JPS6230105B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyester film for magnetic recording media. Conventionally, a vapor-deposited videotape in which a magnetic substance is vapor-deposited on the surface of a polyester film has been used. However, since the thickness of the magnetic layer in this vapor-deposited videotape is very thin, the surface morphology of the base film used is the same as the surface morphology of the vapor-deposited thin film after the magnetic material is vapor-deposited. Therefore, if the surface roughness of the base film is rough, the electromagnetic conversion characteristics of the vapor-deposited videotape will be significantly deteriorated. Considering this electromagnetic conversion characteristic, a base film with a completely smooth mirror surface is preferable, but the deposited film formed on such a base film has extremely slippery properties because the deposited surface maintains its mirror surface. Unfortunately, unless a protective film layer is provided on the vapor deposition surface, a large amount of scratches will occur in the tape forming process after the vapor deposition process, making it completely impractical. Furthermore, a serious problem in actual use of vapor-deposited videotape is the runnability of the vapor-deposited surface. In the case of conventional coated video tapes, which are made by mixing magnetic powder into an organic binder and coating it on a base film, it is possible to add a lubricant to the binder to improve the running properties of the magnetic surface. In the case of tape,
The runnability of the vapor deposition surface cannot generally be used unless a protective film layer is provided, and it is difficult to uniformly provide a protective film layer on the vapor deposition surface. In particular, there were drawbacks such as the inability to improve running performance under harsh conditions when actually used, ie, under high temperature and high humidity conditions. An object of the present invention is to provide a base film capable of forming a deposited film with excellent smoothness, scratch resistance, and runnability not only in normal environments but also under high temperature and high humidity conditions. The present invention has the following configuration to achieve the above object. That is, a polyester film with a thickness of 50 to 500 Å closely adhered to at least one side of the film.
It consists of a discontinuous film mainly composed of a water-soluble polymer and a silane coupling agent, and fine particles present in the film and on the film surface, and the diameter and height of the fine particles are both 50 to 1000 Å, and the number of particles present is is 10 ⁴ ~ 10 ⁸
The film is characterized by a polyester film for magnetic recording media that has a diameter of 1.5 mm/ ^mm2 . The polyester film of the present invention is a polyester film formed by a conventional method, that is,
A film made by melting polyester and extruding it into a sheet or cylindrical shape and stretching it in at least one direction.The mechanical properties of the film include a normal balanced type, a uniaxially strengthened type, and a biaxial type. It is desirable that it be one of the types that is strengthened in the direction. In addition, it is desirable that the surface of the polyester film be smooth;
Specifically, the roughness of the film surface is preferably such that the Ra value is 0.015μ or less, more preferably within the range of 0.010 to 0.002μ, using a cutoff value of 0.08mm using a stylus surface roughness meter. Note that the Ra value is calculated using an appropriate cut-off value from the cross-sectional curve obtained from a stylus surface roughness meter.
Arithmetic of the absolute value of the height (lowness) of the roughness curve from the center line (calculated so that the areas above and below the center line are equal) in a roughness curve excluding waviness. Average (according to DIN4768). The polyester forming the film may be of any type as long as it is mainly composed of linear polyester. For example, polyethylene terephthalate, polytetramethylene terephthalate,
Representative examples include poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, and polyethylene-p-oxybenzoate. Further, the above polyester may be a homopolyester or a copolyester. In the case of copolyester, the components to be copolymerized are:
For example, diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol, 1.4
-Diol components such as cyclohexanedimethanol, adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, 5-
Examples include dicarboxylic acid components such as sodium sulfoisophthalic acid, polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, and p-oxyethoxybenzoic acid. In addition, in the case of copolymerization,
The amount of components to be copolymerized is 20 mol% or less. Furthermore, the above-mentioned polyester is mixed with at least one of an alkali metal salt derivative of sulfonic acid that is non-reactive with the polyester, a polyalkylene glycol that is substantially insoluble in the polyester, etc., to an extent not exceeding 5% by weight. It's okay. Furthermore, when the film is stretched, it may contain internal particles consisting of polymerization residues that cause protrusions on the film surface, or insoluble particles added from the outside. When biaxially stretched, the thickness should be 30μ or less and the haze per sheet should be 5% or less. The discontinuous film of the present invention is formed from a composition mainly consisting of a water-soluble polymer, a silane coupling agent, and fine particles. Further, the thickness of the discontinuous film is 50 to 500 Å, preferably 50 to 300 Å or less. When the thickness exceeds 500 Å, the electromagnetic conversion characteristics of the deposited thin film, especially the S/N ratio, deteriorate. On the other hand, if it is less than 50 Å, the slipperiness of the deposited thin film will deteriorate. The reason why the film is discontinuous is to reduce the contact area with the head and improve running performance. The water-soluble polymer used in the present invention has a molecular weight of 10,000 to 2,000,000, preferably 100,000 to 1,000,000. When the molecular weight is less than 10,000, the film described below becomes soft, it becomes difficult to maintain the structure, and the durability deteriorates. When the molecular weight exceeds 2 million,
