JP2723213B2 - Film for magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a base film for a magnetic recording medium. More specifically, the present invention relates to a base film for a magnetic recording medium having a high recording density when used as a magnetic recording medium and having excellent characteristics. [Prior Art] Conventionally, biaxially oriented polyester films have been widely used as base films for magnetic recording media. However, in a binder type magnetic recording medium in which a magnetic paint is applied to the film, dust adheres due to static electricity generated while the magnetic tape is running or the magnetic disk is rotating. Or, in some cases, the deformation of the magnetic recording medium or the damage of the equipment used. For this reason, it is essential that the magnetic recording medium has antistatic properties. Examples of the magnetic recording medium having antistatic properties include: (1) A magnetic recording medium having antistatic properties provided by uniformly dispersing conductive particles such as carbon and metal powder in a magnetic layer. (2) A magnetic recording medium provided with antistatic properties by using a polyethylene terephthalate film having antistatic properties by applying or kneading a surfactant or the like. (3) PE with a metal thin film formed on the surface by vacuum evaporation, sputtering, ion plating, electroplating, etc.
Magnetic recording media with antistatic properties using T film. (4) A magnetic recording medium in which the above (1) to (3) are combined as necessary. Etc. are known. [Problems to be Solved by the Invention] However, the above-described magnetic recording medium having antistatic properties has the following problems. In the above item (1), if conductive particles are mixed in the magnetic layer, the magnetic material is adversely affected and the coercive force is reduced, so that high-density recording is not possible. Is more likely to occur. In the above item (2), since a durable static electricity preventing effect cannot be obtained, the charge amount increases during use, so that dust and the like are adsorbed and dropout easily occurs. Furthermore, in the case of surfactants, etc., environmental conditions during use, especially relative humidity 5% RH
Antistatic properties are not exhibited in a dry atmosphere such as the following. In the above item (3), the adhesion between the PET film and the formed metal thin film is weak, so that the running durability is poor, and the magnetic layer is peeled off. When metal powder is interposed as a conductive layer, rust is generated due to moisture absorption of the magnetic material,
There is a problem that the conductivity changes and "blisters" occur on the surface of the magnetic layer. The present invention solves these disadvantages of the prior art and aims to provide a base film for a magnetic recording medium which can achieve high density recording, has no dropout, and has excellent antistatic properties when used as a magnetic recording medium. Things. [Means for Solving the Problems] The present invention provides a polyester film having at least one selected from the group consisting of tin oxide, antimony oxide, indium oxide, zinc oxide and bismuth oxide having an average particle diameter of 1
A magnetic recording medium comprising: a conductive layer composed of a conductor mainly composed of a metal oxide fine powder of not more than μm and an organic polymer binder; and a magnetic recording layer laminated on at least one surface of the conductive layer. The layer is intended to be a film for a magnetic recording medium having a surface roughness Ra of 0.03 μm or less and a surface specific resistance in the range of 10 ⁵ to 10 ⁹ Ω. The polyester in the present invention is a known polyester, specifically, for example, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, bis-α, β (2-chlorophenoxy) ethane-4,4′-dicarboxylic acid, Obtained by polycondensing at least one kind of bifunctional carboxylic acid such as adipic acid and sebacic acid and at least one kind of glycol such as ethylene glycol, triethylene glycol, tetramethylene glycol, hexamethylene glycol, and decamethylene glycol. Polyester can be mentioned. Further, the polyester may be blended with another polymer within a range not to impair the object of the present invention, and may contain an antioxidant, a heat stabilizer, a lubricant, a pigment, an ultraviolet absorber and the like. . Inherent viscosity of polyester (25
C. (measured in orthochlorophenol) is from 0.4 to 2.0, preferably from 0.5 to 1.0. In the present invention, polyethylene terephthalate (hereinafter abbreviated as PET) as a polyester, polyethylene 2,6-
When naphthalate is used, particularly excellent effects can be obtained. The conductive layer in the present invention is a layer mainly composed of a metal oxide fine powder and an organic polymer binder. When a metal oxide is selected in the present invention, even if a predetermined conductivity can be obtained by optimizing the addition amount of the metal powder, even if the magnetic material is left in an environment such as high temperature and high humidity This is not preferable because rust is generated by the reaction between the moisture absorbing metal and the metal, and the gas generated by the reaction causes the magnetic layer to swell and impair the function as a recording medium. It is because it is significantly improved by the thing. The metal oxide fine powder has a composition of at least one selected from tin oxide, antimony oxide, indium oxide, zinc oxide and bismuth oxide, and has an average particle diameter of 1 μm.
