, and produced using para-xylene as a raw material Polyester film made of dimethyl terephthalate (hereinafter abbreviated as Virgin DMT) and a polyester film for a magnetic recording medium which can be easily identified and has the same quality as the polyester film made of Virgin DMT.

[0002]

2. Description of the Related Art At present, polyethylene terephthalate (hereinafter abbreviated as PET) is widely used in the world as fibers, resins, packaging materials, films, and other molded articles. Disposal has become a major issue in recent years. In recent years, used PE
After being collected, the T bottle undergoes a crushing process, a separation process from other materials, and a washing process, and a circulation loop of material recycling to be reprocessed into fibers, sheets, and the like is formed, and the T bottle has begun to function.

[0003] However, the materials processed by this system are limited in reprocessing equipment and conditions, and there is also a problem of deterioration in the quality of reprocessed resin products, and their applications are also restricted. Further, it has not been possible to easily distinguish a material recycled reworked resin product from a resin product made of a resin made of a virgin material.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyester film which can easily identify the use of a recycled resin and has a small difference in quality from a film using a virgin resin, and a method for identifying the same. And

[0005]

Means for Solving the Problems As a result of intensive studies, the present inventors have completed the present invention.

[0006] That is, an object of the present invention is to provide a magnetic recording medium in which the average roughness of the center plane of the surface coated with a magnetic material is 10 nm or less, and which further contains 1 to 500 ppm by weight of an inorganic compound as a discrimination compound based on dimethyl terephthalate. Achieved by polyester film.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the identification method of the present invention, first, an inorganic compound to be an identification compound is required. Among the inorganic compounds, it is preferable to be a simple substance and / or an inorganic compound composed of at least one noble metal selected from the group consisting of the noble metals ruthenium, rhodium, palladium, silver, osnium, iridium, platinum, and gold. . Among them, the characteristics are that the analysis method is easy and easy to detect, that the film is easy to be made into a fine powder that does not contain coarse particles that are surface defects, that it is chemically stable, and that it has low toxicity. Desirable compounds having, for example, ruthenium, ruthenium oxide, ruthenium chloride, rhodium, rhodium oxide, rhodium chloride, palladium, palladium oxide, palladium chloride, palladium nitrate, palladium sulfate, silver, silver oxide, silver chloride, silver bromide, Particularly preferred is one composed of at least one compound selected from the group consisting of silver sulfide, silver nitrate, osnium, iridium, iridium oxide, iridium chloride, iridium sulfide, platinum, platinum oxide and gold. The amount of the inorganic compound to be added is preferably 1 to 500 ppm by weight, more preferably 1 to 50 ppm by weight, based on dimethyl terephthalate. 1 ppm by weight
If it is less than 500 wt.
If it exceeds pm, coarse particles are formed in the film to cause surface defects, which adversely affects thermal stability and moldability.

Next, the polyester is subjected to a depolymerization reaction in EG in the presence of a known depolymerization catalyst. Here, the polyester preferably includes polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyhexamethylene terephthalate. If necessary, the mixture obtained in the depolymerization reaction is extracted with excess EG used in the depolymerization reaction, then introduced into a reactor together with MeOH, and subjected to substitution esterification reaction and cooling crystallization to obtain crude terephthalic acid. Obtain dimethyl. Further, by distilling and purifying the obtained crude dimethyl terephthalate,
High-purity dimethyl terephthalate can be obtained.

The high-purity recovered dimethyl terephthalate obtained through the above steps is kept in a molten state at 140 to 170 ° C., and an inorganic compound can be added by a known method. Can be adopted without any problems. For example, as a form when adding an inorganic compound,
Raw material recycled DMT can be obtained by a method in which a fine powder of an inorganic compound or a slurry of an organic solvent represented by, for example, methanol is added, and the mixture is added and then uniformly dispersed in dimethyl terephthalate by stirring or liquid circulation.

