JPH0481260B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a flexible support for magnetic recording media. More specifically, the present invention relates to a flexible support for magnetic recording media that has an appropriate surface roughness and a low thermal shrinkage rate. (Prior art) Generally, so-called tensilized polyester film, which is stretched and strengthened in the longitudinal direction, is widely used as a support for magnetic recording media because of its excellent strength and dimensional stability. It is used. Magnetic recording media (for example, audio tapes and video tapes mounted in cassettes) obtained using such supports have conventionally been used or stored in environments where temperature changes are gradual, such as indoors. However, in recent years, radio cassette players, car stereos,
2. Description of the Related Art Small video tape recorders and the like have become widely used, and magnetic recording media are increasingly being used and stored in high or low temperature environments such as outdoors or in automobiles. For example, according to the High and Low Temperature Test Method for Automotive Parts (JISD0204), it is reported that the maximum temperature inside a car during the daytime in summer reaches 104°C. However, when a magnetic recording medium that uses a tensilized polyester film as a support is exposed to such high temperatures, the magnetic recording medium will shrink and curl, or one edge will shrink more and the length will change. This causes arcuate deformation, or the hub is deformed or pushed out by the winding and drawing force during contraction. For this reason, if a magnetic recording medium on which music or the like is recorded is exposed to high temperatures, the output level will fluctuate greatly during playback, not only preventing normal playback but also causing poor running. In particular, magnetic recording media using thin supports (e.g. audio compact cassette C
-80, C-90, C-120, etc.), the magnetic tape stored in the cassette half, such as an audio cassette or video cassette, is long and has to be wound around the hub many times, causing the above problems due to shrinkage. is noticeable. It has been found that the heat shrinkage phenomenon of such magnetic recording media is greatly influenced by the heat shrinkage of the flexible support used therein. Furthermore, it has been found that magnetic recording media using flexible supports whose surfaces are too smooth do not provide good running performance when used repeatedly. Conventionally, as a method for reducing the heat shrinkage rate of a flexible support, in the case of a polyester film, a method is known in which the residual strain inside the film is reduced by lowering the stretching ratio. However, when performing such an operation, although it is possible to lower the heat shrinkage rate of the support, at the same time,
The elastic modulus of the support also decreases, making it difficult to obtain sufficient mechanical strength in thin films. The inventors of the present invention conducted extensive studies to resolve these drawbacks, and found that the heat shrinkage rate was significantly improved by heat-treating the flexible support while it was wound around a core. I came up with an invention. (Objective of the Invention) That is, the first object of the present invention is to provide a flexible support that has a small thermal shrinkage rate when exposed to high temperatures without reducing the elastic modulus of the flexible support. The second object is to provide a flexible support having an appropriate surface roughness. Thirdly, by using the flexible support of the present invention for a magnetic recording medium, even when the magnetic recording medium encounters high temperatures, the magnetic recording medium is less deformed due to heat contraction and has dimensional stability, resulting in output The object of the present invention is to provide a magnetic recording medium having a stable level, a small frequency shift, and stable running performance. (Structure of the Invention) The above-mentioned objects of the present invention are (1) a magnetic recording medium comprising a magnetic layer provided on a flexible support, in which the flexible support is wound around a core with a A flexible support for a magnetic recording medium, characterized in that it has been heat-treated in an atmosphere of 130°C for 6 hours or more, and (2) the flexible support has a longitudinal heat shrinkage rate after being left at 110°C for 4 hours. 1.5% or less, and the surface roughness of the support on the side opposite to the side on which the magnetic recording layer is provided is 0.01 to 0.1 μm. This can be achieved by Flexible supports used in the present invention include polyethylene terephthalate, polyethylene-2,6
- Polyesters such as naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, and cellulose acetate propionate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; Examples include plastic films such as polycarbonate, polyimide, polyetherimide, and polyamideimide. These flexible supports may be transparent or opaque depending on the intended use. Appropriate dyes and pigments may be added to adjust the light transmittance, and an antistatic layer may be applied to prevent static electricity. Further, the heat-treated flexible support may be used in any form such as a film, tape, sheet, disk, card, etc., and various materials may be selected as necessary depending on the form. The thickness of these flexible supports is about 1 to 100 .mu.m, preferably 2 to 80 .mu.m when they are in the form of films, tapes, or sheets. In addition, in the case of a disk or card shape, it is about 0.5 to 10 mm. In the present invention, the heat treatment of the flexible support is carried out at a rolling tension of 0.1 to 20 kg/m, preferably 0.5 to 10 kg/m.
