JPH0481259B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a magnetic recording medium. More specifically, the present invention relates to a magnetic recording medium that has excellent running performance, durability, and electromagnetic modification characteristics during repeated use, and has a low thermal shrinkage rate. (Prior Art) Conventionally, magnetic recording media (for example, audio tapes and video tapes loaded in cassettes) are used or stored in environments where temperature changes are gradual, such as indoors. In recent years, radio cassette players, car stereos, small video tape recorders, etc. have become widely used, and are increasingly being used and stored in high temperature, high temperature, high humidity, and low temperature environments. For example, according to the High and Low Temperature Test Method for Automotive Parts (JIS D0204), it is reported that the maximum temperature inside a car during the daytime in summer reaches 104°C. However, magnetic recording media exposed to such high temperatures may shrink and curl, one ear may shrink more than the other, resulting in bow-shaped deformation in the length direction, or the hub may become distorted due to the tightening force during shrinkage. deforms or extrudes. 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, in the case of magnetic recording media using thin supports (e.g. audio compact cassettes C-80, C-90, C-120, etc.),
The long length of magnetic tape housed in a cassette half, such as an audio or video cassette, results in a large number of windings onto the hub, and shrinkage exacerbates the above problem. 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. Furthermore, since magnetic recording materials, especially audio cassette tapes, have recently been used for music recording, tapes with well-developed frequency characteristics and excellent original sound reproduction capabilities are required. On the other hand, extremely high-density recording is now possible on video cassette tapes by shortening the recording wavelength and narrowing the track width. Therefore, the output is high,
There is a demand for tapes with a high S/N ratio and excellent ability to reproduce original pictures. In addition, while the total thickness has become thinner to less than 20 μm, the running durability is far better than before due to the spread of portable VTRs.
A VTR tape is requested. That is, there is a strong demand for audio and video tapes that have better electromagnetic conversion characteristics, runnability, and durability than those of the past. Conventionally, as a support for magnetic recording media, it has been stretched and crystallized (particularly by increasing the stretching ratio in the longitudinal direction,
A polyester film (mechanically reinforced in the longitudinal direction) is used. When searching for the reason why magnetic recording media using these supports are undesirable when used at high temperatures, we found that the thermal shrinkage rate of such magnetic recording media (110°C, 4 o'clock or longitudinal direction after standing) Noting that it was 1.5 to 2.6%, further investigation was conducted. Also, regarding the surface roughness of the side of the non-magnetic flexible support on which the magnetic layer is provided, the surface roughness and electromagnetic conversion characteristics of the magnetic layer, or the surface of the non-magnetic flexible support on the side opposite to the side on which the magnetic layer is provided. As a result of detailed examination of the running performance during repeated use of the surface roughness of the magnetic recording medium and the surface roughness of the back surface of the magnetic recording medium, the inventors discovered that the above-mentioned drawbacks could be overcome, and arrived at the present invention. (Objective of the Invention) Therefore, the object of the present invention is, firstly, to provide a magnetic recording medium that has good running performance during repeated use, and secondly, to provide a magnetic recording medium that has good running performance during repeated use, and secondly, to The purpose is to provide a magnetic recording medium with little deformation and a stable output level.Thirdly, the purpose is to provide a magnetic recording medium with excellent electromagnetic conversion characteristics.Fourthly, the purpose is to provide a magnetic recording medium with excellent heat shrinkage rate. Fifthly, it is an object of the present invention to provide a magnetic recording medium that has a small coefficient of thermal shrinkage, has dimensional stability, and has a small frequency shift of recording signals. Sixth, thin magnetic recording media (e.g. tapes for audio compact cassettes C-80, C-90, C-120, etc.)
It is an object of the present invention to provide a magnetic recording medium that has a low thermal shrinkage rate, stable runnability, output level, and dimensional stability. (Structure of the Invention) The above objects of the present invention are (1) to improve the surface roughness Ra (M') of the magnetic layer of a magnetic recording medium in which a magnetic layer is provided on one surface of a non-magnetic flexible support;
0.03 μm or less, and the surface roughness Ra (B′) of the back surface of the magnetic recording medium is 0.02 to 0.1 μm;
This can be achieved by a magnetic recording medium characterized in that the magnetic recording medium has a heat shrinkage rate of 1.0% or less after being left at 110° C. for 4 hours. (2) Preferably, the above object of the present invention is such that the surface roughness Ra (M) of the side on which the magnetic layer is provided of the non-magnetic flexible support is 0.03 μm or less, and the surface roughness Ra (M) of the side on which the magnetic layer is provided is 0.03 μm or less, and Surface roughness Ra(B) is 0.02 to 0.1 μm
