JP7528994B2 - Polyester composition, polyester film and magnetic recording medium - Google Patents

Description

The present invention relates to a polyester composition using a copolymer polyester copolymerized with a specific dimer diol, a biaxially oriented polyester film, and a magnetic recording medium.

Aromatic polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate have excellent mechanical properties, dimensional stability, and heat resistance, and are therefore widely used in films, etc. In particular, polyethylene-2,6-naphthalate has mechanical properties, dimensional stability, and heat resistance superior to those of polyethylene terephthalate, and is therefore used in applications with strict requirements, such as base films for high-density magnetic recording media, etc.

In recent years, there has been a strong demand for higher recording density in magnetic recording media, and the dimensional stability required for base films has become difficult to achieve, not only with polyethylene terephthalate films but also with polyethylene-2,6-naphthalate films.

Therefore, Patent Document 1 discloses copolymerization of a 4,4'-(alkylenedioxy)bisbenzoic acid component, and Patent Document 2 discloses copolymerization of a 2,6-naphthalenedicarboxylic acid component (component A) with a terephthalic acid component, an isophthalic acid component, or a 1,4-cyclohexanedicarboxylic acid component (component B).
It has been proposed to improve the dimensional stability against changes in humidity by copolymerizing the copolymer with an ethylene glycol component (component C) and an aliphatic dimer diol component (component D) as glycol components.

JP 2012-268375 A JP 2013-173870 A

However, in Patent Document 1, the 4,4'-(alkylenedioxy)bisbenzoic acid component has a very complicated structure and it is difficult to obtain the raw materials, and in the method of Patent Document 2, the copolymerization of as many as four types of raw materials makes the production very complicated. In addition, since it is a polyester consisting of four components, the film elongation in the longitudinal direction at 110°C is large, and when the magnetic layer or backcoat layer is applied, troughs are generated, which causes coating unevenness.

Therefore, an object of the present invention is to provide a biaxially oriented polyester film which is easily produced and has excellent dimensional stability, particularly against environmental changes such as temperature and humidity, and which has a small film elongation at 110°C.

In biaxially oriented polyester films, both the humidity expansion coefficient and the temperature expansion coefficient are very closely related to the Young's modulus, and the higher the Young's modulus, the lower the coefficient generally becomes. However, the Young's modulus cannot be increased as much as one desires, and there is a natural limit in terms of film formability and securing the Young's modulus in the perpendicular direction. Therefore, we conducted extensive research to see if we could obtain a film with a lower expansion coefficient for temperature and humidity at the same Young's modulus, and found that the above-mentioned polyethylene-1,
A film made of 2-diphenoxyethane-4,4'-dicarboxylate exhibits a low humidity expansion coefficient and was therefore considered to be a suitable film, although it has problems with film formability.

Therefore, the present inventors have found that when a specific dimer diol component is used as a copolymerization component,
Surprisingly, it has been found that a film having excellent properties of both polyalkylene-1,2-diphenoxyalkylene-4,4'-dicarboxylate and its copolymerizable partner, an aromatic polyester, can be obtained, and this has led to the present invention.

Thus, according to the present invention, there is provided a polyester resin composition according to the following (1) and (2):
The polyester film according to any one of (3) to (8) and the magnetic recording medium according to (9) are provided.

(1) A polyester composition in which the dicarboxylic acid component is an aromatic dicarboxylic acid component having 6 or more carbon atoms, the glycol component contains an alkylene glycol component having 2 to 4 carbon atoms and an aliphatic dimer diol component having 31 to 50 carbon atoms, and the content of the dimer diol component is in the range of 0.3 to 5.0 mol % based on the number of moles of the aromatic dicarboxylic acid component.
(2) The above-mentioned (1) which contains, in addition to the copolymer polyester, at least one selected from the group consisting of polyimide, polyetherimide, polyether ketone, and polyether ether ketone in an amount of 0.5 to 25% by weight based on the mass of the copolymer polyester.
) The polyester composition according to claim 1.
(3) A polyester film comprising at least one layer made of the polyester composition described in (1) or (2).
(4) The polyester film according to the above (3), which has a Young's modulus of 4.5 GPa or more in at least one direction along the film surface.
(5) The polyester film according to the above (3), having a film elongation in the longitudinal direction at 110° C. of 3.0% or less.
(6) The humidity expansion coefficient in at least one direction in the film plane is 1 to 8.5 (ppm/
% RH) in at least one direction, the temperature expansion coefficient being in the range of -10 to 15 (ppm/°C).
(7) The above (3) to (6) in which the water contact angle of at least one surface is in the range of 75 to 90 degrees.
13. The polyester film according to claim 12,
(8) The polyester film according to any one of (3) to (7) above, which is used as a base film for a magnetic recording medium.
(9) A magnetic recording medium comprising the polyester film according to (8) above and a magnetic layer formed on one side thereof.

According to the present invention, it is possible to more easily provide a polyester film which has excellent dimensional stability, particularly against environmental changes such as temperature and humidity, and further has a small film elongation at 110°C and is less likely to cause coating unevenness during the coating process.

Therefore, the present invention provides a film suitable for applications requiring high dimensional stability, taking into account the effects of humidity and temperature, particularly as a base film for high-density magnetic recording media. Furthermore, the use of the film of the present invention can provide high-density magnetic recording media with excellent dimensional stability.

<Copolymer polyester>
The copolymer polyester in the present invention comprises a dicarboxylic acid component and a glycol component.

First, the specific dicarboxylic acid component is a phenylene group or a naphthalenediyl group, and examples of the dicarboxylic acid component include a terephthalic acid component, an isophthalic acid component, a 2,6-naphthalenedicarboxylic acid component, and a 2,7-naphthalenedicarboxylic acid component. Among these, from the viewpoint of the effects of the present invention, the terephthalic acid component and the 2,6-naphthalenedicarboxylic acid component, which are relatively easy to improve physical properties such as mechanical strength, are preferred.
A 2,6-naphthalenedicarboxylic acid component is preferred, and a 2,6-naphthalenedicarboxylic acid component is particularly preferred.

Examples of the glycol component include alkylene glycols having 2 to 4 carbon atoms, specifically ethylene glycol components, trimethylene glycol components, tetramethylene glycol components, etc. Among these, from the viewpoint of the effects of the present invention, ethylene glycol components are preferred because they are relatively easy to improve physical properties such as mechanical strength.

The present invention is characterized in that an aliphatic dimer diol component having 31 to 50 carbon atoms is copolymerized. Specific dimer diols preferably contain a branched chain and have an alicyclic portion such as a cyclohexane ring structure, and are particularly preferably those having both a branched chain and a cyclohexane ring. The number of carbon atoms of the preferred dimer diol is in the range of 34 to 46.

