JPH0411112B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a biaxially stretched laminated polyester film for magnetic recording, and more specifically, to provide a magnetic recording medium with excellent electromagnetic conversion characteristics and excellent running durability and abrasion resistance during repeated use. This invention relates to a biaxially stretched laminated polyester film. [Prior Art] Magnetic recording media based on polyester films, such as video tapes, audio tapes, computer tapes, and floppy disks, are known and widely used. In recent years, demands for high-density recording and high quality have been increasing in these application fields, and with this, the polyester film that serves as the base has a flat surface and excellent slipperiness, as well as durable running properties and abrasion resistance. The demand for superior performance is becoming stronger and stronger. Conventionally, methods for improving slipperiness have been proposed, such as adding inorganic particles such as silicon oxide or calcium carbonate to polyester, or precipitating fine particles containing calcium, lithium, or phosphorus in the polymerization system during polyester synthesis. ing. In both methods, when polyester is formed into a film, protrusions are formed on the film surface due to fine particles.
This improves the slipperiness of the film. However, in the method of improving the slipperiness of the film using projections made of fine particles as described above, the slipperiness usually improves as the film surface becomes rougher, but on the other hand, due to the roughening, the magnetic paint After coating, the surface tends to become rough and the electromagnetic conversion characteristics tend to deteriorate. As a way to solve these contradictory problems of flatness and slipperiness, a method has been proposed that uses composite particles that combine large-sized particles and small-sized particles. Since both sides of the film have the same surface properties, there is a limit and the level is not satisfactory. Therefore, several different surface films have been proposed in which one exposed surface has excellent slipperiness and the other exposed surface is flat, and laminated films are also used as a means for this purpose. There is. However, the conventional method using this means also has the following problems. That is, if one attempts to make the surface rough to make it slippery, the other surface will also be affected by this, and the flatness will be impaired. This tendency becomes particularly noticeable as the film thickness becomes thinner. Even if the film surface on which the magnetic paint is applied to a flat, easily slippery film with different surfaces is flat, if the opposite side is too rough, the unevenness of the rough surface of the film will appear on the surface of the applied magnetic layer. As a result of image transfer, unevenness occurs on the surface of the magnetic layer, resulting in loss of flatness and insufficient electromagnetic conversion characteristics. Generally, when trying to provide excellent slipperiness, the protrusions on the film surface become taller, and as a result, the taller protrusions are scraped off during the cleaning process with nonwoven fabric in the magnetic recording tape production process or the calendering process, which causes dropouts. wake up
Since the distribution of additive particles as a means of forming protrusions on the film surface is hardly controlled in the prior art, it is difficult to adjust the protrusions on the film surface as designed. There are other problems. The present inventor has solved the above-mentioned problems and succeeded in developing a laminated film that has flatness, slipperiness, and abrasion resistance that can be applied to high-quality magnetic recording applications. [Object of the Invention] An object of the present invention is to provide a base film that can be used as a magnetic recording medium for high-density recording, high quality, and can withstand repeated use.Furthermore, there are no large protrusions on the film surface, and there are no dropouts or the like. A flat surface (B side) that does not cause noise and does not easily deteriorate electromagnetic conversion characteristics, and a low coefficient of friction during repeated running, due to contact with the processing process of the magnetic recording medium and the part of the magnetic recording/reproducing device. Provides a biaxially oriented laminated polyester film that has extremely low abrasion, has good durability during continuous use, and has an easy-smooth surface (Side A) with few large protrusions that cause transfer to the magnetic layer surface. It's about doing. [Configuration/Effects of the Invention] According to the present invention, an object of the present invention is to provide a biaxially stretched laminate comprising a film-forming aromatic polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. It is a film, and one exposed surface (side A) of the film has a surface roughness RaA of 0.025 μm or less 0.010 μm.
The above is the number of protrusions (y: ke/mm ² ) and the height of the protrusions (x: μm) found in an area with 20 protrusions/mm ² or more.
_The distribution curve representing the relationship _between If the portion of the protrusion distribution curve that is larger than the maximum value is within the range of formula (2) log ₁₀ y≧−18x+3.7 (2), and the protrusion height (x) is 0.87 μm or more, it is practically considered The other exposed surface (Side B) has a rough surface.
RaB is 0.012 μm or less and 0.004 μm or more, and the number of protrusions is
Number of protrusions found in an area of 20 pcs/mm ² or more (y: pcs/mm2)
mm ² ) and the height of the protrusion (x: μm), the curve of the portion larger than the maximum value of the protrusion distribution curve is expressed by the formula (3) log ₁₀ y = -18x + 3.7 ... (3 ), and is also within the range of equation (4) log ₁₀ y≧−44.1x+4.33 ……(4), and does not substantially contain any protrusions with a height (x) of 0.13 μm or more. Furthermore, the surface roughness RaA of the A side (smooth surface) and the surface roughness RaB of the B side (flat surface) satisfy the formula (5) 1.3≦RaA／RaB≦5 ...(5), And the density ρ and the refractive index n _z in the thickness direction of the laminated film are expressed by equations (6), (7) 1.352≦ _nz −ρ/10≦1.366 ……(6) 1.385≦ρ≦1.405 ……(7) This is achieved by a biaxially stretched laminated polyester film for magnetic recording that satisfies the following. The biaxially stretched laminated polyester film of the present invention is a laminated film comprising a layer providing a smooth surface and a layer providing a flat surface. The layer that provides this smooth surface (Side A) has a surface roughness RaA of 0.025 μm or more as a film surface characteristic.
