JPH045533B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a polyester film for magnetic recording, and more specifically, a biaxially oriented polyester film that has excellent electromagnetic conversion properties, excellent running durability during repeated use, and is useful for manufacturing magnetic recording media with a high Young's modulus. Regarding polyester film. [Prior Art] As magnetic recording media based on polyester films, for example, video tapes, audio tapes, computer tapes, floppy disks, etc. are known and widely used. In recent years, high-density recording,
As the demand for longer working hours and smaller size continues to increase, the polyester film used as the base has a flat surface, excellent slipperiness and ease of handling.
Moreover, the demand for thin films is becoming stronger and stronger. In particular, for long runs, it is necessary to incorporate longer tapes into cassettes of the same standard, so there is a strong demand for such thin films, and at the same time, it is also necessary to increase the Young's modulus of the film. The reason why a high Young's modulus is required is that as the film becomes thinner, its stiffness decreases.
This is because troubles occur in the tape running system and it cannot withstand repeated running, and in the case of video tapes, there is insufficient contact between the rotating cylinder head and the tape, resulting in a decline in electromagnetic conversion characteristics. [Object of the Invention] The present inventor has created a tape with a high Young's modulus, a flat surface, and a smooth surface, which satisfies the above-mentioned requirements and is applicable to a tape in the field of magnetic recording for high-quality long-term recording and playback. We have successfully developed a biaxially oriented polyester film that is easy to handle. An object of the present invention is to provide a polyester base film that is useful as a magnetic recording material, particularly a tape for long-term recording and playback, and further provides (1) a surface with a uniform protrusion distribution and no large protrusions; ,(2)
It is an object of the present invention to provide a biaxially oriented polyester film having sufficient strength to cope with the thinning of tapes. [Configuration/Effects of the Invention] According to the present invention, an object of the present invention is to provide a biaxially oriented polyester film, which comprises a polyester containing 0.1 to 0.1 to 0.1 to 2.0 μm of aluminum hydrated silicate mineral having an average particle size of 0.2 to 2.0 μm. 0.6% by weight, or 0.01 to 0.01% of calcium carbonate with an average particle size of 0.2 to 1.5 μm
0.4% by weight dispersed therein, and on the film surface,
Number of protrusions 20/mm ² Number of protrusions found in an area of 2 or more (Y:
The distribution curve representing the relationship between the projection height (X: ^μm ) and the projection height (X: μm) does not intersect with the straight line expressed by the following formula: log ₁₀ Y = -9.8X + 4.4 within the range of log ₁₀ Y > 1.3. distribution, the maximum value of the protrusion distribution is in the range of log ₁₀ Y≧−18X+3.7, and the surface roughness (Ra) is 0.025 μm.
This is achieved by a polyester film for magnetic recording, which is characterized in that the Young's modulus in the longitudinal direction of the film is 650 Kg/mm ² or more. The polyester used in the present invention is mainly an aromatic polyester having an aromatic dicarboxylic acid as the main acid component and an aliphatic glycol as the 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,
Examples include naphthalene dicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone carboxylic acid, and anthracene dicarboxylic acid. 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, and alicyclic glycols such as cyclohexanedimethanol. Examples include group diols. In the present invention, polyesters containing alkylene terephthalate and/or alkylene naphthalate as main constituents are preferably used. Among such polyesters, including polyethylene terephthalate and polyethylene naphthalate, for example, 80 mol% or more of the total dicarboxylic acid component is terephthalic acid and/or naphthalene dicarboxylic acid, and 80 mol% of the total glycol component
Particularly preferred are copolymers in which the above is ethylene glycol. In this case, up to 20 mol% of the dicarboxylic acids based on the total components can be the above-mentioned aromatic dicarboxylic acids, and also, for example, aliphatic dicarboxylic acids such as adipic acid and sebacic acid; alicyclic acids such as cyclohexane-1,4-dicarboxylic acid. It can also be a group dicarboxylic acid and the like. Also, 20 mol% of total glycol components
The following can be the above glycols other than ethylene glycol, or aromatic diols such as hydroquinone, resorcinol, 2,2-bis(4-hydroxyphenyl)propane; aromatic diols such as 1,4-dihydroxymethylbenzene. Aliphatic diols containing polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. In addition, the aromatic polyester used in the present invention may contain components derived from aromatic oxyacids such as hydroxybenzoic acid; oxycarboxylic acids such as aliphatic oxyacids such as ω-hydroxycaproic acid;
It also includes those containing 20 mol% or less based on the total amount of dicarboxylic acid components and oxycarboxylic acid components. Furthermore, the aromatic polyester in the present invention contains a trifunctional or higher functional polycarboxylic acid or a polyhydroxy compound, such as trimellitic acid, in a substantially linear amount, for example, 2 mol % or less based on the total acid components. 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. The biaxially oriented polyester film of the present invention has many fine protrusions on its surface.
