JPH0460424B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a biaxially oriented polyester film, and more particularly to a biaxially oriented polyester film useful as a base film for high-density recording magnetic recording media, particularly metal tapes. [Prior Art] Polyester films have conventionally been widely used as base films for magnetic recording media.
In recent years, magnetic recording media have been required to have higher image quality and higher recording density. For this reason, there is an increasing demand for smoother surface properties on the magnetic layer side of magnetic recording media. Accordingly, polyester films used as base films for magnetic recording media are also required to have flat surfaces. Under these circumstances, polyester films used in conventional magnetic tapes for household VCRs have rough surfaces, and no film that satisfies the above-mentioned required characteristics and can be put to practical use has yet to be found. Therefore, for high-density recording, it is necessary to have extremely low surface roughness. However, in general, when the surface roughness is reduced, the slipperiness between the films deteriorates, and the escape of the air layer between the films becomes difficult, making it extremely difficult to wind up the film into a roll. Further, the difficulty of winding becomes more significant as the film becomes thinner. For example, the drawbacks of film rolls are:
This can cause bump-like protrusions on the roll, wrinkles in the longitudinal direction of the film, and misalignment of the end face of the film roll. The above-mentioned problems tend to occur when winding a flat film with a high tension for the purpose of preventing wrinkles, and when winding a flat film with a low tension for the purpose of preventing wrinkles in the longitudinal direction of the film. Additionally, in the processing process for making magnetic tapes, etc., if the film becomes flat, it may become wrinkled due to poor sliding on the metal rolls during the process, and problems may occur, such as the film meandering as it travels. come. Therefore, the base polyester film is required to have not only flatness but also good film winding appearance, good processing workability, good air escape properties, and excellent slip properties. be done. Conventionally, as a method to obtain a good winding appearance, processing workability, and air escape property of the film, and as a method to improve slipperiness, there has been a method of adding inorganic particles such as silicon oxide or calcium carbonate to polyester, or a method of adding inorganic particles such as silicon oxide or calcium carbonate to polyester. A method has been proposed in which fine particles containing calcium, lithium, or phosphorus are precipitated in the polymerization system during synthesis. In either method, when polyester is formed into a film, projections are formed on the surface of the film due to fine particles, thereby improving the slipperiness and air escape property of the film. However, in the method of improving the slipperiness and air escape properties of a film using projections made of fine particles as described above, the slipperiness and air escape properties usually improve as the film surface becomes rougher, but on the other hand, the roughness Due to surface formation, for example, in magnetic recording media applications, the surface after applying the magnetic paint becomes rough and the electromagnetic conversion characteristics deteriorate. As one of the measures to solve these contradictory problems of flatness, slipperiness, and air escape properties, many methods have been proposed to utilize composite-sized inorganic fine particles in which large-sized particles and small-sized particles coexist. There is. However, these methods also have problems, and if they are not used as they are, it will not be possible to achieve higher grade magnetic recording media, such as higher density,
It is difficult to meet demands such as higher quality. The reason for this is that the size of the large particles used in composite inorganic particles is too large for the quality required for high-grade grades, and the larger the particles, the higher the protrusions on the film surface. The electromagnetic conversion characteristics in magnetic recording media applications deteriorate, and the larger the particles, the higher the protrusions on the film surface and the larger the voids surrounding the particles. During the cleaning process or calendering process, high protrusions are scraped off, causing drop-outs (missing information that occurs during recording and playback), and calendar stains during the processing process and dust fabric for cleaning the base fluid surface. This causes scratches and dirt, which greatly impairs the properties of the magnetic recording medium. Furthermore, as the tape and base film become thinner, their rigidity decreases, and when used as a magnetic tape, the contact force with a magnetic head becomes weaker, resulting in the problem that sufficient electronic conversion characteristics cannot be obtained. As described above, with the conventional technology, it has been difficult to simultaneously solve the above-mentioned problems. [Object of the Invention] The present inventor has solved the above-mentioned problems and developed a polyester film that has flatness, good film winding appearance, and processing workability that can be applied to high-quality magnetic recording applications. As a result of extensive research, we discovered that by imparting a specific anisotropic unevenness to the surface of the film, it is possible to maintain flatness while obtaining a good film winding appearance and good processing workability.
