JPH04291019A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the mechanical strength sufficient for practical use even if the overall thickness of the magnetic recording medium is below prescribed length mum by specifying the product Et<3> of the Young's modulus E at the time of 1% elongation of the magnetic recording medium and the cube of a total thickness to specific mm or above in either of a longitudinal direction and transverse direction. CONSTITUTION:The mechanical strength sufficient for practical use is obtd. even if the total thickness of the magnetic recording medium is <=15mum by using a polyethylene naphthalate film or aramid film or the like as a base film and incorporating a polyurethane resin having >=-25 deg.C glass transition temp. as a binder component of a magnetic layer into this layer to adjust the glass transition temp. of the magnetic layer to >=40 deg.C, thereby specifying the product Et<3> of the Young's modulus E of the magnetic recording medium having <=15mum total thickness and the cube of the total thickness t to >=1.7g.mm in either of a longitudinal direction and transverse direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as magnetic tapes, and more particularly, to magnetic recording media such as magnetic tapes, which have a total thickness of 15 μm or less and are sufficiently thin for practical use. Strong magnetic tape
related to magnetic recording media such as discs. [0002] In recent years, especially in magnetic tapes for video, etc., in order to lengthen the recording and playback time as much as possible when incorporated into a cartridge case, the thickness of the magnetic tape has been reduced as much as possible. Attempts are being made to make it thinner. However, reducing the thickness of the magnetic tape weakens the tape's mechanical strength, which deteriorates the contact with the rotating video head during recording and playback, making it impossible to obtain a normal playback waveform and causing the envelope to deteriorate. It becomes defective. Also, when recording, playing, fast forwarding, rewinding, or loading and unloading, magnetic tape
The edge of the magnetic tape may come into contact with the guide member that regulates the running of the magnetic tape or the magnetic tape regulating flange of the loading post, causing buckling or breakage. It becomes easy to form wrinkles and wrinkles. For this reason, when manufacturing plastic films such as polyester films, a reinforced plastic film that has been stretched and strengthened in the longitudinal or width direction is used as the base film of the magnetic tape, resulting in thinner magnetic tapes. Attempts have been made to strengthen the mechanical strength of the [Problems to be Solved by the Invention] However, in a product that is stretched and strengthened in a balanced manner in the longitudinal direction and the width direction, the Young's modulus (hereinafter abbreviated as Young's modulus) at 1% elongation is lower in both the longitudinal direction and the width direction. 550 to 600 kg/mm2, and the Young's modulus is 7 in the longitudinal direction when stretched and strengthened in the longitudinal direction.
50~850kg/mm2, 350~430 in width direction
kg/mm2, and if the total thickness is 15 μm or less, it will not have sufficient mechanical strength for practical use, especially when applied to VHS type and VHS-C type VTRs, and the test material will not be able to withstand contact with the magnetic head. - The envelope rigidity decreases and cannot be optimized, making it impossible to obtain a normal envelope waveform or stable running in various running modes. [Means for Solving the Problems] This invention was made as a result of various studies in view of the current situation, and uses a polyethylene naphthalate film or an aramid film as a base film, and magnetically The Young's modulus E of a magnetic recording medium with a total thickness of 15 μm or less is achieved by incorporating a polyurethane resin with a glass transition temperature of -25°C or higher as a binder component in the layer and making the glass transition temperature of the magnetic layer 40°C or higher. By setting the product Et3 of t and total thickness t to the third power to 1.7 g/mm or more in both the longitudinal and width directions, a practically sufficient mechanical strength can be obtained even if the total thickness of the magnetic recording medium is 15 μm or less. This is how it was done. The base film used in this invention has a Young's modulus of 650 in both the longitudinal direction and the width direction.