According to the present invention, these many fine protrusions are derived from a large number of microparticles of aluminium hydrated silicate mineral, or microparticles of aluminium and calcium carbonate, which are dispersed and contained in the polyester. Polyesters containing such fine particles are usually produced at any time during the reaction to form the polyester, such as at the transesterification center when using the transesterification method or during the polycondensation reaction or at any time when using the direct polymerization method. can be produced by adding the microparticles (preferably as a slurry in glycol) into a reaction system. Preferably, the fine particles are added to the reaction system at the beginning of the polycondensation reaction, for example, until the intrinsic viscosity reaches about 0.3. This aluminum hydrated silicate mineral can also be referred to as kaolin, and preferred specific examples thereof include kaolin, kaolin clay, chiaina clay, and the like. This mineral has an average particle size of 0.2~
Used as 2.0 μm fine particles, 0.1 μm in polyester
Contain ~0.6% by weight. Further, calcium carbonate having an average particle size of 0.2 to 1.5 μm is used, and is contained in the polyester in an amount of 0.01 to 0.4% by weight. The average particle size and content of the aluminum hydrated silicate mineral or the aluminum carbonate and calcium carbonate may be appropriately selected in consideration of the film surface characteristics described below. The biaxially oriented polyester film of the present invention has film surface characteristics that are determined by the number of protrusions (Y: x/mm ² ) and the height of the protrusions (X: μm) determined in an area with the number of protrusions of 20/mm ² or more. The distribution curve representing the relationship has a protrusion distribution that does not intersect with the straight line expressed by the following formula log ₁₀ Y = -9.8X + 4.4 in the range of log ₁₀ Y > 1.3, and the maximum value of the protrusion distribution curve is log ₁₀ Y ≧-18X+3.7 and surface roughness (Ra) is 0.025μm
It has the following characteristics: The distribution curve of the relationship between the number of protrusions (Y) and the height of protrusions (X) determined in an area where the number of protrusions of polyester film is 20 protrusions/mm ² or more is expressed by the following formula: log ₁₀ Y = -9.8X + 4.4. If the straight line intersects with the straight line in the range of log ₁₀ Y > 1.3, the electromagnetic conversion characteristics will deteriorate, and the protrusions will be scraped off during the tape processing process, especially the calendering process, and the friction coefficient will be reduced due to scraping when the tape is used repeatedly. This is undesirable because as it rises, scraped powder adheres to the tape surface, increasing dropout. Furthermore, if the maximum value of the above distribution curve is not within the range of log ₁₀ Y≧−18X+3.7, the film surface will become too flat.
The friction coefficient (μk) after 200 repetitions, which will be described later, is
This is not preferable because it becomes difficult to satisfy the range of 0.15 to 0.35. In the above distribution curve, it is preferable that the curve on the side exceeding the maximum value satisfies the range -18X+3.7≦log ₁₀ Y≦−9.8X+4.4 (however, log ₁₀ Y>1.3). Furthermore, if the surface roughness (Ra) of the polyester film is greater than 0.025 μm, the surface of the base film will be too rough and the magnetic surface cannot be made sufficiently flat even by calendering, which is undesirable since the electromagnetic conversion characteristics will deteriorate. The preferred surface roughness (Ra) is 0.020 μm or less. Polyester films for magnetic recording are used in a wide variety of applications, and there is a strong demand for films that not only have good initial quality but also maintain quality even after repeated use after magnetic coating or commercialization. Taking the videotape field as an example in particular, high image quality demands flat surface properties of the base film. However, if the surface is made flat, the slipperiness deteriorates, so it is difficult to satisfy both properties at the same time, but the above-mentioned biaxially oriented polyester film satisfies both properties at the same time. From this flatness,
Furthermore, it is preferable that no protrusions with a protrusion height (X) of 0.87 μm or more exist. 0.87μ on the film surface
If there are protrusions of m or more in length, the running properties of the tape will be improved, but it will be difficult to obtain high magnetic exchange characteristics, and it will also cause dropouts. It is preferable that the biaxially oriented high polyester film has the above-mentioned film surface characteristics and at the same time has a high Yang modulus. The reason why a high Young's modulus is required is that as the film becomes thinner, its stiffness (stiffness) decreases, which causes problems in the tape running system and cannot withstand repeated running. This is because the contact between the rotating cylinder head and the tape is not sufficient and the electromagnetic conversion characteristics deteriorate. From this point of view, in the present invention, the Young's modulus in the longitudinal direction (film longitudinal direction) is 650.
