JP2007196511A - Laminated biaxially oriented polyester film and magnetic recording tape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated biaxially oriented polyester film having not only extremely high flatness properties, which are required in the field of a base film such as a metal thin film type magnetic recording medium, but also self-recovery properties. <P>SOLUTION: A layer A and a layer B are formed using a titanium catalyst and the amount of the titanium element (TiA) of the layer A is within a range of 2-15 mmol% while the amount of the titanium element (TiB) of the layer B is within a range of 0.2-0.8 mmol% with respect to the amount of the titanium element (TiA) of the layer A. The surface roughness of the layer A is 0.3-4 nm and the surface roughness of the layer B is 1.5-50 times the surface roughness of the layer A and the thickness of the layer A is within a range of 0.5-5 μm and the thickness of the layer B is larger than that of the layer A. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laminated biaxially oriented polyester film. More specifically, edge scraps and the like generated in the film manufacturing process are remelted and used as a raw material, that is, even if a self-circulating type recovery polymer is used, the obtained film has excellent surface flatness, particularly a high-density magnetic recording medium The present invention relates to a laminated biaxially oriented polyester film suitable for a base film.

  A biaxially oriented polyester film represented by a polyethylene terephthalate film is widely used because of its excellent physical and chemical properties, particularly as a base film of a magnetic recording medium.

  In recent years, in magnetic recording media, higher density and higher capacity have been promoted, and accordingly, flatness of the base film and thinning of the thickness have been demanded. Wrinkles or blocking occurs when winding up, and the surface of the film roll becomes uneven, reducing the yield of the product, and the appropriate range of tension, contact pressure and speed when winding up is narrowed, so it is very easy to wind up In order to solve the problem that it becomes difficult, improvement of winding property is also desired. And, as a means to achieve the contradictory properties of improving the winding property and improving the electromagnetic conversion characteristics, by using a laminated film, the surface on which the magnetic layer is applied is flattened to improve the electromagnetic conversion characteristics. Means for improving the slipperiness by roughening the surface are widely known. Specifically, on the surface of the laminated polyester film on the side where the magnetic layer side is formed (hereinafter referred to as a flat layer), a lubricant having a small particle size is used, or the amount added is reduced, and the other magnetic layer is used. A lubricant having a large particle size is used on the surface on which the surface is not formed (hereinafter referred to as a running surface), and the amount added is increased.

  Therefore, the characteristics of the lubricant used, for example, the lubricant type, particle size, addition amount, etc. are greatly different between the flat surface and the running surface, and when trying to use the recovered chip of the laminated film itself, the lubricant composition is rough. Also, since it differs from the lubricant composition of the flat layer, when it is re-introduced in the production of the laminated film, the lubricant composition of the re-introduced layer is changed and the film characteristics are hindered.

  Therefore, in Japanese Patent Application Laid-Open No. 11-34262 (Patent Document 1), it is also possible to dilute the concentration of inert particles in the self-recovered polymer and use it on a flat surface. In literature 2), it is proposed that the concentration of inert particles in the self-recovering polymer is increased and used on the running surface side.

  However, in recent years, the demand for higher density has become stricter, and laminated films having self-recoverability and high flatness required in the field of base films such as metal thin-film magnetic recording media have been developed. The fact is that it was not provided.

JP-A-11-34262 JP 2000-246857 A

  An object of the present invention is to provide a laminated biaxially oriented polyester film having an extremely high flatness as required in the field of base films such as a metal thin film type magnetic recording medium and also having a self-recovering property. There is.

  As a result of diligent research to achieve this object, the present inventor has made the rough surface layer thicker than the flat layer and uses a titanium compound at a specific ratio as a catalyst for the polyester constituting both surface layers. The present inventors have found that the laminated film obtained even when the recovered polymer is self-circulated in the production of the film itself can have the flatness required for a high-density magnetic recording medium, etc.

Thus, according to the present invention, a laminated biaxially oriented polyester film in which a polyester B layer is laminated on one side of a polyester A layer,
The polyester of the A layer and the B layer contains the titanium compound used as a catalyst, and the content thereof is based on the number of moles of repeating units of the polyester of each layer, and the amount of titanium element (Ti _A ) in the A layer. Is in the range of 2 to 15 mmol%, and the amount of titanium element (Ti _B ) in the _B layer is in the range of 0.2 to 0.8 with respect to the amount of titanium element (Ti _A ) in the A layer,
The surface roughness of the A layer is 0.3 to 4 nm, the surface roughness of the B layer is in the range of 1.5 to 50 times the surface roughness of the A layer, and the thickness of the A layer is 0.00. A laminated biaxially oriented polyester film in which the thickness of the B layer is thicker than the A layer in the range of 5 to 5 μm is provided.

  Moreover, according to this invention, the magnetic recording tape which consists of the laminated biaxially-oriented polyester film of the said invention and the magnetic layer laminated | stacked on the surface by the side of the A layer is also provided.

  According to the present invention, there is provided a laminated biaxially oriented polyester film having an extremely high flatness as required in the field of a base film such as a metal thin film type magnetic recording medium and also having a self-recovering property. Specifically, when used as a high-density magnetic recording medium, it is possible to provide a magnetic recording tape that has very few dropouts and is excellent in cost merit.

The laminated biaxially oriented polyester film of the present invention is one in which a polyester B layer is laminated on one side of a polyester A layer.
In the present invention, it is necessary for the polyesters of the A layer and the B layer to use a titanium compound as a catalyst in order to increase the surface flatness. From this viewpoint, the polyester of the A layer needs to have a titanium element amount (Ti _A ) in the range of 2 to 15 mmol% based on the number of moles of repeating units of the polyester of the A layer, and 3 to 12 mmol%. Further, it is preferably in the range of 4 to 10 mmol%. If Ti _A is less than the lower limit, a sufficient polyester polymerization reaction rate cannot be obtained with a titanium compound alone, and if it is covered with another polycondensation catalyst such as antimony, coarse protrusions due to catalyst residues are generated. On the other hand, if Ti _A exceeds the upper limit, the thermal degradation during melting of the polyester is large, and the flatness of the surface is impaired by the deteriorated foreign matter.

In addition, the polyester of the B layer has a titanium element amount (Ti _B ) in the range of 0.2 to 0.8 with respect to Ti _A based on the number of moles of repeating units of the polyester of the B layer. Is required, and is preferably in the range of 0.25 to 0.75, more preferably 0.3 to 0.7. By making Ti _B / Ti _A in the above range, even when a self-recovering polymer is used for the B layer, thermal degradation of the polymer due to the titanium catalyst, and further generation of foreign substances consisting of the degraded product can be suppressed, and excellent flatness Can be granted.