We have arrived at the present invention. An object of the present invention is to provide a base film that can cope with high-density recording and high-quality magnetic recording media. The object of the present invention is to provide a biaxially stretched polyester film which has unevenness to the extent that it does not cause noise, (b) has a good film roll appearance, and has good processing workability. [Configuration and Effects of the Invention] According to the present invention, an object of the present invention is to improve surface roughness.
Ra is 0.003μm to 0.015μm, and at least one surface has a width of 1μm to 20μm and a length of 40μm to 100μm.
m, height 0.01μm ~ 0.2μm and depth 0.02μm ~ 0.5μm
This is achieved by using a biaxially oriented polyester film characterized by the presence of 10 ³ to 10 ^{6 m stripe-like irregularities at a ratio of 10 3 to 10 6} pieces/cm ² . The 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 polyester is substantially linear;
It also has film-forming properties, particularly film-forming properties by melt molding. Examples of aromatic dicarboxylic acids include terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenyl dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, and anthracene dicarboxylic acid. Examples include 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, decamethylene glycol, and alicyclic glycols such as cyclohexanedimethanol. Diols and the like can be mentioned. 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, not only polyethylene terephthalate and polyethylene-2,6-naphthalate, but also terephthalic acid and/or 2,6-naphthalene dicarboxylic acid account for 80 mol% or more of the total dicarboxylic acid component, and the total glycol component A copolymer in which 80 mol% or more of the ethylene glycol is ethylene glycol is preferred. At that time, the total acid component
Up to 20 mol% of the dicarboxylic acid can be an aromatic dicarboxylic acid other than the above-mentioned terephthalic acid and/or 2,6-naphthalene dicarboxylic acid, and can also be an aliphatic dicarboxylic acid such as adipic acid, sebacic acid, etc.; cyclohexane- It can be an alicyclic dicarboxylic acid such as 1,4-dicarboxylic acid. In addition, less than 20 mol% of the total glycol component is
Can be the above glycols other than ethylene glycol, or aromatic diols such as hydroquinone, resorcinol, 2,2-bis(4-hydroxyphenyl)propane, etc.; 1,4-
Aliphatic diols with aromatic rings such as dihydroxydimethylbenzene; polyethylene glycol,
Polyalkylene glycols (polyoxyalkylene glycols) such as polypropylene glycol, polytetramethylene glycol, etc. can also be used. In addition, the polyester used in the present invention includes, for example, an aromatic oxyacid such as hydroxybenzoic acid;
Also included are those in which a component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as -hydroxycaproic acid is copolymerized or combined in an amount of 20 mol % or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component. Furthermore, the polyester in the present invention has a substantially linear amount, e.g.
Also included are those copolymerized with trifunctional or less polycarboxylic acids or polyhydroxy compounds, such as trimellitic acid, pentaerythritol, etc., in an amount of mol % or less. The above polyester is known per se, and can be produced by a method known per se. The polyester preferably has an intrinsic viscosity of about 0.4 to about 0.9 as measured as a solution in o-chlorophenol at 35°C. The biaxially oriented polyester film of the present invention needs to have a surface roughness (Ra) of 0.003 to 0.015 μm. When Ra is larger than 0.015μm,
It is no longer possible to maintain the electromagnetic conversion characteristics necessary for magnetic tape for high-density recording, and Ra
If it is smaller than 0.003 μm, the coefficient of friction increases, making it extremely difficult to handle the film and wind it up into a roll. Such surface roughness is mainly controlled by incorporating a large number of fine, substantially inert solid particles dispersed in the polyester. A polyester containing a large number of inert solid particles is usually prepared at any time during the reaction to form the polyester, for example, during the transesterification reaction using the transesterification method or during the polycondensation reaction.
