JP2581970B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium having a multilayered magnetic layer.

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, floppy disks, and the like. The magnetic recording medium is basically formed by laminating a magnetic layer in which a ferromagnetic material is dispersed in a binder (binder) on a non-magnetic support.

The magnetic recording medium is required to be at a high level in various characteristics such as electromagnetic conversion characteristics, running durability and running performance. That is, audio tapes for recording and reproducing music are required to have higher original sound reproduction capabilities. Also, video tapes are required to have excellent electromagnetic conversion characteristics such as excellent original image reproduction capability.

At the same time as having such excellent electromagnetic conversion characteristics, the magnetic recording medium is required to have good running durability as described above. In order to obtain running durability, the functions of the abrasive and the lubricant usually play an important role.

However, in order to obtain excellent running durability by the abrasive, it is necessary to increase the addition amount to some extent, so that the content of the ferromagnetic material decreases. When an abrasive having a large particle diameter is used to obtain excellent running durability, the abrasive tends to excessively protrude from the surface of the magnetic layer. Therefore, improvement of the running durability by the abrasive often causes deterioration of the above-mentioned electromagnetic conversion characteristics, which is a problem.

Even when the above-mentioned running durability is improved by a lubricant, it is necessary to increase the amount of the added lubricant. Therefore, the binder is easily plasticized, and the durability of the magnetic layer tends to decrease.

As another method for improving the running durability, a method of increasing the hardness of a magnetic layer using a hard binder has been used. However, as an adverse effect of increasing the hardness of the magnetic layer, there is a problem that the brittleness of the magnetic layer becomes remarkable, dropout occurs due to contact with the magnetic head, and still characteristics deteriorate.

Furthermore, polyisocyanates, molecular weight having hydroxyl groups
A magnetic recording medium having a structure comprising a polyurethane resin having less than 10,000 and a resin having active hydrogen is disclosed in JP-A-58-15.
It is disclosed in Japanese Patent No. 3224. As described above, polyurethane-based resin (or other resin) having active hydrogen (such as hydroxyl group) has high reactivity with polyisocyanate,
Since the reaction (crosslinking) with the polyisocyanate proceeds sufficiently, the magnetic layer becomes extremely tough. This allows
It is stated that a magnetic layer with little output reduction and good durability can be obtained even after long-term storage. However, such a magnetic layer does not always have sufficient running durability because the adhesive strength with the nonmagnetic support is not sufficient.

Japanese Patent Application Laid-Open No. 63-103429 discloses a two-layer magnetic material containing a ferromagnetic material having a coercive force of 500 Oe or more dispersed in a binder on a non-magnetic support as a method for achieving both such electromagnetic conversion characteristics and running durability. In a magnetic recording medium having a layer, the lower magnetic layer (first magnetic layer) provided on the nonmagnetic support has a Young's modulus of 500 to 1000 kg / mm ² and is provided on the lower magnetic layer. Young's modulus of the upper magnetic layer (second magnetic layer) is 13
00 kg / mm ² or more and the Young's modulus of the entire magnetic layer is 900 kg / mm
More than ^two magnetic recording media have been developed. According to the present invention, the lower magnetic layer is flexible so that it has a high buffering action and adhesiveness, and the upper magnetic layer has a high hardness so that deformation does not easily occur even when stored under high temperature conditions. It was found that the durability was improved.

In order to obtain such a Young's modulus, a binder having a lower Young's modulus than the binder of the second magnetic layer (upper layer) is used as the binder of the first magnetic layer (lower layer) by using substantially the same amount of ferromagnetic material. Using the same binder, using less ferromagnetic material in the first magnetic layer than in the second magnetic layer, and using ferromagnetic material It is stated that a method of adjusting both the Young's modulus of the first magnetic layer and the Young's modulus of the second magnetic layer by adjusting both the binder and the type of the binder can be used.

[Problems to be solved by the invention]

However, specific examples in JP-A-63-103429 are a first magnetic layer (lower layer) and a second magnetic layer (upper layer).
A predetermined Young's modulus by using the same binder (also referred to as a binder) and changing the amounts of the relatively hard binder vinyl chloride / vinyl acetate / vinyl alcohol copolymer and the relatively soft binder polyester polyurethane. Have gained. That is, in such a combination, in the lower layer (first magnetic layer) having a small Young's modulus, the amount of the vinyl chloride copolymer having relatively good dispersibility is reduced, and the amount of polyester polyurethane having poor dispersibility is relatively increased. Therefore, the dispersibility of the lower layer tends to deteriorate. As a result, the surface properties of the upper layer (second magnetic layer) could not be sufficiently obtained, and the strength was sometimes insufficient.