In addition, the copolymer polyester in the present invention may be copolymerized with a copolymerization component known per se, such as an aliphatic dicarboxylic acid component, an alicyclic dicarboxylic acid component, an alkylene glycol component not falling under any of the above, a hydroxycarboxylic acid component, an acid component having three or more functional groups such as trimellitic acid, or an alcohol component, within a range that does not impair the effects of the present invention. From this viewpoint, when the alkylene glycol component having 2 to 4 carbon atoms is an ethylene glycol component, the ratio of the diethylene glycol component is preferably in the range of 0.5 to 3 mol% based on the mole number of the total aromatic dicarboxylic acid component from the viewpoint of film formability and dimensional stability of the obtained product. A range of 1.0 to 2.5 mol% is particularly preferable.

The copolymer polyester of the present invention is characterized in that, based on the number of moles of the total aromatic dicarboxylic acid component constituting the copolymer polyester, the total aromatic dicarboxylic acid component is 0.3 mol % or more and 5.0 mol % or less.
If the proportion of the dimer diol component is less than the lower limit, it is difficult to achieve the effect of reducing the humidity expansion coefficient.
On the other hand, if the content exceeds the upper limit, the film formability is impaired, it becomes difficult to improve mechanical properties such as Young's modulus by stretching, it becomes difficult to reduce the temperature expansion coefficient, and in the worst case, the film breaks during the film formation process such as stretching. Surprisingly, the effect of reducing the humidity expansion coefficient by the specific dimer diol component is efficiently expressed even in a relatively small amount. From such a viewpoint, the upper limit of the content ratio of the specific dimer diol component is preferably 5.0 mol% or less, further 4.0 mol% or less, and further 3.0 mol% or less, while the lower limit is 0.3 mol% or less.
1 mol % or more, further 0.5 mol % or more, and even further 0.7 mol % or more.

By using a copolymerized polyester in which such a specific amount of a specific dimer diol component is copolymerized, a molded article, such as a film, having both a low temperature expansion coefficient and a low humidity expansion coefficient can be produced.

The copolymerization amount of the specific dimer diol component can be adjusted by adjusting the composition of the raw materials so that the desired copolymerization amount is obtained at the polymerization stage, or by preparing a homopolymer or a polymer having a large copolymerization amount thereof using only the specific dimer diol component as the diol component, and a non-copolymerized polymer or a polymer having a small copolymerization amount, and then subjecting these to transesterification by melt kneading so that the desired copolymerization amount is obtained.

<Method of producing copolymer polyester resin>
The method for producing the copolymer polyester of the present invention will now be described in detail.

The above-mentioned preferred specific dimer diol components include dimer diol "Pripol 2033" manufactured by Croda and dimer diol "SOVERMO" manufactured by Cognis.
L 908" or the like.

The copolymer polyester of the present invention can be obtained by polycondensation of a polyester precursor.
A polyester precursor can be obtained by subjecting dimethyl 6-naphthalenedicarboxylate to an ester exchange reaction with a specific dimer diol and a linear glycol component having 2 to 6 carbon atoms, such as ethylene glycol. The polyester precursor thus obtained can then be polymerized in the presence of a polymerization catalyst, and may be subjected to solid-phase polymerization, etc., as necessary. The aromatic polyester P-chlorophenol/1,1,2,2
The intrinsic viscosity measured at 35° C. using a mixed solvent of tetrachloroethane (weight ratio 40/60) is 0.4 to 1.5 dl/g, preferably 0.5 to 1.2 dl/g, and more preferably 0.55 to 0.8
From the viewpoint of the effects of the present invention, it is preferable that the viscosity is in the range of dl/g.

The reaction temperature for producing the polyester precursor is preferably in the range of 190° C. to 250° C., and is carried out under normal pressure or under pressure. If the temperature is lower than 190° C., the reaction does not proceed sufficiently, and if the temperature is higher than 250° C., a by-product such as diethylene glycol is likely to be produced.

In addition, in the reaction process for producing the polyester precursor, a known esterification or transesterification catalyst may be used. For example, manganese acetate, zinc acetate, an alkali metal compound, an alkaline earth metal compound, a titanium compound, etc. are listed. Titanium compounds are preferred because they can suppress the surface high protrusions when made into a film.

Next, the polycondensation reaction will be described. First, the polycondensation temperature is equal to or higher than the melting point of the polymer to be obtained and is within a range of 230 to 300° C., more preferably within a range of 5° C. or higher than the melting point to 30° C. higher than the melting point. The polycondensation reaction is preferably carried out under reduced pressure of 100 Pa or less.

The polycondensation catalyst may be a metal compound containing at least one metal element. The polycondensation catalyst may also be used in the esterification reaction. The metal element may be titanium, germanium, antimony, aluminum, nickel, zinc, tin, cobalt, rhodium, iridium, zirconium, hafnium, lithium, calcium, magnesium, etc. More preferred metals are titanium, germanium, antimony, aluminum, tin, etc., and as mentioned above, when a titanium compound is used, it is preferable to use it because it can suppress high protrusions on the surface caused by the influence of the residual metal used as the catalyst when the film is made.

These catalysts may be used alone or in combination. The amount of the catalyst is preferably 0.001 to 0.1 mol %, more preferably 0.005 to 1.0 mol %, based on the number of moles of the repeating unit of the copolymer polyester.
Preferably, it is up to 0.05 mol %.

Specific examples of titanium compounds as esterification catalysts, transesterification catalysts, and polycondensation catalysts include tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetraisobutyl titanate, tetra-tert-butyl titanate, tetracyclohexyl titanate, tetraphenyl titanate, tetrabenzyl titanate, lithium oxalate titanate, potassium oxalate titanate, ammonium oxalate titanate, titanium oxide, titanium orthoesters or condensed orthoesters, reaction products of titanium orthoesters or condensed orthoesters and hydroxycarboxylic acids, reaction products of titanium orthoesters or condensed orthoesters, hydroxycarboxylic acids, and phosphorus compounds, and reaction products of titanium orthoesters or condensed orthoesters and polyhydric alcohols having at least two hydroxyl groups, 2-hydroxycarboxylic acids, or bases.

As described above, the copolymerized polyester in the present invention may be polymerized to obtain a copolymerized polyester having a desired copolymerization amount, or, since an ester exchange reaction proceeds during melt kneading, two or more aromatic polyesters having different copolymerization amounts may be prepared, and these may be melt kneaded and blended to obtain a desired copolymerization amount.

<Polyester Composition>
The polyester composition of the present invention is characterized by containing the above-mentioned copolymerized polyester. The composition may be prepared by blending additives known per se or other resins within a range that does not impair the effects of the present invention. Examples of additives include stabilizers such as ultraviolet absorbers, antioxidants, plasticizers, lubricants, flame retardants, release agents, pigments, nucleating agents, fillers, glass fibers, carbon fibers, layered silicates, etc., and may be appropriately selected according to the requirements of the intended use. Examples of other resins include aliphatic polyester resins, polyamide resins, polycarbonates, A
Examples of the resin include BS resin, liquid crystal resin, polymethyl methacrylate, polyamide elastomer, polyester elastomer, polyetherimide, and polyimide.