The film becomes too hard and brittle, resulting in poor durability. Such water-soluble polymers include polyvinyl alcohol, gum tragacanth, gum arabic, casein, gelatin, methyl cellulose,
Hydroxyethyl cellulose, carboxymethyl cellulose, etc. can be used. The fine particles present in the discontinuous film and on the film surface of the present invention have a diameter and a height of 50 to 1000 Å, preferably 50 to 500 Å. Here, the diameter refers to the maximum length of fine particles as determined by observing the surface of the film of the present invention with an electron microscope. The shape of the fine particles may be spherical, ellipsoidal, rectangular, cubic, etc., but flat particles are more preferable. Particle height refers to the maximum height of fine particles existing on the discontinuous film surface from the discontinuous film forming surface (the surface of the polyester film). The types of fine particles include inorganic compound particles, such as MgO, ZnO,
_MgCO3 , _CaCO3 , _CaSO4 , _BaSO4 , _{Al2O3 ,}
SiO ₂ , TiO ₂ , acid salts such as Ca, Ba, Zn, Mn, or organic compound particles such as polyethylene spheres,
Polystyrene balls, polyester balls, etc. can be used. A plurality of types of fine particles may be used in combination. Fine particles exist in the discontinuous film and on the film surface, and the number of particles is 10 ⁴ to 10 ⁸ particles/
It must be mm ² . Number of particles is 10 ⁴ pieces/
If the diameter or height is less than mm ² or less than 50 Å, the running properties of the deposited thin film obtained by depositing a magnetic material on the discontinuous film will not improve. Number of particles is ¹⁰⁸ /
If it exceeds mm ² , the electromagnetic conversion characteristics of the magnetic surface will be
In particular, the S/N ratio deteriorates. Further, the fine particles tend to fall off, which is not preferable. The diameter or height of fine particles
When the thickness exceeds 1000 Å, dropout, which is one of the electromagnetic conversion characteristics, increases significantly, which is not preferable. Silicone may be included as a structural component of the discontinuous coating for the purpose of improving the slipperiness and scratch resistance of the discontinuous coating. Furthermore, in order to strengthen the bond between the water-soluble polymer and the fine particles and to strengthen the adhesion between the coating and the polyester film, it is necessary to add a silane coupling agent to the components of the discontinuous coating. Silane coupling agents are organosilicon monomers that have two or more different reactive groups in their molecules; one of the reactive groups is a methoxy group, ethoxy group, silanol group, etc., and the other is a silane coupling agent. Examples of reactive groups include vinyl, epoxy, methacrylic, amino, and mercapto groups. The reactive group is selected to be one that bonds with the water-soluble polymer side chain, terminal group, and polyester.As a silane coupling agent, vinyltrichlorosilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-glycidoxy Propyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane Methoxysilane, γ
-Mercaptopropyltrimethoxysilane, γ-
Aminopropyltriethoxysilane and the like can be used. The usage ratio of water-soluble polymer [A], silane coupling agent [B], and fine particles [C] as components of the discontinuous film is [A]: [B]: [C] = 20:
1-10: 0.1-20. [B] is used to improve the bonding strength between components. Moreover, if [B] exceeds the upper limit, the discontinuous film structure becomes too hard and the film becomes brittle, which is not preferable. Fine particles are characterized by being present on the surface of the discontinuous film at a ratio of 10 ⁴ to 10 ⁸ particles/mm ² , but when [C] is below the above lower limit, the presence becomes sparse, and the runnability as a vapor deposition surface is affected. becomes worse. If the upper limit is exceeded, 10 ⁸ pieces/mm ² If the upper limit is exceeded,
This is undesirable because the fine particles fall off from the film more frequently and the electromagnetic conversion characteristics also deteriorate. The discontinuous film in which fine particles of the present invention are present inside and on the surface is schematically illustrated in FIGS. 1 and 2. FIG. 1 shows a film partially covering the surface and particles present on the surface of the film, which can be obtained by electron microscopic observation at a magnification of 10,000 times or more. FIG. 2 shows a cross-sectional view of the film, showing the presence of fine particles inside and on the surface of the film. In FIGS. 1 and 2, 1 is a polyester film, 2 is a discontinuous film, and 3 is fine particles. The thickness of the discontinuous coating of the present invention is indicated by h in FIG. The thickness is measured using a stylus surface roughness meter.