Alternatively, it can be prepared by adding inert solid microparticles (preferably as a slurry in glycol) to the reaction system at any point in the direct polymerization process. Preferably, inert solid particles are added to the reaction system at the beginning of the polycondensation reaction, for example, until the intrinsic viscosity reaches about 0.3. In the present invention, the inert solid particles are preferably silicon dioxide (including hydrates, diatomaceous earth, silica sand, quartz, etc.); alumina;
Silicates containing 30% by weight or more of SiO ₂ (e.g. amorphous or crystalline clay minerals, aluminosilicates (including calcined products and hydrates), warm asbestos, zircon, fly ash, etc.); Mg, Zn, Zr, and
Ti oxide; Ca, and Ba sulfate; Li,
Phosphates of Na and Ca (including monohydrogen salts and dihydrogen salts); Benzoates of Li, Na, and K; Ca,
Terephthalates of Ba, Zn, and Mn; Mg,
Titanates of Ca, Ba, Zn, Cd, Pd, Sr, Mn, Fe, Co, and Ni; Chromates of Ba and Pb; Carbonates (e.g. carbon black, graphite, etc.); Glasses (e.g. glass powder) , glass beads, etc.); carbonates of Ca and Mg; fluorite; and ZnS. More preferably,
Anhydrous silicic acid, hydrated silicic acid, aluminum oxide, aluminum silicate (including fired products, hydrates, etc.),
Monolithium phosphate, trilithium phosphate, sodium phosphate, calcium phosphate, barium sulfate, titanium oxide, lithium benzoate, double salts of these compounds (including hydrates), glass powder, clay (kaolin, bentonite, clay, etc.) ), talc, diatomaceous earth,
Examples include calcium carbonate. Particularly preferred are silicon dioxide and calcium carbonate. In addition, the average particle size of inert solid fine particles is
0.02~0.8μm, further 0.04~0.5μm, especially 0.06~
0.3 μm is preferable, and the amount added is
0.01-2.5% by weight (based on polyester), even 0.05
It is preferably 1.2% by weight (same), particularly 0.1-0.6% (same) by weight. If the average particle size is larger than the above-mentioned average particle size or if the amount added is increased, the flatness of the film will be lost and the electromagnetic conversion characteristics will deteriorate for magnetic recording media, which is not preferable. Moreover, if the average particle size is smaller than the above-mentioned average particle size, and if the amount added is small, the film will become flat, but it will be difficult to obtain a good film winding appearance, which is not preferable. Two or more kinds of the above-mentioned inert solid fine particles can be used simultaneously. The biaxially oriented polyester film of the present invention further has a width of 1 to 20 μm on at least one side of the film.
It is necessary that streak-like irregularities having a length of 40 to 10,000 μm, a height of 0.01 to 0.2 μm, and a depth of 0.02 to 0.5 μm exist at a rate of 10 ³ to ^{10 6} pieces/cm ² . Here, the length direction of the unevenness is the longitudinal direction of the film. Due to the presence of the striped unevenness, even in the case of a flat film, a good winding appearance as a film roll and good handling and workability in the processing process can be obtained. If the width of the streak-like irregularities is less than 1 μm and the length is less than 40 μm, the effect of the streak-like irregularities will be weakened, and the end faces will tend to shift when winding a long film, which is not preferable. Moreover, if the width and length become too large, the electromagnetic conversion characteristics will deteriorate, which is not preferable. From these points, the stripe-like irregularities have a width of 2 to 18 μm and a length of
Preferably 100-5000μm, width 4-12μm
m, the length is more preferably 200 to 1000 μm, and particularly preferably the width is 5 to 9 μm, and the length is 200 to 500 μm. In addition, the height of the streak-like irregularities is less than 0.01μm, and the depth is less than 0.01μm.
If it is less than 0.02 μm, the effect of the streak-like unevenness will be weakened, and end face misalignment will easily occur when winding a long length.
