CN1922244A - Biaxially oriented polyester film - Google Patents

Abstract

A biaxially oriented polyester film of 8 to 15 cm<-1> microscopic Raman crystallization index (Ic) as measured in the direction of film thickness wherein the difference between Ic maximum and Ic minimum is 1 cm<-1> or less. There is further provided a biaxially oriented polyester film of -25 to 0 dB relative power (I<10>TD) of space frequency 1/mm as measured along the width of at least one surface of polyester film having undergone heat treatment at 100 DEG C for 24 hr. These biaxially oriented polyester films excel in microplanarity even after high-temperature storage or heat loading during processing. These biaxially oriented polyester films are useful as polyester films for use in a magnetic recording material, an electronic material, a plate making film, a sublimatic ribbon and a packaging material. In particular, these biaxially oriented polyester films are highly useful when employed as a base film for high-density magnetic recording medium, especially double layer metal coated digital recording medium according to linear recording system.

Description

Biaxially oriented polyester film

Technical field

The present invention relates to be used for the polyester film of magnetic recording material, electronic material, plate-making film, subliming type colour band, wrapping material.Useful biaxially oriented polyester film when specifically, relating to plied timber application type digital recording medium as high-density magnetic recording media, particularly linear recording mode and use with basement membrane.

Background technology

In recent years, the magnetic recording media used etc. with, digital video band of data-carrier store becomes the magnetic recording media of high-density, heavy body.In general, the recording mode that this magnetic recording media adopted have as shown in Figure 1 the spiral record mode and linear recording mode as shown in Figure 2.The spiral record mode is to draw belt from the tape drum with two spools, and the round tube type magnetic head of high speed rotating is scanned, and sideling belt is read and write.The linear recording mode is guided belt into magnetic head from the tape drum with a spool, and belt is read and write along straight line along its length.Compare with the spiral record mode, the recording density of linear recording mode is lower, but since belt with respect to being involved in slowly of magnetic head, so less to the damage of belt, as data-carrier store with having high reliability.

Recently, about the LTO that adopts this linear recording mode ( LInear TApe OPen) and SDLT ( SUper DIgital LInear TApe), developed one and rolled up belt with the above heavy body of 100GB.

For high capacity, the track number of increasing is generally arranged, shorten recording wavelength, increase by three kinds of ways of belt length.

If the increase track number, the narrowed width of each magnetic track then is so the control of the dimensional stability of belt width direction becomes important.And, after shortening recording wavelength,, require surface smoothing in order to realize sufficient electromagnetic conversion characteristic.And then, because the size of the tape drum of magnetic recording media is immutable basically, so, then necessarily require the filming of belt and high strength thereupon in order to increase the belt length of every volume.From these 3, also need more research.Open 2002-329312 communique, WO00-076749 communique the spy, the spy opens in the 2003-67913 communique about high strength following record: the high strength that promptly utilizes the optimizing of the temperature expansion coefficient of belt width direction and humidity expansion coefficient, the pathization, the stretching ratio that add particle to improve to carry out basement membrane, utilize metal to strengthen carrying out high strength.But, even adopt these technology, have the magnetic recording media usefulness of linear recording mode of the heavy body more than the 100GB as a volume, can not obtain sufficient electromagnetic conversion characteristic.From up to now result as can be known, the planarity deterioration that the film surface due to the thermal load when high temperature keeping and processing film is small exerts an influence to the characteristic of magnetic recording media.

Generally speaking because the belt of linear recording mode is involved in slowly, the power that magnetic head is vertically pushed a little less than, so than the easier generation spacing loss of the situation of spiral record mode.Spacing loss is the gap of the Nano grade that can form between magnetic head and belt, if spacing loss is big, then electromagnetic conversion characteristic worsens.In order to realize heavy body, require the low wavelength of recording wavelength of magnetic recording media to turn to be lower than 0.6 μ m about, and require further surface detail microcontroller.But technique known is still being studied aspect the rerum natura of the expression film integral mean value of temperature expansion coefficient, humidity expansion coefficient, intensity, crystallization degree and so on.With the characteristic of temperature expansion coefficient, humidity expansion coefficient, intensity, crystallization degree, can not carry out as the planarity control of the small level of problem at present.

Summary of the invention

The present invention is directed to the problems referred to above, by difference of the micro-Raman's crystallization index on the film thickness direction, micro-Raman's crystallization exponential maximum value and minimum value etc. is controlled at certain specified range, thereby the film of the small planarity deterioration of the film surface due to a kind of thermal load can prevent high temperature keeping and processing film the time is provided, a kind of film useful to the high-density magnetic recording media of linear recording mode is provided especially.

Biaxially oriented polyester film of the present invention is that micro-Raman's crystallization index Ic of film thickness direction is 8cm ^-1～15cm ^-1, the maximum value of Ic and the difference of minimum value be smaller or equal to 1cm ^-1Biaxially oriented polyester film.

And then, biaxially oriented polyester film of the present invention, be 100 ℃ apply 24 hours thermal treatment after, relative power (Relative Power) I of the spatial frequency 10 (1/mm) on the width of at least one face of polyester film ¹⁰ _TDBiaxially oriented polyester film for-25～0dB.

According to the present invention, can obtain in high temperature keeping and after adding the thermal load in man-hour, also good film of small plane performance.

Description of drawings

Fig. 1 is the sketch of general spiral record mode.

Fig. 2 is the sketch of general linear recording mode.

Embodiment

The biaxially oriented polyester film of first mode of the present invention, the micro-Raman's crystallization index Ic on its film thickness direction is 8～15cm ^-1Micro-Raman's crystallization index Ic on the film thickness direction is preferably 10～14.5cm ^-1, 12～14cm more preferably ^-1Micro-Raman's crystallization index can be under micron unit the crystal property of analysed film.Micro-Raman's crystallization exponential value is more little, and the expression structure is stable more.Ic is greater than 15cm ^-1The time, the contraction that thermal load causes takes place in structural instability, and small planarity worsens.On the other hand, in order to make up to Ic less than 8cm ^-1Till structure all stablize, need increase considerably stretching ratio, improve the heat setting temperature, therefore break again and again, aspect production, problem is arranged.

The biaxially oriented polyester film of first mode of the present invention, the maximum value of the Ic of thickness direction and the difference of minimum value are smaller or equal to 1cm ^-1The maximum value of the Ic of thickness direction and the difference of minimum value are preferably smaller or equal to 0.8cm ^-1, more preferably smaller or equal to 0.5cm ^-1In the difference of maximum value and minimum value greater than 1cm ^-1Situation under, the small thermal contraction degree varies on the film thickness direction during thermal load causes, the small planarity of film surface worsens.

