JPS6230106B2 - - 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 deposited surface is generally disadvantageous unless a protective film layer is provided. Since it is difficult to uniformly provide a protective film layer on a vapor-deposited surface, in the case of vapor-deposited tape, it is necessary to improve the runnability of the vapor-deposited surface, especially under harsh conditions when actually used, that is, under high temperature and high humidity conditions. The drawback was that the improvement in running performance could not be measured. 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. In order to achieve the above object, the present invention has the following configuration:
That is, it consists of a polyester film and a discontinuous film mainly consisting of a water-soluble polymer with a thickness of 50 to 500 Å and fine particles with a particle size of 30 Å or more and less than 100 Å, closely adhered to at least one side of the film,
The present invention is characterized by a polyester film for magnetic recording media in which fine particles are present on 10% or more and 80% or less of the area of the discontinuous film. 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 0.010μ to 0.0002μ, using a cutoff value of 0.08mm using a stylus type 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 DIN 4768). 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-xylene 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 inert particles added from the outside, and the content thereof is determined by When the polymer is biaxially stretched, it is sufficient that the thickness is 30 μm or less and the haze per sheet is 5% or less. The discontinuous film of the present invention is formed from a composition mainly containing a water-soluble polymer and fine particles, preferably containing silicone, and more preferably containing silicone and a silane coupling agent. Moreover, the thickness of the discontinuous film of the present invention is 50 to 500
Å, preferably 50 to 300 Å. When the thickness exceeds 500 Å, the electromagnetic conversion characteristics of the deposited thin film, especially the S/N
The ratio worsens. 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 of the discontinuous film forming component of the present invention have a size of 30 Å to 400 Å or more and less than 100 Å, preferably 50 Å or more and less than 100 Å. Here, size refers to the maximum particle diameter of fine particles, and the size is 30 Å.
If it is less than this, the runnability of the vapor-deposited thin film obtained by vapor-depositing a magnetic material on this discontinuous film will not improve. Moreover, if the size is 100 Å or more, the electromagnetic conversion characteristics of the magnetic surface will deteriorate. The shape of the fine particles may be spherical, ellipsoidal, rectangular, cubic, or the like. In addition, the particle types include inorganic compound particles such as MaO, ZnO, MgCO ₃ , CaCO ₃ , CaSO ₄ ,
BaSO ₄ , Al ₂ O ₃ , SiO ₂ , TiO ₂ , Ca, Ba, Zn, Mn
Acid salts such as, or organic compound particles such as polyethylene spheres, polystyrene spheres, polyester spheres, etc. can be used. Multiple types of fine particles may be used in combination. It is desirable to include silicone as a film structural component for the purpose of improving the slipperiness of the discontinuous film and improving its scratch resistance. The silicone that can be used has a molecular weight of 30,000 to 300,000, and is preferably used as a chain component. However, R ₁ : CH ₃ , C ₆ H ₅ , H R ₂ : CH ₃ , C ₆ H ₅ , H or a functional group (e.g.
epoxy group, amino group, hydroxyl group) n: 100 to 7000, and is a silicone compound having an integer that satisfies the above molecular weight with _R1 and _R2 , and has an epoxy group, amino group, hydroxyl group, or other functional terminal at the end. It has a group. In the present invention, the silicone compound is not necessarily a homopolymer, but may be a copolymer or a mixture of several types of homopolymers. The molecular weight of silicone is preferably 30,000 to 300,000. When the molecular weight is less than 30,000, the film becomes too soft and the structure tends to deform. On the other hand, if it exceeds 300,000 yen, the film becomes brittle. Furthermore, in order to strengthen the bond between the water-soluble polymer, silicone and fine particles, and to strengthen the adhesive force between the film and the polyester film, it is desirable to add a silane coupling agent to the constituent components of the discontinuous film. 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] silicone [B], silane coupling agent [C], and fine particles [D] as components of the discontinuous film is [A]:
[B]: [C]: [D] = 20:0~10:0~10:2
~40. [B] and [C] are preferably used to improve slipperiness, scratch resistance, and bonding strength between components, but are not essential components. If [B] exceeds the upper limit, the adhesion strength of the deposited film will be poor.