0.010 μm or less, substantially does not include any protrusions with a protrusion height (x) of 0.87 μm or more, and the number of protrusions is 20/mm ²
The distribution curve representing the relationship between the number of protrusions (y: ke/mm ² ) and the height of the protrusions (x: μm) obtained in the above region is expressed by the following formula (1) log ₁₀ y = -9.8x + 4.4... ...It has a protrusion distribution that does not intersect with the straight line represented by (1) in the range of log ₁₀ y>1.3, and the curve of the portion larger than the maximum value of the protrusion distribution curve is expressed by the following formula (2) log ₁₀ y≧−18x+3 .7 It has the characteristics within the range of (2). This surface roughness
If RaA is larger than 0.025 μm, the surface of the base film becomes too rough, and the flatness of the magnetic surface is impaired due to show-through transfer, which deteriorates the electromagnetic conversion characteristics, which is not preferable. Moreover, when RaA is smaller than 0.010 μm, running properties deteriorate, which is not preferable. A preferable surface roughness RaA is 0.020 μm or less and 0.0125 μm or more. Furthermore, the distribution curve representing the relationship between the number of protrusions (y) and the height of the protrusions (x) obtained in an area of 20 protrusions/mm ² or more is the straight line expressed by the above equation (1) and log ₁₀ y
If they intersect within the range of >1.3, the flatness of the magnetic surface will be impaired due to show-through transfer, and the electromagnetic conversion characteristics will deteriorate, which is undesirable. At the same time, protrusions may be scraped off during the tape processing process, especially during the calendering process, and the tape may be repeatedly used. This is undesirable because it causes problems such as abrasion during use, which increases the friction coefficient and also causes abrasion particles to adhere to the tape surface and increase dropout. Furthermore, if the portion of the distribution curve larger than the maximum value is not within the range of formula (2) above, the film surface will become too flat, and the friction coefficient (μk) after 200 repetitions will satisfy the range of 0.15 to 0.35. This is not desirable because it makes it difficult to do so. In the above distribution curve, it is preferable that the curve on the side exceeding the maximum value satisfies the following range: -18x+3.7≦ _log10y ≦-9.8x+4.4 (however, _log10y >1.3). Furthermore, if there are protrusions of 0.87 μm or more on the film surface, the running properties of the tape will be improved, but this is not preferable because the protrusions may be scraped during the processing process and the protrusions may also cause dropouts. In the laminated polyester film of the present invention, the layer that provides a flat surface (side B) has a surface roughness RaB of 0.012 μm or more and no protrusions with a protrusion height (x) of 0.13 μm or more as film surface characteristics. , and from the maximum value of the protrusion distribution curve representing the relationship between the number of protrusions (y: protrusions/mm ² ) and the protrusion height (x: μm) determined in an area with the protrusion count of 20 protrusions/mm ² or more. The large part of the curve intersects the following formula (3) log ₁₀ = −18x + 3.7 ……(3), and further falls into the range of the following formula (4) log ₁₀ y≧−44.1×+4.33 ……(4) It has certain characteristics. This surface roughness
If RaB is larger than 0.012 μm, it is not preferable because the magnetic surface cannot maintain the electromagnetic conversion characteristics necessary for a high-quality magnetic recording tape. Preferred surface roughness RaB is 0.010μm or less
It is 0.004μm or more. In addition, in the distribution curve that expresses the relationship between the number of protrusions (y) and the protrusion height (x) determined in an area with the number of protrusions of 20 protrusions/mm ² or more, the portion of the protrusion distribution curve that is larger than the maximum value is The above formula
If it does not intersect (3), for example, if the portion of the protrusion distribution curve that is greater than the maximum value always satisfies equation (2) above, the film surface is too rough and the protrusion height is too high.
There are many cases where protrusions of 0.13 μm or more are present,
This is not preferable because the electromagnetic conversion characteristics deteriorate and the characteristics necessary for a high-quality magnetic recording tape cannot be maintained. Conversely, if the protrusion distribution curve always satisfies log ₁₀ y < -18x + 3.7 in an area where the number of protrusions is 20 protrusions/mm ² or more, the film surface becomes too flat and the coefficient of friction becomes large. This is not preferable because it is difficult to handle the film during film formation or during the processing of magnetic recording materials, and it causes problems such as wrinkles. The biaxially stretched laminated polyester film of the present invention has the above-mentioned film surface characteristics, and at the same time has a relationship between the surface roughness RaA of the easily slippery surface (side A) and the surface roughness RaB of the flat surface (side B) as shown below ( 5) It has characteristics that satisfy the relational expression 1.3≦RaA/RaB≦5 (5). If the value of RaA/RaB is less than 1.3, it will not be possible to exhibit characteristics that satisfy both flatness and slipperiness, and the electromagnetic conversion characteristics will deteriorate.
This is not preferable because one of the running properties will be insufficient. Furthermore, when the value of RaA/RaB is greater than 5, the difference in slipperiness between the front and back surfaces of the laminated film is too large.