m, preferably 0.5 μm or less. If the average particle diameter is 1 μm or more, the surface roughness of the conductive layer becomes large, and the abrasion resistance is deteriorated. If necessary, aluminum oxide or magnesium oxide may be added to the metal oxide fine powder in an amount of 10% by weight or less of the total metal oxide amount, and antimony in an amount of 20% by weight or less. Here, the average particle size is a value obtained by measuring a metal fine powder as an ethylene glycol slurry using a centrifugal sedimentation type particle size distribution analyzer (SA-CP2 manufactured by Shimadzu Corporation). The main component means that it occupies 50% or more of the conductor. As the organic polymer binder, a resin soluble in a known solvent, for example, an acryl-based, vinyl-based, urethane-based, epoxy-based, polyester-based, polypropylene-based, copolymer, or a mixed system thereof can be used. It is desirable to apply a polyester resin to the polyester film referred to in the present invention in view of the adhesiveness and abrasion resistance of the conductive layer. The solvent is
As the organic solvent, for example, alcohols, carboxylic esters, ketones, aliphatic hydrocarbons, alicyclic or aromatic hydrocarbons, and mixtures thereof can be used. Further, in the conductive coating material, a dispersant such as a surfactant and a silane coupling agent may be used in order to uniformly disperse the metal oxide fine powder in the organic polymer binder. The concentration of the metal oxide fine powder in the conductive layer is 55 to 85 wt.
% Is preferable, and the range of 65 to 75 wt% is more preferable. When the concentration of the metal oxide fine powder is less than 55% by weight, a conductive layer having a desired surface specific resistance cannot be obtained. If the content exceeds 85% by weight, the surface of the conductive layer is significantly roughened, and the wear resistance of the conductive layer is reduced. The polyester film constituting the film of the present invention,
It is at least biaxially oriented by a conventional method, and preferably has a thickness of 5 to 150 μm, more preferably 6 to 100 μm, and is excellent in handleability in practical use as a base for a magnetic recording medium. The surface roughness of the polyester film is 0.05μm
The thickness is preferably 0.03 μm or less in order to prevent surface roughness of the conductive layer formed on the film. The laminated thickness of the conductive layer constituting the film of the present invention is preferably 0.05 to 2.0 μm on each side of the polyester film,
The range of 0.1 to 1.0 μm is more preferable. Lamination thickness 0.05μ
If it is less than m, a magnetic recording medium having desired surface specific resistance cannot be obtained. When the thickness exceeds 2.0 μm, when the magnetic recording medium is used, a crack may be generated in the conductive layer due to bending in handling depending on the conductive layer. The surface roughness of the film of the present invention must be 0.03 μm or less, preferably 0.01 μm or less, and more preferably 0.005 μm or less. If the surface roughness is 0.03 μm or more, when the magnetic recording medium is used, the coercive force and dropout become poor, which is not preferable. The surface specific resistance of the film of the present invention needs to be in the range of 10 ⁵ to 10 ⁹ Ω, preferably 10 ⁶ to 10 ⁸ Ω. If the surface resistivity is less than 10 ⁵ Ω, the surface resistivity is too low when used as a magnetic recording medium, which may adversely affect the coercive force of the magnetic material, roughen the surface, or cause excessive current to flow through the equipment used. Not preferred. On the other hand, a magnetic recording medium having a resistivity exceeding 10 ⁹ Ω is not preferable because the surface resistivity of the magnetic recording medium is increased, and the antistatic property is reduced during use. The magnetic layer in the present _{invention, γ-Fe 2 O 3,} Co -doped γ-Fe ₂ O _3, oxide-based magnetic powder such as CrO ₂ and Fe, Co, Ni
This is a well-known magnetic layer formed by a so-called coating method in which a metal-based ferromagnetic powder such as described above and an auxiliary additive are uniformly dispersed in a known organic polymer binder such as a thermoplastic resin or a thermosetting resin. The thickness of the magnetic layer is 0.5 ~ 10μ
m, preferably in the range of 1 to 5 μm. Next, a method for producing the film of the present invention will be described. (1) Manufacturing method of polyester film An example in which a PET film is used as a polyester film will be described. A PET chip polymerized by a conventional method is melt-extruded from a slit-shaped die at 260 to 310 ° C. while applying an electrostatic charge.