In the surface roughness curve when measuring the surface film-formed surface using a cutoff value of 0.08 mm and a vertical magnification of 500,000 times, the peak portion due to fine particles was removed.
This is done by finding the average height interval between peaks and valleys. The height of fine particles is the height of the peak seen from the valley of the peak portion of the roughness curve, and refers to h _nax . Tape characteristics were evaluated by repeatedly recording and playing back using a commercially available VHS VTR. The tape runnability was evaluated at normal temperature and humidity, and at high temperature and high humidity.
This was done by performing playback under these conditions and observing screen fluctuations due to disturbances in tape running.
The evaluation criteria are as follows. 〇: Running smoothly and there is no fluctuation in the playback screen. ×: The running becomes slow in some places, and the playback screen fluctuates. The scratch resistance was evaluated by observing scratches on the tape thin film after repeatedly running the tape 100 times under normal temperature and humidity conditions and high temperature and high humidity conditions.
The evaluation criteria are as follows. ◎: Almost no scratches are observed on the thin film surface of the tape. ○: A few extremely weak scratches are observed on the thin film surface of the tape. ×: Severe scratches occur on the thin film surface of the tape. Note that normal temperature and humidity is 25°C and 60% RH, and high temperature and high humidity is 40°C and 80% RH. For the S/N ratio, record a 50% white level signal at the optimum recording current for each tape, and use a video noise meter to measure the signal-to-noise ratio contained in the video demodulated signal during playback, using a commercially available VHS standard tape as φdB. Comparative measurements were made. Dropout records a three-step wave signal on a magnetic recording tape at the optimum recording current, and the attenuation of the video head amplifier output during playback is 18 dB and the duration is 20 dB.
Dropout of μsec or more was measured using a dropout counter for 10 minutes, and the average per minute was taken. S/N ratio and dropout measurements were carried out at room temperature and humidity. The ferromagnetic thin film provided in the polyester film for magnetic recording media of the present invention is provided on the fine particle-forming discontinuous film. The surface area of the fine particle-forming discontinuous film structure of the present invention is extremely large, and the contact area with magnetic heads, guides, etc. is extremely small, so that the running properties of the ferromagnetic thin film surface are extremely good. Next, the manufacturing method of the present invention will be explained. An aqueous solution containing a water-soluble polymer with a molecular weight of 10,000 to 2 million and a silane coupling agent containing inorganic fine particles was applied to at least one side of a smooth polyester film after being stretched in one direction using a conventional method, and then dried. Thereafter, the film is stretched in the perpendicular direction, or after the perpendicular stretching, it is further stretched again in the one direction and heat-treated. Furthermore, specifically, using the polyester raw material described above, a longitudinally stretched film is melt-extruded using an ordinary film-forming machine, cooled, and uniaxially stretched 3 to 5 times, and then fine particles are added in a step before preheating and stretching. An aqueous solution containing a water-soluble polymer and a silane coupling agent as main components is coated on at least one side by various coating methods. The amount of this aqueous solution applied is 3 to 1000 solids per surface.