  In the laminated biaxially oriented polyester film of the present invention, the surface roughness of the A layer needs to be in the range of 0.3 to 4.0 nm, preferably 0.5 to 3.0 nm. When the surface roughness of the A layer is in the above range, the laminated biaxially oriented polyester film capable of obtaining flatness and running property can be highly provided. In addition, in a film having a surface roughness of the layer A exceeding the upper limit, the influence of foreign matters due to thermal deterioration during melting hardly becomes a problem, and the effects of the present invention are hardly exhibited. On the other hand, the surface roughness of the B layer is 1.5 to 50 times, preferably 2.5 to 30 times the surface roughness of the A layer. A biaxially oriented polyester film can be highly equipped. Further, as with the A layer, a rough film in which the surface roughness of the B layer exceeds the upper limit is less likely to be a problem due to foreign matters due to thermal degradation at the time of melting, and the effects of the present invention are also hardly exhibited. Particularly preferred surface roughness of the B layer is in the range of 5.0 to 10.0.

  In the laminated biaxially oriented polyester film of the present invention, the thickness of the A layer needs to be in the range of 0.5 to 5.0 μm, preferably 1.0 to 4.0 μm, and the thickness of the B layer is the A layer. It is necessary to be thicker than the thickness. If the thickness of the A layer is less than the lower limit, the influence of the rough surface of the B layer on the running surface side affects the surface of the A layer, and flatness is impaired. On the other hand, when the thickness of the A layer exceeds the upper limit or the thickness of the B layer is thinner than the thickness of the A layer, when the self-recovering polymer is used for the B layer, it depends on the titanium compound contained in the polyester of the A layer. There is a problem that the thermal deterioration tends to proceed or the rate at which the self-recovering polymer can be used cannot be sufficiently increased. In addition, as a usage method of a self-recovery polymer, the method shown in FIG. 2 is mentioned. FIG. 2 is a schematic diagram of the self-circulation system. In FIG. 2, reference numerals 21 to 27 respectively denote 21 an unused polymer I, 22 an unused polymer II, 23 a recovered polymer, 24 a layer A, and 25 a B The layer 26 is a commercialized laminated film, and 27 is a collected laminated film. First, the laminated film is formed by laminating and polymerizing the unused polymer I and the unused polymer II, respectively, to form a laminated film. At this time, a portion having no problem becomes a productized laminated film 26, but a portion such as an edge that cannot be used as a product (collected laminated film 27) is inevitably generated. The recovered laminated film 27 is again subjected to melt extrusion as the recovered polymer 23.

In the laminated biaxially oriented polyester film of the present invention, the A layer preferably contains a phosphorus compound as a stabilizer. The content of the phosphorus compound contained is based on the number of moles of the repeating unit of the polyester of the A layer, the phosphorus element amount (P _A , mmol%) of the phosphorus compound and the titanium element amount (Ti _A ) described above. When the ratio (P _A / Ti _A ) is in the range of 0.1 to 3, and further 0.3 to 2.5, it is possible to suppress precipitation of catalyst residues and the like while suppressing generation of foreign matters due to thermal deterioration. . On the other hand, it is preferable that the B layer also contains a phosphorus compound as a stabilizer, and the phosphorus element amount (P _B , mmol%) of the phosphorus compound and the titanium, based on the number of moles of repeating units of the polyester of the B layer. The ratio of the amount of elements (Ti _B ) (P _B / Ti _B ) is in the range of 2 to 20, more preferably 4 to 16, and even when using a self-recovery polymer, the generation of foreign matters due to thermal degradation can be suppressed. Precipitation of catalyst residues and the like can be suppressed to an extent that does not affect the surface properties of the flat surface. In particular, the fact that (P _B / Ti _B ) is in the range of 2 to 10 times that of (P _A / Ti _A ) indicates that even if a self-recovering polymer is used for the B layer, the generation of foreign matter and catalyst due to thermal degradation It is preferable because precipitation of residues and the like can be suppressed and the flatness of the A layer can be made extremely excellent.

  By the way, in order to reduce the amount of the titanium compound in the B layer as compared with the A layer as described above, it is possible to use a polyester having a small amount of the titanium compound in combination with the self-recovery polymer. Since a sufficient polymerization reaction rate cannot be obtained, it is not very practical. Preferably, as the polymerization reaction catalyst, a polyester containing at least one catalyst selected from the group consisting of an antimony compound, a germanium compound, and an aluminum compound, which is superior in thermal stability as compared with the titanium compound, is used as the polyester for the B layer. preferable. Among these, an antimony compound is preferable because it is particularly excellent in thermal stability. In addition, the antimony compound has a problem that precipitates due to the catalyst residue are likely to be generated. However, in the present invention, the polyester containing the titanium compound, which is difficult to deposit the catalyst residue, is contained in the B layer. can do.

  As understood from the above description, the laminated biaxially oriented polyester film of the present invention is a polyester containing a specific amount of a titanium compound having a small amount of precipitation such as a catalyst residue as a polycondensation catalyst, while the B layer is A. Even if a self-recovering polymer is used for the B layer by using a polyester having a titanium compound content of a specific ratio or less compared to the layer and making it thicker than the A layer, it is required for a metal thin film type magnetic recording medium or the like. Such a high level of flatness can be achieved. Therefore, the laminated biaxially oriented polyester film of the present invention can exhibit an excellent effect even when it is made of all unused polyester, but the effect is maximized when a self-recovery polymer is used in the B layer. Will be.

Furthermore, the preferable aspect of this invention is explained in full detail below.
In the present invention, it is preferable that the polyesters constituting the A layer and the B layer are the same in view of using a self-recovery polymer for the B layer. Examples of the polyester in the present invention include aromatic polyesters having an aromatic dicarboxylic acid as the main acid component and an aliphatic glycol as the main glycol component, and are substantially linear and have film-forming properties, particularly by melt molding. It is necessary to have film formability. Specific aromatic dicarboxylic acids include, for example, terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, anthracene dicarboxylic acid, etc. Can be mentioned. Examples of the aliphatic glycol include alicyclic groups such as polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, and cyclohexanedimethanol. A diol etc. can be mentioned. Among these, those having alkylene terephthalate or alkylene naphthalate as the main constituent are preferable, and polyethylene terephthalate and polyethylene-2,6-naphthalate are particularly preferable. Of course, for example, a copolymerization component known per se may be copolymerized within a range not impairing the object of the present invention.

In the present invention, the polyester constituting the A layer and the B layer contains a sulfonic acid quaternary phosphonium salt compound in an amount of 0.02 to 45 mmol%, further 0.1 to 20 mmol%, based on the repeating unit of the polyester. It is preferable. When the content is less than the lower limit, the effect of increasing the casting speed is small, and as a result, the heat history received by the self-recovery polymer and the like is increased, and foreign matters due to thermal degradation are easily promoted. On the other hand, if the content exceeds the upper limit, the discharge function of the discharge electrode when the film is electrostatically adhered may deteriorate over time. From these viewpoints, the polyester constituting the A layer and the B layer has an AC volume resistivity of the melt film of 1 × 10 ⁶ Ω · cm to 9 × 10 ⁸ Ω · cm, and further 5 × 10 ⁶ Ω · cm to 5 It is preferably in the range of × 10 ⁸ Ω · cm. When this AC volume resistivity exceeds the upper limit, the effect of speeding up the casting speed is small, and as a result, the thermal history received by the self-recovery polymer and the like is increased, and foreign matter due to thermal deterioration is easily promoted, whereas when it is less than the lower limit The film may break down during electrostatic adhesion in the casting process. FIG. 1 shows an apparatus for measuring AC volume resistivity. In FIG. 1, reference numerals 1 to 11 denote a polymer to be measured, 2 is a lower electrode, 3 is an upper electrode, and 4 is a charging device. 5 is a temperature detection end, 6 is an ammeter, 7 is a reading thermometer, 8 is a power source, 9 is a standard resistance, 10 is an electron meter, and 11 is a heat insulation box. AC volume resistivity can be measured.