Incidentally, the polyester composition of the present invention may further contain 0.5 to 25% by weight of another thermoplastic resin in addition to the above-mentioned copolymer polyester. By blending, heat resistance such as glass transition temperature can be increased, and the effect of reducing the elongation of the film when applying a magnetic layer or the like can be expected. Examples of the thermoplastic resin to be blended include polyimide, polyetherimide, polyether ketone, polyether ether ketone, etc., and preferably polyetherimide. If the blend amount is too small, the effect of improving heat resistance is small, and if it is too large, phase separation occurs, so that the content is generally limited to a range of 0.5 to 25% by weight based on the mass of the copolymer polyester. Preferably, it is 2 to 20% by weight, more preferably 4 to 18% by weight, and even more preferably 5 to 15% by weight. Specific examples of polyetherimide include those disclosed in JP-A-2000-355631 and the like. In addition, from the viewpoint of further improving dimensional stability against environmental changes, the 6,6'-
Copolymers of (ethylenedioxy)di-2-naphthoic acid, 6,6'-(trimethylenedioxy)di-2-naphthoic acid and 6,6'-(butylenedioxy)di-2-naphthoic acid are also preferred.

<Film>
The polyester film of the present invention is preferably a stretched oriented film, since it is easy to increase the Young's modulus, etc., which will be described later, and is particularly preferably a biaxially oriented polyester film oriented in two perpendicular directions. For example, the polyester composition described above can be melt-formed into a film, extruded into a sheet, and stretched in the film-forming direction (hereinafter sometimes referred to as the longitudinal direction, longitudinal direction, or MD direction) and in a direction perpendicular thereto (hereinafter sometimes referred to as the width direction, transverse direction, or TD direction).

Of course, since the film is a film obtained by melt-casting the above-mentioned copolymerized polyester, it also has the excellent mechanical properties of the aromatic polyester composed of a specific dimer diol component, the above-mentioned dicarboxylic acid component, and a linear glycol component. In addition, the polyester film of the present invention is not limited to a single layer, and may be a laminated film, and in that case, it will be easily understood that it is sufficient that at least one layer is a film layer composed of the above-mentioned polyester composition of the present invention.

The polyester film of the present invention has a temperature expansion coefficient (αt) of 14 ppm/s at least in one direction in the plane direction of the film in order to exhibit excellent dimensional stability.
° C. or less. It is preferable that the temperature expansion coefficient (αt
By making the temperature expansion coefficient (αt) in at least one direction of the film equal to or less than the upper limit, for example, by matching it with the direction of the film in which dimensional stability is most required, the film can be made to have excellent dimensional stability against environmental changes.
The lower limit is -10 ppm/°C or more, further -7 ppm/°C or more, particularly -5 ppm/°C or more, and the upper limit is 10 ppm/°C or less, further 7 ppm/°C or less, particularly 5 ppm/°C or less. In addition, when used as a magnetic recording tape, for example, excellent dimensional stability can be exhibited against dimensional changes due to changes in the temperature and humidity of the atmosphere, so that the direction in which the above temperature expansion coefficient is satisfied is
It is preferably in the width direction of the polyester film.

The biaxially oriented polyester film of the present invention preferably has a Young's modulus of at least 4.5 GPa or more in at least one direction of the film plane, preferably in a direction in which the above-mentioned temperature expansion coefficient is 14 ppm/°C or less, and although there is no particular upper limit, it is usually preferably about 12 GPa. A particularly preferred Young's modulus range is 5 to 11 GPa, particularly 6 to 10 GPa. Outside this range, it may be difficult to achieve the above-mentioned αt and αh, or the mechanical properties may be insufficient. Such a Young's modulus can be adjusted by the above-mentioned blend or copolymer composition and the stretching described below.

In addition, when the biaxially oriented polyester film of the present invention is used as a base film for a magnetic tape, the temperature expansion coefficient is preferably 15p in at least one direction of the film surface.
The humidity expansion coefficient in the direction of the temperature is 1 to 8.5 (ppm/% RH), and further 3 to 8
0.5 (ppm/% RH), particularly 4 to 7 (ppm/% RH),
The lower limit is not particularly limited, but is usually preferably about 1 (ppm/% RH). Outside this range, dimensional changes due to humidity changes become large. Such a humidity expansion coefficient can be adjusted by the composition of the blend or copolymer described above and the stretching described below.

In addition, regarding the direction in which the thermal expansion coefficient is 14 ppm/° C. or less, at least one direction,
As described above, it is preferable that the width direction is satisfied. Of course, from the viewpoint of dimensional stability, it is also preferable that the direction perpendicular to the width direction also satisfies the same temperature expansion coefficient, humidity expansion coefficient, and Young's modulus.

By the way, the surface energy of the polyester composition when it is made into a film varies depending on the content of dimer diol. Specifically, the higher the content of dimer diol, the higher the contact angle of water. And, since it is possible to lower the humidity expansion coefficient by making the film surface more hydrophobic, the water contact angle of at least one surface of the polyester film of the present invention is preferably 75 degrees or more, more preferably 77 degrees or more. Even more preferably 78 degrees or more. Also, from the viewpoint of the coating process, the upper limit of the contact angle is preferably 90 degrees or less. This is because if the surface energy is too different from that of the polyester film, problems that have not occurred in the past may occur in the coating process. The upper limit is more preferably 88 degrees or less, and even more preferably 86 degrees or less.

Incidentally, when a magnetic layer, a backcoat layer, or the like is applied to a polyester film, the film is heated in an oven for drying. The film elongation at 110°C described below is considered as one index of the process suitability in this drying process. If the film elongation is high, a trough will occur in the process, causing coating spots, so the lower the film elongation, the better, and it is preferably 3.0% or less. The film elongation is preferably 2.5% or less, and more preferably 2.
It is preferably 0% or less, and more preferably 1.5% or less.

<Method of producing polyester film>
As described above, the polyester film of the present invention is preferably an oriented polyester film, and particularly preferably one that has been stretched in the film-forming direction and the width direction to enhance the molecular orientation in each direction. For example, it is preferable to produce such a polyester film by the following method, since it is easy to increase the Young's modulus and reduce the temperature expansion coefficient and humidity expansion coefficient while maintaining the film-forming property.

First, the polyester composition of the present invention is used as a raw material, which is dried and then fed to an extruder heated to a temperature between the melting point (Tm:° C.) of the aromatic polyester and (Tm+50)° C., and extruded into a sheet from a die such as a T-die. The extruded sheet is quenched and solidified by a rotating cooling drum or the like to form an unstretched film, which is then biaxially stretched.

In order to achieve the αt, αh, and Young's modulus defined in the present invention, it is necessary to facilitate the subsequent stretching, and since the polyester composition of the present invention tends to have a high crystallization rate, it is preferable to perform cooling by a cooling drum very quickly from this viewpoint. From this viewpoint, it is preferable to perform cooling at a low temperature of 20 to 60° C. By performing the cooling at such a low temperature, crystallization in the unstretched film state is suppressed, and it becomes possible to perform the subsequent stretching more smoothly.