The biaxially oriented polyester film of first mode of the present invention, the viewpoint of the contraction inequality when preventing thermal load, the micro-Raman's crystallization exponential maximum value of thin film planar direction and the difference of minimum value are preferably smaller or equal to 1cm ^-1, be more preferably less than and equal 0.8cm ^-1, more preferably smaller or equal to 0.5cm ^-1

First mode of the present invention is characterised in that, found that the percent thermal shrinkage that adopts in prior art and Young's modulus analyze the problem that spacing loss in the linear recording mode of difficulty and electromagnetic conversion characteristic worsen like that in macroscopical assay method, the micro-Raman's crystallization exponential representation that can measure by unusual microcosmic.Therefore, even percent thermal shrinkage is identical with Young's modulus, micro-Raman's crystallization index surpasses above-mentioned scope can not obtain effect.

The biaxially oriented polyester film of second mode of the present invention is the relative power I of the spatial frequency 10 (1/mm) on the width of at least one face of 100 ℃ of polyester films after applying 24 hours thermal treatment ¹⁰ _TDBiaxially oriented polyester film for-25～0dB.The relative power I of the spatial frequency 10 (1/mm) on the width of a face ¹⁰ _TDBe preferably-20～-1dB, more preferably-15～-5dB.Relative power is with 1nm ²External waviness be designated as the value that 0dB comes benchmark on analysis software, be worth greatly more in a positive side, represent that then the small planarity of film surface is poor more.Determine the ripple of the film surface of small planarity roughly to be divided into two kinds, promptly have long wavelength's ripple of 100 μ m levels and short wavelength's ripple of 10 μ m levels.If the intensity I of long wavelength's ripple of the 100 μ m levels that width exists ¹⁰ _TDGreater than+5dB, then long wavelength's ripple became strong, thus the electromagnetic conversion characteristic due to the spacing loss worsens easily.I ¹⁰ _TDMore little, then long wavelength's ripple diminishes, and is preferred, but the small ripple that can not avoid thermal load to produce, I ¹⁰ _TDBe actually value more than or equal to-25dB.

In addition, if the intensity difference I of the short wavelength's of the represented 5 μ m levels of the long wavelength's of the represented 100 μ m levels of the intensity of spatial frequency 10 (1/mm) ripple and spatial frequency 200 (1/mm) ripple ^10-200 _TDBe 5～20dB, effect then of the present invention is more obvious, so be preferred.I ^10-200 _TD6～18dB more preferably.The particle dia that adds in the short wavelength's of the wavelength 5 μ m levels that spatial frequency 200 (1/mm) is represented ripple and the film is closely related, demonstrates, with I ^10-200 _TDCompared by the ripple that adds the short wavelength that particle forms at film surface during greater than 20dB, the long wavelength's of 100 μ m levels ripple prevails.Under this state, when forming belt, produce spacing loss sometimes, electromagnetic conversion characteristic worsens.On the contrary, at I ^10-200 _TDBeing under the situation of 5～20dB, suitably forming and interpolation particle dia, the corresponding projection of addition, be difficult to produce spacing loss, is preferred.On the other hand, owing to thermal load produces few long wavelength's ripple, this also can't avoid current, in fact I ^10-200 _TDBecome value more than or equal to 5dB.

Second mode of the present invention is characterised in that, comes the long wavelength of the small planarity of decision thermal treatment rear film and short wavelength's ripple are clearly defined with spatial frequency and intensity.Thus, expectation improves as the WRa that prior art adopted, and the macroscopic value that adds up to long wavelength and short wavelength's ripple is difficult to the spacing loss in the high-density linearity recording mode magnetic recording media of explanation and the problem of electromagnetic conversion characteristic deterioration.Therefore, even WRa is identical, I ¹⁰ _TDThe greater can not obtain effect of the present invention.

The biaxially oriented polyester film of first mode of the present invention and second mode, the Young's modulus of the length direction of preferred polyester film and the Young's modulus of width and be 11,000～15,000MPa.The Young's modulus of length direction and width and more preferably 11,500～14,000MPa, more preferably 12,000～13,000MPa.If Young's modulus and less than 11,000MPa, undercapacity then dies down so contact with magnetic head, produces spacing loss sometimes.On the other hand, for make in Young's modulus and greater than 15, therefore 000MPa need increase stretching ratio significantly, breaks sometimes.

The percent thermal shrinkage of the length direction of the biaxially oriented polyester film of first mode of the present invention and second mode and the percent thermal shrinkage of width and, be preferably smaller or equal to 3.0%, more preferably smaller or equal to 2.5%.If percent thermal shrinkage and greater than 3.0%, then the film when high temperature keeping or thermal load shrinks and becomes fierce, small sometimes planarity becomes and worsens easily.The linear recording mode does not apply tension force along the thin-film width direction substantially.Therefore, for contraction and the small planarity of the consequent that prevents the belt width direction worsens, the percent thermal shrinkage of width preferably is controlled at 0.0～1.0%.The percent thermal shrinkage of width can suitably be adjusted by known method such as relaxation processes.

The polyester of the biaxially oriented polyester film of first mode of the present invention and second mode gets final product so long as pass through the polyester that molecular orientation forms high-strength thin-film, not special the qualification.Polyester film of the present invention is preferably mainly and is made of polyethylene terephthalate, polyethylene glycol 2.The preferred especially good polyethylene terephthalate of creep properties of polyester film among the present invention.As the polyester copolymer composition except that polyethylene terephthalate, for example can use, glycol ether, propylene glycol, neo-pentyl alcohol, polyoxyethylene glycol, p-Xylol glycol, the glycol component of 1,4 cyclohexane dimethanol etc., the di-carboxylic acid composition of hexanodioic acid, sebacic acid, phthalic acid, m-phthalic acid, m-phthalic acid 5-sulfo group sodium etc., trimellitic acid, 1,2,4, the polyfunctional group dicarboxylic acid composition of 5-pyromellitic acid etc. is to oxidation ethoxybenzoic acid etc.

Biaxially oriented polyester film of the present invention can be an individual layer, also can be the rhythmo structure more than 2 layers.Biaxially oriented polyester film of the present invention for the formation of the protrusion of surface of layer (B) that can control magnetospheric layer of coating (A) and opposition side easily, and is preferably bilayer structure when using as magnetic recording media.