Undesirable. On the other hand, this height is 0.2 μm, and the depth is
If it exceeds 0.5 μm, the surface roughness Ra will also change and the electromagnetic conversion characteristics will deteriorate when used as a magnetic tape, which is not preferable. From these points, the height of the striped irregularities is 0.01 to 0.15 μm,
The depth is preferably 0.03 to 0.3 μm, and the height
More preferably, the thickness is 0.02 to 0.1 μm and the depth is 0.04 to 0.20 μm. Furthermore, if the distribution density of the streak-like unevenness is less than 10 ³ pieces/cm ² , it is not preferable because the end face is likely to shift when the film is wound, and the winding appearance becomes strong.
On the other hand, if the number exceeds 10 ⁶ pieces/cm ² , the electromagnetic conversion characteristics will deteriorate when processed into a magnetic tape, which is not preferable. From these points, the distribution density is 5 × 10 ³ ~ 10 ⁶
It is preferably 10 ⁴ to 10 5 pieces/cm ² , more preferably 10 4 to 10 ⁵ pieces/cm ² . The biaxially oriented polyester film of the present invention can be produced in accordance with conventional methods for producing biaxially oriented films. For example, polyester containing solid fine particles is melt-formed to form an amorphous unstretched film, then the unstretched film is stretched biaxially, heat set, and if necessary subjected to relaxation heat treatment. can be manufactured. At that time, the film surface characteristics depend on the formation, particle size, amount, etc. of solid fine particles.
Also, since it changes depending on the stretching conditions, it should be selected appropriately. For example, the stretching temperature ranges from (Tg− ₁₀ ) to (Tg+
45) °C (Tg: glass transition temperature of polyester), the second-stage stretching temperature (for example, transverse stretching temperature: T ₂ ) is from (T ₁ +10) to (T ₁ +40) °C.
It is recommended to select from the range of . Further, the film may be further stretched again in the longitudinal direction. The overall stretching ratio is preferably selected from a range in which the area ratio is 12 times or more and less than 28 times, particularly 16 times or more and less than 24 times. Furthermore, the heat fixing temperature is 180~250℃, and even 200~230℃.
It is recommended to select from the range of ℃. The streak-like unevenness on the surface of the film in the present invention may be provided by any method, and for example, the following method may also be used. For example, by polishing (scratching) the surface of the metal roll in the circumferential direction with a metal brush or the like, the film is passed between the metal roll and a rubber roll that is pressed into contact with the metal roll.
Streak-like unevenness can be provided. In this case, the width, length, height, depth, distribution density, etc. of the streaks are determined by the thickness, length, hardness, distribution density, etc. of the metal brush needle, as well as the polishing (scratching) time, number of times, etc. It can be adjusted by The biaxially oriented polyester film of the present invention is preferably used as a base film for magnetic recording media, particularly for high-density magnetic recording media. [Examples] The present invention will be further explained below based on Examples. Note that various physical property values and characteristics in the present invention are measured and defined as follows. (1) Film surface roughness (Ra) This is the value defined in JIS-BO601 as the centerline average roughness (Ra). −
30C). The measurement conditions are as follows. (a) Stylus tip radius: 2μm (b) Measuring pressure: 30mg (c) Cut-off: 0.25mm (d) Measuring length: 0.5mm (e) How to summarize data Repeat measurements on the same sample 5 times and find the highest value Exclude one, round off the average value of the remaining four data to the fourth digit after the decimal point, and display up to the third digit after the decimal point. (2) Characteristics of streak-like irregularities and their number After applying aluminum vapor deposition to the film surface, take 50 photographs with a differential interference microscope, count the number of streak-like irregularities, and calculate the number per 1 cm ² .
In addition, the height and depth of the striped irregularities are determined using multiple interference photographs. (3) Winding appearance The film is wound into a roll with a width of 800 mm and a length of 6000 m, and the appearance of this rolled roll is inspected in detail and graded from 1st to 5th grade. The end face misalignment is graded as follows based on the distance of the end face misalignment in the width direction. Regarding lump-like protrusions, the number of lump-like protrusions with a major diameter of 2 mm or more as schematically shown in Figure 1 is counted and graded as follows.