[Object of the invention]

An object of the present invention is to provide a novel multilayer magnetic recording medium. Second, it is to provide a magnetic recording medium having excellent electromagnetic conversion characteristics. Third, to provide a magnetic recording medium having excellent running durability.

[Means for solving the problem]

The present invention relates to a magnetic recording medium in which a magnetic layer formed by dispersing a ferromagnetic material in a binder on a non-magnetic support is formed in a multilayer structure. Or the lower layer) has a glass transition temperature (T
g) contains at least one polyurethane resin having a temperature of −50 ° C. to −10 ° C., and the upper magnetic layer (hereinafter also referred to as “second magnetic layer” or “upper layer”) has a glass transition temperature (Tg) of 20 ° C.
From 40 ° C. containing at least one polyurethane resin, and the difference between the glass transition temperature of the polyurethane resin using the upper and lower magnetic layers is at least 30 ° C. (ie,
The glass transition temperature of the polyurethane resin used for the upper layer is at least 10 ° C. higher than the glass transition temperature of the polyurethane resin used for the lower layer.

Preferred embodiments of the magnetic recording medium of the present invention are as follows.

1) A lower magnetic layer is coated on a support, and an upper magnetic layer is coated thereon while in a wet state.
A magnetic recording medium obtained by drying and surface treatment.

2) A magnetic recording medium wherein the amount of polyurethane resin in each of the lower magnetic layer and the upper magnetic layer is 10% by weight to 70% by weight of the total binder in each layer.

3) A magnetic recording medium wherein the difference between the glass transition temperatures of the polyurethane resin of the lower magnetic layer and the polyurethane resin of the upper magnetic layer is at least 20 ° C. or more.

4) A magnetic recording medium, wherein the amount of the binder in each of the lower magnetic layer and the upper magnetic layer is 10% by weight to 70% by weight of the ferromagnetic material in each layer.

5) A magnetic recording medium, wherein the lower magnetic layer and the upper magnetic layer further contain a polyisocyanate curing agent as a binder component.

6) A magnetic recording medium, wherein the lower magnetic layer and the upper magnetic layer further contain a vinyl chloride copolymer resin or a cellulose resin as a binder component.

7) A magnetic recording medium, wherein the dry thickness of the lower magnetic layer is 2 μm or more, and the dry thickness of the upper magnetic layer is 1.5 μm or less.

8) A magnetic recording medium, wherein the coercive force of the upper magnetic layer is 400 Oe to 2200 Oe, and the coercive force of the lower magnetic layer is 1 to 0.1 times that of the upper magnetic layer.

〔The invention's effect〕

In the present invention, the calender moldability is improved by using a polyurethane resin having a low Tg for the lower magnetic layer (first magnetic layer) in the multilayer magnetic layer, and the upper magnetic layer (second magnetic layer) is molded. Although a binder with poor properties is used, it is thin and depends on the smoothness of the lower layer.

Further, after curing, since the upper layer is made of a polyurethane resin having a high Tg, running durability at high temperature and high humidity is improved. On the other hand, since the lower layer uses a polyurethane resin with a low Tg, although it is slightly lower than the upper layer in terms of durability,
Since the head is not directly touched, durability as high as that of the upper layer is not required.

Further, since the lower layer has a low Tg, the adhesion between the lower layer and the nonmagnetic support is particularly improved.

The present invention does not change the use ratio of a binder having a high hardness (for example, a vinyl chloride copolymer) and a soft binder (for example, a polyurethane), that is, without lowering the Young's modulus (durability) of the lower magnetic layer. The dispersibility and adhesion of the lower magnetic layer can be improved.

[Detailed Description of the Invention]

The polyurethane resin used in the present invention is a polyester polyol, a polyether polyol, a polycarbonate polyol, a polyester polycarbonate, a polyester polyether, a polyol such as polycaprolactone and an isocyanate and, if desired, a chain extender,
It was made to react with others.