The surfaceness WRa layer of double-deck biaxially oriented polyester film (A), that adopt contactless 3 dimension roughmeters to measure ^ABe preferably 0.2～6nm, more preferably 0.5～4nm.If WRa ^ALess than 0.2nm, then the slip of magnetic head and belt sometimes worsens.If WRa ^ASurpass 6nm, then the surface becomes too coarse, as high-density magnetic recording media with, can not obtain sufficient electromagnetic conversion characteristic sometimes.On the other hand, the surfaceness WRa of the layer of opposing face (B) ^BBe preferably 1～10nm, more preferably 3～8nm.If WRa ^BLess than 1nm, then produce wrinkle in the coiling of film sometimes, reeling condition is not good.On the other hand, if WRa ^BGreater than 10nm, then because the surface becomes too coarse, so when reeling, bring easily sometimes to be needed on the baneful influence that is coated with magnetospheric layer (A) etc. as film rolling.

Below, in order to satisfy above-mentioned surfaceness, preferably in layer, add inactive particle, in the present invention, be used for the inactive particle I of layer (A), median size dI is preferably 0.04～0.30 μ m, more preferably 0.05～0.10 μ m, content is preferably 0.001～0.30 weight %, more preferably 0.01～0.25 weight %.With in the medium, if adopt the particle of median size greater than 0.30 μ m, then electromagnetic conversion characteristic worsens sometimes at high density magnetic recording.

In double-deck polyester film, the thickness t B of layer (B) is preferably 0.1～2.0 μ m, more preferably 0.2～1.5 μ m.If this thickness is less than 0.1 μ m, then particle becomes and comes off easily, if greater than 2.0 μ m, the protrusion-shaped of then adding particle sometimes becomes effect to reduce.

In double-deck polyester film, the particle that layer (B) is comprised can be a kind, also can be more than 2 kinds.The ratio (tB/dII) of median size dII of the laminated thickness tB of polyester layer (B) and the maximum inactive particle II that adds layer (B) to is preferably more than and equals 0.3 and less than 1.0, more preferably more than or equal to 0.4 and less than 0.8.If tB/dII is more than or equal to 1.0 μ m, then the B laminar surface becomes too coarse, though to coating during magnetospheric transfer printing at normal temperatures, small sometimes planarity also worsens.The median size dII of inactive particle II is preferably 0.3 μ m～1.0 μ m, more preferably 0.4 μ m～0.9 μ m.The content of inactive particle II is preferably 0.002 weight %～0.10 weight %, more preferably 0.005～0.05 weight %.The median size of inactive particle III is preferably less than particle II.The median size of inactive particle III is preferably 0.1 μ m～0.5 μ m, more preferably 0.2 μ m～0.4 μ m.The content of inactive particle III is preferably 0.1 weight %～1.0 weight %, more preferably 0.2～0.4 weight %.

In double-deck polyester film, the inactive particle that contains in layer (A) and the layer (B) is preferably inorganic particulates such as spherical silicon dioxide, pure aluminium silicate, titanium dioxide, lime carbonate, and is preferably cross-linked polystyrene resin particle, cross linking polysiloxane resin particle, crosslinked acrylic resin particle, cross-linked styrene-acrylic resin particle, cross-linked polyester particle, polyimide particle, melamine resin particle etc. as other organic system polymer particles.Can from these, select to use more than a kind or 2 kinds.

In double-deck polyester film, the inactive particle that contains in layer (A) and the layer (B) is preferably the uniform particle of particle shape particle distribution, and volume shape factor is preferably f=0.3～π/6, more preferably f=0.4～π/6.Volume shape factor f is shown below.

f＝V/Dm ³

Here, V is particle volume (μ m ³), Dm is the maximum diameter (μ m) on the projection plane of particle.

In addition, when particle was ball, volume shape factor f got maximum π/6 (=0.52).Preferably filter as required etc.Wherein, spherical silicon dioxide is excellence aspect monodispersity, controls projection easily and forms, and effect of the present invention is become better, so be preferred.In addition, as required, the viewpoint of strengthening from surface (flesh), can contain primary particle size in the scope that does not influence protrusion of surface formation is 0.005～0.10 μ m, is preferably the inactive particle that is selected from alpha-type aluminum oxide, γ type aluminum oxide, δ type aluminum oxide, θ type aluminum oxide, zirconium white, silicon-dioxide, titanium particle etc. of 0.01～0.05 μ m.

The biaxially oriented polyester film of first mode of the present invention and second mode, the Young's modulus of the length direction of film and width Young's modulus are preferably 3500～10000MPa respectively.The length direction Young's modulus of film is preferably 0.7～2.5 with the ratio (length direction/width) of width Young's modulus, and more preferably 1.2～2.4, more preferably 1.5～2.3.If the ratio (length direction/width) of length direction Young's modulus and width Young's modulus is less than 0.7, then since the dimensional change of the width when the length direction working tension increase, so produce track skew sometimes.For the ratio that makes Young's modulus greater than 2.0, need to give the very large stretching ratio of length direction, when film system film, take place frequently sometimes and break.

Generally speaking, in linear recording mode, from preventing the viewpoint of track skew, the width size changing rate when being preferably working tension along its length is less.Along under the state of 49 ℃ of load, the temperature of the length direction effect 32MPa of film, humidity 90%RH, when carrying out handling in 72 hours, the dimensional change of the width before and after handling is preferably-0.40～0%, more preferably-and 0.30-0.10%.If less than-0.35%, when then using, produce track skew sometimes as tape.Length direction intensity is big more, and the size changing rate of width has the tendency that diminishes more, and the Young's modulus of length direction is preferably greater than and equals 5, and 000MPa is more preferably greater than equaling 6,000MPa.But, if the length direction Young's modulus greater than 10,000MPa, then the stretching ratio during film system film uprises, and film breaks often takes place, sometimes the remarkable variation of the yield rate of product.On the other hand, if the intensity of length direction less than 3,500MPa then can not obtain enough intensity sometimes when forming tape.

The biaxially oriented polyester film of first mode of the present invention and second mode, the temperature expansion coefficient of the width of film is preferably-10 * 10 ^-6～20 * 10 ^-6/ ℃, more preferably-5 * 10 ^-6～15 * 10 ^-6/ ℃.And then the humidity expansion coefficient of thin-film width direction is preferably 0～20 * 10 ^-6/ %RH, more preferably 5 * 10 ^-6～15 * 10 ^-6/ %RH.If temperature expansion coefficient and humidity expansion coefficient surpass this scope, then under the situation that temperature head when the data typing and during data read and psychrometric difference are bigger, fixed head can not correctly read and be entered into magnetic information on the belt.Even, preferably each coefficient of expansion is controlled in the above-mentioned scope for also correct reading of data under the situation that the humiture environmental change is arranged.