Wrinkles may occur during winding of the film, creases may occur during the processing process, and scratches may occur, which is undesirable. From these points, it is more preferable that 1.5≦RaA/RaB≦3. The biaxially stretched laminated polyester film of the present invention has the above-mentioned film surface characteristics, and furthermore, the refractive index n _z and density ρ in the thickness direction of the film satisfy the following formulas (6) and (7) 1.352≦n _z −ρ /10≦1.366 …(6) 1.385≦ρ≦1.405 …(7). If the value of ( _nz −ρ/10) is lower than 1.352, it is not preferable because the running performance deteriorates. Furthermore, the larger the value of (n _z −ρ/10), the better the machinability and runnability, but 1.366
Exceeding this is not preferable because thickness unevenness becomes worse when forming a film and it becomes difficult to obtain a product with good winding. The value of (n _z −ρ/10) is preferably 1.355 or more and 1.362 or less, particularly preferably 1.356 or more
It is less than or equal to 1.360. Furthermore, if the density ρ exceeds 1.405 [g/cm ³ ], it is not preferable because the machinability becomes poor and scratches are likely to occur. On the other hand, if the density ρ is less than 1.385 [g/cm ³ ], the heat shrinkage rate will increase and wrinkles will easily form in the heating process part during the magnetic tape manufacturing process, which is not preferable. Density ρ is 1.390g/cm3 or ^more
1.400g/cm ³ or less is preferable, 1.394g/cm ³ or more
Particularly preferred is 1.398 g/cm ³ or less. The aromatic polyester in the present invention is a polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such polyesters are substantially linear and have film-forming properties, particularly by melt molding. Examples of aromatic dicarboxylic acids include 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, and anthracene. Examples include dicarboxylic acids. Examples of aliphatic glycols include polymethylene glycols having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, and decamethylene glycol, or alicyclic diols such as cyclohexanedimethanol. etc. can be given. In the present invention, polyesters containing, for example, alkylene terephthalate and/or alkylene naphthalate as main constituents are preferably used. Among such polyesters, for example, polyethylene terephthalate, polyethylene naphthalate, etc., as well as all dicarboxylic acid components,
Particularly preferred are copolymers in which 80 mol% or more of the glycol component is terephthalic acid and/or naphthalene dicarboxylic acid, and 80 mol% or more of the total glycol component is ethylene glycol. In this case, the dicarboxylic acids accounting for up to 20 mol% of the total acid composition can be the above-mentioned aromatic dicarboxylic acids, and also, for example, aliphatic dicarboxylic acids such as adipic acid and sebacic acid; cyclohexane-1.4-
It can be an alicyclic dicarboxylic acid such as dicarboxylic acid. In addition, up to 20 mol% of the total glycol component can be the above-mentioned glycols other than ethylene glycol, or aromatic diols such as hydroquinone, resorcinol, 2,2-bis(4-hydroxyphenyl)propane; , 4-dihydroxymethylbenzene; and polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. In addition, the aromatic polyester used in the present invention includes a dicarboxylic acid component and a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid; an aliphatic oxyacid such as ω-hydroxycaproic acid; It also includes those containing 20 mol% or less based on the total amount of oxycarboxylic acid components. Further, the aromatic polyester in the present invention contains a trifunctional or higher functional polycarboxylic acid or a polyhydroxy compound, such as trimellitic acid, in an amount within a substantially linear range, for example, an amount of 2 mol% or less based on the total acid component. Copolymerized pentaerythritol is also included. The above-mentioned aromatic polyester is known per se, and can be produced by a method known per se. The aromatic polyester preferably has an intrinsic viscosity of about 0.4 to about 0.9, measured as a solution in o-chlorophenol at 35°C. In the polyester film layer forming one surface (A side: easy-slip surface) exposed in the present invention,
Inert particles, preferably consisting of large particles and small particles, are included. The particles that can be used as the large particles constituting the inert particles are compositionally composed of calcium carbonate, and may be produced by either light calcium carbonate or calcium bicarbonate. These large particles of calcium carbonate have a characteristic particle size distribution, and when the particle size distribution of calcium carbonate particles is plotted on logarithmic probability paper, it is expressed as the ratio to the particle diameter when the cumulative weight of calcium carbonate is 75%. The particle size distribution ratio [γ] is expressed by the following formula (8) [γ] = Diameter when the calculated particle weight is 25% / Diameter when the calculated particle weight is 75%... (8) The particle size distribution is controlled so that the value of is in the range of 1.5 to 2.3, preferably in the range of 1.5 to 2.2, and more preferably in the range of 1.5 to 2.1. A controlled particle size distribution of the calcium carbonate particles used in the present invention is a particularly preferable condition for achieving the above-mentioned object of the present invention, and the lower the value of this particle size distribution ratio [γ], the smaller the particle size of the calcium carbonate particles. This shows that the distribution is sharp. Calcium carbonate particles having such a particle size distribution ratio in a specific range cannot be obtained simply by using commercially available products, but they must be crushed or crushed in a solvent such as ethylene glycol, and then coarse particles can be removed by sedimentation. It can only be obtained after separation and further pretreatment such as filtration. Further, the small particles constituting the inert particles are compositionally composed of titanium dioxide, and crystalline form is anatase titanium dioxide. More preferred is a special titanium dioxide containing specific amounts of phosphorus and potassium as described below. These anatase-type titanium dioxide particles are characterized by their particle size distribution, and have a particle size distribution ratio [γ] expressed by the above formula (8).