Some of these polyurethane resins have a yield point and others do not have a yield point depending on the skeleton of the polyester and the urethane group concentration. In the present invention, the polyurethane resin is not used alone, but is mixed with another resin, and is preferably used in an amorphous state, regardless of the presence or absence of a yield point.

If desired, a so-called functional group-containing polyurethane resin having a functional group such as sulfonic acid in polyester or the like can also be used.

The glass transition temperature (Tg) of the polyurethane resin used for the first magnetic layer (lower layer) is from -50C to -10C. −50
If the temperature is lower than ℃, the running durability is inferior, and if it exceeds -10 ° C, the electromagnetic conversion characteristics are inferior.

The glass transition temperature (Tg) of the polyurethane resin used for the second magnetic layer (upper layer) is from 20 ° C to 40 ° C. If it is lower than 20 ° C., the running durability is inferior, and if it exceeds 40 ° C., the electromagnetic conversion characteristics are inferior.

Also, when the Tg of the polyurethane resin of the lower layer and the Tg of the polyurethane resin of the upper layer have a difference of 30 ° C or more (that is, the Tg of the polyurethane resin used for the upper layer is at least 30 ° C higher than the Tg of the polyurethane resin used for the lower layer), Properties and electromagnetic conversion characteristics are compatible, and the electromagnetic conversion characteristics are better than when there is no difference. 10 difference
If the temperature is above ℃, the electromagnetic conversion characteristics are good, but especially the difference is 30 ℃
In the above cases, the electromagnetic conversion characteristics are excellent.

Examples of polyurethane resins having a glass transition temperature of −50 ° C. to −10 ° C. that can be used for the first magnetic layer include N-2304 and FR-11 manufactured by Nippon Polyurethane, Chrisbon 7209 manufactured by Dainippon Ink and Pandex. 5102S and MB-148.

The glass transition temperature usable for the second magnetic layer is from 20 ° C to 40 ° C
Examples of polyurethane resins at ° C include N-2301 and N-5033 manufactured by Nippon Polyurethane, UR-8300 and UR- manufactured by Toyobo.
8600, and the like. It is also preferable that these polyurethane resins have polar functional groups. Examples of these functional groups include a hydroxyl group, a carboxyl group, a sulfonic acid group, a metal sulfonate group, a phosphate group, a phosphate ester group, a metal phosphate group, an epoxy group, an amino group, a cyano group, and the like.

The polyurethane resin of the present invention is contained in at least 5% by weight or more, preferably 10% by weight or more, based on the total amount of the binder used in each magnetic layer. The upper limit is 100% by weight
And preferably up to 70% by weight. If it is less than 5% by weight, the electromagnetic conversion characteristics are inferior and are not preferred. 70% by weight
If it exceeds, the running durability under high temperature and high humidity conditions is slightly inferior.

Other binders used in combination with the polyurethane resin of the present invention are resins which are compatible with the polyurethane resin and have a glass transition temperature of 50 ° C. or higher, and curing agents. Preferred examples thereof include a vinyl chloride copolymer resin or a cellulose resin, and a polyisocyanate curing agent.

The vinyl chloride copolymer resin means various copolymers mainly containing vinyl chloride, and examples thereof include copolymers with vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and vinyl alcohol. Polymers. Further, the vinyl chloride copolymer resin preferably has polar functional groups. Examples of these functional groups include a hydroxyl group, a carboxyl group, a sulfonic acid group, a metal sulfonate, a phosphate group, and a phosphate group. , A phosphate metal base, an epoxy group, an amino group, a cyano group and the like.

Examples of the cellulose resin include nitrocellulose, acetylcellulose, methylcellulose, ethylcellulose, cellulose acetate butyrate, cellulose propionate, cellulose acetate propionate, hydroxyethylcellulose, carboxymethylcellulose, and the like.

The number average molecular weight of the vinyl chloride copolymer resin or cellulose resin used in the present invention is preferably from 5,000 to 50,000.

The difference between the weight% of the upper vinyl chloride copolymer resin or cellulose resin relative to the magnetic material and the weight% of the lower vinyl chloride copolymer resin or cellulose resin relative to the magnetic material is within 30%. Is preferred. The difference
If it exceeds 30%, the surface properties of the multilayer are remarkably deteriorated, which is not preferable.