After winding around the core at Kg/m, the temperature is 100-130.
The heat treatment is carried out in an atmosphere at .degree. C. for 6 hours or more, preferably 10 hours or more, and by performing such heat treatment, residual strain inside the support can be gradually removed. The flexible support thus obtained had a heat shrinkage rate of 1.5 after being left at 110°C for 4 hours.
% or less. The surface roughness of the support on the side opposite to the side on which the magnetic recording layer is provided is 0.1 to 0.01 μm, preferably 0.02 to 0.01 μm.
The thickness is preferably 0.08 μm, particularly preferably 0.03 to 0.06 μm. Such surface roughness can be determined by a method using so-called external particles, which adds fine particles, or a method using internal particles, which precipitates particles inside, as well as stretching film forming process conditions, stretching ratio, stretching temperature, etc. It can be adjusted by In the present invention, it is particularly preferable to heat-treat a polyester film that has a high modulus of elasticity in the longitudinal direction and is inexpensive. A magnetic layer containing a ferromagnetic material, a binder, and optionally additives is coated on the above-mentioned support. Furthermore, if necessary, it is also possible to provide a back layer on the surface of the support opposite to the magnetic layer. Generally, when a magnetic layer is applied to a support as described above, the resulting magnetic recording medium has a thermal shrinkage rate of 1% or less. The magnetic layer used in the present invention is produced by coating a support with a magnetic paint containing a binder composition, ferromagnetic powder, additives, etc. dispersed together with an organic solvent and drying it. As the ferromagnetic powder, in addition to γ-Fe ₂ O ₃ , Fe ₃ O ₄ , C ₀ modified iron oxide, alloy fine powder mainly composed of iron is particularly preferable. In particular, tapes using fine metal (alloy) powder are suitable for the present invention because they are less prone to deterioration during transfer and erasure over time. For details on ferromagnetic powder, additives, organic solvents, dispersion, coating methods, etc., see JP-A-52-108804 and JP-A-54.
-21805, 54-46011, etc. (Effects of the Invention) The magnetic recording medium using the flexible support of the present invention has the following advantages. (1) Even in environments where temperature and humidity change slowly, such as indoors, the tape does not deform much even after repeated use, and good running performance can be obtained. In particular, good running performance can be obtained even with thin magnetic recording media (eg, audio compact cassettes C-80, C-90, C-120, etc.). (2) Even at temperatures of 100°C or higher, the tape or sheet does not deform much and a stable output level can be obtained. (3) The thermal shrinkage rate is small, and the frequency shift of the recorded signal can be suppressed from a small range that cannot be discerned audibly or visually. (4) Even if the hub is wrapped with tape and stored at high temperatures of 100°C or higher, changes in the inner diameter of the hub (shrinkage) can be minimized. Therefore, the cassette can be loaded and unloaded into the recording/reproducing device smoothly. (5) With audio cassette tape, even if the tape is wrapped around the hub and stored at a high temperature of 100℃ or higher, the tape has a small thermal shrinkage rate, so the hub will not be pushed out due to tight wrapping, resulting in the inability to run. I have nothing to do. (6) Even when stored at a high temperature of 100°C or higher, there is little deformation of the tape, and the number of stops due to repeated running can be reduced. (Examples) The present invention will be described in more detail with reference to Examples below, but the present invention should not be limited to these Examples. In the examples, "parts" indicate "parts by weight." Example 1 Polyethylene terephthalate chips with an average diameter of 2.0μ and 0.1% kaolin were thoroughly dried and then
It was melt extruded at 285°C and rapidly cooled to obtain an unstretched film. This unstretched film was subjected to a temperature of Tg to Tg+80°C, and the longitudinal (longitudinal direction) and transverse stretching ratios were varied to obtain samples No. 1 to No. 4 in Table 1. The properties of this sample are shown in Table 1. In Table 1, the heat shrinkage rate refers to the heat shrinkage rate in the longitudinal direction of the magnetic tape. The obtained samples No. 1 to No. 4 were wound around a winding core with a winding tension of 6 kg/m and left in an atmosphere of 120°C for 10 hours, then left in an atmosphere of 23°C with 60% RH for 24 hours. We investigated the characteristics.
The results are shown in Table 2 No.B-1 to No.B-4.