It has a controlled particle size distribution with a value of in the range 1.2 to 2.3, preferably in the range 1.4 to 2.2, more preferably in the range 1.4 to 2.1. A controlled particle size distribution of the titanium dioxide particles used in the present invention is a particularly preferable condition for achieving the above-mentioned object of the present invention, and the smaller the value of this particle size distribution ratio [γ], the smaller the particle size distribution of the titanium dioxide particles. This shows that the particle size distribution is sharp. However, it is empirically very difficult and difficult to achieve a particle size distribution with a particle size distribution ratio [γ] value of less than 1.2. Titanium dioxide particles having such a particle size distribution ratio in a specific range cannot be obtained simply by using commercially available products, but are pulverized or crushed in a solvent such as ethylene glycol, and coarse particles are separated by sedimentation. However, it is a specific particle with a controlled particle size distribution that can only be obtained by performing a pretreatment such as filtration in combination. When the value of this particle size distribution ratio [γ] exceeds 2.3, the number of coarse particles in the inert particles increases, and the protrusion shape on the film surface becomes large. The electromagnetic conversion characteristics of the product also tend to deteriorate rapidly. In addition, even if the value of the particle size distribution ratio [γ] of either calcium carbonate particles or titanium particles exceeds 2.3, the number of coarse particles in the inert particles is small even though the weight percentage is small. The number of protrusions with three or more rings of interference fringes caused by Na rays on the film surface increases, and the number of protrusions becomes more than 20 per 100 cm ³ . The calcium carbonate particles used in the present invention have an average particle diameter in the range of 0.3 to 0.9 μm, preferably 0.35 to 0.9 μm.
It is characterized by being in the range of 0.8 μm, more preferably in the range of 0.4 to 0.7 μm. The content of calcium carbonate particles in the film (W _B ) is 0.06-0.5% by weight
, preferably in the range of 0.1 to 0.4% by weight, more preferably in the range of 0.15 to 0.3% by weight. When the average particle size of the calcium carbonate particles is larger than 0.9 μm and the content of calcium carbonate in the film (W _B ) is larger than 0.50% by weight, the base film has good slipperiness, but the film surface The frequency of unevenness increases, and noise during magnetic recording tends to increase. The content of calcium carbonate particles in the film is 0.1 to 0.5% by weight
and 0.06% or more and less than 0.1% (weight) (especially
0.06 to 0.09% by weight), the former tends to increase the roughness of the film surface (RaA value), and the latter tends to increase the running friction coefficient [μk] of the film running surface due to repeated use. shows a tendency to remain unchanged. Therefore, if the content of calcium carbonate is less than 0.1% by weight, the running (use) of the film will be difficult.
This causes instability in durability and sliding properties. The titanium dioxide particles among the inert particles used in the present invention have an average particle size in the range of 0.10 to 0.50 μm, preferably in the range of 0.15 to 0.50 μm, and more preferably in the range of 0.15 to 0.50 μm.
It is preferably in the range of 0.20 to 0.40 μm. Content of titanium dioxide particles in the film used in the present invention (W _B )
ranges from 0.10 to 0.60% by weight, preferably from 0.12 to
It is characterized by being in the range of 0.50% by weight, more preferably in the range of 0.15 to 0.40% by weight. The average grain size of titanium dioxide particles is smaller than 0.10μm,
If the content ( _WS ) in the film is less than 0.10% by weight, the surface of the base film will have low slipperiness, and problems such as unwinding during film forming will occur frequently. In the present invention, the ratio between the average particle size of calcium carbonate particles and the average particle size of titanium dioxide particles is 1.5 to 10.