As the biaxial stretching, a method known per se can be adopted, and either sequential biaxial stretching or simultaneous biaxial stretching may be used.

Here, a method for producing a film by sequential biaxial stretching, in which longitudinal stretching, transverse stretching and heat treatment are carried out in this order, is described as an example. First, the first longitudinal stretching is performed at a temperature of 100° C. until the glass transition temperature (
The film is stretched 3 to 8 times at a temperature of (Tg+40)°C (Tg:°C), then stretched 3 to 8 times in the transverse direction at a temperature of (Tg+10) to (Tg+50)°C, which is higher than the temperature of the previous longitudinal stretching, and then heat-treated at a temperature of (Tg+50) to (Tg+15)°C or lower than the melting point of the copolymer polyester.
It is preferable to heat set the film at a temperature of 0° C. for 1 to 20 seconds, and more preferably for 1 to 15 seconds.

Although the above description has been given of sequential biaxial stretching, the polyester film of the present invention can also be produced by simultaneous biaxial stretching in which longitudinal and transverse stretching are carried out simultaneously, by referring to the stretching ratio and stretching temperature described above, for example.

The polyester film of the present invention is not limited to a single layer film, but may be a laminated film. In the case of a laminated film, two or more molten polyesters are laminated in a die and then extruded into a film shape, preferably at the melting points (Tm: °C) or (Tm
+70°C, or two or more molten polyesters are extruded through a die and then laminated, rapidly cooled and solidified to form a laminated unstretched film, which is then biaxially stretched and heat-treated in the same manner as in the case of the monolayer film described above. In addition, when the above-mentioned coating layer is provided, it is preferable to coat one or both sides of the unstretched film or uniaxially stretched film with a desired coating liquid, and then to biaxially stretch and heat-treat in the same manner as in the case of the monolayer film described above.

According to the present invention, the above-mentioned polyester film of the present invention can be used as a base film, and a nonmagnetic layer and a magnetic layer can be formed in that order on one side of the base film, and a backcoat layer can be formed on the other side to produce a magnetic recording tape for data storage, etc.

By the way, the biaxially oriented polyester film of the present invention is not limited to a single layer film as mentioned above, but may be a laminated film, which makes it easier to achieve both flatness and windability. For example, by applying a magnetic layer to a flat surface with a small surface roughness and a backcoat layer to a rough surface with a large surface roughness, the required flatness and transportability can be achieved at a higher level. From this point of view, when used as a base film for a magnetic recording medium, the upper limit of the surface roughness of the rough surface with a large surface roughness is preferably 8.0 nm, more preferably 7.0 nm, and particularly preferably 6.0 nm, while the lower limit is preferably 2.0 nm, more preferably 3.0 nm, and particularly preferably 4.0 nm. In addition, the upper limit of the surface roughness of the flat surface with a small surface roughness is preferably 5.0 nm, more preferably 4.5 nm,
In particular, 4.0 nm is preferable, while the lower limit is 1.0 nm, further 1.5 nm, and particularly 2.0 nm. Such surface roughness can be adjusted by incorporating inactive particles and adjusting the particle size or content of the inactive particles, or by providing a coating layer on the surface.

Hereinafter, the case where the biaxially oriented polyester film of the present invention is a biaxially oriented laminated polyester film will be described.

When the biaxially oriented polyester film of the present invention is a biaxially oriented laminated polyester film having a film layer A and a film layer B laminated thereto, at least one of the film layers A and B may be made of the above-mentioned polyester composition, and the other film layer may be made of a material other than the above-mentioned polyester composition. In this case, from the viewpoint of suppressing curling, it is preferable that the film layers A and B have almost the same dimer diol content, and from such a viewpoint, it is preferable that the film layers A and B are made of the same polyester, and the difference in the dimer diol content is, for example, less than 0.3 mol %.

Specific examples of polyesters other than the above-mentioned copolymer polyesters include polyalkylene terephthalates having alkylene terephthalate repeating units such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate; polyethylene-2,6-naphthalenedicarboxylate; polytrimethylene-2,6-naphthalate;
Preferred examples include polyalkylene-2,6-naphthalates having alkylene-2,6-naphthalate as a repeating unit, such as polybutylene-2,6-naphthalate. Among these, polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate are preferred from the standpoint of mechanical properties, and polyethylene-2,6-naphthalenedicarboxylate is particularly preferred.

The aromatic polyester in which a specific dimer diol component is copolymerized in a specific amount and the polyester forming the other layer may be copolymerized with other known copolymer components as long as the effects of the present invention are not impaired.

The present invention will be described in more detail below with reference to examples and comparative examples.
The properties were measured and evaluated by the following methods.

(1) Young's modulus The obtained film was cut into a sample having a width of 10 mm and a length of 15 cm, and the chuck distance was 100 mm.
The specimen is pulled using a universal tensile testing device (manufactured by Toyo Baldwin, product name: Tensilon) under conditions of a tension speed of 10 mm/min and a chart speed of 500 mm/min. Young's modulus is calculated from the tangent to the rising portion of the obtained load-elongation curve.

(2) Temperature expansion coefficient (αt)
The obtained film was cut into a length of 15 mm and a width of 5 mm so that the film formation direction and the width direction of the film were the measurement directions, and the film was set in a TMA3000 manufactured by Shinku Riko Co., Ltd., pretreated at 60° C. for 30 minutes in a nitrogen atmosphere (0% RH), and then cooled to room temperature.
The temperature was raised from 50° C. to 70° C. at a rate of 2° C./min, the length of the sample was measured at each temperature, and the thermal expansion coefficient (αt) was calculated by the following formula.
The measurement was performed multiple times, and the average value was used.
αt={(L ₆₀ -L ₄₀ )}/(L ₄₀ ×△T)}+0.5
Here, in the above formula, L ₄₀ is the sample length (mm) at 40° C., L ₆₀ is the sample length (mm) at 60° C., ΔT is 20 (=60-40)° C., and 0.5 is the temperature expansion coefficient of quartz glass (×10 ^-6 /° C.).

(3) Humidity expansion coefficient (αh)
The obtained film was cut into a length of 15 mm and a width of 5 mm so that the film formation direction and width direction of the film were the measurement directions, and the length of each sample was measured at a humidity of 30% RH and 70% RH in a nitrogen atmosphere at 30°C, and the humidity expansion coefficient was calculated by the following formula. The measurement direction was the longitudinal direction of the cut sample, and the measurement was performed five times, and the average value was taken as αh.
αh=(L ₇₀ -L ₃₀ )/(L ₃₀ ×△H)
In the above formula, _L30 is the sample length (mm) at 30% RH, and _L70 is the sample length (mm) at 70% RH.
Sample length (mm) at RH, ΔH: 40 (=70-30)% RH.

(4) Contact Angle of Water Using a contact angle measuring image analyzer (G-1-1000) manufactured by Elma Sales Co., Ltd., the contact angle was measured 10 seconds after water was dropped.