  Moreover, such AC volume resistivity can be adjusted by including the sulfonic acid quaternary phosphonium salt described above. Specific examples of the sulfonic acid quaternary phosphonium salt include compounds represented by the following formulae.

ここで、上記式中の、Ａは芳香族基又は脂肪族基、Ｘ₁ 及びＸ₂ はそれぞれ同一若しくは異なるエステル形成性官能基又は水素原子、Ｒ₁ 、Ｒ₂ 、Ｒ₃ 及びＲ₄ はそれぞれアルキル基及びアリール基よりなる群から選ばれた同一又は異なる基、ｎは正の整数である。

In the above formula, A is an aromatic group or aliphatic group, X ₁ and X ₂ are the same or different ester-forming functional groups or hydrogen atoms, R ₁ , R ₂ , R ₃ and R ₄ are each The same or different group selected from the group consisting of an alkyl group and an aryl group, n is a positive integer.

  Preferred examples of the sulfonic acid quaternary phosphonium salt include 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt, 3,5-dicarboxybenzenesulfonic acid tetraphenylphosphonium salt, 3,5-dicarbomethoxybenzene. Tetrabutylphosphonium sulfonate, tetraphenylphosphonium 3,5-dicarbomethoxybenzenesulfonate, tetrabutylphosphonium 3, carboxybenzenesulfonate, tetrabutyl 3,5-di (β-hydroxyethoxycarbonyl) benzenesulfonate Phosphonium salt, 4-hydroxyethoxybenzenesulfonic acid tetrabutylphosphonium salt, bisphenol A-3,3'-di (sulfonic acid tetrabutylphosphonium salt), 2,6-dicarboxynaphthalene-4-sulfur It can be mentioned phosphate tetrabutylphosphonium like, which only may be used in combination also two or more used alone type.

  In the present invention, the titanium compound used for producing the polyester of the A layer and the B layer is not particularly limited as long as it is a compound containing a titanium atom. For example, a titanium compound in which the substituent of the titanium compound is at least one selected from the group consisting of an alkoxy group, a phenoxy group, an acylate group, an amino group, and a hydroxyl group is preferable, and a titanium oxide is also preferable. Specific alkoxy groups include tetraethoxide, tetrapropoxide, tetraisopropoxide, tetrabutoxide, titanium tetraalkoxide such as tetra-2-ethylhexoxide, β-diketone functional groups such as acetylacetone, lactic acid, Examples include hydroxy polyvalent carboxylic acid functional groups such as malic acid, tartaric acid, salicylic acid, citric acid, and ketoester functional groups such as methyl acetoacetate and ethyl acetoacetate, with aliphatic alkoxy groups being particularly preferred. Examples of the phenoxy group include phenoxy and cresylate. The acylate group includes tetraacylate groups such as lactate and stearate, phthalic acid, trimellitic acid, trimesic acid, hemimellitic acid, pyromellitic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid , Functional groups of polycarboxylic acids such as sebacic acid, maleic acid, fumaric acid, cyclohexanedicarboxylic acid or their anhydrides, ethylenediaminetetraacetic acid, nitrilotripropionic acid, carboxyiminodiacetic acid, carboxymethyliminodipropionic acid, diethylenetria Nitrogenous polyvalent carboxylic acid functional groups such as minopentaacetic acid, triethylenetetraminohexaacetic acid, iminodiacetic acid, iminodipropionic acid, hydroxyethyliminodiacetic acid, hydroxyethyliminodipropionic acid, methoxyethyliminodiacetic acid Especially aliphatic asylum Group is preferred. Examples of the amino group include aniline, phenylamine, diphenylamine and the like. Further, diisopropoxybisacetylacetone and triethanolaminate isopropoxide containing two kinds of these substituents can be mentioned. Among these, since it is easy to suppress precipitation of catalyst residues, titanium tetrabutoxide, titanium isopropoxide, titanium oxalate, titanium acetate, titanium benzoate, titanium trimellitic acid, tetrabutyl titanate and a reaction product of trimellitic anhydride Etc.

  In the present invention, examples of the polycondensation catalyst other than the titanium compound used for producing the polyester of the B layer include an antimony compound, a germanium compound, and an aluminum compound as described above. As these polycondensation reaction catalysts, antimony compounds used as preferred polycondensation reaction catalysts which can be employed per se are preferably antimony trioxide, antimony pentoxide, antimony acetate and the like. Examples of germanium compounds include those described in, for example, Japanese Patent No. 2792068. (a) Amorphous germanium oxide, (b) crystalline germanium, and (c) germanium oxide as an alkali metal or alkaline earth metal. Or the solution which melt | dissolved in glycol in presence of those compounds, (d) the solution of germanium oxide which melt | dissolved germanium oxide in water, and added glycol to this and distilled water away, etc. are mentioned. Furthermore, the aluminum compounds include aluminum formate, aluminum acetate, aluminum propionate, aluminum oxalate, aluminum acrylate, aluminum laurate, aluminum stearate, aluminum benzoate, aluminum trichloroacetate, aluminum lactate, aluminum citrate, and aluminum salicylate. Carboxylates such as aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, inorganic carbonates such as aluminum carbonate, aluminum phosphate, aluminum phosphonate, aluminum methoxide, aluminum ethoxide, aluminum n-propoxide, aluminum iso- Aluminum alkoxides such as propoxide, aluminum n-butoxide, aluminum t-butoxide, aluminum Aluminum chelate compounds such as minium acetylacetonate, aluminum acetylacetate, aluminum ethylacetoacetate, aluminum ethylacetoacetate diiso-propoxide, organoaluminum compounds such as trimethylaluminum and triethylaluminum and their partial hydrolysates, aluminum oxide, metal Among them, carboxylate, inorganic acid salt and chelate compound are preferable, and aluminum acetate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride and aluminum acetylacetonate are particularly preferable.

  The content in these B layers varies depending on the type of each polycondensation catalyst, but in the case of an antimony compound, from the viewpoint of suppressing thermal degradation when using a recovered polymer while suppressing precipitation of catalyst residues. 3 to 30 mmol%, more preferably 5 to 20 mmol%, preferably 1 to 20 mmol% for germanium compounds, more preferably 3 to 15 mmol%, and 0.5 to 50 mmol% for aluminum compounds. Furthermore, the range of 1-30 mmol% is preferable.