Cool to 20-80 ° C to make unstretched film. At this time, the intrinsic viscosity of the unstretched film is 0.5
It is desirable that this is the case. Next, the unstretched film is biaxially stretched and oriented. As the stretching method, a sequential biaxial stretching method, a simultaneous biaxial stretching method, or a combination thereof can be used. The biaxial orientation conditions are not particularly limited, and are usually 70 to 180 ° C., preferably 90 to 90 in both the longitudinal direction and the width direction of the film.
At a stretching temperature of ~ 150 ° C, the stretching ratio is 2.0 to 7.5, respectively.
Times, preferably 2.5 to 6.0 times. In addition, a PET film obtained by further stretching a biaxially oriented film in at least one direction is not only more improved in mechanical properties, but also exhibits in-plane balanced properties, so that it is more preferable as a base film. The stretching conditions in this case, the stretching temperature is 100 to 180 ° C., the stretching ratio is 1.1 to 3.5 times in the longitudinal direction and width direction, preferably 1.4 times to
3.0 times. Further, the biaxially oriented film is heat-treated as necessary. The heat treatment conditions are a temperature of 150 to 240 ° C. and a time of 0.5 to 120 seconds, preferably 1.0 to 60 seconds. (2) Method of forming conductive layer To form a conductive layer on the polyester film,
What is necessary is just to apply the coating material containing the above-mentioned conductive fine powder to both surfaces of the polyester film and dry the coating film. In this case, the conductive layer can be more firmly formed on the film surface by subjecting the polyester film to a corona discharge treatment or a plasma treatment (in air, in nitrogen, in carbon dioxide, or the like) which is known in advance. The coating method of the coating material is a known air doctor coating method, air knife coating method, dipping method,
A reverse roll coating method, a gravure coating method, a kiss coating method, a cast coating method, or the like can be applied, but the gravure coating method is preferred from the viewpoint of the accuracy of the coating thickness. The concentration of the coating material and the conditions for drying the coating film are not particularly limited, but the drying conditions for the coating film are desirably performed within a range that does not adversely affect the polyester film. The characteristic values of the present invention are based on the following measurement methods and evaluation criteria. (1) Surface resistivity The surface resistivity of 10 ⁶ Ω or more was measured using “Super insulation meter VE-40” manufactured by Kawaguchi Electric Works, Ltd. When the surface specific resistance was less than 10 ⁶ Ω, a copper electrode having a width of 3.5 cm and a thickness of 5 mm was prepared, a counter electrode was placed in parallel at a position separated by 3.5 cm, a load of 500 g was applied, and a tester was applied. (2) Surface roughness Ra was measured using a stylus type surface roughness meter according to JIS-B-0601. The cutoff was 0.25 mm and the measurement length was 4 mm. (3) Abrasion resistance The abrasion resistance of the conductive layer was measured by applying a load of 500 g using a “Gakushin type friction fastness tester” manufactured by Daiei Kagaku Seiki Co., Ltd. No. 3), and the coating film appearance (scratch, abrasion amount) after rubbing 200 times was observed and evaluated. The evaluation criteria were ○: good, Δ: slightly poor, ×: poor. (4) Blocking resistance The blocking property of the conductive layer is 5 according to JIS-Z-0219.