(5) Identification of dimer diol and diethylene glycol 20 mg of a sample was dissolved in a mixed solvent of deuterated trifluoroacetic acid: deuterated chloroform = 1:1 (volume ratio) for 0.5 mL.
The amount of dimer diol and diethylene glycol in the polymer chip and film was calculated by ¹ H-NMR at 500 MHz.

(6) Intrinsic viscosity (IV)
The intrinsic viscosity of the resulting polyester copolymer and film was determined by dissolving the polymer in a mixed solvent of p-chlorophenol/tetrachloroethane (40/60 by weight) and measuring at 35°C.

(7) Glass transition point (Tg) and melting point (Tm)
The glass transition point (extrapolated onset temperature) and melting point were measured by DSC (manufactured by TA Instruments, product name: Thermal Analyst 2100) using a sample weight of 10 mg and a heating rate of 2.
The measurement was performed at 0° C./min.

(8) Film elongation at 110° C. The obtained film was cut into a length of 20 mm and a width of 4 mm so that the film formation direction was the measurement direction.
The specimen was cut into pieces of 1 mm, set in an SII EXSTAR 6000, and stored in a nitrogen atmosphere (0% RH).
After holding at 30° C., a stress of 20 MPa was applied in the film formation direction at a rate of 2° C./min for 15 min.
The temperature was raised to 0°C, and the length of the sample was measured at each temperature. The extent to which the sample expanded in the longitudinal direction was calculated using the following formula, based on the film length at 110°C (L110) compared to the film length before heating (L30) after holding at 30°C.
Coating suitability (%) = (L110 - L30) / L30 x 100

(9) Surface roughness (Ra)
Measurements were performed using a non-contact three-dimensional surface roughness meter (ZYGO: New View 5022) under conditions of a measurement magnification of 10 times and a measurement area of 283 μm×213 μm (=0.0603 mm ² ). The central surface average roughness (R
a) was carried out for each surface, and when the difference in surface roughness was 0.1 nm or less, the average value was recorded as the same surface roughness.

(10) Film Layer Thickness In the case of an unstretched film, the cross section in the direction perpendicular to the film-forming direction is microtomed (ULT
After cutting out a sample using a microscope (RACUT-S), the thicknesses of each of the layers A and B were calculated using an optical microscope. In the case of an oriented laminated polyester film, the sample was cut out in the same manner, and the thicknesses of each of the layers A and B were calculated using a transmission electron microscope to determine the thickness ratio dA/dB.

(11) Preparation of magnetic tape A backcoat layer paint having the following composition is applied to the rough surface layer side surface of the laminated biaxially oriented polyester film having a width of 1000 mm and a length of 1000 m obtained in each Example and Comparative Example by using a die coater (tension during processing: 20 MPa, temperature: 120°C, speed: 200 m/min) and dried, and then a non-magnetic paint and a magnetic paint having the following composition are simultaneously applied to the flat layer side surface of the film by using a die coater with different film thicknesses, followed by magnetic orientation and drying. Furthermore, the film is calendered by a small test calendering device (steel roll/nylon roll, 5 stages) at a temperature of 70°C and a linear pressure of 200 kg/cm, and then cured at 70°C for 48 hours. The above tape is slit to 12.65 mm and assembled into a cassette to prepare a magnetic recording tape. The coating amount is adjusted so that the thicknesses of the backcoat layer, non-magnetic layer, and magnetic layer after drying are 0.5 μm, 1.2 μm, and 0.1 μm, respectively.

<Composition of non-magnetic paint>
Titanium dioxide fine particles: 100 parts by weight; S-LEC A (vinyl chloride/vinyl acetate copolymer manufactured by Sekisui Chemical Co., Ltd.): 10 parts by weight; Nipporan 2304 (polyurethane elastomer manufactured by Nippon Polyurethane Co., Ltd.): 10 parts by weight; Coronate L (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.): 5 parts by weight; Lecithin: 1 part by weight; Methyl ethyl ketone: 75 parts by weight; Methyl isobutyl ketone: 75 parts by weight; Toluene: 75 parts by weight; Carbon black: 2 parts by weight; Lauric acid: 1.5 parts by weight <Composition of magnetic paint>
Iron (major axis: 0.037 μm, acicular ratio: 3.5, 2350 Oersted): 100 parts by weight; S-LEC A (vinyl chloride/vinyl acetate copolymer manufactured by Sekisui Chemical Co., Ltd.): 10 parts by weight; Nipporan 2304 (polyurethane elastomer manufactured by Nippon Polyurethane Co., Ltd.): 10 parts by weight; Coronate L (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.): 5 parts by weight; Lecithin: 1 part by weight; Methyl ethyl ketone: 75 parts by weight; Methyl isobutyl ketone: 75 parts by weight; Toluene: 75 parts by weight; Carbon black: 2 parts by weight; Lauric acid: 1.5 parts by weight <Composition of backcoat layer paint:>
Carbon black: 100 parts by weight Thermoplastic polyurethane resin: 60 parts by weight Isocyanate compound: 18 parts by weight (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.)
Silicone oil: 0.5 parts by weight Methyl ethyl ketone: 250 parts by weight Toluene: 50 parts by weight

(12) Electromagnetic conversion characteristics For measuring the electromagnetic conversion characteristics, a 1/2 inch linear system with a fixed head was used. For recording, an electromagnetic induction type head (track width 25 μm, gap 0.1 μm) was used, and for reproduction, an MR head was used.
A head (8 μm) was used. The relative speed of the head/tape was 10 m/sec., and the recording wavelength was 0.
A 2 μm signal was recorded, and the reproduced signal was frequency-analyzed using a spectrum analyzer. The ratio of the output C of the carrier signal (wavelength 0.2 μm) to the integrated noise N over the entire spectrum was taken as the C/N ratio, and the relative value was calculated with Example 1 prepared by the method described above as 0 dB, and evaluated according to the following criteria.
◎: +1dB or more ○: -1dB or more, less than +1dB ×: Less than -1dB

(13) Error Rate The raw tape prepared in (11) above was slit into a width of 12.65 mm (1/2 inch) and assembled into an LTO case to prepare a data storage cartridge with a magnetic recording tape length of 850 m. This data storage was recorded in an environment of 23°C and 50% RH (recording wavelength 0.55 μm) using an IBM LTO5 drive, and the cartridge was then stored in an environment of 50°C and 80% RH for 7 days. After storing the cartridge at room temperature for one day,
The entire length was played back, and the error rate of the signal during playback was measured. The error rate was calculated using the following formula from the error information (number of error bits) output from the drive. Dimensional stability was evaluated according to the following criteria.
Error rate = (number of error bits) / (number of written bits)
⊚: Error rate is less than 1.0×10 ⁻⁶ ◯: Error rate is 1.0×10 ⁻⁶ or more and less than 1.0×10 ⁻⁴ ×: Error rate is 1.0×10 ⁻⁴ or more

(14) Dropout (DO)
The data storage cartridge for which the error rate was measured in (13) above was loaded into an IBM LTO5 drive, and 14 GB of data signals were recorded and then reproduced. A signal with an amplitude (P-P value) of 50% or less of the average signal amplitude was defined as a missing pulse, and four or more consecutive missing pulses were detected as a dropout. The dropout was 850
One roll of wires measuring 1 m in length is evaluated, converted into the number of wires per 1 m, and judged according to the following criteria.
◎: Dropouts less than 3/m ○: Dropouts 3/m or more, less than 9/m ×: Dropouts 9/m or more

[Example 1]
Dimethyl 2,6-naphthalenedicarboxylate as a dicarboxylic acid component and ethylene glycol as a diol component were subjected to an ester exchange reaction in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to prepare polyethylene naphthalate pellets A1 (IV=0.58 dl/g, Tg=115° C., Tm=263° C.).