This can be achieved by a magnetic recording medium characterized by the following. (3) More preferably, the above object of the present invention is
(M′) and Ra(B′) and Ra(M) and Ra(B) are always in the relationship of Ra(M′)<Ra(B′) Ra(M)<Ra(B). It can be achieved. In a preferred embodiment of the present invention, the non-magnetic flexible support has a heat shrinkage rate of 1.8% or less, preferably 1.5% or less in the longitudinal direction after being left at 110° C. for 4 hours. By changing the stretching conditions, such a support can have a Young's modulus in the longitudinal direction of 450 to 650.
Kg/mm ² , the heat obtained by heat-treating a polyester film with a small difference in Young's modulus depending on the direction, such as a Young's modulus in the width direction of 450 to 550 Kg/mm ² , or a stretched polyester film in an atmosphere of 110°C or higher. There are polyester films, polycarbonate films, polyamide films, polysulfone films, polypropylene films, polyethersulfone films, etc. with reduced shrinkage rates. Particularly preferred is a polyester film that has a high Young's modulus in the longitudinal direction and is inexpensive. In addition, the non-magnetic flexible support has a surface roughness Ra (M) of 0.03 μm or less, preferably 0.02 μm or less on the side on which the magnetic layer is provided, and a surface roughness Ra (M) on the side opposite to the side where the magnetic layer is provided. Ra(B) is 0.02 to 0.1μm, preferably
The thickness is preferably 0.03 to 0.08 μm, particularly preferably 0.03 to 0.06 μm. Such surface roughness can be achieved by adding fine particles, a method using so-called external particles, or by using internal particles, in which particles are precipitated inside, as well as by stretching film forming process conditions, stretching ratio, stretching temperature, and mechanical It can be adjusted by adding unevenness to the surface. Alternatively, it can be obtained by a composite film made by combining films with different surface roughnesses. It can also be obtained by the coextrusion method described in JP-A-49-74910 and JP-A-51-149006. When a magnetic layer is applied to a non-magnetic flexible support such as the one described above, the resulting magnetic recording medium has a heat shrinkage rate of 1% or less after storage at 110°C for 4 hours, and the surface of the magnetic layer becomes smooth and magnetic. Layer surface roughness Ra (M′)
is 0.03 μm or less, preferably 0.02 μm or less, and has excellent electromagnetic conversion characteristics. The surface roughness Ra (B') of the back surface of the obtained magnetic recording medium (tape) is 0.02 to 0.1 μm, preferably 0.03 to 0.08 μm, particularly preferably 0.03 to 0.06 μm.
It is m. The magnetic recording medium of the present invention is manufactured by applying and drying a magnetic coating material containing a binder composition, ferromagnetic powder, additives, etc. dispersed together with an organic solvent onto a support. As the ferromagnetic powder, in addition to γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-modified iron oxide, alloy fine powder containing iron as a main component 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, spraying methods, etc., see JP-A-52-108804 and JP-A No. 54.
-21805, 54-46011, etc. (Effects of the Invention) The magnetic recording medium 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 to a small range that cannot be discerned audibly or visually. (4) Even when 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, the tape does not deform much, and the number of stops during repeated running can be reduced. (7) Even if the hub is wrapped with tape and stored at a high temperature of 100°C or higher, the magnetic layer side support has a small surface roughness and a low thermal shrinkage rate, so the magnetism generated by the shrinkage pressure remains. Changes in layer surface roughness are also reduced, and output level fluctuations, especially at recording symbols of 10 KHz or higher, can be suppressed to a small level. (8) It can have excellent electromagnetic conversion characteristics. (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 γ-Fe ₂ O ₃ (Hc400Oe acicular ratio 10/1 average particle length
0.4μm) 100 parts vinyl chloride/vinyl acetate/vinyl alcohol copolymer (Sekisui Chemical Co., Ltd.'s "Esletsu A") 20 parts polyurethane resin (Dainippon Ink Chemical Co., Ltd. "Crisbon 6119") 5 parts oleic acid 1 part dimethyl poly Siloxane (degree of polymerization: approx. 60) 0.1 part α-olefin oxide (18 carbon atoms) 1 part Carbon black 2 parts The above composition was placed in a ball mill, kneaded and dispersed for 48 hours, filtered through a filter with an average pore size of 3μ, and A layer coating solution was obtained. The obtained coating solution was coated on the non-magnetic flexible support shown in Table 1 using a reverse roll so that the dry thickness was 5 μm, and while the coated layer was barely dry, it was subjected to magnetic field alignment treatment using a 1000 Gauss electromagnet. and dried. After drying, the magnetic layer was smoothed by supercalendering and slit to a width of 3.81 mm to obtain an audio cassette tape. 135m of this cassette tape was stored in an audio compact cassette. The properties of the obtained tapes are shown in Table 3 Nos. T-1 to T-14. Comparative Example 1 A magnetic layer was formed using the magnetic layer coating solution obtained in Example 1 on a non-magnetic flexible support shown in Table 2, and an audio cassette tape was obtained in the same manner as in Example 1. . The properties of the obtained tapes are shown in Table 3 No. T-15 to T-
Shown in 17.