A blocking force of 24 hours was evaluated by applying a load of 500 g / 12 cm ² in 0 ° C. and 80 to 90% RH. The criterion is ○: good,
Δ: slightly poor, ×: poor. (5) Chemical resistance The chemical resistance of the conductive layer is as specified in JIS-K-711 for toluene.
The appearance (cloudiness, cracks, discoloration, swelling, etc.) after the end of the test was observed and evaluated according to 4. The measurement criteria were ；: good, Δ: slightly poor, ×: poor. (6) Adhesive strength The adhesive strength of the conductive layer / base film is JIS-
After applying an adhesive tape with a width of 18 mm specified in C-2338, apply a load of about 5 kg using a hand roller, reciprocate twice in the length direction (about 10 cm), and press the adhesive tape by hand. After peeling, the degree of peeling of the conductive layer was observed and evaluated. The evaluation criteria were ○: good, Δ: slightly poor, ×: poor. (7) Coercive force of magnetic recording medium A magnetic material having the following composition was applied to a sample film by a coating method, and dried to form a magnetic layer having a thickness of 2.5 μm to obtain a magnetic recording medium. The magnetic properties of this magnetic recording medium were measured with a sample vibration magnetometer, and the coercive force was determined from the hysteresis curve. The criterion was that a holding power of 500 Oe or more was good, and a holding power of less than 500 Oe was bad. (Magnetic material composition) ・ γ-Fe ₂ O ₃ powder 68 parts by weight ・ Carbon black 7 parts by weight ・ Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 26 parts by weight ・ Acrylonitrile-butadiene copolymer 5 parts by weight ・ Poly Isocyanate 2 parts by weight ・ Methyl isobutyl ketone 75 parts by weight ・ Toluene 75 parts by weight (8) Dropout magnetic tape of magnetic recording medium It was a tape. This magnetic tape is run continuously for 100 hours on a home VTR (helical scan). After holding the tape at 40 ° C. for 48 hours, the tape was returned to room temperature and recorded and reproduced, and those having a signal output of 50% or less were counted using a dropout counter. In addition, measurement is performed for 10 rolls with 1/2 inch width and 780 m as one roll. Dropout is performed when the number per roll is less than 2; good when 2 or more is dropped out; Judged. Magnetic Disk The magnetic tape raw material prepared in the above section (7) was punched out on a disk to obtain a magnetic disk having a diameter of 8 inches. This magnetic disk was recorded and reproduced by a floppy disk drive, and the RF signal was subjected to envelope detection, the waveform was shaped by a selection circuit, and the number of dropouts per unit time was measured. The measurement is preferably performed with a dropout of 10 / min or less. (9) Electrification evaluation method SHISHID CORPORATION “Static Honest Meter” S-410
Judgment criteria were ○: good (1 second or less), Δ: slightly poor (2 to 30 seconds), ×: poor (30 seconds or more). (10) Moisture resistance The magnetic material having the structure of “base film / conductive layer / magnetic layer” is left for 2 months in an environment of 50 ° C. and 90% RH, and the surface of the magnetic layer is observed with a 500 × optical microscope, and “bloated” Are evaluated as "x" and those not generated as "o". [Function of the Invention] The present invention uses a conductive coating