  In the present invention, the polyester constituting the A layer and the B layer preferably contains a phosphorus compound in order to improve thermal stability. Examples of the phosphorus compound include phosphoric acid esters such as phosphoric acid and trimethyl phosphate, phosphorous acid esters such as phosphorous acid and trimethyl phosphite, and phosphonic acid esters. Among these, the phosphorus compound represented by the following general formula can be preferably used from the viewpoint of suppressing precipitated foreign matter.

（式中のＲ^５〜Ｒ^７は炭素数１〜４のアルキル基、Ｘは−ＣＨ_２−または−ＣＨ（Ｙ）−（Ｙはフェニル基）を示す。）

(In the formula, R ^{5 to} R ⁷ represent an alkyl group having 1 to 4 carbon atoms, and X represents —CH ₂ — or —CH (Y) — (Y represents a phenyl group).)

  Among these, preferred phosphorus compounds include phosphonoacetic acid compounds or alkyl esters having 1 to 4 carbon atoms of phosphonophenylacetic acid, and examples include ethyl diethoxyphosphonoacetate and methyl diethoxyphosphonoacetate. These phosphonate compounds may be those in which part or all of the alkyl chain is substituted with glycol. The amount of these phosphorus compounds is about 2 to 50 mmol%, and further 4 to 30 mmol%, based on the repeating unit of the polyester of the A layer, with respect to the A layer, while suppressing the precipitation of catalyst residues. It is preferable because it is easy to suppress foreign matters due to thermal degradation occurring in the case. On the other hand, with respect to the B layer, on the basis of the repeating unit of the polyester of the A layer, being in the range of 5 to 100 mmol%, more preferably 10 to 50 mmol%, while suppressing precipitation of catalyst residues to the extent that does not affect the flat surface, Even if a self-recovery polymer is used, it is preferable because foreign matters due to thermal degradation can be suppressed.

  In the present invention, the polyester constituting the A layer is easy to obtain surface flatness required for a metal thin film type magnetic recording medium and the like. Inactive particles having a diameter of 0.03 to 0.3 μm and further 0.05 to 0.2 μm are contained in an amount of 0.5 wt% or less and further 0.2 wt% or less based on the weight of the A layer. preferable. Particularly preferred are those that do not contain inert particles. The term “not containing inert particles” as used herein means that the content of inert particles having a particle size of 0.05 μm or more is 0.001 wt% or less. Preferred inert particles are preferably heat-resistant polymer particles and spherical silica particles because of excellent dispersibility. Examples of the heat-resistant polymer particles include crosslinked polystyrene resin particles, crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, crosslinked polyester particles, polyimide particles, and melamine resin particles. Among these, crosslinked polystyrene resin particles and crosslinked silicone resin particles are preferable.

In the present invention, the B layer has an average particle size (d _B ) of 0.05 to 1.0 μm, more preferably 0.1 to 0.5 μm of inert particles based on the weight of the B layer. It is preferable to contain 0.0 wt%, and further 0.1 to 0.5 wt% because it is easy to provide high flatness and running property.

By the way, in the present invention, the ratio of (t _B / d _B ) obtained by dividing the average particle diameter (d _B ) of the inert particles contained in the B layer by the thickness of the B layer (t _B ) is 5 to 100, Furthermore, it is preferable that it is 10-50. When this ratio (t _B / d _B ) is less than the lower limit, that is, when the thickness of the B layer is made too thin, or when the average particle size of the lubricant particles contained in the B layer is made too large, it can be recovered in the B layer. The amount of recovered polymer is small and the manufacturing cost of the film is increased, or the large lubricant particles contained in the rough surface layer affect the surface of the A layer, the flatness is impaired, and the electromagnetic conversion characteristics are likely to deteriorate. On the other hand, when the ratio of t _B / d _B exceeds the upper limit, i.e. to the thickness of the B layer, the average particle size of the lubricant particles contained in the rough surface layer becomes too small, sufficient protrusions are formed on the running surface In some cases, the overlap between the inert particles generated in the B layer in the thickness direction of the film increases and abnormal coarse protrusions are generated.

  In the present invention, the inert particles contained in the layer B may be either a single component system or a multi-component system, but preferably a multi-component system containing at least two types of inert particles having different average particle diameters. More preferably, the inert particles B1 having an average particle size of 0.2 to 1.0 μm, and more preferably 0.25 to 0.6 μm, in a range not deteriorating the electromagnetic conversion characteristics, 0.01 to 0.5 wt%, further 0.05 to 0.3 wt% inclusive, inert particles B2 having an average particle size of 0.02 to 0.2 μm and 0.05 to 0.18 μm based on the weight of the B layer 0.05 to 1.0 wt%, and further 0.08 to 0.5 wt% is preferable because it can easily provide sufficient air squeezing properties and electromagnetic conversion characteristics. The inert particles contained in the B layer are not particularly limited, but are preferably the same inert particles as described for the A layer because of excellent dispersibility and difficulty in forming coarse protrusions.

When the laminated biaxially oriented polyester film of the present invention is used as a base film for a metal thin film type magnetic recording medium or the like, it is easy to obtain the runnability of the surface of the magnetic layer of the obtained magnetic recording medium. Fine protrusions having an average protrusion height of 3 nm or more and 50 nm or less are formed in a range of 3 × 10 ⁶ pieces / mm ² or more and 60 × 10 ⁶ pieces / mm ² or less on the surface of the layer not in contact with the B layer. It is preferable. If the average height or frequency of the protrusions is less than the lower limit, the flatness may be impaired by transferring the surface shape of the blocking or B layer to the surface of the A layer when stored in the state of a film roll, Further, the magnetic layer formed on the A layer side becomes too smooth, and the magnetic layer is likely to be worn by the video head when recording and reproduction are repeated with a digital video tape recorder after becoming a video tape, for example. On the other hand, when the average height or frequency of the protrusions exceeds the upper limit, the output characteristics are deteriorated when the protrusions are scraped off and dropped or are made into a magnetic recording medium.

  A method for forming such protrusions is not particularly limited, but it is preferable to provide a film layer made of inert particles and an organic resin on the surface of the A layer. The inert particles contained in the coating layer are not particularly limited. For example, crosslinked silicone resin, acrylic resin, polystyrene, melamine-formaldehyde resin, aromatic polyamide resin, polyamideimide resin, crosslinked polyester, wholly aromatic polyester, etc. Preferably, particles composed of organic particles, silicon dioxide (silica), calcium carbonate, and the like are used. Of these, crosslinked silicone resin particles, acrylic resin particles, silica particles, and core-shell type organic particles (core: crosslinked polystyrene, shell: polymethyl methacrylate particles, etc.) are particularly preferable. The particle diameter of the inert particles in the coating layer is preferably in the range of 1 to 100 nm, more preferably 5 to 50 nm, from the viewpoint of the effect of the present invention.