Kg/mm ² or more, preferably 700 Kg/mm ² or more, more preferably 750 Kg/mm ² or more. Furthermore, maintaining a high stiffness in the longitudinal direction of the film increases the rigidity of the tape and is extremely effective in solving the above-mentioned problems. In addition, in order to obtain a biaxially oriented polyester film having these Young's modulus and stiffness, it is effective to set the refractive index to 1.670 or more in the longitudinal direction (Ny) and 1.485 or more in the film thickness direction (Nz). . In addition, if the density of the biaxially oriented polyester film is too high, even if the film has the above-mentioned surface characteristics, it will be prone to abrasion and have poor durability; if it is too low, the thermal shrinkage will be too large and the shrinkage phenomenon Skew problems occur on the tape, making it unsatisfactory for high-end video use. From this point of view, the density should be 1.385 to 1.385 for durability, scratch prevention, etc.
1.410 (g/cm ³ ), further 1.387 to 1.400 (g/cm ³ ),
Particularly preferred is 1.387 to 1.395 {g/cm ³ ). Also 70℃
If the heat shrinkage rate in the longitudinal direction of the film when heat treated under no load for 1 hour is too high, skew due to shrinkage will occur in the tape even after repeated use, which is undesirable. From this point of view, the heat shrinkage rate is 0.15% or less,
Further, it is preferably 0.1% or less, particularly preferably 0.06% or less. Furthermore, the biaxially oriented polyester film is
Friction coefficient (μk) after 200 repeated runs is 0.15~
Preferably it is 0.35. This friction coefficient (μk)
If it is larger than 0.35, it is undesirable because it has poor slip properties and may cause problems such as tape running stopping when a videotape is used repeatedly, for example. On the other hand, if the coefficient of friction (μk) is less than 0.15, the slippage is too large and, for example, when a videotape is used repeatedly, the tape slips too much and the tension position on the guide post becomes loose.
This is undesirable because it can cause problems such as blurring of the screen. The coefficient of friction (μk) is preferably 0.30 or less, more preferably 0.25 or less. The biaxially oriented polyester film of the present invention can be manufactured according to conventional methods for manufacturing biaxially oriented films, and is not particularly limited. - It can be produced by a method such as sequential stretching such as transverse-re-lengthwise-re-transverse stretching or a combination with simultaneous biaxial stretching. [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) Film surface roughness (Ra) Measured according to JIS B 0601. Tokyo Precision Co., Ltd.
Using a stylus surface roughness meter (SURFCOM3B) manufactured by Co., Ltd., a chart (film surface roughness curve) was drawn under conditions of a needle radius of 2 μm and a load of 0.07 g.
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 ), when expressed as
The value (Ra: μm) given by the following formula is defined as the film surface roughness. Ra=1/L∫ ^Lo |f(x)|dx In the present invention, eight measurements were taken with a reference length of 0.25 mm, and Ra was expressed as the average value of the five measurements, excluding three from the largest value. (2) Protrusion distribution measurement method Using a three-dimensional roughness meter (SE-3CK) manufactured by Koita Research Institute, needle diameter 2μmR, needle pressure 30mg, measurement length 1mm,
Sampling pitch 2μm, cutoff 0.25mm,
20,000x vertical magnification, 200x horizontal magnification,
The protrusion distribution was measured under the condition of 150 scans.
For the protrusion height (x-axis), the protrusion height (z level) at the point where the area ratio from the reference level is 70% is the 0 level, and the difference from that height is the protrusion height.
The corresponding number of protrusions was blotted on the y-axis. (3) Young's Modulus Measurement A film sample was cut into 10 mm width and 15 cm length, and stretched using an Instron type universal tensile tester at a chuck spacing of 100 mm at a tensile speed of 10 mm/min and a chatch speed of 500 mm/min. Young's modulus was calculated from the tangent to the rising portion of the obtained load-elongation curve. (4) Stiffness Grip both ends of a test piece of a predetermined length with a chuck to form a loop, and place this loop so that it touches the U-gauge until the distance between the chuck and the U-gauge reaches a preset distance. The stiffness of the film is measured by reading the load exerted by the sample against the U-gauge using a millivolt meter. Stiffness (mg) = Measured total value (μV) / Measured n number Sample width: 12.65 mm Sample length: 100 mm Distance between U gauge and chuck: 20 mm Measured n number: 5 (5) Density Carbon tetrachloride and n-hebutane Measure the film using the float-sink method at 25°C in a mixed solvent with (6) Refractive index Using Atsube refractometer, light wavelength is 589 nm.