[Table] (4) Coefficient of Static Friction (μs) A fixed glass plate is placed on the underside of two stacked films, and the film on the bottom side of the stacked films (the film in contact with the glass plate) is rolled at a constant speed. The detector is fixed at one end of the upper film (the opposite end to the direction in which the lower film is pulled) and the tensile force of the film is detected. The thread used at this time weighs 1 kg and has a lower surface area of 70 cm ² . (5) Processing workability The handling and workability when processing a biaxially oriented polyester film are evaluated as follows. ○: Good, with no creases occurring during the processing process. △: Wrinkles occur in the metal roll part during the process, but
There is no diagonal running or folding of the film,
Processing is possible. ×: Wrinkles occur at the metal roll portion during the process, and the film runs diagonally, causing folds and wrinkles, making it impossible to process. (6) Electromagnetic conversion characteristics of magnetic coating tape A commercially available home VTR is used to convert a 50% white level signal (a 100% white level signal has a peak-to-peak voltage of 0.714 volts) into a 100% chroma signal. Record the signal with a level signal superimposed and use the reproduced signal as a noise meter: type
Measurement is performed using 952R. The definition of chroma S/N is as follows according to Shibasoku's definition. Chroma S/N (dB) = 20logES (p-p)/EN (rms
) Here, 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. Example 1 Dimethyl terephthalate and ethylene glycol were used as an ester conversion catalyst, manganese acetate as an ester conversion catalyst, antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and titanium dioxide particles with an average particle size of 0.27 μm as a lubricant. Polyethylene terephthalate with an intrinsic viscosity (orthochlorophenol, 35°C) of 0.62 was obtained by polymerization according to the method. This polyethylene terephthalate pellet
After drying at 170℃ for 3 hours, feed it to the extruder hopper.
The polymer was melted at a melting temperature of 280 to 300°C, and the molten polymer was extruded through a 1 mm slit die onto a rotating cooling drum with a surface temperature of 20°C to obtain an unstretched film. The unstretched film thus obtained was heated at 75°C.
The film was then preheated at low speed and between constrained rolls with an IR heater at a surface temperature of 800°C from 15mm above, stretched to 3.6 times, rapidly cooled, and then fed to a stenter at 105°C in the transverse direction. It was stretched 3.7 times. The obtained biaxially oriented film was heat set at a temperature of 205° C. for 5 seconds to obtain a heat set biaxially oriented film having a thickness of 10 μm. This was further passed between a metal roll (temperature: 100° C.) with streak-like irregularities and a rubber roll pressed against the metal roll at a linear pressure of 80 kg/m to obtain a biaxially oriented film with streak-like irregularities. Meanwhile, put the composition shown below in a ball mill,
After kneading and dispersing for 16 hours, 5 parts by weight of an isocyanate compound (Desmodyur L manufactured by Bayer AG) was added and dispersed under restrained shear for 1 hour to obtain a magnetic coating material. Composition of magnetic paint Acicular Fe particles 100 parts by weight Vinyl chloride-vinyl acetate copolymer (Eslec 7A manufactured by Sekisui Chemical Co., Ltd.) 15 parts by weight Thermoplastic polyurethane resin 5 Chromium oxide 5 Carbon black 5 Lecithin 2 Fatty acid ester 1 〃 Toluene 50 〃 Methyl ethyl ketone 50 〃 Cyclohexanone 50 〃 This magnetic material was coated on one side of the above-mentioned polyester film to a coating thickness of 3 μm, and then subjected to orientation treatment in a 2500 Gauss DC magnetic field.
After drying by heating at 100°C, it was subjected to super calender treatment (linear pressure 200 kg/cm, temperature 80°C) and wound up. Place this rolled roll in an oven at 55℃ for 3
I left it for days. Furthermore, a back coat layer with the following composition was applied to a thickness of 1 μm.
The magnetic tape was coated, dried, and cut to obtain a magnetic tape. Back coat layer composition Carbon black 100 parts by weight Thermoplastic polyurethane resin 60 〃 Isocyanate compound (Coronate L manufactured by Nippon Polyurethane Industries Co., Ltd.) 18 parts by weight Silicone oil 0.5 〃 Methyl ethyl ketone 250 〃 Toluene 50 〃 The properties of the obtained film and magnetic tape are shown below. Shown in 1. As is clear from this table, both the winding form and the electromagnetic conversion characteristics were good. Example 2 Dimethyl terephthalate and ethylene glycol were transesterified using manganese acetate as a catalyst.