  Moreover, as an organic resin which forms a membrane | film | coat layer, a water-based polyester resin, a water-based acrylic resin, a water-based polyurethane resin etc. are mentioned preferably, for example, A water-based polyester resin is especially preferable. As the aqueous polyester resin forming the coating layer, the acid component is, for example, isophthalic acid, phthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, adipic acid, From polyvalent carboxylic acids such as sebacic acid, dodecanedicarboxylic acid, succinic acid, sodium 5-sulfoisophthalate, potassium 2-sulfoterephthalate, trimellitic acid, trimesic acid, trimellitic acid monopotassium salt and p-hydroxybenzoic acid The glycol component is at least one selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, p-xylylene glycol, for example. , Dimethylo Propane, a polyester resin is at least one selected from the group consisting of polyhydroxy compounds such as ethylene oxide adduct of bisphenol A is preferably used.

  In addition, the water-based polyester resin may be a graft polymer or block copolymer in which an acrylic polymer chain is bonded to a polyester chain, or a specific physical structure (IPN (interpenetrating polymer network)) in a micro particle of two kinds of polymers. Acrylic-modified polyester resin in which a mold, a core-shell type, or the like is formed may be used. As this aqueous polyester resin, a type that dissolves, emulsifies and finely disperses in water can be freely used, but a type that emulsifies and finely disperses in water is preferable. Moreover, since these impart hydrophilicity, for example, a sulfonate group, a carboxylate group, or a polyether unit may be introduced into the molecule.

  If desired, the coating layer may contain other components such as surfactants, stabilizers, dispersants, UV absorbers, thickeners, release agents and the like as long as the effects of the present invention are not impaired. May be. The thickness of the coating layer is usually 1 to 50 nm, preferably 2 to 30 nm, more preferably 3 to 10 nm.

  The time for forming the coating layer is not particularly limited and may be applied to the laminated biaxially oriented polyester film, but is preferably applied to the longitudinally uniaxially stretched polyester film. The uniaxially stretched polyester film coated with the aqueous coating liquid is dried and guided to processes such as transverse stretching, re-longitudinal stretching as desired, and then heat setting treatment. For example, a longitudinally uniaxially stretched polyester film coated with an aqueous coating solution is guided by a stenter to be stretched in the transverse direction, optionally re-longitudinally stretched, and heat-set. During this time, the coating solution dries to form a continuous film on the film. Drying is preferably carried out before transverse stretching or during transverse stretching or heat setting.

  In the present invention, the intrinsic viscosities of the polyesters of the A layer and the B layer are intrinsic viscosities determined by measuring at 35 ° C. as a solution in o-chlorophenol, and are 0.4 to 0.9, and further 0.5 to 0. .7, particularly in the range of 0.51 to 0.65 is preferable because the mechanical properties and film-forming properties of the resulting film are easily provided. In addition, when a self-recovering polymer is used for the B layer, it is not necessary to prepare a polymer having a particularly high intrinsic viscosity. Therefore, the intrinsic viscosity of the B layer polyester is preferably lower than that of the A layer polyester. .

  The laminated biaxially oriented polyester film of the present invention preferably has a Young's modulus in the longitudinal direction and the transverse direction of 4.5 to 20 GPa, respectively, and a ratio (length / width) of 0.3 to 2.5. More preferably, the Young's modulus in the vertical direction and the horizontal direction is 5 to 14 GPa, respectively, and the ratio (horizontal / vertical) of both is preferably 0.4 to 2.0, particularly preferably 0.6 to 1.6. When the Young's modulus in the longitudinal direction is less than the lower limit, the strength in the longitudinal direction of the magnetic tape is weakened, and when it is applied to the magnetic recording apparatus, it is easily broken when a strong force is applied in the longitudinal direction. On the other hand, if the Young's modulus in the transverse direction is less than the lower limit, the transverse strength of the magnetic tape becomes weak, the contact between the tape and the magnetic head becomes weak, and satisfactory electromagnetic conversion characteristics cannot be obtained. On the other hand, when the Young's modulus in the vertical direction or the horizontal direction exceeds 20 GPa, the stretch ratio becomes high during film formation, the film breaks frequently, and the product yield is remarkably deteriorated. Also, if the ratio between the longitudinal Young's modulus and the transverse Young's modulus is less than the lower limit, sufficient longitudinal strength of the magnetic tape cannot be obtained, and when a strong force is applied in the longitudinal direction when applied to a magnetic recording device, the tape is cut. It occurs frequently. On the other hand, if the ratio of the longitudinal Young's modulus and the lateral Young's modulus exceeds the upper limit, sufficient transverse strength of the magnetic tape cannot be obtained, and if the tape is run, damage will occur on the tape edge and satisfactory durability Sex cannot be obtained. The ratio of the longitudinal Young's modulus to the lateral Young's modulus is 0.9 to 2.5 when used as a base for a linear magnetic recording medium, and 0.3 when used as a base for a helical magnetic recording medium. More preferably, it is -1.0.

  The overall thickness of the laminated biaxially oriented polyester film of the present invention is not particularly limited, but when used as a high-density magnetic recording medium base film, the overall thickness is preferably 3 to 10 μm. More preferably, it is 4-9 micrometers, Most preferably, it is 4-7 micrometers. If this thickness exceeds 10 μm, the length of the magnetic tape put in the cassette becomes short, and a sufficient recording capacity cannot be obtained. On the other hand, when the thickness is less than 3 μm, film breakage frequently occurs during film formation, and the winding property of the film is deteriorated, and the yield is greatly reduced.

  The laminated biaxially oriented polyester film of the present invention is produced by first producing an unoriented laminated film and then biaxially orienting the film according to a conventionally known method or a method accumulated in the industry. Obtainable. This unoriented laminated film is prepared by preparing polyesters for layer A and layer B that satisfy the above-mentioned ratio of the titanium compound, and laminating these polyesters in a molten state or in a cooled and solidified state, that is, coextrusion, It can be manufactured by a method such as a rouge lamination. For example, in the case of producing only with an unused polymer, a polyester for A layer containing no or very little inert particles using a titanium compound as a polycondensation catalyst, and a titanium compound and an antimony compound are used in combination as a polycondensation catalyst. What is necessary is just to prepare the polymer for B layers containing an inert particle, and when using a self-recovery polymer, what is necessary is just to use a self-recovery polymer as a polymer for B layers. At this time, it is preferable to use an unused polymer containing inert particles polymerized with a titanium compound, an antimony compound, or the like in order to match the ratio of the inert particles and the titanium compound with those without using the self-recovering polymer.

  The unoriented laminated film obtained by the above method can be made into a laminated biaxially oriented film according to the production method of the biaxially oriented film accumulated conventionally. For example, polyester is melted and coextruded at a temperature of melting point (Tm) to (Tm + 70) ° C. to obtain an unstretched laminated film, and the unstretched laminated film is uniaxially (longitudinal or transverse) (Tg-10) It is stretched at a temperature of ˜ (Tg + 70) ° C. (where Tg is the glass transition temperature of the polyester) 2.5 times or more, preferably 3 times or more, and then Tg˜ (Tg + 70) ° C. in the direction perpendicular to the stretching direction. The film is preferably stretched 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 transverse direction. Thus, the total draw ratio is preferably 9 times or more, more preferably 12 to 35 times, and particularly preferably 15 to 30 times as the area draw ratio. Furthermore, the biaxially oriented film can be heat-set at a temperature of (Tg + 70) ° C. to (Tm−10) ° C., for example, preferably heat-set at 180 to 250 ° C. The heat setting time is preferably 1 to 60 seconds.