【table】

[Table] As shown in the above results, when any polyester base is heat-treated while being wound around a core, the heat shrinkage after being left at 110°C for 4 hours can be reduced without lowering the elastic modulus. Example 2 Using the polyester film sample No. 1 obtained in Example 1, the winding tension and temperature treatment time during heat treatment were varied, and the characteristics of the obtained sample were investigated. The results are shown in Table 3. . The results can be summarized as follows. Samples with winding tension 0.1~20Kg/m
Nos. B-5 to B-9 are preferable because they can reduce the heat shrinkage after being left at 110° C. for 4 hours. Especially No.B-6
~No.B-8 is preferable because it has good operability and a small heat shrinkage rate. No. B-11, which was treated at a treatment temperature of 90℃, was unable to sufficiently reduce the thermal shrinkage rate, and No. B-11, which was treated at a treatment temperature of 90℃, was unable to sufficiently reduce the heat shrinkage rate.
In B-14, the base surface became matte due to the high temperature.
This is undesirable because it causes vertical wrinkles. No. B-15, in which the treatment time was 4 hours, was not preferred because the heat shrinkage rate could not be sufficiently reduced.

【table】

[Table] Example 3 Ferromagnetic powder (γ-Fe ₂ O ₃ ) 100 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (weight ratio 90:3:7) 20 parts Thermoplastic polyurethane 5 parts Carbon black 2 parts Oleic acid 1 part Dimethylpolysiloxane (degree of polymerization approximately 60) 0.1 part α-olefin oxide (carbon number 18) 1 part The above composition was dispersed in a ball mill to prepare a magnetic coating material, which was mixed in Table 1 of Example 1. Sample No.1
~4 and Sample No. B-7, B- of Example Table 3
8, B-9, B-10, B-11, and B-12 supports using a reverse roll so that the dry film thickness was 5 μm. Magnetic field orientation treatment was performed while the coating film was still wet, and calender treatment was performed after drying. This was slit to a width of 3.81 mm to obtain an audio cassette tape. This cassette tape was stored in an audio compact cassette. Table 4 shows the properties of the audio compact cassette tape obtained.

【table】

[Table] As shown in Table 4, sample No. uses a support with a heat shrinkage rate of 1.5% or less (see Tables 1 and 3).
It was found that T-2, T-4 to T-7, and T-10 had no problems in their properties after being left at 110°C for 4 hours. However, even if the heat shrinkage rate is small, if the elastic modulus (especially in the longitudinal direction (MD)) of the support is small, the tape will easily deform during multiple runs, such as 100 reciprocating runs, especially if the thickness of the support is small. It was found that this tendency is stronger when the thickness is thinner. Example 4 Co was used instead of the ferromagnetic powder (γ-Fe ₂ O ₃ ) in Example 3.
Deposited beltride iron oxide (Co3.0atomic% deposited,
FeO1.4, Hc660Oe needle ratio 10/1, average particle length
An audio cassette tape was obtained in the same manner as in Example 3, except that a cassette tape (0.4 μm) was used. The properties of the resulting audio cassette tapes are shown in Table 5, Nos. T-11 to T-20.

【table】

[Table] Example 5 Fe instead of the ferromagnetic powder (γ-Fe ₂ O ₃ ) in Example 3
-Zn alloy fine powder (Fe:Zn=95:5, Hc1300Oe,
An audio cassette tape was obtained in the same manner as in Example 3 except that the needle ratio was 10/1 and the average particle length was 0.3 μm. However, the thickness of the magnetic recording layer is from 5μ.
Changed to 4μ. The properties of the audio cassette tapes obtained are shown in Table 6, Nos. T-21 to T-30.

【table】

【table】

【table】

[Table] Example 6 Thickness 7μ with vertical-horizontal-longitudinal stretching ratio of 3.5-3.5-1.5
Samples No. 5 to No. 10 in Table 7 with varying surface roughness using 12μ polyester film were wound around the winding core at a winding tension of 6 kg/m, left in an atmosphere of 120°C for 10 hours, and then heated at 23°C at 60°C. It was left in an atmosphere of %RH for 24 hours. The characteristics of the sample are shown in Table 8 No.B-18 to No.B-
Shown in 23. The magnetic coating obtained in Example 3 was applied onto the polyester films No. B-18 to No. B-23 in Table 8 above in the same manner as in Example 3 to obtain audio cassette tapes. The properties of the resulting audio cassette tapes are shown in Table 9, Nos. T-31 to T-36.