If [C] exceeds the upper limit, the discontinuous film structure becomes too hard and the film becomes brittle, which is not preferable. The fine particles are characterized by being extremely densely present over the entire surface of the discontinuous film, that is, by area fraction of 10% or more and 80% or less, but when [D] is below the above lower limit, their presence becomes sparse and the vapor deposition Running performance as a surface deteriorates. If the upper limit is exceeded, fine particles will fall off from the film more frequently, which is not preferable. The discontinuous film mainly composed of a water-soluble polymer and fine particles according to the present invention refers to the film schematically shown in FIGS. 1 and 2, for example. FIG. 1 is a plan view schematically showing a discontinuous coating in which particles are present over almost the entire surface of the coating, as viewed from above using an electron microscope (approximately 10,000 times magnification). Figure 2 is a cross-sectional view of the film, showing that fine particles are densely present both on the surface and inside the film, and h indicates the thickness of each discontinuous film. . In FIGS. 1 and 2, 1 is a polyester film, 2 is a discontinuous film, and 3 is fine particles. The proportion of fine particles present in the discontinuous film is determined by taking an electron micrograph at a magnification of 10,000 times or more and calculating the ratio of the area of the fine particles to the area of the discontinuous film, that is, the area fraction. The proportion of the fine particles of the present invention is extremely dense, with an area fraction of 10% or more and 80% or less. When the area fraction falls below 10%,
The runnability of the deposited thin film obtained by depositing a magnetic material on this discontinuous film cannot be improved. On the other hand, 80%
If it exceeds this, fine particles will fall off from the surface of the discontinuous film more frequently, scratches will easily form on the thin surface of the deposited film, and the durability will deteriorate significantly. 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.
This is done by determining the average height interval between peaks and valleys in the surface roughness curve when measuring the surface on which the discontinuous film is formed using a cutoff value of 0.08 mm and a longitudinal magnification of 500,000 times. FIG. 3 shows a specific measurement example. Tape characteristics were evaluated by repeatedly recording and playing back using a commercially available VHS VTR. The tape runnability was evaluated based on two criteria: normal temperature and humidity, and high temperature and high humidity.
This was done by performing playback under these conditions and observing screen fluctuations due to sloping tape running.
The evaluation criteria are as follows. ○: The vehicle runs smoothly and there is no fluctuation in the playback screen. ×: The vehicle runs slowly 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 very 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 under normal temperature and normal humidity conditions. 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 discontinuous film structure having fine particles 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. A water-soluble polymer having a molecular weight of 10,000 to 2,000,000 containing inorganic fine particles, organic fine particles, or a mixture thereof, more preferably silicone, is applied to at least one side of a smooth polyester film after being stretched in one direction by a conventional method. An aqueous solution consisting of a silane coupling agent is applied, dried, and then stretched in the orthogonal direction, or after stretched in the orthogonal direction, further stretched in the one direction and heat treated. Furthermore, specifically,
Using the polyester raw material described above, a water-soluble polymer containing fine particles is melt-extruded using a normal film-forming machine, cooled, and then uniaxially stretched 3 to 5 times to form a longitudinally stretched film. More preferably, an aqueous solution containing silicone or a silane coupling agent as a main component is coated on at least one side by various coating methods. The amount of 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. After drying is completed and the film is completely formed, the film surface is stretched horizontally.