【table】

【table】

【table】

[Table] Example 2 A magnetic layer was formed using the magnetic layer coating solution obtained in Example 1 on a non-magnetic flexible support shown in Table 4, and an audio cassette tape was prepared in the same manner as in Example 1. Obtained. I stored 90m of this tape in an audio compact cassette. The properties of the obtained tapes are shown in Table 5, Nos. T-18 to T-29.

【table】

【table】

【table】

[Table] Example 3 Co-coated beltride iron oxide (Co3.0atomic% deposited, FeO _1.4 Hc650Oe acicular ratio 10/1 average particle length 0.4μ
m) 100 parts vinyl chloride/vinyl acetate/vinyl alcohol copolymer (Sekisui Chemical Co., Ltd.'s "Eslec A") 20 parts polyurethane resin (Dainippon Ink Chemical Co., Ltd. "Crisbon 6119") 5 parts oleic acid 1 part dimethylpolysiloxane (Polymerization degree approximately 60) 0.1 part α-olefin oxide (carbon number 18) 1 part carbon black 2 parts The above composition was made into a magnetic layer coating solution in the same manner as in Example 1, and the results are shown in Tables 1 and 2. A magnetic layer was provided on the nonmagnetic flexible support shown in Example 1, and an audio cassette tape housed in a compact cassette was obtained in the same manner as in Example 1. The properties of this tape are shown in Table 6, Nos. T-30 to T-46.

【table】

[Table] Example 4 Fe-Zn alloy fine powder (Fe:Zn=95:5)
(Hc1300Oe acicular ratio 10/1, average particle length 0.3μ)
100 parts vinyl chloride-vinyl acetate-vinyl alcohol copolymer (Sekisui Chemical Co., Ltd.'s "Eslec A") 20 parts polyurethane resin (Dainippon Ink Chemical Co., Ltd. "Crisbon 6119") 5 parts oleic acid 1 part dimethylpolysiloxane (polymerization degree Approximately 60) 0.1 part α-olefin oxide (18 carbon atoms) 1 part carbon black 2 parts The above composition was made into a magnetic layer coating solution in the same manner as in Example 1, and is shown in Tables 1 and 2. Example 1: Providing a magnetic layer on a non-magnetic flexible support
An audio cassette tape stored in a compact cassette was obtained by the same operation as above. The properties of this tape are shown in Table 7, Nos. T-47 to T-63.