kg/mm2 or more, and the Young's modulus in the width direction is preferably larger than the Young's modulus in the longitudinal direction.If either the Young's modulus in the longitudinal direction or the width direction is less than 650 kg/mm2, this Even if a magnetic layer is formed thereon, a magnetic recording medium such as a magnetic tape with sufficient rigidity cannot be obtained, and practically sufficient mechanical strength cannot be obtained. Furthermore, it is advantageous to make the Young's modulus in the width direction larger than the Young's modulus in the longitudinal direction in order to prevent the rigidity from decreasing and to obtain a practically sufficient mechanical strength. Furthermore, since conventional polyester films have limited strength, it is preferable to use polyethylene naphthalate films or aramid films, which have higher strength, and whose Young's modulus in the width direction is higher than that in the longitudinal direction. By using a large polyethylene naphthalate film or aramid film with a Young's modulus of 650 kg/mm2 or more in both the longitudinal and width directions, the rigidity will not decrease even if the total thickness is reduced to 15 μm or less, which is sufficient for practical use. A magnetic recording medium having high mechanical strength can be obtained. Note that both para-type and meta-type aramid films are preferably used. The magnetic layer formed on such a base film has a binder resin with a glass transition temperature of -25°C.
It is preferable that the magnetic layer contains the above polyurethane resin and has a glass transition temperature of 40°C or higher after being cured with a commonly used curing agent, and such a magnetic layer is formed on the above-mentioned highly rigid base film. Even if the total thickness is 15 μm or less, the Young's modulus E of the magnetic recording medium and the total thickness t are 3
The product Et3 can be set to 1.7 g·mm or more in both the longitudinal and width directions, and a magnetic recording medium with high rigidity and mechanical strength sufficient for practical use can be obtained. [0008] Such polyurethane resins with a glass transition temperature of -25°C or higher have a glass transition temperature of -25°C or higher by increasing the urethane group concentration or introducing a benzene ring or the like into the molecular chain. For example,
Manufactured by Toyobo; UR-8300 (glass transition temperature 23°C)
, manufactured by Nippon Polyurethane Kogyo Co., Ltd.; N-2309 (glass transition temperature: 26°C), etc. are preferably used. [0009] Further, as the curing agent, isocyanate compounds are preferably used. For example, Coronate L
(manufactured by Nippon Polyurethane Kogyo Co., Ltd.; trifunctional low molecular weight isocyanate compound) and the like are preferably used. In addition, binder resins generally used in magnetic recording media are preferably used in combination with these polyurethane resins and curing agents, such as cellulose resins, vinyl chloride-vinyl acetate copolymers, polyvinyl butyl Ral resin, polyester resin, etc. are used in combination. The magnetic layer is formed by mixing and dispersing magnetic powder, a binder resin containing a polyurethane resin with a glass transition temperature of -25° C. or higher, a hardening agent such as an isocyanate compound, an organic solvent, and other necessary components. A magnetic paint was prepared by using the magnetic paint, and this magnetic paint was coated with polyethylene naphthalene having a Young's modulus in both the longitudinal direction and the width direction of 650 kg/mm2 or more, and a Young's modulus in the width direction being larger than the Young's modulus in the longitudinal direction. It is formed by coating and drying on a base film such as a base film or an aramid film. [0011] Here, as the magnetic powder, γ-Fe2
O3 powder, Fe3 O4 powder, Co-containing γ-Fe2
O3 powder, Co-containing Fe3 O4 powder, CrO2
Any conventionally known magnetic powder such as powder or metal magnetic powder such as Fe powder may be used. In addition, as an organic solvent,
Organic solvents commonly used in magnetic recording media, such as methyl isobutyl ketone, cyclohexanone, ethyl acetate, tetrahydrofuran, dioxane, toluene, and xylene, may be used alone or in a mixture of two or more. In addition, fillers, lubricants, antistatic agents,
A dispersant or the like may also be included. [0012] Further, a back coat layer may be further formed on the back surface of the base film on which the magnetic layer is formed, and this back coat layer contains non-magnetic powder, binder resin, lubricant,
A paint for the back coat layer is prepared by mixing and dispersing an organic solvent etc. with other necessary ingredients, and this paint for the back coat layer is applied to the back side of the base film on which the magnetic layer is formed and dried. It is formed by Nonmagnetic powders used for such a back coat layer include α-Fe2O3, TiO2, C
ACO3, carbon black, etc., which are normally used in the back coat layer of magnetic recording media, are widely used.As the binder resin and organic solvent, the same binder resin and organic solvent as those used in the magnetic layer are generally used. Any organic solvent is used. [Example] Next, an example of the present invention will be described. Example 1 The Young's modulus in the longitudinal direction is 700 kg/mm2, the Young's modulus in the width direction is 740 kg/mm2, and the thickness is 10.7μ.
A magnetic coating consisting of the following composition was applied to the surface of a polyethylene naphthalate film of 3.0 mm to a dry thickness of 3.0 μm, and dried to form a magnetic layer with a glass transition temperature of 55° C. A back coat consisting of the following composition is added to
Apply the paint for the second layer to a dry thickness of 0.8 μm.
It was dried to form a back coat layer. Thereafter, it was cut into a predetermined width to produce a magnetic tape with a total thickness of 14.0 μm. Magnetic paint Co-containing γ-Fe2 O3 powder