  Since the laminated biaxially oriented polyester film of the present invention thus obtained has excellent flatness not only with unused polymer but also with a self-recovery polymer, extremely excellent flatness is required. It can be preferably used as a base film for a metal thin film type magnetic recording medium, particularly a high density magnetic recording medium or a high density digital recording medium (data cartridge, digital video tape, etc.).

  Hereinafter, the present invention will be described in further detail with reference to examples. Various physical property values and characteristics in the present invention are measured and evaluated as follows.

(1) Average particle diameter of inert particles in the coating layer A platinum thin film deposition layer is provided on the surface of the coating layer of the film with a thickness of 2 to 3 nm by a platinum sputtering apparatus, and a scanning electron microscope (Hitachi High-Technologies S-4700). ), The area equivalent circle diameter was determined for at least 100 particles, and the average value thereof was taken as the average particle size.

(2) Average particle size (DP) of inert particles in the polyester film
The polyester is removed from the film surface by a plasma low-temperature ashing method (for example, P3-3 type manufactured by Yamato Kagaku) to expose the particles. The treatment conditions are such that the polyester is ashed but the particles are not damaged. This was observed with an SRM (scanning electron microscope), and the image of the particles (light density produced by the particles) was linked to an image analyzer, and 5000 particles were measured by changing the observation location. The diameter d is an average particle diameter.

ここで、ｄｉは粒子の円相当径（μｍ）、ｎは個数である。サンプルをポリエステルは溶解するが粒子は溶解しない溶媒を用いて溶解し、溶液から粒子を遠心分離し、粒子の全体量に対する比率（重量％）をもって粒子含有量とする。

Here, di is the equivalent-circle diameter (μm) of the particles, and n is the number. The sample is dissolved using a solvent in which the polyester is dissolved but the particles are not dissolved, and the particles are centrifuged from the solution to obtain the particle content in a ratio (% by weight) to the total amount of the particles.

(3) Film thickness Ten films are stacked while excluding air between layers, and the thickness is measured by a 10-sheet stack method using a dial gauge MDC-25S manufactured by Mitutoyo Co., Ltd. according to JIS C2151. Calculate the film thickness per sheet. This measurement was repeated 10 times, and the average value was defined as the film thickness per sheet.

  On the other hand, the thicknesses of the A layer and the B layer are obtained by fixing a small piece of film with an epoxy resin and cutting an ultrathin section (cut in parallel with the film forming direction and the thickness direction) of about 60 nm with a microtome. create. A sample of this ultrathin section is observed with a transmission electron microscope (H-800, manufactured by Hitachi, Ltd.). The layer with more inert particles is the B layer and the layer with fewer inert particles is the A layer. The thickness positions at which the abundance changes were determined at 100 locations, and the thicknesses of the A layer and the B layer were determined from their average values.

(4) Thickness of coating layer A small piece of film is fixed and molded with an epoxy resin, and an ultra-thin section (cut parallel to the film forming direction) of about 60 nm in thickness is made with a microtome, and this sample is transmitted. It was observed with a scanning electron microscope (H-800 type manufactured by Hitachi, Ltd.), 100 boundary lines of the layer due to the difference in resin type were measured, and the thickness of the coating layer was determined from those values. Note that this measurement was performed in a portion without particles.

(5) Height and frequency of protrusions Using an atomic force microscope (trade name: NanoScope III) manufactured by Digital Instruments and an AFM J-scanner, 10 areas of 2 μm × 2 μm were measured under the following conditions, and AFM images The number of protrusions having a height of 1 nm or more is counted, and the average value is calculated as the number of protrusions per piece / mm ² by area conversion. Also, the height of each counted protrusion is measured, and the average value is taken as the average height of the protrusion.
Deep needle: Single crystal silicon nitride Scanning mode: Tapping mode Area number: 256 × 256 Data points Scanning speed: 2.0 Hz
Measurement environment: room temperature, air

(6) Young's modulus The film is cut into a sample width of 10 mm and a length of 15 cm, and the distance between chucks is 100 mm, and the film is pulled with an Instron type universal tensile tester under the conditions of a tensile speed of 10 mm / min and a chart speed of 500 mm / min. The Young's modulus is calculated from the tangent of the rising part of the obtained load-elongation curve.

(7) Element amount in polymer:
The titanium element amount, phosphorus element amount, antimony element amount, germanium element amount and aluminum element amount in the A layer or the B layer were prepared by heating and melting the sample to create a circular disk, and using a fluorescent X-ray measuring apparatus 3270 manufactured by Rigaku Corporation. Measured. In addition, when titanium oxide particles, alumina particles, or the like are added as inert particles, not as a catalyst, the ratio thereof is excluded from the above element amounts.

(8) Dropout characteristics After a cobalt-oxygen thin film having a thickness of 180 nm is formed by vacuum deposition on one side (A layer side) of the obtained laminated biaxially oriented polyester film, a diamond-like carbon protective film is formed thereon by sputtering. Was formed in a conventional manner with a thickness of 10 nm, and then a fluorine-containing fatty acid ester lubricant was applied with a thickness of 3 nm. Subsequently, a back coat layer made of carbon black, polyurethane, and silicone is provided on the surface on the B layer side with a thickness of 400 nm, slitted to a width of 6.35 mm by a slitter, and wound on a reel to form a magnetic recording tape (DVC video tape). Created.

By recording and playing back this magnetic recording tape in a quiet room using the LP mode of a commercially available camera-integrated digital video tape recorder (DCR-VX2100 manufactured by Sony Corporation), and obtaining the number of dropouts (DO) went. The number of DOs was measured by recording on a prepared DVC tape with a commercially available DVC camera, playing back for 1 minute, counting the number of block-like mosaics displayed on the screen, and evaluating according to the following criteria. The traveling conditions are 25 ° C. and 60% RH.
◎: No occurrence ○: Less than 3 pieces / minute △: 3 pieces / minute or more, less than 10 pieces / minute ×: 10 pieces / minute or more

(9) Surface roughness (WRa)
Using a non-contact type three-dimensional roughness meter (WYKO NT-2000) manufactured by Veeco, the number of measurements (n) is 10 or more under the conditions of a measurement magnification of 25 times and a measurement area of 247 μm × 188 μm (0.046 mm ² ). And the center plane average roughness (WRa) is obtained by surface analysis software built in the roughness meter. The center plane average roughness (WRa) is a value calculated and output by the following equation.

ここで上記式中の、Ｚ_jkはＸ軸方向（２４７μｍ）、それと直行するＹ軸方向（１８８μｍ）をそれぞれＭ分割、Ｎ分割したときの各方向のｊ番目、ｋ番目の位置に於けるＸ、Ｙ平面における直行するＺ軸方向の高さである。また、Ａ層の表面に皮膜層がある場合は、皮膜層の表面を積層二軸配向ポリエステルフィルムのＡ層の表面として測定した。

Here, Z _jk in the above formula is X at the j-th and k-th positions in each direction when the X-axis direction (247 μm) and the Y-axis direction (188 μm) perpendicular thereto are divided into M and N, respectively. , The height in the Z-axis direction perpendicular to the Y plane. Moreover, when there was a film layer on the surface of the A layer, the surface of the film layer was measured as the surface of the A layer of the laminated biaxially oriented polyester film.