The biaxially oriented polyester film of first mode of the present invention and second mode in the scope that does not hinder effect of the present invention, can be provided with easy tack coat by the coating at least one face coating water soluble paint or organic solvent system.

The thickness of the polyester film that is adopted in the biaxially oriented polyester film of first mode of the present invention and second mode is followed high capacity, filming progress, is preferably 2.0～7.0 μ m, more preferably 4.0～6.5 μ m.If polyester film is thicker than 7.0 μ m, the belt length in the box of then packing into shortens, and can not obtain competent recording capacity sometimes.If the thickness of polyester film can not obtain enough intensity less than 2.0 μ m when then forming belt sometimes.

Below, the preferable production process of biaxially oriented polyester film of the present invention is described.

At first, make the method that contains inactive particle in the polyester be, for example, make inactive particle I be slurry form with the regulation ratio in the ethylene glycol as glycol component and disperse, any stage before polyester is finished is added this ethylene glycol slurry.Here, if when adding particle, for example can the resulting water-sol of the not involutory granulating period of the day from 11 p.m. to 1 a.m, alcosol temporarily adds particle dryly, then dispersion of particles is good, and can make sliding, electromagnetic conversion characteristic all good.In addition, the direct polyester granulate with regulation of the water slurry of particle is mixed, supply to the twin-screw mixer forcing machine of hole mode, mixing method in polyester is also effective to effect of the present invention.As the method for regulating particle content, make the particle master batch of high density in advance with aforesaid method, method that the polyester that when the system film its usefulness is not contained particle in fact dilutes the content of regulating particle is effective.

After the mixed and drying of polyester granulate with above-mentioned method gained, supply to known fusion lamination forcing machine, filter polymkeric substance with strainer with regulation.In being coated with extremely thin magnetospheric high-density magnetic recording media purposes, because minimum foreign matter also becomes the reason that the magnetic recording defective is DO (drop out), be effective so strainer adopts the high-precision filter of the foreign matter more than the 1.5 μ m that for example can capture more than 95%.Then, be laminar from the slot die of slit-shaped and extrude, cooling curing on casting roll is made non-stretched film.That is, adopt 1～3 forcing machine, 1～3 layer branch manifold or interflow parts (the interflow parts that for example have rectangle interflow portion), carry out lamination as required, extrude thin slice,, make non-stretched film with casting roll cooling from the mouth mould.In the case, from the stabilization of back pressure and the viewpoint of inhibition thickness variation, the method that static mixer, toothed gear pump are set in the polymkeric substance stream is effective.

Drawing process can be one by one biaxial stretch-formed, also can be simultaneously biaxial stretch-formed.

In biaxial stretch-formed at the same time,,, control micro-Raman's crystallization index easily, thereby be preferred as drawing process so be difficult for the generation local heating at film surface because film does not contact with roller when stretching.

At first, with non-stretched film along its length with width, be 80～130 ℃ for example at draft temperature, be preferably under 85～110 ℃ and stretch simultaneously.If draft temperature is lower than 80 ℃, then film easily breaks, if draft temperature is higher than 130 ℃, can not obtain enough intensity sometimes during then as magnetic recording media.In addition, from preventing the uneven viewpoint that stretches, amounting to multiplying power is 4～20 times for example, is preferably 6～15 times.If stretching ratio is less than 4 times, then sometimes as the high-density magnetic recording media of object of the present invention with, be difficult to obtain necessary full intensity.On the other hand, if multiplying power greater than 20 times, then film breaks easily, is difficult to produce stable film sometimes.In order to obtain the necessary intensity of high-density magnetic recording media, preferably 140～200 ℃ of temperature, more preferably 160～190 ℃ along its length and/or width stretch once more.In addition, in order to obtain the necessary intensity of high-density magnetic recording media, preferably with 1.2～2.0, more preferably 1.3～1.7 times stretch once more.Then, for example carry out for example 0.5～20 second, preferred 1～15 second heat setting 205～235 ℃ of temperature, preferred 210～220 ℃.If the heat setting temperature is lower than 205 ℃, then because film does not carry out crystallization, so structural instability, the thermal contraction during owing to high temperature keeping and thermal load causes that sometimes small planarity worsens.On the other hand, if the heat setting temperature greater than 235 ℃, the then polyester amorphous chain portion mitigation that becomes sometimes, Young's modulus diminishes.In addition, in order to reach purpose of the present invention, make film temperature head up and down for for example smaller or equal to 20 ℃, preferably smaller or equal to 10 ℃, be more preferably less than and equal 5 ℃.If film temperature head up and down is greater than 20 ℃, then the micro-Raman's crystallization index on the thickness direction becomes unequal sometimes, causes the deterioration of small planarity during thermal load.

In biaxial stretch-formed at the same time, Contact Heating is different with being undertaken by roller, because only by high temperature air heating film, so be difficult for producing partial heating.On the other hand, simultaneously biaxial stretch-formed is a kind of like this drawing process: since from initial draft temperature promptly the temperature of 90 ℃ of front and back promptly all relate to length direction in 220 ℃ zone to the heat setting temperature, so easily up and down and width generation temperature head at film by the unrestricted flow of following high temperature airs such as air-flow.As the method that reduces temperature head, there is no particular limitation, is effective but equipment such as suppressing the free-pouring shutter of high temperature air is set between the different zone of temperature.Especially, in order to be made as film feature of the present invention, that suppressed micro-Raman's crystallization exponential inequality, the gap of film and shutter is 1～250mm for example, is preferably 2～100mm, more preferably 3～50mm.If the gap is less than 1mm, then film contacts with shutter and breaks sometimes.If the gap is greater than 250mm, then micro-Raman's crystallization exponential is uneven to become big, and small sometimes planarity worsens.For film is not contacted with shutter, it is effective suitably regulating the wind speed that blows out from nozzle.

On the other hand, biaxially oriented polyester film of the present invention also can adopt to stretch one by one and make.Under tensile situation one by one, initial length direction stretches more important, and draft temperature is 90～130 ℃ for example, is preferably 100～120 ℃.If draft temperature is lower than 90 ℃, then film easily breaks, if draft temperature is higher than 130 ℃, then film surface can be subjected to thermal damage sometimes.In addition, from the viewpoint of prevent to stretch uneven and flaw, stretch preferably to be divided into more than 2 stages and carries out, the total multiplying power is 2.5～3.5 for example, is preferably 2.8～3.3 times.If stretching ratio less than 2.5 times, then is difficult to obtain the necessary intensity used as magnetic recording media sometimes.On the other hand, if multiplying power greater than 3.5 times, then because film is easy to generate flaw, so not only be difficult to as magnetic recording media, and film can break when carrying out once more longitudinal stretching sometimes.