【table】

[Table] According to Table 3, Ra (M) according to the present invention is
No. T-2 to T-8, which uses a support with Ra(B) of 0.03 μm or less and 0.02 to 0.1 μm, and has a heat shrinkage rate of 1.0% or less after storage at 110°C for 4 hours.
and No. T-11 to T-14 are excellent in electromagnetic conversion characteristics, runnability, and various properties after storage at 110° C. for 4 hours. In particular, Nos. T-3 to T-7 and T-11 to T-14 are excellent. Furthermore, Nos. T-3 to T-5 and t-116 to T-14 are superior to other samples in electromagnetic conversion characteristics and 10 KHz output level fluctuation after storage at 110° C. for 4 hours. Regarding No. T-2, since Ra(B) is slightly small, the running performance is slightly inferior on a thin base, but there is no problem in practical use. No.T-6 has a slightly rough M side and a rough B side as well.
10KHz output level fluctuation becomes slightly worse. This is because the magnetic layer undergoes plastic flow during high-temperature storage, and this causes the surface roughness of the support to appear on the magnetic layer surface, which affects the output level in the high-temperature band (short wavelength band) of 10KHz. In addition, as a comparative example, the surface roughness of the support was within the range of the present invention (Table 2 No. 16, 17) and outside the range (Table 2 No. 1).
15), and the heat shrinkage rate after storage at 110℃ for 4 hours is 3%.
The characteristics of the tape using the larger support are as follows:
Regarding Nos. T-15 to T-17 in Table 3, the properties after storage at 110° C. for 4 hours were poor and they could not be used practically. In Example 2, the thickness of the support was increased to 12μ, and the same characteristics as in Example 1 were measured, and Ra(B) was
The tape (No. T-19 in Table 5) using a support having a diameter of 0.020 μm (No. 19 in Table 4) also had improved audio running characteristics. This is because the base thickness is thicker and is used advantageously for running performance. For other sample characteristics, see Example 1.
The results were similar to those of Comparative Example 1. In addition, in Examples 3 and 4, the types of ferromagnetic powder were changed and the supports of Example 1 and Comparative Example 1 were used as tapes to investigate the characteristics of tapes used in chrome Bias and metal Bias. However, the results were similar to those of Example 1 and Comparative Example 1. From the above results, Ra (M) according to the present invention is
When using a support with Ra(B) of 0.03 μm or less and 0.02 to 0.1 μm, and the heat shrinkage rate of the magnetic recording material after storage at 110°C for 4 hours is 1.0% or less, electromagnetic conversion characteristics and running characteristics It was found that various properties were excellent after storage at 110°C for 4 hours. 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) Solvent resistance A test sample was immersed in a solvent, and the state of the sample was examined after 24 hours. ○...No change △...Some swelling or curling of the sample. (c) 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. Thermal contraction rate = A-A'/A x 100 (%) (d) MOL315 Maximum output level of 315Hz (distortion rate 3%) when reference tape is 0dB (Reference tape ・Bias: NORMAL/EQ: 120μs Fuji Photo Film ER C-90 ・Bias: Chrome/EQ: 70μs Fuji Photo Film FR-C-90 ・Bias: Metal/EQ: 70μs Fuji Photo Film FR METALC-90 Measuring device Nakamichi Model 582 ) (e) SOL10K Saturation output level at 10kHz when reference tape is set to 0dB (f) Frequency characteristics Indicates the difference between the output of 10KHz and 315Hz. (g) Audio running performance A running test was conducted using 40 commercially available audio cassette decks, and the quality of the winding, the presence or absence of running stops, and the 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. (h) 3KHz output level fluctuation After recording a 3KHz, -10dB signal in advance, leave the tape wrapped around a hub in an atmosphere of 110℃ for 4 hours, then take it out to a room temperature atmosphere, 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. (i) 10KHz output level fluctuation After recording a 10KHz, -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 play the signal after 1 hour. I then read the fluctuations in the output level. For each type of test sample, 20 turns were performed 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 tape wrapped around it, then leave it in an atmosphere of 110℃ 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. (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. Surface roughness Ra (M') of the magnetic layer of a magnetic recording medium in which a magnetic layer is provided on one surface of a non-magnetic flexible support.
0.03 μm or less, the surface roughness Ra (B') of the back surface of the magnetic recording medium is 0.02 to 0.1 μm, and the heat shrinkage rate of the magnetic recording medium after being left at 110°C for 4 hours is 1.0.
% or less. 2. The surface roughness Ra (M) of the side on which the magnetic layer is provided of the non-magnetic flexible support is 0.03 μm or less,
The surface roughness Ra(B) of the opposite side to the side where the magnetic layer is provided is
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a thickness of 0.02 to 0.1 μm. 3 Confirm that Ra(M′) and Ra(B′) and Ra(M) and Ra(B) always have the relationship Ra(M′)<Ra(B′) Ra(M)<Ra(B). Characteristic Claim 2
A magnetic recording medium described in .