It is preferably in the range of 1.5 to 8, particularly 1.6 to 5. The ratio of the average particle size of calcium carbonate particles to the average particle size of titanium dioxide particles is 10
If it is larger than , the unevenness of the film surface becomes large and the reproducibility of magnetic recording is poor. In addition, when the ratio of the average particle diameter of calcium carbonate particles is smaller than 1.5, the winding properties during base film formation are poor, and there is a tendency for differences in the winding hardness in the width direction of the base film to occur in many cases. be. The titanium dioxide particles used in the present invention have a composition of 0.25% by weight _or more, preferably in the range of 0.25% to 1.0% by weight, more preferably in the range of 0.28% to 1.0% by weight, calculated as _P 2 O 5. phosphorus element, and 0.1% by weight or more calculated as K ₂ O,
It is characterized by containing potassium element preferably in a range of 0.1% to 0.30% by weight, more preferably in a range of 0.1% to 0.28% by weight. In the composition of titanium dioxide particles, if the content of phosphorus element in terms of P ₂ O ₅ is less than 0.25% by weight, or if the content of potassium element in terms of K ₂ O is less than 0.1% by weight, There is a tendency that the color tone of the titanium dioxide particles tends to deteriorate and the agglomeration stability of the titanium dioxide particles in ethylene glycol tends to decrease. The titanium dioxide particles preferably used in the present invention are characterized by exhibiting low wear resistance because they contain the phosphorus element and potassium element within the above ranges. As a result, there is less damage to the equipment used, especially the blades of the diamond slitter, and the effect of low wear is seen in terms of workability, equipment maintenance, cost, etc. Furthermore, there is also the effect that scratches and scratches are less likely to occur on the film surface. The other surface exposed in the present invention (Side B:
The polyester film layer forming the flat surface preferably contains inert particles to an extent that does not impair flatness. The inert particles are preferably small particles, particularly titanium dioxide particles, contained in the polyester film layer forming the easy-slip surface (A-side). The description of the titanium dioxide particles can basically be applied as described above. The average particle size of these titanium dioxide particles is
Range of 0.10 to 0.50μm, preferably 0.12 to 0.50μm
, more preferably in the range of 0.15 to 0.40 μm. Furthermore, the content ( _WS ) of the titanium dioxide particles in the film is in the range of 0.01 to 1.0% by weight, preferably in the range of 0.02 to 0.60% by weight, and more preferably in the range of 0.05 to 0.40% by weight. There is. If the average particle diameter of the titanium dioxide particles is smaller than 0.10 μm and the content of titanium dioxide particles in the film (W _S ) is less than 0.01% by weight, the base film surface has poor lubricity, and it is difficult to roll the film during film forming. There are many problems where it cannot be removed. The thickness structure of the laminated film in the present invention is not particularly limited, but in order to maximize the effect of the added inert particles, the layer thickness of the easy slip layer (A side) after biaxial stretching is 2 μm. It is preferably at least 3 μm, more preferably at least 4 μm. If the thickness of the slippery layer is too thin, it becomes difficult for projections to form due to small particles, resulting in poor running performance and scratch resistance. Also,
In order to maintain flatness, the layer providing a flat surface (B surface) preferably has a layer thickness of 3 μm or more after biaxial stretching, more preferably 4 μm or more, particularly 5 μm.
It is preferable that it is above. If the thickness of the flat layer is too thin, flatness will be impaired due to the influence of inert particles in the slippery layer, which is not preferable. Although the laminated film of the present invention has a multilayer structure of two or more layers, a two-layer structure is particularly preferable. In the case of a laminated film having three or more layers, as long as the outermost layer is the polyester film layer of surfaces A and B described above, the intermediate layer may be any polymer layer. The laminated film of the present invention can be manufactured using conventional laminated film manufacturing methods. For example, a polyester layer forming surface A and a polyester layer forming surface B can be laminated in a molten state or in a cooled and solidified state. More specifically, it can be produced by methods such as coextrusion and extrusion coating. The films laminated by the above-mentioned method are sequentially or simultaneously biaxially stretched in accordance with conventional methods for producing biaxially stretched films, and further heat treated. At this time, since the film surface characteristics change depending on the shape, particle size, amount, etc. of the solid fine particles, and also depending on the stretching conditions, the film surface characteristics are appropriately selected from conventional stretching conditions. For example, the stretching temperature ranges from (Tg− ₁₀ ) to (Tg+
45) If the second-stage stretching temperature (for example, transverse stretching temperature: T ₂ ) is selected from the range of (T ₁ +15) to (T ₁ +40) °C from the range of (Tg polyester glass transition temperature) good. Further, the stretching ratio is preferably selected from a range in which the uniaxial stretching ratio is 2.5 or more, particularly 3 times or more, and the area magnification is 8 times or more, especially 10 times or more. Furthermore, the heat setting temperature is 180
It is preferable to select from the range of ~250°C, more preferably 200~230°C. In addition, in order to satisfy the above-mentioned relationship between n _z and density ρ, the longitudinal stretching temperature must be (Tg + 25) °C.
As mentioned above, it is desirable that the stretching speed in the longitudinal direction is 1500%/second or less, preferably 900%/second or less. The biaxially stretched laminated polyester film of the present invention has excellent properties for use in magnetic recording media, especially high-grade magnetic tapes. [Example] Hereinafter, the present invention will be further explained with reference to Examples. Note that various physical property values and characteristics in the present invention were measured and defined as follows. (1) Average particle size of inert solid particles Measured using a Shimadzu CP-50 Centrifugal Particle Size Analyzer. From the cumulative curve of particles of each particle size and their abundance calculated based on the centrifugal sedimentation curve obtained, 50 mass percent
The particle size corresponding to the particle size was read, and this value was taken as the above-mentioned average particle size (see "Particle Size Measurement Technique", published by Nikkan Kogyo Shimbun, 1975, pp. 242-247). (2) Particle size distribution ratio of inert solid particles [γ] Based on the centrifugal sedimentation curve obtained in measuring the average particle size of inert inorganic particles, calculate the cumulative curve of particles of each particle size and their abundance. The particle size corresponding to an integrated weight of particles of 25 mass percent and the particle size corresponding to an integrated weight of particles of 75 mass percent are read, and the former value is divided by the latter value to calculate each inertness. Particle size distribution ratio of solid particles [γ]
Calculate. (3) Film surface roughness (Ra) Measured according to JIS B 0601. Tokyo Precision Co., Ltd.
Stylus type surface roughness meter (SURFCOM 3B) manufactured by Co., Ltd.
Using this method, a film surface roughness curve was drawn on the chart under the conditions of a needle radius of 2μ and a load of 0.07g.