The value for the light ray (center of the D line of Na) is the temperature
Measure at 20℃. (7) Coefficient of friction of film (μk) Measured as follows using the apparatus shown in Figure 2. In Figure 2, 1 is an 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 SUS304
(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 = 152/180π radians (152°) and moved (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 exit tension (T ₂ : g) is detected by the exit tension detector after the film has traveled 90 m.
Calculate the running friction coefficient μk using the following formula. μk=2.303/θlogT ₂ /T ₁ =0.868logT ₂ /35 (8) Electromagnetic conversion characteristics of magnetic coating film (chromatography S/N) On the film of the present invention, 100 parts by weight of Co-containing oxide powder with the following composition ESLEC A ( Vinyl chloride-vinyl acetate copolymer manufactured by Sekisui Chemical) 10 〃 Nitsuporan 2304 (Polyurethane elastomer manufactured by Nippon Polyurethane) 10 〃 Coronate L (Polyisocyanate manufactured by Nippon Polyurethane) 5 〃 Lecithin 1 〃 Methyl ethyl ketone 75 〃 Methyl isobutyl ketone 75 parts by weight Toluene 75 〃 A magnetic powder paint with additives (lubricant, silicone resin) of 0.15 〃 is applied using a gravure roll, the magnetic paint layer is smoothed with a doctor knife, and while the magnetic paint is still dry, it is magnetically oriented using a conventional method, and then Then put it in the 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 in which a 100% chroma level signal is superimposed on a 50% white level signal (a 100% white level signal has a peak-to-peak voltage of 0.714 volts), and then play it back. Measure the signal using a Shibasoku Noise Meter Type 925R. The definition of chroma S/N is as follows according to Shibasoku's definition. Chroma S/N (dB) = 201log 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) (9) Dropout Apply the tape (1/2 inch width) coated with magnetic powder paint in (8) above to a commercially available dropout counter (for example, Shibasoku VH01BZ). type)
Count the dropout of 5 μsec x 10 dB,
The number of counts per minute was calculated. (10) Scratch Slit the base film to 1/2 inch width,
Similar to the friction coefficient measurement in (7) above, the film was placed on a fixed rod up to an angle of 152°, and the film was run for 10 m at a film running speed of 20 cm/sec. After repeating this 50 times, the 1/2 inch width base film was measured. The thickness, depth, and number of scratches that entered the surface were evaluated in the following five stages. <5-level judgment> ◎: No scratches were observed on the 1/2 inch wide base film. ○: Almost no scratches were observed on the 1/2 inch wide base film. △: Several scratches are observed on the 1/2 inch wide base film. ×: Several thick scratches are observed on the 1/2 inch wide base film. XX: Many thick and deep scratches are observed all over the 1/2 inch wide base film. (11) Skew Skew characteristics are determined by measuring the amount of deviation at the head switching point by heat-treating a videotape recorded at room temperature (20°C and humidity) at 70°C for 1 hour with no load, then playing it back at room temperature and humidity. Read it. Example 1 Ethylene glycol (hereinafter abbreviated as EG) 90
After adding 10 parts by weight of kaolin (average particle size 0.5 μm) to the parts by weight, mixing and stirring were performed to obtain a slurry. Next, 100 parts by weight of dimethyl terephthalate and
After transesterifying 70 parts by weight of EG using 0.035 parts by weight of manganese acetate tetrahydrate as a catalyst in a conventional manner, the kaolin obtained above (concentration 0.3% by weight to polymer) was added under stirring. Subsequently, 0.03 parts by weight of trimethyl phosphate and 0.03 parts by weight of antimony trioxide were added, and then a polycondensation reaction was carried out in a conventional manner under high temperature vacuum to obtain polyethylene terephthalate pellets having an intrinsic viscosity of 0.620. Furthermore, this polyethylene terephthalate (hereinafter
After drying the pellets (abbreviated as PET) at 170°C for 3 hours, they are fed to the extruder hopper and melted at a melting temperature of 280 to 300°C.The molten polymer is passed through a 1 mm slit die with a surface finish of about 0.38 and a surface temperature of 20°C. The product was molded and extruded into the shape of a rotating cooling drum to obtain an unstretched film with a thickness of 190 μm. The unstretched film thus obtained was heated at 70°C.