Dimethyl 2,6-naphthalenedicarboxylate as a dicarboxylic acid component, ethylene glycol as a diol component, and Pripol 2033 were subjected to an ester exchange reaction in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to prepare copolymerized polyethylene naphthalate pellets B1 in which dimer diol was copolymerized (IV=0.56 dl
/g, Tg = 76°C, Tm = 252°C). The content of dimer diol as a diol component was found to be 8.0 mol% by NMR analysis.

The pellets A1 and B1 were blended at a mass ratio of 93:7 to obtain resin C1. The composition ratio of dimer diol contained in this resin C1 was 0.5 mol%. In addition, the resin C1 contained spherical silica particles with an average particle size of 0.1 μm at 0.25 mass% based on the mass of the film, and spherical silica particles with an average particle size of 0.3 μm at 0.04 mass% based on the mass of the film.

The resin C1 thus obtained was extruded at 290°C onto a rotating cooling drum at a temperature of 60°C to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 130°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 4.5 times to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (
The film was stretched in the width direction (transverse direction) at a stretch ratio of 5.0 times, and then heat-set at 210° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.
The polyester compositions used and the results of the biaxially oriented polyester films obtained are shown in Table 1.

[Example 2]
Pellets A1 and B1 were blended in a mass ratio of 83:17, respectively, to obtain resin C2.
The dimer diol component contained in this resin C2 was 1.2 mol %. In addition, the resin C2 contained 0.25 mass % of spherical silica particles having an average particle size of 0.1 μm and 0.04 mass % of spherical silica particles having an average particle size of 0.3 μm based on the mass of the film.

The resin C2 thus obtained was extruded at 280°C onto a rotating cooling drum at a temperature of 60°C to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 130°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 4.0 to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (
The film was stretched in the width direction (transverse direction) at a stretch ratio of 5.0 times, and then heat-set at 200° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.
The polyester compositions used and the results of the biaxially oriented polyester films obtained are shown in Table 1.

[Example 3]
Pellets A1 and B1 were blended in a mass ratio of 46:54, respectively, to obtain resin C3.
The dimer diol component contained in this resin C3 was 4.0 mol %. In addition, the resin C3 contained 0.25 mass % of spherical silica particles having an average particle size of 0.1 μm and 0.04 mass % of spherical silica particles having an average particle size of 0.3 μm based on the mass of the film.

The resin C2 thus obtained was extruded at 280°C onto a rotating cooling drum at a temperature of 60°C to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 120°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 4.0 to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (
The film was stretched in the width direction (transverse direction) at a stretch ratio of 5.0 times, and then heat-set at 190° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.
The polyester compositions used and the results of the biaxially oriented polyester films obtained are shown in Table 1.

[Example 4]
The unstretched film obtained in Example 2 was heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 130°C, and stretched in the longitudinal direction (film-forming direction) at a stretching ratio of 3.7 to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (width direction) at a stretching ratio of 5.0 at 130°C, and then heat-set at 200°C for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.
The polyester compositions used and the results of the biaxially oriented polyester films obtained are shown in Table 1.

[Example 5]
The unstretched film obtained in Example 2 was heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 130°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 4.5 to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (width direction) at a stretching ratio of 4.0 at 130°C, and then heat-set at 200°C for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.
The polyester compositions used and the results of the biaxially oriented polyester films obtained are shown in Table 1.

[Example 6]
Dimethyl terephthalate as a dicarboxylic acid component and ethylene glycol as a diol component were subjected to an ester exchange reaction in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to prepare polyethylene terephthalate pellets A2 (IV=0.58
dl/g, Tg=76°C, Tm=254°C).

Dimethyl terephthalate as a dicarboxylic acid component and ethylene glycol as a diol component were subjected to an ester exchange reaction in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to prepare copolymerized polyethylene terephthalate pellets B2 in which dimer diol was copolymerized (IV=0.55 dl/g, Tg=51° C., Tm=251° C.).
The content of dimer diol as a diol component was adjusted to be 8.0 mol %.

Pellets A2 and B2 were blended in a mass ratio of 83:17, respectively, to obtain resin C4.
The dimer diol component contained in this resin C4 was 1.2 mol %. In addition, the resin C4 contained 0.25 mass % of spherical silica particles having an average particle size of 0.1 μm and 0.04 mass % of spherical silica particles having an average particle size of 0.3 μm based on the mass of the film.

The resin C4 thus obtained was extruded at 280°C onto a rotating cooling drum at a temperature of 25°C to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 100°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 3.5 times to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (
The film was stretched in the width direction (transverse direction) at a stretch ratio of 4.5 times, and then heat-set at 200° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.
The polyester compositions used and the results of the biaxially oriented polyester films obtained are shown in Table 1.

[Example 7]
As polyetherimide, "Ultem" manufactured by SABIC Innovative Plastics was used.
The prepared polyetherimide was blended with pellets A2 and B2 in a mass ratio of 5:78:17 to prepare resin C5. The dimer diol component contained in resin C5 was 1.2 mol %. Resin C5 also contained 0.15 mol % of dimer diol.
The amount of spherical silica particles having an average particle size of 0.3 μm is 0.04% by mass based on the mass of the film.
The content was adjusted so as to obtain the following.

The resin C5 thus obtained was extruded at 280°C onto a rotating cooling drum at a temperature of 25°C to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 100°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 3.6 times to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (
The film was stretched in the width direction (transverse direction) at a stretch ratio of 4.6 times, and then heat-set at 200° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.
The polyester compositions used and the results of the biaxially oriented polyester films obtained are shown in Table 1.

[Example 8]
The prepared polyetherimide and pellets A2 and B2 were mixed in a mass ratio of 20:63.
The resin C6 was prepared by blending the dimer diol component at a ratio of 1.5 mol % to 1.7 mol %. The resin C6 contained 0.25% by mass of spherical silica particles having an average particle size of 0.1 μm and 0.04% by mass of spherical silica particles having an average particle size of 0.3 μm based on the mass of the film.

The resin C6 thus obtained was extruded at 280°C onto a rotating cooling drum at a temperature of 25°C to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 100°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 3.6 times to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (
The film was stretched in the width direction (transverse direction) at a stretch ratio of 4.8 times, and then heat-set at 200° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.
The polyester compositions used and the results of the biaxially oriented polyester films obtained are shown in Table 1.