A part of measurement length L is extracted from the film surface roughness curve in the direction of its center line, the center line of this extracted part is taken as the X axis, the direction of longitudinal magnification is taken as the Y axis, and the roughness curve is expressed as Y=f ] When expressed as
The value (Ra: μm) given by the following formula is defined as the film surface roughness. Ra=1/L∫ ^L _p ｜f(x)｜dx In the present invention, 8 measurements were taken with the reference length as 0.25 mm, and Ra was expressed as the average value of the 5 measurements, excluding 3 from the largest value. . (4) Number of surface protrusions Aluminum was uniformly vacuum-deposited on the surface of the film to a thickness of 400 to 500 Å or less, and collodion was applied to the opposite non-vapor-deposited surface (film surface) and attached, followed by drying. Tl monochromatic light multi-interference reflection microscope (for example, manufactured by Carl Leiss JENA)
An arbitrary 100 cm ² of the aluminum-deposited surface was observed at a magnification of 100 times. Number of protrusions with interference fringes of 3 or more rings (0.87 μm or more) that occur corresponding to the protrusion height in the microscope field of view H ₃ (pieces)
was counted. (5) Film friction coefficient (μk) Measured as follows using the apparatus shown in Figure 2. In Figure-2, 1 is the unwinding reel, 2
is tension controller, 3, 5, 6, 8,
9 and 11 are free rollers, 4 is tension detector (inlet), 7 is stainless steel SUS 304
fixed rod (outer diameter 5 mmφ), 10 is a tension detector (outlet), 12 is a guide roller, 13
indicate the take-up reels. In an environment with a temperature of 20℃ and a humidity of 60%, cut the film into 1/2 inch width with a fixing rod (7) (with surface roughness)
0.3μm) at an angle θ = 152/180x radian (152°) and move (friction) at a speed of 200cm/min. When the tension controller 2 is adjusted so that the inlet tension T ₁ is 35 g, the outlet tension (Tig) is detected by the outlet tension detector after the film has traveled 90 m, and the running friction coefficient μk is calculated using the following formula. . μk=2.303/θlogT ₂ /T ₁ =0.868logT ₂ /35 (6) Scrapability The scratchability of the running surface of the base film was evaluated using a 5-stage mini super calendar. The calender was a five-stage calender consisting of nylon rolls and steel rolls, and the processing temperature was 80°C, the linear pressure applied to the film was 200 kg/cm, and the film was run at a speed of 50 m/min. After running the running film for a total length of 2000 m, the abrasion resistance of the base film was evaluated based on the dirt that adhered to the top roller of the calendar. <5-level evaluation> ◎ No stains on the nylon roll 〇 Almost no stains on the nylon roll △ Nylon roll gets dirty × Nylon roll gets very dirty ×× Nylon roll gets very dirty (7) Electromagnetic conversion characteristics of magnetic coating film (chroma S/N) On the film, apply the following composition Co-containing iron oxide powder 100 parts by weight Eslec A (vinyl chloride-vinyl acetate copolymer manufactured by Sekisui Chemical) 10 〃 Nitsuporan 2304 (polyurethane elastomer manufactured by Nippon Polyurethane) 10 〃 Coronate L (Japan) (Polyurethane polyisocyanate) 5 Lecithin 1 Methyl ethyl ketone 75 parts by weight Methyl isobutyl ketone 75 Toluene 75 Additives (lubricant, silicone resin) 0.15 Apply magnetic powder paint with a gravure roll, and apply the magnetic paint with a doctor knife. The layer is smoothed and magnetically oriented in a conventional manner while the magnetic paint is still dry, and then introduced into an oven for dry curing. Furthermore, it is calendered to make the coating surface uniform, and then slit to approximately 5μ.
A 1/2 inch wide magnetic coating tape with a magnetic layer formed thereon is prepared. The electromagnetic conversion characteristics (chroma S/N) of this magnetic coating tape are measured by the following method. Using a commercially available home VTR, record a signal that combines a 100% chroma level signal with a 50% white level signal (the 100% white level signal has a peak voltage of 0.714 volts) and play it back. Signal Noise Meter: Type 925
Measurements are made using R. The definition of chroma S/N is as follows according to Shibasoku's definition. Chroma S/N (dB) = 20log ES (p-p) / EN (rms) where ES (p-p) is the peak-to-peak voltage difference (p-p) of the reproduced signal of the white level signal
It is. ES (p-p) = 0.714V (p-p) EN (rms) is the square root value of the peak voltage of the reproduced signal of the chroma level signal. EN (rms) = AM noise effective value voltage (V) (8) Dropout Apply the tape (1/2 inch width) coated with magnetic powder paint in (7) above to a commercially available dropout counter (for example, Shibasoku VH01BZ). type)
Count the dropout of 5 μsec x 10 dB and calculate 1
The number of counts per minute was calculated. (9) Scratch Judgment Slit the base film into 1/2 inch width, and at the same time as measuring the friction coefficient in (5) above, place the film on a fixed rod at an angle of 152° and run it for 10m at a film speed of 20cm/sec. After 50 repetitions, the thickness, depth, and number of scratches on the surface of the 1/2 inch wide base film were evaluated in the following five grades. <5-level judgment> ◎ No scratches are observed on the 1/2 inch wide base film. ○ Almost no scratches are observed on the 1/2 inch wide base film. △ Scratches are observed on the 1/2 inch wide base film. (Several) × Several thick scratches are observed on the 1/2 inch wide base film × × Many thick and deep scratches are observed all over the 1/2 inch wide base film (10) Protrusion distribution measurement method Kosaka research Using a manufactured three-dimensional roughness meter (SE-3OK), needle diameter μmR, needle pressure 30mg, measurement length 1mm, sampling pitch 2μm, cutoff 0.25mm, vertical magnification 20,000 times, horizontal magnification 200 times,
The protrusion distribution was measured under the condition of 150 scans.