And then, as draw roll, cohesionless silicone roller of preferred control surface roughness easily etc.When using ceramic roller, テ Off ロ Application (registered trademark) roller, metallic roll as prior art, sometimes owing to bonding is that film surface is locally heated, film surface is uneven with inner micro-Raman's crystallization index generation.And then the surface roughness Ra of draw roll for example is 0.005～1.0 μ m, is preferably 0.1～0.6 μ m.If Ra is greater than 1.0 μ m, the concavo-convex film surface that is transferred to sometimes on roller surface when then stretching.If Ra is less than 0.005 μ m, then roller and film surface bond sometimes, and film is subjected to thermal damage easily.For the control surface roughness, suitably adjust abrasive granularity, to grind number of times etc. be effective.And then for example be below 0.1 second total duration of contact of roller in the extension section and film, be preferably below 0.08 second, this make aspect the film effective especially.If greater than 0.1 second, then owing to the heat of draw roll film surface is locally heated sometimes the duration of contact of roller and film, and produces micro-Raman's crystallization index inequality between the film inside, even cause that when thermal load small planarity worsens.Here, so-called duration of contact, be with film and draw roll contact distance divided by the adding roller time time of film speed gained; When stretching, it is its summation time by a plurality of rollers.As the method that shortens duration of contact, hug that to carry out the tensile method on roller just passable though adopt, for example not with winding film on draw roll, and it is effective especially only to carry out the tensile method between niproll abreast.

In stretching one by one, after this preferably 85～140 ℃, more preferably at 90～110 ℃, broad ways preferably stretches 2.5～4.5 times, more preferably stretches 3.0～3.5 times.If depart from this temperature, multiplying power scope, then cause problems such as stretching inequality or film breaks sometimes, be difficult to obtain film as feature of the present invention.In order to obtain micro-Raman's crystallization index,,,, more preferably carry out longitudinal stretching once more with 1.6～1.8 times preferably with 1.4～2.0 times more preferably at 135～145 ℃ preferably at 130～160 ℃ as the object of the invention.Particularly, if draft temperature is lower than 130 ℃, then film breaks sometimes.On the other hand, if draft temperature is higher than 160 ℃, then therefore film surface is not preferred owing to heat sustains damage sometimes.In addition,, then can not obtain sufficient belt intensity sometimes if stretching ratio is lower than 1.4 times, if greater than 2.0 times, film breaks sometimes then.Then, for example once more behind 1.0～1.5 times of the cross directional stretchs,,, preferably carry out 0.5～20 second, more preferably 1～15 second heat setting more preferably at 210～220 ℃ preferably at 205～235 ℃.Especially, if the heat setting temperature is lower than 205 ℃, then sometimes because film does not carry out crystallization, so structural instability, when high temperature keeping, thermal load, small complanation worsens sometimes.On the other hand, if the heat setting temperature greater than 235 ℃, then polyester amorphous chain portion slows down sometimes, Young's modulus diminishes.In order to reach purpose of the present invention, make film temperature head up and down for for example smaller or equal to 20 ℃, preferably smaller or equal to 10 ℃, be more preferably less than and equal 5 ℃.If film temperature head up and down is greater than 20 ℃, then the micro-Raman's crystallization index on the thickness direction becomes inhomogeneous sometimes, causes the deterioration of small planarity during thermal load.Then, preferably indulging and/or laterally implementing 0.5～7.0% relaxation processes.

Embodiment

Below, describe the present invention in detail with embodiment.

The measuring method of characteristic value of the present invention and Evaluation on effect method are as described below.

A. the median size of particle

From film, remove polymkeric substance with plasma low-temperature ashing treatment method, particle is exposed.But the treatment condition selective polymer is not subjected to the condition of doing one's utmost to damage by the ashing particle.(SEM) observes this particle with scanning electron microscope, and handles particle picture with image analyzer.The multiplying power of SEM is suitably selected from about 5,000～20,000 times.Changing the observation place is more than 5,000, according to particle diameter and its volume fraction, obtains volume mean diameter d by following formula with population.When containing the different particle more than 2 kinds of particle diameter, respectively every kind of particle is carried out same mensuration, try to achieve particle diameter.d＝∑(di·Nvi)

Here, di is a particle diameter, and Nvi is its volume fraction.Particle is subjected to by plasma low-temperature ashing treatment method using transmission electron microscope (TEM) 3,000～100,000 times of following viewing film cross section under the situation of greatly damage.The slice thickness of TEM is about 100nm, changes 500 of position findings more than the visual field, obtains volume mean diameter d by following formula.

B. the volume shape factor of particle

With scanning electron microscope at for example 5,000 times of photos of taking down the particle in 10 visuals field.And then, adopt image analysis processing device, calculate the average-volume of the maximum diameter and the particle on projection plane, obtain volume shape factor by following formula.

f＝V/Dm ³

Here, V is average-volume (the μ m of particle ³), Dm is the maximum diameter (μ m) on projection plane.

C. pellicular cascade thickness

Carrying out the etched while from the surface, measuring the depth profile (depth profile) of this particle concentration with XPS (x-ray photoelectron light method), IR (infrared measure) or confocal microscope etc.Carried out in the top layer of film of lamination at a face, at the interface of the air-resin on so-called surface, particle concentration is lower, along with particle concentration uprises away from the surface.Carried out at a face of the present invention under the situation of film of lamination, the degree of depth [I] is in case become maximum value, and then particle concentration begins again to diminish.Based on this concentration profile, will become 1/2 the degree of depth [the II] (II＞I) as laminated thickness here of the particle concentration of maximum value.

And then, under the situation that contains inorganic particulate etc., adopt secondary ion mass spectrometry device (SIMS), the concentration ratio (M+/C+) of the carbon of the element of the particle that concentration is the highest in the particle that derives from the film and polyester as particle concentration, is carried out the analysis of the degree of depth (thickness) direction from the surface of layer (A).And, obtain laminate thickness by method same as described above.