The polyester film of the present invention is characterized in that an inorganic compound as an identification compound is used in an amount of 1 to 50 with respect to dimethyl terephthalate unit constituting polyalkylene terephthalate.
It is a polyester film containing 0 ppm by weight.

The polyester film of the present invention is a thermoplastic polyester comprising a terephthalic acid unit and a diol unit, and it is preferable that the terephthalic acid unit is a component of 80 mol% or more of the total acid component.

The terephthalic acid unit is derived from an ester derivative, and the derivative is preferably dimethyl terephthalate, which is a methyl ester.

The above-mentioned dimethyl terephthalate is obtained by depolymerizing polyalkylene terephthalate with ethylene glycol and then transesterifying with methanol, and adding the above-mentioned inorganic compound as an identification compound to the dimethyl terephthalate in an amount of 1 to 500 ppm by weight. , More preferably 1 to
It is preferably dimethyl terephthalate added at 50 ppm by weight.

In the range of less than 20% of the total acid component, for example, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid,
1,7-naphthalenedicarboxylic acid, other isomers of naphthalenedicarboxylic acid, aromatic dicarboxylic acids such as isophthalic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, hexane, etc. Alicyclic dicarboxylic acids such as hydroterephthalic acid and hexahydroisophthalic acid, aliphatic dicarboxylic acids such as adipic acid, sebacic acid and azelaic acid, p-β-hydroxyethoxybenzoic acid and ε-oxycaproic acid At least one or more acid components selected from bifunctional carboxylic acids such as oxyacids can be copolymerized.

The diol component constituting the polyester film includes, for example, ethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, neopentyl glycol, and the like. , Diethylene glycol, 1,1
Diols such as -cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2-bis (4'-β-hydroxyphenyl) propane, bis (4'-β-hydroxyethoxyphenyl) sulfone; It can be more than a species.

In the present invention, the polyester film may be copolymerized with a compound having three or more functional groups in a range of 2% or less.

The film of the present invention has a molding process and
In order to smoothly carry out the chemical processing step, it is general to make inert fine particles be present as long as the object of the present invention does not hinder the identification of the polyester film using recycled DMT.

The inert fine particles in the present invention are not particularly limited as long as they can improve the slipperiness for the purpose of facilitating the film forming and processing steps. For example, (1) silicone resin, cross-linked polystyrene, cross-linked acryl Particles made of a heat-resistant polymer such as resin, melamine-formaldehyde resin, aromatic polyamide resin, polyimide resin, polyamideimide resin, and crosslinked polyester, (2) aluminum trioxide (alumina), titanium dioxide, silicon dioxide (silica), and oxidation Particles composed of metal oxides such as magnesium, zinc oxide, and zirconium oxide; (3)
Particles composed of metal carbonates such as magnesium carbonate and calcium carbonate, (4) particles composed of metal sulfates composed of calcium sulfate, barium sulfate and the like, (5) particles composed of carbon such as carbon black, graphite and diamond, And (6) particles composed of an organic compound and an inorganic compound, such as particles composed of clay minerals such as kaolin, clay and bentonite.

The average particle size of the inert particles in the present invention is preferably in the range of 0.01 to 2 μm, more preferably 0.02 to 3 μm, and particularly preferably 0.05 to 1 μm. When the average particle size is less than 0.01 μm, it is difficult to obtain the effect of improving running properties and blocking resistance.
If it is 2 μm or more, it is difficult to obtain surface flatness of the film, which is not preferable. The content of the inert particles in the production of the polyester resin composition is from 0.01 to 3% by weight, preferably from 0.03 to 1% by weight. When the content is less than 0.01% by weight, the productivity as a polymer is low and inefficient.
On the other hand, if it exceeds 3% by weight, the dispersion in the polyester becomes insufficient.

In the film of the present invention, the center line roughness of the surface coated with the magnetic material must be 10 nm or less. If the average roughness of the center plane of the magnetic material applied surface exceeds 10 nm, the film surface after the application of the magnetic material becomes rough, and electromagnetic conversion characteristics are remarkably deteriorated.