【table】

[Table] With a surface roughness of about 0.01μ, thin tape No. T-32 has poor audio running performance and stops due to repeated running after being left at 110°C for 4 hours, but thick tape No. T-31 has poor running performance. There are no problems with drivability. Furthermore, the greater the surface roughness, the worse the electromagnetic conversion characteristics, especially the frequency characteristics SOL. In the present invention, sample No. T-31, T-33, T-
No. 34, T-35 are preferred, and No. T-35 is more preferred.
31, T-33, and T-34. The characteristics shown in the examples were measured as follows. (a) Surface roughness This is the center line average roughness defined in Section 5 of JIS-B0601, and the cutoff value is 0.25 mm. (b) Heat shrinkage rate measurement method Approximately 10 cm in an atmosphere of 23℃ and 60%RH
Make marks at intervals of , and measure the intervals (A) with a micrometer. Then, on the measurement sample
A tension of 0.4 g/10 mm width was applied and the sample was left in an atmosphere of 110° C. for 4 hours, and then taken out into the above atmosphere and 1 hour later, the interval (A') was measured. Heat shrinkage rate = A-A'/A x 100 (%) (c) Operability during heat treatment Refers to the operability when winding the film around the core and transporting the roll for heat treatment. △...When winding the film around the winding core, the winding tends to be disordered, and the winding misalignment occurs when the roll is transported. ○...Since the roll is a little weak, misalignment may occur during roll transportation. ◎...No particular problem. (d) MOL315 Maximum output level of 315Hz when reference tape is 0dB (distortion rate 3%) (Reference tape ●Biss: NORMAL/EQ: 120μs Fuji Photo Film ER C-90 ●Biss: Chrome/EQ: 70μs Manufactured by Fuji Photo Film FR-C-90 ●Biss: Metal/EQ: 70μs Manufactured by Fuji Photo Film FR METAL C-
90 Measuring device Nakamichi Model 582) (e) SOL10K Saturation output level at 10KHz when the reference tape is set to 0dB. (f) Frequency characteristics Shows the difference in output between 10KHz and 315Hz. (g) Tape deformation after running back and forth 100 times After running back and forth 100 times using a commercially available audio cassette deck, tape deformation was visually observed and evaluated. ×...The tape becomes stretched and becomes seaweed-like, which affects the sound quality. △...The edges of the tape are stretched and become seaweed-like, but the sound quality is not affected. ○...The edges of the tape are slightly stretched. ◎...There are almost no abnormalities. (h) Audio runability A test was conducted by running 40 commercially available audio cassette decks, and the quality of the winding, presence or absence of running stops, and presence or absence of tape deformation were evaluated. ○...There is no running stop and no winding disorder. Δ...There is no stopping of running, but winding disorder occurs in 1 to 3 machines. x... Winding disturbance occurs in 4 to 6 machines, and running stop occurs in 1 to 2 of them. (i) 3KHz output level fluctuation After recording a 3KHz, -10dB signal in advance, leave the tape wrapped around a hub in a 110℃ atmosphere for 4 hours, then take it out to room temperature, and after 1 hour, change the signal. I played it back and read the fluctuations in the output level. 20 turns were made for each type of test sample, and the incidence of output level fluctuation of 6 dB or more was determined. (j) Frequency shift After recording a 3KHz-10dB signal in advance, the tape was wrapped around a hub and left in a 110℃ atmosphere for 4 hours, then taken out to room temperature, and after 1 hour, the signal was played back. The frequency of the reproduced signal was investigated, and the shift rate with respect to the recorded signal of 3KHz was determined. (k) Shrinkage rate of hub inner diameter Measure the inner diameter of the hub with the tape wrapped around it, then leave it in an atmosphere of 110°C for 4 hours, take it out to room temperature, and measure the inner diameter of the hub after 1 hour. The shrinkage rate was determined. (l) Rate of occurrence of hub extrusion A tape was wrapped around the hub, and after leaving it in an atmosphere of 110° C. for 4 hours, it was visually determined whether the hub was being extruded. The number of test samples used was 20 rolls for each type. (m) Running stoppage rate after leaving at 110℃ for 4 hours After leaving the cassette tape in an atmosphere of 110℃ for 4 hours, 20 commercially available car stereo cassette decks
The vehicle was run for a period of time and the stop rate at that time was determined.

Claims (1)

[Claims] 1. In a magnetic recording medium comprising a magnetic layer provided on a flexible support, the flexible support is wound around a core and kept in an atmosphere of 100 to 130°C for 6 hours. A flexible support for a magnetic recording medium characterized by being subjected to the above heat treatment. 2. The flexible support has a longitudinal heat shrinkage rate of 1.5% or less after being left at 110°C for 4 hours, and a surface roughness of 0.01 to 0.1 on the side opposite to the side on which the magnetic recording layer is provided. 2. The flexible support for a magnetic recording medium according to claim 1, wherein the flexible support has a diameter of μm.