A discontinuous film structure is formed in which the fine particles are present very densely on the surface, and this contributes to the slippage of the film. Furthermore, this horizontally stretched film
Heat treatment at 180 to 220℃, or heat treatment at 180 to 220℃ after longitudinal stretching to 1.1 to 1.8 times, results in a smooth polyester film surface with a thickness of 50 Å or more and 500 Å or less, in which fine particles are extremely densely present. A biaxially stretched polyester film having at least one surface on which a discontinuous film is formed is obtained. As described above, the present invention has a discontinuous film mainly composed of a water-soluble polymer and fine particles adhered to the surface of a polyester film. will improve dramatically. Moreover, since the thickness of the discontinuous film in which the fine particles are present over the entire surface is less than 500 Å, the electromagnetic conversion characteristics of the vapor-deposited tape are not impaired. 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 residue, etc., was melt-extruded onto a rotating drum maintained at about 20°C, and then extruded using a machine 3.4 times larger. After that, the following aqueous solution was applied to both sides at a solid content concentration of 20 mg/m ² using a metering bar coater. An aqueous solution containing 0.19 wt% methyl cellulose and 0.35 wt% ultrafine silica with an average particle size of 60 Å was prepared. 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° C., a polyethylene terephthalate film with a thickness of 12 μm was obtained, in which a discontinuous film with a thickness of 260 Å covered almost the entire surface of the film was formed on both sides. 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, 0.40% of epoxidized polydimethylsiloxane emulsion (solid content concentration 20%) and a silane coupling agent N-β (aminoethyl)γ were added to the aqueous solution used.
-Aminopropylmethyldimethoxysilane 0.05%
Using an aqueous solution added at a ratio of
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. Example 3 The base film was produced in the same manner as in Example 1, except that the ultrafine silica in the aqueous solution used was replaced with 0.37 wt% of ultrafine titanium oxide with an average particle size of 70 Å. A polyethylene terephthalate film with a thickness of 12 μm was obtained in which a discontinuous film was formed in which fine particles covered almost the entire surface of the film. 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 the production of the base film of Example 1, an aqueous solution with a methyl cellulose aqueous solution concentration of 0.39% 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 polyethylene terephthalate film with a thickness of 12 μm was obtained in which a discontinuous film with fine particles covering the entire surface of the film 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. Comparative Example 2 The base film of Example 1 was produced in the same manner as in Example 1, except that the amount of ultrafine silica added was 0.03 wt%, and the thickness was 260 Å on both sides, and fine particles were sparsely present in the film. A polyethylene terephthalate film with a thickness of 12 μm on which a discontinuous film was formed 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 In manufacturing the base film of Example 1, the average particle size of the silica used was 700 Å, and the amount added was
A polyethylene terephthalate film with a thickness of 12 μm was obtained in the same manner as in Example 1 except that the concentration was 0.10 wt%, on both sides of which a discontinuous film with a thickness of 750 Å and fine particles densely covered the entire surface of the film was formed. Ta. 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 with a diameter of 500 Å or less and fine particles with a particle size of 30 Å or more and less than 100 Å, and is characterized by the presence of fine particles in a specific area fraction over the entire surface of the discontinuous film. A magnetic recording medium in which a ferromagnetic thin film is formed on a discontinuous film containing fine particles of polyester film has excellent runnability and scratch resistance in actual use at room temperature and humidity, as well as at high temperature and high humidity. It is smooth and has excellent electromagnetic conversion characteristics.

[Brief explanation of the drawing]

Fig. 1 is a plan view schematically showing a film on which a discontinuous film of the present invention is formed, and Fig. 2 is a cross-sectional view of the film of the present invention, where h is the thickness of the discontinuous film. be. FIG. 3 is a roughness curve chart obtained by measuring the discontinuous coating surface of the film of the present invention using a stylus-type surface roughness meter with a longitudinal magnification of 500,000 times. h is the thickness of the film. 1: Polyester film, 2: Discontinuous film,
3: Fine particles.

Claims (1)

[Claims] 1 Consisting of a polyester film and a discontinuous film mainly consisting of a water-soluble polymer with a thickness of 50 to 500 Å and fine particles with a particle size of 30 Å or more and less than 100 Å, which is adhered to at least one side of the film, and the discontinuous A polyester film for magnetic recording media, characterized in that the fine particles are present on 10% or more and 80% or less of the surface area of the film.