The film of the present invention is preferably a laminated film comprising at least two layers. Generally, as the average roughness of the center surface of the film surface is larger, the film is more slippery and the processing characteristics are improved, but the electromagnetic conversion characteristics are unfavorably deteriorated. In the laminated film, the magnetic material coated surface and the other surface can have different compositions, that is, different center plane average roughnesses, and can improve processing characteristics without deteriorating electromagnetic conversion characteristics. is there.

The film of the present invention can be used in one or more layers of the above laminated film.

Next, a method for identifying a polyester film according to the present invention will be described. The method for identifying a polyester film according to the present invention comprises a step of subjecting a raw material containing dimethyl terephthalate containing an inorganic compound as the identification compound and diol to a transesterification reaction in the presence of a transesterification catalyst to obtain a bis (β- (Hydroxyethyl) terephthalate and / or an oligomer thereof, followed by melt polycondensation under high temperature and reduced pressure in the presence of a polycondensation catalyst and a stabilizer,
Obtain a polyester resin composition. The above-mentioned polyester resin composition or a mixture thereof with another polyester resin is melt-extruded, quenched to form an unstretched film, and the unstretched film is stretched biaxially, heat-fixed and, if necessary, subjected to relaxation heat treatment. This can be achieved by obtaining a polyester film.

As the transesterification catalyst, alkaline earth metal salts such as magnesium and calcium, and metal compounds such as titanium, zinc and manganese are preferably used. Known polycondensation catalysts include germanium compounds, antimony compounds, titanium compounds, cobalt compounds, and tin compounds. Examples of the stabilizer include phosphoric esters such as trimethyl phosphate, triethyl phosphate and triphenyl phosphate, phosphites such as triphenyl phosphite and trisdecyl phosphite, methyl acid phosphate, dibutyl phosphate and monobutyl phosphate. Phosphorus compounds such as acidic phosphoric acid ester, triethylphosphonoacetate, phosphoric acid, phosphorous acid, hypophosphorous acid and polyphosphoric acid are preferred.

The supply of the transesterification catalyst can be carried out at the initial stage of the transesterification reaction in addition to the preparation of the raw materials. The supply of the stabilizer can be performed before the initial stage of the polycondensation reaction, but is preferably added at the end of the transesterification reaction. Further, the polycondensation catalyst can be supplied by the beginning of the polycondensation reaction step. The reaction temperature during the transesterification reaction is usually 200 to 260 ° C,
The reaction pressure is from normal pressure to 0.3 MPa. The reaction temperature during the polycondensation is usually from 250 to 300 ° C, and the reaction pressure is usually from 60 to 0.1 Kpa. Such transesterification reaction and polycondensation reaction may be performed in one stage or may be performed in a plurality of stages.

As a method of causing the inert fine particles to be present in the polyester resin, it is preferable to disperse the diol component in the form of a slurry of ethylene glycol and polymerize the ethylene glycol with a predetermined dicarboxylic acid component. In addition, a method is known in which the inert fine particles alone and / or a water slurry are directly mixed with predetermined polyester pellets and kneaded into a polyester resin using a vent-type biaxial kneading extruder.

The polymer thus obtained has an intrinsic viscosity of usually 0.4 to 0.90 dl / g and is formed into chips by a conventional method. The average particle size of the polymer chips is generally in the range of 2.0 to 5.5 mm, preferably 2.2 to 4.0 mm.

In the film forming step, a relaxation heat treatment may be performed if necessary during or after heat setting. Production conditions such as stretching conditions for forming into a film may be appropriately selected in accordance with physical properties such as surface characteristics, density, and heat shrinkage of the target film.
For example, the above unstretched film is 2.5 times or more at a temperature of [Tg-10] to [Tg + 60] ° C (where Tg: glass transition temperature of polyester) in a uniaxial direction (longitudinal or transverse direction). Preferably, the film is stretched at a magnification of 3 times or more, and then Tg to [Tg + 70] ° C. in a direction perpendicular to the stretching direction.
It is preferable to stretch at a temperature of 2.5 times or more, preferably 3 times or more. Further, if necessary, the film may be stretched again in the machine direction and / or the cross direction. The area stretch ratio obtained by multiplying the stretch ratio in the longitudinal direction and the transverse direction is preferably 9 times or more, more preferably 12 to 35 times, and particularly preferably 15 to 30 times. Furthermore, heat setting is performed between [Tg + 70] and [Tg + 70].
m-10] ° C. (Tm: melting point of polyester), for example, preferably at a temperature of 180 to 250 ° C., and the heat fixing time at that time is preferably 1 to 60 seconds.