Examples of the polyisocyanate curing agent used as the binder component of the present invention include aliphatic, alicyclic and aromatic di- and aromatic compounds such as benzene, naphthalene, biphenyl, diphenylmethane and triphenylmethane having at least two isocyanate groups. , Tri- and tetraisocyanates and their additional products. As a specific example,
Ethane diisocyanate, butane-ω, ω'-diisocyanate, hexane di-ω, ω'-diisocyanate,
2,2-dimethylpentane-ω, ω′-diisocyanate, 2,2,4-trimethylpentane-ω, ω′-diisocyanate, decane-ω, ω′-diisocyanate, ω,
ω'-diisocyanate-1,3-dimethylbenzol,
ω, ω′-diisocyanate-1,2-dimethylcyclohexane, ω, ω′-diisocyanate-1,4-diethylbenzol, ω, ω′-diisocyanate-1,5-dimethylnaphthalene, 1,3-phenylene diisocyanate,
1-methylbenzol-2,4-diisocyanate, 1,3-
Dimethylbenzol-2,6-diisocyanate, naphthalene-1,4-diisocyanate, 1,1'-dinaphthyl-2,
2'-diisocyanate, biphenyl-2,4'-diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, 2,2'-dimethyldiphenylmethane-4,4 ' -Diisocyanate, 3,3'-dimethoxydiphenylmethane-
4,4'-diisocyanate, 4,4'-diethoxyphenylmethane-4,4'-diisocyanate, 1-methylbenzol-2,4,6-triisocyanate, 1,3,5-trimethylbenzol-2,4 Isocyanates such as 1,6-triisocyanate, diphenylmethane-2,4,4'-triisocyanate, triphenylmethane-4,4 ', 4 "-triisocyanate, tolylene diisocyanate, 1,5-naphthylene diisocyanate; And addition products of these isocyanates with dihydric or trihydric polyalcohols, such as trimethylolpropane and tolylene diisocyanate. There are additional products with hexamethylene diisocyanate and the like.

Among the above polyisocyanate curing agents, those having three or more isocyanate groups in one molecule are particularly preferable.

Known magnetic materials can be used, but the coercive force of the magnetic material used for the upper layer is preferably 350 to 2,500 Oe, particularly,
400-2,200 Oe is preferred. Specific surface area (S _BET ) is 15m ² / g ~
80 m ² / g, the crystallite size is preferably 150 to 500 Å, and the particle size is preferably 0.03 to 0.3 μm.

If the coercive force is less than 350 Oe, the high-frequency characteristics of an audio normal position tape are inferior, which is not preferable. Also,
If it exceeds 2,500 Oe, recording and erasing with a normal magnetic head becomes difficult, which is not preferable.

The magnetic material used in the lower layer preferably has the same or lower coercive force, a smaller specific surface area, and a larger crystallite size than the magnetic material in the upper layer.

The coercive force of the lower layer is preferably equal to or lower than that of the upper layer.
It is preferably about 0.5 times and 1.0 times to 0.1 times since those recorded on the surface layer such as video and digital are hardly recorded in the lower layer.

It is preferable that the specific surface area of the magnetic material in the lower layer is smaller than that of the magnetic material in the upper layer because transfer characteristics and cost are excellent.

 The crystallite size is the same as the specific surface area.

In the present invention, the magnetic layer may contain a non-magnetic powder such as carbon black and an abrasive in addition to the magnetic substance. As these nonmagnetic powders, those conventionally known in the field of magnetic recording media can be used.

The dry thickness of the upper layer in the present invention is preferably 1.5 μm or less, more preferably 1 μm or less. If the thickness of the upper layer exceeds 1.5 μm, electromagnetic conversion characteristics are not improved, which is not preferable.

The dry thickness of the lower layer in the present invention is preferably 2.0 μm or more, and more preferably 2.5 μm or more. When the thickness of the lower layer is less than 2.0 μm, it is not preferable because the moldability in a calender is reduced or the electromagnetic conversion characteristics are not improved.

The reason why a magnetic recording medium having excellent electromagnetic conversion characteristics can be obtained by the present invention is not clear, but is considered as follows.

Since the Tg of the lower polyurethane resin is lower than the Tg of the upper polyurethane resin, the moldability in the calender treatment is improved. Further, since the upper layer of the polyurethane resin has a high Tg, it is considered that irregularities on the base surface are unlikely to appear on the surface of the magnetic layer during calendering, and the electromagnetic conversion characteristics are excellent. Further, since the upper magnetic layer after the calender is hard and the lower layer is slightly soft, the entire magnetic layer is supple, but the surface layer is hard and excellent in running durability.