82 parts by weight Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 10
Polyurethane resin (glass transition temperature 10℃)
6 〃
isocyanate compound
2
〃 Carbon black

5 〃 α-Al2 O3
powder
4 〃
myristic acid

0.7 n-butyl stearate

1.0 〃 Cyclohexanone
83.5 〃
toluene

83.5〃0016 Back coat layer paint carbon black

60 parts by weight α-Fe2 O3 powder

7 Nitrocellulose
18
〃 Polyurethane resin

12 Isocyanate compound
5 〃 Cyclohexanone
150
〃 Toluene

150 Example 2 In Example 1, the Young's modulus in the longitudinal direction was 700 kg/
mm2, Young's modulus in the width direction is 740 kg/mm2, and the thickness is 10.7 μm.
A magnetic tape having a total thickness of 11.5 .mu.m was prepared in the same manner as in Example 1, except that an aramid film having a width of 7.7 .mu.m and a Young's modulus in the width direction of 1650 kg/mm 2 was used. Comparative Example 1 In Example 1, the Young's modulus in the longitudinal direction was 700 kg/
mm2, the Young's modulus in the width direction is 740 kg/mm2, and the thickness is 10.7 μm. Instead, the Young's modulus in the longitudinal direction is 620 kg/mm
2. A polyethylene terephthalate film having a Young's modulus in the width direction of 580 kg/mm2 and a thickness of 10.7 μm was used in the same manner as in Example 1, except that the total thickness was 14 μm.
．． A 5 μm magnetic tape was made. Comparative Example 2 In Example 1, the Young's modulus in the longitudinal direction was 700 kg/
mm2, Young's modulus in the width direction is 740 kg/mm2, and the thickness is 10.7 μm.
2. The entire thickness was 13.2 mm in the same manner as in Example 1, except that a polyethylene naphthalate film having a Young's modulus in the width direction of 740 kg/mm2 and a thickness of 9.7 μm was used.
A 5 μm magnetic tape was made. Comparative Example 3 In Example 1, the Young's modulus in the longitudinal direction was 700 kg/
mm2, the Young's modulus in the width direction is 740 kg/mm2, and the thickness is 10.7 μm. Instead, the Young's modulus in the longitudinal direction is 850 kg/mm
2. The entire thickness was 14.2 mm in the same manner as in Example 1, except that a polyethylene naphthalate film having a Young's modulus in the width direction of 700 kg/mm2 and a thickness of 10.7 μm was used.
A 5 μm magnetic tape was made. Comparative Example 4 In Example 1, Young's modulus in the longitudinal direction was 700 kg/
mm2, the Young's modulus in the width direction is 740 kg/mm2, and the thickness is 10.7 μm. Instead, the Young's modulus in the longitudinal direction is 620 kg/mm
2. A polyethylene terephthalate film having a Young's modulus in the width direction of 580 kg/mm2 and a thickness of 11.7 μm was used in the same manner as in Example 1, but the total thickness was 15 μm.
．． A 5 μm magnetic tape was made. Comparative Example 5 In Example 1, Young's modulus in the longitudinal direction was 700 kg/
mm2, the Young's modulus in the width direction is 740 kg/mm2, and the thickness is 10.7 μm. Instead, the Young's modulus in the longitudinal direction is 550 kg/mm.
2. A polyethylene terephthalate film having a Young's modulus in the width direction of 450 kg/mm2 and a thickness of 14.7 μm was used in the same manner as in Example 1, except that the total thickness was 18 μm.