A metal component of the added inorganic compound can be detected by fluorescent X-ray analysis, atomic absorption analysis, inductively coupled plasma (hereinafter abbreviated as ICP) emission analysis, or the like.

[0031]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. The characteristics in the examples were measured by the following methods. 1) Intrinsic viscosity: It was determined from a value measured at 35 ° C. in an orthochlorophenol solution. 2) Average particle size of inert particles: “SACP-4L Centrifugal Particle Size Analyzer (Centrifugal) manufactured by Shimadzu Corporation.
Particle Size Analyzer). From the integrated curve of the particles having each particle size and its abundance calculated based on the obtained centrifugal sedimentation curve, the particle size “equivalent sphere diameter” corresponding to 50 mass percent is read, and this value is defined as the above average particle size. (See the book "Granularity Measurement Techniques", published by Nikkan Kogyo Shimbun, 1975, pages 242 to 247). 3) Method of discriminating inorganic compound as discriminating compound: The metal component of the discriminating compound in the film was qualitatively and quantitatively determined using a fluorescent X-ray analyzer (Rigaku Denki Kogyo KK, System 3270). 4) Center surface average roughness WRa: Using a non-contact three-dimensional roughness meter manufactured by WYKO Co., Ltd., trade name "TOPO-3D", measuring magnification 40 times, measuring area 242 μm × 239 μm.
(0.058 mm ² ) to obtain a surface roughness profile (original data). WRa uses the value calculated and output by the following equation by the surface analysis using the built-in roughness meter software.

[0032]

(Equation 1)

Zjk is measured in the measurement direction (242 μm).
m), and the direction (239 μm) perpendicular to it
These are the heights on the three-dimensional roughness chart at the j-th and k-th positions in each direction when divided and divided into N. 5) Fly spec: Observing the film under a microscope under polarized light, and determining whether a single particle and / or a particle having a particle size of 3 μm or more in which primary particles are agglomerated exists in a place where the polarized light is applied, is determined as a fly spec as follows. did. Grade 1: Fly specification is less than 10 pieces / 50 cm ² . Second class: The fly specification is 10 to 30 pieces / less than 50 cm ² . Class 3: Fly spec is 30 pieces / 50 cm ² or more.

Example 1 Polyethylene terephthalate was depolymerized with ethylene glycol and then transesterified with methanol. Dimethyl terephthalate obtained by adding 10 ppm by weight of silver chloride as a discriminating compound to dimethyl terephthalate was obtained. Hereafter, raw material recycling DMT
100 parts by weight) and 70 parts by weight of ethylene glycol (hereinafter abbreviated as “EG”) were subjected to transesterification using manganese acetate tetrahydrate as a catalyst in the usual manner. Add the phosphate,
The transesterification reaction was terminated, and 1.5 parts by weight of a slurry obtained by adding and dispersing 10 parts of spherical silica fine particles (average particle diameter: 0.3 μm) to 90 parts by weight of ethylene glycol (hereinafter abbreviated as EG) was dispersed. Silica fine particles: 0.15% by weight based on the recycled DMT) were added with stirring. Thereafter, antimony trioxide was added as a polymerization catalyst, and a polycondensation reaction was carried out as usual under a high vacuum to obtain polyethylene terephthalate having an intrinsic viscosity of 0.620. Further, the obtained polyester is dried at 180 ° C., formed into a sheet by melt film formation, subsequently biaxially stretched at 90 ° C. to 3.5 times longitudinal stretching ratio and 4.0 times transverse stretching ratio, and further heated at 200 ° C. It was fixed to form a film having a thickness of 15 μm. The properties of the obtained polyester film are as follows. Intrinsic viscosity: 0.56 Silver content: 7 weight pp based on dimethyl terephthalate
m Center plane average roughness: 9 nm Fly spec: Class 1