The protrusion height (z level) at the point where the area ratio from the reference level on the protrusion height (x axis) is 70% is the 0 level, and the difference from that height is the protrusion height.
The corresponding number of projections was plotted on the y-axis. Example 1 [Preparation of slurry] A. Preparation of ethylene glycol slurry of calcium carbonate particles 30 parts by weight of commercially available calcium carbonate particles were added to 70 parts by weight of ethylene glycol with stirring,
Stir at high speed with a homogenizer to achieve a concentration of 30% by weight.
Slurry (1) was prepared. The average particle size of calcium carbonate that makes up this slurry is 1.03μm
The value of the particle size distribution ratio [γ] was 2.6. Next, the 30% by weight ethylene glycol slurry of calcium carbonate was processed using a sand grinder to create a calcium carbonate ethylene glycol slurry (2). The average particle diameter of the slurry particles was 0.56 μm, and the value of the particle size distribution ratio [γ] was 2.9. Next, the slurry (2) is treated with a high-speed rotating decanter classifier to classify coarse particles of calcium carbonate, and then filtered with a filter (commercially available nominal aperture of 3 μm) to obtain the ethylene glycol slurry (3). Created. The average particle diameter of the slurry particles was 0.52 μm, and the value of the particle size distribution ratio [γ] was 1.9. B. Preparation of ethylene glycol slurry of anatase-type titanium dioxide particles Commercially available anatase-type titanium dioxide particles and ethylene glycol were mixed with high speed stirring using a homogenizer mixer to prepare a slurry (1) with a concentration of 30% by weight. Then slurry (1) into the sand grinder crusher
A slurry (2) was prepared by processing the slurry. Furthermore, the slurry (3) was prepared by processing with a high-speed rotating decanter classifier and filtering with a filter. The particle size distribution of each slurry was measured. The results are as follows. Slurry type Average particle size Particle size distribution ratio [γ] (1) 0.64μm 2.7 (2) 0.33μm 2.8 (3) 0.31μm 1.9 [Production method of polymer for film] Dimethyl terephthalate in 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol 0.015 mol% manganese acetate, and 0.010
Mol% of sodium acetate was added, and transesterification was carried out at 150 to 250°C while distilling methanol. At that time, an ethylene glycol slurry of calcium carbonate particles (concentration 10
%) was added. After completion of the transesterification reaction, 0.015 mol% of trimethyl phosphate, which had been heated under reflux in the presence of ethylene glycol, was added to dimethyl terephthalate. Furthermore, antimony trioxide was added in an amount of 0.030 mol % based on dimethyl terephthalate, and a polycondensation reaction was carried out under a high vacuum of 1 Torr or less. After the polycondensation reaction was completed, the polymer was cooled with water and cut to obtain polyethylene terephthalate pellets containing calcium carbonate particles dispersed therein (hereinafter referred to as polyester). Transesterification and polycondensation reactions were carried out in the same manner as above, except that the ethylene glycol slurry of titanium dioxide particles prepared in advance was added instead of the ethylene glycol slurry of calcium carbonate particles, and the titanium dioxide particles were dispersed. Polyethylene terephthalate pellets were obtained [hereinafter referred to as
called polyester]. Next, in the polyester manufacturing method, transesterification and polycondensation reactions were carried out without adding inert particles to obtain polyethylene terephthalate pellets to which no external inert particles were added [hereinafter referred to as
It is called polyester. [Film Formation] Blend A was obtained by mixing polyester, polyester, and polyester such that the content of calcium carbonate particles was 0.35% by weight and the content of titanium dioxide particles was 0.15% by weight. Blend B was obtained by mixing so that the content of titanium dioxide particles was 0.15% by weight. Then, the blend A is supplied to separate extruders of the film forming machine so that it becomes a layer forming the A side, and the blend B becomes a layer forming the B side, and the A side is formed. The polyester layer was extruded through a die so that the thickness accounted for 60% of the thickness of the laminated film, to obtain an unstretched film of 200 μm. This unstretched film was stretched at a longitudinal stretching temperature of 115°C, a longitudinal stretching ratio of 3.1 times, a transverse stretching temperature of 120°C, and a transverse stretching ratio of 3.2 times.