D. micro-Raman's crystallization index

Sample is imbedded Resins, epoxy, grind and expose the cross section.Different 5 places on in-plane, along thickness direction every 1 μ m (if the film of 6 μ m just is 6 points, if the film of 4.5 μ m just is 4 points) the micro-Raman's crystallization index of mensuration, calculate the mean value of same thickness direction position, calculate the poor of maximum value, minimum value and maximum value and minimum value according to its value.After in-plane cuts out the cross section, to the zone of 1 μ m from the film surface to the degree of depth, measure each 6 point (suitable) with width every 2mm along its length under the following conditions by laser Raman mini-prober method (aerial resolution 1 μ m) and add up to 12 points with 1/2 inch belt width, calculate uneven.With 1730cm ^-1The half-amplitude duration note of (stretching vibration of carbonyl) is micro-Raman's crystallization index Ic, and the difference note of maximum value and minimum value is Δ Ic.

The condition determination of laser Raman beam split is as described below.

Device: Jobin Yvon corporate system Ramanor U-1000

Mini-prober: microscope Olympus BH-2 type

Beam splitter: the right side

Object lens: * 100

Light source: Ar ⁺Laser, NEC GLG3300, wavelength 514.5nm

Optical splitter: structure 1m Ce Erni-Te Nashi (Czerny-Turner) type

Double monochromator

Diffraction grating plane holographic (plane holographic)

1,800g/mm，

110×110mm

Chromatic dispersion 9.23cm ^-1/ mm

Backlight clearance 10 ^-14(20cm ^-1)

Detector: PM RCA31034, shore pine electronics system 943-02

MCD DARSS TN-6122(Tracor Northern)

E. the Young's modulus of film

According to the method for JIS-K7127, utilize Instron type tensile testing machine under 23 ℃, 65%RH, to measure Young's modulus.To along vertical (MD) of film and laterally (TD) width of cutting out be that 10mm, length are the sample film of the 100mm mensuration that stretches.

F. temperature expansion coefficient

Film is got the sample of width 4mm, be fixed in vacuum science and engineering (strain) system TMA TM-3000 and heating control section TA-1500, so that specimen length reaches 15mm.The 0.5g load is affacted on the film, after temperature rises to 50 ℃ from room temperature (23 ℃), make temperature temporarily get back to room temperature.Then, make temperature rise to 50 ℃ once more from room temperature.Measure this moment film from 30 ℃ to 40 ℃ displacement (Δ Lmm), calculate temperature expansion coefficient by following formula.

Temperature expansion coefficient (/ ℃)=(Δ L/15)/(40-30)

G. humidity expansion coefficient

Film is made the sample of wide 10mm, the belt tensile testing machine that is fixed in big storehouse イ Application ダ ス ト リ one system is so that sample reaches 200mm, make this sample 30 ℃ of temperature, be changed to 80%RH and kept 30 minutes from humidity 40%RH, measure displacement (Δ Lmm) then, calculate humidity expansion coefficient by following formula.

Humidity expansion coefficient (/ %RH)=(Δ L/200)/(80-40)

H. percent thermal shrinkage

It is that 10mm, length are 250mm that film is cut out width with width along its length, with 2 graticules of interval adding of about 200mm, measures its (it is designated as Xmm) at interval at 23 ℃.Under the state of the front end that 0.15g load is applied to this sample, in 100 ℃ atmosphere, place after 30 minutes, once more at 23 ℃ of intervals (this is designated as Ymm) of measuring down between graticule, with 100 * (X-Y)/X as percent thermal shrinkage.

I. size changing rate

Film is cut out length direction 100mm, width 30mm, the damping temperature adjustment is after 24 hours under 23 ℃, 65%RH, uncharge condition, by static sample is attached on Dai Nippon Printing's (strain) system chrome mask, with the length (L0) of light microscope determining width.Then, under 49 ℃, the condition of 90%RH, under the state that applies the 32MPa load along its length, placed 72 hours.After 72 hours, discharge load, the damping temperature adjustment was measured the length (L1) of width after 24 hours under 23 ℃, 65%RH, uncharge condition.The size changing rate of width is tried to achieve by following formula.

The size changing rate of width (%)=[(L1-L0)/L0] * 100

J. the surfaceness of draw roll

Use the surfaceness meter サ one Off テ ス ト 301 of Mitutoyo (strain) system,, adopt its mean value with by being of a size of 0.25mm, 3 mensuration of pair roller width centerplane mean roughness.

The evaluation of the small planarity due to the K. warm processing

By being placed in 100 ℃ baking box, film heat-treated in 24 hours.Utilizing the noncontact 3 dimension roughmeter TOPO-3D of WYKO corporate system to measure the small planarity of the layer (A) before and after the thermal treatment, is that 41.6 times, mensuration area are 239 * 239 μ m (0.057mm measuring the area multiplying power ²) under measure.By being built in the surface analysis software (ver.4.90) in this coarse meter, try to achieve spatial frequency 10cm ^-1And 200cm ^-1Relative power.Carry out 10 times and measure, with the value of mean value as relative power.With regard to WRa, only measure the preceding film of thermal treatment.

In addition, relative power is that (fx is fy) with the value (dB) represented of logarithmic scale (scale), according to P (fx, fy) 1nm with the power spectrum P of each spatial frequency ²External waviness be designated as 0dB carries out relative power like that with analysis software benchmark.With x as the thin-film width direction, y is measured as the film length direction.(fx fy) calculates by following formula respectively P.

$P(\mathrm{fx},\mathrm{fy})=\frac{1}{A}{\left\{\mathrm{FT}\right[h(x,y)\left]\right\}}^2$

In the formula, P (fx fy) is power spectrum, and A measures area, FT be with ∫ ∫ h (x, y) exp[i2 π (xfx+yfy)] calculation of represented fourier transformation, (x y) is the surface shape data to h, and fx, fy are the frequency coordinates on the space.

$\mathrm{WRa}=\frac{1}{\mathrm{MN}}\underset{k=1}{\overset{M}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}|Z_{\mathrm{jk}}-\stackrel{\&OverBar;}{Z}|$

Here, $\stackrel{\&OverBar;}{Z}=\frac{1}{\mathrm{MN}}\underset{k=1}{\overset{M}{\mathrm{\&Sigma;}}}\underset{j=1}{\overset{N}{\mathrm{\&Sigma;}}}\left|Z_{\mathrm{jk}}\right|$

In addition, Zjk will measure direction and carry out height on the M, when N is cut apart j of all directions, k locational 3 a dimension roughness chart respectively perpendicular to the direction of measuring direction.