[Example 9]
Resin C7 was prepared by changing the lubricant composition of resin C2 so that the spherical silica particles having an average particle size of 0.1 μm were contained in an amount of 0.08 mass% based on the mass of film layer A. Similarly, resin C8 was prepared by changing the lubricant composition of resin C2 so that the spherical silica particles having an average particle size of 0.1 μm were contained in an amount of 0.12 mass% based on the mass of film layer B, and the spherical silica particles having an average particle size of 0.3 μm were contained in an amount of 0.13 mass% based on the mass of film layer B. Resins C7 and C8 were each extruded at 280° C., and layer A and layer B were mixed in a feed block.
The resins C7 and C8 were joined together so that the thickness ratio dA:dB was 3:7.
formed layer B.

The laminated sheet of the joined layers A and B was extruded from a die at 280° C. onto a rotating cooling drum at a temperature of 60° C. to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 130° C., and stretched in the machine direction (film-forming direction) at a stretch ratio of 4.
This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (width direction) at a stretching ratio of 5.5 times at 130°C, and then heat-set at 210°C for 3 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 4.0 μm.
The polyester compositions used and the results of the obtained laminated biaxially oriented polyester films are shown in Table 1.

[Example 10]
Resin C9 was prepared by changing the lubricant composition of resin C4 so that the amount of spherical silica particles having an average particle size of 0.1 μm was 0.08 mass % based on the mass of film layer A.
Similarly, the lubricant composition of resin C4 was changed to spherical silica particles having an average particle size of 0.1 μm, and the film layer B was changed to
Based on the mass of the powder, 0.12% by mass of spherical silica particles having an average particle size of 0.3 μm is
Resin C10 changed to 0.13% by mass based on the mass of film layer B
Resin C9 and resin C10 were extruded at 280° C., and were joined in a feed block so that the thickness ratio of layer A to layer B was dA:dB=3:7.
The resin C10 formed layer A, and the resin C10 formed layer B.

The laminated sheet of the above-mentioned joined layers A and B was extruded from a die at 280°C onto a rotating cooling drum at a temperature of 25°C to obtain an unstretched film. The unstretched film obtained was heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 100°C, and stretched in the longitudinal direction (film-forming direction) at a stretching ratio of 3.0 times to obtain a uniaxially stretched film. The uniaxially stretched film was then introduced into a stenter, stretched in the transverse direction (width direction) at a stretching ratio of 3.5 times at 100°C, and then heat-set at 200°C for 3 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 4.5 μm.
The polyester compositions used and the results of the obtained laminated biaxially oriented polyester films are shown in Table 1.

[Example 11]
The polyetherimide was blended with the pellets A2 and B2 in a mass ratio of 10:73:17 to obtain resin C11. The dimer diol component contained in this resin C11 was 1.2 mol %. In addition, the resin C11 contained spherical silica particles with an average particle size of 0.1 μm in an amount of 0.08 mass % based on the mass of the film layer A.
In addition, the lubricant composition of resin C11 was changed so that the spherical silica particles having an average particle size of 0.1 μm were 0.12 mass% based on the mass of film layer B, and the spherical silica particles having an average particle size of 0.3 μm were 0.13 mass% based on the mass of film layer B.
Resins C11 and C12 were extruded at 280° C. and merged in a feed block so that the thickness ratio of layer A to layer B was dA:dB=3:7.
Resin C 11 formed layer A, and resin C 12 formed layer B.

The laminated sheet of the joined layers A and B was extruded from a die at 280° C. onto a rotating cooling drum at a temperature of 25° C. to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 100° C., and stretched in the machine direction (film-forming direction) at a stretching ratio of 3.
This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (width direction) at a stretching ratio of 3.5 times at 100°C, and then heat-set at 200°C for 3 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 4.5 μm.
The polyester compositions used and the results of the obtained laminated biaxially oriented polyester films are shown in Table 1.

[Example 12]
The same operation as in Example 11 was repeated, except that the thickness ratio of Layer A to Layer B was changed to dA:dB=8.5:1.5.
The polyester compositions used and the results of the obtained laminated biaxially oriented polyester films are shown in Table 1.

[Example 13]
In Example 12, the thickness of the obtained laminated biaxially oriented polyester film was 6.0 μm.
The same operation was repeated except that the thickness of the unstretched film was changed so as to obtain the following:
The polyester compositions used and the results of the obtained laminated biaxially oriented polyester films are shown in Table 1.

[Example 14]
In Example 12, the same operation was repeated except that the thickness of the unstretched film was changed so that the stretching ratio in the longitudinal direction (film-forming direction) was 4.0 times, the stretching ratio in the transverse direction (width direction) was 3 times, and the thickness of the obtained laminated biaxially oriented polyester film was 4.5 μm.
The polyester compositions used and the results of the obtained laminated biaxially oriented polyester films are shown in Table 1.

[Example 15]
In Example 14, the thickness of the obtained laminated biaxially oriented polyester film was 6.0 μm.
The same operation was repeated except that the thickness of the unstretched film was changed so as to obtain the following:
The polyester compositions used and the results of the obtained laminated biaxially oriented polyester films are shown in Table 1.

[Example 16]
The polyetherimide was blended with the pellets A2 and B2 in a mass ratio of 10:80:10 to obtain resin C13. The dimer diol component contained in this resin C13 was 0.6 mol %. In addition, the resin C13 contained spherical silica particles with an average particle size of 0.1 μm in an amount of 0.08 mass % based on the mass of the film layer A.
Resin C14 was prepared by changing the lubricant composition of resin C13 to 0.12% by mass of spherical silica particles with an average particle size of 0.1 μm based on the mass of film layer B, and 0.13% by mass of spherical silica particles with an average particle size of 0.3 μm based on the mass of film layer B. Resins C13 and C14 were extruded at 280° C., respectively, and merged in a feed block so that the thickness ratio of layer A to layer B was dA:dB=8.5:1.5.
Resin C 3 formed layer A and resin C 14 formed layer B.

The laminated sheet of the joined layers A and B was extruded from a die at 280°C onto a rotating cooling drum at a temperature of 25°C to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction until the film surface temperature reached 100°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 2.8 times to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched for 10 minutes.
The film was stretched at a stretch ratio of 4.0 times in the transverse direction (width direction) at 00° C., and then heat-set at 200° C. for 3 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 4.6 μm.
The polyester compositions used and the results of the obtained laminated biaxially oriented polyester films are shown in Table 1.

[Example 17]
The polyetherimide was blended with the pellets A2 and B2 in a mass ratio of 10:74:16 to obtain resin C15. The dimer diol component contained in this resin C15 was 1.1 mol %. In addition, spherical silica particles having an average particle size of 0.1 μm were contained in resin C15 in an amount of 0.08 mass % based on the mass of the film layer A.