material containing a specific metal oxide fine powder on a polyester film to form a conductive layer having a specific surface roughness and a specific surface resistance. The layer and the magnetic layer exhibited a unique interaction, and the following excellent effects could be obtained. [Effects of the Invention] (1) When a magnetic recording medium is used, a recording medium having a high recording density can be obtained, so that the magnetic recording medium can be made compact and the magnetic recording time can be lengthened. (2) When a magnetic recording medium is used, static electricity can be stably obtained over a long period of time without being affected by external temperature and humidity, so that there is little dropout due to deposits and the like. (3) When manufacturing a magnetic recording medium, the magnetic layer is firmly formed on the conductive layer and the surface of the magnetic layer becomes smooth, so that when a magnetic recording medium is used, dropout is small. (4) By using metal oxide as conductive particles, defects such as "bloating" do not occur even under high temperature and high humidity,
The function as a magnetic recording medium can be maintained. [Uses of the Invention] The base film for a magnetic recording medium of the present invention can be applied to a base film for a magnetic recording medium such as a magnetic tape, a magnetic disk, and a magnetic card used for a computer, audio, video, measurement, and the like. However, it is particularly preferably used for a magnetic disk. Example Next, an embodiment of the present invention will be described based on an example. Example 1 A PET homopolymer chip (intrinsic viscosity: 0.62, melting point: 259 ° C.) manufactured by an ordinary method was dried under reduced pressure (3 mmHg) at 180 ° C. for 2 hours. This chip is supplied to an extruder at 280 ° C.
The sheet was melt-extruded from a mold die, wound around a cooling drum having a surface temperature of 20 ° C. and solidified by cooling using an electrostatic application method to obtain an unstretched film. Next, the film is
After stretching 3.3 times in the longitudinal direction by the roll method at ℃,
The film was stretched 3.5 times in the width direction by a tenter method, and heat-treated at 220 ° C. for 5 seconds to obtain a biaxially oriented film having a thickness of 8 μm. Next, methyl ethyl ketone / toluene (mixing ratio 1: 1)
Of metal oxide "ELCOM" (manufactured by Catalyst Chemicals Co., Ltd.) made of tin oxide having an average particle diameter of 0.5 .mu.m doped with antimony at 6% by weight and a polyester resin "VYLON" 200 (Toyobo) (Made by Co., Ltd.) was uniformly dispersed in a composition having a weight-to-solid ratio of 70:30 to prepare a coating material having a concentration of 15 wt%. Apply this coating material to the biaxially oriented PET
Apply the reverse coating method to both sides of the film,
It was dried at 0 ° C. to obtain a conductive film having a conductive layer thickness of 0.7 μm on each side. The conductive layer thus obtained had a surface roughness of 0.018 μm and a surface resistivity of 2 × 10 ⁸ Ω. Further, the conductive layer
The adhesiveness, abrasion resistance, blocking resistance, and solvent resistance were all excellent. When this film was used as a magnetic tape, the characteristics were as shown in Table 1, and the holding power, dropout and antistatic properties were good.