Reference Example 1 A film having a thickness of 15 μm was obtained in the same manner as in Example 1, except that dimethyl terephthalate was changed to Virgin DMT manufactured by Teijin (no identification compound).
The properties of the obtained polyester film are as follows. Intrinsic viscosity: 0.56 Silver content: 0 weight pp based on dimethyl terephthalate
m Center plane average roughness: 9 nm Fly spec: Class 1

Comparative Example 1 The amount of the discriminating compound was 100
Except for 0 ppm, the same procedure as in Example 1 was carried out.
A μm film was obtained. The properties of the obtained polyester film are as follows. Intrinsic viscosity: 0.56 Silver content: 700 weight ppm based on dimethyl terephthalate Center plane average roughness: 11 nm Fly spec: secondary

Example 2 The following four types of polyesters were obtained in the same manner as in Example 1 except that the inert particles were changed. Polyester A: Spherical silica fine particles (average particle size 0.1
μm) Content 0.4% by weight Polyester B: alumina fine particles (average particle size 0.3 μm)
m) Content: 0.4% by weight Polyester C: Spherical silicone fine particles (average particle size: 0.5 μm) Content: 0.2% by weight Polyester D: No inert fine particles added

A mixture of 1 part by weight of polyester A and 3 parts by weight of polyester D, a mixture of 19 parts by weight of polyester B and 1 part by weight of polyester C were separately dried at 180 ° C. A laminated sheet was formed by a membrane method, and subsequently biaxially stretched at 90 ° C. to 3.5 times the longitudinal stretching ratio and 4.0 times to the transverse stretching ratio, and further heat-set at 200 ° C. to a thickness of 1 μm comprising polyesters A and D. And a 5 μm layer composed of polyester B and C and a 6 μm thick two-layer film. The physical properties of the obtained polyester film are as follows. Intrinsic viscosity: 0.56 Silver content: 7 weight pp based on dimethyl terephthalate
m Center plane average roughness: 5 nm layer composed of polyesters A and D Center plane average roughness: 8 nm layer composed of polyesters B and C Fly spec: 1st class

Reference Example 2 A two-layer film having a thickness of 6 μm was obtained in the same manner as in Example 2, except that dimethyl terephthalate was changed to Virgin DMT (no identification compound) manufactured by Teijin. Note that polyesters using virgin DMT are abbreviated as A *, B *, C *, and D *, respectively. The properties of the obtained polyester film are as follows. Intrinsic viscosity: 0.56 Silver content: 0 weight pp based on dimethyl terephthalate
m Center plane average roughness: Layer 5 composed of polyester A * and D *
nm Center plane average roughness: Layer 8 composed of polyester B * and C *
nm fly spec: 1st class

Example 3 100 parts by weight of dimethyl terephthalate was added to Teijin's virgin DMT (without identification compound).
And ethylene glycol (hereinafter abbreviated as “EG”) 7
0 parts by weight were subjected to transesterification using calcium acetate monohydrate and magnesium acetate tetrahydrate as catalysts in the usual manner, and then trimethyl phosphate was added as a stabilizer to terminate the transesterification reaction. 0.5 parts by weight of a slurry obtained by adding and dispersing 10 parts of spherical silica fine particles (average particle size: 0.06 μm) to 90 parts by weight of glycol (hereinafter abbreviated as EG) is 0.5 part by weight (spherical silica fine particles: 0.0
5% by weight of virgin DMT) was added with stirring. Thereafter, tetra-t-butoxytitanium was added as a polymerization catalyst, and a polycondensation reaction was carried out as usual under a high vacuum to obtain polyethylene terephthalate E * having an intrinsic viscosity of 0.620.