Of course, any of various additives such as a lubricant and a dispersant may be added to the magnetic paint according to the purpose according to a known technique.

The coating is performed by applying the magnetic paint prepared from the above materials on a non-magnetic support by the following method. First, a resin component for the first magnetic layer (lower layer), a ferromagnetic material, and a magnetic layer forming component such as a curing agent, if desired, are kneaded and dispersed with a solvent to prepare a coating solution for the first magnetic layer. Then, a coating solution for the second magnetic layer (upper layer) is prepared in the same manner.

The method for producing a magnetic recording medium of the present invention includes, for example, applying a coating solution for a first magnetic layer to the surface of a nonmagnetic support under running, and while the coating layer is in a wet state, continuously coating the coating layer. And the thickness of the second magnetic layer after drying the second magnetic layer
Coating is performed so as to be in a range of 0.03 to 1.5 μm (preferably 0.1 to 1.0 μm). The method of continuous application of the two layers, for example, when an extrusion coat is used as a coating machine, two sets of extrusion coats may be continuously installed so as to sandwich the non-magnetic support under running, and may be applied. Alternatively, two first magnetic layers may be provided at intervals so as to maintain a wet state (that is, a state in which the coating layer still contains a solvent and exhibits tackiness).

Examples of the coating machine for applying the magnetic paint include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, and spray. Coat, spin coat, etc. can be used. In the present invention, an extrusion coat for simultaneous multilayer coating having two slots as disclosed in Japanese Patent Application No. 62-124631 is particularly desirable.

The second magnetic layer (upper layer) obtained by using the above-mentioned manufacturing method has a uniform thickness even if the magnetic layer has a very small thickness of 0.03 to 1.5 μm, and has a very smooth surface. It can be applied in any state. As a result, it is possible to manufacture a magnetic recording medium having excellent running durability according to the present invention and not impairing the electromagnetic conversion characteristics.

The coating layer of the magnetic paint is applied so that the thickness of the magnetic layer (the total thickness of the first magnetic layer and the second magnetic layer) of the obtained magnetic recording medium is usually in the range of 2.5 to 10 μm. You.

A back layer (backing layer) may be provided on the surface of the non-magnetic support used in the present invention on which the magnetic paint is not applied. Normally, the back layer is formed by dispersing a particulate component such as an abrasive, an antistatic agent, a binder, and, if necessary, a lubricant in an organic solvent on the surface of the non-magnetic support on which the magnetic paint is not applied. This is a layer provided by applying a layer forming paint.

Note that an adhesive layer may be provided on the surface of the non-magnetic support on which the magnetic paint and the back layer forming paint are applied.

Usually, the applied layer of the applied magnetic paint is dried after subjecting the ferromagnetic substance contained in the applied layer of the magnetic paint to a process of orienting the ferromagnetic material, that is, a magnetic field orientation process.

After being dried in this manner, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calender roll or the like is used. By performing the surface smoothing treatment, pores generated by removing the solvent during drying disappear, and the filling factor of the ferromagnetic material in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can.

The laminate thus cured is then cut into a desired shape.

Cutting can be performed under normal conditions using a normal cutting machine such as a slitter.

Although the magnetic recording medium of the present invention has been described with respect to the upper and lower two-layer system, it may have three or more layers as long as it retains the above-specified properties and includes two magnetic layers.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. In addition, "parts" indicates parts by weight.

Example 1 First magnetic layer (lower layer) Cobalt-modified iron oxide (Hc680Oe, _SBET 30 m ² / g, crystallite size 250 mm, particle size 0.25 μm) 100 parts vinyl chloride-vinyl acetate-maleic anhydride copolymer (composition) Ratio 86: 13: 1, degree of polymerization 400) 10 parts Polyester polyurethane resin (glass transition temperature is 1st)
5 parts Carbon black (particle size 0.05 μm) 3 parts Butyl stearate 1 part Stearic acid 2 parts Butyl acetate 200 parts Second magnetic layer (upper layer) Cobalt-modified iron oxide (Hc700Oe, S _BET 35m ² / g, (Crystallite size 200 mm, particle size 0.20 μm) 100 parts Vinyl chloride-vinyl acetate-maleic anhydride copolymer (composition ratio 86: 13: 1, degree of polymerization 400) 12 parts Polyester polyurethane resin (glass transition temperature is 1st)
6 parts carbon black (particle size 0.05 μm) 3 parts α-alumina (particle size 0.3 μm 3 parts butyl stearate 1 part stearic acid 2 parts butyl acetate 200 parts For each of the above two paints, The resulting dispersion was kneaded and dispersed using a sand mill, and the resulting dispersion was mixed with a polyisocyanate (Coronate L- manufactured by Nippon Polyurethane KK).
75) was added to 5 parts of the coating solution for the first magnetic layer and 6 parts to the coating solution for the second magnetic layer, and 40 parts of butyl acetate was added to each. Then, a coating solution for forming the first magnetic layer and a coating solution for forming the second magnetic layer were respectively prepared.