However, when the metal oxide of the conductive layer and the particle size thereof are outside the scope of the present invention (Comparative Examples 1 to 4), a base film for a magnetic recording medium having good coercive force, dropout, and antistatic properties is obtained. I couldn't. Examples 2 to 5, Comparative Examples 5 and 6 Biaxially oriented films were produced using the same polymers as in Example 1 with slightly changed film forming conditions. A conductive layer was formed on the film in the same manner as in Example 1 to prepare a film of the present invention in which the surface resistance and the surface roughness of the conductive layer were changed. However, the same solvent as in Example 1 was used in each case. Table 1 shows the characteristics when the films of the present invention were used as magnetic recording media. When the film properties of the present invention were within the range of the present invention (Examples 2 to 5), a magnetic tape having good holding power, dropout, and antistatic properties was obtained. However, cases outside the present invention (Comparative Example 5,
In 6), a magnetic tape having good holding power, dropout, and antistatic properties could not be obtained. Example 6 Using the same polymer as in Example 1, a film forming condition was changed to obtain a 75 μm thick biaxially stretched film having a good orientation balance. Next, a conductive layer having a thickness of 0.8 μm was formed on both surfaces of the film using the same conductive material as in Example 1 by the same method. The surface roughness of this film is 0.015 μm and the surface resistivity is 4 × 10 ⁷ Ω
Met. Furthermore, the conductive layer was excellent in adhesiveness, solvent resistance, and abrasion resistance. When this film was used as a magnetic disk, the holding power was 650 Oersted, the dropout was 1 piece / min, and the antistatic properties were good. Comparative Example 7 A magnetic tape was prepared in the same manner except that the aluminum metal powder used in Comparative Example 4 was used and the amount added was 30% by weight. The surface resistivity of the conductive layer thus obtained is 6
× 10 ⁶ Ω, and the surface roughness was 0.021 μm. Further, the conductive layer was excellent in all of adhesiveness, abrasion resistance, solvent resistance and blocking resistance. When this film was used as a magnetic tape, the properties were good in both holding power, dropout, and antistatic properties. However, this tape was evaluated for moisture resistance by "swelling" under high temperature and high humidity.
There has occurred. Comparative Example 8 A mixed solvent of methyl ethyl ketone and toluene (weight ratio of 1: 1) was used, and the average particle size was 0.1 μm as a conductor.
m of carbon black and 60 parts by weight of a polyester resin ("Vylon" -200 (manufactured by Toyobo Co., Ltd.)) as a binder component were mixed and dispersed to prepare a coating material having a solid content concentration of 15% by weight. A coating layer having a thickness of 0.5 μm per side was provided on both sides of the polyester film in the same manner as in Example 1.
The surface roughness of the conductive layer of this film is 0.074 μm,
The value of the surface resistivity was 1.2 × 10 ⁵ Ω. It is understood that such surface roughness is due to coarse projections which are considered to be due to secondary aggregation of carbon black, and it was difficult to obtain good surface smoothness. A magnetic recording medium was prepared using this film, but the dropout due to the surface roughness was poor. Examples 7 to 9 As in Example 1, a mixed solvent of methyl ethyl ketone and toluene having a mixing ratio of 1: 1 was used.
Indium oxide (Example 7), antimony oxide having an average particle diameter of 0.3 μm (Example 8), metal oxide of bismuth oxide (Example 9) having an average particle diameter of 0.5 μm, and a polyester resin (“Viron”) as a binder component -200 (manufactured by Toyobo Co., Ltd.) was dispersed and mixed to prepare each coating agent.In each case, the solid content weight ratio of the metal oxide to the polyester resin was 40:60, and the solid content of the coating agent was 40:60. Min concentration is 1
It was 5% by weight. Each coating was prepared in the same manner as in Example 1 to a thickness of one side of 0.
A 7 μm conductive layer was provided on both sides. The surface roughness and surface resistivity of these films were 0.019 μm and 5 × 10 ⁶ Ω in Example 7 and 5 × 10 ⁶ Ω in Example 7.
The values were 0.025 μm and 7 × 10 ⁸ Ω, and those of Example 9 were 0.023 μm and 9 × 10 ⁷ Ω. As a result of preparing a magnetic recording medium using these films, the coercive force, the dropout, and the antistatic property were good, and other characteristics were not problematic.

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Claims (1)

(57) [Claims] Conductor and organic polymer composed mainly of metal oxide fine powder having an average particle diameter of 1 μm or less and at least one selected from tin oxide, antimony oxide, indium oxide, zinc oxide and bismuth oxide on both surfaces of the polyester film A magnetic recording medium comprising a conductive layer made of a binder and a magnetic recording layer laminated on at least one surface of the conductive layer,
The conductive layer has a surface roughness Ra of 0.03 μm or less and a surface resistivity of
A film for a magnetic recording medium, which is in the range of 10 ⁵ to 10 ⁹ Ω.