mg/ ^m2 is good. Next, this longitudinally stretched film coated with the coating solution is stretched in the transverse direction, but in order to form a film completely before the transverse stretching, it is necessary to completely evaporate the moisture in the coating solution on the film surface to dryness. This is done by preheating in the stenter preheating section of the biaxial stretching machine at a hot air temperature of 100 to 150°C so as to achieve a moisture drying rate of 5%/sec to 100%/sec. After preheating, the film is horizontally stretched 2.5 to 4.5 times at a stretching temperature of 90 to 120°C. By lateral stretching after completion of drying and complete film formation, a discontinuous film structure containing fine particles is formed in close contact with the film surface, which contributes to film slippage. Furthermore, this horizontally stretched film is heat treated at 180 to 220℃.
Alternatively, by heat-treating the polyester film at 180-220℃ after re-stretching it longitudinally to 1.1-1.8 times, a discontinuous film containing fine particles with a thickness of 50-500 Å is formed on at least one side of the smooth polyester film. A biaxially oriented polyester film is obtained. As described above, the present invention has a discontinuous film mainly composed of a water-soluble polymer attached to the surface of a polyester film, and fine particles are formed in the film and on the film surface. The running performance of the surface of the vapor-deposited film is dramatically improved.
Moreover, since the thickness of this discontinuous film is 500 Å or less, the electromagnetic conversion characteristics of the vapor-deposited tape are not impaired. In addition, the diameter and maximum height of the formed fine particles are 1000
Since it is less than Å, there is no increase in dropout. Next, an example of manufacturing a base film of the present invention and manufacturing a vapor-deposited videotape using the base film will be described. Example 1 A substantially non-oriented, amorphous polyethylene terephthalate raw material containing as little internal particles as possible due to polymerization catalyst residues etc. was melt-extruded onto a rotating drum maintained at about 20°C, and then a 3.4 times larger machine was used. After that, the following aqueous solution was applied to both sides at a solid content concentration of 20 mg/m ² using a methane ring bar coater. As an aqueous solution, methyl cellulose 0.20wt%, silane coupling agent N-B (aminoethyl)-γ
-Aminopropylmethyldimethoxysilane 0.02wt
%, ultrafine silica with an average particle size of 200 Å was prepared in a proportion of 0.15 wt%. The drying, preheating, and stretching temperatures were 115°C, and the moisture drying rate was 15%/sec. At a transverse stretching ratio of 3.4 times and a heat treatment temperature of 200℃, 5×10 ⁶ particles with a thickness of 260 Å and a height of 450 Å were formed on both sides.
A polyethylene terephthalate film with a thickness of 12 μm was obtained in which a discontinuous film existing at a ratio of mm ² was formed. A cobalt-nickel alloy thin film with a thickness of 1500 Å was formed on the surface of this polyester film by vacuum evaporation. Subsequently, the film was cut into a predetermined width in the machine direction to obtain a magnetic tape. This characteristic is shown in Table 1. Example 2 In the production of the base film of Example 1, the process was repeated in the same manner as in Example 1 except that the ultrafine silica in the aqueous solution used was replaced with ultrafine charcoal having an average particle size of 210 Å. A polyethylene terephthalate film with a thickness of 12 μm was obtained in which a discontinuous film containing fine particles of 260 Å and a height of 480 Å existed at a ratio of 5×10 ⁶ particles/mm ² . Using this base film, a vapor-deposited magnetic tape was obtained in the same manner as in Example 1. The tape properties are shown in Table 1. Comparative Example 1 In manufacturing the base film of Example 1, an aqueous solution with a methyl cellulose aqueous solution concentration of 0.40% was used, and the other conditions were the same as in Example 1, so that both sides were coated with a thickness of 600 mm.
A discontinuous film with a thickness of 12 μm was formed in which fine particles with a height of 810 μm were present at a rate of 5×10 ⁶ particles/mm ^{2 .}
A polyethylene terephthalate film was obtained. Using this base film, a vapor-deposited magnetic tape was obtained in the same manner as in Example 1. The tape properties are shown in Table 1. Comparative Example 2 The base film of Example 1 was manufactured in the same manner as in Example 1, except that ultrafine silica with an average particle size of 800 Å was used, with a thickness of 300 Å on both sides.