Read the intensity difference of spatial frequency 10 (1/mm) and 10 (1/mm) and 200 (1/mm), be expressed as I respectively ¹⁰TD, I ^10-200TD.The degree of the small planarity of this value representation film surface, value is big more in positive side, and then small planarity is poor more.Metering equipment is not specific to be WYKO, can adopt noncontact 3 dimension roughmeter ZYGO, the atomic force microscope AFM that can measure equally.

K. the evaluation of small planarity

Because the I before and after the thermal treatment ^10-200The difference of TD is big more, and it is poor more by the small planarity due to the thermal treatment to represent, so estimate with following benchmark.

I before and after the thermal treatment ^10-200The difference of TD is more than or equal to 0 and less than 2dB: 00

I before and after the thermal treatment ^10-200The difference of TD is more than or equal to 2 and less than 4dB: zero

I before and after the thermal treatment ^10-200The difference of TD is more than or equal to 4dB: *

00 and zero is qualified.

Embodiment 1

Making contain median size 0.06 μ m, volume shape factor f=0.51 the spherical silicon dioxide particle polyethylene terephthalate and in fact do not contain the particle of the polyethylene terephthalate of particle, mix 2 kinds of particles like that by reach 0.2 weight % according to the content that makes the spherical silicon dioxide particle, modulate thermoplastic resin A.In addition, it is such that the particle content that reaches 0.26 weight %, 0.8 μ m according to the particle content that makes 0.3 μ m reaches 0.01 weight %, mix the Vinylstyrene/styrene copolymerized crosslinked particle contain median size 0.3 μ m, volume shape factor f=0.52 polyethylene terephthalate, contain median size 0.8 μ m, volume shape factor f=0.52 Vinylstyrene/styrene copolymerized crosslinked particle polyethylene terephthalate and in fact do not contain the particle of the polyethylene terephthalate of particle, modulate thermoplastic resin B.

These thermoplastic resins, are supplied with respectively in the forcing machine after 8 hours at 160 ℃ of following drying under reduced pressure respectively, melt extruded, carry out collaborating lamination with the orthogonal bilayer with the interflow parts, thereby forming double-deck lamination after high precision filters at 275 ℃.Then, applying on the casting drum of electrostatic teeming practice twisting cohesion 25 ℃ of surface temperatures on the cooling roller, carrying out cooling curing, thereby do not stretched laminated film via the slot die, the use that remain in 285 ℃.

Biaxial stretch-formed machine when this laminated film that do not stretch is utilized the linear motor formula, 95 ℃ along its length with width stretch respectively 3.5 times, amount to 12.3 times, then, stretch 1.5 times along its length in 180 ℃ once more, under constant length, 220 ℃ of thermal treatments of carrying out 3 seconds.The distance that makes film and shutter is that 20mm, film temperature head up and down are 1 ℃.Then, apply 1% relaxation processes along its length, broad ways applies 2% relaxation processes, is that the thickness of 6 μ m, layer (B) is the film raw material of 0.5 μ m thereby obtain total thickness.The evaluation result of resulting film is shown in table 1,2,3.

Embodiment 2

Except change is added to the multiplying power of particle diameter (f=0.52), addition, length direction and width of layer (A), the particle of layer in (B) and film temperature head up and down be 10 ℃, all operation similarly to Example 1 obtains biaxially oriented polyester film.The evaluation result of resulting film is shown in table 1,2,3.

Embodiment 3

Making contain median size 0.10 μ m, volume shape factor f=0.51 the spherical silicon dioxide particle polyethylene terephthalate and in fact do not contain the particle of the polyethylene terephthalate of particle, mix 2 kinds of particles like that by reach 0.1 weight % according to the content that makes the spherical silicon dioxide particle, the modulation thermoplastic resin, make the single thin film of 5 μ m, in addition, identical with embodiment 1, obtain biaxially oriented polyester film.The evaluation result of resulting film is shown in table 1,2,3.

Embodiment 4

Except the heat setting temperature was 240 ℃, all operation similarly to Example 1 obtained biaxially oriented polyester film.The evaluation result of resulting film is shown in table 1,2,3.

Embodiment 5

Except the thickness of the addition of the particle of layer in (A) and layer (A), layer (B) is added in change to, all operate similarly to Example 1, make the laminated film that do not stretch, stretch by biaxial stretch-formed method one by one.At first, under 110 ℃ of draft temperatures, be divided into for 2 stages, stretch 3.1 times along its length.It is the non-adhesive polysiloxane roller of 0.40 μ m that the draw roll of contact this moment uses surface roughness Ra, and then stretches abreast between niproll.At this moment, the film in the retained part is 4mm with the distance that contacts of roller, and be 0.011 second in the fs duration of contact of film and roller, is 0.009 second in subordinate phase, adds up to 0.02 second.Then, this single axle drawn membrane is stretched after 3.2 times by tentering machine in 95 ℃ of temperature, broad ways,, under constant length, carry out thermal treatment in 3 seconds in 210 ℃ at 140 ℃ of 1.7 times of longitudinal stretchings once more.Making film temperature head up and down is 1 ℃.Then, broad ways applies 2% relaxation processes, and the thickness that obtains total thickness and be 4.5 μ m, layer (B) is the film raw material of 0.4 μ m.The evaluation result of resulting film is shown in table 1,2,3.

Embodiment 6

To add particle diameter, the addition of the particle of layer in (B), duration of contact of making film and roller to except change be 0.022 second in the fs, subordinate phase is 0.018 second, total 0.04 second, all operation similarly to Example 4 obtains biaxially oriented polyester film.The evaluation result of resulting film is shown in table 1,2,3.

Comparative example 1

Except make draft temperature be 125 ℃, draw roll use surfaceness be 0.6 μ m ceramic roller, make film temperature head up and down is 10 ℃, all operation similarly to Example 4 obtains biaxially oriented polyester film.The evaluation result of resulting film is shown in table 1,2,3.

Comparative example 2

Make draft temperature be 125 ℃, draw roll to use surfaceness be the ceramic roller of 0.6 μ m and then duration of contact of making film and roller by winding film is stretched on roller in the fs is 0.40 second, be 0.29 second, total 0.69 second in subordinate phase, in addition, all operation similarly to Example 4 obtains biaxially oriented polyester film.The evaluation result of resulting film is shown in table 1,2,3.

Comparative example 3

Change length and width stretching ratio, to make the thermosetting temperature be that 200 ℃, film are that 250mm, film temperature head up and down are 30 ℃ with the distance of shutter, in addition, all operates similarly to Example 2, obtains biaxially oriented polyester film.The evaluation result of resulting film is shown in table 1,2,3.