The resulting coating solution for the first magnetic layer has a thickness of 3.0 after drying.
Or 2.0 μm, and immediately thereafter, the thickness of the second magnetic layer thereon becomes 0.5, 0.7, 1.5 μm,
Simultaneous multi-layer coating on a 15 μm thick polyethylene terephthalate support, orientation with a cobalt magnet and solenoid while both layers are still wet, drying, supercalendering, slit to 1/2 inch width Manufactured videotapes. The tapes thus obtained were designated as Sample Nos. 1 to 17, and the characteristics are shown in Table 1. However, Sample No. 12 was a single layer having only the upper layer (second magnetic layer).

Example 2 In place of the vinyl chloride-vinyl acetate-maleic anhydride copolymer of Example 1, nitrocellulose was used. The results are shown in Table 1 as sample No. 18.

Comparative Example 1 5 parts of the vinyl chloride-vinyl acetate-maleic anhydride copolymer of the first magnetic layer (lower layer) of Example 1 was used instead of 10 parts, and 10 parts of the polyester polyurethane resin was used instead of 5 parts.
Parts used. The results are shown in Table 1 as sample No. 19.

Explanation of evaluation items: Video sensitivity 4.2MHz output using VHS type VCR. The following relative value when SAG manufactured by Fuji Photo Film Co., Ltd. is 0 dB. The measuring instrument was AG-3700 manufactured by Matsushita Electric Industrial Co., Ltd. The same applies to standard tapes and measured quantities.

Y-S / N S / N of luminance signal corrected for luminous efficiency. Relative value.

Chroma output 629KHz video output. Relative value.

C / S / N S / N of color signal after luminosity correction. Relative value.

Still life Playback in still mode and the time (minutes) until the S / N drops by 6 dB.

Running durability Whether there is any trouble when running 100 passes on 40 decks.

:: There is no decrease in output of 3 dB or more, and there is no increase in dropout, jitter and the like.

Δ: There is no output drop of 5 dB or more, and there is a slight increase in dropout, jitter, etc.

In Table 1, the Tg of the lower polyurethane resin was −60.
It can be seen that the tape of sample No. 1 having a low temperature of ° C. has excellent electromagnetic conversion characteristics, but has some difficulties in still life and running durability.

In addition, it can be seen that the tape of Sample No. 7 in which the lower layer of the polyurethane resin has a high Tg of 0 ° C. has somewhat poor electromagnetic conversion characteristics.

It can be seen that the still life and running durability are inferior for Sample No. 8 where the Tg is the same for both the upper and lower polyurethane resins.

It can be seen that the sample No. 12 of the single-layer magnetic layer has much lower electromagnetic conversion characteristics than that of the single-layer magnetic layer.

Sample No. 16 having a thick upper coating layer and Sample No. 17 having a thin lower coating layer both have somewhat poor electromagnetic conversion characteristics.

From the above, it can be seen that the magnetic tape according to the present invention is excellent in electromagnetic conversion characteristics and running durability.

Claims (1)

(57) [Claims] In a magnetic recording medium comprising a non-magnetic support and a magnetic layer formed by dispersing a ferromagnetic material in a binder on a non-magnetic support, a glass transition temperature (Tg) is provided in the lower magnetic layer as the binder. Contains at least one polyurethane resin at -50 ° C to -10 ° C, and the upper magnetic layer has a glass transition temperature (Tg)
A magnetic recording medium comprising at least one polyurethane resin having a temperature of 20 ° C. to 40 ° C., and a difference in glass transition temperature between polyurethane resins using an upper magnetic layer and a lower magnetic layer being at least 30 ° C. or more.