Using antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and calcium carbonate with an average particle size of 0.4 μm as a lubricant, polymerization was performed in a conventional manner to obtain polyethylene terephthalate with an intrinsic viscosity (orthochlorophenol, 35°C) of 0.62. Obtained. This polyethylene terephthalate was dried at 160°C, then melt extruded at 280°C, and rapidly solidified on a casting drum kept at 20°C to obtain an unstretched film. Subsequently, this unstretched film was stretched 3.5 times in the machine direction at a temperature of 80° C. between two rolls with a speed difference, and further stretched 4.0 times in the transverse direction at 90° C. by a tenter method. Then, the film was stretched again in the longitudinal direction by a factor of 1.6 at a temperature of 110°C between two rolls with a speed difference, and then heat-treated for 5 seconds while gripping both ends in an oven at 220°C, and then wound up.
After that, a metal roll with streak-like unevenness (temperature 110
A biaxially oriented polyester film (thickness: 9 .mu.m) was obtained by passing the film between a rubber roll pressed with a linear pressure of 70 kg/m. Furthermore, a magnetic tape was obtained in the same manner as in Example 1 using this biaxially oriented polyester film. The properties of this polyester film and magnetic tape are shown in Table 1, and both the winding form and electromagnetic conversion properties were good. Comparative Example 1 A biaxially oriented polyester film was obtained in the same manner as in Example 2, except that 0.15% of kaolin clay with an average particle size of 0.32 μm was used as a lubricant in the polymer. In addition, at this time, the step of imparting streaks and unevenness was not performed. Furthermore, a magnetic tape was obtained in the same manner as in Example 1. Table 1 shows the properties of the obtained biaxially oriented polyester film and magnetic tape. When made into a magnetic tape, the electromagnetic conversion properties were good, but the winding form and processing workability of the film were poor, making it unusable. Comparative Example 2 A biaxially oriented polyester film was obtained in the same manner as in Example 2, except that 0.25% by weight (based on the weight of the polymer) of calcium carbonate having an average particle size of 0.7 μm was used as a lubricant in the polymer. At this time, the step of providing streak-like unevenness was not performed. Furthermore, a magnetic tape was obtained in the same manner as in Example 1. Table 1 shows the properties of the obtained biaxially oriented polyester film and magnetic tape. Although the surface roughness Ra was high and the film winding appearance was good, the electromagnetic conversion characteristics were not good. Comparative Example 3 A biaxially oriented polyester film was obtained in the same manner as in Example 2, except that titanium dioxide having an average particle size of 0.3 μm was used as a lubricant in the polymer. At this time, a metal roll with many streak-like irregularities was used to impart the streak-like irregularities. Furthermore, a magnetic tape was obtained in the same manner as in Example 1. The properties of the obtained film and magnetic tape are shown below.
As shown in No. 1, although the number of streak-like irregularities was large and the film winding appearance was good, the electromagnetic conversion characteristics were insufficient.

【table】 [Brief explanation of drawings]

FIG. 1 is a diagram schematically showing bump-like protrusions that occur when a biaxially oriented polyester film that is flat and has few streak-like irregularities is rolled up. FIG. 2 is a schematic diagram showing an example of the distribution of streak-like unevenness occurring on the surface of the film in the present invention. Figure 3 shows the height of the striped unevenness: 1, depth 2,
FIG. 3 is a cross-sectional view schematically showing an example of width 3;

Claims (1)

[Claims] 1 Surface roughness Ra is 0.003 μm to 0.015 μm, and at least one surface has a width of 1 μm to 20 μm and a length of
40μm~10000μm, height 0.01μm~0.2μm and depth
A biaxially oriented polyester film characterized by having stripe-like irregularities of 0.02 μm to 0.5 μm at a ratio of 10 ³ to 10 ⁶ pieces/cm ² .