Table 1

	Film thickness			Layer (A)			Layer (B)
														Total thickness [μ m]	t B [μm]	t B/dII	Inactive particle I dI[μ m]	Concentration [weight %]	WRa A [nm]	Inactive particle II dII[μ m]	Concentration [weight %]	Inactive particle III dIII[μ m]	Concentration [weight %]	WRa B [nm]	Drawing process
Embodiment 1	6.0	0.5	0.63	0.06	0.2	0.8	0.8	0.01	0.3	0.26	4.4	The while twin shaft
													Embodiment 2	6.0	0.5	0.63	0.3	0.1	4.5	0.8	0.05	0.3	0.60	6.8	The while twin shaft
Embodiment 3	5.0	-	-	0.1	0.1	2.5	-	-	-	-	-	The while twin shaft
													Embodiment 4	6.0	0.5	0.63	0.06	0.2	0.7	0.8	0.01	0.3	0.26	4.5	The while twin shaft
Embodiment 5	4.5	0.4	0.50	0.06	0.05	0.7	0.8	0.01	0.3	0.26	4.3	Twin shaft one by one
													Embodiment 6	4.5	0.4	1.33	0.06	0.05	0.7	0.3	0.01	0.06	0.10	2.8	Twin shaft one by one
Comparative example 1	4.5	0.4	0.50	0.06	0.05	1.0	0.8	0.01	0.3	0.26	4.4	Twin shaft one by one
													Comparative example 2	4.5	0.4	0.50	0.06	0.05	1.4	0.8	0.01	0.3	0.26	4.4	Twin shaft one by one
Comparative example 3	6.0	0.5	0.63	0.3	0.1	4.7	0.8	0.05	0.3	0.60	7.0	The while twin shaft

Table 2

	The film rerum natura							Percent thermal shrinkage
												Length direction Young's modulus [MPa]	Width Young's modulus [MPa]	Length/width	Length+width Young's modulus [MPa]	Temperature expansion coefficient [10 -6/℃]	Humidity expansion coefficient [10 -6/％RH]	Width size changing rate [%]	Thermal contraction and [%]	Length direction [%]	Width [%]
Embodiment 1	8200	4200	2.0	12400	9	10	-0.18	1.8	1.7	0.1
											Embodiment 2	5000	7000	0.7	12000	-1	6	-0.40	2.1	1.7	0.4
Embodiment 3	8300	4100	2.0	12400	10	10	-0.18	1.8	1.7	0.1
											Embodiment 4	7100	3700	1.9	10800	14	14	-0.26	0.9	1.2	-0.3
Embodiment 5	8300	4200	2.0	12500	10	10	-0.20	2.1	2.1	0.0
											Embodiment 6	8200	4200	2.0	12400	10	11	-0.20	2.1	2.0	0.1
Comparative example 1	8200	4200	2.0	12400	10	10	-0.20	2.1	2.1	0.0
											Comparative example 2	8200	4200	2.0	12400	10	10	-0.20	1.8	1.7	0.1
Comparative example 3	5100	4400	1.2	9500	11	11	-0.40	2.3	1.6	0.7

Table 3

	Micro-Raman's crystallization index				Spatial frequency
											Thickness direction			In-plane	Film before the thermal treatment		Film after the thermal treatment		Small planarity
	Maximum value [cm -1]	Minimum value [cm -1]	Δ Ic thickness direction	Δ Ic in-plane	I 10 TD	I 10-200 TD	I 10 TD	I 10-200 TD	100℃×24hr
										Embodiment 1	13.7	13.5	0.2	0.3	-13.5	11.5	-13.0	12.0	○○(0.5dB)
Embodiment 2	14.0	13.4	0.6	0.4	-2.8	12.0	-1.0	14.0	○(2.0dB)
										Embodiment 3	13.6	13.4	0.2	0.3	-5.7	13.3	-5.0	14.0	○○(0.7dB)
Embodiment 4	12.9	12.7	0.2	0.2	-13.4	11.5	-13.0	11.9	○○(0.4dB)
										Embodiment 5	13.9	13.2	0.7	0.5	-11.3	13.7	-8.0	17.0	○(3.3dB)
Embodiment 6	13.9	13.1	0.8	0.6	-11.0	14.0	-7.5	17.5	○(3.5dB)
										Comparative example 1	14.5	13.3	1.2	1.4	-2.8	21.7	2.5	26.8	×(5.1dB)
Comparative example 2	15.1	13.3	1.8	2.3	-0.5	24.0	5.5	30.0	×(6.0dB)
										Comparative example 3	16.0	14.8	1.2	0.5	-3.2	11.8	1.1	16.1	×(4.2dB)

The industry utilizability

Biaxially oriented polyester film of the present invention is useful as the polyester film that uses in magnetic recording material, electronic material, plate-making film, subliming type colour band, the packaging material. Especially, Biaxially oriented polyester film of the present invention is the basement membrane used as the plied timber application type digital recording medium of high-density magnetic recording media, particularly linear recording mode of great use Biaxially oriented polyester film when using.

Biaxially oriented polyester film of the present invention be in high temperature keeping with after adding the thermic load in man-hour, also good film of small flatness.

Claims (8)

1. biaxially oriented polyester film, micro-Raman's crystallization index Ic of film thickness direction is 8cm ^-1～15cm ^-1, the maximum value of Ic and the difference of minimum value are 1cm ^-1Below.

2. biaxially oriented polyester film as claimed in claim 1, the maximum value of micro-Raman's crystallization index Ic of thin film planar direction and the difference of minimum value are 1cm ^-1Below.

3. biaxially oriented polyester film, the relative power I of the spatial frequency (1/mm) on the width of at least one face of 100 ℃ of polyester films after applying 24 hours thermal treatment ¹⁰ _TDBe-25～0dB.

4. biaxially oriented polyester film as claimed in claim 3, the intensity difference I of the relative power of the spatial frequency 10 and 200 (1/mm) on the width of at least one face ^10-200 _TDBe 5～20dB.

5. as claim 1 or 3 described biaxially oriented polyester films, the Young's modulus of length direction and the Young's modulus of width and be 11,000～15,000MPa.

6. as claim 1 or 3 described biaxially oriented polyester films, polyester is a polyethylene terephthalate.

7. as claim 1 or 3 described biaxially oriented polyester films, as the magnetic recording media basement membrane of linear recording mode.

8. as claim 1 or 3 described biaxially oriented polyester films, the basement membrane of using as the magnetic recording media of plied timber application type digital recording mode.

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