(10) Catalyst residue and deteriorated foreign matter 0.1 g of polyester scraped from the film surface was added with a solution (hexafluoroisopropanol / chloroform = 50/50 wt% mixed solution) to dissolve the solution, and a 3 μm pore size Teflon (registered trademark) Filter with a membrane filter (filtration area = 7.1 cm ² ). The filter paper after drying using a scanning electron microscope (Hitachi High-Technologies Ltd. S4700 type), counts the number of particles present on the filter paper, to count the number of particles per 1 cm ² from the observation area. The following criteria are set for evaluation, and an evaluation of ◯ or higher is considered acceptable.
◎: less than the number of particles is 5 / cm ² ○: number of particles of 5 / cm ² or more to 10 / cm less than ² △: number of particles is 10 / cm ² or more 50 / cm ² less ×: number of particles is 50 / cm ² or more

(11) Deteriorated foreign matter When a single-light color wavelength of 0.58 μm is applied to two films with the same surface overlapped so that dust does not enter, this occurs due to coarse protrusions existing between the two films. The interference fringes (Newton rings) to be observed are observed, and the number of coarse projections (height = number of stripes × λ / 2 = 0.44 μm) of 1.0 or more stripes is counted per 100 cm ² area. Further, the counted protrusions were observed with a transmission microscope, and the number of foreign matters caused by deteriorated foreign matters was counted. When the opposite surface analysis was performed, the opposite surfaces were overlapped, the same analysis was performed, and the determination was made according to the following criteria.
Flat surface side ◎: Deteriorated foreign matter 5 / less than 100 cm ² ○: Deteriorated foreign matter 5/100 cm ² or more and less than 20 / cm ² Δ: Deteriorated foreign matter 20/100 cm ² or more and less than 50 / cm ² ×: Deteriorated foreign matter is 50/100 cm ² or more on the rough surface side ◎: Deteriorated foreign matter is less than 10 pieces / 100 cm ² ○: Deteriorated foreign matter is 10 pieces / 100 cm ² or more and less than 30 pieces / cm ² Δ: Deteriorated foreign matter is 30 pieces / 100 cm ² Or more, less than 100 / cm ² ×: 100/100 cm ² or more of deteriorated foreign matters

(12) Measurement of volume resistivity The volume resistivity of the molten film is measured using the apparatus shown in FIG. The measurement sample 1 uses a film having a thickness of about 150 μm. An upper electrode 3 having a diameter of 5.6 cm and a thickness of 0.2 cm capable of holding a parallel gap of 150 μm is disposed on the upper surface of the cylindrical lower electrode 2 having a diameter of 20 cm, and the measurement sample is in close contact with the electrode in the meantime. insert.

  The lower electrode 2 has a built-in charging device 4 and a temperature detection end 5, the variation in the surface temperature measurement of the lower electrode is within 1 ° C, and the temperature difference from the detection end portion is 2 ° C at a heating rate of 8 ° C / min. Configure to be within. The detected temperature is measured with a reading thermometer 7. The entire electrode is placed in the heat insulating box 11.

  The power supply 8 applies the generated voltage between the two electrodes via the standard resistor 9, which is a power supply that generates a direct current of 100V when measuring the DC volume resistivity of the film, and the AC volume of the film. When measuring the resistivity, the power source generates 100 V and 50 Hz. The current flowing in this circuit is read by the eletron meter 10 having an internal impedance of 100 MΩ or more as a voltage generated across the standard resistor.

The AC volume resistivity of the film-like polymer is measured at the temperature rise rate of the lower electrode of 8 ° C./min with the above-mentioned device, and the electrode is melted by DSC of the polymer + 30 ° C. The AC volume resistivity Z Is obtained from the applied voltage E, current I, electrode area S, and electrode interval d by the following equation.

[Reference Example 1] Preparation of Resin 1 Using 100 parts of 2,6-naphthalenedicarboxylic acid dimethyl ester, 70 parts of ethylene glycol and titanium compound (addition of titanium trimellitic acid so as to have an element amount shown in Table 1) was used. After the ester exchange reaction, a phosphorus compound as a stabilizer (trimethyl phosphate was added in Table 1 so as to have an element amount) was added to complete the ester exchange reaction. Then, after adding a sulfonic acid quaternary phosphonium salt compound (3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt) to a concentration of 1 mmol%, a polycondensation reaction is performed under a high vacuum, which is substantially inactive. Polyethylene-2,6-naphthalate containing no particles and having an intrinsic viscosity of 0.6 dl / g was obtained.

Reference Example 2 Preparation of Resin 2 Stable after transesterification using 100 parts of dimethyl terephthalate and 70 parts of ethylene glycol as a transesterification catalyst so that manganese acetate tetrahydrate is 30 mmol%. Trimethyl phosphate was added as an agent as shown in Table 1 to complete the transesterification, and then a sulfonic acid quaternary phosphonium salt compound was added to 1 mmol%, and then as a polymerization catalyst, as shown in Table 1, trioxide Antimony was added and a polycondensation reaction was performed under high vacuum to obtain polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.62 dl / g and substantially free of inert particles.

Reference Example 3 Preparation of Resin 3 The same operation as in Reference Example 2 was repeated except that the inert particles shown in Table 1 were added at the stage of the transesterification reaction.

Reference Examples 4 and 5 Preparation of Resins 4 and 5 The same operation as in Reference Example 1 was repeated except that the amount of the titanium compound was changed as shown in Table 1.

[Reference Example 6] Preparation of Resin 6 The same operation as in Reference Example 1 was repeated except that the inert particles shown in Table 1 were added at the stage of the transesterification reaction.

表１中のＰ１は、トリメチルホスフェートを示す。

P1 in Table 1 represents trimethyl phosphate.

[Example 1]
As a polymer for the A layer, a mixture of 57:43 by weight of the resin 1 and the resin 3 as a polymer for the B layer was prepared, and each was dried at 170 ° C. for 6 hours. Thus, the dried chips were supplied to the two extruder hoppers at a ratio so as to have the layer thickness configuration shown in Table 1, and melted at a melting temperature of 280 to 300 ° C., using a multi-manifold coextrusion die. The B layer was laminated on one side of the A layer to obtain a laminated unstretched film having a thickness of 88 μm. The overall volume resistivity of the laminated unstretched film was 5 × 10 ⁷ Ω · cm.

  The laminated unstretched film thus obtained is preheated to 120 ° C., further heated to 135 ° C. between low-speed and high-speed rolls and stretched 3.5 times, and then rapidly cooled to obtain a longitudinally stretched film. Obtained. Subsequently, the aqueous coating liquid (total solid content concentration 1.0%) of the following composition was apply | coated on the surface which consists of A layer of a longitudinally stretched film.