A discontinuous film with a thickness of 12μ was formed in which fine particles with a height of 1100Å existed at a rate of 6 × 10 ⁶ particles/mm ^{2 .}
A polyethylene terephthalate film was obtained. Using this base film, a vapor-deposited magnetic tape was obtained in the same manner as in Example 1. The tape properties are shown in Table 1. Comparative Example 3 The base film of Comparative Example 2 was manufactured in the same manner as in Example 1 except that ultrafine silica with an average particle size of 40 Å was used.
A polyethylene terephthalate film with a thickness of 12 μm was obtained in which a discontinuous film with a thickness of 280 μm was formed on ^both sides of a polyethylene terephthalate film in which fine particles of 310 μm were present at a ratio of 5×10 ⁶ particles/mm 2 . Using this base film, a vapor-deposited magnetic tape was obtained in the same manner as in Example 1. The tape properties are shown in Table 1. Comparative Example 4 A film with a thickness of 200 mm was prepared on both sides in the same manner as in Example 1, except that the proportion of ultrafine silica used in the production of the base film in Example 1 was changed to 0.001%.
A discontinuous film with a thickness of 12 μm in which fine particles with a height of 450 μm exist at a rate of 3 × 10 ³ particles/mm ² is formed.
A polyethylene terephthalate film was obtained. Using this base film, a vapor-deposited magnetic tape was obtained in the same manner as in Example 1. The tape properties are shown in Table 1. Comparative Example 5 Fine particles with a thickness of 300 Å and a height of 490 Å were coated 3× on both sides in the same manner as in Example 1, except that the proportion of ultrafine silica used in the production of the base film in Example 1 was 1.5%. A polyethylene terephthalate film with a thickness of 12 μm was obtained in which a discontinuous film was formed at a rate of 10 ⁹ films/mm ² . Using this base film, a vapor-deposited magnetic tape was obtained in the same manner as in Example 1. The tape properties are shown in Table 1. Comparative Example 6 In manufacturing the base film of Example 1, an aqueous solution was prepared without using the silane coupling agent N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane in the aqueous solution used, and the other conditions were as in Example 1.
In the same manner as above, a polyethylene terephthalate film with a thickness of 12 μm was obtained, on both sides of which a discontinuous film of fine particles having a thickness of 250 Å and a height of 440 Å was present at a ratio of 5×10 ⁶ particles/mm ² was formed. Using this base film, a vapor-deposited magnetic tape was obtained in the same manner as in Example 1. The tape properties are shown in Table 1.

[Table] As is clear from the characteristic results in Table 1, the thickness of the polyester film of the present invention, that is, the adhered thickness
It consists of a discontinuous film mainly composed of a water-soluble polymer of 500 Å or less and a silane coupling agent, and fine particles mainly formed in the film and on the film surface.
A magnetic recording medium in which a ferromagnetic thin film is formed on a discontinuous film containing fine particles of a polyester film, characterized in that the diameter, height, and number of the fine particles are within a specific range, can be used at room temperature in actual use. It has good runnability and scratch resistance both in humid conditions and at high temperature and high humidity, and is smooth and has excellent electromagnetic conversion characteristics.

[Brief explanation of the drawing]

FIG. 1 is a plan view schematically showing a film in which a discontinuous film containing fine particles of the present invention is formed;
FIG. 2 is a cross-sectional view schematically showing a cross section of a film on which a discontinuous film is formed, and h in the figure is the film thickness. FIG. 3 is a surface roughness curve chart obtained by measuring the discontinuous film surface formed according to the present invention using a stylus type surface roughness meter at a vertical magnification of 500,000 times. h is the film thickness and h _nax is the particle height. 1: Polyester film, 2: Discontinuous film,
3: Fine particles.

Claims (1)

[Claims] 1. A polyester film, a discontinuous film with a thickness of 50 to 500 Å that is mainly composed of a water-soluble polymer and a silane coupling agent, which is closely adhered to at least one side of the film, and fine particles that are present in the film and on the surface of the film. A polyester film for magnetic recording media, characterized in that the diameter and height of the fine particles are both 50 to 1000 Å, and the number of particles present is 10 ⁴ to 10 ⁸ particles/mm ² .