Stretched 5.2 times longitudinally at 90°C, then stretched transversely at 90°C.
Stretched 3.0 times. The obtained biaxially oriented film was 215
Heat treatment (heat fixation) was performed at a temperature of .degree. C. for 5 seconds. Furthermore, this biaxially oriented heat-set film was reheated to 120° C. and relaxed in the longitudinal direction at a relaxation rate of 0.5% (speed difference between the heating roll and the cooling roll). The thickness of the obtained film was about 12 μm. The thus obtained biaxially oriented film was coated with a magnetic substance and evaluated as a tape. The results are shown in Table 1. The distribution of protrusions on the surface of the biaxially oriented film is shown in Figure-1.
As shown by curve A, there were no large protrusions, and the Young's modulus, stiffness, and coefficient of friction (μk) after 200 passes were sufficiently satisfactory.
Further, the evaluation results of the tape after application showed that the electromagnetic change characteristics, dropout, skew, and runnability were sufficiently satisfactory. Examples 2 to 5 and Comparative Examples 1 to 5 The particle types, average particle diameters, amounts added, etc. of the added particles are shown in the table below.
Pellets were obtained under the same conditions as in Example 1, except for the changes shown in Example 1. Furthermore, the conditions for forming these pellets were set to slightly different levels from those in Example 1, as shown in Table 1, and films were made. The thickness of these films was approximately 12 μm. Table 1 shows the physical properties of these films and the evaluation results obtained by coating the films with magnetic substances. The results of various measurements of the base films of Examples 2 to 5 showed that they had good cyclic friction coefficients and other items, as well as electromagnetic conversion characteristics as video tapes, dropouts, skews, scratches, and other items. On the other hand, the biaxially oriented film of Comparative Example 1 was
Although the 1-hour heat shrinkage rate was low and the skew was at a small level, the stiffness was low, the tape runnability and scratching were poor, and the dropout level was also poor. In addition, the biaxially oriented film of Comparative Example 3 had an extremely rough surface with a protrusion distribution curve that far exceeded the limited range (Figure 1, curve C).
The running properties are too slippery and the stiffness is low, so running stability cannot be obtained, and the electromagnetic conversion characteristics are also at a poor level. Furthermore, comparative example 4
The biaxially oriented film has good electromagnetic characteristics, but its surface roughness (Ra) is too flat, resulting in poor runnability and scratch resistance (Figure 1,
Curve D). Furthermore, since the biaxially oriented film of Comparative Example 5 uses a mixture of two types of fine particles, the surface roughness (Ra) is relatively low, but the protrusion distribution curve greatly exceeds the limited range. There are some parts that have poor electromagnetic conversion characteristics. Furthermore, the stiffness is low, and the running properties and scratches are also poor.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the height of protrusions (μm) and the number of protrusions (k/mm ² ) on the film surface. 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 polyester film, which contains 0.1 to 0.6% by weight of a hydrous silicate mineral of aluminum having an average particle size of 0.2 to 2.0 μm in polyester, or an average particle size of 0.1 to 0.6% by weight. Number of protrusions (Y: x/mm ² ) and height of protrusions determined in an area containing 0.01 - 0.4% by weight of calcium carbonate of 0.2 to 1.5 μm and having a number of protrusions of 20 protrusions/mm ² or more on the film surface. (X: μm) has a protrusion distribution that does not intersect with a straight line expressed by the following formula log ₁₀ Y = -9.8X + 4.4 in the range of log ₁₀ Y > 1.3, and furthermore, the protrusion distribution The maximum value of _log10Y ≧−18X+3.7 and the surface roughness (Ra) is 0.025μm
A polyester film for magnetic recording, which is as follows, and has a longitudinal Young's modulus of 650 Kg/mm ² or more. 2. The polyester film for magnetic recording according to claim 1, which has a stiffness in the longitudinal direction of 80 mg or more. 3. The polyester film for magnetic recording according to claim 1 or 2, which has a density of 1.385 to 1.410 g/cm ³ . 4. The polyester film for magnetic recording according to any one of claims 1 to 3, which has a refractive index (Ny) in the longitudinal direction of 1.670 or more and a refractive index (Nz) in the thickness direction of 1.485 or more. . 5. The polyester film for magnetic recording according to any one of claims 1 to 4, which has a longitudinal heat shrinkage rate of 0.15% or less when heat treated at 70°C for 1 hour under no load. 6. The polyester film for magnetic recording according to any one of claims 1 to 5, in which there are no protrusions with a protrusion height of 0.87 μm or more.