Sequential biaxial stretching was performed at 200° C. and heat treatment was performed at 225° C. The properties of the laminated polyester film thus obtained are shown in Table 1, and the distribution of unevenness on the film surface is shown as curve A in Figure 1. In addition,
The symbol A means the A side, and the symbol B means the B side. Further, the density ρ of the laminated film was 1.3980 g/cm ³ , and the [ _nz −ρ/10] value determined from the refractive index n _z in the film thickness direction and the density ρ was 1.3590. This film had different surfaces on the front and back sides, had good abrasion resistance on the easily slippery surface (side A), had few scratches, and had good electromagnetic conversion characteristics and scratchability after coating the magnetic layer. Example 2 and Comparative Examples 1 and 2 A biaxially stretched laminated film was produced in the same manner as in Example 1, except that the calcium carbonate particles and anatase titanium dioxide particles added were changed. The results are shown in Table 1 and Figure 1. In addition, in FIG. 1, curve B shows that of Example 2, curve C shows that of Comparative Example 1, and curve D shows that of Comparative Example 2. Furthermore, the symbol A means the characteristics of the A side, and the symbol B means the characteristics of the B side. The average particle size of the additive particles on the smooth surface in Comparative Example 1
In the case of calcium carbonate having a thickness of 1.1 μm, running properties were good, but there were high protrusions, poor electromagnetic conversion characteristics, and furthermore, calendering was poor, making it unusable. In addition, the easy-slip surface (Side A) in Comparative Example 2
If the surface was too flat, the coefficient of friction (μk) after 200 repetitions would be high, the running performance would be poor, and the surface could not be used. Comparative Examples 3 and 4 A biaxially stretched laminated film was produced in the same manner as in Example 1, except that the calcium carbonate particles and anatase titanium dioxide particles added were changed. The results are shown in Table-1. Note that Comparative Example 3 is a case where the protrusion distribution graph on side A does not satisfy the condition of equation (2), and Comparative Example 4 is a case where the protrusion distribution graph on side A does not satisfy the condition of equation (1). The film of Comparative Example 3 had poor running properties, while the film of Comparative Example 4
The film has high protrusions, poor electromagnetic conversion characteristics, and is also difficult to calendar. Comparative Example 5 A biaxially stretched laminated film was produced in the same manner as in Example 2, except that the longitudinal stretch ratio was changed to 3.7 times and the transverse stretch ratio was changed to 3.5 times. The results are shown in Table-1. This result shows that if the stretching ratio is too high, n _z −ρ/10 becomes low, and the running properties of the film deteriorate.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the height of protrusions (μm) on the film surface and the number of protrusions (k/mm ² ). Figure-2
FIG. 2 is a diagram showing the film flow of the apparatus used for measuring the coefficient of friction (μk).

Claims (1)

[Scope of Claims] 1. A biaxially oriented laminated film comprising a film-forming aromatic polyester containing an aromatic dicarboxylic acid as the main acid component and an aliphatic glycol as the main glycol component, the exposed side of the film comprising: The surface (A side) has a surface roughness RaA of 0.025 μm or less and 0.010 μm or more, and the number of protrusions determined in an area of 20 protrusions/mm ² or more (y:
The distribution curve representing the relationship between the height of the ^protrusion (x:μm) and the height of the protrusion (x: μm) is a straight line expressed by the equation (1) log ₁₀ y = −9.8x + 4.4 ... (1) and log ₁₀ y> It has a protrusion distribution that does not intersect in the range of 1.3, and the curve of the part larger than the maximum value of the protrusion distribution curve is in the range of equation (2) log ₁₀ y≧−18x+3.7...(2), and the protrusion If the height (x) is 0.87 μm or more, it provides a smooth surface that is virtually free of surface roughness, and the other exposed surface (Side B) has a rough surface.
RaB is 0.012 μm or less and 0.004 μm or more, and the number of protrusions is
Number of protrusions found in an area of 20 pcs/mm ² or more (y: pcs/mm2)
mm ² ) and the height of the protrusion (x: μm), the curve of the portion larger than the maximum value of the protrusion distribution curve is expressed by the formula (3) log ₁₀ y = -18x + 3.7 ... (3 ), and is in the range of equation (4) log ₁₀ y≧−44.1 Furthermore, the surface roughness RaA of the A side (smooth surface) and the surface roughness RaB of the B side (flat surface) satisfy the formula (5) 1.3≦RaA／RaB≦5 ...(5) , and the density ρ and the refractive index n _z in the thickness direction of the laminated film are expressed by equations (6), (7) 1.352≦ _nz −ρ/10≦1.366 ……(6) 1.385≦ρ≦1.405 ……(7 ) A biaxially stretched laminated polyester film for magnetic recording, which satisfies the following. 2 The film layer forming the A side (slippery surface) contains 0.1 to 0.5% by weight of calcium carbonate and 0.1 to 0.6% by weight of calcium carbonate.
Contains % by weight of anatase titanium dioxide,
And the calcium carbonate has a particle size distribution ratio [γ] expressed by the following formula (8) [γ] = diameter when the cumulative weight of particles is 25%/diameter when the cumulative weight of particles is 75%... (8) ] is in the range of 1.5 to 2.3, and the average particle diameter is in the range of 0.3 to 0.9 μm, and furthermore, the titanium dioxide has a particle size distribution ratio [γ] expressed by the above formula (8) of 1.2 to 2.3. 2. The biaxially stretched laminated polyester film according to claim 1, which has an average particle diameter of 0.1 to 0.5 μm, which is smaller than the average particle diameter of calcium carbonate. 3 In the film layer forming the B side (flat surface), the value of the particle size distribution ratio [γ] expressed by the above formula (8) is in the range of 1.2 to 2.3, and the average particle size is in the range of 0.1 to 2.3.
Anatase titanium dioxide in the 0.5μm range
The biaxially stretched laminated polyester film according to claim 1, characterized in that the content is 0.01 to 1% by weight.