．． A 5 μm magnetic tape was made. Comparative Example 6 In the composition of the magnetic paint in Example 1, a polyurethane resin with a glass transition temperature of -30°C was used instead of a polyurethane resin with a glass transition temperature of 10°C. A magnetic tape was produced in the same manner as in Example 1 except that the magnetic layer was formed. The Young's modulus E in the longitudinal direction and the width direction at 1% elongation was measured for the magnetic tape obtained in each example and each comparative example, and the Young's modulus E in the longitudinal direction and the width direction and the total thickness were measured. The product Et3 of the cube of t was calculated. In addition, the obtained magnetic tape was loaded into a VHS video tape recorder and the RF output was measured, and the flatness of the reproduced envelope waveform of the video signal (envelope) was evaluated, and the loading/unloading A Cue/Rev scratch test and a Cue/Rev scratch test were conducted. R
The F output is expressed as the output ratio of a 6 MHz single signal recorded and reproduced with respect to a reference tape, and the envelope is expressed as a percentage of the ratio between the maximum value and the minimum value of the video signal output waveform. Also,
In the loading/unloading scratch test, the magnetic tape is loaded/unloaded 10 times at the same location near the end of the cassette winding, and scratches on the magnetic tape are visually determined. and evaluated on a 5-point scale. Furthermore, in the Cue/Rev scratch test, Cue/Rev is repeated 10 times for about 5 seconds at the same location near the end of the magnetic tape cassette winding, and scratches on the magnetic tape are visually determined. and evaluated on a 5-point scale. Table 1 below shows the results. [0025] Effect of the invention: As is clear from Table 1 above, Example 1
The magnetic tape obtained in 2 and 2 was tested for RF output, envelope, load/unload scratch test,
All of the scratch test results were good, indicating that the magnetic tape obtained by this invention has excellent electrical properties even with a total thickness of 15 μm or less, as well as high rigidity and sufficient mechanical strength for practical use. It can be seen that it has.

Claims (1)

[Scope of Claims] [Claim 1] The total thickness of the magnetic layer on the base film is 15 μm or less, and the Young's modulus E at 1% elongation and the total thickness t
A magnetic recording medium in which the product Et3 of the cube of Et3 is 1.7 g/mm or more in both the longitudinal direction and the width direction.Claim 2: Young's modulus at 1% elongation in both the longitudinal direction and the width direction is 650 kg/mm2 3. The magnetic recording medium according to claim 1, wherein the base film has a Young's modulus in the width direction that is larger than the Young's modulus in the longitudinal direction. - The magnetic recording medium according to claims 1 and 2, wherein the base film is a base film.Claim 4: The magnetic recording medium according to claims 1 and 2, wherein the base film is a base film made of aramid.Claim 5: 5. The magnetic recording medium according to claim 1, wherein the magnetic layer is a magnetic layer having a glass transition temperature of 40° C. or higher and comprising a polyurethane resin having a glass transition temperature of −25° C. or higher as a binder component.