Polyetherimide and pellets A2 and B2 were blended at a mass ratio of 10:71:19 to obtain resin C16. The dimer diol component contained in this resin C16 is 1.3 mol%. In addition, the resin C16 contained spherical silica particles with an average particle size of 0.1 μm at 0.12 mass% based on the mass of the film layer B, and spherical silica particles with an average particle size of 0.3 μm at 0.13 mass% based on the mass of the film layer B. Then, resins C15 and C16 were extruded at 280° C., respectively, and merged in a feed block so that the thickness ratio of layer A to layer B was dA:dB=5.0:5.0. Note that resin C15 formed layer A, and resin C16 formed layer B. Note that the dimer diol component in the film total was 1.2 mol%.

The laminated sheet of the joined layers A and B was extruded from a die at 280°C onto a rotating cooling drum at a temperature of 25°C to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction until the film surface temperature reached 100°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 2.8 times to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched for 10 minutes.
The film was stretched at a stretch ratio of 4.0 times in the transverse direction (width direction) at 00° C., and then heat-set at 200° C. for 3 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 4.6 μm.
The polyester compositions used and the results of the obtained laminated biaxially oriented polyester films are shown in Table 1.

[Comparative Example 1]
Using pellets A2, resin C17 was blended so that the spherical silica particles having an average particle size of 0.1 μm were present in an amount of 0.25 mass% based on the mass of the film, and the spherical silica particles having an average particle size of 0.3 μm were present in an amount of 0.04 mass% based on the mass of the film.
Resin C17 was extruded at 280° C. onto a cooling drum at a temperature of 25° C. during rotation to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 120° C., and stretched in the machine direction (film-forming direction) at a stretch ratio of 3.5 times to obtain a uniaxially stretched film.
This uniaxially stretched film was introduced into a stenter and stretched in the transverse direction (width direction) at 120° C. to a stretching ratio of 4.
The film was stretched 5 times and then heat-set at 210° C. for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.
The results for the biaxially oriented polyester obtained are shown in Table 1.

[Comparative Example 2]
Using pellets A1, resin C18 was blended so that the spherical silica particles having an average particle size of 0.1 μm were present in an amount of 0.25 mass% based on the mass of the film, and the spherical silica particles having an average particle size of 0.3 μm were present in an amount of 0.04 mass% based on the mass of the film.

Resin C18 was extruded at 300°C onto a cooling drum at a temperature of 60°C while rotating to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 150°C, and stretched in the machine direction (film-forming direction) at a stretching ratio of 4.5 times to obtain a uniaxially stretched film. This uniaxially stretched film was then introduced into a stenter and stretched in the transverse direction (width direction) at a stretching ratio of 5 at 150°C.
The film was stretched at 0.0 times its original length and then heat-set at 210°C for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 µm.
The results for the biaxially oriented polyester obtained are shown in Table 1.

[Comparative Example 3]
Pellets A1 and B1 were blended in a mass ratio of 97:3, respectively, to obtain resin C19.
The dimer diol component contained in this resin C19 was 0.2 mol %. In addition, the resin C19 contained 0.25 mass % of spherical silica particles having an average particle size of 0.1 μm and 0.04 mass % of spherical silica particles having an average particle size of 0.3 μm based on the mass of the film.

The resin C19 thus obtained was extruded at 290°C onto a rotating cooling drum at a temperature of 60°C to obtain an unstretched film. The unstretched film was then heated from above by an IR heater between two pairs of rollers rotating at different speeds along the film-forming direction so that the film surface temperature reached 120°C, and stretched in the longitudinal direction (film-forming direction) at a stretching ratio of 4.5 times to obtain a uniaxially stretched film. The uniaxially stretched film was then introduced into a stenter, stretched in the transverse direction (width direction) at a stretching ratio of 5.0 times at 120°C, and then heat-set at 210°C for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.

The polyester film obtained had a large elongation when dried, which made it difficult to prepare a magnetic tape from it, so that its characteristics were not evaluated.
The results for the biaxially oriented polyester obtained are shown in Table 1.

[Comparative Example 4]
Pellets A1 and B1 were blended in a mass ratio of 26:78, respectively, to obtain resin C2.
The dimer diol component contained in this resin C20 was 6.0 mol %.
Resin C20 contained 0.25% by mass of spherical silica particles having an average particle size of 0.1 μm, based on the mass of the film, and 0.04% by mass of spherical silica particles having an average particle size of 0.3 μm, based on the mass of the film.

The resin C20 thus obtained was extruded at 270°C onto a rotating cooling drum at a temperature of 60°C to obtain an unstretched film. The unstretched film was heated from above by an IR heater between two pairs of rollers with different rotation speeds along the film-forming direction so that the film surface temperature reached 110°C, and stretched in the longitudinal direction (film-forming direction) at a stretching ratio of 4.2 times to obtain a uniaxially stretched film. The uniaxially stretched film was then introduced into a stenter, stretched in the transverse direction (width direction) at 110°C at a stretching ratio of 5.0 times, and then heat-set at 190°C for 3 seconds to obtain a biaxially oriented polyester film having a thickness of 5.0 μm.

The obtained polyester film was not subjected to evaluation of its characteristics since it showed a large film elongation during drying in the above (11) production of a magnetic tape, making it difficult to produce a magnetic tape.
The results for the biaxially oriented polyester obtained are shown in Table 1.

In Table 1, NDC is 2,6-naphthalenedicarboxylic acid, TA is terephthalic acid, EG is ethylene glycol, DEG is diethylene glycol, PEI is polyetherimide, MD
indicates the film-forming direction, and TD indicates the width direction.

The polyester film of the present invention has excellent dimensional stability and can therefore be suitably used as a base film for high-density magnetic recording media.

Claims (6)

A laminated polyester film comprising a copolymer polyester in which a dicarboxylic acid component is an aromatic dicarboxylic acid component having 6 or more carbon atoms, and a glycol component is an alkylene glycol component having 2 to 4 carbon atoms and an aliphatic dimer diol component having 31 to 50 carbon atoms, and a polyester composition in which the content of the dimer diol component is in the range of 0.3 to 4.0 mol % based on the number of moles of the aromatic dicarboxylic acid component is used in at least one layer,
The laminated polyester film contains inert particles,
Used for the base film of magnetic recording media,
Laminated polyester film. The laminated polyester film according to claim 1, wherein the polyester composition contains, in addition to the copolymer polyester, at least one selected from the group consisting of polyimide, polyetherimide, polyether ketone, and polyether ether ketone in an amount ranging from 0.5 to 25% by weight based on the mass of the copolymer polyester. The laminated polyester film according to claim 1 or 2, in which the Young's modulus in at least one direction in the film plane direction is 4.5 GPa or more. A laminated polyester film according to any one of claims 1 to 3, in which the humidity expansion coefficient in at least one direction in the film plane direction is in the range of 1 to 8.5 (ppm/% RH) and the temperature expansion coefficient in at least one direction is in the range of 14 (ppm/°C) or less. The laminated polyester film according to any one of claims 1 to 4, wherein the water contact angle of at least one surface is in the range of 75 to 90 degrees. A magnetic recording medium comprising the laminated polyester film according to any one of claims 1 to 5 and a magnetic layer formed on one side thereof.