Application aqueous solution on the surface A side:
・ Binder Acrylic-polyester resin 79%
Polyester component: isophthalic acid (95 mol%), 5-sodium sulfoisophthalic acid (5 mol%) / ethylene glycol (92 mol%), diethylene glycol (8 mol%)
Acrylic resin component: methyl methacrylate (90 mol%), glycidyl methacrylate (10 mol%),
Weight ratio of polyester component / acrylic resin component = 5/5
・ Inert particles (acrylic filler (average particle size 25 nm, manufactured by Nippon Shokubai Co., Ltd., trade name: eposter)) 6%
・ Surfactant (manufactured by Sanyo Kasei Co., Ltd., trade name Sannonic SS-70) 15%
Film layer thickness (after drying): 8 nm

  Then, it supplied to the stenter and extended | stretched 5.3 times in the horizontal direction at 150 degreeC. The obtained biaxially stretched film was heat-fixed with hot air at 205 ° C. for 4 seconds to obtain a laminated biaxially oriented polyester film using only an unused polymer having a thickness of 4.7 μm. The Young's modulus of this film was 5.7 GPa in the vertical direction and 10.5 GPa in the horizontal direction. Table 2 shows the properties of the laminated biaxially oriented polyester film obtained using only the unused polymer and the magnetic recording tape.

Next, edge scraps without a coating layer produced when the laminated biaxially oriented polyester film was produced were collected to obtain a recovered polymer. Only the above-mentioned unused polymer is used except that the polymer for layer B is changed from a mixture of resin 1 and resin 3 in a weight ratio of 57:43 to a mixture of recovered polymer and resin 3 in a weight ratio of 78:22. In the same manner as in the laminated biaxially oriented polyester film using, a laminated biaxially oriented polyester film using the recovered polymer for the B layer was obtained.
Table 3 shows the properties of the obtained biaxially oriented polyester film using the recovered polymer and the magnetic recording tape.

[Examples 2-7, Comparative Examples 1-2]
Laminated biaxially oriented polyester film using only unused polymer and recovery in the same manner as in Example 1 except that the thicknesses of the A layer and B layer and the types and ratios of the resins used are changed as shown in Tables 2 and 3. A laminated biaxially oriented polyester film using a polymer was obtained. Table 2 shows the characteristics of the laminated biaxially oriented polyester film using only the obtained unused polymer and the magnetic recording tape, and the laminated biaxially oriented polyester film using the obtained recovered polymer and the same. Table 3 shows the characteristics of the magnetic recording tape.

  The laminated biaxially oriented polyester film of the present invention can exhibit excellent dropout characteristics when used as a high-density magnetic recording medium, and is excellent in cost merit because the recovered polymer can be used efficiently. It is useful as a base film for magnetic recording media, particularly as a digital recording video tape or data storage tape.

It is a schematic diagram of the apparatus which measures the volume resistivity of a molten polymer. It is a schematic diagram which shows the method of self-circulation collection | recovery when using a collection | recovery polymer.

Explanation of symbols

1: Polymer 2: Lower electrode 3: Upper electrode 4: Electric device 5: Temperature detection end 6: Ammeter 7: Reading thermometer 8: Power source 9: Standard resistance 10: Electron meter 11: Insulation box 21: Unused polymer I
22: Unused polymer II
23: Recovery polymer 24: A layer 25: B layer 26: Commercialized laminated film 27: Collected laminated film

Claims (13)

A laminated biaxially oriented polyester film in which a polyester B layer is laminated on one side of a polyester A layer,
The polyester of the A layer and the B layer contains the titanium compound used as a catalyst, and the content thereof is based on the number of moles of repeating units of the polyester of each layer, and the amount of titanium element (Ti _A ) in the A layer. Is in the range of 2 to 15 mmol%, and the amount of titanium element (Ti _B ) in the _B layer is in the range of 0.2 to 0.8 with respect to the amount of titanium element (Ti _A ) in the A layer,
The surface roughness of the A layer is 0.3 to 4 nm, the surface roughness of the B layer is in the range of 1.5 to 50 times the surface roughness of the A layer, and the thickness of the A layer is 0.00. A laminated biaxially oriented polyester film characterized in that the B layer is thicker than the A layer in the range of 5 to 5 µm. A layer contains a phosphorus compound as a stabilizer, and the ratio of the phosphorus element amount (P _A , mmol%) and the titanium element amount (Ti _A ) of the phosphorus compound based on the number of moles of the repeating unit of the polyester of the A layer The laminated biaxially oriented polyester film according to claim 1, wherein (P _A / Ti _A ) is in the range of 0.1 to 3. The B layer contains a phosphorus compound as a stabilizer, and the ratio of the phosphorus element amount (P _B ) to the titanium element amount (Ti _B ) of the phosphorus compound based on the number of moles of repeating units of the polyester of the B layer (P _B The laminated biaxially oriented polyester film according to claim 1, wherein / Ti _B ) is in the range of 2-20. The B layer contains a phosphorus compound as a stabilizer, and the phosphorus element amount (P _B ) and the titanium element amount (Ti _B ) of the phosphorus compound based on the number of moles of repeating units of the polyester of the B layer. The ratio of the phosphorus element amount (P _A , mmol%) and the titanium element amount (Ti _A ) of the phosphorus compound when the ratio (P _B / Ti _B ) is based on the number of moles of the repeating unit of the polyester of the A layer ( 2. The laminated biaxially oriented polyester film according to claim 1, wherein the laminated biaxially oriented polyester film is in a range of 2 to 10 times of (P _A / Ti _A ).   The laminated biaxially oriented polyester according to any one of claims 3 and 4, wherein the layer B contains at least one catalyst selected from the group consisting of an antimony compound, a germanium compound and an aluminum compound in addition to the titanium compound as a catalyst. the film.   The laminated biaxially oriented polyester film according to claim 1, wherein at least a part of the polyester of the B layer comprises a self-recovery polymer obtained by collecting the laminated biaxially oriented polyester film. Fine protrusions having an average protrusion height of 3 nm or more and 50 nm or less are formed in a range of 3 × 10 ⁶ pieces / mm ² or more and 60 × 10 ⁶ pieces / mm ² or less on the surface of the A layer that is not in contact with the B layer. The laminated biaxially oriented polyester film according to claim 1.   The laminated biaxially oriented polyester film according to claim 1, wherein the total thickness of the film is 3 to 10 µm.   The laminated biaxially oriented polyester film according to claim 1, wherein the polyester B layer contains at least two lubricants having different average particle diameters.   The laminated biaxially oriented polyester film according to claim 1, wherein the polyesters of the A layer and the B layer are polyethylene terephthalate or polyethylene-2,6-naphthalate, respectively.   The laminated biaxially oriented polyester film according to any one of claims 1 to 10, which is used for a base film of a magnetic recording tape.   A magnetic recording tape comprising the laminated biaxially oriented polyester film according to claim 1 and a magnetic layer laminated on the surface of the A layer side.   The magnetic recording tape according to claim 12, wherein the magnetic layer is a ferromagnetic metal thin film layer.

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