Example 2 with 4 parts by weight of polyester E *
19% of polyester B obtained by
1 part by weight of each of the mixed parts was separately dried at 180 ° C., and then formed into a laminated sheet by a known melt film-forming method. 2
Polyaxially stretched and heat-set at 200 ° C for polyester E *
Was formed into a two-layer film having a thickness of 6 μm and a layer having a thickness of 1 μm and polyesters B and C having a thickness of 5 μm. Intrinsic viscosity: 0.56 Silver content: 6 weight pp based on dimethyl terephthalate
m Center plane average roughness: 3 nm layer composed of polyesters A and D Center plane average roughness: 8 nm layer composed of polyesters B and C Fly spec: 1st class

Example 4 A mixture of 1 part by weight of polyester B * and 1 part by weight of polyester C and 130 parts by weight of polyester D were separately dried at 180 ° C., and then dried by a known melt casting method. The laminated sheet is then formed at 90 ° C. at a longitudinal stretch ratio of 3.5 times and a transverse stretch ratio of 4.0 times.
Axial stretching, heat-setting at 200 ° C, polyester B *
And C were 15 μm thick three-layer films in which the outermost layers (each having a thickness of 1 μm) and the polyester D became an inner layer (thickness: 13 μm). The physical properties of the obtained polyester film are as follows. Intrinsic viscosity: 0.55 Silver content: 6 weight pp based on dimethyl terephthalate
m Center plane average roughness: 8 nm Fly spec: Class 1

[0043]

According to the present invention, there is provided a magnetic recording medium using a dimethyl terephthalate composition obtained by depolymerizing polyalkylene terephthalate and adding an inorganic compound as a discriminating compound to dimethyl terephthalate esterified with methanol. Polyester film, and Virgin D
A polyester film for a magnetic recording medium having the same quality as a polyester film for a magnetic recording medium made of MT, and a method for identifying the same can be provided.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 67/02 C08L 67/02 F term (Reference) 4F071 AA43 AA46 AB15 AB26 AC15 AF35 AH14 BA09 BC01 BC16 BC17 4F100 AA01A AA17A AA20H AK01B AK01C AK41A AK41B BA02 BA03 BA10A BA10B BA10C CA19 CA23A DD07A GB41 JG06A JK15A YY00A 4J002 CF051 CF061 CF071 CF081 CF181 DA076 DA116 DD076 FD206 GS00 5D006 CB01 CB06

Claims (6)

[Claims] An average roughness of a center surface of a magnetic material applied surface is 10
nm or less, and further contains an inorganic compound as an identification compound in an amount of 1 to 500 ppm by weight based on dimethyl terephthalate. 2. The method according to claim 1, wherein the inorganic compound is ruthenium, rhodium,
The polyester film for a magnetic recording medium according to claim 1, wherein the polyester film is a simple substance and / or an inorganic compound composed of at least one noble metal selected from the group consisting of palladium, silver, osmium, iridium, platinum, and gold. 3. A polyester film for a magnetic recording medium, wherein the polyester film for a magnetic recording medium according to claim 1 is laminated as at least one layer of a laminated film having at least a two-layer structure. . 4. For a magnetic recording medium, wherein the polyester film for a magnetic recording medium according to any one of claims 1 to 2 is laminated as a layer other than the magnetic material coated surface of a laminated film having a two-layer structure. Polyester film. 5. A magnetic recording medium wherein the polyester film for a magnetic recording medium according to claim 1 is laminated as a layer other than the magnetic material coated surface of a laminated film having at least a three-layer structure. For polyester film. 6. A method for producing a polyester film, comprising a simple substance and / or an inorganic compound composed of at least one noble metal selected from the group consisting of ruthenium, rhodium, palladium, silver, osnium, iridium, platinum and gold. 1 to 500 ppm by weight
A method for identifying a polyester film for a magnetic recording medium, comprising using a dimethyl terephthalate composition contained therein.